Medial Patellofemoral Ligament Reconstruction
The patella, also known as the “knee cap” sits at the front part of the knee. As the knee bends, it glides in a groove of the femur called the “trochlear groove”. This groove accommodates the patella so that it smoothly tracks in a straight line. Other factors that hold the patella in its groove are the pull of the quadriceps muscle and surrounding ligaments. When the patella slips out of this groove, the condition is called “patellofemoral instability” (PFI). [Figure 1]
Figure 1. Patellofemoral instability
In most people with PFI, the trochlear groove and the reciprocal shape of the patella can be abnormally flat. This predisposes patients to having the patella potentially coming out of place. Sometimes the patella sits high relative to the trochlea as well which makes it difficult to enter the trochlear groove. The other reasons include having a weak quadriceps muscle, having lax joints or knocked knees. These anatomic variations may run in families. Some times, there are no underlying factors except a significant traumatic injury to your knee.
Recent research has demonstrated that the main stabiliser of the patella, preventing it from moving outwards (lateral) is a ligament called the medial patellofemoral ligament (MPFL). [Figure 2] This ligament is a thin structure that runs at the bottom part of the VMO muscle (lower inner part of the quadriceps muscle). It starts from the inner (medial) edge of the patella and runs across to the inner part of the femur, 2cm above the knee joint. This ligament is torn or becomes stretched when patients dislocate their patella. It then stops functioning, leading to recurrent instability in some patients.
Figure 2. Knee Anatomy from the frontal aspect and the MPF
You are administered a general anaesthetic (put off to sleep) via medication delivered in to your vein. A medial patellofemoral ligament reconstruction involves making a new ligament to compensate for the damaged one. One of your hamstring tendons (gracilis or semitendinosus tendon) are removed through a small incision at the front inner part of the tibia bone. Approximately a 20cm length of tendon is removed and then fashioned into a new ligament. Several other small incisions are then made at the front of the knee to reconstruct this ligament from the front inner edge of the patella to the inner (medial) edge of the femur. This MPFL is held into position with plastic screws or sutures placed in to small drill holes. [Figure 3]
Figure 3. MPFL graft held in position with plastic screws in to patella and femur
The operation involves approximately three small incisions each measuring between 2cm and 4cm long, but also can be done through one large incision. The number of incisions is dependant on what other surgery is required, such as a tibial tubercle osteotomy (see final part of document). The surgery takes approximately 60-90 minutes to perform.
The surgery is usually performed as a day surgery. When you wake up you will have a bandage on your knee. You will be seen by the physiotherapist and instructed on how to use crutches. You will be allowed to take full weight on your leg. Crutches are normally only required for approximately 3-5 days following the operation, and are used mainly to protect your knee from collapsing whilst the soft tissues are healing.
The main aims of early rehabilitation include reducing swelling, applying compression to the knee, elevating your leg and gently tightening muscles so as to minimise any muscle wasting. You will be asked to see your physiotherapist for regular visits, often 2-3 times a week for the first few weeks and then once a week following this. The main aims of physiotherapy in the early period are to restore some motion of the knee joint, reduce swelling and maintain muscle strength. A specific rehabilitation program will need to be given to your physiotherapist so as they comply with the instructions required for such an operation. This will be given to your by your surgeon following your operation.
A patellofemoral stabilising brace is required after MPFL reconstructive surgery whilst the ligament heals. This is used for the first 6-12 weeks following surgery. This should be fitted and arranged prior to your operation.
What should I expect after my operation?
It is common to have some pain after surgery but this will be controlled with regular anti-inflammatory medications for the first five days. You will also be given other medications that can be taken as required to reduce pain. As a general rule, pain is not severe immediately following the surgery as local anaesthetics are used at the time of the operation to reduce significant pain during the early postoperative period. These are administered whilst you are having the operation. It is important to ice your knee regularly, 20 minutes every hour during the first few days, as this also reduces inflammation and decreases pain.
It is normal to have swelling following the operation and some bruising around the leg. Swelling and bruising can occasionally be seen around the ankle and this should not cause concern. Your knee will feel stiff and it is important to gently bend your leg following surgery to overcome this sensation. This will also be worked on with your physiotherapist.
As there are several incisions around the knee, it is common to have areas of numbness surrounding those cuts. These patches of numbness generally dissipate with time. In some patients, numbness is also experienced around the outer part of the leg as there is a nerve adjacent to the gracilis tendon which can be stretched during surgery “saphenous nerve”. This will generally diminish with time but a very small percentage of patients have a permanent area of numbness over the outer side of the leg. In our experience, this has never been incapacitating to patients.
You will also notice that the quadriceps muscle at the front of your knee will decrease (atrophy) in size following your operation. This is experienced by all patients and will recover with appropriate exercise and rehabilitation. It can take many months for this muscle to fully recover and its return in size and strength is a major determining factor on when you can return to full activities.
Most patients require approximately 1-2 weeks off work if they work in an office setting and anywhere between three and five weeks if they work in manual labour. This obviously needs to be discussed with your surgeon prior to surgery.
Most people who have this surgery are able to return to normal activities, including sport. The chance of having further dislocations is generally considered to be between 2 and 4%.
Potential Risks Associated with Surgery
- Infection – There is a 0.5% risk of developing an infection after this surgery. This can either be a minor infection involving the incisions, or a deep infection involving the knee joint. If this occurs, antibiotics will be required. If it is a serious infection involving deeper structures, admission to hospital is required as are intravenous antibiotics. If the infection involves the knee joint, a knee arthroscopic surgery is required to wash the infection out. The chance of this happening is extremely low but cannot be completely eliminated. Antibiotics are given prior to the operation to reduce the risk of infection. There is a higher infection risk in smokers and as such it is highly recommended you cease smoking approximately two weeks prior to your surgery.
- Blood clots “Deep Venous Thrombosis” – Reports vary, but there is between a 2-10% risk of developing a blood clot in one of the veins in your calf. Very rarely these blood clots can travel to your lungs. This is called a “pulmonary embolus”. The risk of developing a pulmonary embolus is exceedingly rare. If you develop calf pain or tenderness following your surgery, you should contact your specialist or general practitioner immediately to notify them of this. An ultrasound examination will be performed of the calf to assess for a blood clot. Medications will be required to prevent these blood clots from getting larger. To minimise the risk of a blood clot, it is important to notify your surgeon if you have any hereditary risk factors for blood clot formation. You should also cease smoking as this increases the risk of this complication.
- Recurrent dislocation – Following medial patellofemoral ligament reconstruction, the risk of a re-dislocation of the patella is approximately 2-4%. This compares to over 50% if you have already experienced two dislocations, and even higher if you have recurrent instability.
- Numbness around the surgical incisions – It is common to have numbness around the surgical incisions. Most of these small patches are temporary and do not bother patients. Occasionally a permanent patch of numbness can be experienced at the upper part of the tibia on its outer side from stretching of the saphenous nerve where the gracilis tendon is harvested from.
- Stiffness – There is a risk of developing some stiffness of the knee following the surgery. If this occurs, you may require a second operation where the knee is either manipulated or scar tissue is released from the inside of the knee joint. In order to prevent stiffness following the operation, it is important to have good range of motion prior to surgery and perform regular stretching exercises. Most importantly, you must participate in the postoperative rehabilitation program under the care of your physiotherapist.
- Patellar fracture – As a drill hole is required across the patella in order to insert the graft, there is a very small risk of the patella fracturing, either at the time of the operation or following the surgery. This is an extremely uncommon complication but has been reported in the literature. If this does occur, additional operations may be required.
- Hardware related complications – As metal clips and screws are required to hold the new medial patellofemoral ligament graft in position, these may become prominent and cause irritability either on the side of the patella or in the inner edge of the femur just above the knee joint. If this does occur, screws sometimes require removal. This is performed once the graft has healed.
- Hamstring weakness – As one of the hamstrings “gracilis” is removed, some patients may develop minor weakness in hamstring strength. However this is extremely rare when only the gracilis tendon is taken as it is one of the weakest hamstrings around the knee joint. Recent research demonstrates that the semitendinosis and biceps femoris are more important hamstring tendons at the back of your knee and these are not used in the reconstruction. In our experience, we have never had a patient report any significant hamstring weakness following utilisation of this graft. At approximately 12 months, MRI and ultrasound studies have confirmed that this tendon does regenerate.
- Ongoing swelling or pain – In patients who have sustained patellar dislocations, it is common to develop injuries to the cartilage of either the patella or the femur. Once this cartilage damage has occurred, it is referred to as “post traumatic osteoarthritis”. Often this damage to the cartilage is irreversible but your surgeon will perform an arthroscopic assessment of the knee and treat any unstable areas of cartilage loss. It is not uncommon for patients to have ongoing pain or swelling following the operation related to this cartilage damage. The reconstruction of the medial patellofemoral ligament will not address this problem, only the instability part of your condition. As a general rule, it is common to have some swelling within the knee which improves with time for approximately three months after your surgery. Any ongoing swelling following this is most likely related to chronic injury to the cartilage which may develop into significant osteoarthritis later in life. Occasionally the medial patellofemoral ligament graft may be too tight and cause acceleration of arthritis in the knee joint.
In a small group of patients, additional operations are required in conjunction with medial patellofemoral ligament reconstruction to assist in stabilising the patella.
- Tibial tubercle osteotomy – This operation is required in some patients where the tibial tubercle and its patellar ligament attachment is positioned too far laterally, predisposing the patella to slip outwards. In addition, the patella may be positioned too high relative to the femur bone (patella alta). A determination of whether your tibial tubercle is too far lateral or high is made via an MRI and x-ray assessment where the relationship of the tibial tubercle in relation to the patella and the femur is made with specific measurements. If a tibial tubercle osteotomy is required, it is most often combined with a medial patellofemoral ligament reconstruction and a lateral release.
- Lateral release – A lateral release is where tight structures on the outer “lateral” side of the patella are cut. This is required in patients who have very tight tissue that pulls the patella outwards, increasing the risk of instability or cartilage degeneration. Only some patients require this operation in conjunction with their medial patellofemoral ligament reconstruction. This operation can be done either through the same incision as the medial patellofemoral ligament reconstruction or through a larger incision around the knee. It allows the patella to sit more centrally within its groove and not tilt as the patella engages in the trochlear groove. It also takes pressure off the outer side of the patella, in some patients reducing pain around this part of the knee. It is common to cause some swelling and bruising around this part of the knee especially for the first few months after surgery and occasionally some numbness.
Please see separate section on tibial tubercle osteotomy, which addresses this component of the surgery in more detail.