The kneecap or patella articulates with a groove on the front of the femur called the trochlea and together they form the patellofemoral joint. The sides of the trochlea act like a ridge to keep the kneecap from dislocating.
When the patella dislocates, it usually tears the structures on the inside that normally prevent it from moving too far to the side. Within this tissue is a thickened band known as the Medial Patellofemoral ligament (MPFL). This ligament runs from the side of the thigh bone (femur) to the side of the patella. An MPFL reconstruction involves recreating this ligament using a portion of hamstrings tendon and thus preventing the patella from moving to the side.
Most patients have other factors that have predisposed their patella to dislocate. If the patella sits quite high up, known as Patella alta, it effectively misses the groove that it normally runs in and thus can be easier to dislocate. If the groove (trochlea) that the patella sits in is unusually shallow (trochlear dysplasia), then it is much easier for the patella to slide out of the groove and dislocate.
In many patients, the pull on their patella from their thigh (quadriceps) muscles is more out to the side rather than directly upwards and thus the net force is to pull the patella outward.Some patients have loose, mobile joints (hyper-mobile) and these individuals can sometimes dislocate their patella and often other joints without any trauma.
Depending on the severity of these factors, a decision is made whether or not the MPFL reconstruction needs to be combined with another procedure. If required, this will usually consist of a Tibial tubercle transfer.
Recurrent dislocations of the kneecap (patella) can be extremely disabling. Whilst the initial dislocation is often the result of a fall or twisting injury, subsequent events may follow little or no trauma. It is generally accepted that rehabilitation is a suitable option following one, two or even three episodes but after this, surgery may be advisable. Overall the success rate of surgery should be approximately 90% but it must be stressed that it involves a considerable amount of rehabilitation afterwards.
X-rays help to determine the height of the patella and if the groove is shallow. A CT or MRI scan gives more information on this and also checks the direction of pull of the quadriceps muscles. Additionally they identify any damage to the undersurface of the patella.
The procedure is usually performed under a general anaesthetic i.e you are fully put to sleep for the duration of the operation. Occasionally, a spinal anaesthetic may be used whereby the legs are numbed from an injection of local anaesthetic into your back however this can be discussed with the Anaesthetist prior to surgery.
A tight band or tourniquet is inflated around your thigh to ensure a bloodless view during the surgery.
The surgery involves 4 separate small incisions around the front of the knee. The first incision allows the surgeon to harvest the hamstrings tendon (graft) that will be used to form the new ligament.The second and third incisions on each side of the patella allow a hole to be drilled through the patella itself that the graft can be passed through and back over the front of the patella.
The final incision allows identification of the correct point on the inside of the femur that the 2 ends of the graft can be plugged into.
The graft then effectively forms a strong sling that prevents the patella from moving to the outside.
Occasionally, a tibial tubercle transfer is also deemed necessary. Through a longer incision down along the front of the knee, the bone at the insertion of the patellar tendon is cut and slid across to improve the line of pull on the patella. It is usually held in place with 2 screws. As the screws are placed over a prominent area of bone, they will frequently need to be removed in the future when healing is complete.
The knee will be immobilised in a brace that holds the knee straight for 4 weeks. This is to protect the new ligament until it begins to heal. During this time, it is fine to put your full weight through the leg but you may require a crutch for balance. The brace can be removed as directed by the physiotherapist to perform exercises. In general, you will be allowed to bend up to 30 degrees in the first week, 60 degrees in the second and up to 90 degrees in weeks 3 and 4.
You will have at least four scars around the kneecap. They are closed with paper stitches (steristrips) that can be removed 10 days after the surgery.
The bulky wool & crepe bandage can be removed 24 hours after surgery. It is normal for the waterproof dressings underneath to have a small amount of blood on them. It is fine to shower but avoid getting too much water directly on the dressings.
At the end of the procedure, some local anaesthetic is injected into the knee joint. This will usually ensure minimal pain following the surgery. However, as the local anaesthetic begins to wear off (usually 12 - 24 hours post surgery), some discomfort can return. Simple analgesia such as Paracetamol or Paracetamol with codeine or occasionally an anti-inflammatory should suffice at this point.
Whilst early activity is generally encouraged, you may also find that elevating the leg and placing an ice pack (or bag of frozen peas), wrapped in a towel, across the knee greatly helps to alleviate both pain and swelling.
Obviously this depends on both the individual & nature of the work. As a rule, an office worker can expect to return to work after 6 weeks whereas a manual worker may require 3 months off. Don't forget to think about how you normally get to and from work when deciding.
These are guides only and you can discuss various sports with your physiotherapist.
🏊🏼 Swimming is not recommended for the first 3 weeks after surgery until the wounds have healed.
🚴🏻 After 4 weeks, you can use an exercise bike with the seat elevated. By 6 weeks, you can drop this down to a normal height. You should wait 3 months before returning to a road bike.
🏃🏻You can go for short walks 1 - 2 days after surgery. Jogging can begin 3 months after surgery with straight line, steady speed activities.
⚽️ Return to competitive sport will depend on your progress but is expected 6 - 9 months after surgery.
You will usually be reviewed 2 weeks following surgery. This allows us to ensure that the incisions are healing and remove any dressings if necessary. It is often the best time to have a talk about the procedure itself and ask any questions regarding returning to normal activities and / or implications for the future.
Excessive bleeding from the wounds, infection & deep vein thrombosis are the most common complications. In addition, patients often notice a small patch of numbness over the knee joint. This tends to be self-limiting and slowly regresses with time but you may have some difficulty kneeling initially. Stiffness can occur. Fractures of the kneecap (due to the tunnel drilled in it) have been rarely reported. Graft failure can occur early, before the graft has fully matured or later, after a full return to sport. Occasionally some patients notice that they have slightly more pain behind their kneecap than they had before surgery.
Seek advice if the pain dramatically worsens a couple of days after surgery. Also call if the knee joint becomes more swollen or you get a significant amount of bleeding from the knee. Symptoms such as calf swelling or tenderness or simply feeling unwell or shortness of breath should also be assessed.
Compiled October 2015
Review date: March 2016
Review date: March 2016