Hip Flexion and Knee Extension Myotomes
Hip flexion is primarily innervated by the femoral nerve (L2-L4 myotome), while knee extension is also innervated by the femoral nerve (L3-L4 myotome).
Hip Flexion Myotome
Primary Nerve Supply
- The femoral nerve provides the primary innervation for hip flexion, with the nerve's main function involving both hip flexion and knee extension movements 1.
- Femoral neuropathy results in weakness of both hip flexion and knee extension, presenting as anterior hip and thigh pain 1.
Clinical Considerations
- Hip flexion beyond 90 degrees can increase tension on multiple nerves and potentially lead to compression symptoms 2.
- Positions that excessively flex the hip should be avoided in patients with suspected femoral nerve pathology 2.
- The femoral nerve can be injured by hip positioning that extends beyond normal comfortable range or excessive hip flexion beyond 90 degrees 1.
Knee Extension Myotome
Primary Nerve Supply
- The femoral nerve innervates the quadriceps muscle group, which is responsible for knee extension 1.
- All five components of the quadriceps (rectus femoris and the four vasti muscles) are active during maximum knee extension, regardless of hip position 3.
Muscle Activity Patterns
- The rectus femoris cannot be isolated from the vasti muscles during knee extension exercises, as all portions of the quadriceps work together in all positions 3.
- Knee extension torques are approximately 40% higher when the knee is at 60 degrees flexion compared to 15 degrees flexion 3.
- The highest electromyographic activity of all quadriceps muscles occurs with the hip at 40 degrees flexion and knee at 15 degrees flexion 3.
Clinical Testing Implications
Position-Dependent Strength
- Isokinetic knee strength is significantly influenced by hip flexion angle, with lower torque values in extended hip positions compared to flexed hip positions 4.
- Maximum knee strength is lower in supine position (hip extended) compared to seated position (hip flexed at 90 degrees), which should be considered during clinical testing 4.