Is Your Back Causing Knee Pain?
Many patients searching for relief from knee pain, chronic knee pain, or persistent knee discomfort assume the problem lies within the knee joint itself—perhaps due to knee arthritis, meniscus tears, or patellofemoral pain syndrome. However, a significant portion of knee pain cases may actually stem from the lumbar spine through a process called lumbar radiculopathy, where irritated or compressed nerve roots refer pain to the knee. Depending on which levels of the lumbar nerve roots are involved can predict where pain in the knee is experienced. Most commonly, pain in the outer (lateral) or back (posterior) knee can often originate from compression of the L5 or S1 nerve roots. Pain in the front or inner portions of the knee can occur from compression of the L3 or L4 nerve roots.
Board-certified orthopedic knee surgeon Thomas Obermeyer, MD frequently evaluates patients with all sources of knee pain including those from lumbar spine issues. Recognizing when knee pain is referred from the lower back is crucial for avoiding unnecessary knee treatments and targeting the true source for effective relief. The testing and diagnostic process for referred pain is not always straightforward and sometimes patients are told different information by multiple specialists. If your treatment is not working or you were told you need surgery for a condition typically treated non-operatively (for example a Baker’s cyst or other benign condition), make a consultation today with orthopedic surgeon Thomas Obermeyer, MD.
The history of your symptoms provides key clues to distinguish intrinsic knee pain (from the knee joint) from referred knee pain due to lumbar radiculopathy.
- Intrinsic knee pain (e.g., osteoarthritis or meniscal injury): Typically localized to the knee, worsened by weight-bearing activities like stair climbing, squatting, or prolonged standing. Pain is often mechanical, with stiffness after inactivity and crepitus (grinding sensation). Patients rarely report associated low back pain.
- Referred pain from lumbar radiculopathy: Pain may radiate from the low back or buttock into the knee, sometimes into the lower leg (shinbone) often described as burning, shooting, or sharp. It can occur without prominent back pain or clear radiation. Pain at the back of the knee is frequently caused by compression of the lower lumbar or S1 nerve roots. Symptoms may worsen with sitting, coughing, or sneezing (increasing intrathecal pressure). Pain that substantially waxes and wanes, is occasionally very severe (“10 out of 10”) is frequently caused by lumbar nerve root compression. Lastly, Patients with knee pain from spinal radiculopathy may have a history of prior low back issues or no clear knee trauma.
- The symptoms can overlap, highlighting the diagnostic challenge in patients with both knee disorders such as arthritis and spinal stenosis, both increasingly common conditions in older age(1).
A thorough exam helps differentiate sources of knee pain.
- Intrinsic knee pathology: Positive findings include joint line tenderness, effusion, crepitus on motion, positive McMurray tests (for meniscus), or patellar grind (patellofemoral issues). Pain is reproduced by knee-specific maneuvers like squatting or palpation.
- Lumbar radiculopathy mimicking knee pain: Normal knee joint exam but positive neural tension tests. Straight-leg raise (SLR) reproduces radiating pain below the knee (sensitivity ~0.8 for radiculopathy). Crossed SLR can cause pain in the painful knee by lifting the unaffected leg. Femoral nerve stretch may provoke symptoms for upper lumbar roots (L3/L4). No knee swelling or mechanical signs.
Imaging and electrodiagnostics can confirm the source, taking in conjunction with other tests. There is no perfect diagnostic tool and sometimes other measures need to be taken to clarify the source such as response to injections.
- For intrinsic knee pathology: Knee X-rays show osteoarthritis (joint space narrowing, osteophytes). MRI reveals meniscal tears, cartilage loss, or ligament injury.
- For lumbar radiculopathy: Lumbar MRI is gold standard, shows disc herniation or stenosis compressing roots (specifically “foraminal stenosis” which means the holes in the bone that transmit nerves are pinched). EMG/NCS confirms radiculopathy if compression of the nerve roots is advanced.
- It should be noted that nerve root compression has stages from mild to severe. Severe nerve root involvement causes weakness and paralysis of muscles, and in these cases EMG is commonly positive. In “milder” forms (pain only), the EMG is often normal(2), meaning EMG is not a very useful screening tool.
Treatment response often reveals the true source.
- Intrinsic knee pain: Improves with knee-directed therapies like injections, physical therapy focusing on quadriceps strengthening, or arthroscopy. Little relief from spine-focused care.
- Lumbar radiculopathy: Radicular symptoms respond to epidural steroid injections, physical therapy emphasizing extension/mobilization, or spine decompression. Knee injections provide minimal benefit if no intrinsic pathology. For these reasons, injection therapy is often an effective screening and testing tool to confirm the true source.
If you’re experiencing knee pain, leg pain with knee involvement, or radiating knee discomfort, consider that the lumbar spine could be the culprit—especially with neurologic symptoms or negative knee findings. Consulting a specialist like Thomas Obermeyer, MD, experienced in both knee and spine conditions, ensures accurate diagnosis and targeted treatment, whether conservative or surgical.
Early recognition prevents delayed recovery and unnecessary procedures.
References
- Govil G, Tomar L, Dhawan P. Knee-Spine Syndrome: Management Dilemma When Knee Osteoarthritis Coexists With Spine Degeneration. Cureus. 2022 May 12;14(5):e24939. doi: 10.7759/cureus.24939. PMID: 35698678; PMCID: PMC9187136.
- Ercan, Merve Bahar; Kuruoglu, Hidayet Reha1. Significance of Pure Sensory Manifestations in Estimating Electromyography Results in Cervical Radiculopathy. Neurological Sciences and Neurophysiology 39(3):p 132-137, Jul–Sep 2022. | DOI: 10.4103/nsn.nsn_10_22
