Total hip replacement (THR) is a common orthopedic procedure designed to alleviate pain and restore mobility. While the surgery generally results in excellent outcomes, it involves working near major neural structures, making nerve injury a possible, though rare, complication. The incidence of nerve injury after a primary THR is low, typically ranging from 0.09% to 3.7%. Understanding the specific signs of nerve damage is important for patients postoperatively.
Identifying the Signs of Nerve Damage
Nerve damage can manifest as distinct sensory and motor deficits, often providing clues about the injured nerve. Sensory symptoms involve changes in feeling, such as persistent numbness (anesthesia) or an uncomfortable pins-and-needles sensation (paresthesia). Patients may also experience sharp, shooting pain that feels like an electric shock, or a deep burning sensation that radiates down the leg and into the foot. These sensations typically follow the path of the affected nerve.
Motor symptoms involve a loss of muscle control. The most recognized motor symptom is foot drop, which is the inability to lift the front part of the foot or the toes. This occurs because the common peroneal division of the sciatic nerve, which controls the muscles that pull the foot upward, has been compromised. Foot drop causes a person to drag their toes while walking, often necessitating a high-stepping gait to clear the ground.
Injury to the femoral nerve, a less common occurrence, results in weakness in the quadriceps muscle. This motor deficit makes it difficult to straighten the knee and can cause the leg to feel unstable or prone to buckling. Any progressive or severe motor weakness, such as an inability to move the foot or straighten the knee, requires immediate medical evaluation. The location of the sensory changes combined with the specific muscles affected helps medical professionals pinpoint the site of the nerve injury.
Differentiating Post-Surgical Sensations
It is normal to experience localized changes in sensation immediately following hip replacement surgery. Transient numbness or a dull ache near the incision site is a common finding. This localized loss of feeling results from the minor disruption of superficial sensory nerves during the surgical approach, a mild injury called neuropraxia that usually resolves on its own. These disturbances typically fade within a few weeks and often resolve completely within three months.
Temporary sensation changes involving the lateral femoral cutaneous nerve (LFCN) are common, especially after an anterior approach. Injury to this nerve causes numbness or tingling over the outer thigh. Because the LFCN is purely sensory, this numbness does not affect muscle strength or movement and is not considered a sign of a major motor nerve complication. True warning signs involve symptoms that are severe, rapidly worsening, or extend significantly beyond the thigh.
Any symptom that affects motor function, such as difficulty lifting the foot, should never be dismissed as a normal part of recovery. Furthermore, pain that is unremitting, sharp, or feels like an intense burning or electrical discharge suggests irritation or damage to a larger nerve. While some discomfort is expected, persistent or progressive symptoms involving loss of movement or control are considered red flags that require prompt attention from the surgical team.
Common Causes and Affected Nerves
The sciatic nerve is the most frequently injured nerve during total hip replacement, with an incidence of palsy around 1% to 3% in primary procedures. Running directly behind the hip joint, the nerve is vulnerable to mechanical forces. The peroneal division is particularly susceptible, which is why foot drop is the most common motor manifestation of nerve injury after THR.
Nerve injury mechanisms fall into three main types. The most common is traction, or excessive stretching, which occurs when the surgeon lengthens the leg to ensure joint stability. Compression is another cause, resulting from prolonged use of surgical retractors, a postoperative blood clot (hematoma), or the extrusion of bone cement pressing directly on the nerve. Direct trauma, such as a laceration from an instrument or thermal injury, is a less common but more severe cause of nerve damage.
The femoral nerve, which controls the quadriceps muscle, is also at risk, particularly during an anterior or anterolateral approach, though its injury rate is lower than that of the sciatic nerve. Injury often occurs due to compression from retractors used to expose the hip joint or from direct trauma in revision surgeries.
Diagnosis, Treatment, and Recovery Outlook
If severe or progressive symptoms of nerve damage appear, patients should immediately contact their orthopedic surgeon for evaluation. Early assessment is crucial to determine if the nerve is under continuous pressure from a correctable cause, such as a large hematoma or misplaced surgical component. A comprehensive neurological examination maps the areas of sensory loss and muscle weakness.
To confirm the diagnosis and assess damage extent, specialized tests like nerve conduction studies (NCS) and electromyography (EMG) are used. These tests measure the electrical activity of the nerve and muscle, differentiating between a mild stretching injury and a more serious structural disruption. The treatment approach is determined by the severity of the injury identified.
For most mild injuries, treatment begins with observation and supportive care, including physical therapy to maintain muscle function and medications to manage neuropathic pain. Physical therapy is a primary component of recovery, aiming to retrain muscles and improve mobility. The majority of nerve injuries after hip replacement are temporary, with recovery beginning within weeks to months and often resolving fully within six months to a year. In rare cases where recovery is incomplete or a mechanical compression persists, surgical intervention may be necessary to decompress the nerve or, in long-standing foot drop, to perform a tendon transfer to restore some function.