Unstable hip arthroplasties. A prospective cohort study on seventy dislocating hips followed up for four years.

PURPOSE: Dislocating hip prosthesis remains a substantial clinical problem. The aim of this study is to describe the risk of recurrent instability after a primary dislocation of primary hip arthroplasty performed for osteoarthritis (OA) or femoral neck fracture (FNF).

METHODS

Seventy patients (male/females: 25/45; mean age 77 [range 46-94]) with dislocating hip arthroplasties were included in a prospective cohort study and followed for four years. Radiographs and all surgical records were reviewed. We compared stable hips to those who either continued to dislocate or were revised due to recurrent instability (unstable group).

RESULTS

Forty-two hips (60 %) had episodes of recurrent instability leading to repeated closed reductions or major revision surgery and were classified as unstable. A diagnosis of FNF and cognitive dysfunction (OR 9.3 [95 % CI 1.4-64.1]) or postoperative radiological discrepancies such as leg-lengthening and offset reduction increased the risk of further instability (OR 13.5 [95 % CI 1.3-148.1]). The surgical approach at primary surgery and ASA class did not significantly influence the risk of continued instability.

CONCLUSIONS

Patients with a FNF and cognitive dysfunction or with sub-optimal postoperative radiographs after hip arthroplasty surgery are at high risk of recurrent instability after a primary dislocation. For hip fracture patients, all efforts should be made to avoid the first dislocation.