Medicine
Peripheral Nerve Injury Patterns in Total Hip Arthroplasty
Quick fact
In total hip arthroplasty, the sciatic nerve is the most commonly injured peripheral nerve, an injury that can present as foot drop and sensory loss on the outside of the leg and top of the foot.
Why this is interesting
You've had a hip replacement, and suddenly your foot drops or your leg feels numb—these are not random symptoms, but signs of specific nerves that may have been injured during surgery. Which nerves are most at risk, and why do the patterns of injury follow such predictable paths?
Read the full explanation
Understanding Peripheral Nerve Injury Patterns in Total Hip Arthroplasty
Think of the hip as a busy intersection, with major nerve 'highways' passing nearby. During surgery to replace the hip joint, the surgeon must work around these nerves. The sciatic nerve, the largest and most important, runs just behind the hip joint, while the femoral nerve runs in front. When instruments or retractors press against these nerves, or when the leg is stretched in a way that pulls the nerve, the nerves can be damaged. This damage leads to temporary or permanent loss of function, such as weakness in the muscles they supply. For the sciatic nerve, this means weakness in the hamstrings and all muscles below the knee, causing difficulty lifting the foot (foot drop). For the femoral nerve, damage leads to weakness in the quadriceps, making it hard to straighten the knee. The pattern of symptoms depends on which specific branch of the nerve is affected, creating a map of where the injury occurred relative to the hip.
A deeper explanation
The mechanism behind these injuries is rooted in the anatomical relationship and the mechanical forces applied during surgery. The sciatic nerve exits the pelvis through the greater sciatic foramen, passing close to the hip joint's posterior capsule. During a posterior approach to the hip, retractors placed under the capsule can directly compress the nerve, or excessive retraction can stretch it. Because the common peroneal division of the sciatic nerve contains more rigidly fixed fascicles and is tethered at the fibular neck, it is particularly vulnerable to stretch, leading to the classic foot drop and sensory loss on the dorsum of the foot. Femoral nerve injury occurs more often in anterior approaches, where retractors can compress it against the pelvic bone. Obturator nerve damage is rarer and can cause weakness in thigh adduction. The severity of injury follows a spectrum from mild crush (neurapraxia) causing temporary conduction block, to axonotmesis with axon disruption but preserved nerve sheath, to complete transection (neurotmesis), which requires surgical repair. Understanding these patterns helps surgeons minimize risk during retraction and positioning, and helps clinicians diagnose post-operative nerve injuries based on the specific sensory and motor deficits that follow the nerve's distribution.