Where Are We Now?
The idea of suture-repairing the native tissues of the ACL fell from favor in the 1990s because the historic outcomes of open repair techniques were marginal at best. A large number of patients had recurrent laxity as a result of the nonselective repair approach (all tear types were repaired), in addition to high rates of stiffness and patellofemoral pain due to the open approach that was followed by casting. The conclusion that the ACL couldn’t heal due to poor blood supply was printed in textbooks and taught to residents across the world, myself included, as reconstructive techniques supplanted suture repairs. However, as many recent studies suggest [1, 4, 6-8], it seems that it is not that the ACL can’t heal, but more likely that only certain types of tears (proximal) have a higher likelihood of healing [1, 4, 6-8, 14, 15]. In the days of open ACL repair, many surgeons realized that their patients with proximal tears seemed to do better . Applying modern diagnostic technology, arthroscopic surgical techniques, and modern rehabilitation principles to the ACL injury problem has led to the concept that perhaps we can selectively repair proximal ACL tears, which have a better potential to heal . This concept, combined with some honest reporting about the limitations of reconstruction [3, 18], has led to an explosion of interest in ACL repair techniques [1, 4, 6-8].
Research on modern ACL repair is divided into two main camps: One group developed a collagen-based sponge that could be soaked in platelet-rich plasma and stitched into place between the ends of the torn ACL. Known as the Bridge Enhanced ACL Repair (BEAR) technique, this promising approach generally is used for midsubstance tears, and has been found to anchor the clot in place, which allows the suture-stabilized ligament ends to heal together . The other group includes many different approaches to selectively repairing proximal ACL tears . The techniques can be divided into nonaugmented, static-augmented, and dynamic-augmented suture repairs. Generally, early results using all of these selective approaches have been encouraging when used on carefully indicated patients with the appropriate ACL-tear type and tissue quality [9, 17].
The current study by Liao and Zhang  fits into the latter category. They reported on their experience applying a nonaugmented pulley technique using suture anchors—an approach more commonly applied to rotator cuff tears—to treat partial, proximal ACL tears in 23 patients in a retrospective study. The authors concluded that the ACL likely has more healing capacity than we once believed to be true. Their findings reinforce the question: Should all patients contemplating surgery for a torn ACL be treated with reconstruction, or can we have a selective approach to ACL injury, one that includes repair, rather than reconstruction, for some patients?
Where Do We Need To Go?
Historically, the evolution of surgical thought follows a predictable course. Novel ideas such as the one being discussed, are generally not so novel, but merely improvements on the previous generations attempts at developing an effective solution to a problem. A paradigm shift usually follows a breakthrough in understanding or, more commonly, technology and more modern techniques evolve. As is typical of the evolution of newer surgical approaches, the early reports on selective arthroscopic ACL repair techniques have generally been encouraging [9, 17]. However, the level of evidence and length of follow-up in the research at this time are insufficient to make firm recommendations for widespread adoption of these approaches.
The resurgent interest in ACL primary repair is predominantly focused on trying to differentiate between “repairable” and “nonrepairable” tears. With this in mind, we also need further clarity in our imaging to help physicians to define these groups. Initial work on classification systems to predict reparability have been published for both adults and children [13, 16]. Although some centers have published regarding the diagnosis and treatment of partial ACL tears [9, 12], greater clarity is needed on how to accurately define a partial tear. In the current study , the authors focus on repair specifically for partial tears and mention that some patients had partial tears of both bundles. Future studies will need to help us determine the exact amount and location of damage to the ACL so that we can further understand when ACL repair might be enough to treat the injury. Along a similar line, it will be especially important that future studies report objective measurements of knee laxity before surgery and after recovery from repair; although to date there seems to be no agreed upon standard for the objective measurement of laxity. Future studies on ACL repair will also need to differentiate outcomes based upon age and activity level because there is overwhelming evidence that points to higher rates of failure with ACL reconstruction in younger age groups [3, 18], and this is also likely to be found with ACL repair results as we go forward. Recently, this exact concern was raised by Gagliardi et al. , when they reported disappointing results in a small group of athletic patients, average age 14 years old, who underwent a button based, static augmented ACL repair technique and suffered nearly 50% failure rates by 3 years. In my experience, we have also seen elevated failure rates using a suture anchor-based, static-augmented ACL repair technique in the younger than 21-year-old cohort, which has given us pause in how we treat our younger patients.
How Do We Get There?
I believe that contemporary ACL repair will, at most, apply to a subset of patients with ACL injury, but in those patients, it is an attractive, minimally morbid, biologic alternative to ACL reconstruction. As such, it is another tool in our surgical toolbox, and it appears, from the early research [1, 4, 6-8], to be an effective one. It is also my belief, that by carefully reevaluating the limitations of the historic studies, we can learn from them and build on them. The resurgent discussion about ACL repair, in conjunction with all of the modern-day advances, will likely lead to a whole new era of research into both ACL injury and treatment.
The next order of business is to develop well-powered, prospective studies that compare subjective and objective measures, patient-reported outcomes, return-to-sport times, forgotten joint scores, and failure rates comparing the outcomes of ACL repair to ACL reconstruction in similar groups of patients. An area of concern with ACL reconstruction is the incidence of arthritis in long term follow-up studies . While these studies require long-term follow-up by nature, and are difficult to perform, I do believe that these comparisons between the long-term incidence of post-traumatic arthritis in patients who had reconstruction versus repair will find a lower risk for the repair patients given the minimal morbidity of the procedure. In addition, more comprehensive and direct comparisons between the multitude of different ACL repair techniques are needed to help us determine the most-effective approach for repairing the ACL ,
Finally, I would like to congratulate the authors on their innovative work , and would also share my personal opinion that it is imperative that we collectively continue to pursue and report on novel techniques, like the authors of this paper, as the seeds of the next big, innovative breakthroughs are often planted by studies like this one.
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