Mechanism of Anterior Cruciate Ligament Injury



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The world today belongs to the fittest of the fit. With increased interest in sports activities over the last few decades, more and more college and school students are participating in athletic activities normal both the competitive and the noncompetitive section. Fame and laurels are part of the sports spectrum, but like all coins there is a flip side to it. One of them is the injury to the Anterior Cruciate Ligament (ACL around the knee region. Acute ACL rupture is a devastating injury that can significantly affect patients’ activity levels and quality of life.

Complete ACL tears can lead to chronic knee problems, such as knee instability, meniscus and chondral surface damage, and osteoarthritis. Up to two thirds of patients with complete ACL tears may develop chronic knee instability and secondary damage to menisci and chondral surfaces, significantly affecting knee function and often forcing patients to decrease their activity levels and change their life styles. In the following sections, an attempt will be made to detail the biomechanics of ACL injury and to understand the preventive and rehabilitative programmes, with an aim of application in prevention and treatment of these injuries. The fact that injury levels differ widely in males and females will be highlighted, and the most disturbing fact more than two-thirds of the injuries are non-contact in nature will be impressed upon. There is an urgent need to develop structured programmes which aim to reduce these injuries, as these injuries cannot be entirely prevented.




Review of Literature




ACL injuries are most often due to low-velocity, noncontact, deceleration injuries (Guiliano, 2000, Hubbell, 2006). The incidence in females is approximately 2-8 times higher than males (Guiliano, 2002). Hubbell (2006) states that the estimated incidence in the population is 1 case per 3500 people in the US, with a total of about 200,000 ACL related injuries and 95,000 ruptures per year. Approximately 60,000-75,000 ACL reconstructions are carried out per year in the US for these injuries. stability of ACL is essential in athletes involved in games which require running, jumping, deceleration, twisting, cutting, and kicking as in football, basketball etc.( Hubbell, 2006)


Anatomy of ACL


Dugan (2005) has given an excellent account of the anatomy of the ligament of the nee joint and of the ACL in particular. The author states that the ACL is composed of densely organized, fibrous collagenous connective tissue that attaches the femur to the tibia. The ACL is composed of 2 groups, the anteromedial and posterolateral bands. During flexion the anterior band is taught while the posterior is loose; during extension, the posterolateral band is tight, while the anterior band is loose. The other ligaments are the PCL, medial and lateral collateral ligaments. The latter act to prevent valgus and varus movement as well as medial and lateral rotation (Dugan, 2005). The cruciate ligaments, including the ACL and posterior cruciate ligament (PCL), restrain the anteroposterior movement of the knee. The ACL prevents anterior displacement of the tibia, primarily in a flexed position, and hyperextension of the knee (Hubbell, 2006). Similarly the PCL prevents hyperflexion of the knee joint. A number of muscles around the knee joint like the quadriceps, hamstrings, gastrocnemii, and hip muscles moderate knee stability. Any instability of these muscle groups may thus be a cause of non-contact injury of the ACL (Dugan, 2005, Childs 2002)


Mechanism of Injury


The mechanisms of ACL injury are well detailed out by Hubbell (2006), Childs (2005), and Cross (1998). Hubbell points out that the ACL causes the greatest restraint to limit anterior translation of the tibia, and this action is maximum in full extension. Thus injury causing anterior translation in the hyperextended position puts a lot of strain on the ACL, promoting chances of rupture. In addtition the ACL is weaker than the PCL. The average tensile strength is 2160, which is half of the PCL(Hubbell, 2006).

ACL ruptures may either be in the form of a non contact injury  or a contact injury.  In the non contact form, the athlete complains of sharp, severe pain, during a sudden twisting movement, or a sudden deceleration movement in a situation where the foot is firmly planted down. In such a situation sharp twisting movements causes internal tibial rotation, and valgus stress on the knee. Later the patient develops a large haemarthroses in a couple of hours due to the injured ligament. In this acute situation, the knee is unable to move, and because the body is in a forward movement,to maintain the centre of gravity, the body rotates externally to balance the sharply internally rotated foot, producing great stress on the knee.  The patient feels instability in the knee, and inability to continue playing. This is the typical feature of a noncontact injury (Childs 2002, Hubbel, 2006, Dugan, 2005, Biondino, 2002)

In the contact form of injury, this is usually associated with other ligament injury. There is usually a collision, leading to a form of shearing force on the knee joint. Typically this occurs while playing soccer, when a sidekick causes a sudden medial movement at the knee with injury to the ACL, MCL, and meniscal tears (the O’Donaghue triad) (Childs, 2002).

Another factor to consider is hip weakness, more so in women. If the hip abductors and the external rotators are weak, additional strain is placed on the knee. Weak lower abdominals and poor muscular control can lead to a forward pelvic tilt, or sway-back position. This forward pelvic tilt also allows more internal rotation than happens when the pelvis is held in neutral alignment. Strengthening the body core muscles, gluteus medius, external hip rotators, lower abdominals and obliques should increase stability and help control knee internal rotation, thus reducing ACL injury risks. Strong quadriceps and hamstrings are also crucial for ACL injury prevention ( Dugan 2005, Childs, 2002, Bing 2002). It is essential that the quadriceps is strengthened so they are capable of controlling rapid knee joint decelerations. However, overtraining the quadriceps compared to hamstrings is detrimental, since the hamstrings must cooperate with the quads during knee joint decelerations to assist the stabilising role of the ACL. It has been shown that athletes with good hamstring/quadriceps strength ratios suffer fewer non-contact ACL injuries (Caraffa, 2002). Strong ankle and calf muscles also help control the knee joint decelerations and help provide more stability from the ankle. Along with good all-round leg, hip and trunk strength, the coordination of the muscular recruitment is important for knee injury prevention. Neuromuscular coordination must occur optimally for the knee joint to be safely controlled. Thus coordination drills and proprioceptive training are equally as important as muscular strength training in preventing ACL injury (Caraffa, 2002, Bing, 2002, Crosss, 1998). Teaching the correct techniques of these movements can also help prevent injury. The landing movement should involve an upright torso position, and increased knee flexion on impact should be encouraged. In addition, continuing to move after landing also helps because less deceleration is required.


Female athletes more affected



There is enough data to prove that female athletes particularly basketball players are affected much more than males (Biondino, 2006, Schultz, 2004). Schultz (2004) outlines the role of the menstrual cycle in this feature. He mentions that knee laxity changed about 3,4, and 4.5 days after changes in estradiol, progesterone and testosterone respectively in the menstrual cycle. A protective role of testosterone has bee suggested in this study. The authors were able to find significant contribution of estrogen and progesterone in reducing ligament laxity and thus making it more prone to injury, particularly in the age group of 18-25 years. Biondino (2006) makes interesting comments in his article. Apart from the role of hormonal influence, he finds a role for many other factors. He notes that the reduced femoral notch width or condyle size was associated with a greater incidence of ACL injury. He quotes the Japanese literature in saying that a smaller notch was more likely to cause ligament impingement than a larger notch. An interesting contribution of the female sports shoes has also been suggested. He feels that the shoe industry indirectly contributes to ACL injury by just miniaturizing male shoes, and not making shoes for the female foot, which differs from the male foot in having a narrow heel, and general being narrower relative to the male foot length. Thus the females’ feet need to strike the ground more often to cover the same distance, and thus face greater striking force. A final very interesting point raised is the level of muscle recruitment, proprioception, and muscle reaction time (Dugan, 2005, Biondino 2002). It is suggested by the authors that the hip muscles and the hamstrings have a slower reaction time in females, thus do not stabilize the knee early during the stress, forcing the ACL to take all the stress. In females the order of recruitment of muscles may be different. 31% of the female athletes recruited the quadriceps first whereas only 17% of the males did. In these athletes, the quadriceps contraction placed an increased strain on the anterior cruciate ligament. Thus there may be a role of endurance training, and fatique drills, muscle strengthening in injury prevention. In females, in addition there is hip anteversion, increased tibial torsion, and pronated feet, which alter patello-femoral mechanics. This lower leg malalignment may be an additional factor (Biondini, 2006). Bing etal ( 2002) highlight role of patella tendon-tibia shaft angle. The increased angle in females causes shearing force of the quadriceps and increases chances if ACL injury.




The treatment for ACL injury is primarily surgical, with the conservative measures limited for the old and less physically active individuals. The torn ACL is reconstructed using autografts from the hamstring tendons, opposite patella (Hubbell, 2006) This is followed up by extensive physiotherapy and a rehabilitation programme.




ACL  injury is a devastating feature of athletic sports. It is found more commonly in non contact injuries, like during sudden deceleration, twisting, and in contact injuries , eg, in soccer, where ACL injury may be associated with other ligament injuries. There is high morbidity, and rehabilitative process is a long drawn out one. It is much more common in females, probably due to the hormonal milieu. Effective preventive strategies need to be drawn out which focus on muscle training, particularly of the hip and the hamstrings, avoiding muscle imbalance, proprioceptive training like video session training. Prevention is certainly better than cure in this difficult situation, as surgical treatment of this injury can be long and frustrating for the athlete.




The high costs of treatment and rehabilitation that the athlete and the state have to endure underline the importance of effective preventive measures that need to be instituted in order to reduce the incidence of ACL injury. With the knowledge that effective muscle balancing exercises, resistance and endurance training and neuromuscular training may play a very large role in reduction of injury. If we first focus on the female athlete, this data gives us the most common causes of the increased injury rate in them, so an effective prevention programme can be chalked out. There needs to be research on the hormonal mileau and its effect vis-à-vis on the laxity of ACL. If research brings out that there are certain phases in the menstrual cycle in which the chances of ligament injury are more than in others, the athlete will be better equipped. It would be possible to change the training schedule accordingly at such times, or perhaps consider reduced exertion in order to prevent injury. Similarly the knowledge that hip and knee musculature also plays a role in ACL injury, would behove the university to institute a programme for more comprehensive pretraining not only during the playing season, but also during the pre-season. Particular efforts must be made to strenghthen these groups of muscles, so that this factor is eliminated. Proprioception is another mechanism that can be suitably modified. Training schedules can be introduced that allow proper neuromuscular coordination to occur. In the text it is highlighted that there is a disturbed neuromuscular coordination in female athletes. Thus a number of interventions are possible in order to reduce injury. There are two more factors worth considering. The shoe industry must step in to manufacture more ergonomic shoes according to the anatomy of the female foot. They may also play a major role. The last factor is the introduction of video session training methods. If the athlete is shown videos of particular movements which are more prone to injury, the athlete will suitably modify her techniques in order to reduce the injury pattern.

The role of physical training and neuromuscular coordination development also holds true for male athletes. The causes in males mostly relate to poor muscle development and very sharp movements that occur during non contact mode. Thus video training and physical training focusing on the hip and knee musculature will reduce the incidence of ACL injury



1                    Bing Y etal. Anterior Cruciate Ligament Injuries in Female Athletes: Anatomy, Physiology, and Motor Control.Sports. Medicine & Arthroscopy Review, Vol 10(1). March 202. 58-63

2                    Biondino.C R Anterior Cruciate Ligament Injuries in Female Athletes. Found at

3                    Caraffa A, Guiliano C, Ponteggia F. Rehabilitation Issues in Women with Anterior Cruciate Ligament Deficiency. Sports Medicine and Arthroscopy Review, Vol 10(1). March 2002. 76-82

4                    Childs SG. Pathogenesis of Anterior Cruciate Ligament Injury. Orthopedic Nursing, Vol 21 (4). July/Aug 2002. 35-40

5                    Cross, M.J. (1998). Anterior cruciate ligament injuries: treatment and rehabilitation. In: Encyclopedia of Sports Medicine and Science, T.D.Fahey (Editor). Internet Society for Sport Science: 26 Feb 1998.

6                    Dugan, Sheila A. Sports-Related Knee Injuries in Female Athletes: What Gives? American Journal of  Physical Medicine & Rehabilitation , Vol 84(2). Feb 2005. 122-130

7                    Hubbell DJ. Anterior Cruciate Ligament Injury, Mar 7, 2006. Retrieved on 2/ 12/06 from http//:www.

8                    Shultz SJ etal. Relationship between Sex Hormones and Anterior Knee Laxity across the Menstrual Cycle. The American College of Sports Medicine, Vol 36(7). July 2004. 1165-1174



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