Long-term Results of Primary Hip Arthroplasty with Cup Inclination Angle Bigger than Fifty Degrees

Most of studies suggest the cup inclination angle is controversial. All of the studies previous have not control the prosthesis type and head diameter, it is difficult to determine relative or synergistic effects of cup angle.

We retrospectively reviewed 54 patients (61 hips) with primary total hip arthroplasties which cup inclination angle bigger than 50⁰ after a mean 11.8 years follow-up. All the prosthesis are noncemented cup with a 28 mm metal head(Trilogy Acetabular Shell, Zimmer). The cup inclination was divided into three groups, 50-55⁰ in 26 hips, 55-60⁰ in 21 hips, and bigger than 60⁰ in 14 hips. An immediate postoperative radiograph was compared with a follow-up radiograph. The polyethylene wear rates and abduction of the acetabular cups was measured in all of the patients.

The preoperative mean Harris hip score improved from 47.36 to 94.3 points at 10 years. The survivorship of the cup was 100% at 10 years. The mean rate of liner wear was 0.144 ± 0.031 mm/y (0.105-0.178 mm/y) in cup inclination angle between 50⁰-55⁰, and 0.260 ± 0.043 mm/y (0.215-0.394 mm/y) in angle between 55⁰-60⁰, 0. 403 ± 0.016 mm/y (0.378-0.423 mm/y) in angle bigger than 60⁰. The different cup inclination groups are different with liner and volumetric wear.

For the metal-on-polyethylene prostheses, the liner wear obvious correlate with cup inclination after angle bigger than 50⁰. It can be concluded that the ideal abduction angle for metal-on-polyethylene prostheses should be less than 55° in hip total replacement.