Quantitative sensory testing of patients with long lasting Patellofemoral pain syndrome

Anterior knee pain, diagnosed as Patellofemoral Pain Syndrome (PFPS), is one of the most common musculoskeletal problems found in adolescents and young adults. There is no consensus in medical literature concerning the aetiology of the PFPS.

To assess by means of Quantitative Sensory Testing (QST) whether patients suffering from long-lasting unilateral PFPS demonstrate somatosensory dysfunction related to afferent fibres from the local pain area.

A descriptive non-experimental study with two independent samples, consisting of 25 men and women between 18 and 44 years of age with unilateral PFPS, and a comparable group of 23 healthy subjects. Somedic Thermotest apparatus was used to assess thresholds of thermal perception, and of heat and cold pain thresholds. Von Frey filaments were used to detect tactile sensitivity. Furthermore, quality and intensity of knee pain, symptoms and signs from a clinical neurological examination were recorded.

Decreased sensitivity to tactile stimulation, when tested with von Frey filaments, was demonstrated on both the painful and pain-free knee in subjects with PFPS, compared to the mean between the knees of the control group (p< or =0.001). The mean detection threshold for warmth was increased by 1.9 degrees C (p< or =0.01) in the painful knee, and 1.4 degrees C (p< or =0.01) in the non-painful knee in the PFPS group, compared to the mean of the healthy control group. The mean detection threshold for cold was increased by 1.6 degrees C (p< or =0.01) in the painful knee of the PFPS group, compared to the control group. These findings were supported by clinical sensory tests. No significant differences of mean thermal pain thresholds between the PFPS group and controls were found, and there were no significant differences in mean detection thresholds for warmth, cold or thermal pain thresholds between the painful and the non-painful knees in the PFPS group.

This study demonstrated an abnormal sensory function in the painful and non-painful knee in some individuals with long lasting unilateral Patellofemoral Pain Syndrome using Quantitative Sensory Testing supported by clinical neurological examinations. A dysfunction of the peripheral and/or the central nervous system may cause neuropathic pain in some subjects with PFPS.