A patient sustains a nerve injury just below the inguinal ligament. Which gait deviation is MOST likely?

A patient sustains a nerve injury just below the inguinal ligament. Which gait deviation is MOST likely?

• A. Increased posterior lean of the trunk in midstance
• B. Increased medial (internal) rotation of the thigh during midswing
• C. Hyperextension of the knee during stance phase
• D. Excessive ankle plantar flexion during foot flat (loading response)

Answer: (C)

Injury just below the inguinal ligament most likely affects the femoral nerve, which supplies the quadriceps—the main knee extensors. When knee extensors are weak, the ability to control knee straightening during the stance phase is impaired. As a result, the knee can end up in a hyperextended position (genu recurvatum) during stance because the body relies on joint alignment and ligaments to stabilize the leg without adequate extensor muscle force. Other gait changes are less consistent with femoral nerve injury: posterior trunk lean is more about compensating for hip or core weaknesses, internal rotation of the thigh in midswing points to problems with hip rotators, and excessive ankle plantarflexion at loading would involve the ankle/pedal mechanics rather than the knee extensors.

Injury just below the inguinal ligament most likely affects the femoral nerve, which supplies the quadriceps—the main knee extensors. When knee extensors are weak, the ability to control knee straightening during the stance phase is impaired. As a result, the knee can end up in a hyperextended position (genu recurvatum) during stance because the body relies on joint alignment and ligaments to stabilize the leg without adequate extensor muscle force.

Other gait changes are less consistent with femoral nerve injury: posterior trunk lean is more about compensating for hip or core weaknesses, internal rotation of the thigh in midswing points to problems with hip rotators, and excessive ankle plantarflexion at loading would involve the ankle/pedal mechanics rather than the knee extensors.