Capsular ligaments provide a passive stabilizing force to protect the hip against edge loading

Area of Science:

• Orthopedic biomechanics
• Hip joint anatomy and function
• Ligamentous stabilization

Background:

• The hip capsular ligaments are known to tighten at extreme ranges of motion.
• These ligaments may passively stabilize the hip joint against edge loading.

Purpose of the Study:

• To quantify the stabilizing force vectors of hip capsular ligaments at extreme range of motion (ROM).
• To examine the ligaments' ability to prevent hip joint edge loading.

Main Methods:

• Torque-rotation curves were generated from nine cadaveric hips.
• A ligament model determined the line-of-action and moment arms of key ligaments.
• Ligament forces and stiffness were assessed at 5 Nm rotational restraint.

Main Results:

• The iliofemoral ligament provided anterior stability in extension and adduction.
• The ischiofemoral ligament offered posterior stability in flexion, adduction, and internal rotation (FADIR).
• Capsular restraint shifted the hip joint reaction force inbound, preventing edge loading.

Conclusions:

• Hip capsular ligaments maintain an inbound joint force vector at extreme ROM.
• Preserving ligament integrity and tension post-surgery is vital for minimizing hip instability complications.