So, you have torn your ACL (Anterior Cruciate Ligament). Beyond my discussion with patients addressing what an ACL is and its function, as rehab and return to sports, I spend a good deal of time helping patients decide what the best graft choice is for them.
The reason we need a “graft” is that this surgery is a reconstruction not a repair. The torn cruciate ligament is not routinely repairable (yet). Although there are ongoing studies using biologic healing agents to help us “primarily” repair the ACL.
Review of the recent literature suggests that there is no ideal graft for ACL reconstruction and the search is still on for the optimal graft. There are advantages and disadvantages with each graft.
Autografts (something harvested from you) are more commonly used than allografts (taken from a cadaver and processed chemically and/or radiated) or synthetic grafts. Three autograft options that are commonly used are Bone Patella Tendon Bone (BPTB), Hamstring (HS) and quadriceps tendon (QT) grafts with or without a patella bone block.
An autograft is associated with earlier incorporation and tendon-bone healing, as well as reduced immunological rejection after transplantation. In addition, there is no risk of disease transmission.
The Multicenter Orthopedic Outcome Network (MOON) is a multicenter prospective longitudinal cohort study designed to identify prognostic factors (risk factors) for validated patient reported outcomes in anterior cruciate ligament (ACL) reconstruction (ACLR). Early MOON studies were able to identify a higher rate of failure with allograft reconstructions that is magnified in young patients.
Let’s look at all the different choice individually:
The major factor in the success of ACL reconstruction with a hamstring autograft is the size of the graft. The graft should be at least 7 mm in diameter, although recent studies have indicated that a diameter of 8 mm or more decreases the risk of graft failure. Some patients have small hamstring tendons however, which may compromise the clinical outcome of the autograft. To solve this problem, many surgeons use hybrid grafting that involves augmentation of small hamstring autografts with allograft tissue.
A distinct advantage of using a hamstring allograft in a younger patient whose growth plates have not closed is a decreased risk of prematurely closing the growth plate, if drilling across it, compared to the use of a bone block in a BPTB graft.
Other advantages include no risk of disease transmission (compared to allograft), no risk of patella fracture (as compared to BPTB), decreased knee pain, smaller incision, and easier initial rehabilitation.
Patella Tendon Autograft
The assessment of postoperative pain after ACL reconstruction suggests a difference between hamstring and BPTB groups, with BPTB graft patients having decreased satisfaction with their pain management.
From a biologic standpoint, the advantage of a patellar tendon graft is that the graft bone heals to host bone in six weeks, which is faster than the 8 to 12 weeks it takes for soft tissue healing. Consistent size and shape of the graft, as well as ease of harvest are arguments in favor of the patellar tendon autograft.
BTB grafts are more likely to restore objective stability in the knee (in other words, residual knee laxity is more common with hamstring grafts, especially in females).
However, a recent study published in the American Journal of Sports Medicine compared the long term (17 year) outcomes between ACL reconstructions with BTB autograft and hamstring autograft. At the 17-year follow-up, no statistically significant differences were seen with respect to graft failure and functional outcome. Interestingly, patients who had undergone reconstruction with a BTB were more likely to have osteoarthritis in their knee. Furthermore, 100% of the BTB patients had some degree of arthritis in their knee (compared to 71% in the hamstring group).
The disadvantages are the harvest site morbidity of patellar tendonitis and anterior knee pain, patellofemoral joint tightness with late chondromalacia, late patella fracture, late patellar tendon rupture, loss of range of motion, injury to the infra-patellar branch of the saphenous nerve.
Quadriceps Tendon Autograft
The quadriceps tendon is the least studied autograft for ACL reconstruction, and although interest in its use seems to be increasing, only 1% of orthopaedic surgeons consider the quadriceps tendon for either primary ACL reconstruction or for revision surgery.
After 1 to 2 years of follow-up, the clinical outcome of the patients treated with this graft have been encouraging. The advantages of the quadriceps tendon graft include, the graft is larger and stronger than the patellar tendon, morbidity of the harvest donor site is less than that of patellar tendon graft, no quadriceps inhibition is seen after the quadriceps harvest, and with aggressive rehabilitation, there is shorter recovery time for the patients.
The use of allograft is appealing particularly to the complete lack of donor site morbidity, reasonably good availability and a range of graft sizes with the options of bone blocks attached to the graft. Also in the case of revision surgery where autograft options have already been exhausted an alternative graft choice may be required.
The commonly used allografts for ACL reconstruction are BPTB grafts, HS grafts, tibialis posterior/anterior and tendo-achilles grafts.
The failure rate of allografts in long-term follow-up studies is higher than for autograft. In a recent review, Wasserstein et al reported an allograft failure rate of 25% at 24 to 51 months after reconstruction, compared with 9.5% to 9.8% for autograft. The failure rates for low-dose irradiated grafts versus non-irradiated grafts was 31% and 19.5%, respectively.
The other disadvantages of the allograft are the risk of disease transmission, a weak graft, if radiated or from an older patient, a longer time to incorporate into the bone tunnels, the graft is not universally available, and is expensive.
All the different types of grafts used in current everyday practice for the reconstruction of a ruptured ACL have a place in this complex field of surgery. There are good data to support all of them. There is no clear “best” graft to use.
A review of the recent literature indicates that autograft is superior to allograft with respect to failure rates and long-term outcomes, particularly in younger and active patients. The major risk factors for ACL re-tear are younger age and high activity level regardless of graft choice.
In a study published in Arthroscopy, Brandon J. Erickson, MD, Cole and their colleagues found 136 (99.3%) National Football League (NFL) and National Collegiate Athletic Association Division I football team orthopedic surgeons chose autografts, of which 86.1% chose BPTB autografts to treat ACL tears in their starting running back.
Our choice usually depends on the activity level of the person. Young patients who have not yet closed their growth plates are ideal candidates for hamstring autograft. Lower-level athletes, and weekend warrior you can use cadaver graft, whereas in the higher-level athletes, [most] people use patella tendon autograft for their primary choice because of the quicker healing and the tissue properties of the graft itself.