Knowledge of the anatomy of the patellofemoral joint is key to understanding why PFPS occurs. Normally, as the knee bends and straightens, the patella (or kneecap) slides up and down a groove formed in the thighbone. This motion is controlled by a number of muscles, ligaments and tissue that surround the knee.
The exact cause of PFPS is not well understood. Most researchers believe it is caused by a breakdown in the structures that control the motion of the kneecap. If the patella moves incorrectly through this groove, it creates the potential for pain and instability in the knee to occur.
Some of the more common reasons that contribute to this breakdown include: muscle tightness, weakness in the hip and an imbalance of the muscles in the front of the thigh.
The quadriceps muscles and ilio tibial band (ITB) tend to be tight in people with PFPS. If the quadriceps muscles are tight, they tend to pull the kneecap much closer to the thigh bone. This increase in tension leads to grinding of the kneecap against the thigh bone which can lead to changes along the surface of the patella causing it to track differently. The ITB has attachments to the outer side of the kneecap. When it is tight, it pulls the kneecap in an outward direction shifting the kneecap away from its groove.
Recent research also shows PFPS is related to hip muscle weakness. The muscles located in the outer and back portion of our hips contribute tremendously to how our leg lands when we walk and run. Normally, these muscles help to slow the leg down before it impacts the ground. Weakness in these muscles can cause the leg to impact the ground with greater force, causing the knee to fall inward and stress the patellofemoral joint. Repeated landing in this position can result in inflammation and poor tracking of the kneecap.
Finally, poor tracking of the patella can also result from an imbalance of the muscles in the front of the thigh. The muscle along the inner part of the thigh called the vastus medialis oblique, or VMO can become weak with repeated landing in a poor mechanical position. When this muscle becomes weak or inflamed, the muscles in the center and outer portion of the thigh begin to overwork causing the kneecap to pull up and out to the side.
Finally, poor tracking of the patella can also result from an imbalance of the muscles in the front of the thigh. The muscle along the inner part of the thigh called the vastus medialis oblique, or VMO can become weak with repeated landing in a poor mechanical position. When this muscle becomes weak or inflamed, the muscles in the center and outer portion of the thigh begin to overwork causing the kneecap to pull up and out to the side.
Treatment of patellofemoral pain is complex. A thorough assessment by a physician or physical therapist to determine the structures involved is key to understanding how to resolve the pain. Most studies show that physical therapy remains the treatment of choice for the management of PFPS. Surgery is typically indicated in cases where therapy has been ineffective or when changes to the surface of the patella are evident.
To learn more about this injury and others, contact your local physician or physical therapist.
References:
1. Cowan et al. Physical Therapy Alters Recruitment of the Vasti in Patellofemoral Pain Syndrome. Med Sci Sports Exerci. 2002. 34:12;1879-1885.
2. Eng et al. Evaluation of Soft Foot Orthotics in the Treatment of Patellofemoral Pain Syndrome. Phys Ther. 1993, 73:2, 62-68.
3. Fagan et al. Patellofemoral pain syndrome: a review on the current associated neuromuscular deficits and current treatment opitions. Br J Sports Med. 2008;42:789-795.
4. Harvie et al. A systematic review of randomized controlled trials on exercise parameters in the treatment of patellofemoral pain: what works? Journal of Multidsciplinary Healthcare. 2011; 4:383-392.
5. Cerny K. Vastus Medialis Oblique/Vastus Lateralis Muscle Activity Ratios for Selected Exercises in Persons With and Without Patellofemoral Pain Syndrome. Phys Ther. 1995; 75(8):672-682.
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