Patellofemoral Pain Syndrome
Patellofemoral pain syndrome (PFPS) is the most common cause of anterior knee pain.
The clinical challenge arises from the many potential factors contributing to PFPS. Unfortunately the literature does not agree on the importance of these variables. This month’s Physio Window will take a brief look at each of the primary factors to provide an evidence based approach to clinical decision making.
Overuse
Although PFPS is classically referred to as an overuse injury, there is little direct evidence that confirms this. Increased body weight, competitive sport and overtraining will increase the biomechanical load on the knee and may, in combination with the other factors mentioned below, contribute to the development of PFPS.
Alignment 
The literature continues to be somewhat controversial on the roles that the Q-angle and rearfoot position play on PFPS. The take home message being that prescribing orthotics to every client with PFPS may be met with mixed results. There does appear to be a significant contribution from lateral patellar tilt and decreased medial glide of the patella as contributing factors to PFPS.
Biomechanics
Hip mechanics have recently come to the forefront of treatment of PFPS. Willson studied single leg jumping in women with PFPS and found they had greater hip adduction excursion and hip abduction impulses. In addition, the University of Calgary Running Injury Clinic has found that the six most significant biomechanical variables are: foot pronation; time to peak pronation; heel whip, pelvic drop, hip inward collapse; and knee thrust (lateral movement velocity).
Flexibility:
Decreased muscle length has been found to alter patellar tracking. Specifically, Puniello found a strong relationship between iliotibial tightness and decreased medial glide of the patella. Clinically, the ITB can be tested with the Ober’s test.Tight quadriceps muscles, particularly the rectus femoris, can lead to PFPS. Test the rectus femoris by the Thomas test or a prone knee bend. Decreased hamstring length has also been found to be an influencing factor in PFPS however statistical significance is inconsistent. Test via a straight leg raise and look for 80-100 degrees of hip flexion. Similarly, gastrocnemius tightness has been reported both positively and negatively in the literature. For the most part we should have 90 - 110 degrees of ankle dorsiflexion in knee extension and 100 - 120 degrees with the knee flexed. The difference between gastrocnemius and soleus should be at least 10 degrees.
Strength:
Again the literature vascillates on the importance of muscle strength, especially around the hips. Most authors have found a correlation between quadriceps weakness and PFPS. Some have specifically looked at the role Vastus Medialis Oblique(VMO) strength and timing plays in normal patellar tracking, however, Syme found similar benefits to clients with PFPS with or without emphasis on selective activation of the VMO component. He suggested limiting the focus on this aspect to the early phase of rehabilitation. There is some evidence of hip abductor weakness in groups with PFPS. De Marche Baldon found a 28% decrease in abduction eccentric mean peak torque compared to the control group.
In order to avoid the shotgun approach to treating PFPS, a few further tests will help guide clinical decision making in choosing the most efficacious treatment options.
REFERENCES:
De Marche Baldon R, Eccentric Hip Muscle Function in Females With and Without Patellofemoral Pain Syndrome, Journal of Athletic Training, 2009; 44(5): 490-496
Puniello MS, Iliotibial band tightness and medial patellar glide in patients with patellofemoral dysfunction, Journal of Orthopaedic & Sports Physiotherapy, Mar 1993; 17 (3): 144-8
Syme G, Disability in patients with chronic patellofemoral pain syndrome: a randominsed controlled trial of VMO selective training versus general quadriceps strengthening, Manual Therapy, Jun 2009; 14 (3); 252-63
Waryasz GR, Patellofemoral pain syndrome (PFPS): a systematic review of anatomy and potential risk factors, Dynamic Medicine, June 2008, 7:9, doi:10.1186/1476-5918-7-9
Willson JD, Lower extremity strength and mechanics during jumping in women with patellofemoral pain, Journal of Sports Rehabilitation, 2009 Feb; 18(1), 79-90