Total Knee Replacement: Nerve Damage Symptoms, Affected Nerves, and Management

What are the symptoms of nerve damage after total knee replacement?

Nerve damage after total knee replacement (TKR) is a rare but possible complication, typically presenting as persistent numbness, tingling (paresthesia), burning pain, or muscle weakness in the lower leg or foot, often immediately or shortly after surgery.

Introduction to Nerve Damage Post-TKR

Total knee replacement (TKR) is a highly successful surgical procedure designed to alleviate pain and restore function in individuals with severe knee arthritis. While generally safe, like any major surgery, it carries potential risks, including injury to surrounding nerves. The intricate anatomy of the knee involves several critical nerves that are in close proximity to the surgical field. These nerves can be susceptible to injury through direct trauma, stretching, compression from swelling or hematoma, or even thermal injury during the procedure. Understanding the symptoms of nerve damage is crucial for early detection and intervention, which can significantly impact recovery and long-term outcomes.

Common Nerves Affected and Their Symptoms

Several nerves around the knee can be affected during TKR, each presenting with distinct symptom profiles based on their sensory and motor functions.

Peroneal Nerve (Common Fibular Nerve)

The peroneal nerve, a branch of the sciatic nerve, is the most commonly injured nerve during TKR due to its superficial course around the fibular head.

• Foot drop: The hallmark symptom, characterized by difficulty lifting the front part of the foot (dorsiflexion) and/or turning the sole of the foot outwards (eversion). This can cause the foot to drag on the ground when walking.
• Numbness or altered sensation: Typically experienced on the top (dorsum) of the foot and the outer (lateral) aspect of the lower leg.
• Weakness: Difficulty with ankle dorsiflexion and eversion.

Tibial Nerve

The tibial nerve, also a branch of the sciatic nerve, is less commonly injured than the peroneal nerve but can lead to significant functional deficits.

• Numbness or altered sensation: Primarily affects the sole of the foot and the toes.
• Weakness: Difficulty with ankle plantarflexion (pointing the foot down), inversion (turning the sole inwards), and toe flexion. This can impact pushing off during walking.

Saphenous Nerve

The saphenous nerve is a purely sensory nerve, a branch of the femoral nerve, that runs along the medial side of the knee.

• Numbness or altered sensation: Experienced along the inner (medial) aspect of the lower leg and sometimes around the inner knee incision site. There is typically no motor weakness associated with saphenous nerve injury.

Femoral Nerve

Injury to the femoral nerve is rare but can be serious, as it innervates the powerful quadriceps muscles.

• Weakness or paralysis of the quadriceps: Difficulty or inability to straighten the knee, leading to instability and difficulty with weight-bearing activities.
• Numbness or altered sensation: Affects the front (anterior) part of the thigh and potentially the inner aspect of the lower leg (via the saphenous nerve branch).

General Symptoms of Nerve Damage

Regardless of the specific nerve involved, several overarching symptoms can indicate nerve compromise after TKR:

• Persistent or Worsening Pain: Neuropathic pain is often described as burning, shooting, electric shock-like, or sharp, and it may not respond well to typical post-surgical pain medications. This pain can be distinct from the incisional pain.
• Numbness or Altered Sensation (Paresthesia): A feeling of pins and needles, tingling, prickling, or a complete loss of sensation in a specific distribution corresponding to the affected nerve's sensory territory.
• Muscle Weakness or Paralysis: Difficulty moving certain parts of the foot, ankle, or knee, or a noticeable decrease in strength that was not present before or immediately after surgery. This can range from mild weakness to complete inability to move a muscle group.
• Difficulty with Balance or Gait: Due to muscle weakness (e.g., foot drop) or altered sensation, an individual may experience instability, stumbling, or changes in their walking pattern.
• Hypersensitivity: An increased sensitivity to light touch or pressure in the affected area, where even gentle contact can cause significant discomfort (allodynia).

When to Seek Medical Attention

It is critical to communicate any new or worsening symptoms to your surgical team promptly. While some transient numbness or altered sensation around the incision site is common and often resolves, persistent or progressive symptoms suggestive of nerve damage warrant immediate evaluation. Do not delay reporting symptoms such as:

• New or worsening foot drop.
• Significant, unexplained weakness in your leg or foot.
• Persistent, severe burning, shooting, or electric shock-like pain.
• Expanding areas of numbness or tingling.

Early diagnosis allows for timely intervention, which can range from observation and physical therapy to medical management or, in rare cases, surgical exploration.

Diagnosis and Treatment

Diagnosis typically involves a thorough clinical examination, assessing sensation, muscle strength, and reflexes. Your surgeon may order diagnostic tests such as:

• Electromyography (EMG) and Nerve Conduction Studies (NCS): These tests measure the electrical activity of muscles and the speed of electrical impulses through nerves, helping to pinpoint the location and severity of nerve damage.
• Imaging studies: MRI or CT scans may be used to rule out other causes of symptoms, such as hematoma or prosthesis impingement on a nerve.

Treatment for nerve damage post-TKR depends on the cause and severity. Many cases of mild nerve irritation or stretch injury improve spontaneously over weeks to months. Management strategies may include:

• Observation: For mild, improving symptoms.
• Medication: Neuropathic pain medications (e.g., gabapentin, pregabalin, tricyclic antidepressants) to manage pain.
• Physical Therapy: To maintain range of motion, strengthen muscles, and improve function, often including gait training and assistive devices (e.g., ankle-foot orthosis for foot drop).
• Nerve Blocks: For temporary pain relief.
• Surgical Intervention: In rare cases of confirmed nerve compression or transection, surgical exploration and repair may be considered, though this is uncommon.

Conclusion

While nerve damage after total knee replacement is infrequent, being aware of its potential symptoms is vital for patients and healthcare providers alike. Persistent or new onset of numbness, tingling, burning pain, or muscle weakness in the lower leg or foot following TKR should always prompt immediate communication with your medical team. Prompt evaluation and diagnosis are key to optimizing outcomes, facilitating appropriate management, and ensuring the best possible recovery from your knee replacement surgery.