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Anatomy and Function of the Knee
Before you start, it will be very helpful to read our knee anatomy information so to better understand the knee, where the patella (knee cap) is located, and how the knee works. You can always refer to this information later in the article.
Anatomy and Function of the Patella
The patella, or kneecap, is the loose, moveable bone on the front of the knee. The patella is a link between the pelvis, hip, and foot. The patella is part of the extensor mechanism of the leg; the extensor mechanism acts as a stabilizer when we straighten our leg. This mechanism is composed of the quadriceps, the quadriceps tendon, patella and patellar tendon. The patella gives power to the quadriceps muscle on the front of the leg. In order for the patella to track up and down normally in the patellofemoral groove formed by the medial and lateral condyles, there has to be balance on both the lateral (outside) and medial (inside) side of the patella as the patella moves up and down the groove throughout the knee’s full range of motion.
The underside of the patella is covered with articular cartilage, which is a smooth, spongy covering on many joint surfaces. This slippery surface helps the patella glide inside the patellofemoral groove in the femur.
How The Patella Causes Knee Problems
Problems develop when the patella suffers wear and tear. The underlying cartilage begins to soften, called chondromalacia patellae. Wear and tear can develop for several reasons. Degeneration can develop from generalized wear and tear—similar to putting a lot of mileage on a car. Problems can also be caused when the muscles on the front or outside of the thigh are way too tight.
A very common knee problem is when the patella moves as the knee bends or straightens. This happens because of a muscle or structural imbalance. Normally the patella moves along a path controlled by the quadriceps muscle. If the inside of this muscle group is weak, a muscle imbalance occurs, and the patella can move from its normal path. In time this abnormal movement can cause wear and tear to the cartilage.
A structural imbalance can exist if there are variations in the anatomy of the bones in the leg or the angle at the knee joint made by the femur and the tibia. Women tend to have a greater angle than men. The patella sits in the femoral groove at the center of this angle. When the quadriceps muscle contracts, the muscle tries to straighten this angle, and pushes the patella out of the groove to the outside of the knee. If this angle is increased, the patella tends to shift outward with more easily.
Another variation in the leg bones can happen when the femoral condyle is smaller than normal. The femoral condyle on the outside part of femur normally keeps the patella in the patello-femoral groove. If the femoral condyle is too small, the patella has a tendency to slip outward.
By viewing the knee joint on end, it’s easy to see how this shift affects the patella. As it slides through the femoral groove, the patella shifts to the outside. This places more pressure on one side of the underlying cartilage than the other. In time this pressure can cause damage to the articular cartilage.
Symptoms Of Patellar Problems
Most patients with chronic patellofemoral problems complain of knee pain when squatting, going up and down stairs, getting up after sitting a while, popping, giving way, a crackling sound in the knee, and possible mild fluid (blood or synovial fluid) on the knee.
Chondromalacia patellae exists when there is softening of the cartilage, which may develop into small fractures in the underside bone of the patella. Some people never have problems with this condition. Others have vague pain in the knee that is hard to figure out where the pain is coming from. Pain may or may not be felt along the inside edge of the patella. Typical complaints include pain when walking down stairs or hills, keeping the knee bent for long periods as in the car or theater, or with pressure to the patella. The knee may feel as if it gives out on occasion, but this is thought to be a reflex response to the pain and not an indication of instability in the knee.
The knee may feel like it’s grinding or your may hear grinding when squatting or going up and down stairs. If there is a lot of wear and tear, you may have a feeling of popping when you bend your knee. Popping and grinding can happen when the uneven surfaces of the patella and the femoral groove rub against each other.
How Are Patella Problems Diagnosed
Diagnosis begins with a complete history, which is your story of your knee problem including did you have an injury and when does it cause you problems. An examination of the knee is done, including the patella to find out the source of your pain and to find the position of your patella. You may be examined standing, sitting and lying down. Muscle strength will also be tested for muscle imbalance that can affect tracking of the patella. Xrays are done on your first visit with the orthopedist. An xray helps decide if the patella is in staying in the normal groove when the knee moves. As chondromalacia progresses, arthritis may be seen between the patella and femur. Chondromalacia is sometimes mistaken for other knee problems because the cause of the symptoms are hard to pinpoint. In these cases, other tests may be done. An MRI scan can help rule out other conditions like a torn cartilage or bone damage.
A physical therapy exam can help decide whether a muscle imbalance or other alignment problem is present. A physical therapy program may be able to resolve symptoms.
If symptoms persist, knee arthroscopy may be needed to diagnose the exact cause of your problem. The arthroscope allows the surgeon to look into the knee joint and actually see the condition of the articular cartilage on the back of the patella.
What Are The Treatments For Patella Problems
The Initial treatment for a patellar problem starts by reducing pain and swelling in the knee before. Strengthening exercises done with a swollen knee can inhibit contraction of the quadriceps causing weakness and wasting of the muscle. Rest and anti-inflammatory medicines, such as aspirin or NSAIDs, can help reduce pain and swelling.
In the early stages, physical therapy can help reduce pain and inflammation. As symptoms are controlled, your physical therapist can offer several treatment choices to correct problems with flexibility, strength, alignment, and muscle balance in the knee and leg.
If non-surgical treatment fails to improve your condition, surgery may be needed. A lateral release may be done to allow the patella to move back into its normal track and relieve pressure on the articular cartilage. In a lateral release, the tight lateral ligaments on the outside of the patella are cut to allow the patella to move towards the center of the femoral groove. These ligaments heal over with scar tissue and fill in the gap created by surgery. Looking at the end view of the knee shows how loosening these ligaments relieve pressure on the articular cartilage.
In cases of more severe misalignment, a lateral release alone may not be enough. The tendons on the inside of the knee (the medial side) may have to be tightened, pulling the patella to the center of the groove.
In very severe cases where the patella keeps dislocating, the attachment of the patellar tendon may also have to be moved. Once the surgery heals, the patella will track up and down in the patellar groove, reducing pressure on the articular cartilage.