By John Hyland, DC, DACBR, DABCO, CSCS, CHES

Research into ruptures of the anterior cruciate ligament (ACL) is now helping us understand and treat this unfortunate and much-too-common athletic injury. As a result of the newly understood concepts, we as Chiropractors might now be able to prevent (or at least minimize) many of these injuries. From a sports injury perspective, this is the best approach—prevent the problem, rather than try to salvage the knee after the damage is done. If certain predisposing postural factors can be identified in athletes, preventive actions can be taken.

Non-Traumatic Causes

Epidemiology and frequency studies have now demonstrated that the vast majority of acute tears of the ACL occur without any contact or direct trauma to the athlete’s knee.¹ While this seems contrary to the previous common understanding of this problem, it has been found in several different studies. We now know that it is the torque, or twisting forces imposed on the knee joint that cause some ACLs to rupture. Some athletes have knee joints that seem to be more susceptible to these torque forces, and certain sports activities have been identified as particularly problematic.

Common Causes of ACL Injury

Landing at foot strike with the knee extended or in slight flexion (less than 20 degrees) and internally rotating the tibia in relation to the femur is by far the most commonly described incident which results in tearing of the ACL.² A rapid change in direction during running (or a similar twist of the leg during a fall skiing) can produce just such an episode. This is especially true in sports that use shoe spikes (which fix the lower leg to the ground). Arnold et al. found that 81% of athletes with injury to the ACL recalled the moment of injury as having their tibia in internal rotation combined with a sudden change of direction at foot strike.³

Markolf et al. used cadaver specimens to measure the forces on the ACL with various types of loading. They found that internal rotation of the tibia places a greater force on the ACL than external rotation. The greatest amount of strain occurred when the knee was hyperextended and in internal rotation. Forces were also quite high when the knee was in 10 degrees or less of flexion and internally rotated.⁴

Pre-Disposing Factors

A recent study by Beckett et al. retrospectively reviewed a group of athletes with acute, non-traumatic ACL ruptures (arthroscopically proven) and compared them to a matched control group. These researchers found excessive pronation of the foot and collapse of the arch during weight bearing in the injured subjects, and they proposed this finding as the mechanism of injury.⁵

In their study, Beckett et al. reviewed the biomechanics of the foot and ankle and described how arch collapse and excessive pronation lead to abnormal internal (medial) tibial rotation, which “pre-loads” the anterior cruciate ligament. Normally, subtalar joint pronation and internal rotation of the tibia occur only during the initial, contact phase of gait. If pronation continues beyond the contact phase, the tibia will remain internally rotated. This abnormal tibial rotation transmits excessive forces upward in the Kinetic Chain to the knee joint, producing medial knee stresses, force vector changes in the quadriceps muscle, and lateral tracking of the patella.⁶ This theory is supported by Copland’s work, which found that passive tibial rotation was statistically greater in hyperpronators than in nonpronators.⁷

Another study found that ruptures of the ACL in female athletes (many of whom are at a high risk for ACL rupture) were directly correlated with the amount of arch collapse and hyperpronation.⁸ Beckett et al. conclude that “hyperpronation of the foot and ankle complex may increase the risk of injury to the ACL.”⁵

Prevention of ACL Ruptures

Prevention is the best treatment for athletic injuries. This is particularly true when the injury is one that may lead to permanent joint instability (even with surgical repair) and could end an athlete’s career or limit a middle-aged runner’s fitness program. With our current knowledge regarding the causes and predisposing factors for ruptures of the ACL, we can now work to prevent these devastating injuries. All physically active patients and local athletes should be examined and evaluated for the existence of excessive pronation at the foot and ankle.

When you find an athlete with arch collapse and/or hyperpronation, the next step is to communicate and describe the risk factors for ACL rupture, then recommend the regular use of custom-made orthotics during all sports activities. The critical factors to look for in an orthotic for an athlete are shock absorption, support for all three arches of the foot, moisture resistance, and little added weight. In addition, the athletic orthotic must have enough flexibility to be comfortable during intense activities, and yet have sufficient stability to prevent excessive pronation and tibial rotation.

As doctors of Chiropractic, we might be able to extend the competitive careers and active lifestyles of many in our communities. When we recommend the use of custom-made functional orthotics, we could be preventing not only arch breakdown and biomechanical foot problems, but also acute ruptures of the ACL.

About the Author
A 1980 graduate of Logan College of Chiropractic, Dr. John Hyland has practiced for more than 20 years in Colorado. In addition to his specialty board certifications in Chiropractic orthopedics (DABCO) and radiology (DACBR), Dr. Hyland is nationally certified as a strength and conditioning specialist (CSCS) and a health education specialist (CHES). He now consults Chiropractors on the concepts and procedures of spinal rehabilitation and wellness exercise.

¹ McNair PJ, Marshall RN, Matheson JA. Important features associated with acute anterior cruciate ligament injury. N-Z Medical Journal 1990; 14:537-539.

² Whittington CF, Carlson CA. Anterior cruciate ligament injuries, arthroscopic reconstruction and rehabilitation. Nursing Clin North Am 1991; 26:149-158.

³ Arnold HA, et al. Natural history of the anterior cruciate ligament. Am J Sports Med 1979; 7:305-313.

⁴ Markolf KL, et al. Direct measurement of resultant forces in the anterior cruciate ligament. J Bone Joint Surgery 1990; 72:557-567.

⁵ Beckett ME, et al. Incidence of hyperpronation in the ACL injured knee: a clinical perspective. J Athl Train 1992; 27:58-62.

⁶ Tiberio D. The effect of excessive subtalar joint pronation on patellofemoral mechanics: a theoretical model. JOSPT 1987; 9:160-165.

⁷ Copland JA. Rotation motion of the knee: a comparison of normal and pronating subjects. JOSPT 1989; 10:366-369.

⁸ Ludon A. Posture and ACL injuries in women. JOSPT 1996; 15:204-209.