PATELLA DISLOCATION
Patellar dislocation occurs when the patella or kneecap slips out of its groove on the front of the lower end of the femur (thigh bone). A subluxation is a partial dislocation in which the patella slips but immediately goes back into place. In a true patellar dislocation the patella goes back into place as a distinct movement, usually when the knee is straightened. This may occur seconds to hours after the dislocation.
When a patella dislocates the chance of another dislocation is quite high, somewhere between 30% and 40%. Predisposing factors include such things as the alignment of the leg, the shape of the groove in the femur for the patella, how high the patella sits in relation to the rest of the knee joint, and the alignment of the foot and ankle.
After two dislocations, the risk of further episodes of dislocation is very high, around 60% to 80%.
NON-SURGICAL TREATMENT
If your patella has dislocated only once or maybe twice, and you do not have any or relatively minor predisposing factors, nonsurgical treatment may be recommended. The emphasis of nonsurgical treatment is to build up the quadriceps muscle on the front of the thigh and in particular the vastus medialis (VMO) muscle which is the part of the quadriceps muscle just above the inside of the knee. Attempts may also be made to stretch the structures on the outside of the knee. These include the iliotibial band (ITB) and the lateral retinaculum.
SURGICAL OPTIONS
If surgery has been recommended, there are different operations that may be performed depending on the individual. The particular operation that is selected for you will depend on the alignment of your knee and patella as well as your age. An MRI scan will be obtained to help with the decision about which operation is best for you.
When the patella dislocates the first time there is a ligament on the medial, or inside, aspect of the patella that is almost always torn. The ligament is called the medial patellofemoral ligament (MPFL). The ligament can be reconstructed by using a piece of hamstring tendon and attaching it to the patella and femur. The tendon is fixed in the tunnels with screws or another type of anchor.
If the patella is sitting too high or too lateral, it can be moved downwards and into its groove on the femur by moving part of the tibia called the tibial tuberosity. This is the bony lump on the front of the upper end of the shin. The patella is attached to the tibial tuberosity by the patellar tendon. By moving the tuberosity downwards or medially, the patella is moved into a better position within its groove. Screws are used to hold the tuberosity in its new position until it heals.
RECOVERY
Most people can be discharged on the day of surgery or the first day after surgery. When you go home you will be placed in a brace for the first two weeks. You will be able to walk in the brace putting weight through your leg as can be tolerated basis and using crutches for support. Most people are walking without support by three weeks. The focus of the early rehabilitation is to reduce the swelling, restore the function of your quadriceps muscle, and to get the knee bending and straightening normally.
If the tibial tuberosity has been moved then it is important to make sure the bone is healed before more aggressive rehabilitation is commenced. Healing can be monitored with X-rays.
Once the swelling has reduced and any bone healing has taken place, progression is essentially on an as tolerated basis. It usually takesup to 3 months before one can recommence running. From here it is really a matter of function and comfort before one can resume sporting activities. It will take 6 months to be able to resume sport on a competitive basis.
COMPLICATIONS
All surgery is associated with some risk of complications. There are general complications and there are specific complications.
INFECTION
Antibiotics are given at the time of surgery to reduce the risk of infection. Despite this, infection of the wound can occur. This is usually easily treated with antibiotics. However, sometimes the infection gets into the joint, which is a serious complication and requires re-admission to hospital, additional surgery and intravenous antibiotics.
THROMBOSIS
A thrombosis is a blood clot that may form in the veins in the legs. This can cause persistent swelling of the foot and ankle and canalso be dislodged and be carried to the lungs (pulmonary embolus), resulting in chest pain and breathing difficulties. Once again, the risk is low. An injection may be given at the time of surgery as well as following the operation to further reduce the risk.
DELAYED BONE HEALING
If a shift of the tibial tuberosity has been performed there is a risk that the bone will be slow to heal or may not heal at all. In either case additional surgery may be required to encourage bone healing. The end result is usually satisfactory.
ONGOING KNEE PAIN
If the medial patellofemoral ligament has been reconstructed there may be some pain on the inside of the knee with deep flexion. It is usually a matter of working through this. It is not usually a long-term problem.
If the hamstring tendon has been harvested to reconstruct the ligament there may be some pain at the back of the knee or thigh some 3-12 weeks after surgery. This may be associated with some bruising but does settle and is not usually a cause of any long-term problems.
It is important to restore quadriceps function as early as possible. A delayed recovery of quadriceps function may be associated with some shortening of the patellar tendon. This may pull the patella lower than ideal and may be associated with some pain in front of the knee.
Whenever there has been recurrent patellar dislocation or a patellar stabilisation has been performed there can be discomfort with kneeling. This is often accentuated after surgery but may be helped by removing screws that have been used to hold the tibial tuberosity in place while it heals. The cuts used for surgery may result in some numbness or altered sensation on the front of the knee and shin. This usually improves with time.
It is common for there to have been some damage to the surface of the patella or femur prior to surgery. This is essentially early osteoarthritis and there may be some ongoing discomfort at the front of the knee.
FURTHER PATELLAR DISLOCATION
Whatever surgery has been performed, there is always a riskof further episodes of patellar dislocation. The risk of a further dislocation is usually less than 10% but the nature of the condition means that we cannot reduce it to 0%.