Anterior dislocation of a total hip replacement. Radiographic and CT-scan assessment. Behavior following conservative management.

BACKGROUND

Hip dislocation is one of the most frequent complications of total hip replacement. The direction of dislocation matters. Most dislocations are posterior; anterior dislocation remains rare and its treatment is controversial.

STUDY OBJECTIVES

To clinically and radiologically evaluate the outcomes of the conservative (orthopaedic without revision surgery) treatment of anterior hip dislocations after total hip replacement by immobilisation of the hip in 45 degrees flexion, 10 to 20 degrees abduction and neutral rotation (deck chair position).

MATERIALS AND METHODS

Between 1997 and 2007, 19 patients (11 women, 7 men), aged between 36 and 89 years old (average age 64.6 years), operated on for hip osteoarthritis using a posterolateral approach, presented with anterior dislocation of their cemented total hip arthroplasty. Instability during extension associated with external rotation was noted at surgery in eight cases. Ten dislocations occurred in the immediate postoperative period (within 48 hours) and nine within an average postoperative delay of 39 days (6-82). After reduction of the dislocation by closed manipulation, the patients were treated by immobilisation in the deck chair position for an average of 2 weeks (10-21 days). Radiological and functional assessment (based on the Merle d'Aubigné score [PMA]) was performed on average at 4 years after surgery. The inclination of the cup in the frontal plane and any lengthening of the operated extremity were measured on an AP pelvic plain film with the patient in the standing position. Cup and femoral stem anteversion were calculated by CT-scan in 16 cases.

RESULTS

At the last follow-up, four patients had had recurrent anterior dislocations (one patient had had two dislocations). They were again treated with immobilisation in the deck chair position for two weeks without further recurrence. None of the patients underwent revision surgery on the temporarily unstable operated hip. Thirteen patients had no pain and eleven had an unlimited walking perimeter. The final average PMA score was 16 (12-18). The patients who presented with one or two recurrences had a PMA of 18 in the final follow-up. Six patients presented with at least 5 mm of shortening (average: 10 mm, maximum 25 mm) with one case of 10 mm of lengthening. The average cup inclination angle in frontal plane views was 48 degrees (40-57 degrees). It was more than 50 degrees in seven cases. The average cup anteversion in CT-scan was 30 degrees (14-60 degrees). The average femoral anteversion in CT-scan was 24 degrees (3-52 degrees). A total of 12 implants (eight cups and four femoral stems) had at least 25 degrees excessive anteversion on CT-scan assessment.

DISCUSSION, CONCLUSION: Anterior dislocation after total hip replacement is associated with approximately 10 degrees of excessive femoral and acetabular anteversion respectively. Nevertheless, correction of these architectural anomalies is not necessary because immobilisation in the deck chair position for 2 weeks effectively prevents recurrence and results in satisfactory medium-term functional results.