Introduction. Dislocation following total hip arthroplasty THA is a major short term complication not infrequently resulting in revision arthroplasty. Malposition of the acetabular component in THA results in a higher rate of dislocation as well as increased wear and osteolysis. The aim of this study was to assess the effect of mode of fixation on positioning of the acetabular component. Patients, materials and methods. For all THAs performed at our hospital in 2008, angle of acetabular inclination was measured using PACS by two independent observers. Interobserver and intraobserver reliability were assessed (Pearson's correlation coefficient, r). We determined whether the number of acetabular components outside the target angle range (eg:45±5°) was significantly different between cemented and cementless THA (chi squared test). An enquiry was made to the National Joint Registry (NJR) in respect to incidence of revision for dislocation of THA using cemented and cementless acetabular components, 2004–2009. Results. During 2008 126 THA were performed, 80 cemented and 46 cementless. There was good reliability of angle measurement (interobserver: r=0.89; intraobserver: r=0.87 and 0.97). More cemented acetabular components were within target angle range compared to cementless (cemented 32/80, cementless 29/46; chi squared=6.39, p<0.05). Using data from NJR comparing the number of primary hip replacement operations with number of revisions due to dislocation found a higher rate for cementless THA, 0.381% (266/69,822) than for cemented, 0.282% (262/92,928) (Odds ratio: 1.35 (95% CI 1.14–1.60; P<0.05). Conclusion. Positioning of the acetabular component is more difficult when using cementless systems as implant position is determined by orientation of reaming whereas with cement there is potential for fine implant position adjustment on insertion. The choice of a cementless acetabular component significantly increases the incidence of dislocation post THA. Acetabular component malposition is likely to be a factor in this increased incidence

Background. An increasing number of hip prostheses are inserted without bone cement. Experimental research has shown that hydroxyapatite (HA) coated implants are strongly fixated in the bone, which is believed to reduce the likelihood of prosthetic loosening. However, in recent years, there has been much debate about the role of HA particles in third-body polyethylene (PE) wear and formerly we have shown the revision rate to be high among older-design HA coated cups. Purpose. We hypothesized increased PE wear-rate using HA coated acetabular components in comparison with non-HA coated components (control group). Materials and Methods. We performed a retrospective comparative clinical study based on two patient populations identified in the Danish Hip Arthroplasty Registry (October 2006). All patients had primary total hip arthroplasty (THA) between 1997 and 2001 with cementless Mallory-Head acetabular components. One group received HA coated acetabular components (75 patients, 77 hips). The other group received identical components without HA (70 patients, 73 hips). In all cases the liner was similar and 28 mm metal femoral heads were used. All patients were invited for a radiographic follow-up in 2007. The AP radiographs were analysed for two-dimensional (2D) polyethylene wear using the semi-automated PolyWare software. All cases of non-responders, stem revisions, hip dislocations and patients with less than 5 years of follow-up were excluded from the analysis. Findings/Results. The 2D linear PE wear-rate of 0.18 mm/year (SD 0.09) was higher (P<0.001) in the group with HA coated cups (n = 54) compared with 0.12 mm/year (SD 0.07) in the group of non-HA coated cups (n = 35). The Effect size of the difference in linear PE wear-rate, established as Cohen's d, was large (0.9). The time of follow-up was similar (p = 0.11) in the HA group (7.2 years) versus the non-HA group (7.6 years). There was no case-mix concerning distribution of gender and operated side in the groups; however, the mean age was lower (P = 0.001) in the HA group (57 years) compared with the non-HA group (63 years). Conclusions. We found a significantly increased PE wear rate in HA coated acetabular components at midterm follow-up. The patients with HA coated cups were younger on average, and this might partly explain the findings because the activity level expectedly is higher in younger patients. Still an effect size of 0.9 is large and should raise concern and supplement considerations in future clinical decisions on component selection. A randomized (RSA) study on newer type crosslinked polyethylene liners is recommended to bring about more information on the clinical performance and longevity of HA coated acetabular components

Aims

To evaluate the outcomes of cemented total hip arthroplasty (THA) following a fracture of the acetabulum, with evaluation of risk factors and comparison with a patient group with no history of fracture.