Why do females have higher ACL injury rates than males in ball/team sports, but not in WC skiing?
Tron Krosshaug, PhD Oslo Sports Trauma Research Center, Norwegian School of Sports Sciences, Oslo, NORWAY
OSTRC focus areas
Team handball ACL injury
Severity
Out of play Pain Disability Quality of life Costs Future OA
Injury frequency females vs males ♀
♂
Soccer: 0.32/0.12
Injury frequency females vs males ♀
♂
Soccer: 0.32/0.12 Handball: 1.48/0.25
Injury frequency females vs males ♀
♂
Soccer: 0.32/0.12 Handball: 1.48/0.25 Basket: 0.28/0.08
Females vs males
4:1
Alpine skiing ACL injury
Females vs males - recreation
2:1
WC alpine diciplines (FIS ISS) Injuries/100 athletes Female Male 13.8 13.8
Alpine
Knee
5.4 15.4
5.6
Freestyle
ACL Knee
ACL Snowboard Knee ACL Telemark Knee ACL
7.8 8.3 4.0 10.9 2.2
4.2 7.3 2.3 3.7 1.7
Injuries/1000 runs Female Male 3.3 4.2 1.2
NB! n= 28 NB! n=9
1.8
Why the discrepancy in sex difference in injury risk??
Risk factors for injury
Injury mechanisms
(distant from outcome)
(proximal to outcome)
Internal risk factors: • Age (maturation, aging) • Gender • Body composition (e.g. body weight, fat mass, BMD, anthropometry) • Health (e.g. history of previous injury, joint instability) • Physical fitness (e.g. muscle strength/power, maximal O2 uptake, joint ROM) • Anatomy (e.g. alignment, intercondylar notch width) • Skill level (e.g. sportspecific technique, postural stability)
Predisposed athlete
Susceptible athlete
Exposure to external risk factors:
INJURY
Inciting event:
• Human factors (e.g. team mates, opponents, referee) • Protective equipment (e.g. helmet, shin guards) • Sports equipment (e.g. skis) • Environment (e.g. weather, snow & ice conditions, floor & turf type, maintenance) Meeuwisse WH: Clin J Sports Med 4: 166-170, 1994
ACL risk factors (ball/team sports) Solid evidence Gender Game vs. training
ACL risk factors (ball/team sports) Some evidence
Surface Footwear Weather conditions Previous injury Muscle strength BMI Familial tendency Race Leg length
Ligament crosssectional area Ligament material properties Knee/notch geometry General joint laxity Foot pronation Phase of menstrual cycle Valgus motion & Valgus moment during landing
ACL risk factors (ball/team sports) Little or no evidence
Age Patella tendon – tibia shaft angle (PTTSA) Knee flexion during landing Anterior knee laxity
Leg dominance during landing Quadriceps dominance Muscle stiffness Muscle reaction time Time to peak force Fatigue
Skiing vs non-skiing
Still limited knowledge, BUT likely a combination of several factors
Muscle strength Ligament strength Joint geometry Joint laxity
Comparison males vs females to explain the 4:1 difference Why will such differences not give different injury rate between males and females in skiing??
Are female skiers «more similar to men» compared with females in ball/team sports?? Risk behaviour?
Skiing vs non-skiing
Comparison males vs females to explain the 4:1 difference Still limited knowledge, BUT likely a combination of several factors
Ski vs non-skiinng injury mechanism!
Muscle strength Ligament strength Joint geometry Joint laxity
Why will such differences not give different injury rate between males and females in skiing??
Are female skiers «more similar to men» compared with females in ball/team sports?? Risk behaviour?
Injury mechanism in ball/team sports??
Plant and cut
One legged landing
A new method for analyzing human movement from video
Matching a model to the background video sequence gives an estimate of the actual 3D body kinematics
Krosshaug & Bahr, J Biomech 2005
A new method for analyzing human movement from video
Matching a model to the background video sequence gives an estimate of the actual 3D body kinematics
Krosshaug & Bahr, J Biomech 2005
ACL injury analysis
Krosshaug et al., SJMSS 2007
Kinematics Impact
33 ms
Hip flexion
19o
20o
Knee flexion
11o
31o
Knee Valgus
2o
15o
Approach velocity: 3.9 m/s
Kinematics
Impact
33 ms
Hip flexion
41o
45o
Knee flexion
26o
40o
Knee Valgus
2o
13o
Horizontal velocity: 2.1 m/s Vertical velocity: 2.2 m/s
Kinematics
Impact
33 ms
Hip flexion
58o
51o
Knee flexion
33o
40o
Knee Valgus
5o
15o
Horizontal velocity: 3.1 m/s Vertical velocity: 1.7 m/s
Knee kinematics Valgus
Sudden valgus increase reached 12o in 40 ms after IC Internal rotation abruptly increased by 8o in 40 ms after IC
IR
Koga et al. AJSM 2010
New hypothesis for the ACL injury mechanism
(a, b) Valgus loading (c) ACL rupture through anterior tibial translation and internal tibial rotation (d) After the injury, external tibial rotation
Koga et al. AJSM 2010
FIS Injury Surveillance System
Matched video
Tibial translation
ACL injury mechanisms in alpine skiing?
Six mechanisms identified
Slip-catch (n=10)
ER/deep flexion (n=1)
Dynamic snowplow (n=3)
ER/valgus (n=1) Landing back-weighted (n=4)
Hyperextension (n=1)
Bere et al. AJSM 2011
Slip-catch (n=10)
Characteristics:
Turning, out of balance inwards/backwards Loses pressure on outer ski, which drifts away Tries to regain grip, knee extends The outer ski catches the inside edge abruptly
Result:
Sudden valgus & internal rotation loading, outer ski
Bere et al. AJSM 2011
Injury analysis – slalom (right knee)
Knee kinematics
IR
Valgus
Injury analysis – downhill (left knee)
IR Valgus
What is then the difference between noncontact and skiing ACL injury mechanism??
Skiing vs non-skiing ACL Injury Mechanism
Both involve valgus + internal tibial rotation Lower compression forces in (recreational) skiing injuries (Speer et al. AJSM 1995)
BUT – higher rotational forces!
Self steering effect of carved ski Pressure on the inside of the rear tail -> large moment arm
Ettlinger et al. 1995
Possible reason for the difference between skiing and non-skiing ACL injury frequency
Males have significantly higher risk for injuries in general -> more often in slip-catch situations? Loads may be too high to resist
Possible reason for the difference between skiing and non-skiing ACL injury frequency
Males have significantly higher risk for injuries in general -> more often in slip-catch situations? Loads may be too high to resist
More research to be done!
The Oslo Sports Trauma Research Center has been established at the Norwegian School of Sport Sciences through generous grants from the Royal Norwegian Ministry of Culture, the South-Eastern Norway Regional Health Authority, the International Olympic Committee, the Norwegian Olympic Committee & Confederation of Sport, and Norsk Tipping AS
