Purpose

The objective of this study was to compare the wear characteristics and damage scores in highly crosslinked (XLPE) and conventional polyethylene (CPE) acetabular liners.

Introduction:

Alignment of the initial femoral guidewire is critical in avoiding technical errors that may increase the risk of failure of the femoral component. A novel alternative to conventional instrumentation for femoral guidewire insertion is a computed tomography (CT) based alignment guide. The aim of this study was to assess the accuracy of femoral component alignment using a CT-based, patient specific femoral alignment guide.

Background:

Polyethylene wear in total knee arthroplasty (TKA) is influenced by patient, surgeon and implant factors. The objective of this study is to assess the effect of limb alignment, implant position and joint line position on the pattern of wear in posterior stabilized (PS) tibial inserts.

Purpose

The mobile-bearing total knee arthroplasty was designed to increase the contact area with the polyethylene bearing, through the functional range of motion, and subsequently decrease the wear rate previously seen in fixed-bearing implants. In the literature there is no clear clinical advantage between the different designs in the short to mid-term follow-up.

The purpose of this study was to compare the results between a cruciate retaining mobile-bearing design (SAL II, Sulzer) and two cruciate retaining fixed-bearing designs (AMK, Depuy, and the Genesis II, Smith and Nephew).

Purpose: The range of motion after TKA depends on many patient, surgical technique, and implant factors. Recently, high-flexion designs have been introduced as a means of ensuring or gaining flexion after TKA. We therefore evaluated factors affecting postoperative flexion to determine whether implant design influences long-term flexion.

Method: We prospectively collected data on patients receiving a primary Genesis II total knee replacement with a minimum of 1-year followup (mean, 5.4 years; range, 1–13 years). We recorded pre – and postoperative outcome measures, patient demographics, and implant design (cruciate retaining [CR, n = 160], posterior stabilized [PS, n = 1177], high-flex posterior stabilized [HF-PS, n = 197]).

Results: Backward stepwise linear regression modeling revealed the following factors that significantly affected postoperative flexion: preoperative flexion, gender, body mass index, and implant design. Independent of gender, body mass index, and preoperative flexion, patients who received a HF-PS and PS design implant resulted in 8° and 5° more flexion, respectively, than those who received a CR implant. Based on analysis examining pre-operative flexion categories, patients with low flexion preoperatively (< 100°) were more likely to gain flexion, whereas those with high flexion preoperatively (> 120°) were most likely to maintain or lose flexion postoperatively. Controlling for implant design, patients with high flexion preoperatively (> 120°) were more likely to gain flexion with the HF-PS design implant (HF-PS = 32.0%; PS = 15.1%; CR = 4.5%).

Conclusion: In summary, our data demonstrate postoperative range of motion after TKA is related to several factors, confirming the important role of the patient’s preoperative range of motion. In addition, our review suggests knee design and, in particular, the use of a so called “high-flexion” PS polyethylene design may be advantageous in maintaining or improving flexion postoperatively, especially in those patients with good pre-operative range of motion.

Purpose: Efforts to decrease polyethylene wear have lead to advances in polyethylene and counter-face technology for total hip replacement. In particular, the use of highly cross-linked polyethylene (XLPE) and more recently, oxidized zirconium (Oxinium) heads, have demonstrated significant in-vitro improvements in THR wear. This study reports on the early clinical performance and wear (measured with RSA) of an randomized controlled trial (RCT) comparing Oxinium and CoCr heads on XLPE and conventional polyethylene (CPE).

Method: Forty patients were enrolled in a RCT and stratified to receive either an Oxinium (Ox) or CoCr head against either XLPE or CPE (ie 10 patients in each group). All patients had otherwise identical THRs and had tantalum beads inserted in the pelvis and polyethylene for wear analysis. There were no significant differences between groups with respect to patient demographics and the average age was 68 years (range 57–76) at index procedure. RSA wear analysis was performed immediately post-op, at six weeks, three and six months and then at one and two years. All patients are a minimum of four years post-op (average 4.6, range 4 – 5.8). Patients were followed prospectively using validated clinical outcome scores (WOMAC, SF-12, Harris Hip scores) and radiographs.

Results: All health-related outcomes were significantly improved from pre-operative with a mean Harris Hip score and WOMAC at last follow-up of 90.9 and 80.2, respectively. Total 3D femoral head penetration at two years for each group were the following: CoCrXLPE (0.068±0.029mm); OxXLPE (0.115±0.038mm); CoCrCPE (0.187±0.079mm); and OxCPE (0.242±0.088mm). Thus, OxCPE was significantly higher than OxXLPE and CoCrXLPE but not CoCrCPE (p=0.001, p> 0.0001 and p=0.094, respectively). In other words, head penetration was higher with CPE compared to XLPE but there was no significant difference between Ox and CoCr heads. Similarily, regardless of head type (ie combining similar poly types), there was a significant difference in 3D head penetration at two years between CPE and XLPE ( CPE 0.213±0.086; XLPE 0.093±0.041, p> 0.0001).

Conclusion: The early results of this RCT, using RSA as the wear analysis tool, indicate a significant improvement in wear with XLPE compared to CPE. However, it failed to show a clear advantage to the use of Oxinium over CoCr against either polyethylene. Longer follow-up is required to determine steady-state wear rates (after bedding-in) and allow comparison between bearing groups.

Purpose: The Genesis II total knee arthroplasty system was introduced in 1996 as the next evolution in TKR design characterized by “built-in” femoral external rotation and improved trochlear design to optimize patellar tracking and femoral/tibial kinematics, as well as a polished tibial base plate and ethylene-oxide sterilized polyethylene to minimize wear. The purpose of this prospective study was to evaluate the long-term (minimum 10 year) clinical and radiographic results and survivorship of this novel TKA implant system.

Method: Between 1996 and 1999, 478 Genesis II Primary TKRs were implanted and followed prospectively in 414 patients (mean follow-up 11.25±1.11 years). Diagnosis at index surgery included: 94% osteoarthritis, 5% inflammatory arthritis, 1% other diagnoses. Average age at index TKR was 68 years (range 38 to 93 years). There were 149 posterior cruciate retaining (31%) and 329 cruciate sacrificing (69%) knees implanted. Patella resurfacing was performed on 89% (432) of the cases. Sixty-seven deaths occurred prior to 10 years follow-up. Patients were followed prospectively using validated clinical outcome scores (WOMAC, SF-12, Knee Society scores) and radiographs. Kaplan-Meier survival analysis was performed.

Results: All health-related outcomes were significantly improved from preoperative with a mean Knee Society Score and WOMAC at last follow-up of 162 and 69, respectively. To date, 16 revision procedures have been performed. Revisions for infection included six two-stage revisions and two cases of irrigation & debridement with polyethylene exchange. In addition, there were three re-operations for stiffness and one for patellar instability. To date, there have been only two revisions for aseptic loosening and/or osteolysis. Excluding revisions for infection, the Kaplan-Meier survivorship analysis of the total knee system was 98.9±0.5% at five years and 98.2±0.6% at 10 years.

Conclusion: The Genesis II total knee arthroplasty system, characterized by “built-in” femoral external rotation, improved trochlear design, a polished tibial base plate and ethylene-oxide sterilized polyethylene, has demonstrated excellent clinical & radiographic results and long-term survivorship (98% at 10 years) at our institution.

Purpose: A ceramic head coupled to a metal liner is a proposed new alternate bearing in THA. The authors participated in an FDA approved multicentre prospective, randomized, blinded clinical trial comparing ceramic-on-metal (CoM) to metal-on-metal (MoM) in patients receiving a THA.

Method: 390 patients received the same acetabular component and metal insert. 194 patients received a delta ceramic head (CoM) and 196 received a metal head (MoM). Metal ions were evaluated in 72 patients (36-CoM, 36-MoM). Harris Hip scores, radiographs, and metal ion levels (cobalt, chromium and titanium in serum, erythrocytes and urine) were evaluated pre-operatively and at three, 12 and 24 months.

Results: No patients were lost to follow-up. There were no differences between groups’ baseline demographics and clinical scores. At two years there were no differences in Harris Hip scores, radiographs, adverse events or postoperative complications. Both groups had overall very low median metal ion profiles with no statistically significant differences. 24 month MoM vs CoM; Serum cobalt ( g/L), mean: 1.2(+/−0.5) vs 1.1(+/−0.3), median: 0.66(range: 0.2–5.6) vs 1.0 (range: 0.3–2.7); Serum chromium ( g/L), mean: 1.1(+/−0.5) vs 1.4(+/−0.4), median: 0.86(range: 0.3–6.9) vs 1.2(range: 0.3–4.9). Urine cobalt and urine chromium ( g/day) demonstrated similar trends to serum ion levels.

Conclusion: While CoM is a new bearing surface in North America and not currently FDA or HPB approved, it has been in clinical use globally since 2006. Results of this non-inferiority RCT demonstrated no clinical outcome, metal ion, radiographic or adverse event differences between CoM and MoM cohorts.

Purpose: Total knee arthroplasty (TKA) is a proven intervention in the management of end-stage knee arthritis. However, the demands of younger, more active patients may result in increased rates of wear and aseptic loosening. The purpose of this study was to assess the long-term outcome of a large cohort of young patients, and to assess if the outcomes of cemented implants differed from non-cemented implants.

Method: Between 1984 and 2003, 350 TKAs were performed in 283 patients who were under 55 years old. Patients were followed a minimum of 5 years. Mean age at time of surgery was 49.0±5.5 years; 64% of patients were female. Primary knee pathologies included degenerative and post-traumatic arthritis (271), inflammatory arthritis (62), and others (17). Multiple implant designs were used; 296 knees were cemented and 54 were non-cemented. The Knee Society Clinical Rating Score (KSCRS) at latest follow-up was calculated. The Kaplan-Meier survivorship was calculated using an endpoint of revision total knee arthroplasty.

Results: Mean follow-up was 8.7±3.4 years. Seventeen knees were revised at a mean of 7.1±4.4 years after the index procedure. Fifteen patients (twenty-five knees) died. Fifty-one patients (sixty-two knees) were lost to follow-up. Sixty patients (sixty-seven knees) had incomplete KSCRS forms. Average function and knee domains of the KSCRS were 70.0±26.7 and 87.3±16.2 respectively. The Kaplan-Meier survival at five, ten, and fifteen years was 0.965±0.011, 0.941±0.015, and 0.933±0.017. The rate of revision was 5.9%. There was no statistically significantly difference observed between the outcomes of cemented and non-cemented implants, male and female patients, or inflammatory versus non-inflammatory arthritis.

Conclusion: This study demonstrates that total knee replacement in younger patients can demonstrate excellent survival rates free of revision. There does not appear to be an obvious survival advantage of cementless designs, or difference in outcomes based on sex of the patient or primary diagnosis of inflammatory or non-inflammatory arthritis.

Purpose: Approximately, 10% of two-stage TKA revisions for deep sepsis become re-infected. The purpose of this study was to determine the success in terms of sepsis eradication and factors associated with failure of repeat two-stage revision TKA.

Method: Between 1991 and 2006, 129 two-stage revision TKRs for deep sepsis were performed. Ten cases which became re-infected were identified. These unfortunate patients, representing 8% of all the two-stage TKA revisions performed during this time period, are the focus of this study. Their progress and treatment interventions were followed for the purposes of this study.

Results: Ten patients were identified with a two-stage revision TKA which became re-infected. Mean patient age was 72 with 40 % being female. Following recurrent sepsis all patients went on to require more than one further two-stage revision (mean 3.67 further revision surgeries). Infection was only successfully eradicated in 28.7% of cases, the remaining require chronic suppressive therapy or have ongoing active infection. Two patients went on to have an arthrodesis (both remain on suppressive anti-biotics) and one patient had trans-femoral amputation. Staph Aureus and Coagulase neg Staph accounted for 80% of primary infective organisms with only one primary infection with methicillin resistant staph aureus (MRSA). Cultures at subsequent revisions were the same organism in 67% cases. Additional organism cultured included Pseudomonas and Propionibacterium. These patients had an increased incidence of multiple medical co-morbidities including Type-2 Diabetes Mellitus and Rheumatoid Arthritis.

Conclusion: Patients with recurrent sepsis after a two-stage revision for infection in TKR all required multiple further surgeries. Eradication of infection was only achieved in 28.7% cases. Risk factors for recurrent sepsis include Rheumatoid Arthritis and Type-2 Diabetes Mellitus.

Purpose: There is no consensus whether the posterior cruciate ligament (PCL)should be preserved (CR) or sacrificed (CS) during primary total knee replacement (TKR). The purpose of this study was to compare the greater than 10 year survivorship and health related outcomes of CR and CS TKRs using a single implant system.

Method: Between 1996 and 2000, 478 Genesis II Primary TKRs were inserted in 414 patients. Excluding those with a primary diagnosis other than osteoarthritis, body mass index greater then 40, history of prior patellectomy, fusion or osteotomy, 358 cases in 310 patients were included. 134 (37%) had a PCL preserving (CR) and 224 (63%) had a PCL sacrificing implant (CS). The two patient cohorts were compared for Kaplan-Meier survivorship, health-related outcomes (Knee Society scores, WOMAC, SF-12), range of motion (ROM) and radiographic loosening or wear.

Results: Mean follow-up was 11.87±1.04 years for CR and 10.96±0.87 years for CS (p=0.001). Four cases were revised for infection. No significant differences were noted between the CR and CS Genesis II cohorts at 10 year Kaplan-Meier survivorship excluding infections (CR 0.984±0.011, CS 0.986±0.008, p=0.30). Overall revisions were two for CR (1.5%, no infections) and seven for CS (1.7%, four for infection; 1.3% excluding infections). Revision rates were not significantly different between groups including or excluding infections (p=0.493 and p=1.00 respectively). CS had significantly greater postoperative ROM than CR (CS=114.20±13.60, CR=111.35±12.38, p=0.024). At 10 years, no differences were observed in satisfaction, health-related outcomes or radiographic wear/loosening. Crepitus was reported more frequently in CS design.

Conclusion: Most studies comparing PCL sacrificing (CS) versus retaining (CR) TKRs are short term. In this large, long term, single implant CR versus CS study, no differences were found in Kaplan-Meier survivorship, health-related outcomes or patient satisfaction. The CS design had more range of motion, but also a higher incidence of peripatellar crepitus than the CR design. We conclude that both CR and CS TKR designs can yield excellent long term clinical outcomes.

Purpose: High contact stresses and wear after total knee replacement (TKR) has been a problem. Mobile bearing TKRs have been advocated as a means to increase load bearing area, reduce contact stresses and minimize wear. The purpose of this study was to compare two, large, consecutive cohorts of TKR patients with greater than 10 years follow-up, one with a fixed bearing and one with a mobile bearing design.

Method: One hundred and three SAL II mobile bearing TKR’s were compared to a gender, age, BMI and time from surgery matched fixed bearing Genesis II cohort of equal size. All surgeries were performed between September 1993 and December 2000 (average follow-up, 11.64±1.64 years). Inclusion criteria included patients with osteoarthritis of the knee. Exclusion criteria included revision arthroplasty, inflammatory arthritis, a prior osteotomy or a prior patellectomy. The > 10 year Kaplan-Meier survivorship, health-related outcomes (Knee Society scores, WOMAC and SF-12), radiographs and retrieved implants for the fixed and mobile bearing TKR cohorts were compared.

Results: Fixed bearing TKRs demonstrated better 10 year Kaplan-Meier survivorships for any re-operation, 1.000±0.000 compared to 0.969±0.018 for mobile bearings (Genesis II and SAL I/II respectively). Revision rates were significantly different between groups with fixed bearing having no revisions and mobile four revisions (3.9%). No cases were revised for sepsis. Mobile bearing revisions were for pain (1), patellar maltracking (1), polyethylene wear (1) and aseptic loosening (1). At 10 years, health-related outcomes were similar between the two cohorts. Fixed bearing TKRs demonstrated more range of motion (111.42±12.76 vs 107.19±14.74 degrees) although not significant (p=0.052). Wear was more frequently noted in mobile bearing TKRs on > 10 year radiographs.

Conclusion: In this comparison of two contemporary TKRs, the fixed bearing TKR outperformed the mobile bearing TKR.

Purpose: The Synergy femoral component was introduced in late 1996 as a second generation titanium proximally porous-coated tapered stem with dual offsets (standard & high) to help better restore femoral offset at THR. The purpose of this prospective study was to evaluate the long-term (minimum 10 year) clinical and radiographic results and survivorship of this second-generation femoral component at our institution.

Method: From December 1996 to December 1999, 256 cementless Synergy femoral components were inserted and followed prospectively in 254 patients requiring THR. 185 were standard offset stems(72.3%) while 71 stems (27.7%) were high offset. The average follow-up was 11.2 years (range 10.0 to 12.9 years). Average age at index THR was 58.9 years (range 19 to 86 years). Two hundred eight stems had standard porous coating while 48 had additional HA coating. Fifty-two cases were either lost to follow-up or had died prior to 10 years follow-up. Patients were followed prospectively using validated clinical outcome scores (WOMAC, SF-12, Harris Hip scores) and radiographs. Kaplan-Meier survival analysis was performed.

Results: All health-related outcomes were significantly improved from pre-operative with a mean Harris Hip score and WOMAC at last follow-up of 91.6 and 81.8, respectively. From the initial 256 femoral stems inserted, only 5 stems have been revised. Two stems have been revised for infection. To date, only one stem has been revised due to subsidence at nine months following surgery likely, as a result of a calcar fracture occurring at the index THR. Two stems were revised for peri-prosthetic fracture as a result of patient falls at six months and 9.8 years post-op. Radiographic review of remaining stems in-situ identified no cases of loosening with all stems showing evidence of osseous integration. The Kaplan-Meier survivorship analysis of the femoral component, with revision for aseptic loosening, was 99.2%±0.008 at five, 10 and 12 years.

Conclusion: The Synergy femoral component, a second generation titanium proximally porous-coated tapered stem design with dual offsets, has demonstrated excellent clinical & radiographic results and long-term survivorship (99% at 10 years) at our institution.

Purpose: The purpose of this prospective blinded randomized control trial was to compare the stem migration of two cemented stem designs using radiostereometric analysis (RSA). This was essentially a safety study in which our hypothesis was that the newer design (CPCS, Smith and Nephew Inc) would demonstrate similar micro-motion to the well-established Exeter (Stryker) design.

Method: Thirty patients were consented and enrolled into a blinded RCT in which 15 patients received a dedicated RSA CPCS stem and 15 patients received a RSA Exeter stem. Both stems are collarless tapered polished cemented stems, the only difference being a slight lateral to medial taper with the CPCS design. Outcome measures were compared (Hip Society Score, WOMAC, SF-12). RSA analysis was conducted immediately postoperatively, at 6 weeks, 3 months, 6 months, 1 year and 2 years.

Results: No difference was found in any of the outcome measures pre-operatively or postoperatively. At 2 years, stem subsidence for the CPCS stem was approximately half that seen for the Exeter stem (0.565±0.189mm and 0.981±0.209mm respectively, p< 0.0001). In contrast, posterior (internal) rotation of the CPCS was approximately twice that of the Exeter stem (1.496±1.215° and 0.716±0.818° respectively, p=0.221). Other migration patterns were no different between stems.

Conclusion: As expected with this stem design, both stems showed some axial and rotational migration within the cement mantle. The subtle differences in design may explain the differences in migration patterns. Our data suggests that the newer CPCS design should perform well over the long-term.

Purpose: The growing trend of morbidly obese (BMI 40+) patients requiring a total joint replacement is becoming major concern in total knee Arthroplasty (TKA). The purpose of this study was to investigate the affects that BMI may have on implant longevity and clinical patient outcome using historical patient data.

Method: A consecutive cohort of 3083 TKA’s in 2048 patients since 1995 (minimum 2 years follow-up) were evaluated. Pre-operative scores, latest scores, and change in clinical outcome scores (KSCRS, SF12, WOMAC) were analyzed using ANOVA and Kaplan-Meier (K-M) survivorship was determined.

Results: K-M cumulative survival at 10 years by BMI group was 0.951±0.033 for Normal and Underweight (< 25, n=277), 0.944±0.024 for Overweight (25–29.9, n=915), 0.882±0.032 for Obese (30–39.9, n=1460) and 0.843±0.076 for Morbidly Obese (40+, n=352). Cumulative revision rates were 1.8% for Normal and Underweight, 1.9% for Overweight, 2.9% for Obese and 2.8% for Morbidly Obese. All pre-operative clinical scores were significantly different between the Morbidly Obese and all other BMI groups (p< 0.05), with the non-morbidly obese having higher scores in all cases. Significant difference was found in the change in WOMAC domain scores and the KSCRS knee score (p< 0.05) between the morbidly obese group and all other BMI groups, with the morbidly obese having the greatest improvement in all domains.

Conclusion: The morbidly obese patient cohort (BMI > 40) undergoing TKA demonstrated the most significant improvement in clinical outcome scores; however also had the lowest cumulative 10 year survivorship. This risk/benefit information is important in pre-operative discussions with this challenging, and increasingly prevalent, patient population.

Purpose: There are two broad-based categories of cementless femoral components performed during total hip arthroplasty: proximally coated versus fully porous coated. While both have enjoyed widespread clinical applications, there remains debate regarding differences in clinical outcome scores, relative incidence of thigh pain and the development of stress shielding. The purpose of this study was to investigate these variables in a multi-center prospective randomized blinded clinical trial.

Method: Between three centers 388 patients were enrolled in this clinical trial. 198 patients received a proximally coated tapered cementless femoral component (Synergy, Smith and Nephew, Memphis) and 190 patients received a fully porous coated cementless femoral component (Prodigy, Depuy, Warsaw). Patients were evaluated pre-operatively, at 3, 6, 12 months and annually thereafter, with multiple validated outcome measures including WOMAC, SF12, HSS, UCLA activity and thigh pain scores. A cohort of 72 patients underwent preoperative and postoperative DEXA scanning.

Results: 367 patients had a minimum of 2 years follow-up (average 6.4 years). There were no differences in age at surgery, BMI, or pre-operative clinical outcome scores (WOMAC, SF12, HSS, UCLA activity, thigh pain) between groups. There were no differences in any post-operative clinical outcome scores at any interval of follow-up. There were no differences in incidence of thigh pain between groups at any time. The only measurable difference between study groups was in bone mineral density evaluation. Bone density change in Gruen zone 7 was 23.7% with the Prodigy stem and 15.3% with the Synergy stem (p=0.011).

Conclusion: Both fully porous coated and proximally porous coated cementless stems performed well, with no clinical differences at a minimum of 2 years follow-up. Only bone mineral density evaluations could detect any differences between these femoral components designs.

We present a case of early retrieval of an Oxinium femoral head and corresponding polyethylene liner where there was significant surface damage to the head and polyethylene. The implants were retrieved at the time of revision surgery to correct leg-length discrepancy just 48 hours after the primary hip replacement. Appropriate analysis of the retrieved femoral head demonstrated loss of the Oxinium layer with exposure of the underlying substrate and transfer of titanium from the acetabular shell at the time of a reduction of the index total hip replacement. In addition, the level of damage to the polyethylene was extensive despite only 48 hours in situ.

The purpose of this report is to highlight the care that is required at the time of reduction, especially with these hard femoral counter-faces such as Oxinium. To our knowledge, the damage occurring at the time of reduction has not been previously reported following the retrieval of an otherwise well-functioning hip replacement.

We evaluated the outcome of primary total hip replacement (THR) in 3290 patients with the primary diagnosis of osteoarthritis at a minimum follow-up of two years. They were stratified into categories of body mass index (BMI) based on the World Health Organisation classification of obesity. Statistical analysis was carried out to determine if there was a difference in the post-operative Western Ontario and McMaster Universities osteoarthritis index, the Harris hip score and the Short-Form-12 outcome based on the BMI.

While the pre- and post-operative scores were lower for the group classified as morbidly obese, the overall change in outcome scores suggested an equal if not greater improvement compared with the non-morbidly obese patients. The overall survivorship and rate of complications were similar in the BMI groups although there was a slightly higher rate of revision for sepsis in the morbidly obese group.

Morbid obesity does not affect the post-operative outcome after THR, with the possible exception of a marginally increased rate of infection. Therefore withholding surgery based on the BMI is not justified.

This was a safety study where the hypothesis was that the newer-design CPCS femoral stem would demonstrate similar early clinical results and micromovement to the well-established Exeter stem. Both are collarless, tapered, polished cemented stems, the only difference being a slight lateral to medial taper with the CPCS stem. A total of 34 patients were enrolled in a single-blinded randomised controlled trial in which 17 patients received a dedicated radiostereometric CPCS stem and 17 a radiostereometric Exeter stem. No difference was found in any of the outcome measures pre-operatively or post-operatively between groups. At two years, the mean subsidence for the CPCS stem was nearly half that seen for the Exeter stem (0.77 mm (−0.943 to 1.77) and 1.25 mm (0.719 to 1.625), respectively; p = 0.032). In contrast, the mean internal rotation of the CPCS stem was approximately twice that of the Exeter (1.61° (−1.07° to 4.33°) and 0.59° (0.97° to 1.64°), respectively; p = 0.048). Other migration patterns were not significantly different between the stems. The subtle differences in designs may explain the different patterns of migration.

Comparable migration with the Exeter stem suggests that the CPCS design will perform well in the long term.

Purpose: The increasing trend of morbidly obese patients (BMI 40+) requiring joint replacement is becoming a growing concern in Total Hip Replacement (THR) surgery. The purpose of this study was to investigate the influence that BMI may have on implant longevity and clinical outcome using prospectively collected patient data.

Method: A consecutive cohort of 2864 THR’s in 2488 patients with osteoarthritis and a minimum 2 years follow-up were evaluated. Patients were divided into appropriate BMI categories; Normal and Underweight (BMI< 25, n=650), Overweight (BMI 25–29.9, n=1069), Obese (BMI 30–39.9, n=981), and Morbidly Obese (BMI 40+, n=164). Pre-operative, latest, and change in clinical outcome scores (HSS, SF12, WOMAC) were analyzed using ANOVA and Kaplan-Meier (K-M) survivorship was determined. Categorical variables such as gender and survival status were analyzed using chi-squared.

Results: Morbidly Obese patients requiring THR’s were significantly younger than all other BMI groups by 5.4±0.83 years (p< 0.0001). Gender was also significant to BMI grouping with more females being Morbidly Obese and Normal or Underweight (p< 0.0001). All pre-operative and latest HHS and WOMAC domain scores were lower for the Morbidly Obese, significantly in all preoperative score domains and latest HHS Function (p< 0.05). The change in clinical scores from pre-operative to latest was greatest in all domains for the Morbidly Obese group. K-M cumulative survival with implant revision as the endpoint at 10 years was not different between the BMI groups. Revision rates for infection for the Morbidly Obese, Obese, Overweight, and Normal were 1.3%, 0.65%, 0.3% and 0.69% respectively. Overall Revision rates for the Morbidly Obese, Obese, Overweight, and Normal were 6.7%, 5.4%, 6.9% and 5.7% respectively and were not found to be significant (p=0.496).

Conclusion: The Morbidly Obese cohort undergoing THR had significantly lower preoperative and lower postoperative clinical outcome scores than all other BMI groups but demonstrated the most significant improvement. No difference was found in the K-M survivorship although revisions and revisions for infection were not equal between the groups