External rotation strength deficit after hip resurfacing surgery

Purpose: The aim was to assess the effect of resurfacing hip arthroplasty on hip muscle function, when, in the posterior approach, the piriformis tendon and outer rotators of the hip joint were divided. The unoperated side was used as a control. Methods: Thirty-three consecutive patients (mean age 55 years, 73% males) were operated using the posterior approach. Main outcome measures were isometric muscle strength of external and internal rotators and extensors of the hip and hip pain. Results: Hip external rotation strength (p > 0.001) and leg extension strength (p < 0.001) were significantly lower on the operated side compared with the un-operated side prior to the surgery. On the operated side external rotation strength decreased by 29% (p < 0001) and internal rotation strength increased by 28% (p < 0.001). The changes of 12% in leg extension strength of the operated side and the changes of 3-10% in all strength measurements in the un-operated side were not significant. Three months post-operatively, the external rotation strength and leg extension strength values were 50%) and 26% lower (p < 0.001) on the operated side compared with those in the un-operated side. The decreases in pain values during the rest, loading as well as during the strain of strength measurements were all significant (p < 0.001). Conclusion: Although hip resurfing surgery gives excellent relief of pain, significant strength deficit was found in the external rotators 3 months post-operatively.