Patellar (patellofemoral) instability surgery
Pre-Operation
Patellar instability can vary from minor to severe, and there are an array of surgical options. Dr. Porter will discuss the options.
Patients may sustain and acute dislocation or subluxation (partial dislocation of the patella) during a twisting injury to the knee, often while playing sport. The knee cap may move in and out of place within seconds to minutes, or may have to be put back in place by a paramedic, or at a casualty department. Following this the patient is usually put in a knee brace, and often referred for physiotherapy. It is important for the patient to perform the physiotherapy, even if surgery is required, as the success of the treatment is dependent upon appropriate rehabilitation.
Although many patients will recovery with non-operative treatment there is a high risk of recurrence. The surgical repair of the torn ligaments sustained during a patellar dislocation can reduce the risk of recurrence dramatically in most cases. If there is a fracture of the joint in conjunction with the patellar dislocation, then surgery may be indicated following the first event. If the patellar dislocation becomes a recurrent problem, more often than not Dr. Porter will recommend a reconstruction of the ligament (the medial patellofemoral ligament or MPFL) using a graft, such as a hamstring graft. Sometimes he combines a repair of the native ligament with augmentation using an artificial ligament to protect the repair ligament while it heals.
As part of the pre-operative assessment Dr. Porter will look for other predisposing factors such as a trochlear dysplasia (flat groove in which the patella sits) and / or patella alta (a patella which sits too high in relation to the groove) and / or increased TT-TG distance (this is similar to the q-angle, but a more accurate measurement of mal-alignment of the quadriceps muscle, patella and patellar tendon).
Although there are techniques which involve making the groove in the trochlea deeper, Dr. Porter does not recommend the technique on account of the significant risk of complications (most notably necrosis and collapse of the joint surface) and early osteoarthritis (as the joint surfaces no longer match each other). Both of these complications may require a partial joint replacement to correct the problem which must be avoided at all costs in a young patient.
Operation
The operation is performed in an operating theatre, under sterile conditions, with the patient under a general anaesthetic. An arthroscopy (key-hole surgery) is performed routinely as the initial part of the operation, during which the diagnosis is confirmed, any damage within the knee fixed, and the surgical technique determined.
Following this the surgeon will make an incision along the medial border (inside) of the patella, and either repair the MPFL using “suture-anchors” (sutures attached to the bone) or perform the MPFL reconstruction. For the latter procedure, a graft is required to achieve a biological repair that becomes a living / growing part of the patient, and a single hamstring graft is used. Dr. Porter most often uses the gracilis tendon, the weakest and smallest of the hamstrings, and there is no clinically significant loss of hamstring strength following this. No muscle is taken only tendon, and the latter can actually grow back. The graft is harvested by a small incision at the upper end of the shin bone. The graft is attached to the medial border of the patella, passed along the course of the native MPFL ligament, and attached the femur (thigh-bone) in manner that allows the surgeon to vary the tension so that the new ligament prevents patellar dislocation, but does not interfere with knee movement. The graft is fixed using screws that either turn to bone or a broken down by your body.
The wounds are closed with bio-absorble sutures and dressings applied. After this bandages are applied and the patient is placed in a range of motion (ROM) brace.