Evaluation and Management of Referred or Radiating Knee Pain
Immediate Priority: Rule Out Referred Pain Sources Before Attributing Symptoms to the Knee
When knee radiographs are normal or show only effusion, you must systematically exclude hip and lumbar spine pathology before proceeding with knee-specific imaging or treatment. 1
Clinical Assessment Algorithm
Step 1: Identify Red Flags for Referred Pain
Hip pathology assessment:
- Ask specifically about groin pain 1
- Test hip range of motion for restrictions 1, 2
- Examine for positive hip impingement signs 2
- If any of these are present, obtain pelvis and proximal femur radiographs immediately 1
Lumbar spine pathology assessment:
- Ask about low-back pain 1
- Assess for radicular symptoms extending from buttock through posterior thigh to knee 1
- Evaluate for neurogenic claudication patterns 2
- If spinal symptoms are present, obtain lumbar spine radiographs before knee MRI 1
Step 2: Initial Knee Imaging
Obtain standard three-view knee radiographs first:
- Anteroposterior (or Rosenberg/tunnel view) 1, 3
- Lateral view 1, 3
- Tangential patellar (skyline) view 1, 3
Critical pitfall: Approximately 20% of patients inappropriately receive knee MRI without recent radiographs within the prior year—this wastes resources and violates evidence-based guidelines 1, 2, 3
Step 3: Interpretation-Based Pathway
If knee radiographs show hip or spine-referred pain is suspected clinically:
- Order hip radiographs (combined pelvis and proximal femur view) for groin pain, restricted hip motion, or unexplained knee pain 1
- Order lumbar spine radiographs for back pain or radicular symptoms 1
- Do not order knee MRI before obtaining hip radiographs when hip disease is suspected—this delays accurate diagnosis 1
If knee radiographs are normal or show only effusion AND referred pain is excluded:
- Proceed to non-contrast knee MRI 1, 2
- MRI detects meniscal tears, cartilage damage, bone marrow lesions, ligament injuries, and occult fractures not visible on plain films 1, 2
Specific Conditions Causing Referred Knee Pain
Hip Pathology
- Developmental dysplasia, femoroacetabular impingement, and early hip arthritis commonly refer pain to the knee 1
- Combined pelvis and proximal femur radiographs are superior to isolated hip films for detecting these conditions 1
Lumbar Radiculopathy
- Spinal pathology can mimic knee pain, particularly when pain radiates from buttock through posterior thigh 1
- Assess for back pain and radicular symptoms before attributing all symptoms to the knee 1, 2
Interim Management While Awaiting Imaging (1–2 weeks)
- Activity modification: Avoid deep squatting, pivoting, or movements that provoke symptoms 1
- NSAIDs: Provide symptomatic relief when not contraindicated 1
- Physical therapy: Initiate quadriceps strengthening and range-of-motion exercises; definitive treatment will be guided by imaging findings 1
Common Pitfalls to Avoid
- Do not assume knee pain originates from the knee when radiographs are unremarkable—hip and spine pathology must be excluded first 1, 2
- Do not order knee MRI before hip radiographs when clinical examination suggests hip disease 1
- Do not skip the tangential patellar view—patellofemoral pathology is a common pain source that requires this view for adequate visualization 1, 3
- Do not attribute clicking to "normal joint sounds" when effusion and chronic pain (≥3 months) are present—this combination indicates structural pathology requiring MRI 1
Post-Imaging Decision Pathway
If hip or spine radiographs reveal pathology:
- Treat the identified source (e.g., hip arthritis, lumbar radiculopathy) rather than pursuing knee-specific interventions 1
If all radiographs are normal and pain persists:
- Proceed to knee MRI without contrast to evaluate soft-tissue structures, bone marrow, and early cartilage damage 1, 2
If knee MRI shows repairable meniscal tear, loose body, or unstable osteochondritis dissecans:
- Refer to orthopedics for arthroscopy 1
If knee MRI shows degenerative changes or mild chondromalacia: