This blog is an amended version of some text from my recent PhD that looked at the assessment and management of patellofemoral pain. As such, my work is a product of supervision and collaboration. So I would like to start by acknowledging and thanking my supervisors Pip Logan and Paul Hendrick, and collaborators Marcus Bateman, Sinead Holden, Chris Littlewood, Fiona Moffatt, Michael Rathleff, James Selfe and Toby Smith.
BIOMEDICAL MODELS OF CARE DOMINATE THE LITERATURE FOR PATELLOFEMORAL PAIN (PFP)
The majority of research for PFP has historically been biomedical based. For example, the best practice guidelines for conservative management of PFP published in 2015 was a systematic review of systematic reviews. It also included expert opinion (experts recruited from the 2009 and 2011 iPFRN*). The included studies all focused on biomedical models of pain, and its main recommendations primarily supported treatments aimed directly at tissue structures, for example, braces, orthotics, taping, stretching and joint mobilisations .
*The iPFRN is the International Patellofemoral Research Network (iPFRN) – a group of researchers and clinicians with a specific interest in patellofemoral pain.
Recent iPFRNs have continued with this trend. Research presented at the last two iPFRNs had a relatively low proportion of submitted abstracts examining pain science, compared with biomechanical themes (6% (3/50; Manchester, UK, 2015) and 29% (15/52; Gold Coast, Australia, 2017) [2–6].
Admiringly, the 6th International Patellofemoral Research Retreat in Milwaukee, October 2019, has identified this. And has set up a Steering Committee for gaining a Consensus in ‘Pain and Psychology of Patellofemoral Pain’; led by Bill Vicenzino and Michael Rathleff. I look forward to attending, listening to all the research, presenting my own research and sharing ideas later this year. Here’s the current schedule. But in the meantime…..
Why do we need to re-think things?
A 2012 mixed methods systematic review investigated the association between health care professional attitudes and beliefs and outcomes of patients with low back pain included 17 studies and measured the quality of the evidence using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) tool . It concluded that there is moderate evidence that healthcare practitioners with a biomedical orientation or high levels of fear-avoidance beliefs (measured on the Fear-Avoidance Beliefs Questionnaire ) are less likely to adhere to treatment guidelines .
Similarly, a 2010 systematic review exploring the attitudes, beliefs and behaviours of general practitioners (GP) regarding exercise for chronic knee pain included 20 studies . Quality of included studies was assessed through the Newcastle Critical Appraisal Worksheet , and the Critical Appraisal Skills Programme Qualitative Research Assessment Tool . The review demonstrated limitations of the studies, including poor methodological quality and limited generalisability ; however, it concluded that GPs generally underused evidence based exercise, of any type, with up to 29% believing rest was optimal .
Attitudes, beliefs and the emotional response are reflected in the National Institute for Health and Care Excellence (NICE) definition of pain as, a complex biopsychosocial issue, associated with expectations, self-efficacy, mood and coping abilities . Indeed, a systematic review of RCTs of self-management interventions for chronic MSK pain that included 16 studies (n=4,047), found self-efficacy and depression were the strongest prognostic factors for pain and disability (irrespective of the intervention) . Improvements in pain catastrophising and physical activity were the strongest mediating factors . This review provides a foundation that interventions should be aimed at reducing pain-related fear and increasing appropriate physical activity, and these could be primary targets in rehabilitation programmes and RCTs for persistent MSK pain .
This view is supported by findings from studies specifically examining PFP. A recent prospective cohort study recruited 47 patients with chronic PFP . Data collected from this cohort included outcomes on anxiety, depression, pain coping strategies, catastrophising and fear of movement beliefs (kinesiophobia) before and six-months after a usual care intervention . The results indicated that patients who improved on catastrophising, kinesiophobia, anxiety and depression, had the greatest improvements in pain and disability scores (p < 0.001) . Similarly, a longitudinal study of 74 patients with PFP demonstrated fear-avoidance beliefs to be the strongest predictor of pain and disability outcomes (p ≤ 0.01) [16,17]. This was a greater predictor than biomedical factors including muscle strength, length, and lower limb alignment and movement patterns [16,17].
Another complexity to the presentation of PFP is the consideration of the central nervous system. It has been suggested that interventions for chronic MSK conditions need to go beyond muscles and joints , to instead consider the concept of central pain mechanisms and in particular central sensitisation . Pain does not provide a measure of the state of tissue and is thought to be modulated by many factors .
Catastrophising and kinesiophobia are thought to play an important role in shaping the physiological responses to pain, and therefore the development and maintenance of persistent pain . Altered central processing of pain may be present in patients presenting with long-standing PFP; for example, individuals with PFP have demonstrated lower pressure pain thresholds at sites around the knee, shin and elbow, suggesting widespread hyperalgesia [22–25], with a spreading of the sensation of pain beyond the patella .
For example, a study of 91 patients with unilateral PFP, with 23 pain-free controls, examined quantitative sensory testing, combining tactile and vibration sensation; warmth and cold thresholds . The authors observed that patients with unilateral PFP pain had significantly increased tactile thresholds and altered thermal threshold on bilateral knees compared to pain-free controls; indicating altered central pain processing .
These findings are supported by other studies demonstrating thermal alterations in patients with PFP [29,30]. Additionally, a 2018 assessor blinded cross-sectional study, assessing cuff pain thresholds, not only demonstrated altered central processing of pain in people with PFP but also in people reporting symptom resolution (median of two years pain-free), suggesting pain processes may be influenced by “somatosensory pain memories”  (as seen with phantom limb pain).
This blog has argued that conventional biomedical models of care dominate PFP literature, and, when viewed in isolation, propose that PFP is peripherally-based nociception, which alone fails to explain the characteristic features associated with PFP.
There is a growing body of evidence that recognises the uncertainty in the presentation and clinical management of PFP, and within the context of such a burdensome disorder, our thinking should be challenged and expanded beyond conventional ideas.
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