[Clinical apprehension on application of metal on metal total hip arthroplasty with large diameter heads].

Objective: To approach the short-term result and clinical application of metal on metal total hip arthroplasty with large diameter heads and evaluate its safety and efficacy clinically.

Methods: From January 2007 to March 2008, 39 hips in 37 patients (24 males and 13 females,ranging in age from 43 to 75 years, with an average of 58.5 years) were treated with metal on metal total hip arthroplasty with large diameter heads (ASRTM XL) included 14 cases of osteonecrosis (ON), 2 cases of osteoarthritis (OA), 18 cases of fresh femoral neck fracture, 3 cases of developmental dysplasia of the hip (DDH). All patients were evaluated by self assessment form, hip function examination, radiographs, preoperative and postoperative Harris hip score. Based on the short-term results, its design characteristic and clinical properties were analyzed.

Results: All the incision healed well and there were not any complications such as femoral fracture, infection, dislocation and neurovascular injury. All patients obtained the follow-up and an average time was 16.5 months (12 to 19 months), all the joints had good or excellent clinical results. Radiographically, the positions of the prostheses were normal, the average limbs length and femoral eccentricity recovered as normal. The average range of motion of the hip improved remarkable, such as flexion improved from (20.1 +/- 8.2) degrees to (85.7 +/- 9.8) (t = 32.86, P < 0.01), abduction improved from (10.2 +/- 4.4) degrees to (41.5 +/- 9.1) degrees (t = 19.34, P < 0.01), adduction improved from (16.3 +/- 8.8) degrees to (40.3 +/- 10.4) (t = 11.00, P < 0.01),external rotation improved from (12.3 +/- 5.2)0 to (42.0 +/- 7.7) degrees (t = 19.96, P < 0.01), internal rotation improved from (3.4 +/- 1.1) degrees to (23.0 +/- 9.8) degrees (t = 12.41, P < 0.01). The Harris score rose from preoperative (39.3 +/- 5.6) to (91.4 +/- 10.3) at the latest follow up (t = 27.75, P < 0.01).

Conclusion: Short-term results show that metal on metal hip joint prosthesis with large diameter heads has advantages of small deformation of acetabular cup, lower wearing, large range of motion and few dislocation. It offers a newly valuable technology for treatment of osteonecrosis, osteoarthritis, femoral neck fracture and DDH with the higher requirement of movement after the operation.