Acetabular component thickness does not affect mid-term clinical results in hip resurfacing

Abstract

Background: The benefits of using thin acetabular components for hip resurfacing have been shown in terms of bone conservation, but there currently are little data available in the literature addressing the mid-term clinical results of these devices.

Questions/purposes: We aimed to determine whether thinner acetabular components altered mid-term postoperative clinical scores, complication rates, survivorship, radiographic appearance, and metal ion levels.

Methods: Two hundred eighty-one patients with unilateral disease received a 5-mm thick acetabular shell and 223 received a 3.5-mm shell. The femoral component implanted in both groups was identical. We compared clinical scores, complication rates, survivorship, radiographic results, and ion levels between these two groups.

Results: UCLA hip scores were similar (pain, p = 0.0976; walking, p = 0.9571; function, p = 0.9316; activity, p = 0.2085). Complications were higher in the 5-mm group (6.4% versus 1.8%, p = 0.0431). Both groups were similar regarding survivorship (p = 0.3181), cup radiolucency at 5 years (p = 0.107), and metal ion levels (cobalt p = 0.404, chromium p = 0.250).

Conclusions: With comparable mid-term clinical results, there is no tangible reason to abstain from using the 3.5-mm acetabular component.

Level of evidence: Level III, retrospective comparative study. See the Guidelines for Authors for a complete description of levels of evidence.

Fig. 1A–B

Shown are (A) a 5-mm shell engaged with the original inserter featuring a three-bayonet locking mechanism, and (B) a 3.5-mm shell engaged with the more advanced inserter also using a three-bayonet system but featuring a more secure one-prong locking mechanism.

Fig. 2

Comparative Kaplan-Meier survivorship curves between the 5-mm and the 3.5-mm thick implants are shown. The time to revision for aseptic loosening of the acetabular component was used as the end point. Ninety-five percent CIs are shown at 7, 10, 13, and 15 years of followup. The sharp decrease at 169 months is attributed to one failure at a level of followup in which only five hips were followed, as indicated by the wide 95% CI.

Fig. 3A–B

(A) An immediate postoperative AP radiograph shows a 2-mm gap (arrow) in DeLee and Charnley Zone 2. (B) One year after surgery, the gap has filled and the bone-cup interface shows good osseointegration.

Fig. 4A–C

(A) An immediate postoperative AP radiograph shows intimate contact of the socket with the bone. (B) One year after surgery, a small (< 1 mm) radiolucency is visible in DeLee and Charnley Zone 3 (arrow). (C) Twelve years later, the same radiolucency is still visible (arrow) but has not progressed. The patient’s UCLA hip scores at last followup were 10, 10, 10, and 8 for pain, walking, function, and activity, respectively.