ACL Reconstruction Graft Choice
Graft Choice
ACL Reconstruction Graft Choice
There are a number of different grafts available for ACL reconstruction including:
* patellar tendon graft
* hamstring tendons
* quadriceps tendon
* synthetic graft
* allograft (sterilized graft from a human cadaver)
* xenograft (graft from an animal source which has been sterilized).
Xenografts are rarely used in Orthopaedic Surgery as there are many better alternatives available.
Synthetic grafts should really never be used as they do not work and will fail sooner or later. They were used in the past very commonly in an attempt to negate morbidity from harvesting from a donor site. However the literature clearly revealed that synthetic grafts will and do fail and do not integrate to become in-grown by new ligament tissue from the knee, which was the commonly held belief that lead to their widespread use, more in Europe than in the USA.
Allografts are uncommon for primary reconstructions but may be used for revision. They have a high failure rate. Rehabilitation must be slow in order to allow the graft to try and become a living tissue, as it is initially dead. There is also a risk of transmitting diseases such as HIV and Jacob-Cruzfeld disease from donor to recipient. In addition to this, they are very expensive and difficult to come by.
The patellar tendon was the most commonly graft used but due to perceived problems with rehabilitation other grafts were sought out and so the popularity of hamstring grafts began. It was felt that patellar tendon grafts were harder to rehabilitate, more painful an operation and had a higher complication rate. Hamstrings were thought to be the ideal solution for the patellar tendon graft problems.
Patella tendon versus hamstring grafts
One of the perceived problems with patellar tendon was the high quoted rate of so called "anterior knee pain" which is pain that occurs on the front of the knee usually around the kneecap area. This was thought to occur from the harvesting of the patellar tendon and the patella bone block and so hamstrings were used specifically to prevent this problem. However, the literature on hamstring grafts is quite clear and shows an anterior knee pain incidence of upwards of 25 to 30%. Therefore, the cause of anterior knee pain is not the harvest of the patellar tendon graft. One of the causes of anterior knee pain is damage to a nerve that runs across the front of the knee and this can be damaged whether the hamstrings are harvested or the patellar tendon is harvested. The second cause of anterior knee pain, in my view, is poor and incomplete rehabilitation and not achieving full hyperextension. If hyperextension is not achieved this means that the patella and extensor mechanism will be constantly loaded, possibly leading to pain. Once again, this can occur either with patellar tendon or hamstring harvest.
Myths about Patella Tendon Grafts (PTG)
* More pain with Patellar Tendon
It was felt that patellar tendon harvest was a more painful procedure and would therefore result in slow rehabilitation. My accelerated rehabilitation programme quite clearly illustrates that this is not the case. Pain has to be controlled ideally with pre-emptive (pain relief before the pain causing stimulus is administered) analgesia and a strong and potent post-operative pain protocol. Early motion will also help to reduce the pain by decreasing stiffness and swelling. Controlling and preventing swelling with a Cryocuff will also reduce pain. Therefore, with an appropriate protocol and an accelerated rehabilitation programme there is no reason that patellar tendon surgery should be any more painful than hamstring. The contrary is also true in that without appropriate rehab protocols and analgesia protocols, whatever graft is used, pain will result causing slower rehabilitation.
* Graft healing
One of the main advantages of patellar tendon is that it has bone blocks at each end of the graft. This allows rapid and essentially guaranteed healing of the graft in the bony tunnels. Bone to bone healing is complete within about 6 weeks.
However, this is not the case with hamstring tendons. Bone to tendon healing is a much slower and less reproducible process. Therefore, the fixation devices are more crucial and rehabilitation has to be slower in order to take account of this delayed healing response. Many of the earlier and some of the current hamstring studies do show that the graft can stretch out, with a slow progressive increase in the KT1000 side to side laxity difference over time. The reasons for this could be due to the graft itself stretching out or due to weaknesses at the hamstring bone interface such as the fixation device not being adequate allowing the tendon to slip within the tunnel as may occur if rehabilitation is too aggressive. One of the main issues with hamstring grafts has been trying to get a strong enough fixation device to prevent this. This is true at both the femoral and the tibial tunnels. This problem does not really exist for patellar tendon as the fixation strength is not as much of an issue.
* Regeneration of the donated graft tissue
One of the principles of an ideal graft would be to prevent morbidity from the donor site. By taking any autologous (graft taken from the same person from one area to be used in another area) graft there will be donor site morbidity. So the secondary principle would be if the morbidity cannot be prevented, it would be to completely heal the donor site and therefore minimalise morbidity from the donor site..
Patellar tendon graft can, if treated appropriately, be allowed to heal from the donor site. This would involve at the time of surgery closing the defect from the harvest site, as well as bone grafting the patella and tibial bone blocks as I always do. This allows the defect to heal which means that potentially, in the future, the same patellar tendon could be re-harvested, if required.
However, this is not the case with hamstring tendons. Once the hamstring is harvested and the hamstring tendons are cut, the remaining tendon retracts up into the muscle belly and the muscle belly itself retracts into the proximal thigh and buttock area. Even though the tendon sheath may be intact the tendon itself and the muscle belly retract. Therefore the hamstring tendon cannot regenerate and will lead to permanent morbidity. This has been clearly demonstrated in studies which show that if isokinetic strength testing is done then patients who have had hamstring tendon harvest are left with a residual permanent weakness of their hamstring muscles and thus permanent weakness of knee flexion power.
* Secondary Stabilizer of the knee
The hamstring tendons are secondary stabilizers of the knee. In other words, if the ACL is torn the hamstring muscles, by contracting appropriately, can prevent anterior translation of the tibia and therefore act in some role to decrease the effect on the knee of having an absent or torn ACL.. Therefore it is completely illogical to then sacrifice these tendons to reconstruct the ACL as in that situation both the primary and secondary restraints have been destroyed.
