Injuries to the lower extremity are common in sports requiring rapid acceleration and deceleration of the body. Injuries to the anterior cruciate ligament (ACL) are one of the most common injuries to the lower extremity; many of them being of the non-contact variety. It has been reported that female athletes have approximately twice the likelihood of this type of injury as compared to males. Several mechanisms have been reported as increasing the incidence of non-contact ACL injuries including:

Increased Q-angle (quadriceps angle) especially in female athletes leading to increased internal rotation and valgus forces through the knee
Increased ligament laxity in the ACL, medial collateral ligament of the knee and other lower extremity ligaments (especially during the menstrual cycle in female athletes)
Poor eccentric control of pronation and ground reaction forces in both male and female athletes

While there has been much written about the aforementioned causes, there are several less known albeit more important causes of ACL injuries. These include poor motor control of the core, hip and/or ankle secondary to previous ankle injuries and improper footwear including the over-use of orthotic support. The first part of this article will describe these mechanisms of injury while the second part will propose a corrective exercise strategy focusing on improving the stability of the entire lower extremity.

MOTOR CONTROL

It is necessary to have a basic concept of how the body produces and controls movement in order to understand why injuries occur. This concept, referred to as motor or neuromuscular control, can be simply thought of as the right amount of joint control, at the right time, while imposing the lowest compressive forces on the joint structures. To illustrate this concept, stand up and squeeze the gluteals tightly. This is an example of how trainers commonly teach clients to improve functional control of the hip. While this is one approach, there is an inherent problem with this approach. First: this approach will compress the head of the femur anteriorly into the socket and disrupts the optimal axes of hip rotation. Therefore, when the gluteals are asked to decelerate pronation of the hip and knee (flexion, adduction and internal rotation) they are unable to generate the adequate forces and proper biomechanical leverage required to control this motion. The other issue with over-activation of the gluteals is that the gluteus maximus is a powerful external rotator of the hip. One of the functions of pronation is to get the big toe in contact with the ground. If the gluteus maximus is over-activated, there is difficulty getting the big toe onto the ground. Therefore the neuromuscular response is to increase internal rotation at the knee and/or drop the medial aspect of the foot towards the ground (eversion). As a result of these biomechanical compensations, the trainer or coach is likely to observe the following compensations during the functional movement screen of the athlete;

Increased pronation of the knee and ankle/foot complex (knee flexion, adduction and internal rotation and ankle dorsiflexion, eversion and foot abduction) during squat and lunge patterns
Instability during multi-planar lunges and other functional movement patterns
Increased knee valgus movements during jumping, bounding and similar plyometrics drills

What’s so alarming about these aforementioned compensatory patterns is that these are the most common movement patterns that lead to ACL injuries. What makes the above patterns even worse, are athletes that use orthotics and/or other supportive type shoes that are not appropriate for their individual foot. It is common to see athletes put into an orthotic or supportive shoe by some well meaning podiatrist or chiropractor (or worse yet, a weekend employee at a running store) and told that this will correct their foot and lower extremity issues.

Orthotics too often cover up or hide the biomechanical and neuromuscular weaknesses and merely stress out another area of the body which often will not present itself until several weeks or months later. Many running shoes will do this as well as most are designed to control pronation through the break in the lateral aspect of the heel and increased support through the medial aspect of the shoe (longitudinal arch). There are as many athletes that supinate and therefore have trouble getting the big toe down on the ground as there are pronators. The coach or trainer has to be aware of this before making general shoe recommendations for the athlete.

Side note: The other important component of pronation is the spreading of the metatarsals (long bones of the foot that connect to the toes) to contact the ground. It is the spreading of the metatarsals that reflexively activates the posterior (extensor) chain. While many authors discuss the importance of the extensor chain, most fail to mention this vitally important connection to the foot. Without proper foot function, there is no way the extensor chain can function optimally or efficiently.

RESEARCH

There has been much written about the causes and prevention of ACL injuries in the last few years. While it is not necessary to understand all the nuances of the research, several key components have been identified that will help set the stage for training and conditioning program that will follow.

Ankle injuries: Injuries to the ankle, particularly inversion ankle sprains, have been shown to inhibit and delay the activation of the gluteus medius. Remember that the gluteus medius is a key stabilizer in the frontal plane. Additionally, researchers noted changes in decelerating ground reaction forces in individuals that have had prior ankle injuries. This again stresses the important linking between the foot and the hip.
Poor landing mechanics: Research has also shown that female athletes demonstrate greater internal rotation forces, decreased hip flexion and increased stiffness in their knees during landing that their male counterparts. Therefore, proper landing mechanics should be addressed during the conditioning program.
Decreased gluteal activity and increased quadriceps activity: This phenomenon likely results from the lack of hip flexion noted above requiring the quadriceps via the knee to increase in activity to decelerate the forward knee translation. Again, this should be corrected through proper motor education in the conditioning program.

CONDITIONING PROGRAM

While an entire book could be devoted to the development and implementation of an optimal training program, the following section will discuss the primary components that are required to insure an effective injury prevention and conditioning program.

There are many varying strategies and schools of philosophy in the rehabilitation, treatment and exercise strategies for ACL injuries. Listed below are some of the general concepts that must be included in an effective program.

1. Ensure proper activation and motor control while addressing appropriate verbal instructions of both the core and lower extremity mechanics. Proper verbal instructions has been shown to improve activation of the local system of the lumbo-pelvic-hip complex. Verbal cueing such as increasing knee and hip flexion during landing has demonstrated improvements in the landing mechanics of female athletes and subsequent anterior shear forces on the knee.

2. Teach proper deceleration techniques. There should be a large amount of time dedicated to teaching the proper mechanics of squatting and multi-planar lunging and how these movements relate to deceleration mechanics.

3. Follow the proper progressions. See the following examples.

Uniplanar prior to multiplanar movements
- Ex. Bodyweight squats to single leg bodyweight squats with a transverse reach
Stable surfaces prior to labile surfaces
- Ex. Squats on the floor to squats on balance board
Stationary movements prior to dynamic movements
- Ex. Squats to squat jumps

The program that will follow in part II is an example of these principles and is extremely effective for lower extremity and knee conditioning. However, please note that this program is not designed to correct muscle inhibition or compensatory patterns. It is assuming that proper strength, stability, mechanics as well as motor control have been addressed prior to instituting this program. This program will emphasize the gluteals although this does not suggest it is the only important muscle group that needs to be addressed. (Please see the last article on preventing hamstring injuries for general concepts of gluteal activation.) The remainder of this article will focus on squat mechanics while the next article will outline the remainder of the program.

SQUAT

The squat is perhaps the most important movement pattern that must be mastered when designing an ACL conditioning program. Unfortunately, the squat has been poorly taught by many strength and conditioning professionals and has led to countless injuries to the knee and low back. Listed below are some of the common mistakes made by athletes.

1. Squatting too deeply. The athlete must squat within their hip range of motion not how deep they can go. Most athletes squat far too deep and beyond their available hip range of motion. This leads to hypermobility of the lumbar spine which often inhibits the gluteals and increases over-activation of the hip external rotators.

2. Over-activation or squeezing of the gluteals at the end top of the squat. Most coaches train their athletes to squeeze the gluteals at the top of the squat, lunge, kettlebell swing and other similar movement pattern. As mentioned above, this drives the head of the femur anteriorly in the socket and disrupts the normal biomechanical placement of the hip joint and muscle recruitment patterns while increasing stress on the low back.

3. Knees too wide apart. Many trainers and coaches correctly recognize that the valgus knee position is stressful to the knee ligaments and is a common cause of ACL injury. However, some of the cueing mechanisms such as pushing the knees out against a theraband or rubber tubing as well as rolling onto the outside of the foot inhibit the normal mechanics of the foot (as noted in previous section).

The description below will describe the mechanics for using the squat pattern to increase optimal function of the lower extremity. These criteria will then set the basis for our entire lower extremity movement patterns as many of the concepts will carry over.

(Please note: The author is not suggesting this is the only squatting style and that all others are ineffective. To the contrary there are many incredibly strong and efficient athletes that owe a lot of their success to the effectiveness of their squatting routine. He is suggesting that it is common for athletes to perform squats in a manner that hinder rather than improves their performance.)

Squat Evaluation (Anterior View)

Begin with feet approximately shoulder width or slightly wider apart.
Hands are held in front of body.
The head, trunk and pelvis should be in neutral position to begin and remain relatively stationary throughout the motion.
Head and eyes should remain level with the horizon- do not look up as this encourages thoraco-lumbar extension.
Core activation should be maintained throughout the motion.
Trunk and pelvis should fall equidistant between feet.
The knees should track in the same plane as feet (knees should track approximately between digits 1-3 of the foot).
The knees should not deviate medially (adduction) or laterally (abduction) at any point throughout the motion.
The tibia (lower leg) and feet should remain neutral throughout the movement.
Maintain a 3-point contact with the foot on the ground- heel, big toe and small toe.
Squat within the available hip range of motion. The depth of the squat should stop just prior to the flexion of the low back (lower lumbar spine flexion).

CONCLUSION

This article has outlined some common mechanisms and discussed a prevention as well as training strategy for preventing ACL injuries. Part II will go into more of the specific exercises and programs to help develop a strong, stable and functional lower extremity. Adhere to the fundamentals of human movement and keep the strategy and training program simple. Persistence and consistency will enhance the effectiveness of this program.

REFERENCES:

Biondino, CR. Anterior Cruciate Ligament Injuries in Female Athletes. http://www.arthroscopy.com.

Osar Evan. Complete Hip and Lower Extremity Conditioning

Watson A, Haddad F. ACL- female anterior cruciate ligament injuries review. http://www.sportsinjurybulletin.com

References as presented at PubMed- www.ncbi.nlm.nih.gov

Caulfield B, Garrett M. Changes in ground reaction force during jump landing in subjects with functional instability of the ankle joint. Clin Biomech (Bristol Avon). 2004 Jul;19(6):617-21.

Cowling EJ, Steele JR. The effect of upper-limb motion on lower-limb muscle synchrony. Implications for anterior cruciate ligament injury. J Bone Joint Surgery Am. 2001 Jan;83-A(1):35-41.

Cowling EJ, Steele JR, McNair PJ. Effect of verbal instructions on muscle activity and risk of injury to the anterior cruciate ligament during landing. Br J Sports Med. 2003 Apr;37(2):126-30.

Cowling EJ, Steele JR. Is lower limb muscle synchrony during landing affected by gender? Implications for variations in ACL injury rates. J Electromyogr Kinesiol. 2001 Aug;11(4):263-8.

Croce RV, Russell PJ, Swartz EE, Decoster LC. Knee muscular response strategies differ by developmental level but not gender during jump landing. Electromyogr Clin Neurophysiol. 2004 Sep;44(6):339-48.

Fagenbaum R, Darling WG. Jump landing strategies in male and female college athletes and the implications of such strategies for anterior cruciate ligament injury. Am J Sports Med. 2003 Mar- Apr;31(2):233-40.

Lephart SM, Ferris CM, Riemann BL, Myers JB, Fu FH. Gender differences in strength and lower extremity kinematics during landing. Clin Orthop Relat Res. 2002 Aug;(401):162-9.

Moeller J, Lamb MM. Anterior Cruciate Ligament Injuries in Female Athletes: Why Are Women More Susceptible? The Physician and Sports Medicine – Vol. 25, No. 4, April 1997.

Salci Y, Kentel BB, Heycan C, Akin S, Korkusuz F. Comparison of landing maneuvers between male and female college volleyball players. Clin Biomech (Bristol, Avon). 2004 Jul;19(6):622-8.

Shultz SJ, Carcia CR, Perrin DH. Knee joint laxity affects muscle activation patterns in the healthy knee. J Electromyogr Kinesiol. 2004 Aug;14(4):475-83.

Swartz EE, Decoster LC, Russell PJ, Croce RV. Effects of Developmental Stage and Sex on Lower Extremity Kinematics and Vertical Ground Reaction Forces During Landing. J Athl Train. 2005 Mar;40(1):9-14.

Zanulak BT, Ponce PL, Straub SJ, Medvecky MJ, Avedisian L, Hewett TE. Gender comparison of hip muscle activity during single-leg landing. J Orthop Sports Phys Ther. 2005 May;35(5):292-9.

About The Author:

Dr. Evan Osar received his bachelor in science and degree in chiropractic from the Palmer College of Chiropractic. He has also received a diploma in clinical massage therapy from the Soma Institute for Clinical Massage Therapy and national certifications from the National Academy of Sports Medicine and the National Strength and Conditioning Association. He holds a faculty position at the Soma Institute for Clinical Massage Therapy where he teaches Kinesiology and Clinical Integration, and has authored a manual on functional anatomy and training.

To learn more about Dr. Osar or to contact him go to his website: www.osarconsulting.com

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