Does Capsular Laxity Lead to Microinstability of the Native Hip?

Area of Science:

• Orthopedic biomechanics
• Hip joint kinematics
• Capsular anatomy

Background:

• Hip microinstability is often attributed to femoral head translation but lacks objective criteria.
• Capsular laxity is hypothesized to cause abnormal articular surface motion, leading to symptoms.

Purpose of the Study:

• To investigate the relationship between hip capsular laxity and abnormal joint rotation and translation.
• To quantify the biomechanical effects of capsular laxity on hip joint motion.

Main Methods:

• Eight cadaveric hips were tested in a hip activity simulator under rotational torque.
• Capsular laxity was induced via ligament incisions ('pie crusting').
• Femoral head translation and joint rotation were monitored using motion analysis.

Main Results:

• Capsular laxity significantly increased hip joint rotations and femoral head translation (P < .05).
• Femoral head translation reached up to 4 mm beyond 30° flexion.
• A hip microinstability index increased significantly with induced laxity (P < .01).

Conclusions:

• Capsular laxity induces hip microinstability, characterized by increased rotations and abnormal femoral head translation.
• Altered hip kinematics due to capsular laxity may contribute to abnormal joint contact and degeneration.