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Original Research
Early Revision Rates of Total Hip Arthroplasty Using the Intellijoint HIP
Computer Navigation System: A Study From the Australian National
Joint Replacement Registry of 1911 Procedures
Ernest C. Lourens, MD (Dist), BPhysio (Hons), GradCertClinRehab
a
,
*
,
Andrew P. Kurmis, FRACS (Ortho), FAOrthA, CIME, PhD (Ortho), BMBS (Hons), BMedRad
(Hons), BAppSc (Med Rad)
b
,
c
, Carl Holder, MBiostat
d
,
Richard N. de Steiger, MBBS, PhD, FRACS (Orth), FAOrthA
e
,
f
a
Lyell McEwin Hospital, Elizabeth Vale, South Australia, Australia
b
Department of Orthopaedic Surgery, Lyell McEwin Hospital, Elizabeth Vale, South Australia, Australia
c
Discipline of Medical Specialties, University of Adelaide, Adelaide, South Australia, Australia
d
South Australian Health and Medical Research Institute (SAHMRI), Adelaide, South Australia, Australia
e
Department of Surgery, Epworth Healthcare, University of Melbourne, Melbourne, Australia
f
Australian Orthopaedic Association National Joint Replacement Registry, Adelaide, South Australia, Autralia
article info
Article history:
Received 13 July 2022
Received in revised form
29 August 2022
Accepted 27 September 2022
Available online xxx
Keywords:
THA
Hip arthroplasty
Navigation
Intellijoint HIP
Technology-assisted surgery
abstract
Background: Total hip arthroplasty (THA) is an effective treatment for symptomatic hip osteoarthritis.
The aim of this study was to determine the revision outcome of commercially available navigation
technologies.
Methods: Data from the Australian Orthopaedic Association National Joint Replacement Registry from
January 2016 to December 2020 included all primary THA procedures performed for osteoarthritis.
Procedures using the Intellijoint HIP navigation system were identified and compared to procedures
using “other”computer navigation systems and to nonnavigated procedures. The cumulative percent
revision (CPR) was compared between the 3 groups using Kaplan-Meier estimates of survivorship and
hazard ratios from Cox proportional hazards models, adjusted for age and gender.
Results: There were 1911 procedures that used the Intellijoint system, 4081 used “other”computer navi-
gation systems, and 160,661 were nonnavigated procedures. The all-cause 2-year CPR rate for the Intelli-
joint system was 1.8% (95% confidence interval [CI], 1.2-2.6), compared to 2.2% (95% CI, 1.8-2.8) for other
navigated cases and 2.2% (95% CI, 2.1-2.3) for nonnavigated cases. A prosthesis analysis identified the
Paragon/Acetabular Shell THAs combined with the Intellijoint system to have a higher (3.4%) rate of
revision than nonnavigated THAs (hazard ratio ¼2.00 [95% CI, 1.01-4.00], P¼.048). When this combination
was excluded, the Intellijointgroup demo nstrated a 2-year CPRof 1.3%. There was no statistical difference in
the CPR between the 3 groups before or after excluding the Paragon/Acetabular Shell system.
Conclusions: The preliminary data presented demonstrate no statistical difference in all-cause revision
rates when comparing the Intellijoint system with “other”navigation systems and “nonnavigated”ap-
proaches for primary THAs.
Level of evidence: III (National registry analysis).
©2022 The Authors. Published by Elsevier Inc. on behalf of The American Association of Hip and Knee
Surgeons. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/
licenses/by-nc-nd/4.0/).
Introduction
Total hip arthroplasty (THA) is a well-established method to
treat hip pain and dysfunction due to end-stage osteoarthritis (OA)
and other medical conditions. Acetabular prosthesis implantation
angles have been shown to affect peri-articular muscle mechanical
*Corresponding author. Alice Springs Hospital, 6 Gap Road, The Gap, Alice
Springs, Northern Territory 0870, Australia. Tel.: þ61 403 467 716.
E-mail address: ernestlourens@hotmail.com
Contents lists available at ScienceDirect
Arthroplasty Today
journal homepage: http://www.arthroplastytoday.org/
https://doi.org/10.1016/j.artd.2022.09.019
2352-3441/©2022 The Authors. Published by Elsevier Inc. on behalf of The American Association of Hip and Knee Surgeons. This is an open access article under the CC BY-
NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Arthroplasty Today 18 (2022) 149e156
advantages, rates of dislocation, gait, limb lengths, impingement,
noise generation, loosening, postoperative range of movement,
liner wear, and overall revision rates [1,2]. Optimizing biome-
chanical and anatomical reconstruction of the joint is therefore
critical to achieve function, longevity, and prevention of avoidable
complications following the surgery [2-4]. Dislocation rates
following primary THAs are acknowledged to occur in 1%-4% of
cases, with “instability”accounting for approximately 23% of all
revisions and remaining the most common reason for revision in
the United States [5,6].
The Australian Orthopaedic Association National Joint Replace-
ment Registry (AOANJRR) began collecting data on the use of
computer-navigated total knee arthroplasty (TKA) in 2003 and has
previously reported on the outcomes [7]. The use of computer
navigation has steadily increased for TKAs, from 2.4% in 2003 to
33.2% in 2018. However, by comparison, the AOANJRR shows that
<2% of THAs recorded to date have utilized navigation assistance
[7,8].
The “safe zone”for acetabular cup placement was described by
Lewinnek et al. (1978) and was claimed to be associated with a
reduced dislocation risk [9]dalthough contemporary research has
cast doubt upon this. Traditional freehand THA techniques rely on
surgeon judgment to manually place acetabular components
accurately. The use of computer navigation to reduce acetabular
malposition has been in practice for more than 20 years, demon-
strating improved attainment of target cup placement and variable
reports of improvement in clinical outcomes, including reducing
the rate of revision [8,10,11]. Computer tomography (CT)-based
navigation has been shown to be highly accurate. However, it is
burdened by the associated cost, the need for dedicated preoper-
ative imaging, and incumbent radiation exposure riskdall of which
have been linked to low levels of clinical utilization [12-15].
The Intellijoint HIP 3D mini-optical navigation tool (Intellijoint
Surgical Inc., Waterloo, Canada) is an intraoperative, surgeon-
controlled, “imageless”mini-navigation system tool that provides
surgeons with real-time data on leg length, offset, and cup position
[16]. The key features of this commercially-available system were
intended to overcome some of the recognized barriers to uptake
associated with imaging-based navigation. However, there remains
a lack of independent research of the clinical outcomes as
compared to other available navigation systems or to nonnavigated
THAs.
Using data from a large national joint registry, the aim of this
study was to determine if there were differences in the rates of all-
cause revision between Intellijoint-navigated, other navigated, and
nonnavigated THA procedures.
Material and methods
The AOANJRR commenced data collection on September 1, 1999,
achieving complete national implementation by mid-2002. Since
then, it has collected data on almost 100% of THAs and other joint
replacements performed in Australia [17]. These data are externally
validated against patient-level data provided by all Australian state
and territory health departments. A sequential, multilevel match-
ing process is used to identify any missing data which are subse-
quently obtained by follow-up with the relevant hospital. Each
month, in addition to internal validation and data quality checks, all
primary procedures are linked to any subsequent revision involving
the same patient, joint, and side. Data are also matched biannually
to the Australian National Death Index data to identify patients who
have died. Information on the use and type of computer navigation
for a procedure has been collected for THAs and TKAs and marked
on the AOANJRR registration form as “computer-assisted”.
Table 1
Summary of primary total conventional hip replacements since 2016 by model (primary diagnosis OA).
Variable Intellijoint Other computer navigated Nonnavigated Total
Age
Mean ±SD 67.3 ±10.9 69.1 ±10.6 67.9 ±10.7 68 ±10.7
Age group, y
<55 230 (12%) 380 (9.3%) 17,673 (11%) 18,283 (11%)
55-64 494 (25.9%) 847 (20.8%) 38,693 (24.1%) 40,034 (24%)
65-74 672 (35.2%) 1525 (37.4%) 58,724 (36.6%) 60,921 (36.6%)
75 515 (26.9%) 1329 (32.6%) 45,571 (28.4%) 47,415 (28.5%)
Gender
Male 988 (51.7%) 1811 (44.4%) 74,915 (46.6%) 77,714 (46.6%)
Female 923 (48.3%) 2270 (55.6%) 85,746 (53.4%) 88,939 (53.4%)
Hospital setting
Private hospital 1518 (79.4%) 3107 (76.1%) 113,747 (70.8%) 118,372 (71%)
Public hospital 393 (20.6%) 974 (23.9%) 46,914 (29.2%) 48,281 (29%)
ASA score
a
1 223 (11.7%) 352 (8.7%) 14,153 (8.8%) 14,728 (8.9%)
2 1005 (52.6%) 2066 (50.8%) 86,729 (54.1%) 89,800 (54%)
3 649 (34%) 1581 (38.9%) 57,132 (35.7%) 59,362 (35.7%)
4 33 (1.7%) 69 (1.7%) 2204 (1.4%) 2306 (1.4%)
5 3 (0%) 3 (0%)
BMI
b
Underweight (<18.50) 9 (0.5%) 32 (0.8%) 1077 (0.7%) 1118 (0.7%)
Normal (18.50-24.99) 367 (19.5%) 895 (22.8%) 31,804 (20.5%) 33,066 (20.6%)
Preobese (25.00-29.99) 702 (37.3%) 1487 (37.9%) 57,113 (36.9%) 59,302 (36.9%)
Obese class 1 (30.00-34.99) 475 (25.3%) 985 (25.1%) 39,510 (25.5%) 40,970 (25.5%)
Obese class 2 (35.00-39.99) 214 (11.4%) 358 (9.1%) 17,042 (11%) 17,614 (11%)
Obese class 3 (40.00) 113 (6%) 171 (4.4%) 8230 (5.3%) 8514 (5.3%)
Surgeon volume
10 53 (68.8%) 119 (83.8%) 330 (33.1%) 502 (41.3%)
10-25 14 (18.2%) 9 (6.3%) 217 (21.8%) 240 (19.7%)
>25 10 (13%) 14 (9.9%) 450 (45.1%) 474 (39%)
Total 1911 4081 160,661 166,653
ASA, American Society of Anesthesiologists; BMI, body mass index (kg/m
2
); SD, standard deviation.
a
Excludes 454 procedures with an unknown ASA score.
b
Excludes 6069 procedures with unknown BMI.
E.C. Lourens et al. / Arthroplasty Today 18 (2022) 149e156150
The study period was from January 1, 2016, (when Intellijoint
HIP THAs were first recorded by the AOANJRR) to 31 December
2020. The study population included all primary THA procedures
for OA inserted using the Intellijoint Navigation System, “other”
computer-navigated systems, or nonnavigated systems. Only THAs
with modern bearing surfaces were included, and these were
defined as ceramic-on-ceramic, metal-on-highly cross-linked
polyethylene, and ceramic-on-highly cross-linked polyethylene.
Metal-on-metal bearing surfaces were excluded because of their
known high rate of revision. There were insufficient comparative
numbers to permit subanalysis of dual-mobility or constrained
liners. The indication for and type of revision performed for cases
during the data collection period were recorded.
Descriptive data for the 3 groups (ie, Intellijoint-assisted, “other”
navigated, and nonnavigated) including patient age at the time of
surgery, gender, assigned American Society of Anesthesiology
score, body mass index, and surgeon procedural volume were
recorded (Table 1).
A prosthesis-specific analysis was also performed restricted to
prosthesis combinations with over 100 procedures and with both
Intellijoint and nonnavigated procedures. There were 3 prosthesis
combinations identified, but only the Paragon/Acetabular Shell
(Global) had enough revision procedures of the Intellijoint for a
comparative analysis to be performed between the Intellijoint and
nonnavigated groups. The other navigated group had too few re-
visions for a comparative analysis to be performed. A revision
comparison was performed, and the analysis was repeated with the
prosthesis combination excluded to account for a prosthesis effect.
The cumulative percent revision (CPR) was calculated for the
Intellijoint-navigated, “other”navigated, and nonnavigated THAs
over the same time period.
Statistical analysis
The AOANJRR uses Kaplan-Meier estimates of survivorship to
describe the time to the first revision of an arthroplasty, with
censoring at the time of death or closure of the database at the time
of analysis. The unadjusted CPR rate with an accompanying 95%
confidence interval (CI) was calculated with the use of unadjusted
pointwise Greenwood estimates to allow for the same-time-
matched comparison of navigated and nonnavigated THA proced-
ures, as the former had a shorter follow-up in the registry. The
unadjusted cumulative incidence functions of the reasons for
revision of navigated and nonnavigated THAs were also calculated.
The hazard ratio (HR) was calculated with the use of Cox propor-
tional hazard models to make statistical comparisons of the revi-
sion rates between the groups. The assumption of proportional
hazards was checked analytically for each model; if the interaction
between the predictor and the log of the postoperative time was
significant in the standard Cox model, then a time-varying model
was used. For this study, the reported HRs pertain to the entire
follow-up period. All tests were 2-tailed with significance set at
Figure 1. Cumulative percent revision of primary total conventional hip replacements since 2016 by model (primary diagnosis OA).
Table 2
Yearly CPR of primary total conventional hip replacements since 2016 by model (primary diagnosis OA).
CPR 1y 2y 3y 4y
Intellijoint 1.7 (1.2, 2.4) 1.8 (1.2, 2.6)
Other computer navigated 1.8 (1.4, 2.2) 2.2 (1.8, 2.8) 2.3 (1.9, 2.9) 2.4 (1.9, 3.0)
Nonnavigated 1.8 (1.7, 1.8) 2.2 (2.1, 2.3) 2.5 (2.4, 2.6) 2.8 (2.7, 2.9)
E.C. Lourens et al. / Arthroplasty Today 18 (2022) 149e156 151
0.05. A statistical analysis was performed using the SAS software
version 9.4 (SAS Institute, Cary, NC).
Source of funding
The AOANJRR is approved by the Australian Federal Government
as a federal quality assurance activity (QAA 3/2017) under Section
124X of the Health Insurance Act, 1973. All investigations were
conducted in accordance with the ethical principles of research
(The Helsinki Declaration II). The AOANJRR is funded by the
Commonwealth of Australia Department of Health. The data of the
AOANJRR are the intellectual property of the Australian Orthopae-
dic Association. The authors declare no relevant financial
disclosures.
Results
There were 166,653 THA procedures performed for OA. Of these,
1911 were Intellijoint-assisted, 4081 used other computer naviga-
tion systems, and 160,661 were nonnavigated. Patient baseline
demographics and surgeon procedural volume can be seen in
Table 1. Mean patient age and age-group stratification for in-
dividuals undergoing THAs was comparable between the 3 groups,
with a tendency of older patients undergoing “other”navigated
THAs. A larger proportion of male patients were seen in the Intel-
lijoint group (51.7%) than in the other navigated (44.4%) and non-
navigated groups (46.6%). The American Society of Anesthesiology
and body mass index scores were similar among all 3 groups. The
maximum follow-up duration for the Intellijoint group was 4.1
Table 3
Revision diagnosis of primary total conventional hip replacements since 2016 by model (primary diagnosis OA).
Revision diagnosis Intellijoint Other computer navigated Nonnavigated
Number % Primaries
revised
% Revisions Number % Primaries
revised
% Revisions Number % Primaries
revised
% Revisions
Infection 12 0.6 40.0 20 0.5 24.1 1081 0.7 30.2
Prosthesis dislocation/instability 4 0.2 13.3 10 0.2 12.0 865 0.5 24.2
Fracture 9 0.5 30.0 25 0.6 30.1 737 0.5 20.6
Loosening 4 0.2 13.3 18 0.4 21.7 515 0.3 14.4
Leg length discrepancy 4 0.1 4.8 79 0.0 2.2
Malposition 2 0.0 2.4 72 0.0 2.0
Pain 1 0.1 3.3 66 0.0 1.8
Implant breakage acetabular insert 28 0.0 0.8
Incorrect sizing 2 0.0 2.4 28 0.0 0.8
Implant breakage stem 1 0.0 1.2 14 0.0 0.4
Implant breakage acetabular 9 0.0 0.3
Lysis 8 0.0 0.2
Metal-related pathology 5 0.0 0.1
Heterotopic bone 4 0.0 0.1
Wear head 4 0.0 0.1
Tumor 3 0.0 0.1
Wear acetabular insert 2 0.0 0.1
Implant breakage head 1 0.0 0.0
Other 1 0.0 1.2 58 0.0 1.6
N Revision 30 1.6 100.0 83 2.0 100.0 3579 2.2 100.0
N Primary 1911 4081 160,661
% Primaries revised: This shows the proportional contribution of each revision diagnosis as a percentage of the total number of primary procedures. This percentage can be
used to approximate the risk of being revised for that diagnosis. Differing percentages between groups, with the same distribution of follow-up time, may identify problems of
concern. % Revisions: The number of revisions for each diagnosis is expressed as a percentage of the total number of revisions. This shows the distribution of reasons for
revision within a group but cannot be used as a comparison between groups.
Table 4
Type of revision of primary total conventional hip replacements since 2016 by model (primary diagnosis OA).
Type of revision Intellijoint Other computer navigated Nonnavigated
Number % Primaries
revised
% Revisions Number % Primaries
revised
% Revisions Number % Primaries
revised
% Revisions
Head/insert 12 0.6 40.0 17 0.4 20.5 1123 0.7 31.4
Femoral component 6 0.3 20.0 46 1.1 55.4 1060 0.7 29.6
Acetabular component 4 0.2 13.3 7 0.2 8.4 594 0.4 16.6
THR (femoral/acetabular) 4 0.2 13.3 7 0.2 8.4 335 0.2 9.4
Head only 3 0.2 10.0 3 0.1 3.6 232 0.1 6.5
Cement spacer 1 0.1 3.3 96 0.1 2.7
Minor components 2 0.0 2.4 57 0.0 1.6
Insert only 41 0.0 1.1
Removal of prostheses 1 0.0 1.2 22 0.0 0.6
Reinsertion of components 8 0.0 0.2
Head/neck/insert 6 0.0 0.2
Bipolar head and femoral 2 0.0 0.1
Cement only 1 0.0 0.0
Head/neck 1 0.0 0.0
Neck only 1 0.0 0.0
N Revision 30 1.6 100.0 83 2.0 100.0 3579 2.2 100.0
N Primary 1911 4081 160,661
THR, total hip replacement.
E.C. Lourens et al. / Arthroplasty Today 18 (2022) 149e156152
years, which was slightly lower than the 5 years for each of the
remaining groups. The mean follow-up duration was 1.2 years
(±0.8) for the Intellijoint group, 2.2 years (±1.5) for the other
navigated group, and 2.4 years (±1.4) for the nonnavigated group.
Of the 1911 Intellijoint THAs, 30 underwent subsequent revision.
The CPR was 1.7% at 1 year (95% CI, 1.2%-2.4%) and 1.8% at 2 years
(95% CI, 1.2%-2.6%) (Fig. 1)(Table 2). The unadjusted Intellijoint 2-
year revision rate (1.8%) was lower than both the “other”navi-
gated and nonnavigated THA rates at the same timepoint with a
CPR of 2.2% (95% CI, 1.8%-2.8%) and 2.2% (95% CI, 2.1%-2.3%),
respectively. Intellijoint CPRs are not yet available for 3- and 4-year
timepoints due to the low current patient numbers. At 4 years, the
“other”navigated and nonnavigated THA CPRs were 2.4% (95% CI,
1.9%-3.0%) and 2.8% (95% CI, 2.7%-2.9%), respectively. There was no
statistical difference in the overall rate of revision when the 3
groups were compared (Fig. 1).
The reason for revision for the 3 THA groups are documented in
Table 3, and the type of THA revision performed is shown in Table 4.
There was a higher percentage of minor revisions (head/insert)
(40%) for the Intellijoint THAs than that for “other”navigation and
nonnavigated THAs (20.5% and 31.4%, respectively). Contrastingly,
Intellijoint THA revisions had a lower percentage (20.0%) of femoral
component revision than “other”navigation and nonnavigated
revisions (55.4% and 29.6%, respectively). There were too few re-
visions with the Intellijoint system to undergo statistical compar-
ison of individual reasons for a revision such as dislocation/
instability or type of revision.
The prosthesis-specific analysis identified the Paragon/Acetab-
ular Shell (Global) as having enough revision procedures of the
Intellijoint for a comparative analysis to be performed between the
Intellijoint and nonnavigated groups (Table 5). The Intellijoint
Paragon/Acetabular Shell (Global) had a higher rate of revision than
the nonnavigated Paragon/Acetabular Shell (Global) (HR ¼2.00
[95% CI, 1.01-4.00], P¼.048) (Fig. 2). When this prosthesis combi-
nation was excluded from the analysis, there was no statistical
difference between the 3 groups (Fig. 3). The indication for an
Intellijoint revision excluding Paragon implants is summarized in
Table 6.
Discussion
To our knowledge, this study represents the largest reported-
to-date analysis of the use of the Intellijoint-navigated system for
THA with comparison to other computer-navigated and non-
navigated THAs. It represents data for all THAs in Australia during a
5-year period and demonstrates an all-cause Intellijoint 2-year CPR
of 1.8%, which was not statistically different to that of “other”
navigated and nonnavigated THAs (2.2%).
The Intellijoint navigation system has previously been demon-
strated on a benchtop phantom model to accurately measure
acetabular cup position and leg-length measurements within 1
and 1 mm, respectively [18]. A cadaveric study involving 3 surgeons
and 12 hips demonstrated a mean absolute difference between
postoperative CT and intraoperative Intellijoint measurements for
inclination of 4.2
(standard deviation, 3.2
) and anteversion angle
of 4.0
(standard deviation, 4.0
)[19]. A previous study has inves-
tigated the correlation between intraoperative Intellijoint naviga-
tion and postoperative CT measurements of cup inclination and
anteversion when used for 53 revision THAs. The authors reported
excellent agreement between navigation and CT measurements for
inclination (r ¼0.89) and anteversion (r ¼0.93), with both mea-
surements being within 10
in 86.8% of cases [20]. Authors of the
aforementioned 3 studies all disclosed potential competing in-
terests in the form of consultancy fees and/or stock options from
Intellijoint Surgical.
The most common indications for revision noted in our registry
analysis were infection, dislocation/instability, fracture, and
Table 5
Revised number of Paragon/Acetabular Shell (Global) primary total conventional hip
replacements since 2016 by navigation (primary diagnosis OA).
Navigation N Revised N Total
Intellijoint Paragon/Acetabular Shell (Global) 10 323
Other navigated Paragon/Acetabular Shell (Global) 2 24
Nonnavigated Paragon/Acetabular Shell (Global) 44 2824
Total 56 3171
Figure 2. Cumulative percent revision of Paragon/Acetabular Shell (Global) primary total conventional hip replacements since 2016 by navigation (primary diagnosis OA).
E.C. Lourens et al. / Arthroplasty Today 18 (2022) 149e156 15 3
loosening. The majority of these events occurred during the first
year after implantation (Figs. 1 and 3). Agarwal et al. (2021) has
previously demonstrated that compared with nonnavigation, the
use of computer navigation was associated with a reduced rate of
revision for dislocation following THAs [8]. However, there was no
observed difference in all-cause revision [8]. Concerning the cur-
rent study, the relative proportions of individual indications for
revision were dissimilar between the 3 groups (Table 3). The
Intellijoint group sample size did not permit a meaningful statis-
tical comparison of subgroups. Further investigation with greater
sample numbers is therefore required to better appreciate the
potential underlying differences in the reason for revision,
including implant-, technology-, or surgeon-specific factors. This
will likely be possible in time as the registry record of navigated
THAs grows, as does the mean follow-up period.
An analysis of implants used in conjunction with the Intellijoint
system highlighted a statistical outlier combination in the Paragon
femoral component with Acetabular Shell (Global) pairing, with a
2-year CPR nearly 3 times higher than the class at 3.4% (Table 5).
The registry level data analyzed in the current study do not provide
enough specific information to confidently elucidate the cause of
this unexpected anomaly in an otherwise well-performing implant
Figure 3. Cumulative percent revision of primary total conventional hip replacements since 2016 by model (excluding Intellijoint Paragon femoral component, primary diagnosis
OA).
Table 6
Type of revision of primary total conventional hip replacements since 2016 by model (excluding Intellijoint Paragon femoral component, primary diagnosis OA).
Type of revision Intellijoint Other computer navigated Nonnavigated
Number % Primaries
revised
% Revisions Number % Primaries
revised
% Revisions Number % Primaries
revised
% Revisions
Head/insert 8 0.6 53.3 17 0.4 20.5 1123 0.7 31.4
Femoral component 3 0.2 20.0 46 1.1 55.4 1060 0.7 29.6
Acetabular component 7 0.2 8.4 594 0.4 16.6
THR (femoral/acetabular) 3 0.2 20.0 7 0.2 8.4 335 0.2 9.4
Head only 3 0.1 3.6 232 0.1 6.5
Cement spacer 1 0.1 6.7 96 0.1 2.7
Minor components 2 0.0 2.4 57 0.0 1.6
Insert only 41 0.0 1.1
Removal of prostheses 1 0.0 1.2 22 0.0 0.6
Reinsertion of components 8 0.0 0.2
Head/neck/insert 6 0.0 0.2
Bipolar head and femoral 2 0.0 0.1
Cement only 1 0.0 0.0
Head/neck 1 0.0 0.0
Neck only 1 0.0 0.0
N Revision 15 1.2 100.0 83 2.0 100.0 3579 2.2 100.0
N Primary 1265 4081 160,661
THR, total hip replacement.
% Primaries revised: This shows the proportional contribution of each revision diagnosis as a percentage of the total number of primary procedures. This percentage can be
used to approximate the risk of being revised for that diagnosis. Differing percentages between groups, with the same distribution of follow-up time, may identify problems of
concern. % Revisions: The number of revisions for each diagnosis is expressed as a percentage of the total number of revisions. This shows the distribution of reasons for
revision within a group but cannot be used as a comparison between groups.
E.C. Lourens et al. / Arthroplasty Today 18 (2022) 149e156154
combination. Whether this result relates to surgeon-, implant-, or
technology-related considerations is not clear and provides an
avenue for further investigation. The Paragon/Acetabular Shell
(Global) made up 17% of the Intellijoint population yet accounted
for 33% of the Intellijoint revisions described in this study. While no
statistical difference was observed between the 3 groups with the
Paragon/Acetabular Shell (Global) excluded, these early results
warrant a longer follow-up duration with greater numbers to
determine if a true clinical difference in rates of revision exists.
This study has several limitations. As the Intellijoint system has
only been available for regulatory-approved use in Australia since
2016, our follow-up was limited to 2 years and represented 30 re-
visions out of 1911 THAs, compared to studies with other naviga-
tion systems approaching 10 years of follow-up with many more
procedures [8]. Given that the majority of prosthetic hip disloca-
tions and instability-related issues classically occur within the first
2 years of the index surgery, early results from this study may yield
valuable clinical information. The AOANJRR does not record THA
dislocation events treated successfully with closed reduction unless
a revision procedure has been performed. Thus, it is likely that the
results presented may underestimate the true numbers of dislo-
cation/instability (although this bias is likely to affect all 3 groups in
a similar fashion). Future research in this regard would require
matching to local administrative data sets. While data are recorded
by the AOANJRR on the use of navigation and the type used, it is
possible that some cases were missed, and therefore, navigated
cases are included in the nonnavigated group. However, we believe
that because of the relative few numbers involved, this would make
minimal difference to the outcomes. The Intellijoint group con-
tained a slightly higher percentage of male patients (51.7%
compared with 46.6% in the nonnavigated group), and almost 9%
more Intellijoint THAs were performed in a private hospital setting
than nonnavigated THAs. Given that public hospital THAs are often
performed by a combination of training and consultant surgeons
(in contrast to private hospitals where THAs are performed almost
exclusively by consultant surgeons), there may be a bias secondary
to surgeon experience; however, we were not able to analyze this.
Previous studies have suggested that both surgeon operative vol-
ume (ie, number of cases per year) and extent of experience can
have significant impact on patient outcomes following THA,
including rates of dislocation and revision [21,22]. Surgeon volume
represented one of the biggest between-group differences in our
analysis with only 13% of Intellijoint and 10% of “other”navigated
cases performed by surgeons completing more than 25 THAs per
year, compared to 45% of nonnavigated cases. We could therefore
propose the value of navigation options for hip arthroplasty may be
even greater than what is shown by our raw data given that the
navigation surgeons included in this analysis (Intellijoint and
“other”navigation) performed comparatively far less cases per year
than the nonnavigated group. While the absolute number of
revised Intellijoint THAs was too small to permit a meaningful
stratified subgroup analysis comparing surgeon volume, one would
reasonably expect that as surgeon experience and annual case
numbers increaseddand as familiarity with the Intellijoint system
itself increaseddclinical outcomes may continue to improve.
Finally, the AOANJRR also does not report radiological data to reflect
final implant positioning. It is therefore impossible to comment if
the Intellijoint navigated or “other”navigated THAs resulted in cup
orientations in a more anatomical alignments than nonnavigated
THAs or how far the definitive cup position differed from the
intended target.
The preliminary data presented demonstrate no statistical dif-
ference when comparing the Intellijoint HIP THA navigation system
to both “other”navigation systems and “nonnavigated”with
respect to all-cause revision rates for primary THAs performed for
OA. A subgroup analysis of prostheses revealed that the Paragon
Acetabular Shell THAs combined with the Intellijoint system had a
higher rate of revision than nonnavigated THAs. The reason for this
remains unclear from the available registry-level data. The current
cohort size included in the registry remains too small to permit
further meaningful subgroup statistical comparisons by reason for
revisions. Further follow-up with a larger sample size is required to
determine if a clinical difference exists between rates of revision
secondary to dislocation, instability, and prosthetic loosening.
Conflicts of interest
A. P. Kurmis is in the speakers' bureau of or gave paid pre-
sentations for Zimmer Biomet; is a paid consultant for Formus Labs
and Zimmer Biomet; is in the editorial or governing board of The
Open Orthopaedics Journal; and is a board member in RACS (SA).
All other authors declare no potential conflicts of interest.
For full disclosure statements, refer to https://doi.org/10.1016/j.
artd.2022.09.019.
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