What is Anterior Knee Pain?
Among all the disorders of the knee, patella femoral pain is the most common in athletes. It is also called runner’s knee, chondromalacia, and anterior knee pain. What that mean is the cartilage on the undersurface of the knee cap is wearing out.
Anatomy of the Knee
A short lesson in anatomy is required to understand this condition. The knee cap also called patella is a big triangular bone, located in the front and middle of the knee joint. The patella resides within the quadriceps tendon. The quadriceps tendon above the knee and the patella tendon below the knee, attach to the patella. On the inside of the knee, muscle called vastus medialis oblique (VMO) is attached to the patella and on the outside of the patella, vastus lateralis muscle (VLM) and the ilio-tibial band (IT band) are attached. There is a ligament called the patello-femoral ligament which attached in the inside of the knee. Moreover, there is a medial and lateral retinaculum which attach on the inside and outside of the patella. Visualizing the anatomy of patella and the surrounding attachments, it gives you the idea that it is pulled in all 4 directions, upward, downward, inside and outside. The different angles of pull keep the patella in the middle of the knee, which then give the quadriceps muscle, the big muscle located on top of the patella, a mechanical advantage to bend and extend the knee. The knee cap acts as a pulley so the legs and move efficiently.
The knee cap has a perfect location, within a groove of the thigh bone. In between the undersurface of the patella and the groove of the thigh bone found a very tough cartilage. This cartilage prevents bone rubbing on bone. It also allows the patella to glide smoothly in the groove during knee and hip motion. In a pain free knee, the balance between the different angles of pull from the muscles, ligaments and retinaculum are in perfect rhythm. This perfect rhythm is controlled by the brain/nervous system. In a painful knee, the perfect rhythm becomes dysfunctional, which eventually caused damage to the tough cartilage or soften it, resulting in pain in the knee. The damages occur when the patella is not perfectly fit into the groove of the thigh bone. It rubs on the bone, on top or on the outside of the groove, because the balance between the angles of pull are disrupted. This is called patella maltracking, meaning the patella is not tracking within the groove. Regaining this balance is the key to success in rehabilitation.
There are other factors which influence the balance of the patella in the groove. Biomechanical factor is one of them. Athlete with excessive flat foot, usually over pronates (inside arch of the foot collapses) and for the leg to compensate, the tibia(the bone above the ankle) turns outward and the femur(the bone above the knee) turns inward. This compensation forces the patella to slide outward (outside the groove), resulting in the cartilage rubbing against the bone. Imagine running with a pronated foot for years. Knocked knees have the similar biomechanical effect as above.
Research studies have agreed on identifying four parameters which increased the risk of anterior knee pain. A shortened (tightness) quadriceps muscles, a hypermobile (loose) patella, an altered VMO muscle reflex response time (VMO is slow to activate/fire), and decreased explosive strength. A tight quadriceps muscle pulls the patella high on the groove and creates stresses on the cartilage and imbalance within the groove.
A loose patella is a patella which move excessively within the groove. The excessive movement s are from side to side movements. There is an increased in outside (lateral) movement than the inside (medial) movement of the patella. This occurs from an imbalance between the medial retinaculum, patello-femoral ligament and the lateral retinaculum, where the lateral retinaculum and ligament are stronger than the medial retinaculum. The lateral retinaculum and ligament pull the patella outward (lateral), resulting in repeated blows on the undersurface of the patella on the thigh bone. With the quadriceps muscles relaxed, the retinaculum are known to restrict motion of the patella and keep the balance within the groove.
The VMO response time is slower in athlete with anterior knee pain
In athlete with no anterior knee pain, the VMO muscles fires fast and before the vastus lateralis (the muscle on the outside of the knee) to maintain the patella in the groove. A delayed in response of the VMO muscle allows the vastus lateralis muscle to pull the patella outward to the side, resulting in damages to the undersurface of the patella when it hits the thigh bone.
In athlete with anterior knee pain, there is a decreased in explosive strength capacity in the leg. Studies hypothesize that a decreased in explosive strength leads to reduced capacity to absorb high patella-femoral forces during fast functional, eccentric sports activities. This reduction in capacity of shock absorbing may lead to higher stress on the knee, resulting in anterior knee pain. Decreased in vertical jump performance in athlete with anterior knee pain is well documented in scientific studies.
Physical therapy to help knee strength
Hence, to decrease the risk of developing chondromalacia, quadriceps muscle stretches is paramount. Increasing strength in the quadriceps muscles and hip muscles limits the excess mobility of the patella in the groove. Eccentric (negative) strength training is the most appropriate exercise to help with the stability of the patella. VMO timing is improved by training the quadriceps muscle as a whole, not just isolating the VMO. Explosive power of the muscles is achieved by plyometric exercises. Additionally, ilio-tibial band and buttock muscles need stretch because the buttock muscle fascia is attached to the ilio-tibial band and the ilio-tibial band is attached to the outside of the patella.
by Raj Issuree, MPT
References:
Witvrouw E, Lysens, R et al. Intrinsic risk factors for the development of anterior knee pain in an athletic population. Am J Sports Med 2000; 26(4): 480-488
McConnell J. The management of chondromalacia patellae: A long term solution. Aust J Phys Ther 1986; 32(4): 215-223
Crossley K, Bennell K et al. Physical Therapy for patellofemoral pain. A randomized double blinded, placebo-controlled trial. Am J Sports Med 202; 30(6): 857-865.
