Eirik Kristianslund

Effect of low pass filtering on joint moments from inverse dynamics: implications for injury prevention.

Analyses of joint moments are important in the study of human motion, and are crucial for our understanding of e.g. how and why ACL injuries occur. Such analyses may be affected by artifacts due to inconsistencies in the equations of motion when force and movement data are filtered with different cut-off frequencies. The purpose of this study was to quantify the effect of these artifacts, and compare joint moments calculated with the same or different cut-off frequency for the filtering of force and movement data. 123 elite handball players performed sidestep cutting while the movement was recorded by eight 240 Hz cameras and the ground reaction forces were recorded by a 960 Hz force plate. Knee and hip joint moments were calculated through inverse dynamics, with four different combinations of cut-off frequencies for signal filtering: movement 10 Hz, force 10 Hz, (10-10); movement 15 Hz, force 15 Hz; movement 10 Hz, force 50 Hz (10-50); movement 15 Hz, force 50 Hz. The results revealed significant differences, especially between conditions with different filtering of force and movement. Mean (SD) peak knee abduction moment for the 10-10 and 10-50 condition were 1.27 (0.53) and 1.64 (0.68) Nm/kg, respectively. Ranking of players based on knee abduction moments were affected by filtering condition. Out of 20 players with peak knee abduction moment higher than mean+1S D with the 10-50 condition, only 11 were still above mean+1 SD when the 10-10 condition was applied. Hip moments were very sensitive to filtering cut-off. Mean (SD) peak hip flexion moment was 3.64 (0.75) and 5.92 (1.80) under the 10-10 and 10-50 conditions, respectively. Based on these findings, force and movement data should be processed with the same filter. Conclusions from previous inverse dynamics studies, where this was not the case, should be treated with caution.

Kinematics and kinetics of an accidental lateral ankle sprain

Ankle sprains are common during sporting activities and can have serious consequences. Understanding of injury mechanisms is essential to prevent injuries, but only two previous studies have provided detailed descriptions of the kinematics of lateral ankle sprains and measures of kinetics are missing. In the present study a female handball player accidentally sprained her ankle during sidestep cutting in a motion analysis laboratory. Kinematics and kinetics were calculated from 240 Hz recordings with a full-body marker setup. The injury trial was compared with two previous (non-injury) trials. The injury trial showed a sudden increase in inversion and internal rotation that peaked between 130 and 180 ms after initial contact. We observed an attempted unloading of the foot from 80 ms after initial contact. As the inversion and internal rotation progressed, the loads were likely to exceed injury threshold between 130 and 180 ms. There was a considerable amount of dorsiflexion in the injury trial compared to neutral flexion in the control trials, similar to the previously published kinematical descriptions of lateral ankle sprains. The present study also adds valuable kinetic information that improves understanding of the injury mechanism.

Correlation between two-dimensional video analysis and subjective assessment in evaluating knee control among elite female team handball players

Poor frontal plane knee control has been shown to be a risk factor for anterior cruciate ligament injuries in ball/team sports. It is necessary to develop simple tests that can identify players with poor knee control and among other factors be able to optimise preventive training programmes. The present study investigated the correlation between a two-dimensional (2D) video analysis and subjective assessment performed by one physiotherapist in evaluating knee control. We also tested the correlation between three simple clinical tests using both methods. A cohort of 186 female elite team handball players completed three tests: single-leg squat (SLS), single-leg vertical drop jump (SLVDJ) and two-leg vertical drop jump (VDJ). Receiver operating characteristic (ROC) analyses showed good to excellent agreement between 2D video analysis and subjective assessment for SLS and VDJ (area under the ROC curve (AUC) 0.83–0.89), but not for SLVDJ (AUC 0.65–0.76). Poor knee control was detected in 25–40% of the players using SLS and VDJ. In contrast, poor knee control was identified in less than 1% of the subjects based on the SLVDJ test. This indicates that SLVDJ may be inadequate for evaluating poor frontal plane knee control. The correlation between the SLS and VDJ tests was found to be low, suggesting that these tests identified different subjects with poor knee control. These results indicate that subjective assessment can be used to screen for poor knee control and that both SLS and VDJ tests should be used in screening athletes for poor knee control.

Comparison of Drop Jumps and Sport-Specific Sidestep Cutting Implications for Anterior Cruciate Ligament Injury Risk Screening

Background: Anterior cruciate ligament (ACL) injuries are a serious problem, with a high incidence and serious consequences. Published clinical screening tests are based on 2-legged and controlled drop jumps, but ACL injuries are known to occur in single-legged landings and sidestep cutting, where the load is predominantly distributed to a single leg. Purpose: To describe knee kinematics and kinetics in drop jumps and sidestep cutting and investigate the rank correlation of knee valgus angles and knee abduction moments between and within these movements. Study Design: Controlled laboratory study. Methods: A total of 120 elite female handball players (mean ± SD: age, 22.4 ± 7.1 years; height, 171 ± 7 cm; weight, 67 ± 7 kg), each performed 3 drop jumps and 3 sport-specific sidestep cuts to each side. Kinematics and kinetics were calculated from high-speed 3-dimensional motion analysis. Results: Knee kinematics and kinetics were significantly different between drop jumps and sidestep cutting. The knee abduction moment was 6 times higher in sidestep cutting (1.58 ± 0.60 Nm/kg vs 0.25 ± 0.16 Nm/kg). There was a poor correlation between knee abduction moments (ρ = 0.135) in the 2 tasks, but a moderate correlation (ρ = 0.706) for knee valgus angles. There was a poor correlation between knee valgus angles in drop jumps and knee abduction moments in sidestep cuts (ρ = 0.238). Conclusion: Motion patterns are different between drop jumps and sidestep cutting. There is a moderate correlation for knee abduction moments between the 2 tasks, but knee abduction moments are less consistent across tasks. Clinical Relevance: Knee valgus angles during drop jumps do not predict knee abduction moments during sidestep cutting. The moderate correlation of knee valgus angles in drop jumps and sidestep cutting indicates that this measure may be more relevant for screening efforts.

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.

Sidestep cutting technique and knee abduction loading: implications for ACL prevention exercises

Background Sidestep cutting technique is essential in programmes to prevent anterior cruciate ligament (ACL) injury. A better understanding of how technique affects potentially harmful joint loading may improve prevention programmes. The purpose of this study was to investigate the effect of sidestep cutting technique on maximum knee abduction moments. Methods Cross-sectional study. Whole-body kinematics and knee joint kinetics were calculated in 123 female handball players (mean±SD, 22.5±7.0 years, 171±7 cm, 67±7 kg) performing sidestep cutting. Three cuts from each side were analysed. Linear regression was applied between selected technique factors and maximum knee abduction moment during the first 100 ms of the contact phase. Furthermore, we investigated to what degree the abduction moment originated from the magnitude of the ground reaction force (GRF) or the knee abduction moment arm of the GRF. Findings Technique factors explained 62% of the variance in knee abduction moments. Cut width, knee valgus, toe landing, approach speed and cutting angle were the most significant predictors. An increase in one of these factors of 1 SD increased the knee abduction moment from 12% to 19%. The effect of the moment arm of the GRF was more important than the force magnitude for maximum knee abduction moments. Interpretation Lower knee abduction loads during sidestep cutting may be achieved if cuts are performed as narrow cuts with low knee valgus and toe landings. These factors may be targeted in ACL injury prevention programmes.

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.

Mechanisms of injuries in World Cup Snowboard Cross: a systematic video analysis of 19 cases

Background Snowboard cross (SBX) became an official Olympic sport in 2006. This discipline includes manoeuvring several obstacles while competing in heats. It is common for the riders to collide, making this sport both exciting and at risk of injuries. Although a recent study from the 2010 Olympic Games has shown that the injury risk was high, little is known about the injury mechanisms. Objective To qualitatively describe the injury situation and mechanism of injuries in World Cup Snowboard Cross. Study design Descriptive video analysis. Methods Nineteen video recordings of SBX injuries reported through the International Ski Federation Injury Surveillance System for four World Cup seasons (2006 to 2010) were obtained. Five experts in the field of sports medicine, snowboard and biomechanics performed analyses of each case to describe the injury mechanism in detail (riding situation and rider behaviour). Results Injuries occurred at jumping (n=13), bank turning (n=5) or rollers (n=1). The primary cause of the injuries was a technical error at take-off resulting in a too high jump and subsequent flat-landing. The rider was then unable to recover leading to fall at the time of injury. Injuries at bank turn was characterised by a pattern where the rider in a balanced position lost control due to unintentional contact with another rider. Conclusion Jumping appeared to be the most challenging obstacle in SBX, where a technical error at take-off was the primary cause of the injuries. The second most common inciting event was unintentional board contact between riders at bank turning.

Expressing the joint moments of drop jumps and sidestep cutting in different reference frames--does it matter?

Joint moments help us understand joint loading and muscle function during movement. However, the interpretation depends on the choice of reference frame, but the different reference frames have not been compared in dynamic, high-impact sporting movements. We have compared the magnitude and the resulting ranking of hip and knee joint moments expressed in the laboratory coordinate system, the local system of the distal segment and projected or decomposed to the Joint Coordinate System (JCS) axes. Hip and knee joint moments of drop jumps and sidestep cutting in 70 elite female handball players were calculated based on recordings from an eight-camera 240 Hz system and two force platforms and expressed with the four methods. The greatest variations in magnitude between conditions were seen for drop jump hip internal rotation (range: 0.31-0.71 Nm/kg) and sidestep cutting knee flexion (2.87-3.39 Nm/kg) and hip internal rotation (0.87-2.36 Nm/kg) and knee internal rotation (0.10-0.40 Nm/kg) moments. The rank correlations were highest between conditions for flexion moments (0.88-1.00) and sidestep cutting abduction moments (0.71-0.98). The rank correlations ranged from 0.64 to 0.73 for drop jump knee abduction moments and between -0.17 and 0.67 for hip and knee internal rotation moments. Expression of joint moments in different reference systems affects the magnitude and ranking of athletes. This lack of consistency may complicate the comparison and combination of results. Projection to the JCS is the only method where joint moments correspond to muscle and ligament loading. More widespread adoption of this convention could facilitate comparison of studies and ease the interpretation of results.

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.