‘Force-closed’, tapered, polished, collar-less stems, (e.g. C-stem, Exeter), are designed to subside in response to expansion of the cement/bone complex over time. Above a certain threshold, distal migration may predict medium-to-long-term failure of ‘shape-closed’ stems. However, no such threshold exists for ‘force-closed’ stems, and these may continue to migrate after 3 years. We believe that the tendency towards stabilisation 2–3 years postoperatively, could be the best predictor of good long-term performance.

Twenty OA patients (12F, mean age 66.6 years) were recruited for primary hip replacement with beaded C-stem femoral components. Tantalum marker beads were injected into the proximal femur, and stems were inserted using CMW1 cement and the latest generation cementing technique via a posterior approach: 17, and a lateral, trochanteric approach: 3. RSA X-ray examinations were performed at 1 week, 6 weeks, and at 3, 6, 12, 24 and 36 months postoperatively. The UmRSA system was used to measure and analyse the radiographs. At 36M the mean stem centroid subsidence was 1.05 mm and had levelled off to a low rate. The mean internal rotation of 2.5° at 36M had not significantly changed during the final year (p = 0.08).

At 36M the mean posterior migration of the stem centroid was 0.54 mm (rate of 0.11 mm/y) and posterior migration of the femoral head was 1.66 mm (rate of 0.25 mm/y).

At 36M the mean subsidence rate was very low and the mean posterior migration was about one third of that reported for another RSA study of the C-stem. Although the mean internal rotation was greater than that reported for the Exeter stem, there was no significant change during the final year. These low rates of migration at 3 years are consistent with the good results found in clinical studies of this femoral component.

Introduction: The clinical results of the modular Charnley Elite total hip system have been the subject of some interest in recent years. Some studies have shown significant subsidence and rotational instability in some stems when used with low-viscosity cement. These unstable stems have been shown to fail early. This purpose of this study is to demonstrate our conflicting clinical results.

Materials and Methods: 616 modular Charnley Elite total hip arthroplasties were inserted between 1995 and 2002 at Wrightington Hospital, which is a tertiary referral centre and centre of excellence for joint replacement in United Kingdom. Both Consultants and trainees performed operations and a variety of surgical approaches were used. Normal viscosity bone cement was used in all patients. All patients were followed up prospectively.

Results: At mean follow-up of 8 years (range 5–12), 471 hips were available for review. 87 patients had died and 12 were lost to follow-up. 2.7% (13 cases) of femoral components and 2.9% (14 cases) of acetabular components had been revised for aseptic loosening. 10 hips (2.1%) underwent revision for deep infection and 2 (0.04%) for recurrent dislocation. The overall survival with aseptic loosening as an end point was 97% and for revision for any reason was 94.5%.

Conclusion: Our results show acceptable clinical survivor-ship for this implant when used with standard viscosity cement. This contrasts with the lower survivorship rates published by other centres. Our result should reassure patients and surgeons alike that this prosthesis can be associated with acceptable results in the medium term.

Introduction: Although acetabular cup wear is usually reported in terms of penetration (measured from radiographs), true wear – wear volume – depends on several variables. This study examined how these variables affect the calculation of the theoretical wear volume at the low wear penetrations found with highly cross-linked polyethylene (XLPE) cups.

Method: A computerised numerical analysis technique was used to calculate the “exact” theoretical wear volume of an acetabular cup under a variety of circumstances, including: variations in wear direction, head size, and initial radial discrepancy (i.e. initial difference between socket and head sizes). The validity of published wear volume formulae was assessed. The effects of creep and wear measurement error were also assessed.

Results: For a given wear penetration, as the wear direction (relative to the cup base) increased, the wear volume increased – almost doubling as the direction reached 60°. The initial radial discrepancy made a substantial difference to the calculated wear volume at penetrations less than 1 mm. At low penetrations, its neglect caused an overestimation of wear volume of well over 100%. Creep volume was substantially overestimated because of this. An analysis of wear measurement error showed that the calculation of wear direction (an important variable in the calculation of wear volume) was severely affected at low penetrations by the precision of penetration measurements. For a penetration precision of ±0.25 mm (as reported for the Martell Hip Analysis Suite), the maximum wear direction error was ±39° at a penetration of 0.4 mm. When the precision was ±0.1 mm (as with RSA), this reduced to ±14°.

Discussion: Many studies have shown the superior wear performance XLPE acetabular cups compared with standard PE cups. In those studies, comparison in terms of wear penetration was possible because of the large difference in penetrations between the two groups. This study has shown that true wear (wear volume) is significantly affected by wear direction (relative to the cup), the initial radial discrepancy, and the femoral head size. The differences in penetrations when comparing two types of XLPE cups would not be so large and it is therefore necessary to compare the two groups in terms of wear volume. Published formulae for estimating the wear volume of acetabular cups do not take the initial radial discrepancy into account, and they can substantially overestimate the wear volume in the penetration range encountered with XLPE cups. Creep volume is also greatly overestimated. Since wear volume varies with wear direction, the wear measurement technique must be capable of accurately determining the wear direction. This analysis has shown that only RSA might have sufficient precision to determine the wear direction at the medium-term penetrations encountered with XLPE cups.

Introduction: “Force-closed”, tapered, polished, collarless stems, (e.g. C-stem, Exeter), are designed to subside in response to a gradual expansion of the cement/bone complex.

Above a certain threshold, distal migration may predict medium-to-long-term failure of “shape-closed” (collared, textured) stems. However, no such threshold exists for “force-closed” stems, and these may continue to migrate after 3 years. We believe that the tendency towards stabilisation 2–3 years postoperatively could be the best predictor of good long-term performance.

Method: Twenty OA patients (12F, mean age 66.6 years) were recruited for primary hip replacement with beaded C-Stem femoral components. Tantalum marker beads were injected into the proximal femur, and stems were inserted using CMW1 cement and the latest generation cementing technique via: a posterior approach (17), and a lateral, trochanteric approach (3). RSA X-ray examinations were performed at 1 week, 6 weeks, and at 3, 6, 12, 24 and 36 months postoperatively. The UmRSA system was used to measure and analyse the radiographs.

Results: By 36M the mean stem subsidence (1.05 mm) had levelled off to a low rate, and the mean internal rotation (2.5°) had not significantly changed during the final year (p = 0.08). The mean posterior migration of the stem centroid was 0.54 mm and posterior migration of the femoral head was 1.66 mm (0.25 mm/y during final year).

Discussion: At 36M the mean subsidence rate was very low, and the mean posterior migration was about one third of that reported by Sundberg et al. (BHS Meeting, 2007). Although the mean internal rotation was greater than that reported for the Exeter stem, it had stabilised during the final year. These low rates of migration at 3 years are consistent with the good results found in clinical studies of this femoral component.

Introduction: The clinical results of the modular Charnley Elite total hip system have been the subject of some interest in recent years. Some studies have shown significant subsidence and rotational instability in stems when used with low-viscosity cement. These unstable stems have been shown to fail early. The purpose of this study is to demonstrate our conflicting clinical results.

Materials and Methods: 616 modular Charnley Elite total hip arthroplasties were inserted between 1995 and 2002 at Wrightington Hospital, which is a tertiary referral centre and centre of excellence for joint replacement in United Kingdom. Both Consultants and trainees performed operations and a variety of surgical approaches were used. Normal viscosity bone cement was used in all patients. All patients were followed up prospectively.

Results: At mean follow-up of 8 years (range 5–12), 471 hips were available for review. 87 patients had died and 12 were lost to follow-up. 2.7% (13 cases) of femoral components and 2.9% (14 cases) of acetabular components had been revised for aseptic loosening. 10 hips (2.1%) underwent revision for deep infection and 2 (0.04%) for recurrent dislocation. The overall survival with aseptic loosening as an end point was 97% and for revision for any reason was 94.5%.

Conclusion: Our results show acceptable clinical survivor-ship for this implant when used with standard viscosity cement. This contrasts with the lower survivorship rates published by other centres. Our result should reassure patients and surgeons alike that this prosthesis can be associated with acceptable results in the medium term.

Introduction: Some reports have suggested an unacceptable failure rate of Elite Plus stem in the medium term. We have previously argued that other measurements must be made in addition to RSA in order to assess reasons for abnormal migrations. This 3-year RSA study of Elite Plus stems assessed the migration pattern and factors that influenced it.

Method: Twenty five patients (23 OA, 2 RA, mean age 60.4 years (37–81)) underwent Elite Plus THR (single surgeon). A-P radiographs were assessed for cementing technique, and measurements (canal widths, stem orientation, cement thickness etc) were taken using CAD software. Activity score and BMI were also recorded. Multiple factors were assessed for correlation with the main components of migration.

Results: One patient’s stem centroid migrated proximally (due to valgus rotation about the shoulder) and the mean subsidence of the others was 0.297 mm at 36 months. Mean internal rotation and posterior head migration (25 patients) at that time were: 1.42° (CI: 0.99° to 1.86°) and 0.801 mm (CI: 0.526 mm to 1.076 mm), neither being significantly different from migrations at 24 months. One patient’s stem migrated continuously. By 36 months, it had subsided 1.279 mm and internally rotated 4.2°. Some significant correlations (p < 0.05, rho > 0.6) were 3M and 36M subsidence with proximal-medial cement thickness; effective offset with 36M medial migration.

Discussion: The one patient with continuous high migration had the highest activity level. This was corroborated by a wear measurement of 3.5 mm in the contralateral (Charnley) hip which had been in place for 9 years (assuming the head was not scratched). If RSA, 3 years postoperatively, can predict future outcome, the 4% failure rate is similar to the ten year results of the Charnley hip.

We performed a three-year radiostereometric analysis (RSA) study of the Elite Plus femoral component on 25 patients undergoing primary total hip replacement. Additional assessments and measurements from standard radiographs were also made.

Subsidence of the stem occurred at the cement-stem interface. At 36 months the subsidence of the stem centroid was a mean of 0.30 mm (0.02 to 1.28), and was continuing at a slow rate. At the same time point, internal rotation and posterior migration of the femoral head had ceased. One stem migrated excessively and additional assessments suggested that this was probably due to high patient demand.

The failure rate of 4% in our study is consistent with data from arthroplasty registers but contrasts with poor results from another RSA study, and from some clinical studies. We believe that the surgical technique, particularly the use of high-viscosity cement, may have been an important factor contributing to our results.

Introduction: Long-term, aseptic loosening is the central problem for total hip replacements (THR)1. Several studies have suggested the possibility of predicting long-term loosening of femoral components (after about 7 years) by assessment of the short-term migration pattern (1 – 2 years) using radiostereometric analysis (RSA)2. During the past 2 years, we have been conducting an RSA study of the Elite Plus (DePuy) femoral component migration in 25 (8M, 17F) primary THR patients (mean age 61 years).

Results: The Table below shows the mean and SD of the stem centroid migrations after 12 months. The mean subsidence rate of 0.71 mm/year (15 patients) during the first month reduced to 0.16 mm/year, (22 patients) during the following two months. By the latter half of the first postoperative year, the mean rate had reduced to 0.13 mm/year.

Discussion: A study by the Oxford group (Alfaro-Adrian et al.³ ) compared the migration of 19 Elite Plus stems with 32 Exeter (Howmedica) stems over a two year period. After 1 year, there is a remarkable similarity in the subsidence, lateral migration and internal rotation between the two groups. However, combining the posterior and anterior migrations in the present study, the mean posterior migration was 0.15 mm. This is about half of that measured by the Oxford group (0.28 mm). Furthermore, the present study shows that varus rotation is predominant – compared to valgus rotation in the Oxford group’s study.