Is there any range-of-motion advantage to using bearings larger than 36 mm in primary hip arthroplasty: A case-control study comparing 36-mm and large-diameter heads

BackgroundLarge-diameter (> 36 mm) total hip arthroplasty (THA) has developed rapidly since the advent of ceramic-on-ceramic (CoC) bearings and highly cross-linked polyethylene. Theoretically, the increase in diameter reduces the risk of instability, although the advantage of calibers beyond 36 mm has not been demonstrated in terms of range-of-motion recovery. We conducted a comparative study with a single prosthesis model to determine whether increasing the caliber beyond 36 mm provides: (1) better recovery of range-of-motion, (2) a higher functional score, and (3) reduction of the dislocation rate.HypothesisIncreasing the range-of-motion by increasing the caliber beyond 36 mm provides better range-of-motion.Material and methodsWe analyzed two consecutive, single-operator cementless THA series performed via the mini posterior approach, which differed only in the bearing system (51 metal-on-metal [MoM] with a mean caliber of 45 mm ± 3.3 [range, 40–54] and 61 CoC with a 36-mm caliber). Both series were comparable preoperatively in terms of age, diagnosis, functional scores, preoperative range-of-motion, body mass index, UCLA activity level, and Charnley score. We compared the joint range of movement at follow-up and the gains in range of movement, onset of dislocation, and functional scores (Oxford, Postel-Merle d’Aubigné [PMA]).ResultsThe mean overall joint range-of-motion was 254° ± 39° (range, 150–310°) for an 81° ± 44° (range, −50 to 180°) gain in the MoM group and 256° ± 23° (range, 200–280°) for an 84° ± 40° (range, 0–160°) gain in the CoC group (NS). The MoM group presented the following results: Oxford = 13.71 ± 3.66 (range, 12–33) for a gain of 24.82 points ± 7.9 (range, −1 to 40), PMA = 17.75 ± 1.06 (range, 11–18) for a gain of 7.78 points ± 4.01 (range, 2–15). The CoC group had: Oxford = 14.98 ± 4.42 (range, 12–36) for a gain of 24.75 points ± 6.55 (range, 12–40), PMA 17.66 ± 0.7 (range, 14–18) for a gain of 8 points ± 3.77 (range, 1–15). None of the gains and scores at follow-up differed significantly between the two groups. No episode of dislocation was identified.DiscussionThe current trend of increasing femoral head diameters beyond 36 mm to improve the gains in joint range-of-motion and function is not warranted. The potential side effects of increasing the caliber call for even greater caution in the use of large-diameter heads because our hypothesis has not been confirmed.Level of evidenceCase-control study, level III.