Total Knee Arthroplasty (TKA), or total knee replacement, is a highly successful orthopedic procedure performed to relieve pain and restore function in damaged knee joints. While generally safe, TKA carries a small risk of complications, including injury to the nerves surrounding the knee. Nerve damage refers to an adverse effect on a nerve’s function, potentially leading to altered sensation or impaired muscle control in the lower leg and foot.
Incidence and Severity
The risk of experiencing a major nerve injury following TKA is quite low, with the overall incidence typically reported in the range of 0.12% to 0.4% of all procedures. This low rate primarily reflects motor nerve injuries, which result in functional deficits like muscle weakness.
The majority of nerve issues that do occur are classified as transient, meaning they are temporary and often resolve spontaneously over time. This temporary damage, known as neuropraxia, involves injury to the myelin sheath—the protective covering of the nerve—while the core axon remains intact. For the less common, more severe palsies, about 39% of complete cases see a full recovery, while 56% achieve partial recovery over time.
In contrast to the low incidence of major motor nerve injury, damage to the superficial sensory nerves is significantly more common, with reported rates ranging from 0.5% to as high as 53%. This disparity exists because the standard surgical incision often crosses the path of these very fine sensory branches. While a high percentage of patients may experience temporary or permanent altered sensation, the development of chronic, painful nerve symptoms (neuralgia) remains much less frequent, affecting up to 18% of patients in some studies.
Identifying Affected Nerves and Symptoms
The nerve most frequently affected by motor dysfunction after TKA is the common peroneal nerve, a branch of the larger sciatic nerve. Injury to this nerve typically results in common peroneal nerve palsy, manifesting as “foot drop”—the inability to actively lift the front part of the foot and toes, causing a characteristic dragging gait.
Sensory loss from common peroneal nerve injury is felt along the outer portion of the lower leg and the top surface of the foot. The sciatic nerve itself is the second most common major nerve affected, though far less frequently than the peroneal nerve. Sciatic nerve injury can result in more widespread weakness and sensory changes throughout the entire leg and foot.
The most common sensory nerve affected is the saphenous nerve, specifically its infrapatellar branch. This nerve provides sensation to the skin over the front and inner side of the knee and shin. Damage often occurs because the surgical incision directly intersects this nerve, leading to symptoms like numbness, tingling, or a burning sensation in the distribution of the nerve. In some cases, the severed nerve ending can form a painful mass called a neuroma, leading to persistent, localized pain on the inner aspect of the knee.
Mechanisms of Injury and Risk Factors
Nerve damage can arise from several intraoperative mechanisms. The nerve may suffer a stretch injury, a common cause, particularly when the surgeon corrects a pre-existing severe angular deformity of the knee, such as a substantial valgus (knock-kneed) alignment. This rapid correction can place excessive tension on the peroneal nerve as it wraps around the fibular head.
Direct trauma is another mechanism, including laceration or contusion from surgical instruments, or thermal damage caused by the heat generated from the setting of bone cement. Compression of the nerve can occur from a large hematoma (blood clot) forming postoperatively near the nerve pathway, or from prolonged use of a pneumatic tourniquet to restrict blood flow during the procedure.
Revision surgeries, which involve replacing a previously implanted joint, carry a significantly higher risk than primary TKA. Patients with pre-existing conditions like diabetes or lumbar spine pathology are also at an elevated risk of developing a postoperative neuropathy.
Diagnosis and Management
When nerve damage is suspected following TKA, a thorough clinical examination is the first step, assessing both motor function and sensory deficits. Electromyography (EMG) and Nerve Conduction Studies (NCS) are the gold standard diagnostic tools, providing electrical measurements of nerve and muscle function to pinpoint the location and severity of the damage.
The initial management approach is almost always conservative, especially for transient injuries. This involves careful observation, supportive care, and physical therapy to maintain muscle strength and joint mobility while the nerve heals. For patients with foot drop, a supportive brace, such as an Ankle-Foot Orthosis (AFO), may be prescribed to prevent falls and assist with walking.
Most temporary nerve injuries show signs of recovery within weeks to months, with function typically returning fully or near-fully within one year. If there are no signs of recovery after a defined period, or if the initial injury is determined to be severe (axonotmesis or neurotmesis), surgical intervention may be considered. Surgical options include nerve decompression to relieve pressure or, in rare cases of complete nerve transection, direct nerve repair or grafting.