ACL Reconstruction Techniques Continue to Evolve, but Hurdles Lie Ahead

Anterior cruciate ligament (ACL) reconstruction remains one of the most common procedures in orthopaedic surgery, with an estimated 100,000 performed annually in the United States alone. Over the past 40 to 50 years, treatment of ACL injuries has evolved, from nonanatomic extra-articular procedures with large incisions to entirely arthroscopic anatomic reconstructions; from postoperative casting and delayed weight bearing to immediate range of motion and early rehabilitation; and from minimal published literature to an abundance, with more than 1,200 articles published on the topic annually in recent years (Fig. 1).

Understanding this history helps surgeons evaluate patients treated with the older techniques. Perhaps more importantly, understanding the evolution of surgical treatment of ACL injury helps surgeons to better recognize strengths and limitations of our current techniques and consider potential future advancements, such as primary ACL repair or lateral capsular (anterolateral ligament) reconstruction, with a more discerning perspective.

The early days

In the 1970s, little literature was available to guide treatment, a variety of procedures were attempted, and the outcomes were variable.

Primary ACL repair gained popularity in the early 1970s. The procedure was performed through open arthrotomy, with sutures passed through the ligament and secured over transosseous drill holes. Although early results were promising, five-year outcomes were poor, with high rates of recurrent instability and pain.

The other approach during that era was to advance, tighten, or reorient extra-articular structures in an attempt to stabilize the knee. At that time, injury to the capsular structures was thought to be the primary problem leading to instability. As a result, surgical treatment focused on the iliotibial band, hamstring tendons, and capsular structures (Fig. 1). Those procedures also led to initial success in terms of stability, but results deteriorated over time, and arthrofibrosis was common.

Open ACL reconstruction

By the 1980s, it became clear that isolated ACL injury was the primary issue. That realization arose from several key developments, including cadaveric studies proving that the ACL is the primary restraint to anterior tibial translation. Clinical assessment improved as the Lachman and pivot shift tests were popularized and MRI and arthroscopy became available to aid in diagnosis.

As a result, intra-articular ACL reconstruction became the procedure of choice. A variety of grafts were used initially, ranging from iliotibial band, synthetic substitutes, and even medial meniscus, before surgeons settled on bone-patella tendon-bone and later hamstring autografts as the preferred graft options.

Intra-articular reconstruction was initially performed with the two-incision technique, which involves independent outside-in drilling of the tibial and femoral tunnels. Independent tunnel drilling enabled surgeons to place tunnels relatively anatomically, and outcomes were quite good.

Fig. 1 The number of scientific papers published annually on the topic of ACL, from 1948 to 2017. Only four papers were published in 1972, whereas more than 1,200 were published in 2017.

Fig. 2 A. Slocum pesplasty: Medial extra-articular reconstruction involving pes tendon transfer proximally, posterior medial capsular reefing, and medial collateral ligament advancement, all aimed at limiting posterior medial rotatory instability. B. MacIntosh I: Lateral extra-articular reconstruction using a strip of iliotibial band passed deep to lateral collateral ligament and through the intermuscular septum. Credit: McCulloch PC, Lattermann C, Boland AL, et al: An illustrated history of anterior cruciate ligament surgery. J Knee Surg. 2007;20:95-104.

Arthroscopic ACL reconstruction: Away from, then back to, anatomy

As arthroscopy gained popularity later in the 1980s, so did the single-incision technique, which involves drilling the femoral tunnel through the tibial tunnel. Constraints of that tunnel-drilling technique led surgeons to move tunnels into less anatomic positions (posterior on the tibia and anterior/vertical on the femur) (Fig. 2). As documented by a number of biomechanical studies, the less anatomic reconstructions reduced anterior translation but did not consistently correct rotational laxity.

In the wake of that revelation, there has been renewed interest over the past 15 years in precise restoration of normal anatomy by placing femoral and tibial tunnels within their normal respective attachment sites or “footprints” (Fig. 3). Independent drilling of femoral and tibial tunnels facilitates more anatomic reconstruction and is again the preferred technique by most surgeons. Other, even more refined attempts to restore normal anatomy have been considered. However, techniques such as double-bundle ACL reconstruction have not been adopted widely, as demonstrated clinical benefit has been limited in most studies and surgical complexity is significantly increased.

Future challenges

Understanding of ACL injuries and techniques for surgical treatment have come a long way over the past 50 years, but substantial challenges remain.

First, recurrent ACL tear rates (ipsilateral and contralateral) remain relatively high despite modern reconstruction techniques and rehabilitation protocols, with several studies documenting recurrent instability rates of 10 percent or more.

Second, return-to-play rates may be lower than previously thought, particularly in competitive athletes, with some studies reporting more than 40 percent of athletes failing to return to the same level of play after ACL reconstruction.

Finally, and perhaps most importantly, the risk of osteoarthritis increases three- to five-fold following ACL injury, and limited evidence suggests that current reconstruction techniques reduce that risk compared to nonsurgical treatment.

Fig. 3 Early single-incision transtibial ACL techniques placed the femoral tunnel high in the intercondylar notch (anterior). In an effort to avoid graft impingement, tibial tunnel was placed posterior to the anatomic center of the tibial insertion. This action led to a more vertical graft, less suitable for resisting rotational loads. Red color represents vertical graft as described above. Green color represents graft with anatomic tunnel positions in the center of the femoral and tibial footprints (ovals with black stripes).

Adapted from Howell SM, Gottlieb JE: Endoscopic fixation of a double-looped semitendinosus and gracilis ACL graft using bone mulch screw. Oper Tech Orthop. 1996;6:152-160.

Given these persistent challenges, researchers are now exploring a variety of new surgical treatment options and investigating the metabolic cascades initiated by ACL injury. For instance, new surgical techniques for primary ACL repair have shown promise in small series, but long-term results are lacking, and ACL reconstruction still leads to more predictable results. In addition, anterior lateral ligament reconstruction may have a role in augmenting ACL reconstruction, particularly in revision, but indications remain unclear at this time. In the future, the most substantial advances may be biologic interventions aimed at altering the catabolic processes that occur after ACL injury and ultimately lead to osteoarthritis. The way orthopaedic surgeons manage ACL injuries may change as much in the next half-century as it has in the previous 50 years.

Matthew Driscoll, MD, is an assistant professor of orthopaedic surgery at the University of Texas at Austin Dell Medical School and chief of orthopaedic surgery at Austin Regional Clinic.