Anterior cruciate ligament reconstruction (ACLR) is a long, challenging process that truly tests your love for your sport. In the past, an ACL rupture often ended an athlete’s career. Thankfully, modern medicine has advanced immensely, allowing athletes to continue their careers long into the future. Despite these advances in surgery and rehabilitation, many athletes still fail to return to sport, and even more never return to their prior level of performance. This is highlighted to emphasize the importance of taking all of the necessary steps in choosing a surgeon, a physical therapist, and so on.
Before diving into the ideal criteria for returning to sport, it’s important to review the surgery itself, the different graft types, and what may come along with them.
The ACL is a 3-dimensional ligament that sits in the middle of the knee joint. It connects the femur to the tibia, along with several other ligaments, to provide stability at the joint. New approaches to repair the native ligament have shown promise; however, the common strategy that a surgeon will use is to reconstruct the ligament using a tissue graft of the quad tendon, patellar tendon, hamstring tendon, or a cadaveric graft. It’s important to keep in mind that while graft harvest is often essential, the procedure itself naturally creates another site of injury to heal.
Quadriceps tendon - connects the quadriceps muscle to the patella. This graft type typically has less knee pain during the rehab process. Despite this, the restoration of quad strength is often delayed compared to other graft options.
Patellar tendon - connects the patella to the tibia. This graft type is often described as the gold standard due to return-to-sport success and stability provided by the inclusion of bony interfaces on both ends. Patellar tendon grafts are typically associated with more knee soreness than other options. The restoration of quad strength is typically quicker than with the quad graft, but slower than with hamstring or cadaveric grafts.
Hamstring tendon - connects the hamstrings to the tibia in the back of the leg. This graft is often associated with less knee soreness than with quad or patellar grafts. Despite this, hamstring strength is typically delayed compared to other graft options.
Cadaver graft - harvested from quadriceps, patellar, hamstring, Achilles, or tibialis anterior tendons from a cadaver. This graft commonly has the least knee soreness and the fastest restoration of strength. This graft type has been shown to have higher re-tear rates than other options.
In the past, ACL rehabilitation often progressed based on how much time had passed since surgery. While time is an essential factor for tissue healing, it does not take physical capacity into account and, as a result, athletes were often cleared to return to sports without proper rehabilitation and testing. The modern approach utilizes a criterion-based approach, which progresses an athlete through the rehabilitation program once they meet specific criteria. A basic rule of thumb is that all assessments should indicate limb symmetry of at least 90% between the surgical leg and the unaffected leg. Actual decision-making is more nuanced, but return-to-sport clearance is largely based on this as the foundation.
A limb symmetry index (LSI) is how values specific to the surgical leg can be compared to the unaffected leg, and is given as a percentage. The equation to calculate LSI = affected leg / unaffected leg x 100.
Quadriceps strength
As it pertains to strength values, quad strength is the most important and toughest to restore. The primary reason for the difficulty restoring this following surgery is due to the graft harvesting from the extensor mechanism of the knee in patellar and quad tendon grafts. Nonetheless, it is imperative that strength is restored to safely progress through each rehab phase and eventually back into sports. Strength is commonly inferred using two methods:
A) MVIC - maximum voluntary isometric contraction - How much force can you produce at a fixed angle?
B) PT: BW - peak torque to bodyweight - How much torque can you produce, relative to your bodyweight? You need MVIC to calculate PT: BW. ***Specific values vary in the research as well as due to considering anecdotal experience.
70% LSI or 1.7 Nm/kg: Progress to running, low-level bilateral plyometrics, begin unilateral force absorption. **Anecdotally, I often introduce lower-level plyometrics ahead of initiating running, as a means to prepare the body for the forces of running.
80% LSI: Progress to moderate bilateral plyometrics and low-level unilateral plyometrics. Initiate change of direction training, cutting/planting.
90% LSI: Progress to high-level running, deceleration, cutting, and pivoting. **May begin reintegration into sport-specific activities if deemed ready based on other comprehensive assessments.
Hamstring strength
Goal = >90% LSI. Special consideration is made for hamstring tendon graft cases when progressing through the return to sport phase, due to the high demands on the hamstring to act synergistically with the reconstructed ACL, as well as normal loading in running and sprinting.
Hip abductor/adductor strength
Goal = >90% LSI. Hip abductor strength is especially important in stabilizing the hip and knee with activities that expose the leg to unilateral loading. Hip adductor strength is also very important, as this muscle group functions 3-dimensionally in athletic movement.
Horizontal hop tests
Goal = >90%. The importance of these tests has been downplayed over time, but they do hold value in the big-picture of return-to-sport decision-making. Horizontal hopping is a better appraisal of glute and calf function vs. knee function; however, in ACL rehabilitation, I believe that it’s important to evaluate more data than less data to provide the most complete picture of the athlete. The act of landing during horizontal hopping is a good measure of qualitative knee function.
Vertical jump tests
Goal = >90% asymmetry. Due to the higher demands placed on the knee with vertical jumping, these tests have gained popularity and rightfully so. They are an excellent assessment tool to compare one leg against the other in a manner that exposes deficiencies in knee function. These tests are often done using force plates.
Movement quality
Qualitative movement cannot be measured with a number like the aforementioned tests. Movement quality is a subjective assessment completed by the rehab specialist. Some examples of movement quality include symmetrical weight distribution, dynamic knee alignment, motor control, squat depth, or shin angles, to name a few.
A comprehensive return to sport assessment should include many areas discussed, including objective strength testing, hop testing, and force plate testing when access to equipment is available. Additional testing specific to the athlete's sport may also be considered. Upon meeting the criteria set by the surgeon and physical therapists, athletes often enter a modified reintegration into sport for a period of time, which allows a gradual ramp-up in activity. A successful reintegration is typically followed by the ultimate clearance by the medical team.
In summary, ACL rehab is a complicated, challenging experience to maneuver through. It’s extremely important that the athlete is being guided through this process with sound advice and oversight. Not knowing when certain things are permissible or not is a key piece in maintaining safety. If this speaks to someone you know, we would love to help. Call or text us at 404-548-8263, or complete a contact form, and we will reach out to you.
Best,
Board Certified Orthopedic Clinical Specialist
Certified Strength and Conditioning Specialist
Owner/Founder - Stamina Performance Physical Therapy
