The medial patellofemoral ligament (MPFL) is attached from the inside edge of the patella (knee cap) to the femur (thigh bone). This helps to keep the patella centred within the v-shaped trochlear groove when it slides during bending and straightening of the knee. Some people have a MPFL that is too stretchy and it is not able to keep the patella tracking centrally. This may lead to subluxation of the patella, meaning that the knee cap partially moves out of its groove during knee motion. If there is an injury to the knee, such as a direct blow, the patella might dislocate which means it is either pushed or pulled out of the trochlear groove. When this happens, the MPFL tears and can no longer act as a “guide rope” to stop the patella moving sideways during knee movement. If this ligament does not heal, the patella might become unstable and the continue to dislocate.
Some people do not experience pain when their patella is subluxed but dislocations are usually very painful and interfere with function of the knee. Recurrent dislocations can cause damage to other parts of your knee.
Your surgeon might recommend an MPFL reconstruction, either by itself or as part of other knee surgery, to help stabilise your patella if you have:
- had more than one dislocation of your patella
- dislocated your patella only once, but have injured your MPFL as well as other structures in and around your knee
- tried non-surgical treatments, such as strengthening the muscles around your knee, but your patella continues to subluxate or dislocate
The surgery is usually accompanied by a diagnostic arthroscopy(keyhole surgery) to look inside your knee using a special camera and if required, perform other procedures at the same time. An example might be removing a piece of bone or cartilage (loose body) from inside the knee and making the under surface of the patella smooth before reconstructing the MPFL. Theligament is not usually able to simply be sewn back together when it has torn and instead, the surgeon must reconstruct it using another thick, band-like tissue called a tendon. This tendon (graft) may come from the patient (an autograft) or from a cadaver donor (an allograft). It is usually preferable to use the patient’s own tissue, which is taken from the large group of muscles at the back of the thigh (the hamstrings). Borrowing a tendon from the hamstrings does not usually cause problems with the functioning of this muscle group.
To perform the MPFL reconstruction, further incisions must be made to harvest the graft and anchor it securely to the femur and patella.Once the tendon has been carefully removed from the hamstrings group, it is folded in half lengthways to make a stronger structure. One end of the graft is attached to the patella, usually using two special surgical anchors to attach the tendon to the bone. A small tunnel is then created in the femur and the other end of the graft is passed into it and secured it place. When the reconstruction is complete, your surgeon will carefully bend and straighten your knee to make sure that the graft tendon is secure and that your patella is gliding smoothly in the centre of the v-shaped trochlear.