Capsular Ligament Function After Total Hip Arthroplasty

Area of Science:

• Orthopedic surgery
• Biomechanics
• Arthroplasty research

Background:

• The hip joint capsule is vital for limiting extreme motion and protecting the native hip.
• Total hip arthroplasty (THA) may compromise the capsule's protective function due to reduced femoral head size.

Purpose of the Study:

• To investigate the biomechanical function of the hip capsule after THA.
• To evaluate the impact of femoral head size and neck length on capsular function post-THA.

Main Methods:

• Cadaveric study involving THA with preserved capsule.
• Measurement of capsular function across different hip rotation positions.
• Comparison of three femoral head sizes (28, 32, 36 mm) and three neck lengths (0, +5, +10 mm).

Main Results:

• Post-THA, increased internal and external rotation indicated reduced capsular function (p < 0.05).
• Increasing neck length mitigated hypermobility, but excessive lengthening caused restricted external rotation.
• Larger head sizes showed minimal effect on reducing hypermobility.

Conclusions:

• The reduced femoral head in THA prevents the capsule from effectively restraining extreme motion.
• Posterior capsule function is significantly affected, questioning the benefit of its preservation in the short term.
• Neck length critically influences capsular function, with insufficient length causing dysfunction and excessive length leading to overtightening.