„ a ... Normal sheath used in combination with a ɂ 4 mm arthroscope. „ b ... Practical embodiment of the proposed sheath- scope combination. The partition consists of a tube with two fins, one on each side. „ c ... The ɂ 2.7 mm arthroscope and the partition can be placed simultaneously in the sheath. „ d ... Fron- tal view of the practical embodiment with in its center the tip of the arthroscope. Around it, the partition with fins is placed. Finally, the pins can be seen at the tip of the sheath used for the inflow stream „ upper right part ... . „ e ... Apart from an unmodi- fied tip of the sheath, three other sheath tips are tested: tip with two holes „ this implies that if the partition is used there is one hole in the inflow and one in the outflow ... , tip with six pins in the inflow stream, and tip with four holes. 

Contexts in source publication

Context 1

... of variables can only be set within strict limits. First, the intra-articular pressure level is limited for safety reasons. High pressures lead to extravasation of saline fluid and potentially tissue rupture ͓ 9,16,17 ͔ . Second, to the authors’ knowledge, no sub- stitute fluid exists for saline. Third, the lengths of the sheath and the cannula are bounded by the length of existing arthroscopes, and by the thickness of the tissues between the skin and the actual joint space. Finally, the outer diameter of the sheath and the cannula is limited by the maximum size of the skin incisions that are used to obtain access to a joint. From this analysis, two concepts were developed: one for the three-portal technique and one for the two-portal technique. 2.2.1 Three-Portal Technique . In this configuration, separated inflow and outflow streams are already present, due to the use of a separate outflow cannula for suction. Hence, the focus was on decreasing the restriction of the scope-sheath combination. The most promising concept was to increase the cross-sectional area of the annulus, because the flow would increase by a power of 2, and the Reynolds number would be increased proportionally. Since the value of the outer diameter was bounded, the following concept was proposed: Use a smaller diameter arthroscope ͑ 2.7 mm ͒ than normal ͑ 4 mm ͒ in combination with a conventional sheath ͑ Fig. 2 ͒ . With the current advances in technology, 2.7 mm arthroscopes can produce images of equal quality and size as 4 mm arthroscopes. Both types have equal direction of view ͑ 30 deg ͒ as well as field of view ͑ 105 deg ͒ . This new configuration more than doubles the cross-sectional area of the scope-sheath combination. Additionally, the stopcocks can be placed at a smaller angle than 90 deg to minimize losses caused by pipe bending. 2.2.2 Two-Portal Technique . For this technique, the first focus was on creating separate inflow and outflow streams to guarantee that all incoming fluids would enter and leave the joint continu- ously. To start up the design process, the analysis of existing patents on sheaths or cannulas was performed. Several patents of multilumen sheaths with separate inflow and outflow channels were found ͓ 18–24 ͔ . The concept of a multilumen sheath was combined with the concept of the new scope-sheath combination as presented for the three-portal technique. The Reynolds number was used to choose an allocation of the cross-sectional area that would stimulate the initiation of a turbulent flow, maximally. Thereto, the mean velocity ͑ v average ͒ in Eq. ͑ 3 ͒ was replaced with Q / A , and D was replaced with the hydraulic diameter ͑ D h ͒ , which is defined as 4 A / O , ͓ 12 ͔ ␳ ·4· Q Re = ͑ 4 ͒ ␩ · O where O is the wetted perimeter. Equation ͑ 4 ͒ shows that high values of Re can be achieved by minimizing the wetted perimeter. This implies that in the ideal situation the cross-sectional area of the inflow channel should resemble a circle. Lastly, to stimulate the initiation of turbulent flow, another concept was added: dis- rupting the inflow stream by placing bodies in the cross-sectional area at the tip or by introducing holes at the tip ͑ Fig. 2 ͒ . 2.3 Practical Embodiments. Fluid mechanics theory gave substantial leads to improve irrigation, but experiments are necessary to assess empirical values, and to evaluate the impact of the different concepts in the new sheath. Thereto, practical embodiments were fabricated of the proposed concepts ͑ Fig. 2 ͒ . Care was taken to avoid pointy shapes and sharp edges in the prototypes. An arthroscopic sheath, normally used with a 4 mm arthroscope ͑ Trocar Sleeve 5.6, 8885.041, Richard Wolf GmbH, Gent, Belgium ͒ , was lengthened to fit with the 2.7 mm arthroscope ͑ 8672.422, Richard Wolf GmbH, Gent, Belgium ͒ , and its stopcocks were replaced at an angle of 45 deg. A separate embodiment to divide the sheath in a multilumen construction consisted of a tube ͑ 3.2– 2.8 mm ͒ with two fins, one on each side ͑ height: 0.83 mm; width: 0.36 mm ͒ ͑ Fig. 2 ͒ . This way the cross-sectional area of the inflow stream has the shape of half a donut. This shape was as close to a circle as possible ͑ Fig. 2 ͒ . The fins’ widths were minimized and silver soldered on the tube using a special mold. The partition can be inserted simultaneously with the 2.7 mm arthroscope in the sheath. This design allows an existing obturator to be inserted in the sheath for safe access in a joint, which takes place prior to the scope being inserted in the sheath. As only a single piece embodiment was fabricated, stainless steel metal was used. This is not the first choice in achieving a watertight sealing between inflow and outflow lumens. Therefore, a thin layer of bee wax was added between the sheath and partition when performing the laboratory tests. Lastly, several tips of the sheath were con- structed: having two larger holes, four smaller holes, or pins ͑ 0.4 mm ͒ inserted in the inflow channel ͑ Fig. 2 and Table 2 ͒ . The total surface of the holes was kept constant and equal to the total surface of the three holes that are present in the routinely used sheath ͑ 9.42 mm 2 ͒ . A connector was fabricated to use the same embodiment for testing different tips ͑ Fig. 2 ͒ . 2.4 Evaluation. The evaluation took place in a physical simulation environment for an arthroscopic knee joint surgery ͓ 25 ͔ . In this setup, routinely used three- and two-portal irrigation configurations were compared with the new practical embodiments. Ma- terials included a separate outflow cannula ͑ 8672.422, Richard Wolf GmbH, Gent, Belgium ͒ , inflow tubing ͑ Y-irrigation system urology, B. Braun Medical BV, Oss, NL ͒ , and outflow tubing ͑ suction tubing PVC 2 connectors, 6 ϫ 9 mm, L 3.50 m, Medica Europe BV, Oss, NL ͒ . The simulation environment was equipped with a video and data acquisition system that could simultaneously record two pressure signals, two flow signals, and two digital video streams ͓ 25 ͔ . The most important objective measure was the irrigation time ͑ t ir ͒ . The irrigation time was defined as the time from the first appearance of a disturbance until the view completely cleared. This measure is directly linked to the arthroscopic image quality. The condition for which t ir is the shortest gives the fastest irrigation of the joint. In the experimental evaluation, the irrigation time was visualized by injecting a volume of 0.5 ml blue-colored ink mixed with milk ͑ 1:10 ͒ in the inflow stream. Video images of the blue streams were recorded of the view from the arthroscope, and of the view from underneath a transparent tibial surface of knee joint phantom ͑ Fig. 3 ͒ . The irrigation time of the arthroscopic view was determined with image processing. Additionally, the percentage of the remaining blue-colored areas was determined from the overview video stream at each irrigation time. The pressure and the flow of each condition were measured in the inflow tubing just before the sheath or cannula ͑ P 1 and Q ͒ . The intra-articular pressure was measured in the knee joint phantom ͑ P 2 ͒ ͑ Fig. 3 ͒ . The initial pressure was set by placing a 3 liter saline fluid bag at a height of 0.66 m above the knee phantom ͑ 6.5 kPa or 49 mm Hg ͒ ͑ Fig. 1 ͒ . This pressure is equal to the normal set pressure used in the Daycare Surgical Center of the AMC. An active suction device was connected to the outflow stream, which had a set suction pressure of Ϫ 10 kPa ͑ Ϫ 75 mm Hg ͒ . The measurements were repeated ten times for each experimental condi- tion. The scope-sheath combination was inserted in the anteromedial portal, and repositioned after each repetition to visualize the different parts of the medial compartment of the knee. The same order of repositioning was used for each condition. The fluid bag was refilled after performing ten repetitions of each condition. A detailed scheme of the conditions is shown in Table 1. A comparison of the three-portal technique is presented in Row A, where two conventional configurations are shown in Conditions 1 and 2, the new sheath with and without partition, and separate outflow in Conditions 3 and 4, respectively. For all conditions in Row A, clinical practice was mimicked by allowing leakage of saline along the instrument portal through a hole ͑ 0.35 mm ͒ . The same leakage was also allowed for Condition 1 in Row B, where irrigation was performed by intermittently opening and closing the stopcocks by hand with a frequency of about 0.2 Hz ͑ Table 1 ͒ . Conditions 2 and 3 of Row B had continuous streams due to the new sheath with partition. Both conditions are also included in Row C, where the effect of different tips is compared. Finally, the effect of using the shaver for suction was compared in Row D with again the conventional setup presented in Condition 1. The shaver is an instrument that cuts and sucks tissue simultaneously. Data processing was performed with MATLAB , version 7.0.4.365 ͑ R14 ͒ ͑ The Mathworks, Natick, MA ͒ . A specially designed segmentation routine as described in Tuijthof et al. ͓ 14 ͔ was used to detect the blue-colored areas in the video streams. The video images were resampled to 5 Hz, and downsized to a quarter of the recorded image to speed up the segmentation. A data set of one condition consisted of the irrigation time ͑ t ir ͒ , the pressure before the sheath ͑ P 1 ͒ , the pressure in the knee phantom ͑ P 2 ͒ , the overall flow ͑ Q ͒ , and the percentage of blue-colored area in the overview image for each of the ten repetitions ͑ Table 1 ͒ . Statistical analysis was performed with SPSS 12.0.2 ͑ SPSS Inc., Chicago, IL ͒ . The pres- ence of a normal distribution for all data sets was determined with the Kolmogorov–Smirnov and Shapiro–Wilk tests. With the help of a one-way analysis of variance ͑ ANOVA ͒ test significant dif- ferences were assessed. Posthoc Bonferroni-tests ͑ p Ͻ 0.05 ͒ were performed to highlight the significant internal differences ...

Context 2

... Q is the flow. The flow can be increased by increasing the pressure and the diameter, and by decreasing the density and f ͑ Re, L / D , k / D ͒ ͑ Eq. ͑ 2 ͒͒ . The characteristic nature of the flow is determined by the Reynolds number, which is calculated as the ratio of the friction and the inertia forces, ␳ · v · D Re = ͑ 3 ͒ where is the dynamic fluid viscosity. As a rule of thumb, the flow in a pipe is laminar if Re Ͻ 2000, and turbulent if Re Ͼ 3000 ͓ 12 ͔ . In between these values the flow is transitional, and it is impossible to determine the friction factor. The Reynolds number can be increased by increasing the fluid density, the mean velocity, and the diameter of the tubing, and by decreasing the dynamic viscosity ͑ Eq. ͑ 3 ͒͒ . Given the arthroscopic setting, the values of a significant number of variables can only be set within strict limits. First, the intra-articular pressure level is limited for safety reasons. High pressures lead to extravasation of saline fluid and potentially tissue rupture ͓ 9,16,17 ͔ . Second, to the authors’ knowledge, no sub- stitute fluid exists for saline. Third, the lengths of the sheath and the cannula are bounded by the length of existing arthroscopes, and by the thickness of the tissues between the skin and the actual joint space. Finally, the outer diameter of the sheath and the cannula is limited by the maximum size of the skin incisions that are used to obtain access to a joint. From this analysis, two concepts were developed: one for the three-portal technique and one for the two-portal technique. 2.2.1 Three-Portal Technique . In this configuration, separated inflow and outflow streams are already present, due to the use of a separate outflow cannula for suction. Hence, the focus was on decreasing the restriction of the scope-sheath combination. The most promising concept was to increase the cross-sectional area of the annulus, because the flow would increase by a power of 2, and the Reynolds number would be increased proportionally. Since the value of the outer diameter was bounded, the following concept was proposed: Use a smaller diameter arthroscope ͑ 2.7 mm ͒ than normal ͑ 4 mm ͒ in combination with a conventional sheath ͑ Fig. 2 ͒ . With the current advances in technology, 2.7 mm arthroscopes can produce images of equal quality and size as 4 mm arthroscopes. Both types have equal direction of view ͑ 30 deg ͒ as well as field of view ͑ 105 deg ͒ . This new configuration more than doubles the cross-sectional area of the scope-sheath combination. Additionally, the stopcocks can be placed at a smaller angle than 90 deg to minimize losses caused by pipe bending. 2.2.2 Two-Portal Technique . For this technique, the first focus was on creating separate inflow and outflow streams to guarantee that all incoming fluids would enter and leave the joint continu- ously. To start up the design process, the analysis of existing patents on sheaths or cannulas was performed. Several patents of multilumen sheaths with separate inflow and outflow channels were found ͓ 18–24 ͔ . The concept of a multilumen sheath was combined with the concept of the new scope-sheath combination as presented for the three-portal technique. The Reynolds number was used to choose an allocation of the cross-sectional area that would stimulate the initiation of a turbulent flow, maximally. Thereto, the mean velocity ͑ v average ͒ in Eq. ͑ 3 ͒ was replaced with Q / A , and D was replaced with the hydraulic diameter ͑ D h ͒ , which is defined as 4 A / O , ͓ 12 ͔ ␳ ·4· Q Re = ͑ 4 ͒ ␩ · O where O is the wetted perimeter. Equation ͑ 4 ͒ shows that high values of Re can be achieved by minimizing the wetted perimeter. This implies that in the ideal situation the cross-sectional area of the inflow channel should resemble a circle. Lastly, to stimulate the initiation of turbulent flow, another concept was added: dis- rupting the inflow stream by placing bodies in the cross-sectional area at the tip or by introducing holes at the tip ͑ Fig. 2 ͒ . 2.3 Practical Embodiments. Fluid mechanics theory gave substantial leads to improve irrigation, but experiments are necessary to assess empirical values, and to evaluate the impact of the different concepts in the new sheath. Thereto, practical embodiments were fabricated of the proposed concepts ͑ Fig. 2 ͒ . Care was taken to avoid pointy shapes and sharp edges in the prototypes. An arthroscopic sheath, normally used with a 4 mm arthroscope ͑ Trocar Sleeve 5.6, 8885.041, Richard Wolf GmbH, Gent, Belgium ͒ , was lengthened to fit with the 2.7 mm arthroscope ͑ 8672.422, Richard Wolf GmbH, Gent, Belgium ͒ , and its stopcocks were replaced at an angle of 45 deg. A separate embodiment to divide the sheath in a multilumen construction consisted of a tube ͑ 3.2– 2.8 mm ͒ with two fins, one on each side ͑ height: 0.83 mm; width: 0.36 mm ͒ ͑ Fig. 2 ͒ . This way the cross-sectional area of the inflow stream has the shape of half a donut. This shape was as close to a circle as possible ͑ Fig. 2 ͒ . The fins’ widths were minimized and silver soldered on the tube using a special mold. The partition can be inserted simultaneously with the 2.7 mm arthroscope in the sheath. This design allows an existing obturator to be inserted in the sheath for safe access in a joint, which takes place prior to the scope being inserted in the sheath. As only a single piece embodiment was fabricated, stainless steel metal was used. This is not the first choice in achieving a watertight sealing between inflow and outflow lumens. Therefore, a thin layer of bee wax was added between the sheath and partition when performing the laboratory tests. Lastly, several tips of the sheath were con- structed: having two larger holes, four smaller holes, or pins ͑ 0.4 mm ͒ inserted in the inflow channel ͑ Fig. 2 and Table 2 ͒ . The total surface of the holes was kept constant and equal to the total surface of the three holes that are present in the routinely used sheath ͑ 9.42 mm 2 ͒ . A connector was fabricated to use the same embodiment for testing different tips ͑ Fig. 2 ͒ . 2.4 Evaluation. The evaluation took place in a physical simulation environment for an arthroscopic knee joint surgery ͓ 25 ͔ . In this setup, routinely used three- and two-portal irrigation configurations were compared with the new practical embodiments. Ma- terials included a separate outflow cannula ͑ 8672.422, Richard Wolf GmbH, Gent, Belgium ͒ , inflow tubing ͑ Y-irrigation system urology, B. Braun Medical BV, Oss, NL ͒ , and outflow tubing ͑ suction tubing PVC 2 connectors, 6 ϫ 9 mm, L 3.50 m, Medica Europe BV, Oss, NL ͒ . The simulation environment was equipped with a video and data acquisition system that could simultaneously record two pressure signals, two flow signals, and two digital video streams ͓ 25 ͔ . The most important objective measure was the irrigation time ͑ t ir ͒ . The irrigation time was defined as the time from the first appearance of a disturbance until the view completely cleared. This measure is directly linked to the arthroscopic image quality. The condition for which t ir is the shortest gives the fastest irrigation of the joint. In the experimental evaluation, the irrigation time was visualized by injecting a volume of 0.5 ml blue-colored ink mixed with milk ͑ 1:10 ͒ in the inflow stream. Video images of the blue streams were recorded of the view from the arthroscope, and of the view from underneath a transparent tibial surface of knee joint phantom ͑ Fig. 3 ͒ . The irrigation time of the arthroscopic view was determined with image processing. Additionally, the percentage of the remaining blue-colored areas was determined from the overview video stream at each irrigation time. The pressure and the flow of each condition were measured in the inflow tubing just before the sheath or cannula ͑ P 1 and Q ͒ . The intra-articular pressure was measured in the knee joint phantom ͑ P 2 ͒ ͑ Fig. 3 ͒ . The initial pressure was set by placing a 3 liter saline fluid bag at a height of 0.66 m above the knee phantom ͑ 6.5 kPa or 49 mm Hg ͒ ͑ Fig. 1 ͒ . This pressure is equal to the normal set pressure used in the Daycare Surgical Center of the AMC. An active suction device was connected to the outflow stream, which had a set suction pressure of Ϫ 10 kPa ͑ Ϫ 75 mm Hg ͒ . The measurements were repeated ten times for each experimental condi- tion. The scope-sheath combination was inserted in the anteromedial portal, and repositioned after each repetition to visualize the different parts of the medial compartment of the knee. The same order of repositioning was used for each condition. The fluid bag was refilled after performing ten repetitions of each condition. A detailed scheme of the conditions is shown in Table 1. A comparison of the three-portal technique is presented in Row A, where two conventional configurations are shown in Conditions 1 and 2, the new sheath with and without partition, and separate outflow in Conditions 3 and 4, respectively. For all conditions in Row A, clinical practice was mimicked by allowing leakage of saline along the instrument portal through a hole ͑ 0.35 mm ͒ . The same leakage was also allowed for Condition 1 in Row B, where irrigation was performed by intermittently opening and closing the stopcocks by hand with a frequency of about 0.2 Hz ͑ Table 1 ͒ . Conditions 2 and 3 of Row B had continuous streams due to the new sheath with partition. Both conditions are also included in Row C, where the effect of different tips is compared. Finally, the effect of using the shaver for suction was compared in Row D with again the conventional setup presented in Condition 1. The shaver is an instrument that cuts and sucks tissue simultaneously. Data processing was performed with MATLAB , version 7.0.4.365 ͑ R14 ͒ ͑ The Mathworks, Natick, MA ͒ . A specially designed ...

Context 3

... flow can be increased by increasing the pressure and the diameter, and by decreasing the density and f ͑ Re, L / D , k / D ͒ ͑ Eq. ͑ 2 ͒͒ . The characteristic nature of the flow is determined by the Reynolds number, which is calculated as the ratio of the friction and the inertia forces, ␳ · v · D Re = ͑ 3 ͒ where is the dynamic fluid viscosity. As a rule of thumb, the flow in a pipe is laminar if Re Ͻ 2000, and turbulent if Re Ͼ 3000 ͓ 12 ͔ . In between these values the flow is transitional, and it is impossible to determine the friction factor. The Reynolds number can be increased by increasing the fluid density, the mean velocity, and the diameter of the tubing, and by decreasing the dynamic viscosity ͑ Eq. ͑ 3 ͒͒ . Given the arthroscopic setting, the values of a significant number of variables can only be set within strict limits. First, the intra-articular pressure level is limited for safety reasons. High pressures lead to extravasation of saline fluid and potentially tissue rupture ͓ 9,16,17 ͔ . Second, to the authors’ knowledge, no sub- stitute fluid exists for saline. Third, the lengths of the sheath and the cannula are bounded by the length of existing arthroscopes, and by the thickness of the tissues between the skin and the actual joint space. Finally, the outer diameter of the sheath and the cannula is limited by the maximum size of the skin incisions that are used to obtain access to a joint. From this analysis, two concepts were developed: one for the three-portal technique and one for the two-portal technique. 2.2.1 Three-Portal Technique . In this configuration, separated inflow and outflow streams are already present, due to the use of a separate outflow cannula for suction. Hence, the focus was on decreasing the restriction of the scope-sheath combination. The most promising concept was to increase the cross-sectional area of the annulus, because the flow would increase by a power of 2, and the Reynolds number would be increased proportionally. Since the value of the outer diameter was bounded, the following concept was proposed: Use a smaller diameter arthroscope ͑ 2.7 mm ͒ than normal ͑ 4 mm ͒ in combination with a conventional sheath ͑ Fig. 2 ͒ . With the current advances in technology, 2.7 mm arthroscopes can produce images of equal quality and size as 4 mm arthroscopes. Both types have equal direction of view ͑ 30 deg ͒ as well as field of view ͑ 105 deg ͒ . This new configuration more than doubles the cross-sectional area of the scope-sheath combination. Additionally, the stopcocks can be placed at a smaller angle than 90 deg to minimize losses caused by pipe bending. 2.2.2 Two-Portal Technique . For this technique, the first focus was on creating separate inflow and outflow streams to guarantee that all incoming fluids would enter and leave the joint continu- ously. To start up the design process, the analysis of existing patents on sheaths or cannulas was performed. Several patents of multilumen sheaths with separate inflow and outflow channels were found ͓ 18–24 ͔ . The concept of a multilumen sheath was combined with the concept of the new scope-sheath combination as presented for the three-portal technique. The Reynolds number was used to choose an allocation of the cross-sectional area that would stimulate the initiation of a turbulent flow, maximally. Thereto, the mean velocity ͑ v average ͒ in Eq. ͑ 3 ͒ was replaced with Q / A , and D was replaced with the hydraulic diameter ͑ D h ͒ , which is defined as 4 A / O , ͓ 12 ͔ ␳ ·4· Q Re = ͑ 4 ͒ ␩ · O where O is the wetted perimeter. Equation ͑ 4 ͒ shows that high values of Re can be achieved by minimizing the wetted perimeter. This implies that in the ideal situation the cross-sectional area of the inflow channel should resemble a circle. Lastly, to stimulate the initiation of turbulent flow, another concept was added: dis- rupting the inflow stream by placing bodies in the cross-sectional area at the tip or by introducing holes at the tip ͑ Fig. 2 ͒ . 2.3 Practical Embodiments. Fluid mechanics theory gave substantial leads to improve irrigation, but experiments are necessary to assess empirical values, and to evaluate the impact of the different concepts in the new sheath. Thereto, practical embodiments were fabricated of the proposed concepts ͑ Fig. 2 ͒ . Care was taken to avoid pointy shapes and sharp edges in the prototypes. An arthroscopic sheath, normally used with a 4 mm arthroscope ͑ Trocar Sleeve 5.6, 8885.041, Richard Wolf GmbH, Gent, Belgium ͒ , was lengthened to fit with the 2.7 mm arthroscope ͑ 8672.422, Richard Wolf GmbH, Gent, Belgium ͒ , and its stopcocks were replaced at an angle of 45 deg. A separate embodiment to divide the sheath in a multilumen construction consisted of a tube ͑ 3.2– 2.8 mm ͒ with two fins, one on each side ͑ height: 0.83 mm; width: 0.36 mm ͒ ͑ Fig. 2 ͒ . This way the cross-sectional area of the inflow stream has the shape of half a donut. This shape was as close to a circle as possible ͑ Fig. 2 ͒ . The fins’ widths were minimized and silver soldered on the tube using a special mold. The partition can be inserted simultaneously with the 2.7 mm arthroscope in the sheath. This design allows an existing obturator to be inserted in the sheath for safe access in a joint, which takes place prior to the scope being inserted in the sheath. As only a single piece embodiment was fabricated, stainless steel metal was used. This is not the first choice in achieving a watertight sealing between inflow and outflow lumens. Therefore, a thin layer of bee wax was added between the sheath and partition when performing the laboratory tests. Lastly, several tips of the sheath were con- structed: having two larger holes, four smaller holes, or pins ͑ 0.4 mm ͒ inserted in the inflow channel ͑ Fig. 2 and Table 2 ͒ . The total surface of the holes was kept constant and equal to the total surface of the three holes that are present in the routinely used sheath ͑ 9.42 mm 2 ͒ . A connector was fabricated to use the same embodiment for testing different tips ͑ Fig. 2 ͒ . 2.4 Evaluation. The evaluation took place in a physical simulation environment for an arthroscopic knee joint surgery ͓ 25 ͔ . In this setup, routinely used three- and two-portal irrigation configurations were compared with the new practical embodiments. Ma- terials included a separate outflow cannula ͑ 8672.422, Richard Wolf GmbH, Gent, Belgium ͒ , inflow tubing ͑ Y-irrigation system urology, B. Braun Medical BV, Oss, NL ͒ , and outflow tubing ͑ suction tubing PVC 2 connectors, 6 ϫ 9 mm, L 3.50 m, Medica Europe BV, Oss, NL ͒ . The simulation environment was equipped with a video and data acquisition system that could simultaneously record two pressure signals, two flow signals, and two digital video streams ͓ 25 ͔ . The most important objective measure was the irrigation time ͑ t ir ͒ . The irrigation time was defined as the time from the first appearance of a disturbance until the view completely cleared. This measure is directly linked to the arthroscopic image quality. The condition for which t ir is the shortest gives the fastest irrigation of the joint. In the experimental evaluation, the irrigation time was visualized by injecting a volume of 0.5 ml blue-colored ink mixed with milk ͑ 1:10 ͒ in the inflow stream. Video images of the blue streams were recorded of the view from the arthroscope, and of the view from underneath a transparent tibial surface of knee joint phantom ͑ Fig. 3 ͒ . The irrigation time of the arthroscopic view was determined with image processing. Additionally, the percentage of the remaining blue-colored areas was determined from the overview video stream at each irrigation time. The pressure and the flow of each condition were measured in the inflow tubing just before the sheath or cannula ͑ P 1 and Q ͒ . The intra-articular pressure was measured in the knee joint phantom ͑ P 2 ͒ ͑ Fig. 3 ͒ . The initial pressure was set by placing a 3 liter saline fluid bag at a height of 0.66 m above the knee phantom ͑ 6.5 kPa or 49 mm Hg ͒ ͑ Fig. 1 ͒ . This pressure is equal to the normal set pressure used in the Daycare Surgical Center of the AMC. An active suction device was connected to the outflow stream, which had a set suction pressure of Ϫ 10 kPa ͑ Ϫ 75 mm Hg ͒ . The measurements were repeated ten times for each experimental condi- tion. The scope-sheath combination was inserted in the anteromedial portal, and repositioned after each repetition to visualize the different parts of the medial compartment of the knee. The same order of repositioning was used for each condition. The fluid bag was refilled after performing ten repetitions of each condition. A detailed scheme of the conditions is shown in Table 1. A comparison of the three-portal technique is presented in Row A, where two conventional configurations are shown in Conditions 1 and 2, the new sheath with and without partition, and separate outflow in Conditions 3 and 4, respectively. For all conditions in Row A, clinical practice was mimicked by allowing leakage of saline along the instrument portal through a hole ͑ 0.35 mm ͒ . The same leakage was also allowed for Condition 1 in Row B, where irrigation was performed by intermittently opening and closing the stopcocks by hand with a frequency of about 0.2 Hz ͑ Table 1 ͒ . Conditions 2 and 3 of Row B had continuous streams due to the new sheath with partition. Both conditions are also included in Row C, where the effect of different tips is compared. Finally, the effect of using the shaver for suction was compared in Row D with again the conventional setup presented in Condition 1. The shaver is an instrument that cuts and sucks tissue simultaneously. Data processing was performed with MATLAB , version 7.0.4.365 ͑ R14 ͒ ͑ The Mathworks, Natick, MA ͒ . A specially designed segmentation routine as described in Tuijthof et al. ͓ 14 ͔ was used to detect the blue-colored areas in the video streams. The video images were ...

Context 4

... Q is the flow. The flow can be increased by increasing the pressure and the diameter, and by decreasing the density and f ͑ Re, L / D , k / D ͒ ͑ Eq. ͑ 2 ͒͒ . The characteristic nature of the flow is determined by the Reynolds number, which is calculated as the ratio of the friction and the inertia forces, ␳ · v · D Re = ͑ 3 ͒ where is the dynamic fluid viscosity. As a rule of thumb, the flow in a pipe is laminar if Re Ͻ 2000, and turbulent if Re Ͼ 3000 ͓ 12 ͔ . In between these values the flow is transitional, and it is impossible to determine the friction factor. The Reynolds number can be increased by increasing the fluid density, the mean velocity, and the diameter of the tubing, and by decreasing the dynamic viscosity ͑ Eq. ͑ 3 ͒͒ . Given the arthroscopic setting, the values of a significant number of variables can only be set within strict limits. First, the intra-articular pressure level is limited for safety reasons. High pressures lead to extravasation of saline fluid and potentially tissue rupture ͓ 9,16,17 ͔ . Second, to the authors’ knowledge, no sub- stitute fluid exists for saline. Third, the lengths of the sheath and the cannula are bounded by the length of existing arthroscopes, and by the thickness of the tissues between the skin and the actual joint space. Finally, the outer diameter of the sheath and the cannula is limited by the maximum size of the skin incisions that are used to obtain access to a joint. From this analysis, two concepts were developed: one for the three-portal technique and one for the two-portal technique. 2.2.1 Three-Portal Technique . In this configuration, separated inflow and outflow streams are already present, due to the use of a separate outflow cannula for suction. Hence, the focus was on decreasing the restriction of the scope-sheath combination. The most promising concept was to increase the cross-sectional area of the annulus, because the flow would increase by a power of 2, and the Reynolds number would be increased proportionally. Since the value of the outer diameter was bounded, the following concept was proposed: Use a smaller diameter arthroscope ͑ 2.7 mm ͒ than normal ͑ 4 mm ͒ in combination with a conventional sheath ͑ Fig. 2 ͒ . With the current advances in technology, 2.7 mm arthroscopes can produce images of equal quality and size as 4 mm arthroscopes. Both types have equal direction of view ͑ 30 deg ͒ as well as field of view ͑ 105 deg ͒ . This new configuration more than doubles the cross-sectional area of the scope-sheath combination. Additionally, the stopcocks can be placed at a smaller angle than 90 deg to minimize losses caused by pipe bending. 2.2.2 Two-Portal Technique . For this technique, the first focus was on creating separate inflow and outflow streams to guarantee that all incoming fluids would enter and leave the joint continu- ously. To start up the design process, the analysis of existing patents on sheaths or cannulas was performed. Several patents of multilumen sheaths with separate inflow and outflow channels were found ͓ 18–24 ͔ . The concept of a multilumen sheath was combined with the concept of the new scope-sheath combination as presented for the three-portal technique. The Reynolds number was used to choose an allocation of the cross-sectional area that would stimulate the initiation of a turbulent flow, maximally. Thereto, the mean velocity ͑ v average ͒ in Eq. ͑ 3 ͒ was replaced with Q / A , and D was replaced with the hydraulic diameter ͑ D h ͒ , which is defined as 4 A / O , ͓ 12 ͔ ␳ ·4· Q Re = ͑ 4 ͒ ␩ · O where O is the wetted perimeter. Equation ͑ 4 ͒ shows that high values of Re can be achieved by minimizing the wetted perimeter. This implies that in the ideal situation the cross-sectional area of the inflow channel should resemble a circle. Lastly, to stimulate the initiation of turbulent flow, another concept was added: dis- rupting the inflow stream by placing bodies in the cross-sectional area at the tip or by introducing holes at the tip ͑ Fig. 2 ͒ . 2.3 Practical Embodiments. Fluid mechanics theory gave substantial leads to improve irrigation, but experiments are necessary to assess empirical values, and to evaluate the impact of the different concepts in the new sheath. Thereto, practical embodiments were fabricated of the proposed concepts ͑ Fig. 2 ͒ . Care was taken to avoid pointy shapes and sharp edges in the prototypes. An arthroscopic sheath, normally used with a 4 mm arthroscope ͑ Trocar Sleeve 5.6, 8885.041, Richard Wolf GmbH, Gent, Belgium ͒ , was lengthened to fit with the 2.7 mm arthroscope ͑ 8672.422, Richard Wolf GmbH, Gent, Belgium ͒ , and its stopcocks were replaced at an angle of 45 deg. A separate embodiment to divide the sheath in a multilumen construction consisted of a tube ͑ 3.2– 2.8 mm ͒ with two fins, one on each side ͑ height: 0.83 mm; width: 0.36 mm ͒ ͑ Fig. 2 ͒ . This way the cross-sectional area of the inflow stream has the shape of half a donut. This shape was as close to a circle as possible ͑ Fig. 2 ͒ . The fins’ widths were minimized and silver soldered on the tube using a special mold. The partition can be inserted simultaneously with the 2.7 mm arthroscope in the sheath. This design allows an existing obturator to be inserted in the sheath for safe access in a joint, which takes place prior to the scope being inserted in the sheath. As only a single piece embodiment was fabricated, stainless steel metal was used. This is not the first choice in achieving a watertight sealing between inflow and outflow lumens. Therefore, a thin layer of bee wax was added between the sheath and partition when performing the laboratory tests. Lastly, several tips of the sheath were con- structed: having two larger holes, four smaller holes, or pins ͑ 0.4 mm ͒ inserted in the inflow channel ͑ Fig. 2 and Table 2 ͒ . The total surface of the holes was kept constant and equal to the total surface of the three holes that are present in the routinely used sheath ͑ 9.42 mm 2 ͒ . A connector was fabricated to use the same embodiment for testing different tips ͑ Fig. 2 ͒ . 2.4 Evaluation. The evaluation took place in a physical simulation environment for an arthroscopic knee joint surgery ͓ 25 ͔ . In this setup, routinely used three- and two-portal irrigation configurations were compared with the new practical embodiments. Ma- terials included a separate outflow cannula ͑ 8672.422, Richard Wolf GmbH, Gent, Belgium ͒ , inflow tubing ͑ Y-irrigation system urology, B. Braun Medical BV, Oss, NL ͒ , and outflow tubing ͑ suction tubing PVC 2 connectors, 6 ϫ 9 mm, L 3.50 m, Medica Europe BV, Oss, NL ͒ . The simulation environment was equipped with a video and data acquisition system that could simultaneously record two pressure signals, two flow signals, and two digital video streams ͓ 25 ͔ . The most important objective measure was the irrigation time ͑ t ir ͒ . The irrigation time was defined as the time from the first appearance of a disturbance until the view completely cleared. This measure is directly linked to the arthroscopic image quality. The condition for which t ir is the shortest gives the fastest irrigation of the joint. In the experimental evaluation, the irrigation time was visualized by injecting a volume of 0.5 ml blue-colored ink mixed with milk ͑ 1:10 ͒ in the inflow stream. Video images of the blue streams were recorded of the view from the arthroscope, and of the view from underneath a transparent tibial surface of knee joint phantom ͑ Fig. 3 ͒ . The irrigation time of the arthroscopic view was determined with image processing. Additionally, the percentage of the remaining blue-colored areas was determined from the overview video stream at each irrigation time. The pressure and the flow of each condition were measured in the inflow tubing just before the sheath or cannula ͑ P 1 and Q ͒ . The intra-articular pressure was measured in the knee joint phantom ͑ P 2 ͒ ͑ Fig. 3 ͒ . The initial pressure was set by placing a 3 liter saline fluid bag at a height of 0.66 m above the knee phantom ͑ 6.5 kPa or 49 mm Hg ͒ ͑ Fig. 1 ͒ . This pressure is equal to the normal set pressure used in the Daycare Surgical Center of the AMC. An active suction device was connected to the outflow stream, which had a set suction pressure of Ϫ 10 kPa ͑ Ϫ 75 mm Hg ͒ . The measurements were repeated ten times for each experimental condi- tion. The scope-sheath combination was inserted in the anteromedial portal, and repositioned after each repetition to visualize the different parts of the medial compartment of the knee. The same order of repositioning was used for each condition. The fluid bag was refilled after performing ten repetitions of each condition. A detailed scheme of the conditions is shown in Table 1. A comparison of the three-portal technique is presented in Row A, where two conventional configurations are shown in Conditions 1 and 2, the new sheath with and without partition, and separate outflow in Conditions 3 and 4, ...

Context 5

... Q is the flow. The flow can be increased by increasing the pressure and the diameter, and by decreasing the density and f ͑ Re, L / D , k / D ͒ ͑ Eq. ͑ 2 ͒͒ . The characteristic nature of the flow is determined by the Reynolds number, which is calculated as the ratio of the friction and the inertia forces, ␳ · v · D Re = ͑ 3 ͒ where is the dynamic fluid viscosity. As a rule of thumb, the flow in a pipe is laminar if Re Ͻ 2000, and turbulent if Re Ͼ 3000 ͓ 12 ͔ . In between these values the flow is transitional, and it is impossible to determine the friction factor. The Reynolds number can be increased by increasing the fluid density, the mean velocity, and the diameter of the tubing, and by decreasing the dynamic viscosity ͑ Eq. ͑ 3 ͒͒ . Given the arthroscopic setting, the values of a significant number of variables can only be set within strict limits. First, the intra-articular pressure level is limited for safety reasons. High pressures lead to extravasation of saline fluid and potentially tissue rupture ͓ 9,16,17 ͔ . Second, to the authors’ knowledge, no sub- stitute fluid exists for saline. Third, the lengths of the sheath and the cannula are bounded by the length of existing arthroscopes, and by the thickness of the tissues between the skin and the actual joint space. Finally, the outer diameter of the sheath and the cannula is limited by the maximum size of the skin incisions that are used to obtain access to a joint. From this analysis, two concepts were developed: one for the three-portal technique and one for the two-portal technique. 2.2.1 Three-Portal Technique . In this configuration, separated inflow and outflow streams are already present, due to the use of a separate outflow cannula for suction. Hence, the focus was on decreasing the restriction of the scope-sheath combination. The most promising concept was to increase the cross-sectional area of the annulus, because the flow would increase by a power of 2, and the Reynolds number would be increased proportionally. Since the value of the outer diameter was bounded, the following concept was proposed: Use a smaller diameter arthroscope ͑ 2.7 mm ͒ than normal ͑ 4 mm ͒ in combination with a conventional sheath ͑ Fig. 2 ͒ . With the current advances in technology, 2.7 mm arthroscopes can produce images of equal quality and size as 4 mm arthroscopes. Both types have equal direction of view ͑ 30 deg ͒ as well as field of view ͑ 105 deg ͒ . This new configuration more than doubles the cross-sectional area of the scope-sheath combination. Additionally, the stopcocks can be placed at a smaller angle than 90 deg to minimize losses caused by pipe bending. 2.2.2 Two-Portal Technique . For this technique, the first focus was on creating separate inflow and outflow streams to guarantee that all incoming fluids would enter and leave the joint continu- ously. To start up the design process, the analysis of existing patents on sheaths or cannulas was performed. Several patents of multilumen sheaths with separate inflow and outflow channels were found ͓ 18–24 ͔ . The concept of a multilumen sheath was combined with the concept of the new scope-sheath combination as presented for the three-portal technique. The Reynolds number was used to choose an allocation of the cross-sectional area that would stimulate the initiation of a turbulent flow, maximally. Thereto, the mean velocity ͑ v average ͒ in Eq. ͑ 3 ͒ was replaced with Q / A , and D was replaced with the hydraulic diameter ͑ D h ͒ , which is defined as 4 A / O , ͓ 12 ͔ ␳ ·4· Q Re = ͑ 4 ͒ ␩ · O where O is the wetted perimeter. Equation ͑ 4 ͒ shows that high values of Re can be achieved by minimizing the wetted perimeter. This implies that in the ideal situation the cross-sectional area of the inflow channel should resemble a circle. Lastly, to stimulate the initiation of turbulent flow, another concept was added: dis- rupting the inflow stream by placing bodies in the cross-sectional area at the tip or by introducing holes at the tip ͑ Fig. 2 ͒ . 2.3 Practical Embodiments. Fluid mechanics theory gave substantial leads to improve irrigation, but experiments are necessary to assess empirical values, and to evaluate the impact of the different concepts in the new sheath. Thereto, practical embodiments were fabricated of the proposed concepts ͑ Fig. 2 ͒ . Care was taken to avoid pointy shapes and sharp edges in the prototypes. An arthroscopic sheath, normally used with a 4 mm arthroscope ͑ Trocar Sleeve 5.6, 8885.041, Richard Wolf GmbH, Gent, Belgium ͒ , was lengthened to fit with the 2.7 mm arthroscope ͑ 8672.422, Richard Wolf GmbH, Gent, Belgium ͒ , and its stopcocks were replaced at an angle of 45 deg. A separate embodiment to divide the sheath in a multilumen construction consisted of a tube ͑ 3.2– 2.8 mm ͒ with two fins, one on each side ͑ height: 0.83 mm; width: 0.36 mm ͒ ͑ Fig. 2 ͒ . This way the cross-sectional area of the inflow stream has the shape of half a donut. This shape was as close to a circle as possible ͑ Fig. 2 ͒ . The fins’ widths were minimized and silver soldered on the tube using a special mold. The partition can be inserted simultaneously with the 2.7 mm arthroscope in the sheath. This design allows an existing obturator to be inserted in the sheath for safe access in a joint, which takes place prior to the scope being inserted in the sheath. As only a single piece embodiment was fabricated, stainless steel metal was used. This is not the first choice in achieving a watertight sealing between inflow and outflow lumens. Therefore, a thin layer of bee wax was added between the sheath and partition when performing the laboratory tests. Lastly, several tips of the sheath were con- structed: having two larger holes, four smaller holes, or pins ͑ 0.4 mm ͒ inserted in the inflow channel ͑ Fig. 2 and Table 2 ͒ . The total surface of the holes was kept constant and equal to the total surface of the three holes that are present in the routinely used sheath ͑ 9.42 mm 2 ͒ . A connector was fabricated to use the same embodiment for testing different tips ͑ Fig. 2 ͒ . 2.4 Evaluation. The evaluation took place in a physical simulation environment for an arthroscopic knee joint surgery ͓ 25 ͔ . In this setup, routinely used three- and two-portal irrigation configurations were compared with the new practical embodiments. Ma- terials included a separate outflow cannula ͑ 8672.422, Richard Wolf GmbH, Gent, Belgium ͒ , inflow tubing ͑ Y-irrigation system urology, B. Braun Medical BV, Oss, NL ͒ , and outflow tubing ͑ suction tubing PVC 2 connectors, 6 ϫ 9 mm, L 3.50 m, Medica Europe BV, Oss, NL ͒ . The simulation environment was equipped with a video and data acquisition system that could simultaneously record two pressure signals, two flow signals, and two digital video streams ͓ 25 ͔ . The most important objective measure was the irrigation time ͑ t ir ͒ . The irrigation time was defined as the time from the first appearance of a disturbance until the view completely cleared. This measure is directly linked to the arthroscopic image quality. The condition for which t ir is the shortest gives the fastest irrigation of the joint. In the experimental evaluation, the ...

Context 6

... Q is the flow. The flow can be increased by increasing the pressure and the diameter, and by decreasing the density and f ͑ Re, L / D , k / D ͒ ͑ Eq. ͑ 2 ͒͒ . The characteristic nature of the flow is determined by the Reynolds number, which is calculated as the ratio of the friction and the inertia forces, ␳ · v · D Re = ͑ 3 ͒ where is the dynamic fluid viscosity. As a rule of thumb, the flow in a pipe is laminar if Re Ͻ 2000, and turbulent if Re Ͼ 3000 ͓ 12 ͔ . In between these values the flow is transitional, and it is impossible to determine the friction factor. The Reynolds number can be increased by increasing the fluid density, the mean velocity, and the diameter of the tubing, and by decreasing the dynamic viscosity ͑ Eq. ͑ 3 ͒͒ . Given the arthroscopic setting, the values of a significant number of variables can only be set within strict limits. First, the intra-articular pressure level is limited for safety reasons. High pressures lead to extravasation of saline fluid and potentially tissue rupture ͓ 9,16,17 ͔ . Second, to the authors’ knowledge, no sub- stitute fluid exists for saline. Third, the lengths of the sheath and the cannula are bounded by the length of existing arthroscopes, and by the thickness of the tissues between the skin and the actual joint space. Finally, the outer diameter of the sheath and the cannula is limited by the maximum size of the skin incisions that are used to obtain access to a joint. From this analysis, two concepts were developed: one for the three-portal technique and one for the two-portal technique. 2.2.1 Three-Portal Technique . In this configuration, separated inflow and outflow streams are already present, due to the use of a separate outflow cannula for suction. Hence, the focus was on decreasing the restriction of the scope-sheath combination. The most promising concept was to increase the cross-sectional area of the annulus, because the flow would increase by a power of 2, and the Reynolds number would be increased proportionally. Since the value of the outer diameter was bounded, the following concept was proposed: Use a smaller diameter arthroscope ͑ 2.7 mm ͒ than normal ͑ 4 mm ͒ in combination with a conventional sheath ͑ Fig. 2 ͒ . With the current advances in technology, 2.7 mm arthroscopes can produce images of equal quality and size as 4 mm arthroscopes. Both types have equal direction of view ͑ 30 deg ͒ as well as field of view ͑ 105 deg ͒ . This new configuration more than doubles the cross-sectional area of the scope-sheath combination. Additionally, the stopcocks can be placed at a smaller angle than 90 deg to minimize losses caused by pipe bending. 2.2.2 Two-Portal Technique . For this technique, the first focus was on creating separate inflow and outflow streams to guarantee that all incoming fluids would enter and leave the joint continu- ously. To start up the design process, the analysis of existing patents on sheaths or cannulas was performed. Several patents of multilumen sheaths with separate inflow and outflow channels were found ͓ 18–24 ͔ . The concept of a multilumen sheath was combined with the concept of the new scope-sheath combination as presented for the three-portal technique. The Reynolds number was used to choose an allocation of the cross-sectional area that would stimulate the initiation of a turbulent flow, maximally. Thereto, the mean velocity ͑ v average ͒ in Eq. ͑ 3 ͒ was replaced with Q / A , and D was replaced with the hydraulic diameter ͑ D h ͒ , which is defined as 4 A / O , ͓ 12 ͔ ␳ ·4· Q Re = ͑ 4 ͒ ␩ · O where O is the wetted perimeter. Equation ͑ 4 ͒ shows that high values of Re can be achieved by minimizing the wetted perimeter. This implies that in the ideal situation the cross-sectional area of the inflow channel should resemble a circle. Lastly, to stimulate the initiation of turbulent flow, another concept was added: dis- rupting the inflow stream by placing bodies in the cross-sectional area at the tip or by introducing holes at the tip ͑ Fig. 2 ͒ . 2.3 Practical Embodiments. Fluid mechanics theory gave substantial leads to improve irrigation, but experiments are necessary to assess empirical values, and to evaluate the impact of the different concepts in the new sheath. Thereto, practical embodiments were fabricated of the proposed concepts ͑ Fig. 2 ͒ . Care was taken to avoid pointy shapes and sharp edges in the prototypes. An arthroscopic sheath, normally used with a 4 mm arthroscope ͑ Trocar Sleeve 5.6, 8885.041, Richard Wolf GmbH, Gent, Belgium ͒ , was lengthened to fit with the 2.7 mm arthroscope ͑ 8672.422, Richard Wolf GmbH, Gent, Belgium ͒ , and its stopcocks were replaced at an angle of 45 deg. A separate embodiment to divide the sheath in a multilumen construction consisted of a tube ͑ 3.2– 2.8 mm ͒ with two fins, one on each side ͑ height: 0.83 mm; width: 0.36 mm ͒ ͑ Fig. 2 ͒ . This way the cross-sectional area of the inflow stream has the shape of half a donut. This shape was as close to a circle as possible ͑ Fig. 2 ͒ . The fins’ widths were minimized and silver soldered on the tube using a special mold. The partition can be inserted simultaneously with the 2.7 mm arthroscope in the sheath. This design allows an existing obturator to be inserted in the sheath for safe access in a joint, which takes place prior to the scope being inserted in the sheath. As only a single piece embodiment was fabricated, stainless steel metal was used. This is not the first choice in achieving a watertight sealing between inflow and outflow lumens. Therefore, a thin layer of bee wax was added between the sheath and partition when performing the laboratory tests. Lastly, several tips of the sheath were con- structed: having two larger holes, four smaller holes, or pins ͑ 0.4 mm ͒ inserted in the inflow channel ͑ Fig. 2 and Table 2 ͒ . The total surface of the holes was kept constant and equal to the total surface of the three holes that are present in the routinely used sheath ͑ 9.42 mm 2 ͒ . A connector was fabricated to use the same embodiment for testing different tips ͑ Fig. 2 ͒ . 2.4 Evaluation. The evaluation took place in a physical simulation environment for an arthroscopic knee joint surgery ͓ 25 ͔ . In this setup, routinely used three- and two-portal irrigation configurations were compared with the new practical embodiments. Ma- terials included a separate outflow cannula ͑ 8672.422, Richard Wolf GmbH, Gent, Belgium ͒ , inflow tubing ͑ Y-irrigation system urology, B. Braun Medical BV, Oss, NL ͒ , and outflow tubing ͑ suction tubing PVC 2 connectors, 6 ϫ 9 mm, L 3.50 m, Medica Europe BV, Oss, NL ͒ . The simulation environment was equipped with a video and data acquisition system that could simultaneously record two pressure signals, two flow signals, and two digital video streams ͓ 25 ͔ . The most important objective measure was the irrigation time ͑ t ir ͒ . The irrigation time was defined as the time from the first appearance of a disturbance until the view completely cleared. This measure is directly linked to the arthroscopic image quality. The condition for which t ir is the shortest gives the fastest irrigation of the joint. In the experimental evaluation, the irrigation time was visualized by injecting a volume of 0.5 ml blue-colored ink mixed with milk ͑ 1:10 ͒ in the inflow stream. Video images of the blue streams were recorded of the view from the arthroscope, and of the view from underneath a transparent tibial surface of knee joint phantom ͑ Fig. 3 ͒ . The irrigation time of the arthroscopic view was determined with image processing. Additionally, the percentage of the remaining blue-colored areas was determined from the overview video stream at each irrigation time. The pressure and the flow of each condition were measured in the inflow tubing just before the sheath or cannula ͑ P 1 and Q ͒ . The intra-articular pressure was measured in the knee joint phantom ͑ P 2 ͒ ͑ Fig. 3 ͒ . The initial pressure was set by placing a 3 liter saline fluid bag at a height of 0.66 m above the knee phantom ͑ 6.5 kPa or 49 mm Hg ͒ ͑ Fig. 1 ͒ . This pressure is equal to the normal set pressure used in the Daycare Surgical Center of the AMC. An active suction device was connected to the outflow stream, which had a set suction pressure of Ϫ 10 kPa ͑ Ϫ 75 mm Hg ͒ . The measurements were repeated ten times for each experimental condi- tion. The scope-sheath combination was inserted in the anteromedial portal, and repositioned after each repetition to visualize the different parts of the medial compartment of the knee. The same order of repositioning was used for each condition. The fluid bag was refilled after performing ten repetitions of each condition. A detailed scheme of the conditions is shown in Table 1. A comparison of the three-portal technique is presented in Row A, where two conventional configurations are shown in Conditions 1 and 2, the new sheath with and without partition, and separate outflow in Conditions 3 and 4, respectively. For all conditions in Row A, clinical practice was mimicked by allowing leakage of saline along the instrument portal through a hole ͑ 0.35 mm ͒ . The same leakage was also allowed for Condition 1 in Row B, where irrigation was performed by intermittently opening and closing the stopcocks by hand with a ...

Context 7

... fluid exists for saline. Third, the lengths of the sheath and the cannula are bounded by the length of existing arthroscopes, and by the thickness of the tissues between the skin and the actual joint space. Finally, the outer diameter of the sheath and the cannula is limited by the maximum size of the skin incisions that are used to obtain access to a joint. From this analysis, two concepts were developed: one for the three-portal technique and one for the two-portal technique. 2.2.1 Three-Portal Technique . In this configuration, separated inflow and outflow streams are already present, due to the use of a separate outflow cannula for suction. Hence, the focus was on decreasing the restriction of the scope-sheath combination. The most promising concept was to increase the cross-sectional area of the annulus, because the flow would increase by a power of 2, and the Reynolds number would be increased proportionally. Since the value of the outer diameter was bounded, the following concept was proposed: Use a smaller diameter arthroscope ͑ 2.7 mm ͒ than normal ͑ 4 mm ͒ in combination with a conventional sheath ͑ Fig. 2 ͒ . With the current advances in technology, 2.7 mm arthroscopes can produce images of equal quality and size as 4 mm arthroscopes. Both types have equal direction of view ͑ 30 deg ͒ as well as field of view ͑ 105 deg ͒ . This new configuration more than doubles the cross-sectional area of the scope-sheath combination. Additionally, the stopcocks can be placed at a smaller angle than 90 deg to minimize losses caused by pipe bending. 2.2.2 Two-Portal Technique . For this technique, the first focus was on creating separate inflow and outflow streams to guarantee that all incoming fluids would enter and leave the joint continu- ously. To start up the design process, the analysis of existing patents on sheaths or cannulas was performed. Several patents of multilumen sheaths with separate inflow and outflow channels were found ͓ 18–24 ͔ . The concept of a multilumen sheath was combined with the concept of the new scope-sheath combination as presented for the three-portal technique. The Reynolds number was used to choose an allocation of the cross-sectional area that would stimulate the initiation of a turbulent flow, maximally. Thereto, the mean velocity ͑ v average ͒ in Eq. ͑ 3 ͒ was replaced with Q / A , and D was replaced with the hydraulic diameter ͑ D h ͒ , which is defined as 4 A / O , ͓ 12 ͔ ␳ ·4· Q Re = ͑ 4 ͒ ␩ · O where O is the wetted perimeter. Equation ͑ 4 ͒ shows that high values of Re can be achieved by minimizing the wetted perimeter. This implies that in the ideal situation the cross-sectional area of the inflow channel should resemble a circle. Lastly, to stimulate the initiation of turbulent flow, another concept was added: dis- rupting the inflow stream by placing bodies in the cross-sectional area at the tip or by introducing holes at the tip ͑ Fig. 2 ͒ . 2.3 Practical Embodiments. Fluid mechanics theory gave substantial leads to improve irrigation, but experiments are necessary to assess empirical values, and to evaluate the impact of the different concepts in the new sheath. Thereto, practical embodiments were fabricated of the proposed concepts ͑ Fig. 2 ͒ . Care was taken to avoid pointy shapes and sharp edges in the prototypes. An arthroscopic sheath, normally used with a 4 mm arthroscope ͑ Trocar Sleeve 5.6, 8885.041, Richard Wolf GmbH, Gent, Belgium ͒ , was lengthened to fit with the 2.7 mm arthroscope ͑ 8672.422, Richard Wolf GmbH, Gent, Belgium ͒ , and its stopcocks were replaced at an angle of 45 deg. A separate embodiment to divide the sheath in a multilumen construction consisted of a tube ͑ 3.2– 2.8 mm ͒ with two fins, one on each side ͑ height: 0.83 mm; width: 0.36 mm ͒ ͑ Fig. 2 ͒ . This way the cross-sectional area of the inflow stream has the shape of half a donut. This shape was as close to a circle as possible ͑ Fig. 2 ͒ . The fins’ widths were minimized and silver soldered on the tube using a special mold. The partition can be inserted simultaneously with the 2.7 mm arthroscope in the sheath. This design allows an existing obturator to be inserted in the sheath for safe access in a joint, which takes place prior to the scope being inserted in the sheath. As only a single piece embodiment was fabricated, stainless steel metal was used. This is not the first choice in achieving a watertight sealing between inflow and outflow lumens. Therefore, a thin layer of bee wax was added between the sheath and partition when performing the laboratory tests. Lastly, several tips of the sheath were con- structed: having two larger holes, four smaller holes, or pins ͑ 0.4 mm ͒ inserted in the inflow channel ͑ Fig. 2 and Table 2 ͒ . The total surface of the holes was kept constant and equal to the total surface of the three holes that are present in the routinely used sheath ͑ 9.42 mm 2 ͒ . A connector was fabricated to use the same embodiment for testing different tips ͑ Fig. 2 ͒ . 2.4 Evaluation. The evaluation took place in a physical simulation environment for an arthroscopic knee joint surgery ͓ 25 ͔ . In this setup, routinely used three- and two-portal irrigation configurations were compared with the new practical embodiments. Ma- terials included a separate outflow cannula ͑ 8672.422, Richard Wolf GmbH, Gent, Belgium ͒ , inflow tubing ͑ Y-irrigation system urology, B. Braun Medical BV, Oss, NL ͒ , and outflow tubing ͑ suction tubing PVC 2 connectors, 6 ϫ 9 mm, L 3.50 m, Medica Europe BV, Oss, NL ͒ . The simulation environment was equipped with a video and data acquisition system that could simultaneously record two pressure signals, two flow signals, and two digital video streams ͓ 25 ͔ . The most important objective measure was the irrigation time ͑ t ir ͒ . The irrigation time was defined as the time from the first appearance of a disturbance until the view completely cleared. This measure is directly linked to the arthroscopic image quality. The condition for which t ir is the shortest gives the fastest irrigation of the joint. In the experimental evaluation, the irrigation time was visualized by injecting a volume of 0.5 ml blue-colored ink mixed with milk ͑ 1:10 ͒ in the inflow stream. Video images of the blue streams were recorded of the view from the arthroscope, and of the view from underneath a transparent tibial surface of knee joint phantom ͑ Fig. 3 ͒ . The irrigation time of the arthroscopic view was determined with image processing. Additionally, the percentage of the remaining blue-colored areas was determined from the overview video stream at each irrigation time. The pressure and the flow of each condition were measured in the inflow tubing just before the sheath or cannula ͑ P 1 and Q ͒ . The intra-articular pressure was measured in the knee joint phantom ͑ P 2 ͒ ͑ Fig. 3 ͒ . The initial pressure was set by placing a 3 liter saline fluid bag at a height of 0.66 m above the knee phantom ͑ 6.5 kPa or 49 mm Hg ͒ ͑ Fig. 1 ͒ . This pressure is equal to the normal set pressure used in the Daycare Surgical Center of the AMC. An active suction device was connected to the outflow stream, which had a set suction pressure of Ϫ 10 kPa ͑ Ϫ 75 mm Hg ͒ . The measurements were repeated ten times for each experimental condi- tion. The scope-sheath combination was inserted in the anteromedial portal, and repositioned after each repetition to visualize the different parts of the medial compartment of the knee. The same order of repositioning was used for each condition. The fluid bag was refilled after performing ten repetitions of each condition. A detailed scheme of the conditions is shown in Table 1. A comparison of the three-portal technique is presented in Row A, where two conventional configurations are shown in Conditions 1 and 2, the new sheath with and without partition, and separate outflow in Conditions 3 and 4, respectively. For all conditions in Row A, clinical practice was mimicked by allowing leakage of saline along the instrument portal through a hole ͑ 0.35 mm ͒ . The same leakage was also allowed for Condition 1 in Row B, where irrigation was performed by intermittently opening and closing the stopcocks by hand with a frequency of about 0.2 Hz ͑ Table 1 ͒ . Conditions 2 and 3 of Row B had continuous streams due to the new sheath with partition. Both conditions are also included in Row C, where the effect of different tips is compared. Finally, the effect of using the shaver for suction was compared in Row D with again the conventional setup presented in Condition 1. The shaver is an instrument that cuts and sucks tissue simultaneously. Data processing was performed with MATLAB , version 7.0.4.365 ͑ R14 ͒ ͑ The Mathworks, Natick, MA ͒ . A specially designed segmentation routine as described in Tuijthof et al. ͓ 14 ͔ was used to detect the blue-colored areas in the video streams. The video images were resampled to 5 Hz, and downsized to a quarter of the recorded image to speed up the segmentation. A data set of one condition consisted of the irrigation time ͑ t ir ͒ , the pressure before the sheath ͑ P 1 ͒ , the pressure in the knee phantom ͑ P 2 ͒ , the overall flow ͑ Q ͒ , and the percentage of blue-colored area in the overview image for each of the ten repetitions ͑ Table 1 ͒ . Statistical analysis was performed with SPSS 12.0.2 ͑ SPSS Inc., Chicago, IL ͒ . The pres- ence of a normal distribution for all data sets was determined with the Kolmogorov–Smirnov and Shapiro–Wilk tests. With the help of a one-way analysis of variance ͑ ANOVA ͒ test significant dif- ferences were assessed. Posthoc Bonferroni-tests ͑ p Ͻ 0.05 ͒ were performed to highlight the significant internal differences of the conditions. Additionally, a Pearson correlation was determined between the five variables of the data sets. As there is a known relationship between the pressure and the flow ͑ namely, the fluid restriction R ͒ , the value of the Pearson correlation of these ...