Clinical update: diagnosing patellofemoral pain

Patellofemoral pain (PFP) is common throughout all stages of life and may start as early as adolescence¹. It can occur in both physically active and sedentary people, and is proposed to result in eventual osteoarthritis. PFP can have a significant negative impact on quality of life³. Physical activity is often limited, levels of anxiety and fear of movement are raised⁴, and a higher body mass index is often the result⁵. The long-term consequences of these knee symptoms are therefore broad and can potentially speed the development of other problems associated with inactivity.    

Despite considerable evidence that conservative management, including multimodal physiotherapy, is effective, these interventions do not appear to have positive long-term effects⁶. The current evidence clearly indicates that the natural history of this common complaint is not one of spontaneous recovery, meaning that an early and accurate diagnosis is vital. The effectiveness with which important deficits are identified, and the appropriateness of the subsequent management plan, is likely to have a significant positive impact on long-term outcomes.  

This clinical commentary aims to present the current thinking about PFP diagnosis, considering the role for imaging and the methods through which important treatment targets should be identified.  

Listen to their story

As with all other musculoskeletal complaints, the subjective history offers the clinician a critical insight into the patient’s symptoms and should offer clues about the possible drivers of their pain. PFP is most commonly reported as having a gradual onset, aggravated by activities that load the extensor mechanism of the knee (including stairs, squatting and running) and should be located at, around or underneath the patella⁷. While of some diagnostic benefit, these subjective features alone are by no means conclusive, with patella tendinopathy, iliotibial band syndrome and Hoffa’s fat pad irritation all presenting with similar patterns. Further exploration of symptom onset is of benefit, in particular exploring changes in activity or load (frequency, intensity, duration) and the patient’s global health (including previous injury, psychological wellbeing and co-existing pain complaints), to guide subsequent management planning and help in ruling out ‘red flag’ pathology.    

Watch them move 

The objective examination serves to rule in or out your subjective hypothesis of PFP. While not diagnostic in isolation, asking the patient to perform a squat and then a single leg squat, can offer useful insight into movement deficits. A willingness to load the knee joint with such tasks gives the clinician insight into the severity of pain, levels of apprehension to movement and commonly adopted movement patterns. A comparison with the contralateral side should help to determine significant differences in movement patterns, which might form a treatment target (ie unilateral dynamic knee valgus).  

Subsequent examination should start the process of a diagnosis by exclusion. A combination of an insidious onset and anterior knee pain presentation, with the addition of localised tenderness at inferior pole of patella, should increase the index of suspicion for patella tendinopathy. In turn, eliciting pain during compression of the fat pad (using the thumb and forefinger) during passive knee extension should lead more towards the Hoffa’s fat pad as the main nociceptive driver. Retropatellar tenderness, in the absence of tibiofemoral joint line tenderness, full flexion/extension range of motion and ligamentous integrity, should significantly elevate the index of suspicion for PFP. Patellofemoral compression, or a Clarke’s test, can be of useful negative diagnostic value. But it is important to remember that up to 70 per cent of people with no complaint of knee pain will find this test painful.  

What does imaging add?

Given that the diagnosis of PFP is one of both exclusion and inclusion, magnetic resonance imaging (MRI) can be a useful tool in guiding the exclusion component.  MRI can offer insight in other structural deficits within the knee which, when combined with an appropriate clinical examination, may contribute to reaching a diagnosis and help guide management planning. For example, a large bone bruise or a significant osteochondral defect within the patellofemoral joint, should slow the rate of load progression during rehabilitation⁸, and may require involvement of the multidisciplinary team in future decision making. 
What has consistently been demonstrated, however, is the absence of MRI findings that are associated with PFP. Cartilage changes in isolation (often reported as chondromalacia patellae) are of little value, with a large cohort study reporting no differences in cartilage volume, when comparing those with anterior knee pain to well-matched, asymptomatic controls⁹. As a result, the structural insight that imaging affords the clinician can, and should when available, be used to educate the patient. Combined with appropriate education, imaging can serve to allay fears of a serious problem and encourage adherence to a conservative management plan.  

For those with an interest in further developing their knowledge of PFP, readers are directed to a masterclass in Physical Therapy in Sport published in July 2018

• Simon Lack is head of research at Pure Sports Medicine in London and leads the sports and exercise MSc programme at Queen Mary University of London. 
• Brad Neal is head of research at Pure Sports Medicine in London and a PhD candidate at Queen Mary University of London

Further information

Visit the Pure Sports Medicine website here.   @simonthephysio; @Brad_Neal_07  @puresportsmed

Bringing it all together

References

¹ Smith BE, Selfe J, Thacker D, Hendrick P, Bateman M, Moffatt F, et al. Incidence and prevalence of patellofemoral pain: A systematic review and meta-analysis. PloS one. 2018;13(1):e0190892.
² Crossley KM. Is patellofemoral osteoarthritis a common sequela of patellofemoral pain? British journal of sports medicine. 2014;48(6):409-10.
³ Coburn SL, Barton CJ, Filbay SR, Hart HF, Rathleff MS, Crossley KM. Quality of life in individuals with patellofemoral pain: A systematic review including meta-analysis. Physical Therapy in Sport.
⁴ Maclachlan LR, Collins NJ, Matthews MLG, Hodges PW, Vicenzino B. The psychological features of patellofemoral pain: a systematic review. British journal of sports medicine. 2017;51(9):732-42.
⁵ Hart HF, Barton CJ, Khan KM, Riel H, Crossley KM. Is body mass index associated with patellofemoral pain and patellofemoral osteoarthritis? A systematic review and meta-regression and analysis. British journal of sports medicine. 2017;51(10):781-90.
⁶ Lankhorst NE, van Middelkoop M, Crossley KM, Bierma-Zeinstra SM, Oei EH, Vicenzino B, et al. Factors that predict a poor outcome 5-8 years after the diagnosis of patellofemoral pain: a multicentre observational analysis. British journal of sports medicine. 2016;50(14):881-6.
⁷ Crossley KM, Stefanik JJ, Selfe J, Collins NJ, Davis IS, Powers CM, et al. 2016 Patellofemoral pain consensus statement from the 4th International Patellofemoral Pain Research Retreat, Manchester. Part 1: Terminology, definitions, clinical examination, natural history, patellofemoral osteoarthritis and patient-reported outcome measures. British journal of sports medicine. 2016;50(14):839-43.
⁸ Stefanik JJ, Gross KD, Guermazi A, Felson DT, Roemer FW, Zhang Y, et al. The relation of MRI-detected structural damage in the medial and lateral patellofemoral joint to knee pain: the Multicenter and Framingham Osteoarthritis Studies. Osteoarthritis and cartilage. 2015;23(4):565-70.
⁹ van der Heijden RA, Oei EH, Bron EE, van Tiel J, van Veldhoven PL, Klein S, et al. No Difference on Quantitative Magnetic Resonance Imaging in Patellofemoral Cartilage Composition Between Patients With Patellofemoral Pain and Healthy Controls. The American journal of sports medicine. 2016;44(5):1172-8.