ACL Injury: What are the Risk Factors?

Kenneth G. Swan, Jr., M.D.

June 2, 2015

• I have no disclosures

www.UOANJ.com

• ACL injuries (ACLIs) are 3-6x more common in females than males……But there’s more to it than that.

• What does the Evidence say about ACL injury Risk Factors?

www.UOANJ.com

ACL Injury Risk Factors?

• Non-modifiable – Genetics – Female Gender – Notch width – Posterior tibial slope – ACL size – Ligamentous laxity

• Modifiable – High BMI – Jump landing mechanics – Hormonal – Playing surface

www.UOANJ.com

Non-modifiable Risk Factors

www.UOANJ.com

ACLI and Genetics

• Many anecdotal reports of ACL injuries running in families

• Two case-control studies support this theory

– Harner, AJSM 1994; Flynn, AJSM 2005

• However, overall Evidence is poor, level III at best

• Genetic studies exist, but few

• Cannot make definitive conclusions or practice recommendations….yet

www.UOANJ.com

Does the size of the intercondylar notch effect the risk of ACLI?

www.UOANJ.com

ACL Injury Risk Factors: Intercondylar Notch Width

• Notch Width Index (NWI) = width of intercondylar notch/width of distal femur at level of popliteal groove – as seen on tunnel view radiographs

Souryal, AJSM, 1988

www.UOANJ.com

Notch Width

• Several* prospective level II evidence cohort studies have shown:

a) Females have smaller NWIs than males

b) Male and female athletes with ACLIs have significantly more notch stenosis than athletes without ACLIs

*Souryal, AJSM, 1993; LaPrade, AJSM, 1994; Uhorchak, AJSM, 2003

++ Zeng, Knee Surg Sports Traumatol Arthrosc, 2013 Meta-analysis (III)

www.UOANJ.com

Does the geometry of the tibial slope play a role in ACLI?

www.UOANJ.com

Bony geometry of tibial plateau and ACLI

• Both the concavity depth of the medial plateau and the degree of posterior-inferior tibial slope have been studied

• Studies suggest that increased posterior tibial slope places athletes at higher risk for non-contact ACLIs

www.UOANJ.com

Posterior Tibial Slope: What’s the Evidence?

• Best evidence implicating increased posterior tibial slope as a risk factor for ACLIs is LEVEL III

• Radiograph-based, case control studies

• A recent Level III study suggests it is a combination of increased posterior slope and tight intercondylar notch that places female athletes at risk*

– Stijak, Knee Surg Sports Traumatol Arthrosc 2008; Simon, J Biomech 2010; Todd, AJSM 2010; Hashemi, AJSM 2010

– *Sturnick, AJSM 2015

www.UOANJ.com

ACL size: Does size matter?

• Females suffer higher rates of ACL injuries than men • ACL in females is smaller than male counterparts

– Chandrashekar, AJSM 2005

• Smaller ACL (MRI) found in c/l knee of ACLI patients vs controls – Chaudhari, AJSM 2009

• Smaller ACL (U/S) diameter is a predictor of ACL injury – Mahajan, BioMed Research Int’l 2015

• Evidence: poor, few studies, two Level III

www.UOANJ.com

Ligamentous Laxity

• Is generalized or focal pre-injury laxity a risk factor for ACLI?

www.UOANJ.com

Ligamentous Laxity

• Generalized ligamentous laxity, as measured by 5th MCP hyperextension, thumb-to-forearm test, and elbow hyperextension has been suggested as a RF for ACL tear.

• Healthy females have greater ligamentous laxity about the knee and ankle compared to males (Beynnon, AJSM 2005 Level II)

• Knee laxity alone (passive hyperextension or via KT-1000) or as part of systemic laxity, has also been associated with ACLI in several studies

www.UOANJ.com

Ligamentous Laxity and ACLI: What’s the Evidence?

• Level of Evidence II • Uhorchak, AJSM, 2003

– Prospective cohort of 859 West Point cadets followed over 4 years

– Male RFs: small notch and generalized laxity – Female RFs: small notch, generalized laxity, and high BMI

and KT-2000

• Vauhnik, KSSTA 2008 – Prospective cohort of Slovenian female athletes – Passive knee hyperextension and anterior laxity

preseason a significant RF for ACL injury

www.UOANJ.com

Non-modifiable Risk Factors

• Genetics/Family history

• Female Gender

• Small Notch size

• Increased posterior tibial slope

• Small ACL size

• Ligamentous laxity

www.UOANJ.com

Non-modifiable Risk Factors

• Genetics/Family history

• Female Gender

• Small Notch size

• Increased posterior tibial slope

• Small ACL size

• Ligamentous laxity

www.UOANJ.com

ACL Injury: Modifiable Risk Factors

www.UOANJ.com

Does BMI play a role in ACLI?

• Higher than avg. BMI found to significantly increase risk of ACL injury in female (but not male) military cadets

– Uhorchak, AJSM 2003

– Single study, level II

www.UOANJ.com

Neuromuscular Control

• Several studies have implicated female jump landing and pivoting techniques as different than males and a risk factor for ACL injury

• Basis for several successful ACL prevention programs – PEP, SportsMetrics

• Hewett, AJSM 1999, 2005 – Prospective cohort studies, level II – Adolescent females who participated in a pre-season

plyometrics program had lower rates of ACL injuries – Adolescent female basketball players who jump land with

increased knee abduction (valgus knee) had higher rate of ACL injuries

www.UOANJ.com

At Risk Jump-Landing technique

www.UOANJ.com

Jump Landing Technique

www.UOANJ.com

www.UOANJ.com

Do hormonal factors play a role in ACLI?

• Higher incidence of ACLI in females

– this difference is not seen until ~puberty

• Ligamentous laxity

• Relaxin

• Hormone receptors found on ACL

• Highest incidence of ALCI during follicular, pre-ovulatory phase?

• What about oral contraceptives?

www.UOANJ.com

Ovarian Cycle

www.UOANJ.com

Hormones and ACLI: The Evidence

• Very little evidence

• Conflicting data from level III and IV studies

• OCPs have not been proven to have a protective or deleterious effect on the ACL…..

www.UOANJ.com

Extrinsic Risk Factors

• Cleat type – Higher torsion, higher risk

• Weather conditions – Hot, dry worse than moist

• Field surface – Bermuda grass>> Rye grass

– FieldTurf >> Grass • Hershman, AJSM 2009

• 67% higher risk of ACL injury on FieldTurf!

www.UOANJ.com

Extrinsic Factors: What’s the Evidence

• Too few studies to make conclusions regarding cleat type, field condition and turf type

www.UOANJ.com

Summary: What does the evidence say about ACL injury risk factors?

www.UOANJ.com

ACL Injury Risk Factors?

• Modifiable – High BMI – Jump landing mechanics – Hormonal? – Playing surface?

• Non-modifiable – Female Gender – Genetics? – Notch width – ACL size? – Tibial slope? – Ligamentous laxity

www.UOANJ.com

• “Screeing programs designed to identify those athletes who will best benefit from ACL prevention programs are desirable”

• “Those [female] athletes with a prior ACL injury, poor jump landing mechanics, ligamentous laxity, and perhaps a family history are good candidates for such a program”

• “Identifying those with anatomic risk factors (small ACL and tight intercondylar notch) may be in our future”

www.UOANJ.com

• “Screeing programs designed to identify those athletes who will best benefit from ACL prevention programs are desirable”

• RECOMMENDATION: “Those [female] athletes with a prior ACL injury, poor jump landing mechanics, ligamentous laxity, and perhaps a family history are good candidates for such a program”

• “Identifying those with anatomic risk factors (small ACL and tight intercondylar notch) may be in our future”

www.UOANJ.com

Evidence Based References

• (Level II or higher)

www.UOANJ.com

Modifiable Risk Factors

• Hewett TE, Lindenfeld TN, Riccobene JV, et al. The effect of neuromuscular training on the incidence of knee injury in female athletes: A prospective study. Am J Sports Med 1999;27(6):699-705

• Hewett TE, Myer GD, Ford KR et al. Biomechanical measures of neuromuscular control of valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes: A prospective study. Am J Sports Med 2005;33(4):492-501

www.UOANJ.com

Non-modifiable risk factors

• LaPrade RF, Burnett QM. Femoral intercondylar notch stenosis and correlation to anterior cruciate ligament injuries. Am J Sports Med 1994;22:198-203

• Souryal TO, Freeman TR. Intercondylar notch size and anterior cruciate ligament injuries in athletes. Am J Sports Med 1993;21:535-539

• Uhorchak JM, Scoville CR, Williams GN et al. Risk factors associated with noncontact injury of the anterior cruciate ligament: a prospective four-year evaluation of 859 West Point cadets. Am J Sports Med 2003;31:832-842

• Vahunik R, Morrissey MC, Rutherford OM, et al. Knee anterior laxity: A risk factor for traumatic knee injury among sportswomen? Knee Surg Sports Traumatol Arthrosc 2010;19(3):372-377

www.UOANJ.com

THANK YOU

www.UOANJ.com