Abstract
Introduction
Squeaking is a potential problem of all hard on hard bearings yet it has been less frequently reported in metal-on-metal hips. We compared a cohort of 11 squeaking metal-on-metal hip resurfacings to individually matched controls, assessing cup inclination and anteversion between the groups to look for any differences.
Methods
We retrospectively reviewed the patient records of 332 patients (387 hip resurfacings) who underwent hip resurfacing between December 1999 and Dec 2012. 11 hips in 11 patients were reported to squeak postoperatively. Each of these patients, except one, were matched by age, sex, BMI and implant to 3 controls. The final patient only had one control due to his high BMI.
The latest post-operative radiographs of the squeaking group and controls were analysed using EBRA (Einzel-Bild-Roentgen-Analysis, University of Innsbruck, Austria) software to evaluate cup inclination and anteversion.
Results
Post- operative audible squeaking occurred in 11 out of 387 hips (2.84%). The mean follow up of the squeaking group was 88.6 months (19–131 months). The mean time to squeak was 11.3 months (3–22 months). 8 (73%) patients were male, 10 (91%) patients had a Birmingham hip resurfacing and 9 (82%) patients had an operation on the left hip. The mean inclination angle of the cups in the squeaking group was 48.4° (43.9°–55.4°) compared to 50° (37.8° −63°) in the control group. The mean anteversion of the cups in the squeaking group was 17.1°(6.3°–25.7°) compared to 14.6° (4.3° −33.5°) in the control group. There was no statistically significant difference between the cases and their controls for cup inclination (p = 0.36) or cup anteversion (p = 0.31). The mean head size in the squeaking group was smaller at 49.3 mm (46 mm-54 mm), compared to 51.4 mm (48 mm-54 mm) in the control group (p = 0.026). The mean cup size in the squeaking group was also smaller at 56.5 mm (54 mm-62 mm), compared to 57.9 mm (48 mm-60 mm) in the control group (p = 0.007). Overall, 4 (40%) male patients in the squeaking group had a head size less than 50 mm, compared to 0 (0%) in the control group. 3 (27%) patients with squeaking resurfacings underwent revision surgery. 1 (9%) at 72 month for a pseudotumour, 1 (9%) at 114 months for persistant squeaking and 1 (9%) at 117 months for a subtrochanteric fracture after a fall.
Conclusions
No difference was found between the radiographic inclination or anteversion of squeaking metal-on-metal hip resurfacing cups compared to a control group. Male patients with squeaking hips were noted to have smaller head and cup sizes than their controls.
