Introduction and Objective

Osteochondral allograft (OCA) transplants have been used clinically for more than 40 years as a surgical option for joint restoration, particularly for young and active patients. While immediate graft rejection responses have not been documented, it is believed that the host's immunological responses may directly impact OCA viability, incorporation, integrity, and survival, and therefore, it is of the utmost importance to further optimize OCA transplantation outcomes. The influences of sub-rejection immune responses on OCA transplantation failures have not been fully elucidated therefore aimed to further characterize cellular features of OCA failures using immunohistochemistry (IHC) in our continued hopes for the successful optimization of this valuable surgical procedure.

The effects of metal ion release and wear particle debris in metal-on-metal articulation warrants an investigation of alternative material, like ceramics, as a low-wear bearing couple [1]. Short-stem resurfacing femoral implant, with a stem-tip located at the centre of the femoral head, appears to provide a better physiological load transfer within the femoral head and therefore seems to be a promising alternative to the long-stem design [2]. The objective of this study was to investigate the effect of evolutionary bone adaptation on load transfer and interfacial failure in cemented metallic and ceramic resurfacing implant.

Bone geometry and material properties of 3D finite element (FE) models (intact, short-stem metallic and ceramic resurfaced femurs of 44 mm head diameter) were derived from the CT scan data. The FE models consisted of 170352 quadratic tetrahedral elements and 238111 nodes with frictional contact at the implant-cement (μ = 0.3) and stem-bone interfaces (μ = 0.4) and fully bonded cement-bone interface. Normal walking and stair climbing were considered as two different loading conditions. A time-dependant “site specific” bone remodelling simulation was based on the strain energy density and internal free surface area of bone [3]. The variable time-step was determined after each remodelling iteration. The Hoffman failure criterion was used to assess cement-bone interfacial failure.

Predicted change in bone density due to bone remodelling was very much similar in both the metallic and ceramic resurfaced femurs (Fig. 1). Both the metallic and ceramic implant resulted in strain reduction in the proximal regions (Region of interest, ROI 2 and 4) and subsequent bone resorption, average bone density reduction by 72% (Fig. 1). Higher strains were generated in ROI 5 and 7, which caused bone apposition, an average increase in bone density of 145% (Fig. 1). The tensile stresses in the resurfacing implants increased with change in bone density; a maximum stress of 83 MPa and 63 MPa were observed in the ceramic and the metallic implants, respectively. The tensile stress in the cement mantle also increased with bone remodelling. Although the cement-bone interface was secure against interface debonding in the post-operative situation, calculations of Hoffman number indicated that risk of cement-bone interfacial failure was increased with peri-prosthetic bone adaptation.

During the remodelling simulation, maximum tensile stress in the implant and the cement was far below its strength. However, with bone adaptation greater volume of cement mantle was exposed to higher stresses which, in-turn, resulted in greater risk of interfacial failure around the periphery of the cement mantle. Both the short-stem ceramic and metallic resurfacing component, under debonded stem-bone interface, resulted in more physiological stress distribution across the femoral head. Based on these results, short-stem ceramic resurfacing component appears to be a viable alternative to the metallic design.

Background: This study was done to compare the early failure of primary cemented unicompartmental knee arthroplasties (UKA) with that of total knee arthroplasties (TKA).

Methods: The Kaplan-Meier survial-method and the Cox multiple regression model were used to compare the failure rates of the primary cemented UKAs (n=1410) and the primary cemented TKAs (patellar resurfaced) (n=2818) that were reported to the Norwegian Arthroplasty Register between 1st January 1994 and 1st April 2003.

Results: 8 years survival for UKAs was 85.2 % (95% CI: 81.5–88.9) compared to 93.0 % (91.5–94.5) for TKAs, relative revision risk (RR) 1.8 (1.4–2.4), p< 0.001. The increased revision risk in UKAs was seen in all age categories. Among the UKAs the 8 years survival showed no statistically significant difference for MOD III, Genesis uni and Oxford II. However, Duracon uni knees had, statistically significantly higher rates of revision, although the numbers of prostheses were low. Two UKAs were introduced recently and the follow up was short. After 3 years the Miller Galante uni had 82.8 % (75.6–90.0) survival compared to 93.8 (91.0–96.6) for the Oxford III knee, p< 0.002. The higher failure rates of the Miller Galante and Duracon knees were mainly due to more loosening of the tibial components. UKAs had an increased risk of revision due to pain, aseptic loosening of the tibial and femoral components and periprosthetic fractures compared to TKAs. The UKAs had a lower risk of infection compared to TKAs.

Conclusions: This prospective study has shown that the prostheses survival of cemented UKAs was not as good as for cemented TKAs. There were differences between the UKAs, but the best UKA had results inferior to the average of the TKAs.

The October 2012 Oncology Roundup³⁶⁰ looks at: the causes of primary bone tumours; adjuvant chemotherapy in the longer term; vascularised fibular grafts to salvage massive femoral allografts; a new look at old risks; reconstruction with excised irradiated bone; predicting chemosensitivity in osteosarcoma ; and chemotherapy, osteoporosis and the risk of fracture.