G57.31

Lesion of lateral popliteal nerve, right lower limb

Lesion of the lateral popliteal nerve, also commonly referred to as the common peroneal nerve, involves damage or compression of the nerve as it branches from the sciatic nerve and travels around the head of the fibula in the right lower limb. This nerve is particularly vulnerable to external pressure and trauma because of its superficial location where it wraps around the neck of the fibula. Damage to this nerve disrupts motor control to the muscles responsible for dorsiflexion and eversion of the foot, as well as toe extension. Additionally, it impairs sensation along the lateral aspect of the lower leg and the dorsal surface of the foot. Clinical evaluation typically reveals 'foot drop,' a significant neurological deficit where the patient is unable to lift the front part of the foot, resulting in a characteristic gait. Proper diagnosis often requires electromyography (EMG) and nerve conduction studies (NCS) to distinguish this localized mononeuropathy from more proximal sciatic nerve lesions or L5 radiculopathy.

Clinical Symptoms

  • Foot drop (inability to dorsiflex the right ankle)
  • Weakness in toe extension
  • Weakness in foot eversion
  • Steppage gait (lifting the knee higher than normal to prevent toes from dragging)
  • Foot slapping during the loading response of the gait cycle
  • Numbness or paresthesia along the lateral lower leg
  • Sensory loss on the dorsal surface of the right foot and the first interdigital space
  • Pain at the site of compression near the fibular head
  • Muscle wasting of the anterior and lateral compartments of the right leg (chronic cases)

Common Causes

  • Prolonged external compression at the fibular head (e.g., crossing legs for long periods)
  • Trauma or direct impact to the lateral aspect of the right knee
  • Fracture of the right fibular neck
  • Knee dislocations
  • Iatrogenic injury during orthopedic surgeries, such as total knee replacement
  • Improper positioning during long surgical procedures (e.g., lithotomy or lateral decubitus)
  • Tight casts, braces, or knee wraps applied to the right leg
  • Ganglion cysts or synovial cysts originating from the proximal tibiofibular joint
  • Rapid significant weight loss causing loss of protective fat around the fibular head
  • Complications of diabetes mellitus (diabetic mononeuropathy)

Documentation & Coding Tips

Explicitly identify the anatomical location of the compression or lesion to differentiate from more proximal sciatic nerve issues or more distal peroneal branches.

Example: Assessment: Right lateral popliteal nerve lesion localized to the fibular head. Patient exhibits classic foot drop and sensory deficit in the right first dorsal webspace. No evidence of sciatic notch tenderness. Billing Focus: Right laterality and specific nerve segment documented. Risk Adjustment: Chronic neurological deficit documented as a persistent condition requiring ongoing orthotic management.

Billing Focus: Documentation must specify the right lower limb and the lateral popliteal (common peroneal) nerve to support G57.31.

Distinguish between traumatic and non-traumatic etiology, as traumatic injuries may require coding from the S84 series.

Example: Diagnosis: Non-traumatic lesion of the right lateral popliteal nerve. Onset was gradual, likely secondary to prolonged habit of crossing legs during work. No history of acute fracture or blunt force trauma to the knee. Billing Focus: Use G57.31 for non-traumatic or chronic compression. Risk Adjustment: Differentiates from acute injury codes which may have different payment parameters and follow-up requirements.

Billing Focus: Specifying non-traumatic etiology ensures the use of the G series (mononeuropathies) rather than S series (injuries).

Document associated functional deficits such as foot drop or gait instability to support medical necessity for orthotics or physical therapy.

Example: The patient presents with right lateral popliteal nerve lesion (G57.31) manifested by right foot drop (M21.361) and steppage gait. Prescribed a custom right-sided ankle-foot orthosis (AFO) to improve safety and prevent falls. Billing Focus: Co-occurrence of foot drop provides specificity for functional impact. Risk Adjustment: Gait instability and fall risk are significant factors in patient complexity scoring.

Billing Focus: Laterality of both the nerve lesion and the resulting foot drop must be consistent (Right).

Include relevant physical exam findings such as Tinels sign at the fibular head and motor strength grading for dorsiflexion and eversion.

Example: Physical Exam: Positive Tinel sign at the right fibular head. Muscle strength: Right ankle dorsiflexion 2/5, eversion 2/5, hallux extension 1/5. Sensation decreased over the lateral right calf. Diagnosis: Right lateral popliteal nerve lesion. Billing Focus: Objective findings support the clinical validity of the diagnosis code. Risk Adjustment: Detailed motor deficits provide evidence of condition severity.

Billing Focus: Clinical findings validate the diagnosis and protect against audits regarding medical necessity for diagnostic testing.

Note any contributing factors such as rapid weight loss, diabetes, or external compression sources like casts or knee braces.

Example: Diagnosis: Right lateral popliteal nerve lesion due to external compression from a knee immobilizer. Patient also has Type 2 Diabetes Mellitus with neuropathy (E11.40). Billing Focus: Identification of external cause. Risk Adjustment: Presence of diabetes mellitus as a comorbidity increases the risk of non-recovery and complicates management.

Billing Focus: Identifying the cause (e.g., cast compression) helps in determining if the code is primary or secondary to another condition.

Relevant CPT Codes

Related Diagnoses

Hierarchy