Cotyloplasty in cementless total hip arthroplasty for an insufficient acetabulum

Abstract

Background: Cotyloplasty is a technique that involves making a perforation of the medial wall of a shallow acetabulum and then inserting an acetabular cup with the medial aspect of its dome beyond the Kohler line. The purpose of this study was to evaluate the results of cementless total hip arthroplasty (THA) using cotyloplasty with focusing on the amount of medial cup protrusion.

Methods: Sixteen hips with insufficient acetabulum in sixteen patients were treated by cementless THA using cotyloplasty. The average patient age was 47 years. The diagnoses included dysplastic hip (12) and infection sequelae (4). All the patients were followed up for at least 2 years. Clinically, the Harris hip scores were assessed and radiologically, the amount of cup protrusion, the hip center movement and cup fixation were evaluated.

Results: The average Harris hip score improved from 57 to 94 postoperatively. The average proportion of cup surface beyond the Kohler line was 44.1% and the hip centers were medialized by an average of 23 mm. Stable fixation of the acetabular cup was achieved in all the cases except one. In this one case, migration of the cup was detected 2 weeks postoperatively and a reoperation was performed.

Conclusions: Using cotyloplasty, good coverage of the acetabular cup was obtained without a block bone graft, and the hip joint centers were medialized. However, the safety margin for the amount of protrusion should be established.

Keywords: Cementless; Cotyloplasty; Hip dysplasia; Insufficient acetbulum; Total hip replacement.

Fig. 1

Radiographs of a sixty-two-year-old male patient who underwent total hip arthroplasty using the cotyloplasty technique. (A) The preoperative radiograph showing Crowe's type I dysplasia in the left hip with secondary degenerative arthritis. The superior coverage is expected to be insufficient. (B) The radiograph taken immediately after the operation. Note the ilioischial line on the right side (marked with dots). The acetabular cup is beyond the ilioischial line (black line) on the left side.

Fig. 2

The amount of cup protrusion beyond the ilioischial line was measured as a percentage of the 180 degree arc of the cup on the anteroposterior radiograph. (Percentage of the cup beyond the Kohler line = α / 180°).

Fig. 3

Radiographs of a forty-five-year-old male patient who underwent total hip arthroplasty using the cotyloplasty technique. (A) The radiograph taken immediately after the operation. The medial wall defect was filled with cancellous bone chips acquired from the resected femoral head. Bone grafts are visible on this radiograph. (B) The radiograph taken at sixth month after the operation. A new medial wall had formed from the bone grafts.

Fig. 4

Radiographs of a forty-eight-year-old female patient who had early failure of the acetabular cup after cotyloplasty. (A) The preoperative radiograph showing Crowe's type IV dysplasia in the right hip due to an infection sequela. (B) The radiograph taken immediately after the operation. The acetabular cup protrusion beyond the ilioischial line was sixty-six percent. (C) The radiograph taken after two postoperative weeks. Note the migration of the acetabular cup. (D) The radiograph taken immediately after the revision of the acetabular cup, which was performed at 1 month after the initial operation.