Patellofemoral pain syndrome : clinical and pathophysiological considerations

Abstract: Patellofemoral pain syndrome (PFPS) is one of the most common musculoskeletal disorders and is reported to affect 15%-33% of the active adult population and 21%-45% of adolescents. Among adolescents, the incidence is reported to be higher for girls. PFPS affects athletes and nonathletes of both genders and is consistently reported in activities such as ascending or descending stairs and squatting or subsequent to long periods of sitting still (theatre or movie sign). Patients commonly report that the development of their pain is insidious and that the pain is either sharp and acute or diffuse and chronic. Since no consensus on the definition, classification, assessment, or management has been reached, no validation of clinical tests and signs is possible. PFPS is often a diagnosis of exclusion. The most widely accepted theory regarding the etiology behind PFPS suggests that the symptoms are the result of excessive, patellofemoral joint stress (force per unit area) due to abnormal patellar tracking. Reports, however, have questioned a causal relationship between malalignment and knee discomfort in PFPS. The overall purpose of this thesis was to explore possible pain mechanisms in PFPS. In the first study, we compared symptoms and clinical findings in a group of PFPS patients with a group of knee-healthy subjects. The main finding was that patients with a clinical diagnosis (made on two occasions and by different physicians) of PFPS may have additional diagnoses that are undetectable in the patient's history or in commonly used clinical tests. In the second study, we treated PFPS patients using two modalities of sensory stimulation: clectroacupuncture and subcutaneous needling. Patients with PFPS reported alleviation of pain from both methods. The pain-relieving effect remained for at least half a year. None of the variables height, velocity, power, or force increased during observed physical function, the one-legged explosive jump. The activity score was unchanged in both treatment groups. The skin temperature at three locations on the leg did not change. In the third study, we used bone scintigrams to examine patients suffering from PFPS. Diffuse uptake was found in 44% of the knees of patients with PFPS and in all three bony compartments of the knee: in 27 patellae, in 25 proximal tibiae, and in 19 distal femora. Uptake in the femur and the tibia occurred solely in the condyles. Diffuse uptake on scintigraphy is regarded as a sign of accelerated bone remodeling. Apart from mechanical loading, hypoxia is a physiological factor that may be involved in triggering this remodeling. In the fourth study we evaluated a new photoplethysmographic (PPG) technique in healthy subjects to monitor local pulsatile blood flow in the patella. Different provocation procedures were applied to influence blood perfusion both superficially in the skin and in the patellar bone. Blocking blood flow in the skin significantly decreased the PPG signal from the skin but not from the patellar bone. During venous stasis, signals from both tissues decreased but the blood flow in the skin deteriorated more. Occlusion of arterial blood flow minimized both PPG signals. The application of liniment to the skin increased the PPG signal from the skin significantly more than from the patella. In a parallel study on a physical model with a rigid tube, we showed that the AC component of the PPG signal originates from pulsations of blood flow in a rigid structure and not necessarily from volume pulsations. This study indicated that photoplethysmography can be used to measure local bone blood flow continuously and noninvasively. Because these first studies supported the hypothesis that the supply of oxygen to the knee region in patients with PFPS is diminished we used the novel PPG method to compare the pulsatile blood flow in the patellar bone in patients and healthy controls in the fifth study. We found that pulsatile blood flow in PFPS patients was markedly reduced compared with knee-healthy patients during flexion of the knee to 90 degrees. From this thesis it is concluded that: ' PFPS is a clinical diagnosis in which the patients can be divided into different subgroups according to radiological findings. ' The pain experienced by patients suffering from PFPS decreases after various types of sensory stimulations. ' Diffuse uptake on scintigraphy will be present in approximately half of the PFPS patients and may occur in any bony compartment of the knee. ' Pulsatile blood flow in the patellar bone can be studied continuously and non-invasively with photoplethysmography. ' Patients diagnosed with PFPS exhibit reduced levels of patellar pulsatile blood flow compared with healthy controls when the knee is flexed.