Recovery of Hip Abductor Muscle Strength after Total Hip Arthroplasty in Patients with Leg Length Discrepancy.

BACKGROUND

Total hip arthroplasty (THA) is an effective treatment to reduce pain and improve function outcomes for osteoarthritis patients. To our knowledge, there were scant of information about effect of preoperative leg length discrepancy (LLD) on recovery of hip abductor muscle strength and functional outcomes.

OBJECTIVE

To evaluate the recovery of hip abductor muscle strength after THA in osteoarthritis patients with LLD and to study the correlation among LLD, recovery of hip abductor muscle strength and functional outcomes.

MATERIAL AND METHOD

Between January 2014 and December 2015, 30 osteoarthritis patients who underwent THA at least six months were divided into two groups, Group 1 (LLD less than 2 cm), and Group 2 (LLD greater than 2 cm). Four parameters were measured on anteroposterior both hip radiographs in the supine position before and after operation: LLD, abductor length, abductor lever arm, and femoral offset (FO). Abductor muscle strength was calculated quantitatively by an isokinetic/isometric dynamometer [Con-Trex MJ]. Hip abductor strengths were calculated as the ratio of operated hip to contralateral healthy hip which used as controls. Functional outcomes were evaluated by two-minute walk test (2MWT) and timed up and go test (TUG).

RESULTS

The mean of hip abductor muscle strength ratio in all patients was 89.50% (standard deviation (SD) 29.94). Patients showed 83.10% (SD 34.58) of mean abductor muscle strength ratio at 6 to 12 months after operation, 88.50% (SD 25.36) at 12 to 24 months after operation, and 112.20% (SD 25.27) after 24 months after operation. Patients in Group 1 had 94.74% (SD 33.54) of mean hip abductor muscle strength ratio. It was greater than 79.02% (SD 18.18) in Group 2, however, there were no statistically significant differences between the two groups (p = 0.18). There were no significant differences of 2MWT and TUG between the two groups either. A weak correlation between preoperative LLD and hip abductor muscle strength ratio (rs = 0.163, p = 0.39), and between preoperative LLD and 2MWT (rs = 0.030, p = 0.874), TUG (rs = -0.067, p = 0.73) were found.

CONCLUSION

The hip abductor muscle strength showed good to excellent recovery after THA. The results from this study showed no correlation among preoperative LLD, the recovery of hip abductor muscle strength, and functional outcomes.