Returning to Sport After ACL Reconstruction: What Athletes Need to Know
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Introduction
The anterior cruciate ligament (ACL) is one of two cruciate ligaments in the knee, and plays a major role in overall stability. The ACL is located at the center of the knee and directly connects the femur (thigh bone) to the tibia (shin bone) (1). The responsibilities of the ACL are most relevant during physical activity, where the ligament acts as a static joint restraint, limiting motion of the joint to ensure proper alignment and maintain stability (2). Certain movements place greater demands on the ACL, including forward movement, rotational motion, and sudden changes in direction (1). The ACL plays a very important role in the regulation of anterior tibial translation (ATT), the movement of the tibia forward relative to the femur. The ACL actually provides between 80- 90 percent of this restraining force, making it incredibly important for movements where force is placed forward over the knee (3). The ACL is also very important in preventing excessive internal rotation of the knee, which is the rotation of the tibia inward relative to the femur. This function makes the ACL extremely important in stabilizing the knee during rotational motion. Due to the excessive forces placed on the knee in these planes during sport, ACL injuries are common in athletes, particularly in sports where the specific above-mentioned movement patterns are required (1).
Prevalence of ACL Injuries in Athletes
As stated above, physical activity during sports places large forces on the ACL, especially during quick, forceful pivots, stops, and jumping (4). Systematic reviews have demonstrated ACL injury rates of up to 0.05% per person per year in Australia in the overall population. Ameteur/casual athletics was associated with a higher rate of incidence, and professional soccer, basketball, and football athletes showed even greater rates of injury, ranging from 0.15 to 3.7% per person per year (5). Other studies have shown that the incidence of ACL injury has increased in recent years and that peak rates of injury are seen among high-school-aged populations in both males and females (6). While clinical expectations regarding return to sport are often set at one year, studies have shown that even at two years after surgery, only 66% percent of patients returned to sport, and only 40% returned to their previous level of sport (6). This distinction is interesting to note, and confirms the necessity of proper ACL function in return to sport. This also suggests that further research and refinements of surgical and physical management are needed.
Surgical Considerations
When surgical reconstruction of the ACL is performed, there are various considerations that must be made in order to promote the best outcome for each patient. One of the largest decisions that comes with every ACL reconstruction is the choice of graft for replacement of the tissue itself (7). Some of the most common autografts, meaning from one’s own body, include the patellar bone-tendon-bone, hamstring tendon, and quadriceps tendon. There are also many choices of allograft, artificially manufactured structures to function in place of the ACL. Grafts are considered on a case-by-case basis and selected based on their properties, similarities to the native ACL, and functional drawbacks (7). Following reconstruction with autographs, the implanted tissue undergoes a process known as “ligamentization,” where it is remodeled through three main phases (8). These include an early healing phase, proliferative phase, and maturation phase, where the tissue structurally transitions from its original form to a ligamentous structure capable of stabilizing the knee. Through animal studies, time frames have been broadly defined for each of these three phases. The early healing phase consists of weeks 0 to 4, the proliferative phase weeks 4 to 10, and the maturation phase 10 weeks and beyond. These animal studies have enabled the temporal determination of ACL graft strength, as depicted below (Fig. 1) (8). The ACL is structurally weakest in weeks 4 to 8, and slowly returns to near full strength at about two years post-reconstruction. Thus, the risk for reinjury with early over-exercision may pose a higher risk for re-tear. However, clinical and biological studies have demonstrated that controlled mechanical stress provided through structured physical rehabilitation is necessary for collagen remodeling, maturation, and strength (9).
Returning to Sport
Safe return to sport depends on regaining strength, stability, and confidence. The recovery
process and return to sport timeline varies widely in each patient, and depends on a variety of pre-, intra-, and post-operative factors (Fig. 2).
Regardless, typical rehabilitation tends to follow some general phases depicted in the figure below (Fig. 3). The immediate post-operative phase involves initial healing and the management of pain and swelling of top priority. During this phase, weight bearing is extremely minimal, and brace immobilization is used along with crutches until basic strength and balance are recovered (11). From weeks 5-12, the primary goal is to build foundational strength, improve walking gait, and general mobility. At this point, resistance training and intense movements remain very limited. After three months, patients often begin to see functional training, where physical therapists employ more intensive weight training and more dynamic sport-like movements. At six months and beyond, physical therapy may transition to very sport-specific movements, including heavy weight-lifting, plyometrics, and sport simulations. Once the physical therapist and physician defined criteria are met, the patient may then begin the official return to sport and full activity.
Take Home Message
Understanding the function of the ACL, its prevalence, and healing process is a prerequisite for specialized health providers, but also very important for athletes who have suffered an injury and make the most seamless return to sport possible. This knowledge can empower athletes to make informed decisions and facilitate meaningful conversations with providers. As the incidence of ACL injuries has increased in recent years, particularly in young people, it is important that
information and awareness regarding risk factors and rehabilitation programs are spread. Further research into optimal graft choice, surgical techniques, rehabilitation, and even non-surgical
options is needed to ensure the best possible treatment is provided in the future.
References
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