The Journal of Arthroplasty 29 (2014) 1030–1037

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The Journal of Arthroplasty

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Comparison of Acetabular Shell Position Using Patient Specific Instruments vs.Standard Surgical Instruments: A Randomized Clinical Trial

Travis Small, DO, Viktor Krebs, MD, Robert Molloy, MD, Jason Bryan, MS,Alison K. Klika, MS , Wael K. Barsoum, MDDepartment of Orthopaedic Surgery, Cleveland Clinic-A41, Cleveland, Ohio

a b s t r a c ta r t i c l e i n f o

The Conflict of Interest statement associatedwith thisdoi.org/10.1016/j.arth.2013.10.006.

Reprint requests: Alison Klika, MS, DepartmentCleveland Clinic 9500 Euclid Ave. Cleveland, OH 44195.

0883-5403/2905-0034$36.00/0 – see front matter © 20http://dx.doi.org/10.1016/j.arth.2013.10.006

Article history:Received 16 July 2013Accepted 7 October 2013

Keywords:total hip arthroplastypatient specific instrumentsacetabular cuppreoperative planning

Total hip arthroplasty (THA) survivorship relies largely upon appropriate acetabular cup placement. Thepurpose of this prospective randomized controlled trial was to determine whether the use of a preoperative3D planning software in combination with patient specific instrumentation (PSI) results in improved cupplacement compared with traditional techniques. Thirty-six THA patients were randomized into standard(STD) or PSI technique. Standard approach was completed using traditional techniques, while PSI cases wereplanned and customized surgical instruments were manufactured. Postoperative CT scans were usedto compare planned toactual results.Differences foundbetweenplannedandactual anteversionwere−0.2° ± 6.9°(PSI) and −6.9° ± 8.9° (STD) (P = 0.018). Use of 3D preoperative planning along with PSIs resulted insignificantly greater anteversion accuracy than traditional planning and instrumentation.

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Total hip arthroplasty (THA) is an extremely successful procedure,improving range of motion and decreasing pain to improve patients'quality of life [1–3]. However, malpositioning of the acetabular cupcan result in premature implant failure requiring revision [4–10]. Thenumber of primary THAs performed in the United States increasedfrom 7.99 per 100,000 people in 2001 to 10.3 in 2007 [11] according toRavi et al. In a study byWera et al, the most common cause of revisionTHA was due to cup malpositioning (33%) [10]. Currently, implantplacement in THA relies on navigation, crude instrumentation, orexclusively on a surgeon's intraoperative assessment of limitedanatomic landmarks with the use of generic, mechanical instrumentsdesigned for all patients with differing severities of pathology andunique anatomy.

Accurate acetabular cup positioning in THA decreases the risk ofdislocation [12–15], impingement [16,17], and all component wearrate [18–20]. Component wear rate on both hard-on-hard and hard-on-soft bearing surfaces from edge loading at high abduction angleshas been reported [20]. The traditional methods of using preoperativeradiographs (e.g., anteroposterior pelvis and hip) for planning andstandard surgical instrumentation have shown potential for inaccu-racy which varies with surgeon experience [21,22]. Factors thatcontribute to inaccurate cup placement include approach, patientpositioning [23] and BMI [24]. Minimizing the risk of cup malalign-ment and subsequent revision THA through correct placement is a

modifiable risk factor that could reduce the rate of revision THA andits burden to the health system. As shown by Bozic et al from thenation-wide inpatient sample (NIS), revision THA had an averagelength of stay of 6.2 days and hospital charges of $54,553 in 2006 andis the leading cause of early revision in THA [25].

Historically the recommended range of values for anteversion is15° ± 10° and abduction is 40 ± 10° as originally described byLewinneck [15]. However, Yoon et al [26] determined that the correctsafe zone changes according to the amount of version and abductionas shown by a circle with a radius of 14° from 39° abduction and 21°anteversion, as opposed to the classic rectangle represented safezones [13,15]. Their study illustrated the importance of understandingsafe zones which should be individualized for each patient due to thedynamic nature of cup positioning and patient anatomy. Once this isachieved, reproducing the values in the OR remains its own separatechallenge. It has been shown that free-hand cup placement is accurateonly 70.5% of the time [22].

The most widely used method of placing a cup involves planningthe surgery with preoperative radiographs and attempting toreproduce the plan with standard surgical instruments which fail toaccount for a patient's unique pelvic anatomy and position on theoperating table. Transferring the plan from the radiographs to the ORcan be difficult due to a patient's unique anatomy and the differencesdefined by Murray [27] between radiographic, operative, andanatomic planes of version and abduction. Surgeon experience usingan alignment guide attached to a reamer handle is used to obtain 45°abduction referencing the floor and 20° anteversion referencing thelongitudinal axis of the patient. Assessing the position of the pelvisrelative to the patient and the OR using standard instruments can leadto malpositioned acetabular components [23].

Table 1Patient Demographics.

STD Group (N = 18)Median (25%, 75%)N (%)

PSI Group (N = 18)Median (25%, 75%)N (%) P Value

Mean age (years) 58.5 (51.0, 69.0) 61.0 (59.0, 66.0) 0.63a

Gender (Males) 10 (55.6) 10 (55.6) 0.99b

Mean BMI (kg/m2) 28.95 (25.2, 32.9) 31.66 (24.9, 36.2) 0.50a

ASA Class (N)1 (2) 2 (11.1) 0 (0.00) 0.65c

2 (13) 6 (33.3) 7 (38.9)3 (18) 8 (44.4) 10 (55.6)4 (3) 2 (11.1) 1 (5.6)

Diagnosis (N)Osteoarthritis (31) 15 (83.3) 16 (88.9) 0.73d

Avascular necrosis (2) 1 (5.6) 1 (5.6)Rheumatoid Arthritis (2) 2 (11.1) 0 (0.00)Dysplasia (1) 0 (0.00) 1 (5.6)

Tönnis Grade of OA1 (N) 0.61c

1 (11) 6 (40.0) 5 (31.3)2 (11) 4 (26.7) 7 (43.8)3 (9) 5 (33.3) 4 (25.0)

1Brückl R, Hepp WR, Tönnis D. [Differentiation of normal and dysplastic juvenilehip joints by means of the summarized hip factor]. Arch Orthop Unfallchir1972;74(1):13–32.Busse J, Gasteiger W, Tönnis D. [A newmethod for roentgenologic evaluation of the hipjoint–the hip factor]. Arch Orthop Unfallchir. 1972;72(1):1–9.

a Wilcoxon rank sum test.b Student's t-test.c Cochran–Mantel–Haenszel.d Fisher's exact test.

Table 2Perioperative Data.

STD Group (N = 18)N (%) OR Median (25%, 75%) PSI Group (N = 18) P Value

LateralityRight (20) 10 (55.6) 10 (55.6) 0.99a

Left (16) 8 (44.4) 8 (44.4)Anesthesia typeSpinal (22) 9 (50) 13 (72.2) 0.31b

General (13) 8 (44.4) 5 (11.1)MAC (1) 1 (5.6) 0 (0.00)

Surgeon1 (26) 13 (72.2) 13 (72.2) 0.99b

2 (6) 3 (16.7) 3 (16.7)3 (4) 2 (11.1) 2 (11.1)

Mean operative time(min)

88.0 (72.0, 110.0) 95.0 (76.0, 114.0) 0.46c

Mean EBL (mL) 150 (150, 200) 200 (150, 250) 0.22c

a Chi-square.b Fisher's exact test.c Wilcoxon rank sum test.

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New methods have recently been developed to assist a surgeon inpreparing the bone and inserting the final implants. These technol-ogies include intraoperative computer navigation [28–31] andpreoperative computer assisted surgical planning with the fabricationof patient specific instruments (PSI) [32]. Designing PSIs based on apatient's unique bony morphologic features of the acetabulum from acomputed tomography (CT) scan is an improvement over genericinstruments by minimizing sources of error from standard surgicalinstruments that depend on appropriate patient positioning, pelvisorientation [8,33], exposure [34], and surgeon experience [21].Currently PSIs available for knee arthroplasty have shown animprovement in component position [35]. Other procedures thatutilize PSI are shoulder arthroplasty [36–39], acetabular fractures [40],spinal surgery [41], corrective osteotomy upper extremity fractures[42], and dental implants [43].

The main objective of this study was to determine if the use ofpreoperative software planning and PSI during THA is more accuratefor acetabular cup placement than traditional techniques, using 2different approaches among 3 fellowship trained surgeons. A secondaim of the study was to determine the precision of the final placementof the cup compared to the preoperatively planned placement intraditional instrumentation versus PSI.

Materials and Methods

This prospective, randomized, controlled trial was performed fromMarch of 2011 through April of 2012 at a single large academicinstitution. This study was approved by our institutional review board(10-1138) and every patient gave written informed consent toparticipate. The study is registered at clinicaltrials.gov: NCT01791738.

Patient Selection

Patients scheduled for an elective primary THA were approachedfor the study. Inclusion criteria were as follows: (1) primary THApatient at our institution, (2) 18–85 years old at time of surgery, and(3) able to get a preoperative CT scan within 21 days of the procedureand postoperative CT scans at our institution. The exclusion criteriawere: (1) significant metal around the operative hip potentiallydistorting the preoperative CT images, (2) pregnancy, (3) incarcer-ation, or (4) condition deemed by physician to be non-conductive topatient's ability to complete the study. There were no exclusionsregarding bony anomalies or complexity of procedure. Once a patientagreed to participate in the study, he or she was randomized into thecontrol or intervention arm of the study using permuted blockedrandomization. Randomization prior to surgery was blinded tosurgeons and patients. A study coordinator generated the randomi-zation, while a different coordinator screened and enrolled patients. Apower analysis based on data from a previous study using sawboneswas used to detect a difference of 9.3 degrees with an experimental-wide error rate of 0.05 using a sample size of 30 for the study (Bulleret al). Demographic information collected on all patients were age,gender, body mass index (BMI), America Society of Anesthesiology(ASA) classification, diagnosis, Tönnis [44,45] grade of osteoarthritis(OA) (Table 1). Perioperative data collectedwere laterality, anesthesiatype, surgeon, operative time, and estimated blood loss (EBL)(Table 2).

Preoperative Planning

Preoperative CT scans of the pelvis and proximal femur wereobtained at least 21 days prior to surgery with 0.6 mm slice thickness,slice pitch factor of 0.45 and pixel spacing 0.856 mm (SiemensSensation 64, Siemens Medical Solutions USA, Inc., Malvern, PA, USA).The CT images were then transferred to the custom designed three-dimensional (3D) surgical simulator (Arthroplan, Custom Orthopaedic

.

Solutions, Delaware, USA) [38,39]. In the simulator, each surgeonvirtually planned the desired orientation (i.e., anteversion andabduction) of the cup and size (Figs. 1 and 2) for all patients (controland treatment groups) in the study [38,39]. The control arm patientswere planned at random after the procedures in a blinded fashionso that preoperative use of the software would not confound theirresults. The planes of version and abduction were described by Murray[27] in accordance to radiographic planes. Abduction was determinedby the angle formed from the face of the cup and the transverse axis,while version is the angle formed by the longitudinal axis andacetabular axis projected onto a coronal plane [27]. Following theplan of the desired position of the acetabular cup, PSIs (Fig. 3)were designed and manufactured to fit within and around theacetabular rim. Patients in the control group of the study hadpostoperative planning only to be used for comparison with thepostoperative CT scans to evaluate differences between PSIs andstandard surgical instruments. Patients in the treatment arm had

Fig. 1. Flow diagram illustrating patient selection, randomization, follow-up, and data analysis throughout the study.

1032 T. Small et al. / The Journal of Arthroplasty 29 (2014) 1030–1037

three different PSIs manufactured using various bony areas of theacetabulum. Surgeons with posterior approaches benefited more fromdesigns utilizing the posterior aspect of the acetabulum, while lateralapproaches were more accommodating to PSIs utilizing the anteriorportion of the acetabulum. Additional PSIs consisted of a preoperativeacetabulum model exposed without soft tissue. This model functionedas a guide for ensuring the correct location of the PSI relative to thepatient (Fig. 4). A second model was a postoperative acetabulumfitted with an artificial cup in the desired position to be comparedwith the actual cup during the procedure (Fig. 4). All PSIs weremanufactured and printed with an SLA 5000 3D printer from 3Dsystems using Watershed XC11122 resin (Astro Manufacturing,Eastlake, OH). Prior to intraoperative usage, PSIs were sterilizedusing Sterrad (low temperature hydrogen peroxide gas plasma).Printouts illustrating the desired location and values of desiredabduction and version were also used during the procedure of thetreatment group.

Surgical Procedure

Three different surgeons fellowship-trained in adult joint recon-struction performed primary THAs on 36 patients using the Tridentacetabular component (Stryker; Mahwah, NJ). The control arm of thestudy consisted of procedures carried out with only standard (STD)mechanical alignment guides to assist with the insertion of theacetabular cup. Procedures in the intervention arm of the studyutilized assistance with our novel planning software and PSI to insert

the acetabular component. Patients in the control arm of the studyhad traditional templating and insertion of the cup using standardsurgical instruments without the assistance of the PSIs.

The operative technique for both groups was completed using 2approaches (i.e., direct lateral and posterior) depending on theoperative surgeon. Surgeons were given a printout of the plannedsurgerywith values for cup size, abduction, and anteversion, as well asdiagrams illustrating the planned location of the cup within theacetabulum for the patients in the PSI arm of the study. Patients werepositioned in the lateral decubitus position for all procedures (Fig. 5).After the exposure and hip dislocation were completed, theacetabulum was visualized (Fig. 6). The STD patients' procedureswere completed by each surgeon using standard mechanical in-struments and 2 dimensional templating.

After exposure of the acetabulum for patients in the PSI group, theacetabulum was cleaned of any soft tissue (e.g., cartilage and labrum)to ensure a secure fit for the PSI. Next, the PSI was placed in a positionto fit within and around the acetabulum in a “best fit” position (Fig. 6).The peripheral guide-wire was drilled through the guide on the outeredge of the PSI into the iliac, superior to the acetabulum (Fig. 6). Theguide-wire served as a reference of trajectory for reaming. Afterreaming was completed, an appropriate sized acetabular componentwas chosen and inserted with an impactor using the guide-wire as areference, similar to the reaming process (Fig. 6). The postoperativesurrogate was then used to compare the planned cup position withthe actual cup position by palpation and direct visualization (Fig. 7).Once it was determined the cup was in satisfactory position, the cup

Fig. 2. Screen shot of surgical simulator software program used for preoperative planning.

1033T. Small et al. / The Journal of Arthroplasty 29 (2014) 1030–1037

was secured and the procedure was completed in standard fashion forall patients.

Post-Operative Evaluation

All patients in the PSI and STD groups received a CT scan prior todischarge using the same technique as the preoperative scans, withthe addition of a metal reduction reconstruction technique within theregistration software to minimize CT scan artifact from the newprosthesis [38]. Evaluation of the final cup positionwas determined bysuperimposing the previous planned cup position to the actual cupposition and compared usingMurray's definitions [27] for version and

Fig. 3. Screen shot of different planes (anatomic, radiographic, and operative) of an

abduction, in the radiographic plane. The trial was completed once thelast patient's postoperative CT scan was obtained.

Statistical Analysis

Baseline characteristics were first evaluated to determine normaldistribution. Categorical data were compared using Chi-square testsfor measures of association. The Fisher's exact test was applied forexpected cell counts b5 and the Cochran Mantel–Haenszel Chi-squaretests were used for ordinal data. Continuous data were comparedusing the student's t-tests for normally distributed data; non-normaldata were compared using the non-parametric Wilcoxon tests.

teversion and inclination used within the surgical simulator software program.

Fig. 4. Three different patient specific instrument (PSI) designs manufactured to fitwithin and around the acetabulum (from left to right, respectively).

Fig. 5. Preoperative, native acetabulum/pelvis model (right) and a postoperativeacetabulum/pelvis model (left) with an implanted acetabular cup in the desiredlocation from preoperative software planning.

1034 T. Small et al. / The Journal of Arthroplasty 29 (2014) 1030–1037

Non-normal data consisted of age, BMI, operative time, EBL,planned anteversion, and planned abduction. A P value ≤ 0.05was considered statistically significant.

Fig. 6. Illustration of a patient in lateral decubitus position, referencing angles

Results

We screened 78 patients and enrolled and randomized a total of 36to 2 parallel study arms: 18 patients to the interventional group (PSI)technique and 18 to the control group with (STD) technique (Fig. 8).There were no significant differences in demographic or perioperativedata between the two study groups (Tables 1 and 2).

The results of cup orientation were compared as planned, actual,and deviation from the planned cup orientation to actual cuporientation in anteversion and abduction (Table 3). All of the resultsare reported in the radiographic planes of anteversion and abduction.The average anteversion for the STD group was 28.4° ± 7.9° andaverage abduction was 43.5° ± 9.0°. The PSI arm had a meananteversion of 18.5° ± 7.8° and mean abduction of 46.4° ± 7.1°(Table 3). Themean difference fromplanned versus actual anteversionwas −6.9° ± 8.9° for STD and −0.2° ± 6.9° for PSI cases (P =0.018)(Table 3). Themean difference in abduction from planned versus actualwas 1.3° ± 9.1° and−2.0° ± 7.3° for STD and PSI groups, respectively(P = 0.25) (Table 3). Results of cup orientation when separated byapproach [i.e. posterior approach (n = 30) and direct lateral approach(n = 6)] showed different patterns (Tables 4a and 4b). There was onecomplication in the STD group of a postoperative anterior dislocation,and none in the PSI group.

Discussion

We aimed to determine if our preoperative software planning andPSI technique for acetabular component placement was useful inimproving the accuracy and precision of acetabular cup placementcompared with standard methods and instrumentation. Our resultsillustrated improvement in attaining the planned cup version,

of anteversion (top) and abduction (bottom) to a peripheral guide wire.

Fig. 7. Stepwise process of using a patient specific instrument (PSI). After adequately exposing the acetabulum (upper left), secure the PSI into a best fit position and insert theperipheral pin (upper right). Then ream the acetabulum to desired cup size, while referencing the peripheral guide wire for orientation (lower left). Lastly, insert the acetabularimplant referencing the peripheral guide wire to the impactor (lower right).

1035T. Small et al. / The Journal of Arthroplasty 29 (2014) 1030–1037

regardless of patient characteristics, approach, or surgeon. Throughour PSI technique, we were able to find significant improvements inboth precision and accuracywith attaining the desired anteversion forour components by deviating −0.2° (SD 6.9°) in PSI methodcompared to −6.9° (SD 8.9°) in the STD group (P = 0.018). TheSTD group was more likely to be deviated towards retroversion thananteversion, and retroversion has been documented as a greatercorrelation to postoperative dislocation [46]. Also of note, our PSItechnology resulted in a mean version of 18.5° (SD 7.8°) compared tothe STD group of 28.4° (SD 7.9°) (P b 0.001) that is closer to 15°,defined by Lewwineck et al [15] as a “safe zone”. Though Lewwineck's

Fig. 8. Intraoperative photograph of the final implant position within a patientcompared to a surrogate model of the acetabulum/pelvis with an acetabular cup in theplanned position.

safe zonewas not our target, each surgeon positioned the cup to his/herdesired location. It is possible that simply having the advantage ofpreoperative 3D planning software leads the surgeon to a different planand location of the implant, biasing the postoperative placement of thecup to a more appropriate location. Results for final abduction and thedifference between planned and actual were not significantly different,illustrating that the PSI technology was no better than the skill offellowship trained surgeons at obtaining the desired location inabduction with STD technique.

The placement of the acetabular cup in the desired position hasproven to be imprecise regardless of training or skill [22,47]. Ingeneral, the use of computer assisted THA has been proven to bemoreaccurate than traditional instrumentation [29–31,48,49]. The preop-erative planning software used in this study has been validated andproven to be effective in determining bony anatomy and removingsoft tissue and loose bodies [38,50]. Using the software allows thesurgeon to clearly define the orientation and unique pathology of eachpatient's native acetabulum and plan the precise location of theacetabular component without the limitations of soft tissue anddistortion inherent to radiographic images. The results reported herewere evaluated using the softwarewithmetal reduction techniques toreduce scatter from the CT images as opposed to radiographicassessment as reported in other studies [49,51–53].

Three separate surgeons using 2 different approaches wereinvestigated, while other computer assisted THA studies have used asingle surgeon [31,52,54,55]. One must be careful not to over-interpret the approach analyses, as the sample size for the directlateral group was small (n = 6). That being said, the direct lateralapproach data show a different pattern than the posterior approachdata, in that the PSI method seems to have more of an effect onabduction than version.

All of the surgeons in the present study were fellowship trained,and perform more than 100 THA procedures per year. Additionallyusing prospective, randomization of PSI or STD treatment, improved

Table 3Differences Between Planned and Actual Orientations by Method.

STD Method (Degrees) Mean (SD) (95% CI) PSI Method (Degrees) Mean (SD) (95% CI) P Valuea

Actual Version 28.44 (7.9) (24.53, 32.36) 18.54 (7.8) (14.64, 22.45) b0.001Difference Version −6.89 (8.9) (−11.33, -2.46) −0.22 (6.9) (−3.68, 3.23) 0.018Actual Abduction 43.49 (9.0) (39.00, 47.99) 46.40 (7.1) (42.88, 49.91) 0.29Difference Abduction 1.28 (9.1) (−3.23, 5.78) −1.96 (7.3) (−5.58, 1.66) 0.25

Median (25%, 75%) Median (25%, 75%)Planned Version 20.4 (16.8, 24.9) 18.4 (16.7, 19.9) 0.13b

Planned Abduction 45.4 (42.9, 46.5) 43.6 (42.4, 45.2) 0.42b

a Student's t-test, unless otherwise noted.b Wilcoxon rank sum test.

Table 4aDifferences Between Planned and Actual Orientations by Method (Posterior Approach).

STD Method (Degrees) Mean (SD) (95% CI) n = 15 PSI Method (Degrees) Mean (SD) (95% CI) n = 15 P Valuea

Actual Version 29.01 (8.2) (24.50, 33.53) 18.79 (7.2) (14.78, 22.79) b0.001Difference Version −8.62 (8.8) (−13.47, -3.77) −0.65 (6.1) (−4.05, 2.75) 0.008Actual Abduction 44.99 (9.0) (39.99, 49.99) 46.42 (7.5) (42.24, 50.60) 0.64Difference Abduction −0.74 (8.2) (−5.29, 3.81) −2.22 (7.9) (−6.62, 2.18) 0.62

Median (25%, 75%) Median (25%, 75%)Planned Version 20.4 (17.9, 22.9) 18.1 (16.3, 20.0) 0.13b

Planned Abduction 44.3 (42.7, 45.8) 44.2 (42.4, 46.0) 0.96b

a Student's t-test, unless otherwise noted.b Wilcoxon rank sum test.

Table 4bDifferences Between Planned and Actual Orientations by Method (Direct Lateral Approach).

STD Method (Degrees) Mean (SD) (95% CI) n = 3 PSI Method (Degrees) Mean (SD) (95% CI) n = 3 P Valuea

Actual Version 25.61 (6.7) (8.85, 42.4) 17.33 (12.5) (−13.63, 48.30) 0.38Difference Version 1.73 (2.4) (−4.12, 7.6) 1.91 (11.7) (−27.26, 31.1) 0.98Actual Abduction 35.99 (4.8) (24.09, 47.91) 46.28 (5.1) (33.68, 58.87) 0.06Difference Abduction 11.35 (6.6) (−4.99, 27.68) −0.68 (2.55) (−6.99, 5.65) 0.07

Median (25%, 75%) Median (25%, 75%)Planned Version 27.3 (5.8, 48.9) 19.2 (16.0, 22.5) 0.25b

Planned Abduction 47.3 (41.8, 52.9) 45.6 (37.1, 54.1) 0.51b

a Student's t-test, unless otherwise noted.b Wilcoxon rank sum test.

1036 T. Small et al. / The Journal of Arthroplasty 29 (2014) 1030–1037

our design compared to other studies using retrospective data forconventional methods and prospective for the computer assistedadding bias to the computer assisted operations due to increasedsurgeon experience at positioning acetabular components over time.

While some navigation techniques depend on superficial land-marks [29–31,48,49,52,55], this PSI technology relies solely on thebony anatomy of the acetabulum eliminating other potential areas oferror such as: soft tissue, patient positioning, or degree of pathology. Ithas been shown that higher BMI correlates with malpositioned cups[56]. Regardless of BMI, patient morphology, or position; if theacetabulum is adequately exposed, the PSIs can adequately determinethe appropriate position of the component if positioned properly.Thus, no patients were excluded from this study on the basis of BMI ordegree of pathology. One patient had severe hip dysplasia, requiring abone graft due to the bony deficiency and another had a BMI of 53.9;both of whom were ultimately randomized into the PSI arm of thestudy. There were no significant differences in length of procedure orblood loss. The lack of any adverse events using the PSI technologydemonstrated that this approach did not place the patient at increasedrisk of injury.

Future studies should involve multiple institutions with a largersample size, using both fellowship trained and non-fellowship trainedsurgeons with differing years of experience and procedure volume.These studies could determine the applicability our technology to allorthopaedic surgeons who perform THA. Finally comparing our

technology against navigation (image based and non-image based)and traditional techniques for THAwould providemore insight on theutility of this novel preoperative planning software and PSI technol-ogy. Finally studies examining mid-term and long-term follow-upwould allow us to compare the results clinically with current methodsof placement.

In conclusion, our study illustrated the PSI technique to be moreaccurate in placing a cup in the intended position of anteversionversus STD technique. This PSI technology was no better than the STDtechnique for obtaining the desired abduction angle. We believe thatby improving cup positioning, this technology can potentiallydecrease postoperative dislocations, component wear, impingement,and subsequent revision THA procedures.

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