Aims

We evaluated a large database with mechanical failure of a single uncemented modular femoral component, used in revision hip arthroplasty, as the end point and compared them to a control group treated with the same implant. Patient- and implant-specific risk factors for implant failure were analyzed.

Background: Currently, total hip replacement (THR) is most commonly performed via a posterior or a direct lateral approach. We compared the one year postoperative outcome of cementless THR using the both approaches in a prospective, randomized trial.

Methods: A prospective 1:1 randomization scheme was implemented to allocate 60 patients with unilateral osteoarthritis. Patients in the lateral approach group were in median 59 years old, in 50% female and had a median BMI of 27 kg/m² versus in median 55 years, 47% females and a median BMI of 29 kg/m² in the posterior approach group. Outcome assessment was performed one day before surgery and 3 months, 6 months and one year after surgery, respectively, using the intra-individual Harris Hip score (HHS) improvement at one year as primary objective. Sample size calculation was based on the assumption of a minimum clinically relevant difference of 5 points and a standard deviation of 6 points in the HHS total score. WOMAC and SF-36 served as secondary objectives.

Results: Patients started with a median HHS of 50 points after lateral approach versus 46 points after posterior approach and showed a median HHS of 95 points versus 94 points one year after surgery. We found a slight tendency towards the posterior approach, but no significant difference in the intraindividual HHS improvement at all the pre- and post-operative assessment points between both treatment groups (Wilcoxon p=0.115 at 3 months, p=0.191 at 6 months and p=0.207 at one year). A comparable tendency was found in the intraindividual WOMAC improvement without statistical significance (Wilcoxon p=0.749). In contrast the SF-36 physical scales were slightly but again not significantly better after lateral approach at the one year assessment (86% versus 80%,Wilcoxon p=0.674).

Conclusions: Not any (algo-) functional and psychometric endpoint investigated showed a statistical significant difference between patients after lateral versus posterior approach for THR.

We conclude that motivation and other patient related factors, the implant and the surgeon itself influence the result much more than the approach used for total hip replacement.

Aim: The purpose of this study was to analyze the in-vivo wear rates of Birmingham Hip Resurfacing (BHR, Midland Medical Technologies Ltd., Birmingham, U.K.) explants and to contrast the results to the wear rates of conventional 28 mm metal-on-metal bearings (Metasul, Zimmer GmbH, Winterthur, Switzerland).

Methods: The wear rates, measured by a coordinate measuring machine (CMM5, SIP, Geneva, Switzerland), of 6 femoral components and two complete pairings of the BHR retrieved from 8 hips were contrasted to 43 28 mm heads from second generation metal-on-metal bearings (Metasul, Sulzer Orthopaedics Ltd., Winterthur, Switzerland).

Results: After 13 months (7 to 24) the BHR femoral heads showed a median volumetric wear rate of 2.9 mm³ (interquartile range: 0.8 to 7.1), slightly, but not significantly higher than the investigated 43 28mm Metasul heads (0.8 mm³/year, p = 0.067, 14 months [7 to 24] in-situ). One BHR case with a cup abduction angle of 70° showed a significant higher wear rate of 17.8 mm³. All BHR cases showed only small amounts of metallic particle histological and correspondingly, a mild histiocytic tissue response without foreign body granuloma formation.

Discussion: During the first two years after surgery the investigated BHR components showed wear rates substantially lower than conventional polyethylene bearings, comparable to Metasul bearings, implanted with very successful clinical results. But whether the wear rates will drop down after the so called running-in period comparable to conventional metal-on-metal bearings and provide young and active patients with a biologically acceptable particle volume over a long time period, still remains to be seen.

Background: This study was undertaken to investigate the differences in the metal ion serum concentrations after implantation of a MetaSUL-THR and a Birmingham Hip Resurfacing in comparison to implant free subjects and to review the influence of factors, possibly influencing the wear behaviour of the articulation.

Methods: Serum levels of cobalt, chromium and molybdenum in 74 patients after primary implantation of a MetaSUL-THR and in 111 patients after BHR were compared with the levels found in 130 control subjects without implants. Serum ion concentration was determined by atomic absorption spectrophotometry. Furthermore, the correlation between serum ion concentration and in-situ time, implant size and cup inclination was studied.

Results: The chromium and cobalt concentrations of BHR-patients as well as the chromium concentration of bilateral MetaSUL-THR-patients, however, were significantly higher as the concentrations of patients with unilateral MetaSUL-THR and the control group. The molybdenum serum concentration was very similar in all investigated groups.

The chromium serum concentration in patients with unilateral MetaSUL-THR and in patients with BHR showed the highest level in the postoperative period from 7 to 12 months.

Analyses of the subgroups showed an association between higher cobalt serum levels and cup inclination greater than 50 in patients with unilateral MetaSUL-THR more than 12 months after implantation. A statistically significant negative correlation was detectable between implant size and chromium as well as cobalt serum concentration in BHR-patients studied more than 12 months after implantation.

Conclusions: Metal-on-metal bearings of large diameter result in a greater systemic exposure of cobalt, chromium and molybdenum ions than bearings of smaller diameter. It is not known to what extent the different levels are due to corrosion of the surfaces of the components or to the amount of wear particles produced.

The chromium concentrations were highest 7–12 months after operation, what may due to a running-in of the bearing like known from hip simulator studies.

Interestingly implant size and metal ion serum levels correlate negatively in the BHR-patients studied more than 12 months after implantation. That could be due to an existing fluid film lubrication in these bearings and may be caused by the thicker fluid film in bearings with greater radius.

Purpose of the study: To find predictors for the clinical outcome in patients who underwent a high tibial osteotomy [HTO].

Method: Between 1984 and 1996 in 155 patients with genu varum a high tibial valgus osteotomy was performed. 133 HTOs were available for follow up at an average post-op time of 9.3 years (3,0 y). The morphology of the knee was evaluated by radiological (Kellgren) and arthroscopical classifications (Outerbridge). Survival time of HTO was estimated using Kaplan-Meier survivorship analysis. Patients outcome was evaluated using the WOMAC score. For statistical analysis Log-rank test and Wilcoxon-Mann Whitney U-Test were used.

Results: During follow up time 19.8% of patients needed a total knee arthroplasty. Survival rate of HTO was 95% after 5 years and 77% after 10 years. In the medial compartment of knee joints with a preoperative Outerbridge stage III/IV or Kellgren stage III/IV the survival rate of HTO was significantly lower when compared to stages I/II (p< 0,05).

Age, sex, dimension of the mechanical medial proximal tibial angle (mMPTA) and severity of arthrosis in the lateral compartment had no influence on survival rates. The pre-postoperative comparison of radiologically visible signs of arthrosis showed either no or only small progress. The patients who underwent a HTO had an average of 1,9 points on the WOMAC score (global index 0–10) which is a good to very good clinical outcome.

Conclusion: We identified the severity of the preoperative radiological signs of arthrosis and the extent of chondromalacia noted intraoperatively as predictors of survival rate.

Question: Is the histopathological response of the peri-prosthetic tissue to metal-on-metal bearings comparable to the well studied reactions to polyethylene debris or do specific reactions exist and are theses reactions depending on the implant design?

Methods: Periprosthetic tissue samples from 19 THR and Hip Resurfacings (11 Birmingham Hip Resurfacings, 2 (historical)McMinn Hybrid Hip Resurfacings, 5 MetaSUL THR) with a variety of failure mechanisms were examined histopathologically and immunohistochemically.

Results: Only the samples of the (historical) McMinn Hybrid resurfacings showed a stronger histiocytic foreign body reaction and a higher grade metallosis. In all other cases only a mild if any histiocytic foreign body reaction was found. Additionally a chronic lymphoplasmacellular tissue reaction was present in all cases. 3 cases showed a higher grade chronic lymphoplasmacellular inflammatory tissue response comparable to a specific immune reaction.

Discussion: We found two different response mechanisms of the periprosthetic tissues to metal-on-metal bearings. In addition to the classic histiocytic foreign body reaction which was usual mild and only stronger in cases with a greater amount of metallic debris a lymphoplasmacellular inflammatory reaction usually was present but did not reach the level of inflammatory alterations associated with potential osteolysis and was not related to the implant or amount of wear. In 3 of our 19 cases the lymphoplasmacellular infiltration was stronger and comparable to a specific immune reaction. The significance of the specific immune reaction could not be further explained because a correlation to the failure mechanisms was not detectable