Resurfaced hips converted to THA show similar clinical results to primary total hips

Converting resurfacing arthroplasty hips to THA required similar operative times and length of postoperative hospitalization.

Hips previously treated with metal-on-metal resurfacing arthroplasty that require conversion to total hip arthroplasty can achieve short-term clinical and radiographic results similar to primary total hip replacement, according to a study by California researchers.

"The theoretical advantage of easy 'revisability' of a resurfacing arthroplasty is supported by our results," the study authors wrote. "With the numbers studied, the procedure was similar to primary total hip arthroplasty (THA) in terms of operative time and blood loss. The radiographic results after conversion were also similar to those in the primary [THA] group in terms of osseointegration, the position of the center of rotation, femoral offset, stem position, and limb-length equality."

Scott T. Ball, MD, and colleagues reviewed outcomes for 21 hips of 20 patients treated with metal-on-metal resurfacing arthroplasty who required conversion to THA. These patients averaged 50.2 years of age. Five hips required conversion because of a femoral neck fracture and 16 hips required conversion because of femoral component loosening, according to the study, published in the American edition of the Journal of Bone and Joint Surgery.

For all resurfacing arthroplasties, the surgeon had implanted a Conserve Plus device [Wright Medical Technology] with an uncemented femoral head. The time between resurfacing and conversion to THA averaged 40.9 months.

In 18 hips, the surgeon revised only the femoral component to a stemmed femoral component. For the three remaining hips, acetabular revision was needed because a unipolar head that matched the cup size was not available at that time, the authors noted. The researchers compared the results to a control group of 64 hips in 58 patients treated with primary THA at an average age of 50.8 years.

Follow-up averaged 64 months for the conversion group and 57 months for the control group.

The researchers found that both groups had similar postoperative scores for pain and function.

For the conversion group, University of California Los Angeles (UCLA) scores averaged 9.3 points for pain, 9.4 points for walking, 9.3 points for function and 6.8 points for activity. Short Form-12 (SF-12) scores averaged 48.6 for the physical component and 54.2 for the mental component, and the Harris Hip Scores (HHS) averaged 92.2 points, according to the study.

For the control group, UCLA scores averaged 9.6 points for pain, 9.2 points for walking, 8.8 points for function and 6.4 points for activity. SF-12 scores averaged 47.1 for the physical component and 50.3 for the mental component, and the HHS averaged 90.3 points.

Both groups also had similar operative times, intraoperative blood loss and length of postoperative hospitalization, according to the study.

"All of the revision cementless stems were integrated into bone, and the fixation scores showed no difference between the conversion group and the control group," the authors reported.

In addition, "Femoral offset and the horizontal position of the center of rotation of the hip were similar between the two groups," they noted.

Stems were in the neutral position for 81% of the conversion group and 84% of the control group, according to the study.

For more information:
Ball ST, LeDuff MJ, Amstutz HC. Early results of conversion of a failed femoral component in hip resurfacing arthroplasty. J Bone Joint Surg Am. 2007;89-A:735-741.