Introduction

Background: Trochanteric bursitis is a common and poorly understood complication following total hip arthroplasty (THA). The purpose of this study was to evaluate the incidence of symptomatic trochanteric bursitis and the change in hip offset among THA patients before and after the introduction of robotic assistance.

Introduction

Wear debris generation in metal-on-metal (MOM) total hip arthroplasty (THA) has emerged as a compelling issue. In the UK, clinically significant fretting corrosion was reported at head-taper junctions of MOM hip prostheses from a single manufacturer (Langton 2011). This study characterizes the prevalence of fretting and corrosion at various modular interfaces in retrieved MOM THA systems used in the United States.

Introduction

Total hip replacements using highly cross-linked polyethylene show excellent clinical outcomes, low wear, and minimal lysis at 5 years follow-up. A recent RSA study reports a significant increase in femoral head penetration between 5 and 7 years. This study is a multi-center radiographic analysis to determine whether the RSA observation is present in a large patient cohort.

Studies of patients having primary THR using highly cross-linked polyethylene show excellent clinical outcomes and very low radiographic wear results at a minimum of 5 years follow-up. Recently, a radiostereometric analysis (RSA) study of a small group of patients reported that after no detectable wear during years 1–5, they found a significant increase in femoral head penetration between 5 and 7 years follow-up. However, this increase in head penetration after 5 years has not been confirmed in a larger patient cohort.

The purpose of this study was to organize a multicenter radiographic study involving leading medical centers in the U.S. having the longest-term follow-up available on this type of highly cross-linked polyethylene in order to determine if the RSA observation can be confirmed in a larger study.

Six academic centers agreed to contribute radiographic data to this study. All patients received primary total hip replacements with Longevity polyethylene liners (Zimmer, Warsaw, IN) coupled with 26, 28, and 32mm cobalt chrome femoral heads. The radiographic inclusion criteria required a minimum of four radiographs per patient: one at 1 year; at least one from 2 to 4.5 years; one 4.5 to 5.5 years; and at least one from 5.5 to 9 years follow-up. The Martell Hip Analysis Suit-eTM software was used for the wear analysis. All wear values were determined by calculating head penetration between the follow-up radiograph and the 1-year radiograph to remove creep, the majority of which has been shown to occur during the first year. Separate linear regressions, representing the wear rates, were computed for the early period from 1 year to 5.5 years and the late period from 5.5 years to 9 years follow-up. The Zar test was used to determine the significance of the difference between these two linear regressions.

We present the completed analysis of 165 hips. When the early and late data points were combined into one data set, the second-order regression indicated an inflection point at 6.3 years with a slightly positive inflection. There were 402 film comparisons in the early time period, and the slope and confidence interval of the regression line was 4.9μm/yr (95% CI of −28μm/yr to 38μm/yr). There were 188 film comparisons in the late period, and slope of the regression line for the late period was 10.8 μm/yr (95% CI of −58μm/yr to 80μm/yr). The Zar test showed no significant difference between the two slopes (Figure 1, p=0.886).

No significant increase in femoral head penetration was found for the late period after 5 years compared to the early period before 5 years follow-up in either analysis. Additionally, no significant late increase in wear was seen within individuals. While we continue to enroll patients, at this time we do not observe the increase in wear seen in the RSA study after 5 years.

Introduction: Dislocation is the most common complication resulting in re-operation after total hip arthroplasty. This study investigates the association between acetabular prosthesis position, changes in femoral offset and leg length and the risk of dislocation.

Patients and Methods: All total hip arthroplasties performed over the past 17 years at one institution were reviewed. The posterolateral approach was used in all cases. Only hips that included all of the following were included in the study: diagnosis of primary osteoarthritis, no previous surgery, unconstrained liner. 3682 hips met the inclusion criteria. 60 hips (1.6%) sustained a dislocation. Cup inclination and version was determined from scanned radiographs using Hip Analysis Suite software (University of Chicago) in all hips that dislocated and a control group of 60 patients matched for femoral head size, sex, age at surgery, side of hip replacement, time from surgery, BMI, type of prosthesis and bearing surface. We compared femoral offset and length against the contralateral normal hip, on standardised radiographs. Therefore dislocation cases where the contralateral hip had been replaced, where arthritic changes were present, or where previous surgery had been undertaken were not included in the analysis. 24 dislocating hips were measured and compared with 48 controls matched using the same criteria as above. Radiographs were analysed using Hip Analysis Suite.

Results: There is a statistically significant difference (p=0.025) in anteversion between dislocators and matched controls. Inclination is not significantly associated with dislocation (p=0.536).

There is a relative risk of 3.0 of dislocation in cups with ≤15 degrees of anteversion compared with > 15 degrees of anteversion. This difference in dislocation is statistically significant (p< 0.01).

Increased femoral offset compared with the normal contralateral hip is statistically significantly associated with an increased risk of dislocation (p=0.03). Change in leg length is not associated with dislocation risk.

Discussion: Decreased cup anteversion is associated with an increased risk of dislocation in hips operated on via the postero-lateral approach. Our results indicate that the surgeon should aim for a minimum of 15 degrees of anteversion to reduce the risk of dislocation.

The increase in femoral offset in the prosthetic hip compared with the normal contralateral hip and its association with dislocation may be due to intraoperative attempts to compensate for an unstable hip by increasing offset. These results indicate that a surgeon should be cautious when increasing femoral offset alone to try and compensate for a potentially unstable hip. Other factors, for example acetabular version should be addressed, with readjustment of cup position intra-operatively if required.

Purpose of the study: The purpose of this propsective randomized study was to evaluate wear resistance of cemented polyethylene cups with the same design but regular or crosslinked polyethylene.

Material and methods: This series included 144 first-intention arthroplasties implanted between July 2000 and July 2002 in 137 patients (92 females, 45 males), mean age 66.2 years (range 16–88 years). The same femoral piece ws used in all patients with a 22.2 mm head. The cup was made of highly crosslinked polyethylene (Durasul™, Zimmer) for 83 hips and regular polyethylene (Duration™, Stryker) for 61 hips). The main outcome criterion was penetration of the femoral head into the cup at two years minimum follow-up (associating true wear and creep) measured with the Martell method modified by the cup manufacturer’s recommendations. Influence of patient-related factors and surgery-related factors was assessed. Non-parametric statistical tests were applied.

Results: The two groups of patients were not significantly different preoperatively. Two patients in the Durasul™ group died at 14 and 31 months follow-up. Median follow-up for the 137 survivors (142 hips) was 28.8 months (range 3–48.8 months) in the Durasul™ group and 24.8 months (ragne 0–47.9) in the Duration™ group. Among these 142 hips, 66 in the Durasul™ group and 51 in the Duration ™ group were reviewed clinically and radiographically with at least two years follow-up. The median penetration was 0.104 mm/yr in the Durasul™ group and 0.242 mm/yr in the Duration™ group (Mann-Whitney test, p=0.01, power 78%). There was a highly significant negative correlation between follow-up time and wear in the Duration™ group (Spearman r = −0.4, p=0.005) but no significant correlation in the Dursul™ group (Spearman r = −0.2, p=0.06).

Discussion and conclusion: The results of this series indicate a notable reduction in wear for highly cross-linked polyethylene cups, with no specific material-related complication. Mid-term results would however be necessary to validate these findings.

Despite favourable wear characteristics of compression molded HMWPE in vitro preliminary data show no statistical difference in wear between RAM extruded HMWPE and compression moulded polyethylene. This study reviews AP and lateral radiographs for wear using the Martell technique at two, five years and maximum follow up (mean 88.2 months).

Reduced implant survivorship due to aseptic loosening has prompted research into alternative bearing materials. Simulator testing is useful but clinical studies are the gold standard to evaluate the wear characteristics of new bearing materials.

On hundred and twelve patients matched for sex, age, body mass index, primary pathology, Charnley grade, and follow up underwent uncemented total hip replacement using an identical implant. Group One (sixty-four patients) had a RAM extruded liner (GUR 4150 HP) and Group Two (forty-eight patients) had a compression molded liner (Montell H 1900). HMWPE sterilisation regimes were identical. AP and lateral radiographs were analysed for wear using the Martell technique at two, five years and maximum follow up (mean 88.2 months).

Preliminary data show a linear and volumetric wear rate in Group One of 0.067 mm/yr and 26 mm3/year respectively between two years to maximum follow up. Similarly, the wear rates for Group Two were 0.132 mm/yr and 45 mm3/year respectively. There was no statistical difference in acetabular osteolysis between Group One (16.3%) and Group Two (15%) patients at maximum follow up.

Despite favourable wear characteristics of compression molded HMWPE in vitro preliminary data show no statistical difference in wear between RAM extruded HMWPE and compression moulded polyethylene. Quality of the wear debris is more likely to be important in producing aseptic loosening than actual wear rate.

Introduction: In total hip arthroplasty (THA) polyethylene (PE) wear debris is major cause of osteolysis and aseptic implant loosening. Wear particle volumes must be reduced to increase implant survival. Various ways of crosslinking the molecular chains of PE have been proposed to increase the wear resistance of the bearing material but prospective long-term follow-up studies are scarce.

Materials & Methods A crosslinked PE acetabular insert was developed by gamma irradiating in a nitrogen atmosphere at a dose of 3MRad and subsequent annealing at 50° C for 144 hours to promote further crosslinking (“Duration” process). The Duration PE was compared to a conventionally prepared PE insert (irradiated at 3 MRad in air, no annealing) in a series of small punch tests, a hip wear simulator study and in-vivo as part of a randomized double-blind clinical study at three medical centers the PE-insert being the only variable. A total of 127 patients with 133 inserts (67 conventional, 66 Duration) were followed up between three and five years post-operatively. Wear was measured yearly by using a computer-based image analysis system. Radiographic appearance of potentially wear related phenomena such as osteolysis or loosening was assessed by an independent reviewer.

Results: Higher load at break during the small punch test confirmed the elevated crosslinking levels of Duration PE against the conventional PE. In the joint simulator Duration PE showed significantly lower volumetric wear rates (Mean SD: 21.7 2.3 mm3/10E6 cycles) than conventional PE (39.7 1.5 mm3/10E6 cycles, p< 0.05). A corresponding and significant level of wear reduction for the Duration PE was identified in-vivo (Duration: 43.7 33.6 mm3/year, conventional: 60.4 42.7 mm3/year, p=0.04). Radiographic analysis at the last follow-up gave evidence of femoral osteolytic lesions in five hips with conventional PE inserts and only one hip with a Duration insert.

Conclusions: Acetabular inserts made of crosslinked PE using the Duration process can significantly reduce in-vivo wear rates and the occurrence of potentially wear related osteolytic effects in the long-term follow-up of THA patients. The reduced clinical wear rates corresponded well with the results from the wear simulator measurements. This suggests that a PE with further increased crosslinking which shows even lower wear rates in simulator studies will lead to even lower wear and associated osteolysis in long-term clinical application.

The purpose of this study was to compare the 2D and 3D linear and volume wear readings of the three most commonly used methods for measuring polyethylene wear: the Livermore, Devane and Martell techniques. Inter-observer variation of measurements using the techniques of Devane and of Martell on conventional radiographs was also performed. The radiographs of 80 patients (mean age 60+/−10 yrs) who had a Harris-Galante I total hip arthroplasty were measured. Nine different reviewers for the Devane technique readings including Dr Devane and eight reviewers for the Martell technique readings including Dr Martell made blinded independent wear observations for each radiograph set. One reviewer measured the 20 annual linear wear rate for all radiograph sets using the 2D Livermore technique. Inter-observer variation as a function of patient, reviewer, and total variation was statistically assessed using variance component analysis. Mean wear measured using the Livermore technique was the same as with the Devane and Martell method, but with a greater variation. Comparison of the Devane and Martell method for patient STD, reviewer STD, error STD (multiple reviews of same radiographs), total STD (randomly picked reviewer), mostly show a mean 50% lower STD with the Devane technique. Correlation (correlation coefficient of two randomly selected reviewers) is significantly better with the Devane technique.