Synthetic graft expanders have recently been developed for use in impaction grafting revision hip arthroplasty, but their true role has yet to be determined. We performed a series of experiments to investigate the properties of one such porous hydroxyapatite material (IG-Pore, ApaTech Ltd). IG-Pore was mixed with fresh-frozen human allograft chips and impacted into composite femoral models with a similar biomechanical profile to human bone (Sawbones Europe). Exeter hip prostheses (Stryker Howmedica Ltd) were implanted with cement and each model was axially loaded for 18000 cycles at physiological levels using an Instron servohydraulic materials testing machine. Four test groups with 0%, 50%, 70% and 90% IG-Pore were used, and there were eight femora in each group. Pre- and post-loading radiostereometric analysis was performed to characterise migration of the prosthesis. Total subsidence was measured and was separated into that occurring at the prosthesis-cement and cement-femur interfaces. Cyclical compression and expansion of the graft-containing models was measured using the Instron. Median values (interquartile range) for total subsidence were 0.43 mm (0.28 to 0.55) for the pure allograft group, 0.31 mm (0.20 to 0.55) for the 50% IG-Pore group, 0.23 mm (0.07 to 0.34) for the 70% allograft group and 0.13 mm (0.06 to 0.18) for the 90% IG-Pore group. These differences were statistically significant (p=0.034, Kruskal-Wallis). Subsidence at the prosthesis-cement interface was also lower for IG-Pore containing models (p=0.019, Kruskal-Wallis), although there was no significant difference at the cement-femur interface. Specimens with a higher proportion of IG-Pore showed smaller cyclical movements on loading (p=0.005, ANOVA). Higher proportions of IG-Pore do appear to reduce subsidence in a mechanical model of impaction grafting. A randomised clinical trial using RSA to compare a 50% IG-Pore/allograft mix with pure allograft is in progress to investigate the use of this material as a bone graft expander in the clinical setting.
Septic arthritis has been regarded as rare in haemophiliacs, but its incidence may have increased since HIV infection has become widespread in these patients. We describe six cases treated at one haemophilia unit over a two-year period and discuss their investigation, diagnosis and treatment. Four of the patients were seropositive to anti-HIV.
A medical and engineering study was made of 1074 car accidents involving 2520 vehicle occupants. The injuries they sustained were correlated with details of the crash and with contact points inside the cars. Where possible the forces which were generated in the crash were estimated and related to the injuries. In all, 39 car occupants suffered femoral shaft fracture, with an incidence of 1.7% and 0.8% for front and rear seat occupants respectively. Of these, 31 had associated injuries to other regions of the body; these were the cause of 13 of the 14 deaths in this group. Associated injuries were more severe in car occupants who were not wearing seat belts but the incidence of femoral fracture was not significantly different. The mean velocity change (delta-V) causing femoral fracture was 26 mph (42 km/h) and there was a higher incidence of femoral shaft fracture when delta-V was over 30 mph. Estimates of forces needed to cause fracture were higher than those found in cadaver studies. The time to union of femoral fractures did not correlate with the severity of the crash but was longer (mean 19 weeks) than the average for other femoral fractures.
Specimens of tissue from haemophilic synovium and articular cartilage were collected from 39 patients during reconstructive surgery. They were studied by histochemistry, electron microscopy and microprobe analysis. The detailed findings are presented and discussed. It is suggested that haemophilic arthropathy is the result of a number of mechanisms affecting the synovial lining which becomes progressively fibrotic and the hyaline cartilage which disintegrates and is eventually lost. Mechanical and chemical processes cause degeneration of cells but enzymatic processes appear to be primarily responsible for the degradation of the matrix of the articular cartilage.
