The patella (also known as knee cap) is a thick, circular-triangular bone which articulates with the femur and covers and protects the anterior articular surface of the knee joint.
It is the largest sesamoid bone in the human body. In the adult the articular surface is about 12 cm2 and covered by cartilage, which can reach a maximal thickness of 6 mm in the centre at about 30 years of age.
The patella is attached to the Quadriceps tendon (of the quadriceps femoris muscle), which contracts to extend/straighten the knee. The vastus lateralis and vastus medialis are attached to lateral and medial borders of patella respectively. The vastus intermedialis muscle, not showed in this picture, is attached to the base of patella.
The patella is stabilized by the insertion of vastus medialis and the prominence of the anterior femoral condyles, which prevent lateral dislocation during flexion. The retinacular fibres of the patella also stabilize it during exercise.
The primary functional role of the patella is knee extension. The patella increases the leverage that the Quadriceps tendon can exert on the femur by increasing the angle at which it acts.
Patellar problems are among the most common causes of knee pain. This disease may be associated with other symptoms, such as instability or giveaway, dislocation, catching, grinding (crepitation), and/or swelling. These symptoms may present spontaneously or following injury (such as subluxations, blows to the front of the knee etc.). In general terms, patellar problems can be organized as:
- Pain alone – “patellofemoral syndrome”,
- Pain from malalignment – tilt and/or displacement,
- Instability – subluxation and dislocation,
- “Wear and tear” – arthritis,
- Other problems – synovial plica, tendonitis, bursitis, Osgood Schlatter’s disease, etc.
Surgery is rarely necessary, and must be carefully considered. For example, for the “pain alone” case, surgery is rarely indicated since it may even make pain worse. In these terms, surgery is best used as a last resort, after all other techniques fail (normally: conservative care trials).
Arthroscopy is the very best way to evaluate the patella and surrounding portions of the knee joint. Surgery will vary depending upon the type of patellar problem. Of course it has risks, such as infection, stiffness, continued instability, weakness, pain, blood clots, fracture, impaired bone healing, etc. Recovery ranges from 6 weeks to 6 months, or even longer, depending upon the type of surgery, healing rates and limitations, and patient rehabilitation and efforts.