How to Reduce ACL Reinjury Risk
Anterior cruciate ligament (ACL) injuries are some of the most common lower-limb injuries among athletes, but unfortunately, these incidences are not always one-and-done. Recent studies reported that re-injury rates among young athletes range of 20%-40%, while division-one athletes who experience an ACL injury prior to their division-one career are 8-fold increased risk of injuring their knee or ACL than non-injured athletes.1-2
Faced with this high re-injury risk, physical therapists and other hands-on healthcare professionals recognize the importance of correctly managing the injury the first time around. Today, we’re diving into three evidence-based rehabilitation factors that can help professionals successfully manage ACL injuries post-reconstruction and potentially decrease re-injury risk: return to activity timing, movement mechanics and strengthening and the utilization of neuromuscular training.
1. RETURN TO ACTIVITY TIMING
Allowing any injury time to heal before returning to activity is generally a good rule to follow, but it seems it may be even more so with ACL injuries. In 2016, a study assessed the relationship between knee re-injury after ACL reconstruction and return to level I sports (sports that involve jumping, pivoting and hard-cutting), timing of return to sport and knee function prior to return. Here’s what they found:3
- 74 of the 83 patients who previously participated in level I sports returned to level I sports within 2 years of ACL reconstruction. The time of return to level I sports varied from 3 to 23 months after surgery, with a median of 8 months after surgery.
- Four patients returned to sport fewer than 5 months after surgery. All four of these patients suffered a knee re-injury within 2 months of return.
- During the first 9 months after surgery, a later return to sport was significantly associated with a lower re-injury rate.
- For every 1 month delay in return to sport, the re-injury rate was reduced by 51%
- In patients who returned between 9 and 23 months after surgery, time to return was not significantly associated with knee re-injury.
- Patients who participated in level I sports earlier than 9 months after surgery sustained 39.5% re-injuries (15 of 38), compared with 19.4% knee re-injuries (7 of 36) in those who returned to level I sports later than 9 months after surgery.
- Of the 55 patients who failed return to sport criteria, 21 (38.2%) suffered knee re-injuries. Only 1 of the 18 patients (5.6%) who passed return to sport criteria suffered a knee re-injury.
2. MOVEMENT MECHANICS AND STRENGTHENING
Mechanics and strength are arguably the most important factors in preventing ACL re-injury rates, as the majority of athletes who suffer an ACL injury have nobody to blame but their own musculoskeletal system and movement patterns. While contact ACL injuries do occur, 70% of ACL injuries occur in non-contact situations.4
In a recent literature review, researchers identified five important mechanics factors that should be assessed when evaluating an athlete for risk or for return to play:.5
- Stability of the limb in the frontal plane
- Stability and impact of fatigue on single limb testing
- Truck stability in stance and core testing
- Limb symmetry index – comparison on right and left limb in closed kinetic chain testing
- Lateral displacement of the pelvis during squatting motion
When looking at these dysfunctions, notice that the hip and ankle are actually responsible for regulating these functions, instead of the knee. But why do the hip and ankle affect the likelihood of an ACL injury? For this, we can thank regional interdependence.
Regional Interdependence and Knee Injuries
Just about all major movements of the body rely on a relationship of alternating stable and mobile joints. Mobile joints have a wider range of motion and are able to produce a variety of desired movements, like the shoulders, thoracic spine, hips, wrists and ankles. Stable joints are meant to resist undesired movements, like the scapulothoracic region, lumbopelvic region, elbow and knee.
These alternating regions work in tandem when they are functioning normally. However, if one of the body’s joints is compromised, it can have a direct, domino-like impact on the rest of joints in its chain, resulting in pain or injuries that can be misleading to the untrained eye. In the case of ACL injuries, if the patient’s hip or ankle joints or surrounding musculature have lost mobility, the needed movement can shift to the knee. This could result in the knee compensating for this lack of mobility in ways that it is not meant to move, resulting in ACL injuries.
When building an ACL rehabilitation program, consider combating regional interdependence by focusing on hip, glute, quadricep and ankle performance.
Hip/Glute Medius-Focused Training
Back in 2009, a research study described the “position of no return” mechanism for ACL injury, or the positions that can contribute to an ACL injury that stem from hip dysfunctions:6
- Trunk forward flexion
- Hip adduction and internal rotation
- Knee valgus
- Tibial external rotation
Additionally, another study looking at ACL injuries in NFL players found that the most common position of the limb during the injuryt was hip adduction/flexion, early knee flexion/abduction and foot abduction/external rotation.7
Weak glute medius muscles are also a culprit in these positions, and are key players in dictating unhealthy movement patterns. Dr. Trent Nessler DPT, MPT, an expert in ACL injury prevention and movement dysfunction, has been exploring this relationship throughout his career. In a recent blog post, he outlined the importance of glute medius strength in ACL re-injury:
“With severe weakness come severe deviations. In the knee, this means that adduction in the frontal plane is of such large magnitude that we are also now starting to see significant internal rotation of the femur. But what does that look like in the hip? In the hip, this results in a trendelenburg along with a rotation (what we define as a corkscrew). In this scenario, the gluteus medius is so weak that the pelvis drops and rotates at the same time. Looking at the origin and insertion of the gluteus medius, the muscle is failing through its full range of motion and hence why these two movements occur in unison… In these cases, and under high loads (jumping and running) the amount and magnitude of shear stress that is imparted to the labrum of the hip significantly higher than it is intended to take or that it is designed to take.
Considering all the above, we can now grade our gluteus medius weakness based off the deviations that we see presented at the pelvis as much as what we see at the knee. At the pelvis, we would expect the following gradients:
- Trendelenburg – mild/moderate gluteus medius weakness
- Retrotrendelenburg – moderate to severe gluteus medius weakness
- Corkscrew – severe gluteus medius weakness”8
As you can see, years of data have identified hip/glute medius strengthening as a critical component of ACL injury rehabilitation and prevention. This data shows that, by strengthening the hip, clinicians can help athletes establish healthier movement patterns that can decrease the likelihood of ACL injuries that occur during activity.
Alongside hip and glute strength, quadricep strength has been identified as an important component of ACL rehabilitation protocol. In one study, of the individual components in the return to sport test battery, quadriceps strength deficit prior to return to level I sport was a significant predictor of a knee re-injury, with a 3% reduced re-injury rate for every one percentage point increase in strength symmetry. Fifteen of the 45 patients (33.3%) who returned to level I sport with quadriceps limb symmetry index less than 90% suffered re-injuries, versus three (12.5%) re-injuries in the 24 patients who had quadriceps limb symmetry index greater than 90% prior to return.3
After an ACL reconstruction, clinicians should focus on returning the quadricep of the affected leg back to symmetry with the unaffected leg prior to return if they wish to decrease the risk of re-injury.
At the opposite end of the leg, ankle weakness is another predictor of ACL re-injury risk. Research has shown that those who demonstrate a lack of dorsiflexion also end up with increase in adduction moment at the knee, concluding that, “dorsiflexion flexibility may serve as a useful clinical measure to predict poor landing postures and external forces that have been associated with increased knee injury risk.”9
Based on this data, physical therapists should integrate ankle strengthening exercises, as well as targeted dorsiflexion flexibility training, into their rehabilitation protocol to improve landing kinematics and kinetics.
3. NEUROMUSCULAR TRAINING
Neuromuscular training is defined as “training enhancing unconscious motor responses by stimulating both afferent signals and central mechanisms responsible for dynamic joint control.”₁₀
Over the years, there has been a wealth of clinical evidence that suggests that neuromuscular training programs are the ‘secret sauce’ to ACL rehabilitation.
- One study comparing the effects of a neuromuscular training program with a traditional muscle strengthening program in patients with ACL deficiency found that patients performing the neuromuscular training program improved significantly more than the traditional group in functional activities and reflex activation of the hamstrings.11
- Another found that the neuromuscular training group demonstrated significantly improved Cincinnati Knee Scores and VAS scores for global knee function compared with the traditional strength training group at the 6-month follow-up.12
- In 2009, researchers found that significantly improved knee function (global function) and reduced pain during activity in the group who followed neuromuscular training protocol, compared with the traditional strengthening group.13
But why does neuromuscular training work so well with post-operative ACL reconstruction patients? According to one study, this is because neuromuscular training:
- Improves the nervous system’s ability to generate a fast and optimal muscle firing pattern, to increase dynamic joint stability
- Decreases joint forces and to relearn movement patterns and skills
- Induces compensatory changes in muscle activation patterns and facilitate dynamic joint stability
- Achieves a state of “readiness” of muscles to respond to joint forces resulting in enhanced motor control.10
Based on all of the previous evidence in this article, it’s safe to conclude that all of the outcomes of neuromuscular training can aid in creating a successful rehabilitation program and reduce the risk of re-injury.
Source: Performance Health Academy
- Webster, K. E., & Feller, J. A. (2016). Exploring the High Reinjury Rate in Younger Patients Undergoing Anterior Cruciate Ligament Reconstruction. The American Journal of Sports Medicine, 44(11), 2827–2832. https://doi.org/10.1177/0363546516651845
- Rugg CM et al. 2014. Effects of prior knee surgery on subsequent injury, imaging, and surgery in NCAA collegiate athletes. Am J Sports Med. 2014 Apr;42(4):959-64. doi: 10.1177/0363546513519951. Epub 2014 Feb 11.
- Grindem H et al. 2016. Simple decision rules can reduce reinjury risk by 84% after ACL reconstruction: the Delaware-Oslo ACL cohort study. Br J Sports Med 2016;50:804-808.
- Griffin LY et al. 2000. Noncontact anterior cruciate ligament injuries: risk factors and prevention strategies. J Am Acad Orthop Surg. 2000 May-Jun;8(3):141-50.
- Nessler T. et al. 2017. ACL Injury Prevention: What Does Research Tell Us? Curr Rev Musculoskelet Med. 2017 Sep;10(3):281-288. doi: 10.1007/s12178-017-9416-5.
- Reiman M.P. et al. Hip Function’s Influence on Knee Dysfunction: A Proximal Link to a Distal Problem. Journal of Sport Rehabilitation, 2009, 18, 33-46.
- Johnston J.T. et al. 2018. Video Analysis of Anterior Cruciate Ligament Tears in Professional American Football Athletes. The American Journal of Sports Medicine, 46(4), 862–868.
- Malloy, P., Morgan, A., Meinerz, C. et al. Knee Surg Sports Traumatol Arthrosc (2015) 23: 3550.
- Rinsberg MA et al. 2011. Design and Implementation of a Neuromuscular Training Program Following Anterior Cruciate Ligament Reconstruction. Journal of Orthopaedic & Sports Physical Therapy 31(11): 620-631.
- Beard D. J. et al 1994. Proprioception enhancement for anterior cruciate ligament deficiency. The Journal of Bone and Joint Surgery 76-B(4):654-659
- RIsberg MA et al. 2007. Neuromuscular training versus strength training during first 6 months after anterior cruciate ligament reconstruction: a randomized clinical trial. Phys Ther 87(6):737-50. Epub 2007 Apr 18
- Risberg MA, Holm I. 2009 . The long-term effect of 2 postoperative rehabilitation programs after anterior cruciate ligament reconstruction: a randomized controlled clinical trial with 2 years of follow-up. Am J Sports Med 37(10):1958-66.