8 Factors to Evaluate in PFPS
Patellofemoral Pain Syndrome (PFPS) is a common syndrome encountered in the sports medicine clinic. The problem is that it is a condition diagnosed by exclusion. As a clinician, you must perform a thorough knee assessment to rule out other competing conditions before diagnosing a patient with PFPS.
Because of the difficulty in categorizing PFPS, there is a lack of consensus in the research surrounding etiologies and appropriate treatments. However, the following is a list of the most current research regarding the factors that influence the development of PFPS.
1. Hip abductor and external rotation strength
By far the most consistent finding in the literature is the relationship between hip strength and PFPS. A few systematic reviews have shown decreased hip strength and lumbopelvic control in patients with PFPS. Clinicians should assess strength and control of the hip in both non-weightbearing and functional tasks (single-leg stance).
2. Knee extensor strength
The overall size and strength of the quadriceps as well as the coordination between the vastus medialis (VMO) and vastus lateralis (VL) has been shown to be an important factor in PFPS. Interestingly, the VMO is not selectively atrophied compared to the VL in the symptomatic knee. Another study showed that the hamstrings can contribute to altered movement of the patella, specifically in knees with previously altered patellofemoral mechanics and VMO weakness. Loading the hamstring in these imbalanced knees can lead to posterior tibial translation and external rotation, impacting the mechanics and position of the patella during movement. Clinicians should evaluate the size, strength and coordination of the quadriceps muscle compared with the uninjured leg, ideally with a validated functional test such as the one-legged hop test.
3. Hamstring muscle tightness
Although many patients with suspected PFPS may be “tight” in both the hip and knee (including hamstring, iliopsoas, iliotibial band, and gastroc-soleus), the one muscle group that is consistently linked to PFPS in the literature is hamstring muscle tightness. Clinicians should evaluate the entire hip and knee region, but special attention should be directed towards any hamstring length-tension differences.
4. Dynamic knee and hip alignment
Studies have shown that patients with PFPS have reduced knee proprioception in both the affected and unaffected leg. In male runners, there was an increase in knee adduction during running and squatting. In female runners, there was a greater increase in hip adduction during these same activities. However, the biomechanics of the lower limb and its relationship to PFPS is variable and poorly understood. Therefore, clinicians should evaluate dynamic movements, such as the eccentric step down test, and either unload or load the knee in various movements to help uncover pain-free positions.
5. Patellar position in weightbearing
Patellar mobility is frequently assessed in the clinical setting and hyper or hypo-mobile retinaculum has been observed in patients with patellofemoral pain syndrome. When assessing the position of the patella, it is common to do so in a supine, knee extended position. However, this position may not adequately reflect patella kinematics during painful activities. Patients with PFPS and patellar maltracking had increased lateral patellar translation and tilt in a weight bearing position compared to supine position. In asymptomatic patients, lateral patellar translation was more evident in a supine position. Therefore, clinicians should evaluate patellar tracking and position in weight bearing activities, especially those which are painful for the patient.
6. Excessive and repetitive loading of patellofemoral joint
Placing excessive demands on any tissue within the body can lead to pain and dysfunction. High intensity activities involving repetitive knee flexion in athletes has been linked to patellofemoral pain. Patellofemoral forces are highest in closed kinetic chain (CKC) exercises in >30 degrees of knee flexion, with a peak force in full knee flexion. Patellofemoral forces also increase from 90 degrees of knee flexion to full extension in open kinetic chain (OKC) activities, with a peak force in <30 degrees of knee flexion. Clinicians should aim to understand all the activities that may be causing an athlete pain, introduce loading restrictions, and gradually return them to loading those movements.
7. Foot pronation and hypermobility
Foot posture is an important aspect to assess distally. Excessive foot pronation and hypermobility has been associated with patellofemoral pain syndrome. It is believed that an increase in foot pronation leads to tibial and femoral internal rotation, with subsequent changes in patellar tracking. Clinicians should evaluate foot posture in weight bearing and during functional activities. An intrinsic foot strengthening program should be incorporated and orthotics should be considered if necessary.
8. Fear of movement and catastrophic thinking
Evaluating a patient’s beliefs and thoughts surrounding their pain is an important prognostic indicator. Two factors, kinesiophobia and catastrophizing, have been shown to predict pain and disability in anterior knee pain. Clinicians should be aware of the role of psychological factors in PFPS in order to maximize treatment success and refer to the appropriate health provider if indicated.