Primary stability of two uncementedacetabular components of different geometry: hemispherical or peripherallyenhanced?

OBJECTIVE: This study compared the primary stability of two commercially available acetabular components from the same manufacturer, which differ only in geometry; a hemispherical and a peripherally enhanced design (peripheral self-locking (PSL)). The objective was to determine whether altered geometry resulted in better primary stability. METHODS: Acetabular components were seated with 0.8 mm to 2 mm interference fits in reamed polyethylene bone substrate of two different densities (0.22 g/cm(3) and 0.45 g/cm(3)). The primary stability of each component design was investigated by measuring the peak failure load during uniaxial pull-out and tangential lever-out tests. RESULTS: There was no statistically significant difference in seating force (p = 0.104) or primary stability (pull-out p = 0.171, lever-out p = 0.087) of the two components in the low-density substrate. Similarly, in the high-density substrate, there was no statistically significant difference in the peak pull-out force (p = 0.154) or lever-out moment (p = 0.574) between the designs. However, the PSL component required a significantly higher seating force than the hemispherical cup in the high-density bone analogue (p = 0.006). CONCLUSIONS: Higher seating forces associated with the PSL design may result in inadequate seating and increased risk of component malpositioning or acetabular fracture in the intra-operative setting in high-density bone stock. Our results, if translated clinically, suggest that a purely hemispherical geometry may have an advantage over a peripherally enhanced geometry in high density bone stock. Cite this article: Bone Joint Res 2013;2:264-9.

Comparison of results of different types of knee arthroplasties.

We summarise our experience gained with knee arthroplasties over 18 years. Between 1976 and 1994 1103 knee arthroplasties (1044 primary cases, 59 revisions) were performed at the Orthopaedic Department of the National Institute of Rheumatology and Physiotherapy in Budapest, Hungary. The diagnoses were osteoarthritis (OA) in 50.9%, rheumatoid arthritis (RA) in 40.7% and other causes in 8.4%. The average age of the patients at the time of the operation was 57.6 years (range 14-81 years). The types of primary implant were as follows: 60 constrained (hinge) prostheses, 876 unconstrained (sledge) prostheses, 108 semiconstrained (total condylar) prostheses. The mean follow-up period was 11.4 years for the hinge-type prostheses, 10.3 years for the unconstrained prostheses and 1.6 years for the semiconstrained prostheses. Reviewing the 59 revision cases, we conclude that complications with the constrained prostheses reached 17.8% and, most presented within the 1st year. Because of this high complication rate, the use of hinge prostheses has been reduced in this department to only selected cases. After sledge prosthesis implantation most of the complications (overall 5.3%) appeared after 1 year in aseptic circumstances. Given the short follow-up period of the semi-constrained total condylar knee replacement, apart from one infection in a patient with rheumatoid arthritis no other complication has been recorded. Summarising these data, it can be concluded that on average the knee function, using a standardised scoring system, improved from 38% to over 80% by introducing the semiconstrained total condylar knee prosthesis.

Arterial pseudoaneurysm of the ankle after plantar flexion-inversion injury. A rare complication and its non-invasive diagnosis.

We report a case of arterial pseudoaneurysm over the lateral side of the ankle caused by plantar flexion-inversion injury and discuss the aetiology of this rarely seen complication. In the English orthopaedic literature, our case is the first of the very few previously reported cases with a similar aetiology which was examined and confirmed by colour Doppler ultrasound.