Is pain in patellofemoral pain syndrome neuropathic?

Objective: There is no consensus among experts regarding the etiology or management of patellofemoral pain syndrome (PFPS). Observations indicating dysfunction of the peripheral nervous system around the patellae have been reported. To what extent these sensory abnormalities cause pain has so far not been investigated. The aim of this study was to assess whether a subgroup of patients with unilateral PFPS have neuropathic pain related to the painful knee. Method: A total of 91 patients with unilateral PFPS, between 18 and 40 years of age, and a comparable group of 23 healthy participants aged 18 to 44 years were included. Level of knee function, pain intensity, and qualities were assessed. Somato- sensory assessments were carried out by bedside neurologic tests and quantitative sensory testing, assessing thermal, tactile, and vibration thresholds. Results: Ample signs of sensory aberrations with considerable heterogeneity and overlap regarding the degree and type of dysfunction of the nervous system were found in the painful area of the PFPS patients. No clear subgroup of patients with neuropathic pain or clustering of features related to neuropathic pain was identified. Discussion: This study hypothesizes that the observed sensory aberrations may cause neuropathic pain in patients with PFPS. There is no validated method for subgrouping patients with possible neuropathic pain and in this study considerable heterogeneity and overlap regarding signs and symptoms of neuropathic pain made subgrouping even more difficult. A mechanism-based understanding of the pain is, however, essential for the selection of adequate treatment strategies in painful musculoskeletal disorders.