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Part 1-Understanding the Mechanisms of ACL Injury

Updated: Aug 2, 2020

In this 9 part series, I will highlight my guideline to assessing, programming, and re-evaluating an athlete who is on the road to returning back to their sport post reconstruction ACL surgery.

Part 1 - Understand the Mechanisms of ACL Injury

Part 2 - Level 1 Assessment

Part 3 - Level 2 Assessment

Part 4 - Phase 1 Training

Past 5 - Phase 2 Training

Past 6 - Phase 3 Training

Part 7 - Phase 4 Training

Part 8 - Evaluation for Return to Sport

Part 9 - Injury Nutrition

Most of the information highlighted in these articles stem from my previous personal work as ACL Return to Sport Coordinator with Hackensack University Medical Center, based in Maywood NJ, where I had very much success. I served there as the coordinator from 2015-2019 where I was able to collaborate with two surgeons who performed different graft surgeries.

The findings I saw in the recovery process during strength training lead me to believe that the patellar graft had the best recovery when comparing injured limb to non-injured limb. Athletes who had the patellar graft had gained greater power outputs quicker than those with hamstring grafts, who were also combating with noticeable limp gait patterns when training in a fatigued state. Ultimately, each surgeon had their reason why they did their preferred method of surgery. Doctor 1 stated "why destroy a piece of the hamstring unit? Now you have to establish normal knee function and proper hip extension with 'less of a hamstring' (although a hamstring graft doesn't take away a lot of the hamstring muscle)." Doctor 2 stated, "why destroy a mechanism that is supposed to be the most resilient supporting structure to the injured area?" Doctor 2 also appoints that a patellar graft should be used in cases of re-tears. However Doctor 1 states, patellar grafts ossify into the femur and tibia at a higher rate than hamstring grafts, therefore leading to greater recovery. Either way, I had success training these athletes back to their sports with zero re-tears or contra-lateral tears. Anyway, enough about doctors, now let's talk about the ACL injury.

The ACL is the primary stabilizer to prevent anterior translation of the tibia on a fixed femur and posterior translation of the femur if the tibia is fixed as in a closed chain. Anterior tibial shearing force is the primary factor that contributes to increased ACL loading, primarily at 0-30 degrees of flexion angles. Isolated knee valgus and tibial rotation also causes ACL loading, but smaller when

compared to anterior shear force. Non-contact ACL injuries lead to decreased sagittal plane joint flexion with increased valgus and leg rotation. Knee hyperextension combined with internal rotation can also produce a tear of the ACL. The stop-jump landing phase has also been considered to produce ACL injuries.

Numerous risk factors for ACL injury have been presented in the literature.

External Risk Factors

Type of competition


Playing surface

Protective equipment

Meteorological conditions

Internal Risk Factors

Anatomical factors

Femoral intercondylar notch size

ACL size

Lower-extremity alignment (Q-angle, pronation, tibial torsion)

Hormonal Risk Factors

Females may be more predisposed to non-contact ACL injuries during the preovulatory phase of the menstrual cycle.

Biomechanical Risk Factors

The roles of the trunk, hip, and ankle may have importance to ACL injury risk. The common at risk situation is decelerating. Neuromuscular factors are important contributors to increased risk on ACL injuries in females. Strong quadriceps activation during eccentric contraction was considered to be a major factor in ACL injuries. VALGUS!!!

I hope I was able to give you a greater understanding of the ACL injury mechanism and the risk factors involved. Overall, this is a catastrophic injury to any athlete, no matter the sport, and there should be proper testing and training involved to ensure the athlete returns as close to their 100% former self as possible. Make sure to subscribe to the website so that you can get updated on when the next part of this ACL series releases.

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