Left Posterior Knee Pain Radiating to Hip with Sitting
This presentation strongly suggests referred pain from the lumbar spine or hip rather than primary knee pathology, particularly given the sitting-specific exacerbation pattern. 1, 2
Diagnostic Approach
Initial Clinical Assessment
The sitting-specific nature of this pain is the critical diagnostic clue:
Lumbar spine pathology is the most likely source when posterior knee pain worsens specifically with sitting, as this position increases intradiscal pressure and can compress nerve roots (particularly L5-S1 or S1) that refer pain down the posterior leg 1, 2
Hip pathology must be considered as a secondary differential, as hip disorders commonly refer pain to the knee and can worsen with hip flexion during sitting 1, 3
Primary knee pathology (popliteal cyst, hamstring tendinopathy, meniscal tears) typically worsens with weight-bearing activities rather than sitting alone 2, 4
Imaging Algorithm
Start with plain radiographs of the knee, lumbar spine, and hip to screen for obvious pathology before advanced imaging: 1
Knee radiographs first (anteroposterior, lateral, and tangential patellar views) to exclude primary knee pathology 1
If knee radiographs are unremarkable, obtain lumbar spine radiographs given the sitting-specific pain pattern 1, 2
Hip radiographs (pelvis and proximal femur views) should be obtained if clinical examination suggests hip involvement 1
Advanced Imaging When Radiographs Are Non-Diagnostic
MRI of the lumbar spine without IV contrast is the next appropriate study if radiographs are negative but symptoms persist with the sitting-specific pattern: 1, 2
MRI lumbar spine can identify disc herniation, nerve root compression, or spinal stenosis causing referred posterior leg pain 1, 2
MRI of the knee without IV contrast should only be pursued if lumbar spine imaging is negative and clinical examination localizes pathology to the knee itself 1, 2
MRI accurately depicts popliteal cysts, meniscal pathology, and hamstring injuries that could cause posterior knee pain 1, 2
MRI of the hip without IV contrast is appropriate if hip pathology is suspected clinically, particularly for soft tissue abnormalities like iliopsoas bursitis, hamstring injuries at the origin, or gluteal tendinopathy 1
Common Diagnostic Pitfalls
The most critical error is attributing all symptoms to knee pathology without evaluating the lumbar spine and hip: 1, 2
Approximately 20% of patients with chronic knee pain undergo MRI without recent radiographs, leading to premature and potentially unnecessary advanced imaging 1
Referred pain from the lumbar spine or hip is frequently overlooked when patients present with "knee pain," yet these are common sources of posterior knee symptoms 1, 2
The sitting-specific exacerbation pattern is highly suggestive of spinal pathology rather than primary knee disease 1, 2
Physical examination must include assessment of:
Lumbar spine range of motion, straight leg raise testing, and neurologic examination of the lower extremity 1, 2
Hip range of motion, FABER test, and assessment for hip flexor or gluteal tenderness 1, 3
Knee-specific tests including popliteal fossa palpation, McMurray test, and assessment for effusion 1, 5