Patellofemoral stresses during open and closed kinetic chain exercises. An analysis using computer simulation

Area of Science:

• Biomechanics
• Orthopedic Rehabilitation
• Sports Medicine

Background:

• Rehabilitation of the symptomatic patellofemoral joint focuses on strengthening quadriceps while minimizing articular cartilage stress.
• Open kinetic chain (OKC) exercises, such as leg extensions, have been questioned for potentially causing supraphysiologic stress on patellofemoral cartilage compared to closed kinetic chain (CKC) exercises like squats.

Purpose of the Study:

• To compare the biomechanical effects of OKC leg extension exercises with varying ankle loads against CKC knee-bend exercises.
• To evaluate quadriceps muscle forces, patellofemoral joint contact forces, stresses, and "benefit indices" across different exercise types and flexion angles.

Main Methods:

• Computer simulations were conducted using geometric data from five cadaveric knees.
• Three OKC leg extension variations (0-N, 25-N, 100-N ankle loads) were compared to CKC knee-bend exercises (20-90 degrees flexion).

Main Results:

• OKC exercises did not produce supraphysiologic stresses on the patellofemoral joint.
• Stresses from OKC exercises were not significantly higher than those from CKC exercises across the tested flexion range.
• Benefit indices indicated favorable outcomes for OKC exercises relative to contact stress.

Conclusions:

• OKC leg extension exercises are a safe and viable option for patellofemoral joint rehabilitation, challenging previous assumptions about their safety.
• Findings support the use of OKC exercises for patients who may not tolerate CKC exercises, such as post-operative individuals.
• OKC exercises at lower flexion angles are suitable for patients with proximal patellar issues limiting deeper flexion loading.