What are ACL injuries and what can I do about them?

ACL injuries are common knee injuries that occur among athletes who participate in sports associated with large amounts of pivoting, decelerating and jumping.¹ Injuries to the ACL can range from mild (such as small tears/sprains) to severe (completely torn). When an ACL has a complete rupture and there are clinical and subjective signs of instability, a surgical reconstruction is required.¹

What is the Anterior Cruciate Ligament (ACL)?

The ACL is a key structure comprising of a dense band of connective tissue attaching the femur to the tibia. It arises from the posteromedial corner of the lateral femoral condyle and inserts anterior to the tibia, blending with the medial meniscus. As it courses across the joint it turns on itself in a slight outward (lateral) spiral.¹ ²

The ACL is designed primarily to resist the anterior tibial translation accounting for 85% of resistance when the knee is kept at 90 degrees of flexion. Secondary to this the ACL restrains tibial rotation as well as varus and valgus forces.²

How do you injure the ACL?

Both contact and non-contact injuries can occur, although non-contact injuries are most common. Retrospective surveys ³ ⁴ and video analysis of ACL ruptures ⁶ ⁷ show that non-contact mechanisms are the most common mechanism of injury, with most injuries occurring during single-leg landing or sidestepping, shortly after initial contact with the knee close to full extension.⁶ ⁸ More ACL injuries are sustained during defending rather than attacking ⁹, consistent with the finding that peak internal rotation and valgus forces are highest when sidestepping and single-leg landing in unplanned situations.¹⁰

The maximal strain on the ACL has been found to occur during the weight acceptance phase of stance, during the deceleration period of landing or side-stepping.¹¹ The weight acceptance phase is also where peak internal rotation and knee valgus moments are observed during single-leg landing and sidestepping.¹⁰ Therefore, a prevention program must focus on adequate strength and control through the deceleration phase of sidestepping and single-leg landing.

The ACL is comprised of both the anteromedial bundle (AMB) and posterolateral bundle (PLB). Cadaveric studies show that the PLB is taut in extension (0-15°), while the AMB is taut in flexion (60-90°).¹² However, with added simulated quadriceps muscle loads, the peak strain of both bundles occurs near full extension (0-15°). This provides rationale for why non-contact ACL injuries typically occur near full extension, and suggests that increasing knee flexion can reduce ACL strain.

Signs and Symptoms:

• At the time of the injury, a ‘pop’ or ‘snap’ can sometimes be heard of felt. The amount of pain experienced at the time of the injury is somewhat variable but can be quite severe.

• Generally the person is unable to continue playing or complete the activity, providing the impression that a significant injury has occurred. It is generally painful to weight bear through the lower limb.

• Immediate swelling of the knee develops at the time of injury within the first several hours

• Decreased range of motion of the joint

• A feeling of instability or ‘giving way’ with weight bearing

What are the risk factors of an ACL injury?

Risk factors for ACL injuries can be divided into two categories which include extrinsic factors and intrinsic factors. Extrinsic factors comprise of those that relate to the type of sports activity, the manner in which the sport is practice, environmental conditions and the equipment used for the sport. Evidence has shown that the type of footwear and friction on the playing surface can increase the risk of ACL. ACL injuries more commonly occur in competition games rather than trainings with weather conditions shown to increase the risk during periods of high evaporation and low rainfall.¹³

Intrinsic factors involve the factors that are individual, physical and psychosocial. Anatomical risk factors that are non-modifiable include a decreased intercondylar notch width and an increased lateral or posterior tibial plateau slope. The neuromuscular and biomechanical risk factors presented as risk factors including limb alignment are modifiable by working on core stability, muscle strength training and neuromuscular exercise programs. The literature has shown that females tend to have a higher incidence rate of ACL injury than males, being between 2.4 and 9.7 times higher in female athletes competing in similar activities. This may be due to a number of reasons including females having a wider pelvis and greater Q angle. The Q angle refers to the femur having a greater greater angle towards the knee, resulting in an increased knee valgus position. Hormonal influences have also been shown to increase the laxity of ligaments during the pre-ovulatory phase of the menstrual cycle and the onset of menarche.¹⁴

Extrinsic factors increasing the risk of ACL injuries: ¹³

• Footwear

• Playing surface

• Type of competition

• Weather

Intrinsic factors increasing the risk of ACL injuries: ¹³

• Anatomical risk factors

• Limb alignment

• Neuromuscular factors

• Previous ACL injury

• Gender

• Hormonal influences

ACL Rehabilitation:

Depending on the severity of the ACL injury and whether surgical intervention is required, changes the rehabilitation required. ACL injuries commonly occur with other damage in the knee and depending on the other.

Conservative treatment for a ruptured ACL can be an option for those patients that are more sedentary in their lifestyle. Therefore, it is important to consider patient age, sports activities and subjective instability during daily life when considering for or against ACL reconstruction.

Acute:

After an ACL injury, regardless of whether surgery will take place or not, physiotherapy management focuses on regaining range of movement, strength, proprioception and stability.

In the acute stage PEACE AND LOVE should be used in order to reduce swelling and pain. This will attempt to regain full range of motion and decrease joint effusion. Appropriate anti-inflammatory medications are used to help control pain and swelling.

In any case exercises should encourage range of movement, initial strengthening of the quadriceps and hamstrings, and eventually proprioception. In fact, strength and proprioceptive alterations occur in both the injured and uninjured limb

The risk of developing a stiff knee after surgery can be significantly reduced if the surgery is delayed until the acute inflammatory phase has passed, the swelling has subsided, a normal or near normal range of motion (especially extension) has been obtained, and a normal gait pattern has been re-established.

Surgical Intervention:

If a surgical procedure is required, it is important to complete some prehab exercises to prepare the knee for the surgery. The main focus before the surgery is to regain full range of motion of the knee, minimise swelling and keep the quadriceps strong.

There are various options for the graft for the ACL, such as hamstring graft, patella tendon, quadriceps tendon and allografts. The most popular is a hamstring tendon graft which uses the semitendinosus hamstring tendon on the inner side of the knee. There are positives and negatives with all of these procedures including decreased pain after surgery and a smaller incision. However, the patient may have decreased hamstring strength after surgery and can be more vulnerable to hamstring strains post rehabilitation.

ACL reconstruction surgery is traumatic to the knee and a period of rest and recovery is required after the operation. Whilst it’s tempting to want to get going and improve strength and range of motion, it’s best to let the knee settle for the first 1-2 weeks with basic range exercises, quadriceps setting drills, ice and compression. Typical exercises and management activities during this phase include regular icing of the knee and graft donor site (usually either the hamstrings, quad or patella tendon), compression of the knee and lower limb, basic quadriceps setting exercises, and gentle range of motion exercises to improve knee extension (straightening) and flexion (bending). Analgesics and other medications should only be used in consultation with your doctor.

Further from this, working closely with the surgeon and physiotherapist an extensive rehabilitation is progressed throughout the different stages of ACL rehabilitation. There are numerous goals to achieve along the way to progress the exercises and towards the end goal of returning to sport in 9-12 months. The goals are focused on limb symmetry and returning the injured limb to be as similar to the other leg as possible.

ACL Injury Prevention Program:

Devising an injury prevention and exercise-based rehabilitation program following an ACL injury requires a strong understanding of the kinematic and neuromuscular factors associated with ACL injury. ACL injury occurs when the load applied to the ligament is greater than what it can tolerate. Therefore, ACL prevention programs should aim to reduce ACL load during movement. Introduction of neuromuscular training programs have been shown to reduce prevalence of ACL injuries by two-thirds.¹⁶

Studies have found mean peak vertical ground reaction force to be 3.2 times bodyweight and occurs 40ms after initial ground contact.8 Based on when peak vertical ground reaction force occurs and when there are sudden changes in joint angular motion, ACL injury is likely to occur approximately 40ms after initial ground contact.  Given there are few protective mechanisms to ACL injuries in the first 40ms after ground contact, ACL prevention strategies must focus on preparatory movements prior to initial contact that limit exposure to vulnerable kinematic positions.⁸

Training programs aimed to reduce the risk of ACL injuries should include several key factors: (1) reduce valgus and internal rotation knee moments; (2) increase muscular strength to provide support against joint moments; (3) increase knee flexion and neuromuscular control of the hip during the deceleration phase of single-leg landing and sidestepping.¹⁵

As most ACL injuries occur with single-leg landing or sidestepping, athletes must practice these movements where vulnerable biomechanical positions are avoided. It is important to practice these scenarios during unplanned movements at greater than 4m/s, as this is where injury is most likely to be sustained. If the player has practiced and reinforced these movement patterns, they are more likely to use these movement strategies when moving subconsciously during a game.

As the maximal load on the ACL has been found to occur during deceleration, athletes must train effective deceleration mechanics and have adequate strength to tolerate the high forces experienced during deceleration. As deceleration has a high eccentric quadriceps load, athletes must have effective eccentric quadriceps strength to ensure safe dissipation of forces and ensure that less load is placed on the ACL. Effective deceleration mechanics must be trained prior to training landing and cutting under high speed and unplanned scenarios.⁹

Resistance, plyometric and balance training implemented alongside an athletes normal training program are effective for reducing risk of ACL injury during side-stepping and single-leg landing tasks.¹⁵ These training strategies were shown to reduce peak knee valgus moments and increase knee flexion angle. There were also reductions in peak valgus and extension moments and elevated hamstring-quadriceps co-contraction during the weight acceptance phase of double-leg landing.¹⁵

Due to their line of action, activation of the hamstrings can reduce ACL tension between 15° and 45° of knee flexion. ACL strain is further reduced when the hamstrings are co-contracted with the quadriceps. Co-contraction of the quadriceps and hamstrings reduces ACL strain between 15° and 60° of flexion by reducing tibial displacement relative to the femur in all planes of motion. Medial knee muscles can support knee valgus moments, and are considered a useful neuromuscular strategy for reducing external knee valgus moments to the ACL.⁸

At Fortis Physio, we design ACL injury prevention training programs, so you can be confident that you are doing everything possible to stay active and injury-free. Book an online appointment with us today.

References

1. Meredith SJ, Rauer T, Chmielewski TL, Fink C, Diermeier T, Rothrauff BB, et al. Return to Sport After Anterior Cruciate Ligament Injury: Panther Symposium ACL Injury Return to Sport Consensus Group. Orthopaedic Journal of Sports Medicine. 2020 Jun 1; 8(6). DOI: https://doi.org/10.1177/2325967120930829

2. Della Villa F, Buckthorpe M, Grassi A, Nabiuzzi A, Tosarelli F, Zaffagnini S, et al. Systematic video analysis of ACL injuries in professional male football (soccer): injury mechanisms, situational patterns and biomechanics study on 134 consecutive cases. British Journal of Sports Medicine. 2020 Jun 19; 54(23): 1423–1432. DOI: http://dx.doi.org/10.1136/

3. Gianotti, S. M., Marshall, S. W., Hume, P. A., & Bunt, L. (2009). Incidence of anterior cruciate ligament injury and other knee ligament injuries: a national population-based study. Journal of science and medicine in sport, 12(6), 622-627.

4. Gianotti SM, Marshall SW, Hume PA, Bunt L. Incidence of anterior cruciate ligament injury and other knee ligament injuries: A national population-based study. Journal of Science and Medicine in Sport. 2009 Nov;12(6): 622–7. DOI: https://doi.org/10.1016/j.jsams.2008.07.005

5. Rochcongar P, Laboute E, Jan J, Carling C. Ruptures of the Anterior Cruciate Ligament in Soccer. International Journal of Sports Medicine. 2009 Feb 6;30(05): 372–8. DOI: https://doi.org/10.1055/s-0028-1105947

6. Cochrane JL, Lloyd DG, Buttfield A, Seward H, McGivern J. Characteristics of anterior cruciate ligament injuries in Australian football. Journal of Science and Medicine in Sport. 2007 Apr 1;10(2): 96–104. DOI: https://doi.org/10.1016/j.jsams.2006.05.015

7. Krosshaug T, Nakamae A, Boden BP, Engebretsen L, Smith G, Slauterbeck JR, et al. Mechanisms of Anterior Cruciate Ligament Injury in Basketball. The American Journal of Sports Medicine. 2007 Mar;35(3): 359–67. DOI: https://doi.org/10.1177/0363546506293899

8. Koga H, Nakamae A, Shima Y, Iwasa J, Myklebust G, Engebretsen L, et al. Mechanisms for Noncontact Anterior Cruciate Ligament Injuries. The American Journal of Sports Medicine. 2010 Jul;38(11): 2218–25. DOI: https://doi.org/10.1177/0363546510373570

9. Lucarno S, Zago M, Buckthorpe M, Grassi A, Tosarelli F, Smith R, et al. Systematic Video Analysis of Anterior Cruciate Ligament Injuries in Professional Female Soccer Players. The American Journal of Sports Medicine. 2021 May 14;49(7): 1794–802. DOI: https://doi.org/10.1177/03635465211008169

10. Besier TF, Lloyd DG, Ackland TR, Cochrane JL. Anticipatory effects on knee joint loading during running and cutting maneuvers. Medicine and Science in Sports and Exercise. 2001 Jul;33(7): 1176–81. DOI: https://doi.org/10.1097/00005768-200107000-00015

11. Jindrich DL, Besier TF, Lloyd DG. A hypothesis for the function of braking forces during running turns. Journal of Biomechanics. 2006 Jan;39(9): 1611–20. DOI: https://doi.org/10.1016/j.jbiomech.2005.05.007

12. Gabriel MT, Wong EK, Woo SL-Y, Yagi M, Debski RE. Distribution of in situ forces in the anterior cruciate ligament in response to rotatory loads. Journal of Orthopaedic Research. 2004 Jan;22(1): 85–9. DOI: https://doi.org/10.1016/s0736-0266(03)00133-5

13. Pfeifer CE, Beattie PF, Sacko RS, Hand A. RISK FACTORS ASSOCIATED WITH NON-CONTACT ANTERIOR CRUCIATE LIGAMENT INJURY: A SYSTEMATIC REVIEW. International Journal of Sports Physical Therapy. 2018 Aug;13(4): 575–87. DOI: 10.26603/ijspt20180575

14. Yoo JH, Lim BO, Ha M, Lee SW, Oh SJ, Lee YS, et al. A meta-analysis of the effect of neuromuscular training on the prevention of the anterior cruciate ligament injury in female athletes. Knee Surgery, Sports Traumatology, Arthroscopy. 2009 Sep 4;18(6): 824–30. DOI: https://doi.org/10.1007/s00167-009-0901-2

15. Donnelly CJ, Elliott BC, Ackland TR, Doyle TLA, Beiser TF, Finch CF, et al. An Anterior Cruciate Ligament Injury Prevention Framework: Incorporating the Recent Evidence. Research in Sports Medicine. 2012 Jun 28;20(3-4): 239–62. DOI: https://doi.org/10.1080/15438627.2012.680989

16. Webster KE, Hewett TE. What is the Evidence for and Validity of Return-to-Sport Testing after Anterior Cruciate Ligament Reconstruction Surgery? A Systematic Review and Meta-Analysis. Sports Medicine. 2019 Mar 23; 49(6): 917–29. DOI: https://doi.org/10.1007/s40279-019-01093-x