The knee joint is composed of the top of the tibia (shin bone) and the bottom of the femur (thigh bone). The patella (kneecap) is also an integral part of the knee joint. Where these three bones contact each other there is a layer of very smooth articular cartilage lining.
These bones are held together by ligaments. Ligaments essentially function as living pieces of rope. They prevent the movement of the bones in relation to one another.
There are many factors involved in normal function of the patella. These include the shape of the patella and femur, the muscles about the knee especially the quadriceps muscle and ligaments about the knee. The medial patellofemoral ligament (MPFL) is a relatively slender band of tissue attached to the medial (inside) edge of the patella.
When the patella dislocates the normal structures are often injured. Portions of the articular surface lining are often broken off (becoming loose in the knee) and the MPFL is torn.
If there are no other injuries then physiotherapy may settle the knee. Often however there will be symptoms from loose bodies in the knee or ongoing instability with recurrent patella dislocation.
The treatment of patients with a first time patella dislocation is relatively straightforward. It involves assessment for other injuries (loose pieces of articular surface or ligament injury) and surgery for those if required. Physiotherapy often for extended periods is also essential.
In the patient who has had multiple dislocations of the patella the treatment is more difficult. Physiotherapy will be required, loose bodies may need to be removed. Stabilisation of the patella to prevent recurrent dislocation can require several different approaches depending on the underlying problem. Initially, investigation of the underlying cause with special xrays and scans will be required. An approach involving various surgeries to the ligaments and bones is often required.