Total knee replacement (TKR) is a surgical procedure designed to alleviate severe knee pain and improve joint function. It involves replacing damaged portions of the knee joint with artificial components, typically made of metal and plastic. The primary goal of TKR is to provide pain relief and restore mobility for individuals suffering from conditions like severe arthritis. While generally successful, some individuals may wonder about potential complications, such as nerve damage.
Understanding Neuropathy
Neuropathy refers to damage or dysfunction of one or more nerves outside the brain and spinal cord, which constitute the peripheral nervous system. These nerves transmit signals between the central nervous system and the rest of the body, serving sensory, motor, and autonomic functions. Sensory nerves carry information about touch, temperature, and pain. Motor nerves control muscle movement, while autonomic nerves regulate involuntary bodily functions like digestion and heart rate. When damaged, their ability to send or receive signals can be impaired, leading to various symptoms.
How Knee Replacement Can Lead to Neuropathy
Knee replacement surgery can sometimes result in nerve damage due to several mechanisms. Direct nerve injury can occur if nerves are cut or stretched by surgical instruments or during tissue manipulation to access the joint. Extensive soft tissue dissection to implant prosthetic components can also affect nearby nerve pathways.
Compression of nerves is another cause. Postoperative swelling, blood clots, or the artificial knee components themselves can press on adjacent nerves, disrupting nerve function. The common peroneal nerve, which wraps around the outside of the knee, is particularly vulnerable to compression or stretching, especially when correcting severe deformities.
Reduced blood flow to nerves (ischemia) can also contribute to damage. A tourniquet, used to minimize blood loss, can temporarily restrict blood supply to nerves if used for too long or with excessive pressure. Scar tissue formation during healing can also entrap or compress nerves around the surgical site.
The saphenous nerve and its infrapatellar branch are often affected due to their superficial location within the surgical field. Incisions can sever the infrapatellar saphenous nerve, leading to numbness or altered sensation. While this may not affect mechanical function, it can cause persistent sensory issues or a painful neuroma. The incidence of nerve injury after TKR is low (0.12% to 0.4%), with the common peroneal nerve most frequently affected.
Recognizing Symptoms and Diagnosis
Symptoms of neuropathy after knee replacement vary depending on the specific nerves affected and the extent of the damage. Sensory symptoms are common and may include numbness, tingling, a burning sensation, or sharp, shooting pain in the knee, lower leg, or foot. Some individuals might experience hypersensitivity to touch or reduced sensation in the affected area.
Motor symptoms can also manifest, such as muscle weakness, difficulty moving the foot or toes, or a condition known as “foot drop,” where an individual struggles to lift the front part of the foot. These symptoms can appear immediately after surgery or develop gradually during the recovery period. While some mild symptoms might be temporary, others can be persistent. If new or worsening symptoms develop, contacting the surgical team or a doctor is important.
Diagnosing neuropathy typically begins with a thorough physical examination where a healthcare provider assesses sensation, muscle strength, and reflexes. To confirm nerve damage and determine its severity, specialized tests may be performed. Nerve conduction studies (NCS) measure how quickly and efficiently electrical signals travel along nerves. Electromyography (EMG) assesses the electrical activity of muscles in response to nerve stimulation, which can help pinpoint the location and nature of nerve injury.
Treatment and Management
Treatment for neuropathy following knee replacement focuses on managing symptoms and promoting nerve recovery. Conservative approaches are typically the first line of management.
Physical therapy helps regain strength and mobility, often using nerve gliding exercises. Assistive devices, like an ankle-foot orthosis (AFO), may support the foot in cases of foot drop.
Pain management includes medications such as non-steroidal anti-inflammatory drugs (NSAIDs) or specific neuropathic pain medications like gabapentinoids or antidepressants. Localized treatments like lidocaine patches or capsaicin creams can provide targeted relief. Nerve blocks, involving injecting an anesthetic near the affected nerve, may also be used.
Many mild cases of neuropathy may resolve over time as initial swelling subsides and nerves have an opportunity to heal. This recovery can be gradual, sometimes taking several months.
Surgical intervention is less common but considered in rare, severe instances where conservative measures are insufficient, especially if a nerve is significantly compressed or entrapped. Nerve decompression procedures aim to relieve pressure. Prognosis varies with nerve damage type and severity, but many patients experience some recovery.