Anatomy/Symptoms
The knee joint is the largest joint in the body. It consists of the bones of the end of the femur (thigh bone), the top of the tibia (shin bone), and the underside of the patella (kneecap). Articular cartilage covers the back of the patella and the ends of the other bones, allowing smooth movement of the bones over each other. The right knee is shown below.
The patella is kept in place in front of the knee by tendons and ligaments. The patella moves within its groove over the end of the femur when bending and straightening the knee.
For various developmental reasons, sometimes the patella does not track properly within its groove over the femur. As a result of this, damage to the undersurface of the patella or instability of the patella, causing dislocation, can occur.
Non-operative Treatment
Physiotherapy and exercises may help strengthen the muscles of the thigh and help to keep the kneecap stable. Wearing a knee brace or support during sporting activities may be recommended. The use of analgesics and/or non-steroidal anti-inflammatories may be prescribed.
If you experience dislocation of the patella or if your pain is disabling, surgery is indicated.
Operative Treatment
Knee Arthroscopy and Lateral Retinacular Release; Tibial Tubercle Osteotomy or Semitendinosus tenodesis
To correct this condition, it is necessary to perform an arthroscopy of the knee joint. A small telescope and arthroscopic instruments are used to smooth off the undersurface of the patella and the groove in which it runs. Fibrous tissue on the outer (lateral) side of the patella is released (lateral retinacular release) to stop it tethering to the patella.
It may also be necessary to move the attachment of the patella tendon to the tibia so that it lines up with the groove that the patella should move in. This is called a Tibial Tubercle Osteotomy. The shifted bone is fixed in place with two screws.
In some cases, patella stabilisation is achieved using a hamstring tendon graft (Semitendinosus tenodesis). In this instance, the harvested tendon is woven through and around the patella, and sutured in place to improve patella stability.
Both knees can be treated simultaneously, as the condition usually affects both patellae.
Post-operative Course
This surgery usually requires a 2-night stay in hospital.
After the surgery, you will have a wound drain in your knee and a removable splint on your leg. On the afternoon of surgery, movement of your knee on a Continuous Passive Motion (CPM) machine is usually started. This helps maintain the range of motion in your knee.
The day after surgery, the wound drain will be removed. The padded dressings will be removed and a waterproof dressing applied over the wounds. You will need to keep the splint on your leg when mobilising to help provide support and stability. Crutches will also be useful with mobilising for the first week or so.
Approximately one week to 10 days after surgery, it is possible to commence rehabilitation by riding on an exercise bike. The knee splint can be taken off for exercising and when resting, but it should again be worn whenever mobilising for 4-6 weeks. As you are able, the length of time you spend on the exercise bike is increased so that at the six-week mark, when the osteotomy is healed, good strength and mobility of the knee has already been achieved. This can be built on over the following six weeks, expecting normal function to return at the three-month stage.
Risks/Complications
Some complications that can occur following this surgery include: