What is the best approach to evaluate posterior leg pain in an adult patient with no significant medical history?

Evaluation of Posterior Leg Pain

Begin immediately with a focused vascular assessment including ankle-brachial index (ABI) measurement to establish or exclude peripheral artery disease, as this represents the most critical life-threatening cause requiring immediate identification. 1, 2

Initial Vascular Assessment (Priority #1)

Perform resting ABI with or without segmental pressures and waveforms as the initial test for all patients with suspected PAD. 1, 2 This takes precedence over all other diagnostic considerations because:

• Patients ≥65 years, or age 50-64 with diabetes, smoking, dyslipidemia, hypertension, chronic kidney disease, or family history of PAD mandate immediate vascular evaluation 1, 2
• ABI ≤0.90 confirms PAD; 0.91-0.99 is borderline; 1.00-1.40 is normal; >1.40 indicates noncompressible arteries 2
• If ABI >1.40, measure toe-brachial index (TBI) as ABI is unreliable in this population 1, 2
• In diabetic patients and those with chronic kidney disease, do not rely on pulse examination or ABI alone due to high incidence of noncompressible arteries 1, 2

Physical Examination for Vascular Disease

• Palpate femoral, popliteal, dorsalis pedis, and posterior tibial pulses bilaterally, rating as 0 (absent), 1 (diminished), 2 (normal), or 3 (bounding) 2
• Auscultate for femoral bruits 2
• Inspect for nonhealing wounds, gangrene, asymmetric hair growth, nail bed changes, calf muscle atrophy, or elevation pallor/dependent rubor 2
• Recognize that diabetic neuropathy can mask critical limb ischemia—always inspect for wounds in diabetic or arterial disease patients 1

Pain Pattern Characterization

After establishing vascular status, determine the specific pain pattern:

Vascular Claudication

• Pain occurs predictably with walking a certain distance and resolves within 10 minutes of rest 2
• May present as bilateral buttock and posterior thigh pain 2

Achilles Tendinopathy

• Posterior heel pain proximal to tendon insertion 3
• Physical examination reveals thickening and tender, palpable nodules 3
• Higher incidence in adult runners with increasing age 3
• Etiology is multifactorial: improper technique, anatomic misalignment, weakness, uneven training surfaces, improperly fitted footwear 3

Deep Posterior Compartment Syndrome

• Pain, tightness, and cramps deep in the calf muscles elicited by exercise 4
• Painful palpation of flexor muscles immediately dorsomedial to the tibial bone 4
• Characterized by pain, plantar hypesthesia, weakness of toe flexion, pain on passive toe extension, and tenseness of fascia between tibia and triceps surae in distal medial leg 5

Sacroiliac Joint Disorders

• Pain and numbness/tingling in lateral to posterior thigh and back of calf 6
• Symptoms do not correspond to dermatome distribution 6
• Pain at or around posterior-superior iliac spine (PSIS) present in 94% of cases 6

Imaging Strategy

Initial Imaging

Radiography is the first imaging study for posterior leg pain of unknown etiology. 3 Conventional radiography distinguishes among different causes and should precede advanced imaging 3.

Advanced Imaging When Radiographs Are Normal

MRI without IV contrast should be ordered when:

• Tendon abnormality is suspected (Achilles tendinopathy) 3
• Pain persists with uncertain etiology after normal radiographs 3
• Concern for occult fracture or osseous stress injury 3
• MRI globally evaluates all anatomic structures including bone marrow, ligaments, tendons, and cartilage 3, 1

Ultrasound is appropriate for:

• Focal soft-tissue abnormalities 3, 7
• Tendon evaluation with dynamic assessment 3, 7
• Real-time assessment with good cost-effectiveness and patient tolerance 7

Compartment Syndrome Diagnosis

• Intracompartmental pressure testing confirms deep posterior chronic exertional compartment syndrome 4

Emergency Red Flags

Patients at risk for critical limb ischemia (ABI <0.4 in non-diabetic, or any diabetic with known PAD) who develop acute limb symptoms—pain, pallor, pulselessness, poikilothermia, paresthesias, or paralysis—represent vascular emergencies requiring immediate vascular specialist consultation. 1, 2

Functional Assessment

Document objective functional capacity including:

• Walking distance before pain onset 1
• Use of assistive devices 1
• Ability to perform activities of daily living 1
• Impact on social participation and general physical fitness 1
• Disability extent, psychological factors, sleep problems, and obesity as contributing factors 1

Treatment Considerations for Common Causes

Achilles Tendinopathy

• Eccentric strength training is particularly effective 3
• Stretching and deep friction massage of gastrocnemius-soleus complex 3
• Shoe orthotics to correct overpronation or pes planus 3
• Heel lift orthotics to unload the tendon for pain relief 3

Deep Posterior Compartment Syndrome

• Fasciotomy of multiple flexor muscles is the only treatment achieving beneficial outcomes 4
• Decompression within 12 hours of onset prevents permanent sequelae 5