Patellofemoral pain syndrome (PFPS) can be a real pain in the knee, but is it really a knee problem? PFPS is a common injury experienced by adults and adolescents and presents as anterior knee pain, pain in or around the patella (Lankhorst, Bierma-Zeinstra & van Middelkoop, 2012). Often pain increases when running, using stairs, kneeling, sitting or squatting (Callaghan & Selfe, 2012). PFPS is the most common diagnosis amongst runners (Aytar et al., 2011) and accounts for 25-40% of all knee injuries seen within sports injury clinics (Kannus, Aho, Järvinen & Nttymäki, 1987). Females are shown to have a 2.23 times higher incidence than males and it is theorised that q‐angle and leg strength differences between genders could be contributing factors (Boling et al., 2010; Daneshmandi, Saki, Shahheidari & Khoori, 2011). Despite its prevalence, there is still little consensus on its exact cause and subsequent treatment. When investigating the cause of pain, Dye, Stäubli, Biedert and Vaupel (1999) found that individuals reporting PFPS often had no identifiable structural abnormalities. In a systematic review by Cook, Mabry, Reiman and Hegedus (2012) looking into clinical tests for diagnosing PFPS, they concluded that the best tests are still unknown. It has been suggested that the best means of diagnosis is one of exclusion, where intra-articular pathologies, tendinopathy, bursitis, Osgood-Schlatter disease or other rare pathologies are ruled out (Lankhorst et al., 2012). A recent cross-sectional observational study found altered patella tendon reflex excitability in females with PFPS. The authors (Pazzinatto et al., 2019) suggested this as a possible clinical test.
To effectively prevent or treat PFPS, it is important to try and understand risk factors. To date, several studies have investigated the hip muscles and their link to PFPS. In a study analysing gluteal muscle activation in female runners, Willson, Kernozek, Arndt, Reznichek and Straker (2011) found that gluteus medius (GMED) activation was delayed and shorter in duration in those experiencing PFPS. Another important finding was a moderate correlation with hip adduction (knee valgus) impacting on gait kinematics, which can also be seen during stair negotiation (Barton, Lack, Malliaras and Morrissey, 2013). More evidence was offered in a study by Neal, Barton, Birn-Jeffery and Morrissey (2019) where runners with PFPS had on average 4.9° greater peak hip adduction than controls without PFPS. Noehren, Scholz and Davis (2011) investigated the impact of gait kinematics on hip mechanics, pain and function in runners with PFPS. Using real-time gait retraining over 2 weeks, subjects were instructed to contract the gluteal muscles and maintain a level pelvis. The result was a 5° reduction in hip adduction and an 86% reduction in pain, which persisted after 1 month. Hip adduction contributing to excessive q-angle, has been identified as a risk factor for knee injury (Daneshmandi et al. (2011) and should be corrected as part of a prehabilitation programme.
When compared to quadriceps (quad) strengthening, hip strengthening has been shown to achieve positive results in a shorter time period. In a study where both were used as a rehabilitation method, pain and function improved in both groups. However, improvements were reported in the hip group after 4 weeks, compared to 8 weeks (Dolak et al., 2011). Activation and strength of the quad muscles, vastus lateralis (VL) and vastus medialis oblique (VMO) have been another large area of research when trying to understand PFPS. Using electromyographic (EMG) to measure the firing pattern of the VMO and VL, Cowan, Hodges, Bennell and Crossley, (2002) found that during sit to stand there was delayed VMO recruitment in subjects with PFPS compared to those without. However, this contradicts earlier research by Sheehy, Burdett, Irrgang and Van Swearingen (1998) who found no significant difference, when using the same method while negotiating stairs. However, changes in relative VMO-VL activation were seen in individuals descending stairs after motor control and quad strengthening exercises were used (Bennell et al., 2010). Delayed VMO activation has a significant correlation to patella maltracking in individuals with PFPS (Pal et al., 2011). Therefore, VMO and/or overall quad strengthening has been shown in many studies to be an effective treatment for PFPS (Bennell et al., 2010; Dolak et al., 2011; Eapen, Nayak & Zulfeequer, 2011; Kaya et al., 2011; Kooiker, Van De Port, Weir & Moen, 2014).
Another hypothesised risk factor is excessive foot pronation or rearfoot eversion. Barton, Bonanno, Levinger and Menz (2010) found individuals with PFPS had greater foot pronation than those without. Ferreira et al. (2018) concluded that foot pronation significantly predicted peak hip internal rotation in females during stair ascent. Barton, Menz & Crossley (2011) looked at the effectiveness of foot orthoses on pain and functional performance on individuals with PFPS. During a single leg squat, individuals with foot pronation had an immediate and significant reduction in pain. These finding are supported in earlier research looking at the role of foot orthoses as an extrinsic treatment for PFPS (Gross & Foxworth, 2003; Johnston & Gross, 2004). Kinesio taping (KT) is another commonly used extrinsic treatment for treating PFPS (Callaghan & Selfe, 2012) although the evidence of its effectiveness is debatable. A Cochrane review concluded that the outcomes were not sufficient enough to recommend KT as an effective treatment. In addition, Aytar et al., 2011 found KT was no better than placebo in improving pain and joint position. Other authors (Aminaka & Gribble, 2008; Whittingham, Palmer & Macmillan, 2004) argue that KT can be effective as part of a rehabilitation programme.
In conclusion, once all other pathologies are ruled out, non-specific anterior or prepatellar pain is classified as PFPS. The research shows that hip strengthening, VMO activation and overall quad strengthening are effective in reducing symptoms of PFPS. Foot orthoses is also effective in individuals with excessive foot pronation. Furthermore, this would suggest muscle dysfunction including delayed VMO activation, quad weakness, hip weakness, specifically GMED and foot pronation are risk factors for PFPS. There is evidence that these dysfunctions can result in knee valgus and maltracking of the patella and that this is more prevalent in females due to their increased q-angle. Therefore, a prehabilitation programme would have a focus on correct knee alignment. This can be achieved by retraining and awareness of knee position through functional movement, which is supported through corrective, strengthening exercises, foot orthoses and possibly use of KT.
In this video we will take a brief look at how to differentiate between PFPS and other, similar conditions sometimes referred to as “runner’s knee”. We will review the anatomy and function of the knee and factors that contribute to increased q-angle and patellar maltracking. Finally, how to prevent PFPS through correcting muscular imbalances by using simple exercises.
References
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