How should I evaluate and manage a patient with left knee pain and a normal knee MRI, without hip symptoms, considering possible referred pain sources?

Evaluation and Management of Referred Left Knee Pain with Normal Knee MRI

When knee pain persists despite a normal knee MRI and no hip symptoms, you must systematically evaluate the hip and lumbar spine as the most likely sources of referred pain, beginning with plain radiographs of the pelvis/proximal femur before considering any additional knee imaging. 1, 2

Immediate Next Steps: Hip Evaluation

Even without overt hip symptoms, hip pathology is the most common source of referred knee pain when knee imaging is normal. 1, 2

• Order pelvis and proximal femur radiographs immediately – A combined pelvis and proximal femur view is superior to isolated hip films for detecting developmental dysplasia, femoroacetabular impingement, and early hip arthritis. 1, 2
• Specifically assess for groin pain and hip range of motion – Hip pathology can refer to the knee even when patients do not spontaneously report hip symptoms; directly inquire about groin discomfort and test hip internal/external rotation. 1, 2
• If hip radiographs show abnormalities or clinical suspicion remains high, proceed to hip MRI without contrast to evaluate for labral tears, cartilage defects, or soft tissue pathology (abductor tendinosis, iliopsoas bursitis). 1

Secondary Evaluation: Lumbar Spine Assessment

• Screen for lumbar radiculopathy – Ask specifically about low-back pain, buttock pain, or any radicular symptoms extending from the back through the posterior thigh to the knee. 1, 2
• Order lumbar spine radiographs if any spinal symptoms are present – Back pain or radicular patterns may mimic knee pain and must be excluded before attributing symptoms to the knee. 1, 2

Critical Pitfall to Avoid

Do not order additional knee MRI or advanced knee imaging when the initial knee MRI is normal. 2 The American College of Radiology explicitly cautions against ordering knee MRI before hip radiographs in patients with normal knee films and clinical suspicion of hip disease, as this sequence wastes resources and delays accurate diagnosis. 2

Diagnostic Injection Strategy (If Hip Radiographs Are Abnormal)

• Consider image-guided intra-articular hip injection of anesthetic ± steroid – An intra-articular injection that relieves the "knee" pain confirms the hip as the pain source and provides both diagnostic information and therapeutic benefit. 1
• Use fluoroscopy or ultrasound guidance – Injections or aspirations should always be image-guided to ensure accurate intra-articular placement. 1

Interim Management While Completing Workup

• Activity modification – Avoid deep squatting, pivoting, or prolonged weightbearing that provokes pain. 2
• NSAIDs or acetaminophen – Provide symptomatic relief when not contraindicated; acetaminophen up to 4 g/day is first-line due to superior long-term safety. 3
• Physical therapy – Initiate quadriceps strengthening and hip-abductor strengthening exercises; definitive treatment will be guided by hip/spine imaging findings. 2, 3

Algorithmic Decision Pathway

1. Normal knee MRI + persistent knee pain → Order pelvis/proximal femur radiographs 1, 2
2. Hip radiographs abnormal → Proceed to hip MRI and consider diagnostic hip injection 1
3. Hip radiographs normal but high clinical suspicion → Proceed to hip MRI to evaluate for labral tears or soft tissue pathology 1
4. Hip workup negative + any back/radicular symptoms → Order lumbar spine radiographs ± MRI 1, 2
5. All imaging negative → Consider bone scan (Tc-99m or 18F-fluoride PET) to detect occult stress injury or bone marrow edema syndrome 1

When to Refer to Orthopedics

• Hip pathology confirmed on imaging – Labral tears, femoroacetabular impingement, or advanced arthritis may require surgical consultation. 1
• Persistent symptoms despite comprehensive workup and 6 weeks of conservative therapy – Specialty referral is appropriate when structural pathology correlates with refractory pain. 3