Jussi Hietamo: Epidemiology and Risk Factors of Acute Knee and Ankle Injury in Youth Team-sports Athletes
The first purpose of this thesis was to describe the incidence and characteristics of injuries in youth floorball (Study I). The second purpose was to investigate associations between lower extremity (LE) muscle strength, knee injury history and knee function and the risk of acute LE injuries in youth basketball and floorball athletes (Studies II–IV).
The study cohort of this thesis comprised a total of 396 (211 male and 185 female) youth basketball and floorball athletes who participated in injury and exposure registration during the seasons 2011–2014. At the preseasons, the athletes completed a baseline questionnaire and muscle strength tests. The LE muscle strength measures included one-repetition maximum (1RM) leg press, concentric quadriceps and hamstrings isokinetic strength and isometric hip abduction strength. The baseline questionnaire includes questions on knee injury history and function. Knee function was measured using the Knee Injury and Osteoarthritis Outcome Score. Unadjusted and adjusted Cox regression models were used to analyze risk factors.
The first study revealed that the total injury incidence in youth floorball athletes was 2.1 (95% confidence interval [CI] 1.7–2.4) injuries per 1,000 player-hours. Injury incidences per 1,000 player-hours during games and practices were 26.9 (95% CI 20.1–33.6) and 1.3 (95% CI 1.0–1.5), respectively. The ankle (37%) and knee (18%) were the most commonly injured body parts, and joint/ligament sprain (54%) was the most common injury type. Eighty-six percent of knee and 77% of ankle ligament injuries occurred without direct contact with the involved LE. Female athletes had significantly higher game injury (incidence rate ratio 1.9, 95% CI 1.1–3.2) and joint/ligament injury rates (incidence rate ratio 1.7, 95% CI 1.1–2.7) compared to male athletes.
The second study revealed that lower maximal hip abduction strength increased the risk of any type of acute injury in the same knee in male youth athletes (hazard ratio [HR] for 1 standard deviation [SD] decrease = 1.8, 95% CI 1.0–3.2, P = 0.04). However, receiver operating characteristics (ROC) curve analysis showed an area under the curve (AUC) of 0.66, indicating “poor” combined sensitivity and specificity of maximal hip abduction strength. None of the strength risk factors were associated with acute knee or anterior cruciate ligament injury risk in youth female athletes. Adjusted risk factor analyses for noncontact acute knee and anterior cruciate ligament injuries in male athletes were not performed due to the low number of these injuries.
In the third study, greater 1RM leg press and maximal isokinetic quadriceps strength were associated with an increase in the risk of any type of acute ankle injury in male youth athletes (HR for 1 SD increase = 1.6, 95% CI 1.1–2.4, P = 0.01, and 1.4, 95% CI 1.0–2.0, P = 0.04, respectively). In youth female athletes, greater 1RM leg press and difference between legs in maximal hip abduction strength increased the risk of noncontact acute ankle injury (HR for 1 SD increase = 1.4, 95% CI 1.0– 2.0, P = 0.03, and 1.4, 95% CI 1.0–2.0, P = 0.03, respectively). However, ROC curve analyses showed AUCs of 0.57–0.64, indicating “fail” to “poor” combined sensitivity and specificity of these risk factors.
In the fourth study, a history of previous acute knee injury increased the risk of any type of acute and noncontact acute knee injury in youth female athletes by 2.6- and 2.4-fold, respectively (HR 2.6, 95% CI 1.3–5.2, P = 0.01, and 2.4, 95% CI 1.1– 5.0, P = 0.03, respectively). However, ROC curve analysis showed an AUC of 0.61 for both injuries, indicating “poor” combined sensitivity and specificity of previous acute knee injury. None of the scores for the Knee Injury and Osteoarthritis Outcome Score subscales were associated with acute knee injury risk in youth female athletes. Adjusted risk factor analyses for acute knee injuries in male athletes were not performed due to the low number of these injuries.
Based on the findings of this thesis, first, injury prevention efforts in youth basketball and floorball athletes should be focused on acute ankle and knee injuries.
Second, hip abductor strengthening exercises can be recommended for male youth athletes. In youth female athletes, it is important to maintain good hip abductor strength balance between the LEs. Greater LE extension strength measured by 1RM leg press increases the risk of acute ankle injury in both male and female youth athletes. Strong athletes are probably able to run and change direction faster than less strong athletes, and this may increase the mechanical forces directed to LEs. In addition, treatment and rehabilitation of the present knee injury and the secondary prevention of reinjury should be emphasized in youth pivoting sports athletes.
Finally, none of the studied risk factors can be used alone as screening tools for an acute knee or ankle injury in these athletes. Correspondingly, more studies are needed on other risk factors and their combinations to allow better prediction of future LE injuries. This would facilitate effectively targeting preventive measures and programs.
The doctoral dissertation of M.D. Jussi Hietamo in the field of Sports Medicine and Orthopaedics titled Epidemiology and Risk Factors of Acute Knee and Ankle Injury in Youth Team-sports Athletes will be publicly examined at the Faculty of Medicine and Health Technology of Tampere University at 12 o'clock on Friday 29 October, 2021. The venue is Arvo building auditorium F114, address: Arvo Ylpön katu 34. Professor Taija Finni from University of Jyväskylä will be the opponent while Professor Ville Mattila will act as the custos.
The dissertation is available online at