ACL Injury Prevention

Chesapeake Orthopaedic and Sports Medicine Center

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Information for our patients and community

ACL Injury

ACL INJURY PREVENTION

Introduction:

Since the mid 1980's there has been an increasing awareness among medical professionals and coaches that Anterior Cruciate Ligament Injuries of the knee are becoming more shot_on_goal.jpg (679744 bytes) frequent particularly among female athletes. I have personally observed this in my Orthopaedic practice and have observed this as a youth soccer coach in our community. Much research has been done to try to determine the cause of ACL injuries and why women seem to be more susceptible to them. This web page is dedicated to providing you with up-to-date information about the cause and prevention of ACL injuries.

- James J. York, M.D.

What is the ACL?

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The knee is a hinge-like joint similar to a finger joint. It is designed to hinge back-and-forth but not side to side. The motion is controlled and limited by ligaments. Side support ligaments are called collateral ligaments. Knees, like finger joints have collateral ligaments to prevent side-to-side bending. The medial collateral ligament (on the inner aspect of the knee) is commonly injured but usually heals with proper care and protection. The cruciate ligaments are two ligaments in the exact center of the knee that criss-cross each other (hence the name cruciate). The cruciate ligament that goes toward the front is the anterior cruciate. The posterior cruciate prevents backward movement of the tibia (lower leg bone) on the femur (thigh bone). The anterior cruciate ligament is injured much more frequently than the posterior cruciate.

How does the injury occur?

About 75% of the time, an injury to the ACL is non-contact. It occurs from a sudden stop, twist or hyperextension and not from a collision. 85% of the time the player is aware of a "pop" or "snap" at the time of injury. The knee may feel like it "partially goes out of joint." Usually it is very painful but occasionally the injury seems minor and the athlete continues to try to play, sometimes successfully for awhile. For this reason all knee injuries even if they seem minor should be evaluated by an orthopedist.

Statistics on ACL injuries

Most injuries are sport specific rather than related to the athletes sex. However non-contact ACL injuries show a 2 - 8 fold increased incidence in female over male athletes. Among several studies the relative incidences reported are: Malone (1983) college athletics 8:1; Lindenfeld (1994) college soccer 6:1; Hosea (1996) high school soccer 6:1; Arendt (1995) college soccer and basketball 3-5:1. Approximately 100,000 ACL injuries occur in the US each year (1/3000) individuals. In the age range where ACL injuries usually occur (16 - 45), the incidence is 1/1750.

What factors contribute to increased non-contact ACL injuries in women?

Contributing factors have been broken down into Intrinsic and Extrinsic factors:

Intrinsic factors include:

Anatomic differences

	in male vs. female hip-knee-ankle alignment
	smaller intracondylar notch in women's knees (the open space in the knee available for the ACL to move)
	relatively smaller ACL size
	Women's joints tend to be relatively more lax ("double jointed") compared to men
	Laxity and relative size and anatomic alignment factors have not been proven to be a significant increased risk factor for ACL injuries in women

Female hormones

	their variation in the menstrual cycle have been studied to see if they play a role in increased risk of ACL injury
	There is no consensus in the studies that estrogen plays a direct role in contributing to ACL injuries.
	There is no evidence to support alteration of sports activity or manipulation of hormones to effect risk of ACL or other injury.

Extrinsic factors include:

	Overall muscular strength and muscular activation (which muscles get recruited and how quickly for a particular instantaneous move).
	propioception (balance sense) and neuromuscular processing and reactivity
	skill and experience:
	this is not a significant relative factor vs. men for women in high level high school and collegiate sports
	coaching - quality of coaching depends on the coaches' own training particularly as regards coaching the fundamentals of skills and moves at the younger age groups

Environmental Factors:

	shoe-surface interface - greater traction between the shoe and the playing surface improves performance but increases the risk of knee (and ankle) injury.
	Weather and field - playing surface conditions: how relatively slippery or "sticky" is the playing surface?"
	Prophylactic knee bracing has not been shown to decrease the risk of ACL injuries. After ACL reconstruction, however, ACL bracing is recommended to protect the reconstructed ACL and relatively weaker knee. The duration of recommended bracing varies.

Biomechanical Factors - ACL Injury Mechanisms

Have been further categorized into Ski injury mechanisms and "Non-Contact, Non-ski" mechanisms:

Ski injury mechanisms

	"Phantom foot" - This is caused by falling backwards with the weight on the inside edge of the downhill ski. This causes the tibia (lower leg bone) to suddenly and sharply rotate; tearing the ACL. This demonstrates the critical importance of keeping your weight downhill when skiing.
	Falling backwards and landing on the tail of the ski causing hyperflexion. If the quadriceps is contracting to try to recover from the backward fall, this combined effect can rupture the ACL.
	Valgus (exaggerated knock-knee bending type force) and rotation: The inside edge of the ski catches on something causing the leg and foot to suddenly rotate outward and causing an outward valgus (exaggerated knock-knee bending type force). This can tear the medial collateral ligament and then the ACL. Frequently the medial meniscus cartilage will tear as well. This is similar in effect to a clipping injury where an athlete is tackled sideways at the knee.

Non-contact, Non-ski mechanisms

Occurs in about 75% of ACL injuries

A study was done that reviewed a large number of films where ACL injuries occurred. Common factors associated with tearing the ACL were:

	sudden stop or landing
	100% of male basketball players were injured landing from a jump. While approximately 50% of women were injured landing from a jump and 50% following an abrupt stop while running down the court
	Center of gravity was behind the knee in 2/3 of females and all males
	ground contact in a flat foot position was noted in 2/3 females and all males
	knee slightly bent
	The leg and foot were externally (outwardly) rotating relative to the knee
	often the player was off balance
	excessive knee valgus (knee positioned in a 'knock-knee' or knee more to the midline and foot further out toward the side)

Biomechanical Factors men vs. women:

When cutting and landing, women tend to be more upright (less bent at the hip and knee) than men.

Compared with men, women tend to

	have less muscle mass
	be a few milliseconds slower at the rate of muscle force development (which can be very significant at the speed where injuries occur)
	have a stronger and quicker reacting quadriceps relative to hamstrings
	When the knee is slightly bent and trying to stop or cut, the sudden quadriceps force relative to the hamstring force can be enough to cause an ACL tear.

These sex-related differences in muscle size, composition, and strength, recruitment order and activation patterns are not well understood. More research is on-going to try to understand this better.

What can be done to help prevent injuries?

Some early studies show that specific neuromuscular training programs can enhance body control in sports and appear to reduce the risk of ACL injury compared to athletes that do not have this training. Neuromuscular training programs may also increase athletic performance.

These training programs focus on:

	Awareness of what situations may cause injury
	plyometric training
	agility exercises

A few of these preventive training programs include:

The Henning program identifies three moves that are at higher risk of causing injury and training athletes to change their technique:

Standard Maneuver	Recommended Maneuver
Plant-and-cut	Accelerated rounded turn
Straight-knee-landing	Bent-knee landing
One-step stop with knees straight	Three-step stop with knees bent

Cincinnati Sportsmetrics Program: http://www.sportsmetrics.net/

Their research indicated that plyometric jump skills added to stretching and strengthening drills can decrease peak landing forces, decrease sharp sideways bending forces at the knee, increase hamstring power. Increase strength and hamstring to quadriceps peak torque ratios.

This is a 3 phase program done three days / week beginning six to eight weeks prior to the season beginning.

	Technique phase: teach proper jump technique
	Fundamental phase: continue to build strength, power and agility
	Performance phase: focus on altering maximum vertical jump height

Santa Monica PEP Program (Prevent Injury - Enhance Performance): www.aclprevent.com

A 15 minute, 5 part program designed to be done at the beginning of practice at least 2 - 3 times a week.

	avoid vulnerable positions
	increase flexibility
	increase strength
	plyometrics
	increase propioception (balance sense) through agility training

Final note:

The research and development of training programs to prevent ACL injuries is evolving rapidly. I am currently evaluating some of these training programs to see how one or more can be best communicated to and adapted to youth and high school athletics.

- James J. York, M.D.

More information about prevention of ACL injuries from the AAOS:

Link to AAOS Patient Info

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