After knee surgery, sensitive disorders due to cutaneous nerve lesions are common and often described as benign. However, some patients may experience abnormally high levels of neuropathic pain. Therefore, we explored the link between the type and intensity of sensitive disorders and neuropathic pain intensity.

In a prospective comparative study, we included every patient admitted for functional rehabilitation after knee surgery in our PRM center, irrespective of the time elapsed since surgery. They were screened for the intensity and the type of pain (nociceptive or neuropathic) using a numerical pain scale, a DN4 questionnaire and a McGill questionnaire (MGQ). The patients were evaluated by a quantitative sensitivity test. First, the main sensitive disorder was qualified and mapped. Second, hypoesthesia was quantified through the pressure and vibration perception thresholds (PPT, respectively VPT), and allodynia through a color code using the monofilaments of Semmes-Weinstein. Sixty patients were evaluated and classified in two groups: 41 in a neuropathic painful group and 19 in a non-painful group.

Our first finding was that every painful patient had an underlying sensitive disorder. For them, we found mostly hypoesthesia (n=31) and in some cases allodynia (n=9) or hyperesthesia (n=1). These disorders were not systematically found in the non-painful group: Three patients did not have any trouble and 16 had hypoesthesia. When comparing the painful with the non-painful group, but with the restriction of elapsed time since surgery (inferior to 6 months), we found a significant difference for PPT (P=0.0053) with a higher level of hypoesthesia for the painful group.

Our results suggest that hypoesthesia intensity is linked to neuropathic pain after knee surgery. Systematic quantitative sensitivity testing of neuropathic painful patients after knee surgery could be proposed to track sensitive disorders. This assessment could lead to an appropriate sensitive rehabilitation that may possibly prevent an evolution to chronic pain.