What could be causing pain in the muscles and joints of the right lower extremity in an otherwise healthy adult?

Differential Diagnosis and Evaluation of Right Lower Extremity Muscle and Joint Pain

The most critical first step is to distinguish vascular claudication from musculoskeletal and neurogenic causes through ankle-brachial index (ABI) measurement, as peripheral arterial disease (PAD) can masquerade as musculoskeletal pain and carries significant morbidity and mortality risk if missed. 1, 2

Initial Clinical Assessment

Key Historical Features to Elicit

Pain characteristics that differentiate etiologies:

• Vascular claudication: Pain occurs predictably with walking a specific distance and resolves within 10 minutes of simple rest 1
• Hip arthritis: Aching discomfort in lateral hip/thigh after variable exercise, improved when not bearing weight, with history of degenerative arthritis 1
• Radiculopathy: Sharp lancinating pain radiating down specific dermatomal distributions, worse with sitting, relieved when supine or standing 1
• Muscle strain: Acute pain during strenuous activity in muscles crossing two joints 3

Physical Examination Priorities

Vascular assessment is mandatory 1:

• Palpate femoral, popliteal, dorsalis pedis, and posterior tibial pulses (rated 0-3)
• Presence of all four lower extremity pulses bilaterally makes PAD unlikely 1
• Evaluate for femoral bruits, elevation pallor/dependent rubor, asymmetric hair growth, calf muscle atrophy 1

Musculoskeletal examination 4:

• Hip range of motion and provocative tests (FABER, FADIR) to exclude intra-articular hip pathology 5
• Palpation for focal muscle tenderness suggesting strain 3
• Dermatomal sensory testing to identify radiculopathy patterns 5

Diagnostic Algorithm

Step 1: Obtain Ankle-Brachial Index (ABI)

ABI measurement is the critical first diagnostic test 1, 6:

• ABI ≤0.90 confirms PAD and requires immediate cardiovascular risk factor modification 1
• ABI 0.91-1.30 (normal) suggests neurogenic or musculoskeletal etiology 6
• ABI >1.30 suggests arterial calcification; obtain toe-brachial index or pulse volume recording 1

Step 2: Initial Imaging Based on ABI Results

If ABI is normal (musculoskeletal/neurogenic suspected) 1:

• Plain radiographs of affected joint are the initial imaging method (rated 9/9 "usually appropriate") 1
• Radiographs may reveal arthritis, fracture, or soft tissue calcification 1

If radiculopathy suspected with normal radiographs 5:

• Lumbar spine MRI without contrast is first-line for nerve root compression 5
• Provides superior visualization of disc herniation and foraminal stenosis 5

If PAD confirmed (ABI ≤0.90) 1:

• CTA or MRA required to determine extent of disease and plan revascularization 1
• CTA is fast and reveals exact nature and level of stenosis 1

Common Causes by Category

Vascular Causes

• Peripheral arterial disease: Most critical to identify due to mortality implications 1
• Acute arterial thrombosis or embolism (sudden onset, diminished pulses) 1

Musculoskeletal Causes

• Hip osteoarthritis: Lateral hip/thigh aching, worse with weight-bearing 1
• Muscle strain: Acute pain during eccentric contraction, involves muscles crossing two joints 3
• Inflammatory arthritis: Requires x-ray initially, then MRI or ultrasound for confirmation 1

Neurogenic Causes

• Lumbar radiculopathy: Sharp pain in dermatomal distribution, worse with specific positions 1, 5
• Spinal stenosis: Bilateral symptoms (though can be unilateral), worse with standing/extension 1, 6

Critical Pitfalls to Avoid

Do not assume musculoskeletal etiology without ABI testing 6, 2:

• PAD frequently masquerades as sciatica or musculoskeletal pain 2
• Concurrent conditions can coexist, with musculoskeletal pain masking underlying PAD 7
• Failure to screen for PAD risks severe disability and permanent sequelae 2

Do not over-rely on advanced imaging without clinical correlation 4:

• Asymptomatic spinal pathology on MRI can lead to incorrect diagnosis 4
• Physical examination findings must correlate with imaging abnormalities 4

Do not overlook recent surgery as a cause 8:

• 43% of complex limb pain patients had prior surgery 8
• Consider implant failure or infection in patients with prior arthroplasty 4

Management Based on Diagnosis

If PAD Confirmed (ABI ≤0.90)

Immediate cardiovascular risk reduction is essential 1:

• Smoking cessation (mandatory)
• Antiplatelet therapy (aspirin or clopidogrel)
• High-intensity statin therapy
• Blood pressure control
• Diabetes management

Revascularization considerations 1:

• Patients with iliac lesions may proceed to revascularization without extensive medical therapy trial 1
• Refer to vascular surgery if critical limb ischemia develops 6

If Musculoskeletal Cause Identified

Conservative management first-line 6, 3:

• Activity modification and physical therapy 5, 3
• NSAIDs for pain control 5, 3
• Rest, ice, compression for acute muscle strain 3
• Monitor for 6-12 weeks unless red flags present 5

If Radiculopathy Confirmed

Conservative management initially 5:

• Physical therapy to restore flexibility and strength 3
• NSAIDs for pain control 5
• Consider epidural steroid injection if conservative management fails after 6-12 weeks 5
• Neurosurgical referral for progressive neurologic deficit 5