Patellofemoral Pain Syndrome. Studies on a treatment modality, somatosensory function, pain and psychological parameters
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Patellofemoral pain syndrome (PFPS) is characterized by long-term diffuse peripatellar and retropatellar localized pain in one or both knees, which worsens during walking uphill or downhill, squatting, kneeling, or prolonged sitting with flexed knees. There is no consensus in the medical literature concerning the definition, aetiology or diagnosis of PFPS. In this thesis PFPS is described as anterior knee pain excluding intra-articular pathology, peripatellar tendonitis and bursitis. Clinical tests used to diagnose PFPS lack acceptable reliability and validity, and radiographic findings in diagnosing PFPS are inconclusive. These limitations need to be addressed given that PFPS is a common musculoskeletal complaint, especially among adolescents and young active adults. The main purpose of the studies described in this thesis was to determine possible pain mechanisms in PFPS patients and to suggest a suitable treatment modality. The first study reported in the thesis was a randomized clinical trial involving the treatment of 36 PFPS patients with sensory stimulation by 8 acupuncture treatments. The control group consisting of 34 PFPS subjects did not receive any treatment. The two groups did not differ at baseline. The Cincinnati Rating System questionnaire was used as the main outcome measure. The results show that the Numbers Necessary to Treat (NNT) was 3.2 to achieve no pain or occasional pain to strenuous sports at the 12-month follow-up, and 3.7 to achieve no functional limitations or some limitations to heavy labour, in favour of the acupuncture group. Hence, sensory stimulation by acupuncture is recommended as a treatment modality to improve pain and function in PFPS patients. The second study assessed the mental status of 25 PFPS patients and related this to pain and function. The health status was significantly lower and mental distress was significantly higher in PFPS patients than in a comparable group comprising 23 healthy subjects. Further, the level of mental distress increased and the health status deteriorated with increased intensity of pain and impairment of knee function. We hypothesize that pain and reduced function produce mental distress in PFPS patients, and that this influences their experience of pain. The third study measured somatosensory functions related to the painful area using thermal and tactile quantitative sensory testing (QST) and bedside neurological tests in 25 PFPS patients. The results were compared to those obtained in 23 healthy controls. We found that QST can be used to detect sensory dysfunctions in patients with PFPS. Patients suffering from unilateral PFPS demonstrated dysfunction of sensory pathways related to the painful and contralateral areas, which might indicate a pathophysiological basis for pain in PFPS. The fourth study assessed if a subgroup of PFPS patients experienced neuropathic pain related to the painful knee by characterizing the somatosensory phenotype and analysing the sensory and clinical patterns related to the knees. A total of 91 subjects with unilateral PFPS and a comparable group of 23 healthy subjects were included in this study with a case– control design. The degree of knee function and intensity of knee pain were assessed. Somatosensory assessments were carried out by bedside neurological tests and by assessing thermal, tactile and vibration thresholds. There was considerable heterogeneity and overlap in the degree and type of aberrations of the nervous system. However, no subgroup of subjects with neuropathic pain or clustering of features related to neuropathic pain was identified. Conclusions from this thesis: Somatosensory stimulation by acupuncture is recommended as a treatment modality for PFPS. Quantitative sensory testing combined with clinical neurological tests can be used to detect altered somatosensory function in PFPS subjects. Sensory assessments of PFPS patients indicate that the pain can have a pathophysiological component. Somatosensory dysfunctions related to the painful and contralateral areas indicate modulations of central neural mechanisms. Ample signs of sensory aberrations related to the painful area were found but a clear subgroup of subjects with neuropathic pain could not be identified. Mental distress is higher and self-perceived health is lower in PFPS patients than in healthy controls. Further, the intensity of knee pain and degree of knee function are strongly correlated with the degree of mental distress.
Paper I: The Journal of Alternative and Complementary Medicine 5(6), Jensen, R.; Gøthesen, Ø.; Liseth, K.; Baerheim, A., Acupuncture treatment of the patellofemoral pain syndrome, pp. 521-527. Copyright 1999 Mary Ann Liebert, Inc. Full text not available in BORA due to publisher restrictions. The published version is available at: http://dx.doi.org/10.1089/acm.1999.5.521Paper II: Journal of Orthopaedic & Sports Physical Therapy 35(9), Jensen, R.; Hystad, T.; Baerheim, A., Knee function and pain related to psychological variables in patients with long-term Patellofemoral Pain Syndrome, pp. 594-600. Copyright 2005 Lippincott Williams & Wilkins. Full text not available in BORA due to publisher restrictions. The published version is available at: http://dx.doi.org/10.2519/jospt.2005.2119Paper III: European Journal of Pain 11(6), Jensen, R.; Hystad, T.; Kvale, A.; Baerheim, A., Quantitative Sensory Testing of patients with long lasting Patellofemoral Pain Syndrome, pp. 665-676. Copyright 2007 European Federation of Chapters of the International Association for the Study of Pain. Published by Elsevier Ltd. Full text not available in BORA due to publisher restrictions. The published version is available at: http://dx.doi.org/10.1016/j.ejpain.2006.10.007Paper IV: The Clinical journal of pain 24(5), Jensen, R.; Kvale, A.; Baerheim, A., Is pain in Patellofemoral Pain Syndrome neuropathic?, pp. 384-394. Copyright 2008 Lippincott Williams & Wilkins. Full text not available in BORA due to publisher restrictions. The published version is available at: http://dx.doi.org/10.1097/AJP.0b013e3181658170