ACL Injury: What are the Risk Factors? Kenneth G. Swan, Jr., M.D. June 2, 2015
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ACL Injury: What are the Risk Factors?
Kenneth G. Swan, Jr., M.D.
June 2, 2015
• I have no disclosures
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• 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?
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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
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Non-modifiable Risk Factors
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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
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Does the size of the intercondylar notch effect the risk of ACLI?
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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
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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)
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Does the geometry of the tibial slope play a role in ACLI?
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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
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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
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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
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Ligamentous Laxity
• Is generalized or focal pre-injury laxity a risk factor for ACLI?
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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
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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
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Non-modifiable Risk Factors
• Genetics/Family history
• Female Gender
• Small Notch size
• Increased posterior tibial slope
• Small ACL size
• Ligamentous laxity
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Non-modifiable Risk Factors
• Genetics/Family history
• Female Gender
• Small Notch size
• Increased posterior tibial slope
• Small ACL size
• Ligamentous laxity
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ACL Injury: Modifiable Risk Factors
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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
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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
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At Risk Jump-Landing technique
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Jump Landing Technique
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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?
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Ovarian Cycle
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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…..
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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!
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Extrinsic Factors: What’s the Evidence
• Too few studies to make conclusions regarding cleat type, field condition and turf type
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Summary: What does the evidence say about ACL injury risk factors?
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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
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• “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”
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• “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”
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Evidence Based References
• (Level II or higher)
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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
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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
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THANK YOU
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