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Impingement-free hip motion: the 'normal' angle alpha after osteochondroplasty
Mirjam Neumann1, Quanjun Cui, Klaus A Siebenrock
1Department of Orthopaedic Surgery, University of Bern, Inselspital, Bern, Switzerland.
Clinical Orthopaedics and Related Research
|November 20, 2008
Summary
The anterior offset angle alpha, crucial for diagnosing femoroacetabular impingement, was found to be 43 degrees in patients with successful surgical outcomes, suggesting a lower normal range than previously believed.
Area of Science:
- Orthopedic Surgery
- Radiology
- Biomechanical Engineering
Background:
- Femoroacetabular impingement (FAI) is a precursor to hip osteoarthritis.
- Cam impingement involves an aspherical femoral head-neck junction causing acetabular cartilage damage.
- The anterior offset angle alpha on lateral radiographs indicates the aspherical region of the femoral head.
Purpose of the Study:
- To determine the specific angle alpha associated with impingement-free hip motion.
- To re-evaluate the normal range for angle alpha in the context of FAI treatment.
Main Methods:
- Preoperative, immediate postoperative, and 1-year postoperative measurements of angle alpha in 45 FAI patients.
- Surgical correction of the femoral head-neck junction and acetabulum.
- Assessment of surgical success based on achieving 20-25 degrees of internal rotation at 90 degrees hip flexion.
Main Results:
- Preoperative mean angle alpha was 66 degrees (range, 45-79 degrees).
- Postoperative mean angle alpha was corrected to 43 degrees (range, 34-60 degrees).
- Achieved angle alpha of 43 degrees correlated with successful impingement-free motion.
Conclusions:
- An angle alpha of 43 degrees, achieved surgically, represents a normal threshold for impingement-free motion.
- The currently accepted normal range for angle alpha (50-55 degrees) may be too high.
- This finding refines the understanding of normal hip biomechanics and FAI diagnosis.