Anteromedial view of left knee. (A) The superficial medial collateral ligament (sMCL) is shown with the location of the femoral origin and the proximal and distal tibial insertions of the sMCL. Also displayed are the pes anserine tendons (sartorius, gracilis, and semitendinosus) coursing distally to their insertion on the tibia anterior to the distal sMCL insertion. Further note the sartorius fascia over- lying the distal sMCL. (B) Anatomic augmented repair of the sMCL in a left knee. Distal tibial fixation of the semitendinosus was performed with 2 double-loaded suture anchors by suturing the semitendinosus to the sMCL remnant 6 cm distal to the joint line. The semitendinosus tendon was passed deep to the sartorius fascia. Anatomic fixation of the femoral tunnel 3.2 mm proximal and 4.8 mm posterior to the medial epicondyle was performed with 60 N of traction applied to the graft at 20 ° of knee flexion and neutral rotation. Proximal tibial fixation was located 12 mm distal to the joint line and directly over the most anterodistal attachment of the anterior arm of the semimembranosus. (C) Anatomic reconstruction of the sMCL. Femoral and distal tibial fixation achieved with an interference screw. Proximal tibial fixation performed with a suture anchor 12 mm distal to the joint line. Arrowheads in (B) and (C) highlight differences between the anatomic augmented repair and anatomic reconstruction techniques. VMO, vastus medialis obliquus. 

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... surgical treatment is postoperative arthrofibrosis. 27-29 Because of a lack of anatomically based surgical techniques, discrepancy still remains regarding the optimal postoperative rehabilitation protocol. Most centers have followed a program of immobilization in full extension for up to 3 weeks to allow for healing of tissue, but this has led to a high risk of arthrofibrosis postoperatively. 18,31,32,36 The basis for postoperative immobilization is to prevent graft elongation after surgical treatment that could poten- tially lead to recurrent instability. 39 The rationale for immediate knee motion is that since a truly anatomic repair or reconstruction will minimize plastic deformation, immediate knee motion can be adapted to decrease the rel- atively high risk of arthrofibrosis that has been reported after MCL surgical treatment. 27-29 The effect of early postoperative motion programs on knee laxity at time zero, when an anatomic augmented repair or anatomic reconstruction is performed, is unknown. A time-zero study, with a rigorous postsurgical testing regimen, would provide baseline information regarding knee laxity and the feasibility of immediate postoperative motion. Additionally, it would provide insight into whether an anatomic augmented repair or anatomic reconstruction restores knee kinematics and which may be best suited to undergo such immediate stresses. The purpose of this study was to compare the kinematics of an anatomic sMCL augmented repair and anatomic sMCL reconstruction to the native intact and sectioned sMCL states by use of a robotic system. We hypothesized that both the anatomic augmented repair and reconstruction techniques would reproduce equivalent knee kinematics when compared with the intact state and would create significant improvements in translational and rotational laxity compared with the sMCL sectioned state. A total of 18 match-paired fresh-frozen cadaveric knees (average age, 52.6 years; range, 40-59 years) without evidence of prior injury, abnormality, prior surgery, or disease, were used in this study based on their medical history and serology. Each specimen was thawed at room temperature for 24 hours before use. All soft tissue was removed from the distal end of the tibia and proximal end of the femur 10 cm from the joint line and potted with polymethylmetha- crylate (Fricke Dental, Streamwood, Illinois). A superficial incision was made spanning from 6 cm proximal to the joint line to 8 cm distal to the joint line and coursing 4 cm medial to the medial aspect of the patella. Each knee was mounted, in an inverted orientation, in a 6 degrees of freedom (DOF) robotic system (KR 60-3, KUKA Robotics, Augsburg, Germany) before surgical and biomechanical testing procedures. 9 A custom fixture attached the tibia to a universal force-torque sensor (Delta F/T Transducer, ATI Industrial Automation, Apex, North Car- olina) at the end effector of the robotic system. Anatomic landmarks on the knee were selected with a coordinate measuring machine (MicroScribe MX-GoMeasure3D, Amherst, Virginia) to define a coordinate system for the tibia, femur, and knee. 14,41 Each knee’s passive flexion path was determined from 0 (full extension) to 90 ° by selecting zero force locations along the flexion path in 1 ° increments. For each flexion angle, forces and torques in the remaining 5 DOF were minimized ( \ 5 N and \ 0.5 N Á m, respectively), while an axial force of 10 N was applied to ensure contact between the femur and tibia. The passive path tibiofemoral positions were recorded and used as the starting points for subsequent biomechanical testing. For biomechanical testing, robotic force and position control were used to replicate clinical examinations through a range of flexion angles. 9,30 All examinations were performed at 0 ° , 20 ° , 30 ° , 60 ° , and 90 ° of knee flexion. Valgus que applied rotation to the was tibia. measured 11 Medial during gapping a 10-N was Á m determined valgus tor- by calculating increases in the translation at the center of the medial compartment of the tibiofemoral joint during applied valgus torques, compared with the intact state. 25 The center of the medial compartment of the tibial plateau was calculated as equidistant between the center of the tibial plateau and the medial-most palpable point of the tibia at the joint line, which was based on the position used clinically to measure valgus stress radiographs. 25 Additionally, rotation limits of the knees were measured with rotation applied torques. 5-N 2,4,12 Á m internal Rotational rotation laxity and in response 5-N Á m external to combined rotatory motion was tested with a simulated pivot shift, consisting of a coupled 10-N Á m valgus torque followed by a 5-N Á m internal rotation torque, and with a coupled 88-N torque. force 8,22,33,42 anterior Each drawer testing and series a 5-N was Á m external repeated rotation on the intact (Figure 1A), sectioned, and augmented/recon- structed states (Figure 1, B and C). The flexion angle testing order was randomized between specimens to prevent incremental testing bias. The anatomic attachment sites of the sMCL on the femur and tibia were identified through the superficial incision and marked with a surgical marking pen. 38 After intact state testing, the sMCL was excised between its femoral and distal tibial attachments, leaving the distal tibial attachment remnant intact, for the sectioned state, which simulated a grade 3 sMCL injury before an augmented repair or reconstruction. 39 The posterior oblique ligament and deep MCL were left intact. All sMCL reconstructions and augmented repairs were performed by a single, experienced, board-certified sports medicine orthopaedic surgeon (R.F.L.). Right and left knees were randomized between the anatomic augmented repair and anatomic reconstruction groups. To reduce testing error introduced from specimen removal, all reconstructions were performed while the knee remained fixed in the robot. The sartorius fascia was left intact. The semitendinosus tendon was identified at its tibial attachment, and an open- ended hamstring stripper detached it proximally. The tendon was then anchored to the tibia at the sMCL distal tibial attachment, 6 cm distal to the joint line, 26 with 2 double-loaded suture anchors (Corkscrew FT, Arthrex Inc, Naples, Florida) and was further sutured to the under- lying remnant of the distal aspect of the sMCL (Figure 1B). The tendon was then passed deep to the sartorius fascia up to the femoral attachment of the sMCL, which has been reported to be 3.2 mm proximal and 4.8 mm posterior to the medial epicondyle. 26 The femoral tunnel was reamed over an eyelet pin, previously drilled anterolaterally across the femur, with a 7-mm reamer to a depth of 25 mm. The semitendinosus graft was then measured to fit into this tunnel; the end was whip-stitched with braided polypropylene No. 2 sutures (FiberWire, Arthrex Inc), and the excess length of the graft was amputated before the graft was passed into the femoral tunnel. While a 60-N traction force was applied to the graft, a 7 3 25–mm polyether ether ketone (PEEK) interference screw (BIOSURE PK, Smith & Nephew, Andover, Massachusetts) was used to secure the sMCL graft in the femoral tunnel with the knee positioned at 20 ° of flexion and neutral rotation in the robot, while the clinician applied a varus reduction torque of approximately 10 N Á m. 25 Finally, a 5 3 15–mm double- loaded suture anchor (Corkscrew FT) was used to anatomically restore the proximal tibial division of the sMCL 12 mm distal to the joint line and directly over the most anterodistal attachment of the anterior arm of the semimembranosus. 4,26,38,39 Similar to the repair technique, the anatomic sMCL reconstruction technique left the sartorius fascia in place. The femoral and distal tibial attachment sites were identified and the femoral attachment site tunnel was prepared in a manner similar to that used for the anatomic augmented repair technique. A tibial reconstruction tunnel was placed 6 cm distal to the joint line in the center of the distal tibial sMCL attachment (Figure 1C). A 7-mm-diameter tunnel was reamed over an eyelet pin passed anterolaterally to a depth of 25 mm. Fresh-frozen bovine digital extensor graft (IMDS Discov- ery Research, Logan, Utah) of 16 cm in total length and sized to a diameter of 7 mm was whip-stitched with braided polypropylene sutures 25 mm from both ends. The prepared graft was passed into the tibial tunnel and secured in place with a 7 3 25–mm PEEK screw. Bovine digital extensor tendons were used because they have been reported to have viscoelastic, structural, and material properties similar to those of human semitendinosus tendons. 6 Further- more, bovine digital extensor tendons were used as a surrogate in several previous human knee ligament biomechanics studies because of their uniform size and diameter compared with human hamstring tendons. 1,5,7,15,24 Once the sMCL graft was fixed in the distal tibial reconstruction tunnel, the knee was positioned at 20 ° of flexion and neutral rotation in the robot, and a varus reduction force was manually applied. The graft was then passed into the femoral tunnel and fixed with a 7 3 25–mm PEEK screw while 60 N of traction was applied with a graft tensioning device. The 60-N traction force was chosen and standardized based on the clinical practice of the senior authors. After fixation of both the distal tibial and femoral attachments, a double-loaded suture anchor was used to fix the proximal tibial attachment site in a manner similar to that used for the anatomic augmented repair technique outlined above. During initial pilot testing, 2 different anatomic augmented femoral fixation repair techniques were used. Two suture anchors were used proximally to attach the augmented graft to the femoral sMCL origin and were compared with an interference screw femoral reconstruction tunnel. Pilot robotic ...