Dislocation after total hip arthroplasty among patients with developmental dysplasia of the hip.

Department of Orthopaedics, Shanghai Ninth People's Hospital, Shanghai Key Laboratory of Orthopaedic Implant, Shanghai Jiao Tong University School of Medicine and Engineering Research Center of Digital Medicine, Ministry of Education, Shanghai, PR China.
The Journal of arthroplasty (Impact Factor: 2.37). 10/2011; 27(5):764-9. DOI: 10.1016/j.arth.2011.08.021
Source: PubMed

ABSTRACT The precise relationship between developmental dysplasia of the hip and dislocation among patients after total hip arthroplasty has not been well clarified. A total of 820 patients with developmental dysplasia of the hip who underwent total hip arthroplasty from January 2000 to December 2009 were categorized according to Crowe classification, and postoperative dislocation rates were analyzed among subgroups. The overall dislocation rate was 2.93%. No statistically significant differences in dislocation rates were observed between these with and without subtrochanteric osteotomy. Femoral head size was the only factor with significant difference between the dislocated and stable groups, especially when femoral head diameter increased from 28 to 32 mm. Of all dislocations, 69.6% were anterior dislocation, and the degree of cup anteversion and combined anteversion of anterior dislocators was higher than that of the posterior dislocators (P = .0082 and P = .001).

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    ABSTRACT: Background and purpose Previous population-based registry studies have shown that larger femoral head size is associated with reduced risk of revision for dislocation. However, the previous data have not included large numbers of hip resurfacing arthroplasties or large metal-on-metal (> 36-mm) femoral head arthroplasties. We evaluated the association between femoral component head size and the risk of revision for dislocation after THA by using Finnish Arthroplasty Register data. Patients and methods 42,379 patients who were operated during 1996-2010 fulfilled our criteria. 18 different cup/stem combinations were included. The head-size groups studied (numbers of cases) were 28 mm (23,800), 32 mm (4,815), 36 mm (3,320), and > 36 mm (10,444). Other risk factors studied were sex, age group (18-49 years, 50-59 years, 60-69 years, 70-79 years, and > 80 years), and time period of operation (1996-2000, 2001-2005, 2006-2010). Results The adjusted risk ratio in the Cox model for a revision operation due to dislocation was 0.40 (95% CI: 0.26-0.62) for 32-mm head size, 0.41 (0.24-0.70) for 36-mm head size, and 0.09 (0.05-0.17) for > 36-mm head size compared to implants with a head size of 28 mm. Interpretation Larger femoral heads clearly reduce the risk of dislocation. The difference in using heads of > 36 mm as opposed to 28-mm heads for the overall revision rate at 10 years follow-up is about 2%. Thus, although attractive from a mechanical point of view, based on recent less favorable clinical outcome data on these large heads, consisting mainly of metal-on-metal prostheses, one should be cautious using these implants.
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