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Meniscus lesions, specifically extrusions, were a risk factor for neuropathic pain in patients with knee osteoarthritis (OA), results of a pilot study suggested.

The presence of meniscal extrusion on MRI, in both medial (P=0.006) and lateral (P=0.023) compartments, was significantly associated with increasing neuropathic pain (NP) pain scores in knee OA patients, according to Camille Roubille, MD, of the in Quebec, and colleagues.

The presence of meniscal tears in the lateral compartment (P=0.011) was also significantly associated with pain scores, they wrote online in .

"Our finding of an association between NP and lateral meniscal tear is somewhat unexpected as literature indicates that meniscal tears are not usually associated with symptoms," the authors wrote.

The multicenter, cross-sectional, observational study included 50 patients with symptomatic knee OA who had moderate to severe pain (visual analog scale [VAS] ≥40) in the most painful knee.

Neuropathic pain was determined through the , a patient-report questionnaire. An neuropathic pain component is unlikely if the score on this questionnaire is ≤12, uncertain if the score is 13 to 18, and likely if the score is ≥19. Half the subjects in the study had unlikely neuropathic pain, nine had uncertain neuropathic pain, and 16 had likely neuropathic pain.

The researchers also evaluated clinical characteristics using the (WOMAC) questionnaire. They assessed knee MRI, including cartilage volume, as well as sedimentation rate and C-reactive protein (CRP) values through blood tests.

They found a statistically significant relationship between WOMAC pain (P<0.001), function (P<0.001), stiffness (P=0.007) and total (P<0.001) scores, as well as higher VAS pain (P=0.023) score, and PainDETECT scores.

The finding of a greater likelihood of NP in patients with meniscal extrusion and lateral meniscal tears suggests that knee OA patients with a neuropathic pain component have more severe symptoms, they wrote. This, to a certain extent, was reflected by a trend towards greater use of non-steroidal anti-inflammatory drugs (NSAIDS), they added (12% of those unlikely to have neuropathic pain were taking these drugs compared with 31% of those with likely neuropathic pain).

Bone marrow lesions in the lateral plateau (P=0.032) were associated with increasing PainDETECT scores, but not in the medial compartment. Synovial membrane thickness in the lateral recess was also associated with these scores.

There was no association between sedimentation rate, CRP values, or cartilage volume, and the PainDETECT scores. And there was no evidence, based on the MRI finding, of an association with more severe disease.

The exact mechanisms underlying neuropathic pain-like symptoms in OA are poorly understood, but the authors noted that OA pain likely includes both nociceptive and neuropathic components. It has been suggested that local damage to innervation as well as other joint structures may cause damage to peripheral nerves, they said.

There are very few data on the relationship between meniscal lesions and NP in knee OA, they commented, noting that this is a promising field of future research.

"The present study is particularly interesting as it is the first to report a clear association of meniscal lesions, more specifically extrusion, with NP. The finding of the association between the presence of meniscal extrusion and the PainDETECT scores makes this structural alteration a definite marker of NP," they wrote.

This finding is clinically relevant for various reasons, they added. Not only does it support the examination for meniscal extrusion in knee OA patients with neuropathic pain, but the predominance of a neuropathic component in such patients should encourage physicians to consider using MRI to establish a proper diagnosis.

A diagnosis of meniscal extrusion may also help identify patients who might benefit from treatment aimed at controlling their symptoms. "There is hope that this 'personalized therapeutic management' would avoid the prolonged use of anti-inflammatory drugs or even narcotic analgesics, preventing potential side effects" the authors wrote.

The observational study was limited by a relatively small sample size, the arbitrary determination of the sample, and the diagnosis of neuropathic pain based solely on the PainDETECT questionnaire.

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