ACL Reconstruction Graft Choice
Graft Types
ACL reconstruction can be successfully accomplished only by using a tendon graft to make a new ligament. In the past attempts were made to sew the torn ligament back together but this technique proved unsuccessful and has been abandoned.
There are primarily three types of tendon grafts that have proven successful in reconstructing the ACL.
They are:
- hamstring (HS)grafts
- bone-patellar tendon-bone grafts (BTB), and
- allografts.
The first two are grafts taken from within the patient’s own body and are called autografts. The third, allograft is taken from the body of a deceased tissue donor, or cadaver, and transplanted into the patient’s knee. Allografts are used less often than autografts. At Illinois Sports Medicine Dr Prodromos uses Hamstring autografts exclusively. In some special circumstances he uses allografts. The following will compare various characteristics of the grafts.
Graft Strength
The quadruple HS graft Dr. Prodromos uses is initially approximately 2.4 times stronger than the ACL it replaces. Ultimately this graft (and all implanted grafts) loses about half its strength so that its ultimate strength, based on animal studies, is estimated to be about 1.2 times stronger than the original ACL. However, the BTB graft is initially only about 1.1 times as strong as the ACL at implantation. Thus after losing half of its strength its final strength is thought to be only about 55% that of the original ACL strength. Thus the Hamstring graft is more than twice as strong as the patellar tendon BTB graft. This is one of the principal reasons we use it rather than BTB.
The strengths of allografts are harder to quantify. There are a variety of different types of allografts. Some studies have shown comparable strength to autografts, others have shown decreased strength.
Attachment Strength: ACL grafts are implanted into bony tunnels above and below the knee. The strength of attachment of the grafts in the tunnels is roughly equal
Tensile Properties: The HS graft has a modulus of elasticity that is very close to native ACL. BTB is significantly stiffer.
Complications
- From Donor Site: BTB harvest results in a low but definite incidence (about 1%) of patellar tendon rupture and patellar fracture (such as occurred in Carolina Panthers kicker John Kasay and all star football player Jerry Rice) after reconstruction. This usually necessitates another operation for correction. Hamstring harvest on the other hand has no significant donor site problems.
- Knee Stiffness: BTB is associated with a higher rate of post-operative knee stiffness than HS grafts
- Kneeling Pain: much higher with BTB than HS
- Quadriceps Weakness: much higher with BTB than HS
- Hamstring Weakness: Some studies have shown no weakness after HS grafting, some have shown slight weakness. No functional problems have been reported.
- Infection/Disease Transmission: Allografts have been associated with a very low but definite incidence of disease transmission from the donor. A few years ago a death occurred from an infection transmitted from an allograft to a patient having ACL reconstructive surgery. There is obviously no risk of disease transmission from HS or BTB autograft.
Knee Stability
The primary goal of ACL reconstruction is restoration of knee stability. Dr Prodromos has recently completed a comprehensive review of all studies of stability after ACL reconstruction from 1990-2004 published in the world’s English language literature. The results of this meta-analysis showed that knees reconstructed with Hamstring grafts and modern fixation had the highest stability rates of all knees. Knees reconstructed in this way, the technique used by Dr. Prodromos, also had the lowest failure rate. Specifically Dr. Prodromos’ series of knees had no graft failures whereas the average failure rate in the BTB knees was 5%. The rate of restoration of normal stability in Dr. Prodromos’ series was also significantly higher than all of the series using the BTB graft. While BTB is also a very good technique , this higher demonstrated stability using the hamstring graft versus Patellar Tendon BTB is the principal reason Dr. Prodromos uses the hamstring graft technique.
