Agnethe Nilstad

Risk Factors for Lower Extremity Injuries in Elite Female Soccer Players

Background: The incidence of lower extremity injuries in female soccer players is high, but the risk factors for injuries are unknown. Purpose: To investigate risk factors for lower extremity injuries in elite female soccer players. Study Design: Cohort study; Level of evidence, 3. Methods: Players in the Norwegian elite female soccer league (N = 12 teams) participated in baseline screening tests before the 2009 competitive soccer season. The screening included tests assessing maximal lower extremity strength, dynamic balance, knee valgus angles in a drop-jump landing, knee joint laxity, generalized joint laxity, and foot pronation. Also included was a questionnaire to collect information on demographic data, elite-level experience, and injury history. Time-loss injuries and exposure in training and matches were recorded prospectively in the subsequent soccer season using weekly text messaging. Players reporting an injury were contacted to collect data regarding injury circumstances. Univariate and multivariate regression analyses were used to calculate odds ratios (ORs) and 95% confidence intervals (CIs) for ±1 standard deviation of change. Results: In total, 173 players underwent complete screening tests and registration of injuries and exposure throughout the season. A total of 171 injuries in 107 players (62%) were recorded; ligament and muscle injuries were the most frequent. Multivariate analyses showed that a greater body mass index (BMI) (OR, 1.51; 95% CI, 1.21-1.90; P = .001) was the only factor significantly associated with new lower extremity injuries. A greater BMI was associated with new thigh injuries (OR, 1.51; 95% CI, 1.08-2.11; P = .01), a lower knee valgus angle in a drop-jump landing was associated with new ankle injuries (OR, 0.64; 95% CI, 0.41-1.00; P = .04), and a previous knee injury was associated with new lower leg and foot injuries (OR, 3.57; 95% CI, 1.27-9.99; P = .02), whereas none of the factors investigated influenced the risk of new knee injuries. Conclusion: A greater BMI was associated with lower extremity injuries in elite female soccer players. Clinical Relevance: Increased knowledge on risk factors for lower extremity injuries enables more targeted prevention strategies with the aim of reducing injury rates in female soccer players.

The vertical drop jump Is a poor screening test for ACL injuries in female elite soccer and handball players: a prospective cohort study of 710 athletes

Background: The evidence linking knee kinematics and kinetics during a vertical drop jump (VDJ) to anterior cruciate ligament (ACL) injury risk is restricted to a single small sample. Still, the VDJ test continues to be advocated for clinical screening purposes. Purpose: To test whether 5 selected kinematic and kinetic variables were associated with future ACL injuries in a large cohort of Norwegian female elite soccer and handball players. Furthermore, we wanted to assess whether the VDJ test can be recommended as a screening test to identify players with increased risk. Study Design: Cohort study; Level of evidence, 2. Methods: Elite female soccer and handball players participated in preseason screening tests from 2007 through 2014. The tests included marker-based 3-dimensional motion analysis of a drop-jump landing. We followed a predefined statistical protocol in which we included the following candidate risk factors in 5 separate logistic regression analyses, with new ACL injury as the outcome: (1) knee valgus angle at initial contact, (2) peak knee abduction moment, (3) peak knee flexion angle, (4) peak vertical ground-reaction force, and (5) medial knee displacement. Results: A total of 782 players were tested (age, 21 ± 4 years; height, 170 ± 7 cm; body mass, 67 ± 8 kg), of which 710 were included in the analyses. We registered 42 new noncontact ACL injuries, including 12 in previously ACL-injured players. Previous ACL injury (relative risk, 3.8; 95% CI, 2.1-7.1) and medial knee displacement (odds ratio, 1.40; 95% CI, 1.12-1.74 per 1-SD change) were associated with increased risk for injury. However, among the 643 players without previous injury, we found no association with medial knee displacement. A receiver operating characteristic curve analysis of medial knee displacement showed an area under the curve of 0.6, indicating a poor-to-failed combined sensitivity and specificity of the test, even when including previously injured players. Conclusion: Of the 5 risk factors considered, medial knee displacement was the only factor associated with increased risk for ACL. However, receiver operating characteristic curve analysis indicated a poor combined sensitivity and specificity when medial knee displacement was used as a screening test for predicting ACL injury. For players with no previous injury, none of the VDJ variables were associated with increased injury risk. Clinical Relevance: VDJ tests cannot predict ACL injuries in female elite soccer and handball players.

Physiotherapists Can Identify Female Football Players With High Knee Valgus Angles During Vertical Drop Jumps Using Real-Time Observational Screening

STUDY DESIGN Clinical measurement, controlled laboratory study. OBJECTIVES To assess the relationships among real-time observational screening of frontal plane knee control and knee valgus angles and abduction moments calculated from 3-D motion analysis during a vertical drop jump. A secondary purpose was to investigate interrater agreement for 3 independent physiotherapists. BACKGROUND Current approaches to screen for anterior cruciate ligament injury risk are based on complex biomechanical analyses or 2-dimensional video reviews. There is a need for simple and efficient, low-cost screening methods. METHODS Sixty Norwegian elite female football (soccer) players performed a vertical drop-jump task. Using real-time observational screening, 3 physiotherapists independently scored each participants frontal plane knee control as good, reduced, or poor, based on specific criteria. Screening test scores were correlated to frontal plane knee kinematics and kinetics using 3-D motion analysis. Interrater agreement was determined using kappa correlation coefficients. RESULTS Knee valgus angles differed significantly among players rated as having poor, reduced, or good knee control (10.3° ± 3.4°, 5.4° ± 4.1°, and 1.9° ± 4.3°, respectively). The correlation between the observation test scores and valgus angles was moderate for all raters (0.54-0.60, P≤.001), but the observation scores correlated poorly with abduction moments (0.09-0.11, P>.05). The highest discriminative accuracy was found for knee valgus angles across all raters (area under the receiver-operating-characteristic curve, 0.85-0.89). The interrater agreement between the physiotherapists was substantial to almost perfect, with percentage agreement and kappa coefficients ranging from 70% to 95% and 0.52 to 0.92, respectively. CONCLUSION Physiotherapists can reliably identify female athletes with high knee valgus angles in a vertical drop-jump landing using real-time observational screening.

Text messaging as a new method for injury registration in sports: A methodological study in elite female football

Methodological differences in epidemiologic studies have led to significant discrepancies in injury incidences reported. The aim of this study was to evaluate text messaging as a new method for injury registration in elite female football players and to compare this method with routine medical staff registration. Twelve teams comprising 228 players prospectively recorded injuries and exposure through one competitive football season. Players reported individually by answering three text messages once a week. A designated member of the medical staff conducted concurrent registrations of injuries and exposure. Injuries and exposure were compared between medical staff registrations from nine teams and their 159 affiliated players. During the football season, a total of 232 time‐loss injuries were recorded. Of these, 62% were captured through individual registration only, 10% by the medical staff only, and 28% were reported through both methods. The incidence of training injuries was 3.7 per 1000 player hours when calculated from individual registration vs 2.2 from medical staff registration [rate ratio (RR): 1.7, 1.2–2.4]. For match injuries, the corresponding incidences were 18.6 vs 5.4 (RR: 3.4, 2.4–4.9), respectively. There was moderate agreement for severity classifications in injury cases reported by both methods (kappa correlation coefficient: 0.48, confidence interval: 0.30–0.66).

Association between Lower Extremity Muscle Strength and Noncontact ACL Injuries.

PURPOSE This study aimed to prospectively investigate the association between isolated and functional lower extremity muscle strength and the risk for noncontact anterior cruciate ligament (ACL) injury in Norwegian female elite handball and football players. METHODS From 2007 through 2015, premier league players participated in strength testing and were prospectively followed for ACL injury risk. At baseline, we recorded player demographics, playing and ACL injury history, and measured peak concentric isokinetic quadriceps and hamstring torques (60°·s), hamstring-to-quadriceps ratio, isometric hip abduction strength, and one-repetition maximum in a seated leg press. We followed a predefined statistical protocol where we generated five separate logistic regression models, one for each of the proposed strength risk factors and adjusted for confounding factors. New ACL injury was the outcome, using the leg as the unit of analysis. RESULTS A total of 57 (6.6%) of 867 players (age = 21 ± 4 yr, height = 170 ± 6 cm, body mass = 66 ± 8 kg) suffered from a noncontact ACL injury after baseline testing (1.8 ± 1.8 yr). The OR of sustaining a new injury among those with an ACL injury history was 3.1 (95% confidence interval = 1.6-6.1). None of the five strength variables selected were statistically associated with an increased risk of ACL rupture when adjusted for sport, dominant leg, ACL injury history, and height. CONCLUSION Peak lower extremity strength was not associated with an increased ACL injury risk among female elite handball and football players. Hence, peak strength, as measured in the present study, cannot be used to screen elite female athletes to predict injury risk.

A simple clinical screening test can identify elite female football players with increased knee valgus angles

Background A link has been suggested between increased dynamic knee valgus and the risk of anterior cruciate ligament (ACL) injuries in female athletes. However, these findings are based on complex time-consuming 3D motion analysis. There is a need for simple screening tools to identify athletes at increased risk of an ACL rupture. Objective To assess whether an experienced clinician can identify athletes with increased valgus angles and moments during a vertical drop jump using a simple screening test. Design Cross-sectional study. Participants Elite female football players. Methods Players in the Norwegian elite league (12 teams) were screened for potential risk factors for ACL injuries. Knee kinematics and kinetics in the landing phase of a 30 cm vertical drop jump were calculated using 3D motion analysis. Using a similar jump task, a physiotherapist assessed how well players stabilised their knees, and scored their knee control as ‘good’, ‘reduced’ or ‘poor’. Results Of the 136 players included, 38% were classified as ‘good’, 34% had ‘reduced’ control and 28% were scored as ‘poor’. Players with good control had significantly lower maximal valgus angles compared to players with poor control (0.5° vs 6.8°, p≤0.001). There were no differences in valgus moments (0.28 Nm/kg vs 0.28 Nm/kg, p=1.0). One-fifth of all players (17.6%) displayed valgus angles more than one SD above the mean in the 3D analyses (3.1° ±4.5°). The screening test captured 87.5% of these players. 22 (16.2%) players were classified in the ‘poor’ group without displaying high valgus angles. Conclusion The screening test identified 87.5% of players with increased valgus angles. No correlation was found between valgus angles and moments, and the test could not identify players with high valgus moments. Further investigations are needed to determine the cut-off value for defining high- versus low-risk groups, as well as the predictive value of the test.

No association between static and dynamic postural control and ACL injury risk among female elite handball and football players: a prospective study of 838 players

Background Research on balance measures as potential risk factors for ACL injury is limited. Objective To assess whether postural control was associated with an increased risk for ACL injuries in female elite handball and football players. Method Premier league players were tested in the preseason and followed prospectively for ACL injury risk from 2007 through 2015. At baseline, we recorded player demographics, playing experience, ACL and ankle injury history. We measured centre of pressure velocity in single-leg stabilisation tests and reach distances in the Star Excursion Balance Test. To examine the stability of postural control measures over time, we examined their short-term and long-term reproducibility. We generated logistic regression models, 1 for each of the proposed risk factors. Results A total of 55 (6.6%) out of 838 players (age 21±4 years; height 170±6 cm; body mass 66±8 kg) sustained a non-contact ACL injury after baseline testing (1.8±1.8 years). When comparing normalised balance measures between injured and uninjured players in univariate analyses, none of the variables were statistically associated with ACL injury risk. Short-term and long-term reproducibility of the selected variables was poor. Players with a previous ACL injury had a 3-fold higher risk of sustaining a new ACL injury compared with previously uninjured players (OR 2.9, CI 1.4 to 5.7). Conclusions None of postural control measures examined were associated with increased ACL injury risk among female elite handball and football players. Hence, as measured in the current investigation, the variables included cannot be used to predict ACL injury risk.

Knee function among elite handball and football players 1 to 6 years after anterior cruciate ligament injury

The aim of the study was to describe objective and self‐reported knee function for athletes who have returned to elite handball and football play after an ACL injury, comparing these to non‐injured players at the same level. A total of 414 handball and 444 football players completed baseline tests from 2007 through 2014, examining lower extremity strength, dynamic balance, knee laxity, and knee function (KOOS questionnaire). Measures were compared between injured and non‐injured legs and between injured legs and legs of controls. Eighty (9.3%) of the 858 players reported a previous ACL injury, 1‐6 years post‐injury (3.5±2.5 years), 49 handball (61.3%) and 31 football players (38.7%). We found no difference in strength or dynamic balance between previously ACL‐injured (N=80) and non‐injured players legs (N=1556). However, lower quadriceps (6.3%, 95% CI: 3.2‐9.2) and hamstrings muscle strength (6.1%, 95% CI: 3.3‐8.1) were observed in previously ACL‐injured legs compared to the non‐injured contralateral side (N=80). ACL‐injured knees displayed greater joint laxity than the contralateral knee (N=80, 17%, 95% CI: 8‐26) and healthy knees (N=1556, 23%, 95% CI: 14‐33). KOOS scores were significantly lower for injured knees compared to knees of non‐injured players. ACL‐injured players who have successfully returned to elite sport have comparable strength and balance measures as their non‐injured teammates. Subjective perception of knee function is strongly affected by injury history, with clinically relevant lower scores for the KOOS subscores Pain, Function, Sport, and Quality Of Life.

Association Between Anatomical Characteristics, Knee Laxity, Muscle Strength, and Peak Knee Valgus During Vertical Drop-Jump Landings

STUDY DESIGN Controlled laboratory study; cross-sectional. OBJECTIVES To investigate the relationship among anatomical variables, knee laxity, muscle strength, and peak knee valgus angles during a vertical drop-jump landing task. BACKGROUND Excessive knee valgus has been associated with anterior cruciate ligament injury in females; however, the influence of anatomical characteristics, knee laxity, and muscle strength on frontal plane knee motion is not completely understood. METHODS Norwegian elite female soccer players (n = 279; mean ± SD age, 21 ± 4 years; height, 167 ± 6 cm; body mass, 63 ± 7 kg) were evaluated from 2009 through 2012. The evaluation included 3-D motion analysis of a vertical drop jump, anatomical measures (height, static knee valgus, leg length, and static foot posture), knee laxity, and muscle strength (quadriceps, hamstrings, and hip abductors). Multiple linear regression analyses were used to investigate the relationships among anatomical characteristics, knee laxity, muscle strength, and peak knee valgus angles. RESULTS Anatomical characteristics explained 11% of the variance in peak knee valgus angles (P<.001), with height and static knee valgus being significant predictors. CONCLUSION Greater body height and static knee valgus were associated with greater peak knee valgus angles during a vertical drop-jump landing task. However, these variables only explained 11% of the variance in peak knee valgus.

A comparison between the star excursion balance test and subjective assessment of knee stability in a single-leg squat

Background Excessive dynamic knee valgus may leave athletes prone to serious knee injuries. The Star Excursion Balance Test (StarReach) is an objective clinical test, well applicable for non-clinicians, to identify athletes with ankle instability, but its potential to detect athletes with reduced knee control has not been examined. Objective To compare StarReach test performance with subjective assessment of dynamic knee valgus during a single-leg squat in female athletes. Design Controlled, laboratory study. Setting Norwegian female elite team handball and football. Participants This study is part of an ongoing cohort study aimed at investigating risk factors for non-contact anterior cruciate ligament injuries. Since 2007, a total of 321 handball and 246 football players (22±4 years) have been included. Main outcome measures A physiotherapist assessed how well players stabilised their knees while performing a single-leg squat, and scored their performance as ‘good’, ‘reduced’ or ‘poor’. Maximum reach distances in the StarReach test were measured on both feet in the antero-, medio- and posterolateral directions. A total of 440 players were tested. Results StarReach test performance (reach distance adjusted for leg length) was significantly better for those players who were scored with ‘good’ versus ‘poor’ knee stability (p<0.01): anterolateral direction 100.1 cm (SD 8.7 cm) vs 92.0 (9.4) right and 93.4 (6.4) vs 88.7 (7.3) left knee; mediolateral 96.7 (6.7) vs 91.0 (7.8) right and 97.1 (6.2) vs 90.3 (6.9) left knee; posterolateral 105.7 (6.5) vs 98.9 (8.7) right and 106.0 (6.2) vs 98.7 (7.8) left knee. However, correlation coefficients between objective and subjective tests varied between 0.18 and 0.32 for knee stability. Conclusion Poor relationships between StarReach-test performance and subjective scores illustrate why these two tests cannot be used interchangeably to assess knee stability. Further investigations are needed to determine whether any of these tests can predict increased knee injury risk.