External loading of the knee joint during running and ...

External loading of the knee joint during running and cutting maneuvers THOR F. BESIER, DAVID G. LLOYD, JODIE L. COCHRANE, and TIMOTHY R. ACKLAND Department of Human Movement & Exercise Science, University of Western Australia, Perth, AUSTRALIA

ABSTRACT BESIER, T. F., D. G. LLOYD, J. L. COCHRANE, and T. R. ACKLAND. External loading of the knee joint during running and cutting maneuvers. Med. Sci. Sports Exerc., Vol. 33, No. 7, 2001, pp. 1168 –1175. Purpose: To investigate the external loads applied to the knee joint during dynamic cutting tasks and assess the potential for ligament loading. Methods: A 50-Hz VICON motion analysis system was used to determine the lower limb kinematics of 11 healthy male subjects during running, sidestepping, and crossover cut. A kinematic model was used in conjunction with force place data to calculate the three-dimensional loads at the knee joint during stance phase. Results: External flexion/extension loads at the knee joint were similar across tasks; however, the varus/valgus and internal/ external rotation moments applied to the knee during sidestepping and crossover cutting were considerably larger than those measured during normal running (P ⬍ 0.05). Sidestepping tasks elicited combined loads of flexion, valgus, and internal rotation, whereas crossover cutting tasks elicited combined loads of flexion, varus, and external rotation. Conclusion: Compared with running, the potential for increased ligament loading during sidestepping and crossover cutting maneuvers is a result of the large increase in varus/valgus and internal/external rotation moments rather than any change in the external flexion moment. The combined external moments applied to the knee joint during stance phase of the cutting tasks are believed to place the ACL and collateral ligaments at risk of injury, particularly at knee flexion angles between 0° and 40°, if appropriate muscle activation strategies are not used to counter these moments. Key Words: LIGAMENT INJURY, SIDESTEPPING AND CUTTING, KNEE JOINT LOADS

T

he etiology of noncontact knee ligament injury is less certain than that for contact or impact injuries that are common to football or skiing (22). In the case of the anterior cruciate ligament (ACL), noncontact injuries appear to have a common feature in that they typically involve sudden changes in direction combined with acceleration or deceleration of the body (22). Cross and colleagues (5) have recognized that sidestep cutting maneuvers are a common mechanism of noncontact or isolated ACL rupture. To understand the mechanisms behind noncontact ACL injury, it is imperative to measure the external loads applied to the knee during tasks that challenge the integrity of the knee joint. “Only when the causal relations between applied forces and resultant injury are established and understood can appropriate programs of intervention and prevention be designed and implemented” (25). To date, there is little documentation regarding the external loads applied to the knee during sport-specific movements that involve rapid changes in direction. Measuring joint loads at the knee during tasks such as sidestepping and crossover cutting therefore appears a logical step in understanding the etiology of noncontact knee ligament injury. Markolf et al. (12,13) and Wascher et al. (24) measured the loads on ACL and PCL in fresh frozen cadaveric knees under combined loads applied to the tibia throughout a range of knee angles. The combination of loads included flexion,

adduction/abduction (varus/valgus, respectively), and internal/external rotation. A combination of externally applied internal rotation and anterior tibial force resulted in the highest load on the ACL. Pure internal rotation moments, as well as varus-valgus moments in conjunction with anterior tibial force produced large loads on the ACL. Markolf et al. (12) also found that the ACL experienced large loads at extended knee angles, particularly between 0° and 20° of knee flexion. This finding is in agreement with other studies that have measured or estimated ACL load at different knee flexion angles (2,19). Movements such as sidestepping and crossover cutting are expected to involve various combinations of external flexion/extension (FE), varus/valgus (VV), and internal/external rotation (IE) moments at the knee and thus place different loads on the soft tissues and supporting structures compared with straight running. The purpose of this investigation was to quantify the three-dimensional external knee moments and knee flexion angle during dynamic sidestepping and crossover cutting, and suggest how knee loading during cutting movements might contribute to increased risk of injury. These parameters were chosen based on the known interactions between the external load, knee flexion angle, and the potential for ligament loading (2,13).

0195-9131/01/3307-1168/$3.00/0 MEDICINE & SCIENCE IN SPORTS & EXERCISE® Copyright © 2001 by the American College of Sports Medicine

Subjects. Eleven healthy, male soccer players without history of lower limb injury volunteered for this investigation (mean ⫾ SD age: 21.3 ⫾ 3.4 yr; height: 179.4 ⫾ 7.8 cm; mass: 74.1 ⫾ 7.1 kg). Subjects with previous ankle or knee injury (sustained within the previous year) were

METHODS

Received for publication May 2000. Accepted for publication October 2000.

1168

excluded from the study. Amateur soccer players from two first grade competition teams were selected for participation as it was expected that this population would be familiar with performing sidestepping and crossover cutting tasks. Before data collection, the testing protocols were explained to the subjects, and their written informed consent obtained. Experimental design. Subjects were asked to perform repeated trials of four tasks in the gait laboratory during three sessions conducted over 3 wk. Subjects were asked to step off both right and left legs during the initial familiarization trials to determine which foot they preferred to step from. After these initial trials, it was found that all subjects preferred performing the tasks from their right leg and were asked to perform the tasks in bare feet to negate any effects due to wearing different running shoes. A thin carpet was laid on the running surface to prevent reflections being picked up by the motion analysis cameras and provided adequate friction between the bare foot and the ground. A few days before the start of testing, subjects completed a 1-h training session to familiarize themselves with each of the tasks and the testing procedures. The tasks were performed in a random order to account for fatigue, with 10 trials of each maneuver recorded, giving a total of 40 trials per session. One-minute intervals were also given between each trial to reduce the effects of fatigue. The testing protocol was chosen to ensure consistency among subjects in regard to the cutting angle and speed maintained. Previous studies on sidestepping or crossover cutting have not restricted the cutting angle or speed of task execution, which could result in a large variation in the loads experienced at the knee joint (3,4). McLean et al. (15) limited their sidestepping tasks within a range of 35– 60° from the direction of travel, whereas Neptune et al. (16) chose 45° as the desired direction of travel during their investigation of sidestepping maneuvers. It was decided to examine the loads at the knee during two sidestepping tasks, one task being relatively easy to perform (30° from the direction of travel) and the other task being more difficult to perform (60° from the direction of travel). The crossover cut was also included in the protocol, as it was believed that this task would produce quite different patterns of external loading compared with the sidestepping tasks. To summarize, the four tasks were a straight run (RUN), sidestep to 30° (S30) and 60° (S60) stepping left off the right foot, and a crossover cut to 30° (XOV) stepping right off the right foot. For each trial, lights on a target board indicated the task direction and tape was placed on the floor to indicate the cutting angle required (see Fig. 1). Subjects were instructed to maintain their running speed as much as possible throughout the task. Infrared timing gates were used to monitor the approach running speed (see Fig. 1), which was delimited to 3 m·s-1 (~10 km·h-1). The speed was chosen to be as fast as possible within the limits of the 50-Hz motion analysis system. Using a similar method to that proposed by Antonsson and Mann (1), a Fourier analysis of the ground reaction forces recorded during each trial confirmed that the 98% of the frequency content of the cutting tasks were at 10 Hz or below. This was considered LOADING AT THE KNEE DURING CUTTING TASKS

FIGURE 1—Target board and gait laboratory set up. The lights on the target board correspond to the desired direction of travel. Note that these lines of travel are also marked on the floor with tape. The force plate lies at the apex of these lines.

to provide an adequate signal-to-noise ratio to reconstruct a smooth signal from the 50-Hz motion analysis system. Data collection. Retro-reflective markers were fixed to lower limb landmarks to record three-dimensional lower limb movements by using a six-camera, 50-Hz VICON motion analysis system (Oxford Metrics Ltd., Oxford, United Kingdom). The VICON Clinical Manager (VCM) marker set was used (6,9), which consisted of 13 lower limb markers placed on: left and right anterior superior iliac spines (ASIS); sacrum; left and right knee joint centers; both lateral malleoli; the head of the second metatarsal on each foot; left and right mid-shank, in line with the malleolus and knee joint markers; and left and right mid-thigh, in line with the greater trochanter and knee joint center. A static trial was collected before dynamic testing. This static trial included markers on each heel (in line with the metatarsal marker) to complete the foot segment and a knee alignment device (KAD) to determine the correct knee joint center and knee joint axis alignment. Tibial torsion (defined as the offset between knee and ankle FE axes) was also measured and used as input into the kinematic model (as required for VCM software). Ground reaction forces (GRF) were recorded at 2000 Hz using a 1200 ⫻ 600 mm force-plate (Advanced Mechanical Technology Inc., Watertown, MA). Subjects were aware of the position of the plate to ensure they were performing the tasks at the same position but were instructed to look straight ahead when performing each task so that they did not “target” the force-plate. To this end, a starting marker was used to alter the subjects’ run-up distances to ensure that the right foot landed in the center of the plate without the need to target. Data analysis. Kinematic data and inverse dynamic calculations were performed using VCM software (Oxford Metrics Inc.). This software was used as it employed standard and accepted methods for processing gait data (6). This method has also been used previously to perform threedimensional analyses of running gait (17,18). Lower limb segment trajectories and ground reaction force data were filtered and interpolated simultaneously within VCM by Medicine & Science in Sports & Exercise姞

1169

FIGURE 2—Schematic of the three stages of stance phase, determined using resultant ground reaction force. WA, weight acceptance; PPO, peak push off; FPO, final push off.

fitting a Bezier spline to the data (VCM, Oxford Metrics Inc.). Joint kinetic data were calculated using an inverse dynamic analysis as described by Kadaba et al. (9) and Davis et al. (6). The joint moments referred to in this paper are the external moments applied to the joint. For example, an external flexion load will tend to flex the knee. Knee flexion angle, GRF, and three-dimensional joint kinetic data were normalized to stance phase by fitting a cubic spline to the data using Microsoft Excel® (Microsoft Corp.) and interpolating the spline to 30 points. Knee moments and flexion angle were averaged across three phases of stance, based upon the magnitude of the resultant GRF (vector summation of Fx, Fy, and Fz). Figure 2 illustrates the three phases during stance, which were determined as follows: 1. Weight acceptance (WA)—from heel strike to the first trough in the resultant GRF. 2. Peak push off (PPO)—10% either side of the peak resultant GRF, and 3. Final push off (FPO)—last 15% of stance. The initial speed of each task was calculated from the infrared timing gates and monitored to ensure that each task was performed at the same speed of ~3 m·s-1. For the determination of the speed and cutting angle throughout the performance of the maneuver, the kinematics of the pelvic center were determined for one stride. One stride was defined from when the thigh of the step leg was vertical before foot contact to when the same thigh was vertical after contact with the force plate. The average speed maintained throughout the maneuver was calculated using the x and y displacements of the pelvic center (anterior/posterior and medio/lateral displacements, respectively), i.e., Speed ⫽ ((xi ⫺ xi⫺1)2 ⫹ (yi ⫺ yi⫺1)2)1/2/(ti⫺ti⫺1), where i

⫽ ith time point (i.e., ti).

and the cutting angle calculated as follows: Cutting angle ⫽ tan⫺1[(yi ⫺ yi⫺1)/(xi ⫺ xi⫺1)], where i ⫽ ith time point.

1170

Official Journal of the American College of Sports Medicine

The speed and cutting angle used in the final analysis was the average of those parameters determined across the final five time points of the stride. Reliability and validity of gait data. Coefficients of multiple determination (R2) were calculated for GRF, knee flexion angle, and three-dimensional moment data across the stance phase to determine the reliability within and between testing sessions (9). Statistical design. The data assembled for the statistical analysis were the three-dimensional joint moments and knee flexion angles in each of the stance phases (WA, PPO, and FPO) and the running speed and cutting angle achieved. All statistical analyses were performed using Datadesk® statistical software (Data Description Inc., Ithaca, NY) and significance indicated with P ⬍ 0.05. Scheffe´ post hoc tests were conducted to determine significant interactions and differences among task. It was found that week 1 had less repeatability in measured ground reaction forces and knee joint moments compared with the second and third testing sessions, with lower R2 values. A two-way ANOVA (stance phase ⫻ week) indicated that there were differences in the calculated knee joint moments, knee flexion angle, and cutting angle achieved during each of the cutting tasks across weeks. There were significant differences (P ⬍ 0.05) in many of the measured VV and IE moments, and knee flexion angles between weeks 1–2 and weeks 1–3. However, there were no differences in any parameters between week 2 and week 3. These results were probably due to learning effects and it was decided to pool data from week 2 and week 3 and treat data from week 1 as a training session. Subsequently, the data parameters pooled from week 2 and week 3 were analyzed using a two-way ANOVA (stance phase ⫻ task).

RESULTS Repeatability of gait data. The GRF and joint moments measured during the running and cutting tasks were very repeatable between and within week 2 and week 3. There was high repeatability between testing sessions, especially in the IE moments (Table 1a). The XOV task was performed with the most variation across testing sessions; however, the data were still repeatable from week to week. Repeatability within each testing session was also high (Table 1b). The speeds and cutting angles measured during each task were similar across weeks 2 and 3, suggesting that no learning had occurred between these testing sessions. Greater variation in the GRF occurred in the frontal (mediolateral) plane during running, compared with the sidestepping tasks. This was not unexpected, however, owing to the small forces in the medial-lateral directions during the RUN task, which could be affected by small trial-to-trial variations. This is in comparison to the cutting tasks that elicited large forces in the medial-lateral directions and would not be affected as much by the small variations between trials. Moments applied to the knee in FE showed the least amount of variation within each testing session (mean R2 ⫽ 0.96 ⫾ 0.03), with the VV and IE loads http://www.acsm-msse.org

TABLE 1a. Between testing session mean (SD) coefficients of multiple determination (R2) for preplanned running and cutting tasks.

Moment

Direction

S60

S30

RUN

XOV

FE VV IE

0.89 (0.04) 0.93 (0.06) 0.99 (0.01)

0.92 (0.04) 0.91 (0.09) 0.99 (0.01)

0.90 (0.05) 0.88 (0.10) 0.99 (0.01)

0.84 (0.10) 0.81 (0.16) 0.98 (0.03)

having greater variation (average VV R2 ⫽ 0.87 ⫾ 0.15 and average IE R2 ⫽ 0.84 ⫾ 0.09). Repeatability of the knee FE angle was very high between and within testing sessions (R2 ⫽ 0.94 ⫾ 0.04). Task performance measures: speed and cutting angle. The run up speed measured between the timing gates was similar for all subjects across all tasks and was consistent for different testing sessions (mean ⫽ 3.13 ⫾ 0.27 m·s-1). The average speed throughout the maneuver was dependent on the task being performed. The S30 and XOV were ~0.2 m·s-1 slower than the RUN (P ⬍ 0.05) and the S60 task was slower than the RUN by ~0.4 m·s-1 (P ⬍ 0.05). The desired cutting angle for the S30 and XOV were attained, albeit with a reduction in speed. However, the angle of 60° for the S60 task was not attained, even with a significant reduction in running speed (mean cutting angle ⫽ 56.0 ⫾ 4.4°). This confirmed that the S60 task was difficult to perform. Flexion/extension moments. During PPO the knee was subject to large flexion moments, with little difference between tasks (Fig. 3). This load was equivalent to 150 N·m for a 75-kg person at PPO. The sidestepping and crossover cutting tasks elicited greater flexion loads compared to the RUN; however, this was only significant for the S30 during PPO (P ⬍ 0.05). The external flexion loads applied to the knee at FPO were negligible compared to the moments measured at WA and PPO. Varus/valgus moments. Significant differences (P ⬍ 0.05) in VV moments were found between the cutting tasks compared to the RUN at all stages of the stance phase (Fig. 4). Both sidestepping tasks placed an external valgus load on the knee at WA and FPO, whereas a varus load was applied to the knee during the RUN and XOV tasks at similar stages of stance. The valgus load during the S60 task was approximately 2 and 6 times greater than the varus load experienced during the RUN at WA and FPO, respectively (~40 N·m for a 75-kg person). The varus load during the XOV was more than twice that experienced during the RUN at similar phases of the stance phase (~40 N·m for a 75-kg person). At PPO, net varus loads were experienced in all tasks and were generally larger than those at WA and FPO

(Fig. 4). The RUN was again significantly different from the other tasks (P ⬍ 0.05). Note the large standard deviations in the VV loads at PPO (Fig. 4). Upon closer inspection, it was found that six of the subjects actually experienced a valgus load at PPO during the S60 and S30 tasks (mean: ⫺0.31 N·m·kg-1). The other five subjects experienced a large varus load at the knee (mean: 0.62 N·m·kg-1) such that the net moment for all subjects was in a varus direction and was smaller than that of the RUN (P ⬍ 0.001). Differences between these groups were significant (P ⬍ 0.01), with no intermediate group apparent. Therefore, these groups shall be referred to as “valgus group” or “varus group,” accordingly. There was also a significant difference in the speed at which the sidestepping tasks were performed between the valgus and varus groups. The valgus group performed the S60 task 0.25 m·s-1 slower than the varus group (P ⬍ 0.01). There were no significant differences in the cutting angles attained by both groups although there was a trend that showed the valgus group did not reach the desired 60° sidestep cutting angle as well as the varus group, with the result limited by the small numbers in each group. Interestingly, there were no differences between these two groups for FE and IE moments. Internal/external rotation moments. Significant differences (P ⬍ 0.05) in the IE moments measured at the knee were found between the S60, S30, and XOV tasks compared with the RUN (Fig. 5). The differences between the tasks were significant for all stages of the stance phase. The IE moments experienced during the cutting tasks appear small when expressed as a percentage of body weight; however, when compared with the moments measured during the RUN, they are quite substantial. During WA, the sidestepping tasks elicited an internal rotation moment up to 4 times the magnitude of the external rotation moment experienced during the RUN (P ⬍ 0.001). The external rotation load applied to the knee during the XOV was more than twice the load experienced during the RUN (P ⬍ 0.001). The internal rotation loads experienced at PPO during the sidestepping tasks were up to 5 times the load experienced during the RUN (~24 N·m for a 75-kg person), whereas the external rotation moment during the XOV was

TABLE 1b. Within session mean (SD) coefficients of multiple determination (R2) for ground reaction forces (GRF) and external knee moments. Parameter GRF Moment

Direction

S60

S30

RUN

XOV

AP ML Vert FE VV IE

0.96 (0.02) 0.94 (0.03) 0.95 (0.03) 0.96 (0.02) 0.86 (0.14) 0.83 (0.08)

0.97 (0.01) 0.94 (0.04) 0.96 (0.02) 0.96 (0.03) 0.85 (0.18) 0.83 (0.08)

0.97 (0.01) 0.74 (0.20) 0.97 (0.01) 0.96 (0.03) 0.90 (0.16) 0.83 (0.11)

0.96 (0.02) 0.88 (0.06) 0.96 (0.02) 0.95 (0.03) 0.87 (0.11) 0.85 (0.09)

AP, Anteroposterior GRF; ML, Mediolateral GRF; Vert, Vertical GRF; FE, Flexion/extension moment; VV, Varus/valgus moment; IE, Internal/external rotation moment; S60, Sidestep to 60°; S30, Sidestep to 30°; RUN, Straight run; XOV, Crossover cut to 30°.

LOADING AT THE KNEE DURING CUTTING TASKS

Medicine & Science in Sports & Exercise姞

1171

FIGURE 3—Flexion/extension moments applied to the knee during running and cutting maneuvers (* significant difference compared with the RUN task; P < 0.05).

more than 5 times that of the RUN (~26 N·m for a 75-kg person). Knee FE angle. Figures 2– 4 also illustrate the mean (SD) knee flexion angle during each stage of the stance phase. The knee flexion angle during PPO was significantly greater (P ⬍ 0.05) than WA and FPO (WA ⫽ 32.8° ⫾ 6.0°; PPO ⫽ 45.9° ⫾ 6.3°; FPO ⫽ 23.7° ⫾ 4.6°). The degree of flexion at the knee was also dependent on the task performed, although the functional significance of these differences is doubtful. At WA and PPO, the cutting tasks were performed with ~2° greater knee flexion than the RUN (P ⬍ 0.05). This trend was reversed at FPO, where the RUN task was performed with ~1.5° more knee flexion than the other tasks (significant for the S60 task only, P ⬍ 0.05).

DISCUSSION Repeatability of gait data. The FE moments measured during the RUN in our study were similar to those reported previously at similar running speeds (17,26). No external IE or VV moments for running have been reported previously. The R2 measures for knee joint moments were higher than those found by Kadaba et al. (8), especially those measured in IE. Kadaba et al. (8) attributed the variability in VV and IE moments to inconsistent alignment of markers. This inconsistency was probably reduced in the present study by: (a) having only one experimenter to align the retro-reflective markers on each subject for all trials; (b)

using a straight edge to align the thigh marker correctly to define the thigh plane/segment; and (c) the use of a knee alignment device contributed to the correct alignment of knee joint center markers and reliability of VV and IE measures. The high R2 values for the IE and VV moments were also due to higher magnitude of these moments during the cutting tasks compared with those recorded by Kadaba et al. (8) in walking trials. It was concluded that the gait data obtained in this study were reliable and repeatable within and between weeks 2 and 3. Speed and cutting angle. The speeds at which these tasks were performed in the laboratory may be less than that commonly seen in some sporting situations (5–7 m·s-1 in Rugby League as reported by McLean et al. (14)). However, this speed ensured that the cutting tasks would be performed within the limits of the 50-Hz motion analysis system, as stated previously. In the interest of preserving subjects’ health, the chosen speed was also fast enough to elicit large VV and IE moments during sidestepping and the crossover cut with minimal risk of knee ligament injury. An increased running speed may increase the magnitude of the external knee joint moments. However, the extent to which the loads change with running speed is not known. Novacheck (17) has shown that external flexion moments applied to the knee actually decrease by ~10% when running speed increased from 3 to 4 m·s-1. Further research is required to investigate the effect of increasing running speed on the knee joint loads during cutting tasks, especially those related to VV and IE.

FIGURE 4 —Varus/valgus moments applied to the knee during running and cutting maneuvers (* significant difference compared with RUN task; P < 0.01).

1172

Official Journal of the American College of Sports Medicine

http://www.acsm-msse.org

FIGURE 5—Internal/external rotation moments applied to the knee during running and cutting maneuvers (* significant difference to RUN task; P < 0.05).

Cutting technique may be more important than running speed or cutting angle in regard to the potential for ligament injury. In our results, there were technique differences observed during the side stepping tasks (the varus group versus valgus group), and McLean and colleagues (15) have reported differences in kinematics to perform the same cutting task. Moreover, athletes routinely perform cutting maneuvers without injury at a range of speeds and cutting angles. So the question should then be asked: what is so different about a cutting task technique that causes an injury? Important technique-related factors associated with increased risk of noncontact knee ligament injury could include the time taken to prepare for a maneuver, inappropriate postural adjustments, or inappropriate muscle activation patterns. These factors, and others, are currently being investigated in our laboratory. It was evident that a compromise between the speed of the task and the desired cutting angle was required to perform the cutting maneuvers. Even though the subjects were instructed to maintain running speed throughout all the tasks, they slowed significantly to perform the cutting maneuvers. This reduction in speed may not only be required to perform the task, but may also reduce the external loads applied to the knee. Technique changes. Five of the subjects performed the sidestepping tasks with a varus moment applied to the knee (varus group), whereas the other six subjects experienced a net valgus moment at PPO (valgus group). McLean et al. (14) found large variations in knee kinematics between individuals performing sidestepping tasks and concluded that the level of experience was a major contributing factor to the degree of consistency. The differences observed in the VV moments at PPO during the sidestepping tasks in this study suggest that technique may affect the external load placed on the joint. Although technique was not measured in this study, the differences in cutting angles and speed maintained throughout the cutting tasks may indicate variations in the way these maneuvers were performed. The varus group was able to maintain a greater speed and achieve a greater angle of sidestep than the valgus group. The varus group also displayed significantly greater varus loading at PPO during the XOV task compared to the valgus group. LOADING AT THE KNEE DURING CUTTING TASKS

Implications for noncontact knee ligament injuries. Perhaps the most important issue to raise here was that there was very little difference in the applied flexion moments at the knee during the different tasks; however, there were significant differences in the VV and IE loading. To counter the large flexion loads applied to the knee, muscles surrounding the joint must apply a large extension moment that may result in a net anterior force on the tibia when the knee is near full extension. The combination of anterior force on the tibia combined with the increased external VV and IE moments during the cutting tasks may be a reason for the increased risk of injury to knee joint ligaments when performing these maneuvers. The applied VV and IE moments during the cutting maneuvers were of sufficient magnitude to place large load on the knee joint ligaments. Piziali et al. (21) performed a series of loading studies on human cadaver knees and found that ligament damage occurred within 35– 80 N·m of IE rotation or 125–210 N·m of VV rotation. The peak IE and VV moments measured during the cutting tasks of this study were within the range measured by Piziali et al. (21) and were coupled with large external flexion loads. Without adequate muscular support, these loads may well be large enough to cause injury to knee joint ligaments. However, the risk of injury depends on many other factors that include: the magnitude and rate of loading, the combination of loads applied, and how these loads are apportioned between muscles and other soft tissues surrounding the joint, ligament strength, and joint geometry. To estimate the loads placed on ligaments in vivo, a modelling approach similar to that of Lloyd and Buchanan (10) should be used, taking into account the individual muscle activation patterns, joint kinematics, and joint geometry. The greatest potential for tension development in the ACL is during sidestepping at WA and PPO, where the knee experiences combined loads of anterior tibial force, internal rotation, and valgus moments (valgus group) and the knee angle is between 30° and 40° of flexion. However, the tension on the ACL from these combined loading directions needs to be qualified, as Markolf et al. (13) only investigated combined loading from two directions. It is therefore difficult to predict the force experienced by the ACL under combined knee loading from all three directions, as Medicine & Science in Sports & Exercise姞

1173

experienced during the cutting maneuvers. Considerable ACL loading occurs with combined anterior tibial force and valgus moments at knee flexion angles between 10° and 40°, but an internal rotation moment with an anterior tibial force reduces loading of the ACL at knee flexion angles greater than 25° compared with anterior tibial force only (13). To complicate matters further, Markolf et al. (13) also showed that combined valgus and internal rotation moments increased ACL load compared with the action of each moment in isolation. Nevertheless, this cadaver work suggests that the periods of WA and, in particular, PPO in the valgus group, where the applied internal rotation and valgus moments are greatest, poses the greatest risk of injury to the ACL. Further work is required to determine the exact loading response of the ACL to combined anterior tibial force with valgus and internal rotation moments. During the crossover cut, even though there were large external varus and flexion moments that potentially load the ACL, the risk of ACL injury would be moderated by the presence of an external rotation moment (13,20). Large valgus and internal rotation moments applied to the knee at WA and PPO (in the valgus group) during sidestepping also have the potential to place high loads on the medial collateral ligament (MCL). Almost 80% of the external valgus load applied to the knee is supported by the MCL at 25– 30° knee flexion (7,23), similar knee angles to that observed at WA. The MCL also supports the large majority of the applied internal rotation moments between 0° and 45° (11,23). As the applied valgus and internal rotation moments increased with the larger cutting angle of the S60 task, so too did the potential for loading of the MCL. Given this relationship, the varus group may reduce the possible loading of the MCL compared with the valgus group without compromising the speed and cutting angle achieved. The large varus loads observed during the crossover cut have greater potential to damage the lateral collateral ligament (LCL) (13,20), particularly with knee postures near full extension (7). Grood et al. (7) showed that the LCL supported close to 70% of an external varus moment applied to the knee. In terms of the potential for ligament injury, the varus group may be at greater risk here compared to the valgus group, owing to the large varus moments applied at PPO. Future directions. Further work should concentrate on the relationships between external knee joint loads and whole body kinematics during these dynamic functional tasks. For example, the load experienced at the knee joint may be related to the position of the foot on the ground with respect to the body’s center of gravity or the angle of the lower limb with respect to the ground. Qualitative exami-

nation of the upper body position suggested that upper body lean affected the magnitude of the valgus load experienced at the knee. Such “postural adjustments” need to be quantified, as there may be potential to reduce external loading at the knee by altering technique. We are also interested in observing the effect of the foot-ground interface on the loads placed on the knee joint. Our subjects performed the running and cutting tasks barefoot to negate any effects that may occur from wearing different shoes. This raises an interesting question: do different shoes alter the external joint loads placed on the knee joint when performing cutting tasks, particularly in VV and IE directions? One may expect the VV and IE loads to increase when wearing shoes compared with barefoot cutting tasks, owing to increased friction between the foot and the ground. Further research is warranted to investigate the effects of shoe design on the external VV and IE loads placed on the knee joint during running and cutting tasks.

SUMMARY The purpose of this study was to quantify the moments at the knee in FE, VV, and IE during running, sidestepping, and crossover cutting tasks and to determine the potential loading of knee ligaments. External flexion loads were similar among tasks, whereas the external VV and IE loads placed on the joint increased dramatically during cutting tasks compared with normal running. These VV and IE moments are believed to be responsible for placing knee joint ligaments at a higher risk of injury. Compared with straight running, the external loads of flexion, valgus, and internal rotation during sidestepping have the potential to substantially increase the load experienced by the ACL and MCL, whereas the combined flexion and varus loads during the crossover could potentially place large loads on the LCL. These external loads are of an order of magnitude that could cause injuries to the knee joint ligaments if the action of the knee muscles do not adequately support the combined loads. However, there are other important factors that may also modulate the risk of injury such as loading rate, muscle fatigue state, previous ligament injury, mechanical properties of the ligaments, and other anatomical/ geometric factors such as knee and intercondylar notch width. Address for correspondence: David Lloyd, Department of Human Movement & Exercise Science, The University of Western Australia, Nedlands, Perth, Western Australia 6907; E-mail: dlloyd@cyllene. uwa.edu.au.

REFERENCES 1. ANTONSSON, E. K., and R. W. MANN. The frequency content of gait. J. Biomech. 18:39 – 47, 1985. 2. BEYNNON, B., J. G. HOWE, M. H. POPE, R. J. JOHNSON, and B. C. FLEMING. The measurement of anterior cruciate ligament strain in vivo. Int. Orthop. 16:1–12, 1992. 3. BRANCH, T. P., R. HUNTER, and M. DONATH. Dynamic EMG analysis of anterior cruciate deficient legs with and without bracing during cutting. Am. J. Sports Med. 17:35– 41, 1989.

1174

Official Journal of the American College of Sports Medicine

4. CICCOTTI, M. G., R. K. KERLAN, J. PERRY, and M. PINK. An electromyographic analysis of the knee during functional activities: I. The normal profile. Am. J. Sports Med. 22:645– 650, 1994. 5. CROSS, M. J., N. J. GIBBS, and G. J. BRYANT. An analysis of the sidestep cutting manoeuvre. Am. J. Sports Med. 17:363–366, 1989. 6. DAVIS, R. B., S. OUNPUU, D. TYBURSKI, and J. R. GAGE. A gait analysis data collection and reduction technique. Hum. Mov. Sci. 10:575–587, 1991. http://www.acsm-msse.org

7. GROOD, E. S., F. R. NOYES, D. L. BUTLER, and W. J. SUNTAY. Ligamentous and capsular restraints preventing straight medial and lateral laxity in intact human cadaver knees. J. Bone Joint Surg. (Am.) 63:1257–1269, 1981. 8. KADABA, M. P., H. K. RAMAKRISHNAN, M. E. WOOTTEN, J. GAINEY, G. GORTON, and G. V. COCHRAN. Repeatability of kinematic, kinetic, and electromyographic data in normal adult gait. J. Orthop. Res. 7:849 – 860, 1989. 9. KADABA, M. P., H. K. RAMAKRISHNAN, and M. E. WOOTTEN. Measurement of lower extremity kinematics during level walking. J. Orthop. Res. 8:383–392, 1990. 10. LLOYD, D. G., and T. S. BUCHANAN. A model of load sharing between muscles and soft tissues at the human knee during static tasks. J. Biomech. Eng. 118:367–376, 1996. 11. MARKOLF, K. L., J. S. MENSCH, and H. C. AMSTUTZ. Stiffness and laxity of the knee: the contributions of the supporting structures. J. Bone Joint Surg. (Am.) 58A:583–593, 1976. 12. MARKOLF, K. L., D. C. WASCHER, and G. A. FINERMAN. Direct in vitro measurement of forces in the cruciate ligaments. Part II: The effect of section of the posterolateral structures. J. Bone Joint Surg. (Am.) 75:387–394, 1993. 13. MARKOLF, K. L., D. M. BURCHFIELD, M. M. SHAPIRO, M. F. SHEPARD, G. A. FINERMAN, and J. L. SLAUTERBECK. Combined knee loading states that generate high anterior cruciate ligament forces. J. Orthop. Res. 13:930 –935, 1995. 14. MCLEAN, S. G., P. T. MYERS, R. J. NEAL, and M. R. WALTERS. A quantitative analysis of knee joint kinematics during the sidestep cutting maneuver: implications for non-contact anterior cruciate ligament injury. Bull. Hosp. Joint Dis. 57:30 –38, 1998. 15. MCLEAN, S. G., R. J. NEAL, P. T. MYERS, and M. R. WALTERS. Knee joint kinematics during the sidestep cutting maneuver: potential for injury in women. Med. Sci. Sports Exerc. 31:959 –968, 1999.

LOADING AT THE KNEE DURING CUTTING TASKS

16. NEPTUNE, R. R., I. C. WRIGHT, and A. J. VAN DEN BOGERT. Muscle coordination and function during cutting movements. Med. Sci. Sports Exerc. 31:294 –301, 1999. 17. NOVACHECK, T. F. The biomechanics of running. Gait & Posture 7:77–95, 1998. 18. OUNPUU, S. The biomechanics of walking and running. Clin. Sports Med. 13:843– 863, 1994. 19. PANDY, M. G., and K. B. SHELBURNE. Dependence of cruciateligament loading on muscle forces and external load. J. Biomech. 30:1015–1024, 1997. 20. PIZIALI, R. L., J. RASTEGAR, D. A. NAGEL, and D. J. SCHURMAN. The contribution of the cruciate ligaments to the load-displacement characteristics of the human knee joint. J. Biomech. Eng. 102: 277–283, 1980. 21. PIZIALI, R. L., D. A. NAGEL, T. KOOGLE, and R. WHALEN. Knee and tibia strength in snow skiing. In R. J. Johnson, W. Hauser, and M. Magi (Eds.). In Ski Trauma and Skiing Safety IV. Munich: TUV Publication Series, 1982, pp. 24 –31. 22. RYDER, S. H., R. J. JOHNSON, B. D. BEYNNON, and C. F. ETTLINGER. Prevention of ACL injuries. J. Sport Rehabil. 6:80 –96, 1997. 23. SEERING, W. P., R. L. PIZIALI, D. A. NAGEL, and D. J. SCHURMAN. The function of the primary ligaments of the knee in varus-valgus and axial rotation. J. Biomech. 13:785–794, 1980. 24. WASCHER, D. C., K. L. MARKOLF, M. S. SHAPIRO, and G. A. FINERMAN. Direct in vitro measurement of forces in the cruciate ligaments. Part I: The effect of multiplane loading in the intact knee. J. Bone Joint Surg. (Am.) 75:377–386, 1993. 25. WHITING, W. C., and R. F. ZERNICKE. Biomechanics of Musculoskeletal Injury. Champaign, IL: Human Kinetics, 1998, p. 177. 26. WINTER, D. A. Moments of force and mechanical power in jogging. J. Biomech. 16:91–97, 1983.

Medicine & Science in Sports & Exercise姞

1175