Lower Pressure Pain Thresholds in Patellofemoral Pain Patients, Especially in Female Patients: A Cross-Sectional Case-Control Study

Objective: It has been suggested that repeated overload might sensitize nociceptors, causing local hyperalgesia in patients with patellofemoral pain (PFP). This might also lead to generalized hyperalgesia, indicative of altered central pain processing. This study aimed to investigate differences in pressure pain threshold (PPT) as a measure of pressure hyperalgesia between patients with PFP and healthy controls and in predefined subgroups and to study associations between PPT and patient characteristics. Design: Case-control study. Setting: Physiotherapy, general practices, and sports medicine practices. Subjects: Sixty-four patients with PFP and 70 healthy controls. Methods: Demographics, pain (numerical rating score), and function (anterior knee pain score) were obtained by questionnaire. The PPT was measured with a handheld dynamometer with algometry tip at the most painful spot of the affected knee (medial facet in controls), the same spot at the contralateral knee, and at the contralateral forearm. Differences between groups were tested using analysis of variance techniques including the variables age, gender, body mass index, and sports participation. Results: Patients had significantly lower PPTs compared with controls at all locations (affected knee: mean difference = -12.2, 95% confidence interval [CI] = -17.3 to -7.1; contralateral knee: mean difference = -4.7, 95% CI = -10.1 to 0.52; contralateral arm: mean difference = -5.7, 95% CI = -10.5 to -0.8). Both male and female patients demonstrated lower PPTs, though a significant subgroup effect was found for female gender (effect size ranging from 0.73 to 0.98). Conclusions: Local and generalized pressure hyperalgesia, suggesting alterations in both peripheral and central pain processing, were present in patients with PFP, though females with PFP were most likely to suffer from generalized hyperalgesia.