ACL surgery - Which graft is best?

A study published in this month's AJSM (July 2018) compared the long term (17 year) outcomes between ACL reconstructions with BTB autograft and hamstring autograft. Graft choice for ACL surgery is an interesting topic in the sports medicine world. With the incidence of ACL ruptures continually increasing, this is a common injury seen by orthopedic sports surgeons and one that draws a lot of attention in the media. The question of 'which graft?' comes up a lot in my practice, so I decided to use this article as the backbone for this latest blog post: graft choice in ACL surgery.

Graft choice in ACL surgery is a continual debate amongst patients and clinicians. Patients are continually asking for my opinion on which graft is best: the patella tendon (aka. BTB or "bone-tendon-bone") or the hamstring tendons (...or maybe even an allograft?!). As with most choices in medicine, there are pros and cons to each side.

To cover this topic, let's first take a step back. ACL grafts should first be broadly classified as either autografts or allografts. An autograft is a graft of tissue taken from the patient's own body; an allograft is a graft from a human cadaver. In the young (< 35 years old), active patient cohort, there is strong evidence to support the use of an autograft for ACL reconstruction. Allograft tissue is associated with a significant higher failure rate (ie. the chance of the graft tearing and requiring revision surgery). The Westpoint trial by Pallis et al. (AJSM 2012) is one good example illustrating this point (allograft reconstructions were 7.7 times more likely to fail compared to autografts in this young, active cohort of military cadets). As a result, our practices around graft choice have changed over time, as shown here (Arthroscopy 2017), with a move away from the use of allografts in younger patients. This recent study by Maletis et al (AJSM 2017) is a good overview of the differences between auto- and allografts, while stratifying for the various allograft processing techniques which has been shown to influence failure rates in allografts (Background: Allograft tissue must be processed - irradiated and/or chemically washed - to decreased the risk of disease transmission prior to implantation in the recipient. This weakens the tissue. There are a variety of ways that allograft tissue is processed. Graft processing techniques have come under review in the literature recently in an attempt to decrease the failure rates associated with the various processing techniques).

The problem with autografts is donor-site morbidity (as the saying goes, "robbing Peter to pay Paul"). Harvesting the graft tissue (ie. removing the central third of the patella tendon or the two hamstring tendons - semitendinosus and gracilis - to reconstruct the ACL) sometimes causes pain or potential complications after the surgery or at some point down the line (ex. anterior knee pain or kneeling pain after BTB graft harvest or knee flexion weakness after hamstring harvest). However, the significantly higher failure rate of allografts is tough to overlook. Their potential benefit (or rather the benefit of avoiding the possible morbidity of autograft harvest) is far outweighed by their significantly higher failure rate, in my opinion.

So, for most young patients, the question is not deciding between an auto- or allograft, but rather which autograft: BTB or hamstring. Unfortunately (or, perhaps, fortunately), the debate between BTB and hamstring autografts is not as clear cut: the literature would suggest that they are both equally as good (ie. the functional outcomes are equivalent in most studies). Yes, there are specific pros and cons to each graft, but most of the literature shows equal functional outcomes between the two. Here is a three-point summary of the large majority of data published comparing the two techniques (and there has been a lot of literature published!):

  1. 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).
  2. BTB grafts are associated with more post-operative donor site morbidity (ex. anterior knee pain and kneeling pain) and have a greater risk of post-operative arthritis at long term follow-up. (It should also be noted that BTB autografts are generally associated with more pain in the immediate post-operative period, as shown here).
  3. In terms of functional outcomes and graft failure, there is no significant difference between the two grafts.

A study published in this month's AJSM compared the long term (17 year) outcomes between ACL reconstructions with BTB autograft and hamstring autograft. This was a follow-up study from the same group's 5 year and 11 year follow up papers. 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). 

Overall, the graft choice decision should be individualized to the patient. Risks and benefits of each graft should be discussed in detail and the patient and doctor should arrive at the decision together, only after all options are considered. In younger, active patients, it's my recommendation to avoid allografts (this is strongly supported in the literature).

In an attempt to summarize most of the data (for anyone interested!), I've grouped the individual papers that compare the results between BTB and hamstring autografts for ACL reconstruction:

Studies showing near equivalent outcomes between hamstring and BTB autografts:

Studies supporting BTB autografts:

Studies supporting Hamstring autografts: