The lateral dislocation is usually blamed on a weak vastus medialis muscle and overly strong vastus lateralis muscle and typical exercise therapy or physical therapy involves quad strengthening exercises to correct this imbalance. I agree that this imbalance is typically present, but I rarely believe it is the cause of the problem, but rather a symptom of, or compensation for, a much bigger problem.
The image and accompanying text below expand the "quad imbalance view" to include a weak rectus femuris, a strong tensor fascia lata (TFL) and a tight iliotibial (IT) band that all play a role in the faulty patellar tracking. The TFL is a strong hip flexor that also abducts and internally rotates the femur and externally rotates the tibia. The TFL via the IT band can thus create internal femur rotation while at the same time creating external tibial rotation and, via the fascia that connects the IT band to the lateral side of the patella, will have the effect of pulling the patella in and out of its groove as the hip and knee flexes and extends. Physical therapists, exercise specialists, and personal trainers who look at this larger picture will include stretching for the IT band and TFL muscle along with the quad strengthening exercises mentioned previously.
What about the iliacus and psoas muscles?
While walking, climbing stairs, or running your feet and knees should point straight ahead and your hips/pelvis should remain almost level. Weakness in the above mentioned muscles allows excessive movement in the transverse and frontal planes which creates forces on the knee and patella that can pull it out of its groove causing PFPS.
How does someone with weak hip muscles move from point A to point B? By compensating for the weak muscles and creating compensatory movement throughout the entire body as can be seen below. The woman on the left is showing proper movement patters. The woman on the right is showing dysfunctional movement caused by weak and imbalanced hip musculature which is creating compensatory movements throughout her body. Those compensatory movements create muscle imbalances up and down the entire body.
The woman on the right shows many postural imbalances: dropped right shoulder, right lateral head tilt, torso offset to left, right elevated pelvis/hip, valgus knee position, externally rotated right femur, everted feet right more than left. If all these imbalances are not corrected, strengthening the vastus medialis and gluteus medius and stretching the IT band will have very little if any long term benefit. The body is a unit and when treated as one patallofemoral pain syndrome and any other musculoskeletal pain can become a thing of the past.
- Lankhorst NE, Bierma-Zeinstra, SMA, and van Middelkoop, M. Factors associated with patellofemoral pain syndrome: a systematic review. Br J Sports Med. 2013;47:193–206.
- Barton CJ, Lack, S, Malliaras, P, and Morrissey, D. Gluteal muscle activity and patellofemoral pain syndrome: a systematic review. Br J Sports Med. 2013; 47:207–214.
- Selkowitz, DM, Beneck, GJ, and Powers CM. Which Exercises Target the Gluteal Muscles While Minimizing Activation of the Tensor Fascia Lata? Electromyographic Assessment Using Fine-Wire Electrodes. J Orthop Sports Phys Ther. 2013; 43(2):54-64.