Background: Modern hip resurfacing implants may increase stability
and preserve more bone than conventional total hip arthroplasty. The purpose
of this retrospective study was to analyze the mid-term results in a
consecutive series of middle-aged patients with developmental dysplasia of the
hip treated with hybrid resurfacing joint arthroplasty.
Methods: Metal-on-metal hip resurfacing was performed in fifty-one
patients (fifty-nine hips), forty-two of whom were female and nine of whom
were male. The average age at the time of surgery was 43.7 years. Radiographic
and clinical data were collected at six weeks, at three months, and at yearly
follow-up visits. Seven hips had Crowe type-II developmental dysplasia of the
hip and fifty-two had type-I.
Results: The follow-up period ranged from 4.2 to 9.5 years (average,
6.0 years). Initial stability was achieved in all but three hips. The clinical
outcomes, as rated with the University of California at Los Angeles (UCLA) hip
score, improved significantly compared with the preoperative ratings. On the
average, the pain rating improved from 3.2 to 9.3 points; the score for
walking, from 6.0 to 9.7 points; the score for function, from 5.7 to 9.6
points; and the score for activity, from 4.6 to 7.3 points (all p = 0.0001).
The mean Short Form-12 (SF-12) mental score increased from 46.6 to 53.5
points, and the mean SF-12 physical score increased from 31.7 to 51.4 points
(both p < 0.0001). The mean postoperative Harris hip score was 92.5 points.
On the average, the range of flexion improved from 106° to 129.6°; the
abduction-adduction arc, from 41.9° to 76.9°; and the rotation arc in
extension, from 32.1° to 84.8° (all p = 0.0001). Four patients
delivered a total of six healthy babies since the time of implantation of the
prosthesis. Radiographic analysis showed a decrease in the mean body weight
lever arm from 118.5 mm preoperatively to 103.9 mm postoperatively (p =
0.007). There were five femoral failures requiring conversion to a total hip
arthroplasty. One hip showed a radiolucency around the metaphyseal femoral
stem. There were no complete acetabular radiolucencies, and all sockets
remained well fixed.
Conclusions: The mid-term results of metal-on-metal resurfacing in
patients with Crowe type-I or II developmental dysplasia of the hip were
disappointing with respect to the durability of the femoral component.
However, the fixation of the porous-coated acetabular components without
adjuvant fixation was excellent despite incomplete lateral acetabular coverage
of the socket. More rigorous patient selection and especially meticulous bone
preparation are essential to minimize femoral neck fractures and loosening
after this procedure.
Level of Evidence: Therapeutic Level IV. See Instructions
to Authors for a complete description of levels of evidence.