What are the possible causes of left popliteal (posterior knee) pain?

Causes of Left Popliteal Pain

Left popliteal pain has multiple potential etiologies that must be systematically evaluated, with vascular causes (popliteal artery aneurysm, deep vein thrombosis, popliteal artery entrapment syndrome) representing the most immediately life- and limb-threatening conditions requiring urgent imaging. 1

Vascular Causes (Highest Priority - Limb-Threatening)

Popliteal Artery Aneurysm

• Most critical diagnosis to exclude: Popliteal aneurysms ≥2.0 cm require surgical repair to prevent thromboembolic complications and limb loss, with 36-70% risk of complications over 5-10 years if left untreated. 2
• Approximately 50% of popliteal aneurysms are bilateral, and 50% have associated abdominal aortic aneurysm. 2, 1
• Presents with absent or diminished pedal pulses (dorsalis pedis, posterior tibial arteries) and may cause acute limb ischemia. 3, 1
• Urgent duplex ultrasonography is the first-line diagnostic test to confirm or exclude this diagnosis. 2, 1

Deep Vein Thrombosis (DVT)

• Can present with sudden popliteal pain and clinically mimic Baker's cyst rupture. 3, 1
• Duplex ultrasonography is the first-line test, and therapeutic anticoagulation should be initiated immediately if proximal DVT is visualized without waiting for confirmatory tests. 1

Popliteal Artery Entrapment Syndrome (PAES)

• Most common cause of surgically correctable lower-extremity vascular insufficiency in young adults. 3
• Presents with calf claudication, paresthesia, and swelling during exercise, with pain relief at rest. 3, 4
• Physical examination shows absence of blood flow in posterior tibial and dorsalis pedis arteries during dorsiflexion and plantar flexion maneuvers. 4
• Predominantly affects males (up to 85%), mean age 28 years, bilateral in 25% of cases. 5
• Surgical decompression should be performed immediately upon diagnosis to prevent progressive arterial wall degeneration. 1

Popliteal Artery Dissection

• Rare cause in athletes, can occur during strenuous exercise (e.g., squatting), presenting with transient acute limb ischemia. 6
• Clinical findings can mimic popliteal entrapment syndrome. 6

Musculoskeletal/Rheumatologic Causes

Baker's Cyst (Popliteal Cyst)

• Fluid accumulation in the bursa of gastrocnemius or semimembranosus muscles, frequently communicating with the joint space. 3
• Diagnosed by visualizing comma-shaped extension between medial head of gastrocnemius and semimembranosus tendon on ultrasound. 3, 1
• Rupture clinically mimics DVT and requires differentiation via ultrasound. 3, 1
• Often associated with knee arthritis history. 1

Popliteus Tendon Ganglion

• Rare cause of deep posterior knee pain. 7
• May require MRI for diagnosis and surgical excision for symptom relief. 7

Hamstring Tendinitis

• Common cause of posterior knee pain, distinguished by tenderness over hamstring insertion sites. 3

Neurologic Causes

Nerve Root Compression/Spinal Stenosis

• Radiating sharp lancinating pain down leg, often bilateral buttocks and posterior leg. 3
• Induced by sitting, standing, or walking; worse with lumbar spine extension, relieved by flexion. 3
• History of back problems is typical. 3

Common Peroneal Nerve Irritation

• Less common cause of posterolateral knee pain. 7

Other Differential Diagnoses

Chronic Compartment Syndrome

• Tight, bursting calf pain after strenuous exercise (jogging), subsides very slowly with rest. 3
• Typically affects heavy-muscled athletes. 3

Venous Claudication

• Entire leg pain (worse in calf), tight bursting quality after walking, subsides slowly. 3
• History of iliofemoral DVT, edema, signs of venous stasis. 3
• Relief speeded by leg elevation. 3

Diagnostic Algorithm

1. Immediate vascular assessment: Check femoral, popliteal, dorsalis pedis, and posterior tibial pulses bilaterally. 3
2. Urgent duplex ultrasonography if any of the following: absent/diminished pulses, sudden onset pain, signs of acute ischemia, or suspicion of DVT. 2, 1
3. Measure ankle-brachial index (ABI): ABI ≤0.90 confirms peripheral artery disease. 2
4. Provocative maneuvers: Assess pulses during dorsiflexion/plantar flexion to evaluate for PAES. 4
5. MRI or CTA if ultrasound inconclusive or to further characterize vascular anatomy before surgical intervention. 2, 4

Critical Pitfalls to Avoid

• Never assume musculoskeletal etiology without excluding vascular causes first - popliteal aneurysm thrombosis and PAES can cause permanent limb loss if diagnosis is delayed. 2, 1
• Always examine the contralateral leg - 50% of popliteal aneurysms and 25% of PAES cases are bilateral. 2, 5
• Do not confuse Baker's cyst rupture with DVT - both require ultrasound differentiation as management differs completely. 3, 1
• Young athletic patients with exertional symptoms warrant high suspicion for PAES - this is the most common surgically correctable vascular cause in this population. 3, 5