Graft selection for anterior cruciate ligament reconstruction
1. Patellar tendon graft
Historically, the gold standard for anterior cruciate ligament reconstruction has been using a patellar tendon graft. This is harvested through a fairly invasive incision to the front of the knee with a small plug of bone from the kneecap (patella) above and a further block of bone from the tibial tuberosity (attachment to the tibial bone).
This is a very robust graft with a bone plug at each end which allows direct bone to bone healing and good, secure initial fixation.
The most common problem that is encountered with anterior cruciate ligament reconstruction using a patellar tendon graft in a large number of patients has been anterior knee pain (pain in the front of the knee). It is difficult to tell the reason for this pain and this can continue for quite a long time after the surgery. It is not recommended for patients who have had anterior knee problems in the past or who are required by profession or sport to squat and kneel frequently.
This weakens the extensor mechanism for many months after the surgery and provides for a slower recovery, so much so that some surgeons in the United States on a routine basis harvest the patellar tendon graft from the other knee in order to not slow down the recovery on the same side. This remains controversial.
Fractures of the patella can be produced either intra-operatively or post-operatively which may mean further surgery.
If the patient does not get the appropriate physiotherapy with it, the gap in the patellar tendon fills with scar tissue which tends to contract gradually and can lead to patella infera (low patella) which, in itself, could cause increased patellofemoral pressures, anterior knee pain and possibly increased joint surface damage in the patellofemoral joint.
2. Hamstrings graft
For the above reasons, most knee surgeons have moved to using hamstring tendon grafts. The clinical results are the same in the vast majority of comparative studies.
The minimally invasive nature is appealing as it is carried out through a small incision which is, incidentally, the same incision as is needed for the drilling of the initial tibial tunnel.
Hamstring tendons have a degree of elasticity that is not present in patellar tendon grafts. This is overcome by putting the graft on to a ‘Graft Master’ under moderate stretch after harvesting and while the tunnel is being prepared during the surgery to effectively ‘take all the elasticity out of it’.
Harvesting of the three medial hamstring grafts leaves the knee with some weakening of the hamstrings. Most studies have shown that this recovers eventually but sometimes it could take over one year. The Knee Clinic experience has shown us that many athletes, if they put in the hours, are able to recover their total hamstring power by the six month mark. In fact, this is one of the pre-conditions which we have in our protocol prior to allowing the patient to get back to contact sports or other sports involving twisting and turning.
With hamstring tendon grafts, we have less control over the girth of the resulting final graft. Two of the three medial hamstrings are harvested and doubled up which leads to a very robust quadruple graft which is in fact 1.7 times as strong as the original anterior cruciate ligament. However, on some occasions, the patient’s hamstrings themselves are not too well developed and, every now and then, we encounter patients whose hamstrings measure <7 mm when doubled up. This is clearly inadequate for ACL reconstruction and requires either augmenting with a single hamstring tendon from the opposite side or going to another source of tendon graft. This, however, is a rare scenario particularly in sporty patients.
3. Quadriceps tendon graft
The quadriceps is another very robust tendon and is harvested from above the kneecap.
A single plug of bone is harvested from the top of the patella.
It allows for kneeling without too many problems.
It, again, weakens the extensor mechanism and, in some cases, recovery can be significantly slower.
It leaves an unsightly scar superior to the patella.
As the quadriceps tendon is virtually attached to the knee joint capsule behind in the suprapatellar pouch, not uncommonly the suprapatellar pouch (an extension of the knee joint space above) could be breached leading to scar tissue and adhesions in this area.