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We investigated factors that were thought to be associated with an increased incidence of squeaking of ceramic-on-ceramic total hip replacements. Between June 1997 and December 2008 the three senior authors implanted 2406 primary total hip replacements with a ceramic-on-ceramic bearing surface. The mean follow-up was 10.6 years. The diagnosis was primary osteoarthritis in each case, and no patient had undergone previous surgery to the hip. We identified 74 squeaking hips (73 patients) giving an incidence of 3.1% at a mean follow-up of 9.5 years (4.1 to 13.3). Taller, heavier and younger patients were significantly more likely to have hips that squeaked. Squeaking hips had a significantly higher range of post-operative internal (p = 0.001) and external rotation (p = 0.003) compared with silent hips. Patients with squeaking hips had significantly higher activity levels (p = 0.009). A squeaking hip was not associated with a significant difference in patient satisfaction (p = 0.24) or Harris hip score (p = 0.34). Four implant position factors enabled good prediction of squeaking. These were high acetabular component inclination, high femoral offset, lateralisation of the hip centre and either high or low acetabular component anteversion. This is the largest study to date to examine patient factors and implant position factors that predispose to squeaking of a ceramic-on-ceramic hip. The results suggest that factors which increase the mechanical forces across the hip joint and factors which increase the risk of neck-to-rim impingement, and therefore edge-loading, are those that predispose to squeaking.

Dislocation is a common reason for revision following total hip replacement. This study investigated the relationship between the bearing surface and the risk of revision due to dislocation. It was based on 110 239 primary total hip replacements with a diagnosis of osteoarthritis collected by the Australian Orthopaedic Association National Joint Replacement Registry between September 1999 and December 2007. A total of 862 (0.78%) were revised because of dislocation. Ceramic-on-ceramic bearing surfaces had a lower risk of requiring revision due to dislocation than did metal-on-polyethylene and ceramic-on-polyethylene surfaces, with a follow-up of up to seven years. However, ceramic-on-ceramic implants were more likely to have larger prosthetic heads and to have been implanted in younger patients. The size of the head of the femoral component and age are known to be independent predictors of dislocation. Therefore, the outcomes were stratified by the size of the head and age. There is a significantly higher rate of revision for dislocation in ceramic-on-ceramic bearing surfaces than in metal-on-polyethylene implants when smaller sizes (< or = 28 mm) of the head were used in younger patients (< 65 years) (hazard ratio = 1.53, p = 0.041) and also with larger (> 28 mm) and in older patients (> or = 65 years) (hazard ratio = 1.73, p = 0.016).

Accurate positioning of the acetabular component in total hip arthroplasty is essential to minimise the risk of dislocation and preserve the range of movement of the hip. It also affects polyethylene wear and the rate of osteolysis. Although there are many tools available to the surgeon to aid placement of the acetabular component, errors still occur, especially in version. We conducted a study of 14 cadaveric hips to investigate whether the transverse acetabular ligament can be used to align implanted cups with the correct degree of anteversion. Radiographic measurement revealed that all of the implanted cups were found to lie within the 'safe zone' for anteversion, when aligned with the ligament.

The Kent hip is a distally-locked femoral stem which was developed to address severe proximal bone loss, severe bony deformity and peri-prosthetic fracture. We reviewed the results of 145 consecutive Kent hips implanted into 141 patients between 1987 and 2000. The indications for implantation were aseptic loosening (75 hips), septic loosening (two), peri-prosthetic and prosthetic fracture (37), severe bony deformity (24), and fracture through a proximal femoral metastasis (seven). The median time to full weight-bearing after surgery was two days and the mean length of follow-up was 5.1 years (2 to 15). Further revisions were required for 13 femoral stems. With removal of the stem for any reason as an end-point, the cumulative survival at five, ten and 15 years was 93%, 89% and 77%, respectively. In patients aged>or=70 years, the cumulative survival at 15 years was 92%, compared with 68% in those aged<70 years. Because of these findings, we recommend the use of interlocking stems in patients aged>or=70 years, particularly in those with a peri-prosthetic fracture, for whom alternative methods are limited. Outcome scores and survival data, compared with other systems, indicate that the Kent hip should be used with caution in younger patients.