Size of cup affects the anterior capsular distance in total hip arthroplasty, as measured with ultrasound.

BACKGROUND: Previously was found that sonography is a reliable method to measure a capsular distance in total hip arthroplasty hips. The aim of our current study was to investigate the relation between the implanted size of the cup and the anterior capsular distance, as measured with ultrasound one year after THA. METHODS: 50 osteoarthritis (OA) patients operated on with total hip arthroplasty one year before were included in the study and the anterior capsular distance was measured sonographically. Patients were grouped with respect to cup size. The correlation between the implanted cup size and capsular distance was determined. RESULTS: The mean capsular distance in the whole group was 1.37 (SD 0.19) cm. The mean capsular distance in the group with small cups was 1.27 (SD 0.13) cm, in large cups it was 1.45 (SD 0.20) cm, p = 0.02. Spearman correlation analysis showed a statistically significant correlation between a greater capsular distance and the larger size of the cup (r = 0.5, p < 0.0001). CONCLUSION: The greater capsular distance in successful THA hips is affected by cup size. We propose that this should be considered when evaluating sonography of the anterior capsular distance after THA.

The short rotators do not influence capsular compliance or pain in severe hip osteoarthritis. A randomised controlled trial.

A randomised controlled trial was performed to investigate if the short rotators affected the compliance of the capsule in osteoarthritis (OA). 68 OA patients admitted for total hip arthroplasty (THA) were randomised to have their compliance estimated during surgery with either their short rotators intact or released. Radiographic severity of OA, range of motion and pain were assessed in the affected hip before surgery. There was no significant difference in the compliance of the capsule whether the short rotators were intact or released (p= 0.5). Furthermore, there was no significant correlation between pain and capsular compliance (p=0.4 and p=0.5). We found no significant effect of the short rotators on compliance of the hip joint capsule, and no significant correlation between pain and capsular compliance.