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Comparison of 2D and 3D kinematic changes during a single leg step down following neuromuscular training
Physical Therapy in Sport 12 (2011) 93e99
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Physical Therapy in Sport journal homepage: www.elsevier.com/ptsp
Original research
Comparison of 2D and 3D kinematic changes during a single leg step down following neuromuscular training Thomas J. Olson a, b, Christian Chebny d, John D. Willson a, *, Thomas W. Kernozek a, J. Scott Straker a, c a
La Crosse Institute for Movement Science, Department of Health Professions e Physical Therapy Program, University of Wisconsin e La Crosse, 1725 State Street, LaCrosse, WI 54601, United States b Howard Head Sports Medicine Centers, Vail Valley Medical Center, 181 W Meadow Drive, Vail, CO 81657, United States c Gundersen Lutheran Sports Medicine, 311 Gundersen Drive, Onalaska, WI 54650, United States d Aurora Sports Medicine Institute, 945 North 12th Street, Suite 1100, Milwaukee, WI 53201, United States
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 May 2010 Received in revised form 21 July 2010 Accepted 12 October 2010
Objectives: Evaluate the effects of a weight-bearing neuromuscular training program on 2D and 3D lower extremity kinematics during a single leg step down. Design: Pre-test, post-test quasi experimental. Setting: Laboratory. Participants: Sixty nine healthy females performed a single leg step down. The 20 females with the most medial knee orientation during this task participated in this study (20.0 yr (1.6 yr), 167.9 cm (6.0 cm), 63.2 kg (8.3 kg)). Main Outcome Measures: 2D knee frontal plane projection angle (FPPA) and 3D lower extremity joint (hip and knee) and segment (pelvis and femur) angles during a single leg step down before and after training were compared using paired t-tests. Pearson correlation coefficients were used to measure the association of 2D and 3D kinematic changes following training. Results: Knee FPPA decreased 4.6 after training (P < 0.001). Hip flexion (P < 0.001) and hip adduction (P ¼ 0.04) increased after training. However, no other 3D joint kinematic changes were observed. Segment angle changes included decreased femoral internal rotation (P ¼ 0.008) and adduction (P ¼ 0.08) and increased anterior pelvic tilt (P < 0.001) and contralateral pelvic drop (P ¼ 0.02). The association between changes in 2D and 3D joint kinematics ranged from 0.12 to 0.34. Conclusions: Exercises intended to improve altered lower extremity kinematics may reduce medial knee 2D FPPA values during a single leg step down. However, this 2D change may not be linked with any specific change in 3D joint kinematics. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Biomechanics Exercise therapy Female Knee valgus
1. Introduction Knee injuries due to either trauma or overuse remain particularly common among females and account for one third of all missed participation in practices and games (Agel, Olson, Dick, Arendt, Marshall, & Sikka, 2007; de Loes, Dahlstedt, & Thomee, 2000). Females are reported to have a 2e7 times greater risk for non-contact anterior cruciate ligament (ACL) tears compared to males (Agel et al., 2007; Arendt, Agel, & Dick, 1999). Females are also more likely to be affected by patellofemoral pain syndrome * Corresponding author. 4075 Health Science Center, Department of Health Professions e Physical Therapy Program, University of Wisconsin e La Crosse, 1725 State Street, La Crosse, WI 54601, United States. Tel.: þ1 608 785 8472; fax: þ1 608 785 8460. E-mail addresses: [email protected] (T.J. Olson), christian.chebny@ aurora.org (C. Chebny), [email protected] (J.D. Willson), kernozek.thom@ uwlax.edu (T.W. Kernozek), [email protected] (J.S. Straker). 1466-853X/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ptsp.2010.10.002
(PFPS) than males (Fulkerson & Arendt, 2000; Taunton, Ryan, Clement, McKenzie, Lloyd-Smith, & Zumbo, 2002). Altered kinematics during weight bearing activities have been associated with knee injuries among female athletes (Hewett et al., 2005; Levinger, Gilleard, & Coleman, 2007; Souza & Powers, 2009; Willson & Davis, 2008a). In a prospective study, athletes with noncontact ACL tears demonstrated greater three-dimensional (3D) knee abduction (i.e. tibial abduction relative to the femur) angles during drop landing compared to those who were not injured (Hewett et al., 2005). Females with PFPS have been found to demonstrate greater hip internal rotation during running, landing, and squatting (Souza & Powers, 2009) as well as greater two-dimensinal (2D) knee medial displacement during a single leg squat compared to healthy controls (Levinger et al., 2007; Willson & Davis, 2008a). Changing altered lower extremity kinematics is of great interest to many health care professionals. Based on several reports of
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decreased hip abduction, extension, and external rotation strength among females with lower extremity injuries, hip strengthening exercises are included in the plan of care for many injured athletes (Bolgla, Malone, Umberger, & Uhl, 2008; Souza & Powers, 2009; Willson, Binder-Macleod, & Davis, 2008). However, progressive resistance training of the hip and knee joint musculature has not been shown to consistently reduce injury risk or make meaningful changes to lower extremity kinematics. A meta-analysis of training interventions to reduce ACL injury risk suggests effective training programs typically include kinematic feedback but may not include strength training (Hewett, Ford, & Myer, 2006). Other recent studies reveal no effect of lower extremity strengthening on hip or knee joint kinematics during landing unless subjects were also provided video feedback of their landing technique (Herman et al., 2009; Herman, Weinhold, Guskiewicz, Garrett, Yu, & Padua, 2008). Finally, hip adduction motion during running increased following a strength training program to increase hip abductor and external rotation strength among healthy female runners (Snyder, Earl, O’Connor, & Ebersole, 2009). These findings suggest that despite the intuitive link between decreased hip strength and altered hip and knee joint kinematics, strength changes may not minimize undesirable joint motions during weight bearing activities. Movement based training, often referred to as neuromuscular training, may improve lower extremity kinematics of female athletes. These programs tend to be 6e12 weeks in duration and frequently utilize visual feedback to focus on reduction of transverse and frontal plane lower extremity joint motion during weight bearing activities (Chappell & Limpisvasti, 2008; Herman et al., 2009; Mandelbaum et al., 2005; Myklebust, Engebretsen, Braekken, Skjolberg, Olsen, & Bahr, 2003; Pollard, Sigward, & Powers, 2007). For example, Pollard, Sigward, Ota, Langford, and Powers (2006) reported reduced hip internal rotation and less hip adduction during landing among soccer players who participated in a neuromuscular training program over the course of a single season. However, due to the extended time frame of these previous interventions, it could be argued that these seemingly positive training effects are due to hypertrophic changes in lower extremity musculature (Moritani & deVries, 1979). Interventions of shorter duration may be necessary in order to differentiate the contribution of neuromuscular training from muscle hypertrophy on lower extremity kinematics. The values of neuromuscular training are increased if it leads to meaningful, objective changes in lower extremity kinematics that are measurable in a clinical setting. Three-dimensional motion analysis has been referred to as the “gold standard” for kinematic evaluation due to its greater reliability and validity compared to many clinical lower extremities kinematic measurements. However, the expense of equipment, skills needed for operation and data interpretation, and time and space requirements appear to prohibit large scale clinical use (McLean, Walker, Ford, Myer, Hewett, & van den Bogert, 2005; Willson & Davis, 2008a). Several authors have suggested that the use of 2D analysis may be a practical alternative for identification of medial knee displacement during task performance (McLean et al., 2005; Willson & Davis, 2008a). Although 2D assessment is not a substitute for 3D motion analysis, some methods have been reported to be reliable in quantifying lower extremity kinematics between and within treatment sessions (Levinger et al., 2007; Miller & Callister, 2009; Willson, Ireland, & Davis, 2006). Relationships between 2D and 3D measures may enable clinical estimates of altered kinematics (McLean et al., 2005; Willson & Davis, 2008a). To our knowledge, there is no evidence regarding how well these 2D measures represent 3D lower extremity kinematic changes following a specific movement training intervention. Clinicians are frequently interested in lower extremity kinematics during running, jumping, and lateral cutting. However, the inadequate sampling rate of most video cameras make it difficult to quantify 2D
kinematics during these high speed activities. Consequently, many investigators use a digital camera and some variation of a single leg step down or squat task to assess 2D lower extremity kinematics. This is a slow movement, yet the frontal plane knee kinematics demonstrated during this movement may relate to the kinematics measured during running and landing (Claiborne, Armstrong, Gandhi, & Pincivero, 2006; Shields et al, 2005; Willson & Davis, 2008b; Zeller, McCrory, Kibler, &Uhl, 2003). This movement has also been advocated as a screening tool in assessing hip strength and frontal and transverse plane control (Earl, Monteiro, & Snyder, 2007; Zeller et al., 2003). Little evidence depicts the effects of neuromuscular training alone among females with altered lower extremity kinematics. Further, it is unknown if 2D techniques used to quantify altered kinematics are valid and sensitive enough to detect changes due to training. Therefore, our purpose was to evaluate the effects of a weight bearing neuromuscular training program on changes in 2D and 3D lower extremity kinematics among subjects with increased medial knee displacement during a single leg step down. We hypothesized that a neuromuscular training program would minimize 2D medial knee orientation and decrease 3D hip adduction, internal rotation, knee abduction, and knee external rotation. Additionally, we hypothesized that this 2D change would be correlated with these 3D kinematic changes. 2. Methods 2.1. Subjects A more medial knee position during weight bearing activities has been associated with patellofemoral pain and may represent increased risk for ACL injury (Levinger et al., 2007; Myer, Ford, Khoury, Succop, & Hewett, 2010; Powers, 2003; Willson & Davis, 2008a). Thus, we aimed to enroll females who demonstrate the greatest medial knee position during a single leg squat as they may be more likely to participate in a structured neuromuscular training program designed by a physical therapist (prior to or after injury). Using a ¼ 0.05, b ¼ 0.2, and a recent estimate of within group variability of 2D and 3D kinematics during a step down (Willson & Davis, 2008a), we determined that 18 subjects were necessary to identify kinematic changes after training with an effect size >0.7. To find these 18 females with the most medial knee position during a single leg squat, we screened 69 active and apparently healthy females with an age range of 18e25 years who were recruited from a university population (Fig. 1). No potential subject had a history of lower extremity surgical intervention or chronic or accidental injury over the last 6 months. Each subject was a regular participant in weight-bearing exercises at least 3 times/week for 30 min. Exclusion criteria included reports of lower extremity injury within the last 3 months requiring medical treatment, history of lower extremity surgery, or pain or restriction with running, jumping, or stair negotiation. Appropriate ethical approval had been granted prior to the commencement of the study and all participants provided informed consent prior to participation. 2.2. Procedures 2.2.1. 2D analysis The 2D medial knee kinematics during a single leg step down using a 20.3 cm step were recorded with a digital camera (Samsung model L200, Samsung Electronics, Ridgefield, NJ USA) for all 69 female volunteers. Similar step heights have been utilized in stair stepping investigations in individuals with patellofemoral pain (Powers, Perry, Hsu, & Hislop, 1997; Salsich, Brechter, & Powers, 2001). This measurement has been described as frontal plane projection angle (FPPA) (Willson & Davis, 2008a). The camera was leveled and placed on a tripod at a height of 70 cm from the floor,
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Fig. 1. Marks used to determine the frontal plane projection angle (FPPA) during single leg step downs.
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7.6 m to the front and perpendicular to the 20.3 cm step. Each participant wore the same shoe model (Running shoe model 629, New Balance Boston, MA, USA) to avoid variability in different sole materials between subjects and all testing sessions. Two millimeter adhesive markers were placed only on the dominant leg (preferred leg used to kick a ball as far as possible). A tape measure was used to bisect the ankle malleoli and femoral condyles. Markers were placed at these locations. The tape was then used to form a line from the anterior superior iliac spine (ASIS) to the knee joint marker and a marker was placed on this line approximately 30 cm above the knee marker. Next, subjects were provided both a demonstration and verbal instruction on performing the step down without specific directions on knee and hip alignment. There was a 60 s rest period between practice trials and measured performance trials (Parcell, Sawyer, Tricoli, & Chinevere, 2002; Theou, Gareth, & Brown, 2008). Each step down was to be completed over a 5-s interval (Willson & Davis, 2008a) from descent to ascent paced by a digital metronome (Qt 3 Digital Metronome, Model 96204X, Mel Bay Publications Pacific, MO) set at 60 beats/minute. The initiation of the step down occurred at 1 s (beat 1), lowering their non-stance leg until their heel lightly touched the floor in front of the step at 3 s (beat 3), and finishing in a standing position at 5 s (beat 5). A digital picture was taken at the second metronome beat during each trial. After demonstrating adequate skill, subjects performed 5 trials for analysis. The FPPA was calculated by measuring the angle formed by lines drawn between the thigh and knee markers and between the ankle and knee markers (CorelDraw v11.6, Corel Corporation, Ottawa, Ontario, Canada) (Fig. 1). Average FPPA value from the trials was calculated for each subject. Knee markers medial to thigh and ankle markers were assigned a negative FPPA value, while knee markers in a lateral position were assigned positive FPPA values. Of the original 69 volunteers, the 20 subjects with the most negative FPPA values were invited to participate in the study [age ¼ 20.0 yr (SD ¼ 1.6 yr), height ¼ 167.9 cm (SD ¼ 6.0 cm), mass ¼ 63.2 kg (SD ¼ 8.3 kg), Tegner Activity Rating mode ¼ 7.0 (range ¼ 5e9)]. Twenty were chosen to account for the possibility of dropouts in this investigation. Eighteen of these 20 subjects participated in all phases of the study and were included in the statistical analysis (Fig. 2). 2.2.2. Strength testing Peak isometric hip abduction and external rotation strength were tested based on the premise that these strength deficiencies may contribute to greater medial knee displacement during functional tasks (Bolgla et al., 2008; Powers, 2003; Willson et al., 2006). Prior to strength testing, subjects warmed up on a stationary bike for 5 min. Hip abduction strength testing was performed with subjects in a side-lying position with the hip in zero degrees of abduction (Bohannon, 1997). A hand-held dynamometer (Model 01160, Lafayette Instruments, Lafayette, IN) was placed 2.5 cm proximal to the lateral femoral condyle and stabilized with a strap around a treatment table. Hip external rotation strength testing was performed in prone with the knee flexed to 90 and the dynamometer positioned 2.5 cm proximal to the medial malleolus. After one sub-maximal practice trial and one maximal practice trial, subjects performed three maximal effort trials lasting 5 s each. 60 s of rest occurred between trials. Average peak force for hip abduction and external rotation was analyzed. These procedures were repeated following the conclusion of the 4 week neuromuscular training program.
Fig. 2. Flowchart of subject progression in this pre-test, post-test quasi experimental study.
2.2.3. 3D analysis Following strength testing, 3D lower extremity kinematics were recorded as subjects repeated the single leg step down performed in the 2D screening. A modified Helen Hayes marker set was used. Specifically, tracking markers were placed on the right and left ASIS,
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the sacrum, the right and left posterior superior iliac spine, the anterior thigh, the lateral femoral condyle, the tibial tuberosity, anterior shank, the lateral malleolus, and the dorsum, heel, and toe of each subject’s shoe. Temporary markers on the medial femoral condyle and medial malleolus were also used to determine the knee and ankle joint centers, which were removed prior to step down trials. The 3D marker coordinate data were captured at 240 Hz using an 8 camera motion analysis system (Motion Analysis Corporation, Santa Rosa, CA, USA). These data were smoothed at 12 Hz using a 4th order recursive Butterworth low pass filter. Hip and knee joint kinematics were calculated from the local coordinate data using Motion Monitor Software (Version 7.0, Innovative Sports Training, Chicago, IL, USA). Pelvis and femur segment kinematics were also calculated with respect to the laboratory coordinate system. The Euler sequence for segment rotations was flexioneextension, abductioneadduction, and internaleexternal rotation. A static trial was used to define joint centers of the knee and ankle. The hip joint center was determined based on pelvis coordinates (Seidel, Marchinda, Dijkers, &Soutas-Little, 1995). Segment and joint kinematics were not normalized to the static trial. Therefore, zero degrees of rotation corresponded with an erect posture at the knee and hip. For the ankle, the foot segment was positioned at a right angle to the shank. Subjects performed 5 metronome paced trials of the step down task as described. An external trigger was utilized to time stamp the 3D kinematic data at the 2-s mark during the step down to coincide with the 2D FPPA obtained previously. Custom software was used to generate the discrete variables of interest from the time series kinematic data including hip and knee joint and pelvis and femur segment angles during the step down at the time of the time stamp of the external trigger from each trial (LabView 8.6; National Instruments, Austin, TX, USA). 2.2.4. Neuromuscular training Subjects participated in a 4-week neuromuscular training program (Table 1). Previous studies that used neuromuscular training and weight bearing exercises with significant gluteus medius and maximus activation were included in our program (Chappell & Limpisvasti, 2008; Distefano, Blackburn, Marshall, & Padua, 2009; Krause, Jacobs, Pilger, Sather, Sibunka, & Hollman, 2009; Mascal, Landel, & Powers, 2003). Subjects received instruction and performance feedback from a licensed physical therapist 1 time/week including verbal and tactile feedback, plus visual feedback using a mirror for all exercises. Instructions regarding keeping the knee in line with the hip and foot in the frontal plane, the pelvis parallel with the floor, and to increase hip flexion to avoid anterior motion of the knee beyond the foot were employed. All exercises were performed independently an additional 2 times/week with Table 1 Exercise progression utilized during 4-week neuromuscular training program.
Week 0e1
Week 1e2
Weeks 2e4
Exercise
Volume
Wall or form squat Forward lunge Lateral step-down 4" step Single-leg stance with ball toss
3 3 3 3
sets sets sets sets
of of of of
10 10 10 30
repetitions repetitions repetitions s
Lateral step-down 7" step Forward step-up 7" step Single-leg deadlift Lateral shuffles with theraband
3 3 3 3
sets sets sets sets
of of of of
10 10 10 40
repetitions repetitions repetitions feet
Forward step-down 7" step Balance lunge Single-leg multidirectional deadlift Single-leg squat with theraband
3 3 3 3
sets sets sets sets
of of of of
10 repetitions 10 repetitions 5 repetitions 10 repetitions
use of a mirror. An exercise log was used to foster home exercise compliance. To standardize results from the program, all subjects followed the same exercise progression (Table 1). After the 4-week training period, subjects returned for post testing where no specific directions regarding lower extremity alignment were provided. A series of paired samples t-statistics (a ¼ 0.05) was used to compare the change in discrete 2D and 3D kinematic variables, as well as isometric hip strength measures following training. Effect sizes were calculated to illustrate the magnitude of change in these variables. Finally, Pearson correlation coefficients were used to describe pre-post training changes in 2D FPPA and changes in 3D joint kinematics. 3. Results Eighteen of 20 subjects completed all phases of the study including neuromuscular training and post testing. (Fig. 2) Exercise logs indicated all subjects who completed the study performed the exercises 3 times/week and that 85% of the exercises were performed using a mirror for alignment based lower extremity visual feedback. Post training there were changes in 2D and 3D kinematics, as well as isometric hip strength. FPPA measured less medial position of the knee during the single leg step down. Specifically, a 4.6 reduction in FPPA occurred following training (effect size ¼ 1.2, P ¼ 0.001). There was a 12% increase in hip abduction strength (P ¼ 0.18) and a 35% increase in isometric hip external rotation strength (P ¼ 0.013). (Table 2) Three dimensional results during the step down after training included decreased femoral internal rotation (effect size ¼ 0.61, P ¼ 0.008), increased contralateral pelvic drop (effect size ¼ 0.60, P ¼ 0.02), increased anterior pelvic tilt (effect size ¼ 2.1, P < 0.001), increased hip adduction (effect size ¼ 0.52, P ¼ 0.04), and increased hip flexion (effect size ¼ 1.9, P < 0.001). No differences in 3D knee abduction, knee external rotation, or hip internal rotation were identified. (Table 3) Changes in 2D FPPA were poorly correlated with 3D joint kinematic changes during the step down (range r ¼ 0.32e0.36). The relationship between the change in 2D and 3D measures with training explained only 10e12% of the variability in FPPA and each discrete 3D variable. (Table 4) 4. Discussion The main purpose of this study was to test for changes in 2D and 3D lower extremity kinematics during a single leg step down following a weight bearing neuromuscular training program among female subjects with a clinical sign of altered lower extremity kinematics. Two-dimensional methods have been reported to be moderately associated with 3D knee abduction, knee external rotation, and hip adduction angles (McLean et al., 2005; Willson & Davis, 2008a). However, to our knowledge, this 2D method has not been compared with 3D kinematic outcomes
Table 2 Two dimensional frontal plane projection angle (FPPA) and hip isometric strength values (Mean SD) for females with greatest medial knee displacement pre and post-training (n ¼ 18). * Statistically significant change (P < 0.05). Group
Pre-training
Post-training
Effect size of change
P-value of change
FPPA ( ) Hip abduction (kg) Hip external rotation (kg)
8.0 3.0 17.7 5.3 5.9 2.4
3.4 4.9 19.8 5.1 7.9 2.8
1.21 0.40 0.77
0.001* 0.18 0.01*
T.J. Olson et al. / Physical Therapy in Sport 12 (2011) 93e99 Table 3 Average ( SD) joint and segment 3D kinematics at the midpoint of the descent phase of a single leg step down among females with greatest medial knee displacement before and after training (n ¼ 18). * Statistically significant change (P < 0.05). Variable (degrees)
Pre-training
Knee flexion Knee adduction Knee external rotation Hip flexion Hip internal rotation Hip adduction Anterior pelvic tilt Contalateral pelvic drop Pelvic internal rotation Femur adduction Femur internal rotation
54.8 1.4 5.5 15.8 1.2 11.6 1.5 2.1 0.7 10.3 5.7
9.6 5.2 8.5 7.0 4.3 4.3 3.8 2.9 5.1 2.2 6.4
Post-training 55.6 0.0 6.3 31.3 0.0 14.1 7.9 4.2 3.4 7.2 1.9
7.9 4.6 7.7 9.3 4.0 5.4 5.3 4.1 4.4 6.7 6.1
Effect size of change
P-value of change
0.09 0.29 0.10 1.90 0.29 0.52 2.07 0.60 0.86 0.76 0.61
0.99 0.11 0.99 0.000 * 0.14 0.04 * 0.000 * 0.02 * 0.01 * 0.08 * 0.008 *
following a neuromuscular training program intended to minimize altered weight bearing kinematics. Therefore, the validity of this 2D method to measure 3D kinematic changes due to training response is unknown. Consistent with our hypotheses, 2D knee FPPA values increased from 8.0 to 3.4 following training. This is indicative of the knee being in a position that is less medial relative to a line from the ankle to the thigh markers during the step down. The mirror feedback and verbal cues such as “knees over toes” or “maintain neutral alignment” during the exercises in this study are representative of contemporary clinical practice for rehabilitation of individuals with PFPS or ACL reconstruction (Mascal et al., 2003; Risberg, Holm, Myklebust, & Engebretsen, 2007). These visual and verbal cues are used on the premise they promote decreased 3D transverse or frontal plane knee and hip joint rotations that may contribute to the etiology or exacerbation of such lower extremity injuries. Indeed, females with PFPS have been found to demonstrate a greater 2D medial orientation of the knee than females without during a single leg squat (Levinger et al., 2007; Willson & Davis, 2008a) as well as increased 3D hip internal rotation, hip adduction, and knee external rotation during a variety of activities (Salsich & Long-Rossi, 2010; Souza & Powers, 2009; Willson & Davis, 2008b). It is logical to conclude then that less negative 2D knee FPPA values after training would be accompanied by 3D kinematic changes believed to be beneficial for these individuals. As such, clinicians would be likely to interpret the 2D kinematic changes observed in this study as a positive rehabilitation outcome. Three dimensional joint rotation changes following the training were not consistent with our hypotheses. For example, subjects demonstrated a 2.5 increase in 3D hip adduction during the step down post-training. Interestingly, the femur of the stance leg was less adducted, i.e. oriented in a more vertical position relative to the floor, during the step down after training. Thus, this increase in hip adduction appears due to increased pelvic drop of the non weight bearing leg rather than increased femoral adduction of the stance leg. Greater contralateral pelvic drop may be related to greater hip flexion during the step down. Dostal, Soderberg, and Andrews (1986)
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reported that the hip abduction moment arm of the gluteus medius muscle decreases with greater hip flexion. Thus, hip abduction torque may be compromised as hip flexion increases. Consequently, it may be difficult for people who participate in this program to maintain a level pelvis. Hip abductor strengthening in addition to this neuromuscular training program may increase the force output associated with a gluteus medius muscle contraction. This greater muscle force may mitigate the effect of the decreased hip abductor moment arm on a person’s ability to generate hip abductor torque. Therefore, clinicians who assert the importance of a neutral pelvis may wish to add specific gluteus medius strength exercises to a neuromuscular training program. Indeed, kinematic training in addition to a lower extremity strengthening program has recently been reported to decrease hip adduction during landing (Herman et al., 2009). Also in contrast to our hypotheses, there was no statistically significant decrease in 3D hip joint internal rotation during the step down after training. Interestingly, however, the step down was performed with less femur internal rotation of the stance leg and more pelvis internal rotation after training. Since hip joint kinematics are calculated from the orientation of the femur relative to the pelvis segment, it seems likely that these two changes would result in decreased hip internal rotation. However, our data reveal only a 1.2 decrease in hip internal rotation angle during the step down (ES ¼ 0.29, P ¼ 0 0.14). Due to a variety of factors including skin movement artifact, order of Euler angle decomposition, and errors replacing segment coordinate system markers between visits, transverse plane joint kinematics are inherently more variable than joint kinematics calculated in the frontal and sagittal plane. It is possible that a meaningful change in hip internal rotation occurred in this study but was obscured due to some combination of the above factors. However, one can also argue that the rotational change of the femur of the stance leg (relative to the lab coordinate system) following neuromuscular training is clinically meaningful despite no decrease in overall hip joint internal rotation. Cadaver and MRI studies suggest that femur internal rotation increases lateral patellar contact pressure (Lee, Anzel, Bennett, Pang, & Kim, 1994; Powers, Ward, Fredericson, Guillet, & Shellock, 2003). Therefore, this decrease in femoral internal rotation may be beneficial if the goal of treatment is to minimize retropatellar pressure thought to be associated with PFPS. The correlation between 2D FPPA changes and 3D frontal plane knee kinematic changes was low. The low correlation between 2D knee FPPA changes and 3D knee abduction kinematics in this study is consistent with a previous study using a single leg squat test movement (Willson & Davis, 2008a). However, 2D medial knee displacement has previously been moderately associated with greater 3D peak knee abduction during a running side cut in healthy athletes (McLean et al., 2005). The FPPA data in this study were recorded at the midpoint of the descent phase of a single leg squat, while McLean compared the 2D and 3D data at the time of peak knee abduction during a cut. The correlation between 2D and 3D knee abduction angles may improve if it is recorded at the point when 3D knee abduction is greatest. Additionally, it is possible that the correlation is greater during more dynamic activities than during our test movement.
Table 4 Pearson correlation coefficients (r) for the association between the change in 2D knee frontal plane projection angles (FPPA) and the change in 3D joint rotations during a single leg step down after movement training. Positive FPPA change values correspond with a less medial knee position. Positive 3D joint changes correspond with flexion, abduction, and internal rotation for the knee and hip.
Correlation of 2D FPPA change with 3D kinematic changes
r P-value (2-tailed)
Knee flexion
Knee abduction
Knee internal rotation
Hip flexion
Hip abduction
Hip internal rotation
0.26 0.30
0.20 0.42
0.12 0.65
0.32 0.19
0.34 0.17
0.15 0.57
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The correlation between 2D FPPA changes and all other 3D hip and knee joint kinematics in this study was also low. More medial 2D FPPA values are reported to have a moderate correlation with greater knee external rotation (r ¼ 0.48) and a low correlation with greater hip adduction (r ¼ 0.32) during single leg squats (Willson & Davis, 2008a). The somewhat higher correlation of the 2D FPPA with knee external rotation in this previous study was recorded among females with PFPS. Females with PFPS often demonstrate increased hip internal rotation and knee external rotation during weight bearing activities (Souza & Powers, 2009; Willson & Davis, 2008a, 2008b). These unique kinematics may facilitate a greater association between the 2D FPPA and 3D knee external rotation than observed among the female subjects in the present study. Our results indicate that the change in 2D knee FPPA following training is not strongly associated with any particular change in 3D joint kinematics. At best, the variance in 2D FPPA describes only 10e12% of the variability in any single 3D joint rotation in this study. Thus, the “clinical improvement” in knee alignment measured with the FPPA during a single step down does not appear to represent any unique change in 3D hip or knee joint rotation. Rather, the 2D change is likely a result of a combination of 3D joint kinematic changes or a change in the orientation of the subject relative to the digital camera during the step down, resulting in less femoral internal rotation of the stance leg relative to the lab coordinate system. It is important to clarify that we do not wish to imply that these 2D methods are not valuable. Indeed, there may be many uses for this clinical measure. For example, our results suggest that this 2D change during a step down may be indicative of less femoral internal rotation or adduction. Additionally, we believe 2D methods such as these may be useful in other ways including the use as a screening tool for future ACL injury (Myer et al., 2010). However, this 2D measure may not be a good choice for clinicians as a surrogate measure for 3D joint kinematic changes due to an intervention program. In order to examine the influence that neuromuscular training has on lower extremity kinematics it was necessary to minimize the potential contribution of hypertrophic muscle tissue changes during the study. Muscle strength changes up to 4 weeks are thought to be associated with increased recruitment rather than muscle hypertrophy (Moritani & deVries, 1979). Therefore, our intervention was designed as a 4-week program. Subjects demonstrated a 2.0 kg (34%) increase in isometric hip external rotation strength and a 2.1 kg (12%) increase in hip abduction strength following training. If increased isometric hip external rotation strength was not a consequence of gluteal muscle hypertrophy, it may represent a neuromuscular response such as increases in rate coding, synchronization, and/or recruitment post-training. Greater hip external rotation strength has been shown to be associated with less negative FPPA (r ¼ 0.4, p < 0.01) (Willson et al., 2006). Therefore, it is possible that neuromuscular adaptations to our training program increased force output of the hip external rotators and contributed to the smaller FPPA identified following training. Further studies using electromyography seem justified in order to substantiate this theory. To our knowledge, this is the first study to report 2D and 3D kinematic changes following an isolated neuromuscular training program among females who displayed altered kinematics during a weight bearing task. Our results provide some details on the efficacy of a 4 week training program on kinematics measured clinically and with 3D motion analysis. However, there are several notable limitations with our investigation. First, the absence of a control group with similar lower extremity alignment during the step down limits our ability to discern the effects of the neuromuscular training versus other influences such as repeated testing. Second, despite a 90% follow-up rate, 2 out of 20 subjects did not
return for post-testing which may overestimate or underestimate our findings. Third, we did not include a long term follow up. Thus, it is unknown if the neuromuscular training had a lasting effect on the lower extremity kinematic changes observed. Finally, these kinematics were recorded only during a single leg step down and only on female subjects who did not have lower extremity injury. Although this task is used routinely in clinical settings and may be an important aspect of sit to stand transitions and stair negotiation, evidence as to how well that the kinematics of a step down predict kinematics of more dynamic activities is limited. 5. Conclusion A 4-week neuromuscular training protocol to minimize transverse and frontal plane hip and knee joint excursion during weight bearing activities resulted in a more neutral 2D alignment of the leg during a single leg step down. Three-dimensional kinematic changes were also observed such as decreased femoral internal rotation, decreased femoral adduction, increased contralateral pelvic drop, increased anterior pelvic tilt, increased hip adduction, and increased hip flexion. Decreased femoral internal rotation and adduction may be beneficial changes for patients for whom increased retropatellar stress is a concern. However, 3D hip and knee transverse and frontal plane joint kinematics did not correlate well with FPPA changes. While the change in FPPA and decreased femoral internal rotation and adduction may be considered a positive clinical outcome, our results suggest this 2D change in lower extremity alignment should not be associated with any particular change in lower extremity 3D joint kinematics assessed during the step down task. Clinicians should not infer a change in any particular 3D hip or knee joint rotation based on a change in the 2D knee FPPA. Conflict of interest The authors assert that no financial or personal relationships exist that may lead to a conflict of interest for any author of this manuscript. Ethical statement The authors affirm that this research was conducted with respect to all basic ethical considerations for the protection of human participants in research. The protocol for this study was approved by the University of WisconsineLa Crosse Institutional Review Board and all subjects participated with informed consent. References Agel, J., Olson, D. E., Dick, R., Arendt, E. A., Marshall, S. W., & Sikka, R. S. (2007). Descriptive epidemiology of collegiate women’s basketball injuries: national collegiate athletic association injury surveillance system, 1988e1989 through 2003e2004. Journal of Athletic Training, 42(2), 202e210. Arendt, E. A., Agel, J., & Dick, R. (1999). Anterior cruciate ligament injury patterns among collegiate men and women. Journal of Athletic Training, 34(2), 86e92. Bohannon, R. (1997). Reference values for extremity muscle strength obtained by hand-held dynamometry from adults aged 20 to 79. Archives of Physical Medicine and Rehabilitation, 78, 26e31. Bolgla, L. A., Malone, T. R., Umberger, B. R., & Uhl, T. L. (2008). Hip strength and hip and knee kinematics during stair descent in females with and without patellofemoral pain syndrome. The Journal of Orthopaedic and Sports Physical Therapy, 38(1), 12e18. Chappell, J. D., & Limpisvasti, O. (2008). Effect of a neuromuscular training program on the kinetics and kinematics of jumping tasks. The American Journal of Sports Medicine, 36(6), 1081e1086. Claiborne, T. L., Armstrong, C. W., Gandhi, V., & Pincivero, D. M. (2006). Relationship between hip and knee strength and knee valgus during a single leg squat. Journal of Applied Biomechanics, 22(1), 41e50. de Loes, M., Dahlstedt, L. J., & Thomee, R. (2000). A 7-year study on risks and costs of knee injuries in male and female youth participants in 12 sports. Scandinavian Journal of Medicine & Science in Sports, 10(2), 90e97.
T.J. Olson et al. / Physical Therapy in Sport 12 (2011) 93e99 Distefano, L. J., Blackburn, J. T., Marshall, S. W., & Padua, D. A. (2009). Gluteal muscle activation during common therapeutic exercises. The Journal of Orthopaedic and Sports Physical Therapy, 39(7), 532e540. Dostal, W. F., Soderberg, G. L., & Andrews, J. G. (1986). Actions of hip muscles. Physical Theraphy, 66(3), 351e361. Earl, J. E., Monteiro, S. K., & Snyder, K. R. (2007). Differences in lower extremity kinematics between a bilateral drop-vertical jump and a single-leg step-down. The Journal of Orthopaedic and Sports Physical Therapy, 37(5), 245e252. Fulkerson, J. P., & Arendt, E. A. (2000). Anterior knee pain in females. Clinical Orthopaedics and Related Research, 372, 69e73. Herman, D. C., Onate, J. A., Weinhold, P. S., Guskiewicz, K. M., Garrett, W. E., Yu, B., et al. (2009). The effects of feedback with and without strength training on lower extremity biomechanics. The American Journal of Sports Medicine, 37(7), 1301e1308. Herman, D. C., Weinhold, P. S., Guskiewicz, K. M., Garrett, W. E., Yu, B., & Padua, D. A. (2008). The effects of strength training on the lower extremity biomechanics of female recreational athletes during a stop-jump task. The American Journal of Sports Medicine, 36(4), 733e740. Hewett, T. E., Ford, K. R., & Myer, G. D. (2006). Anterior cruciate ligament injuries in female athletes: part 2, a meta-analysis of neuromuscular interventions aimed at injury prevention. The American Journal of Sports Medicine, 34(3), 490e498. Hewett, T. E., Myer, G. D., Ford, K. R., Heidt, R. S., Jr., Colosimo, A. J., McLean, S. G., et al. (2005). Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes: a prospective study. The American Journal of Sports Medicine, 33(4), 492e501. Krause, D. A., Jacobs, R. S., Pilger, K. E., Sather, B. R., Sibunka, S. P., & Hollman, J. H. (2009). Electromyographic analysis of the gluteus medius in five weightbearing exercises. Journal of Strength and Conditioning Research, 23(9), 2689e2694. Lee, T. Q., Anzel, S. H., Bennett, K. A., Pang, D., & Kim, W. C. (1994). The influence of fixed rotational deformities of the femur on the patellofemoral contact pressure in human cadaver knees. Clinical Orthopaedics and Related Research, 302, 69e74. Levinger, P., Gilleard, W., & Coleman, C. (2007). Femoral medial deviation angle during a one-leg squat test in individuals with patellofemoral pain syndrome. Physical Therapy in Sport, 8, 163e168. Mandelbaum, B. R., Silvers, H. J., Watanabe, D. S., Knarr, J. F., Thomas, S. D., Griffin, L. Y., et al. (2005). Effectiveness of a neuromuscular and proprioceptive training program in preventing anterior cruciate ligament injuries in female athletes: 2year follow-up. The American Journal of Sports Medicine, 33(7), 1003e1010. Mascal, C. L., Landel, R., & Powers, C. (2003). Management of patellofemoral pain targeting hip, pelvis, and trunk muscle function: 2 case reports. The Journal of Orthopaedic and Sports Physical Therapy, 33(11), 647e660. McLean, S. G., Walker, K., Ford, K. R., Myer, G. D., Hewett, T. E., & van den Bogert, A. J. (2005). Evaluation of a two dimensional analysis method as a screening and evaluation tool for anterior cruciate ligament injury. British Journal of Sports Medicine, 39(6), 355e362. Miller, A., & Callister, R. (2009). Reliable lower limb musculoskeletal profiling using easily operated, portable equipment. Physical Therapy in Sport, 10(1), 30e37. Moritani, T., & deVries, H. A. (1979). Neural factors versus hypertrophy in the time course of muscle strength gain. American Journal of Physical Medicine, 58, 115e130. Myer, G. D., Ford, K. R., Khoury, J., Succop, P., & Hewett, T. E. (2010). Clinical correlates to laboratory measures for use in non-contact anterior cruciate ligament injury risk prediction algorithm. Clinical Biomechanics (Bristol, Avon), 25, 693e699. Myklebust, G., Engebretsen, L., Braekken, I. H., Skjolberg, A., Olsen, O. E., & Bahr, R. (2003). Prevention of anterior cruciate ligament injuries in female team handball players: a prospective intervention study over three seasons. Clinical Journal of Sport Medicine, 13(2), 71e78. Parcell, A. C., Sawyer, R. D., Tricoli, V. A., & Chinevere, T. D. (2002). Minimum rest period for strength recovery during a common isokinetic testing protocol. Medicine and Science in Sports and Exercise, 34(6), 1018e1022.
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Pollard, C. D., Sigward, S. M., Ota, S., Langford, K., & Powers, C. M. (2006). The influence of in-season injury prevention training on lower-extremity kinematics during landing in female soccer players. Clinical Journal of Sport Medicine, 16(3), 223e227. Pollard, C. D., Sigward, S. M., & Powers, C. M. (2007). Gender differences in hip joint kinematics and kinetics during side-step cutting maneuver. Clinical Journal of Sport Medicine, 17(1), 38e42. Powers, C. M., Perry, J., Hsu, A., & Hislop, H. J. (1997). Are patellofemoral pain and quadriceps femoris muscle torque associated with locomotor function? Physical Therraphy, 77(10), 1063e1075. Powers, C. M. (2003). The influence of altered lower-extremity kinematics on patellofemoral joint dysfunction: a theoretical perspective. The Journal of Orthopaedic and Sports Physical Therapy, 33(11), 639e646. Powers, C. M., Ward, S. R., Fredericson, M., Guillet, M., & Shellock, F. G. (2003). Patellofemoral kinematics during weight-bearing and non-weight-bearing knee extension in persons with lateral subluxation of the patella: a preliminary study. The Journal of Orthopaedic and Sports Physical Therapy, 33(11), 677e685. Risberg, M. A., Holm, I., Myklebust, G., & Engebretsen, L. (2007). Neuromuscular training versus strength training during first 6 months after anterior cruciate ligament reconstruction: a randomized clinical trial. Physical Theraphy, 87(6), 737e750. Salsich, G. B., Brechter, J. H., & Powers, C. M. (2001). Lower extremity kinetics during stair ambulation in patients with and without patellofemoral pain. Clinical Biomechanics (Bristol, Avon), 16(10), 906e912. Salsich, G. B., & Long-Rossi, F. (2010). Do females with patellofemoral pain have abnormal hip and knee kinematics during gait? Physiotherapy Theory and Practice, 26(3), 150e159. Seidel, G. K., Marchinda, D. M., Dijkers, M., & Soutas-Little, R. W. (1995). Hip joint center location from palpable bony landmarksea cadaver study. Journal of Biomechanics, 28(8), 995e998. Shields, R. K., Madhavan, S., Gregg, E., Leitch, J., Petersen, B., Salata, S., et al. (2005). Neuromuscular control of the knee during a resisted single-limb squat exercise. The American Journal of Sports Medicine, 33(10), 1520e1526. Snyder, K. R., Earl, J. E., O’Connor, K. M., & Ebersole, K. T. (2009). Resistance training is accompanied by increases in hip strength and changes in lower extremity biomechanics during running. Clinical Biomechanics (Bristol, Avon), 24(1), 26e34. Souza, R. B., & Powers, C. M. (2009). Differences in hip kinematics, muscle strength, and muscle activation between subjects with and without patellofemoral pain. The Journal of Orthopaedic and Sports Physical Therapy, 39(1), 12e19. Taunton, J., Ryan, M., Clement, D., McKenzie, D., Lloyd-Smith, D., & Zumbo, B. (2002). A retrospective case-control analysis is 2002 running injuries. British Journal of Sports Medicine, 36, 95e101. Theou, O., Gareth, J. R., & Brown, L. E. (2008). Effect of rest interval on strength recovery in young and old women. Journal of Strength and Conditioning Research, 22(6), 1876e1881. Willson, J. D., Ireland, M. L., & Davis, I. (2006). Core strength and lower extremity alignment during single leg squats. Medicine and Science in Sports and Exercise, 38(5), 945e952. Willson, J. D., Binder-Macleod, S., & Davis, I. S. (2008). Lower extremity jumping mechanics of female athletes with and without patellofemoral pain before and after exertion. The American Journal of Sports Medicine, 36(8), 1587e1596. Willson, J. D., & Davis, I. S. (2008a). Utility of the frontal plane projection angle in females with patellofemoral pain. The Journal of Orthopaedic and Sports Physical Therapy, 38(10), 606e615. Willson, J. D., & Davis, I. S. (2008b). Lower extremity mechanics of females with and without patellofemoral pain across activities with progressively greater task demands. Clinical Biomechanics (Bristol, Avon), 23(2), 203e211. Zeller, B. L., McCrory, J. L., Kibler, W. B., & Uhl, T. L. (2003). Differences in kinematics and electromyographic activity between men and women during the singlelegged squat. The American Journal of Sports Medicine, 31(3), 449e456.
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Physical Therapy in Sport journal homepage: www.elsevier.com/ptsp
Original research
Comparison of 2D and 3D kinematic changes during a single leg step down following neuromuscular training Thomas J. Olson a, b, Christian Chebny d, John D. Willson a, *, Thomas W. Kernozek a, J. Scott Straker a, c a
La Crosse Institute for Movement Science, Department of Health Professions e Physical Therapy Program, University of Wisconsin e La Crosse, 1725 State Street, LaCrosse, WI 54601, United States b Howard Head Sports Medicine Centers, Vail Valley Medical Center, 181 W Meadow Drive, Vail, CO 81657, United States c Gundersen Lutheran Sports Medicine, 311 Gundersen Drive, Onalaska, WI 54650, United States d Aurora Sports Medicine Institute, 945 North 12th Street, Suite 1100, Milwaukee, WI 53201, United States
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 May 2010 Received in revised form 21 July 2010 Accepted 12 October 2010
Objectives: Evaluate the effects of a weight-bearing neuromuscular training program on 2D and 3D lower extremity kinematics during a single leg step down. Design: Pre-test, post-test quasi experimental. Setting: Laboratory. Participants: Sixty nine healthy females performed a single leg step down. The 20 females with the most medial knee orientation during this task participated in this study (20.0 yr (1.6 yr), 167.9 cm (6.0 cm), 63.2 kg (8.3 kg)). Main Outcome Measures: 2D knee frontal plane projection angle (FPPA) and 3D lower extremity joint (hip and knee) and segment (pelvis and femur) angles during a single leg step down before and after training were compared using paired t-tests. Pearson correlation coefficients were used to measure the association of 2D and 3D kinematic changes following training. Results: Knee FPPA decreased 4.6 after training (P < 0.001). Hip flexion (P < 0.001) and hip adduction (P ¼ 0.04) increased after training. However, no other 3D joint kinematic changes were observed. Segment angle changes included decreased femoral internal rotation (P ¼ 0.008) and adduction (P ¼ 0.08) and increased anterior pelvic tilt (P < 0.001) and contralateral pelvic drop (P ¼ 0.02). The association between changes in 2D and 3D joint kinematics ranged from 0.12 to 0.34. Conclusions: Exercises intended to improve altered lower extremity kinematics may reduce medial knee 2D FPPA values during a single leg step down. However, this 2D change may not be linked with any specific change in 3D joint kinematics. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Biomechanics Exercise therapy Female Knee valgus
1. Introduction Knee injuries due to either trauma or overuse remain particularly common among females and account for one third of all missed participation in practices and games (Agel, Olson, Dick, Arendt, Marshall, & Sikka, 2007; de Loes, Dahlstedt, & Thomee, 2000). Females are reported to have a 2e7 times greater risk for non-contact anterior cruciate ligament (ACL) tears compared to males (Agel et al., 2007; Arendt, Agel, & Dick, 1999). Females are also more likely to be affected by patellofemoral pain syndrome * Corresponding author. 4075 Health Science Center, Department of Health Professions e Physical Therapy Program, University of Wisconsin e La Crosse, 1725 State Street, La Crosse, WI 54601, United States. Tel.: þ1 608 785 8472; fax: þ1 608 785 8460. E-mail addresses: [email protected] (T.J. Olson), christian.chebny@ aurora.org (C. Chebny), [email protected] (J.D. Willson), kernozek.thom@ uwlax.edu (T.W. Kernozek), [email protected] (J.S. Straker). 1466-853X/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ptsp.2010.10.002
(PFPS) than males (Fulkerson & Arendt, 2000; Taunton, Ryan, Clement, McKenzie, Lloyd-Smith, & Zumbo, 2002). Altered kinematics during weight bearing activities have been associated with knee injuries among female athletes (Hewett et al., 2005; Levinger, Gilleard, & Coleman, 2007; Souza & Powers, 2009; Willson & Davis, 2008a). In a prospective study, athletes with noncontact ACL tears demonstrated greater three-dimensional (3D) knee abduction (i.e. tibial abduction relative to the femur) angles during drop landing compared to those who were not injured (Hewett et al., 2005). Females with PFPS have been found to demonstrate greater hip internal rotation during running, landing, and squatting (Souza & Powers, 2009) as well as greater two-dimensinal (2D) knee medial displacement during a single leg squat compared to healthy controls (Levinger et al., 2007; Willson & Davis, 2008a). Changing altered lower extremity kinematics is of great interest to many health care professionals. Based on several reports of
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decreased hip abduction, extension, and external rotation strength among females with lower extremity injuries, hip strengthening exercises are included in the plan of care for many injured athletes (Bolgla, Malone, Umberger, & Uhl, 2008; Souza & Powers, 2009; Willson, Binder-Macleod, & Davis, 2008). However, progressive resistance training of the hip and knee joint musculature has not been shown to consistently reduce injury risk or make meaningful changes to lower extremity kinematics. A meta-analysis of training interventions to reduce ACL injury risk suggests effective training programs typically include kinematic feedback but may not include strength training (Hewett, Ford, & Myer, 2006). Other recent studies reveal no effect of lower extremity strengthening on hip or knee joint kinematics during landing unless subjects were also provided video feedback of their landing technique (Herman et al., 2009; Herman, Weinhold, Guskiewicz, Garrett, Yu, & Padua, 2008). Finally, hip adduction motion during running increased following a strength training program to increase hip abductor and external rotation strength among healthy female runners (Snyder, Earl, O’Connor, & Ebersole, 2009). These findings suggest that despite the intuitive link between decreased hip strength and altered hip and knee joint kinematics, strength changes may not minimize undesirable joint motions during weight bearing activities. Movement based training, often referred to as neuromuscular training, may improve lower extremity kinematics of female athletes. These programs tend to be 6e12 weeks in duration and frequently utilize visual feedback to focus on reduction of transverse and frontal plane lower extremity joint motion during weight bearing activities (Chappell & Limpisvasti, 2008; Herman et al., 2009; Mandelbaum et al., 2005; Myklebust, Engebretsen, Braekken, Skjolberg, Olsen, & Bahr, 2003; Pollard, Sigward, & Powers, 2007). For example, Pollard, Sigward, Ota, Langford, and Powers (2006) reported reduced hip internal rotation and less hip adduction during landing among soccer players who participated in a neuromuscular training program over the course of a single season. However, due to the extended time frame of these previous interventions, it could be argued that these seemingly positive training effects are due to hypertrophic changes in lower extremity musculature (Moritani & deVries, 1979). Interventions of shorter duration may be necessary in order to differentiate the contribution of neuromuscular training from muscle hypertrophy on lower extremity kinematics. The values of neuromuscular training are increased if it leads to meaningful, objective changes in lower extremity kinematics that are measurable in a clinical setting. Three-dimensional motion analysis has been referred to as the “gold standard” for kinematic evaluation due to its greater reliability and validity compared to many clinical lower extremities kinematic measurements. However, the expense of equipment, skills needed for operation and data interpretation, and time and space requirements appear to prohibit large scale clinical use (McLean, Walker, Ford, Myer, Hewett, & van den Bogert, 2005; Willson & Davis, 2008a). Several authors have suggested that the use of 2D analysis may be a practical alternative for identification of medial knee displacement during task performance (McLean et al., 2005; Willson & Davis, 2008a). Although 2D assessment is not a substitute for 3D motion analysis, some methods have been reported to be reliable in quantifying lower extremity kinematics between and within treatment sessions (Levinger et al., 2007; Miller & Callister, 2009; Willson, Ireland, & Davis, 2006). Relationships between 2D and 3D measures may enable clinical estimates of altered kinematics (McLean et al., 2005; Willson & Davis, 2008a). To our knowledge, there is no evidence regarding how well these 2D measures represent 3D lower extremity kinematic changes following a specific movement training intervention. Clinicians are frequently interested in lower extremity kinematics during running, jumping, and lateral cutting. However, the inadequate sampling rate of most video cameras make it difficult to quantify 2D
kinematics during these high speed activities. Consequently, many investigators use a digital camera and some variation of a single leg step down or squat task to assess 2D lower extremity kinematics. This is a slow movement, yet the frontal plane knee kinematics demonstrated during this movement may relate to the kinematics measured during running and landing (Claiborne, Armstrong, Gandhi, & Pincivero, 2006; Shields et al, 2005; Willson & Davis, 2008b; Zeller, McCrory, Kibler, &Uhl, 2003). This movement has also been advocated as a screening tool in assessing hip strength and frontal and transverse plane control (Earl, Monteiro, & Snyder, 2007; Zeller et al., 2003). Little evidence depicts the effects of neuromuscular training alone among females with altered lower extremity kinematics. Further, it is unknown if 2D techniques used to quantify altered kinematics are valid and sensitive enough to detect changes due to training. Therefore, our purpose was to evaluate the effects of a weight bearing neuromuscular training program on changes in 2D and 3D lower extremity kinematics among subjects with increased medial knee displacement during a single leg step down. We hypothesized that a neuromuscular training program would minimize 2D medial knee orientation and decrease 3D hip adduction, internal rotation, knee abduction, and knee external rotation. Additionally, we hypothesized that this 2D change would be correlated with these 3D kinematic changes. 2. Methods 2.1. Subjects A more medial knee position during weight bearing activities has been associated with patellofemoral pain and may represent increased risk for ACL injury (Levinger et al., 2007; Myer, Ford, Khoury, Succop, & Hewett, 2010; Powers, 2003; Willson & Davis, 2008a). Thus, we aimed to enroll females who demonstrate the greatest medial knee position during a single leg squat as they may be more likely to participate in a structured neuromuscular training program designed by a physical therapist (prior to or after injury). Using a ¼ 0.05, b ¼ 0.2, and a recent estimate of within group variability of 2D and 3D kinematics during a step down (Willson & Davis, 2008a), we determined that 18 subjects were necessary to identify kinematic changes after training with an effect size >0.7. To find these 18 females with the most medial knee position during a single leg squat, we screened 69 active and apparently healthy females with an age range of 18e25 years who were recruited from a university population (Fig. 1). No potential subject had a history of lower extremity surgical intervention or chronic or accidental injury over the last 6 months. Each subject was a regular participant in weight-bearing exercises at least 3 times/week for 30 min. Exclusion criteria included reports of lower extremity injury within the last 3 months requiring medical treatment, history of lower extremity surgery, or pain or restriction with running, jumping, or stair negotiation. Appropriate ethical approval had been granted prior to the commencement of the study and all participants provided informed consent prior to participation. 2.2. Procedures 2.2.1. 2D analysis The 2D medial knee kinematics during a single leg step down using a 20.3 cm step were recorded with a digital camera (Samsung model L200, Samsung Electronics, Ridgefield, NJ USA) for all 69 female volunteers. Similar step heights have been utilized in stair stepping investigations in individuals with patellofemoral pain (Powers, Perry, Hsu, & Hislop, 1997; Salsich, Brechter, & Powers, 2001). This measurement has been described as frontal plane projection angle (FPPA) (Willson & Davis, 2008a). The camera was leveled and placed on a tripod at a height of 70 cm from the floor,
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Fig. 1. Marks used to determine the frontal plane projection angle (FPPA) during single leg step downs.
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7.6 m to the front and perpendicular to the 20.3 cm step. Each participant wore the same shoe model (Running shoe model 629, New Balance Boston, MA, USA) to avoid variability in different sole materials between subjects and all testing sessions. Two millimeter adhesive markers were placed only on the dominant leg (preferred leg used to kick a ball as far as possible). A tape measure was used to bisect the ankle malleoli and femoral condyles. Markers were placed at these locations. The tape was then used to form a line from the anterior superior iliac spine (ASIS) to the knee joint marker and a marker was placed on this line approximately 30 cm above the knee marker. Next, subjects were provided both a demonstration and verbal instruction on performing the step down without specific directions on knee and hip alignment. There was a 60 s rest period between practice trials and measured performance trials (Parcell, Sawyer, Tricoli, & Chinevere, 2002; Theou, Gareth, & Brown, 2008). Each step down was to be completed over a 5-s interval (Willson & Davis, 2008a) from descent to ascent paced by a digital metronome (Qt 3 Digital Metronome, Model 96204X, Mel Bay Publications Pacific, MO) set at 60 beats/minute. The initiation of the step down occurred at 1 s (beat 1), lowering their non-stance leg until their heel lightly touched the floor in front of the step at 3 s (beat 3), and finishing in a standing position at 5 s (beat 5). A digital picture was taken at the second metronome beat during each trial. After demonstrating adequate skill, subjects performed 5 trials for analysis. The FPPA was calculated by measuring the angle formed by lines drawn between the thigh and knee markers and between the ankle and knee markers (CorelDraw v11.6, Corel Corporation, Ottawa, Ontario, Canada) (Fig. 1). Average FPPA value from the trials was calculated for each subject. Knee markers medial to thigh and ankle markers were assigned a negative FPPA value, while knee markers in a lateral position were assigned positive FPPA values. Of the original 69 volunteers, the 20 subjects with the most negative FPPA values were invited to participate in the study [age ¼ 20.0 yr (SD ¼ 1.6 yr), height ¼ 167.9 cm (SD ¼ 6.0 cm), mass ¼ 63.2 kg (SD ¼ 8.3 kg), Tegner Activity Rating mode ¼ 7.0 (range ¼ 5e9)]. Twenty were chosen to account for the possibility of dropouts in this investigation. Eighteen of these 20 subjects participated in all phases of the study and were included in the statistical analysis (Fig. 2). 2.2.2. Strength testing Peak isometric hip abduction and external rotation strength were tested based on the premise that these strength deficiencies may contribute to greater medial knee displacement during functional tasks (Bolgla et al., 2008; Powers, 2003; Willson et al., 2006). Prior to strength testing, subjects warmed up on a stationary bike for 5 min. Hip abduction strength testing was performed with subjects in a side-lying position with the hip in zero degrees of abduction (Bohannon, 1997). A hand-held dynamometer (Model 01160, Lafayette Instruments, Lafayette, IN) was placed 2.5 cm proximal to the lateral femoral condyle and stabilized with a strap around a treatment table. Hip external rotation strength testing was performed in prone with the knee flexed to 90 and the dynamometer positioned 2.5 cm proximal to the medial malleolus. After one sub-maximal practice trial and one maximal practice trial, subjects performed three maximal effort trials lasting 5 s each. 60 s of rest occurred between trials. Average peak force for hip abduction and external rotation was analyzed. These procedures were repeated following the conclusion of the 4 week neuromuscular training program.
Fig. 2. Flowchart of subject progression in this pre-test, post-test quasi experimental study.
2.2.3. 3D analysis Following strength testing, 3D lower extremity kinematics were recorded as subjects repeated the single leg step down performed in the 2D screening. A modified Helen Hayes marker set was used. Specifically, tracking markers were placed on the right and left ASIS,
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the sacrum, the right and left posterior superior iliac spine, the anterior thigh, the lateral femoral condyle, the tibial tuberosity, anterior shank, the lateral malleolus, and the dorsum, heel, and toe of each subject’s shoe. Temporary markers on the medial femoral condyle and medial malleolus were also used to determine the knee and ankle joint centers, which were removed prior to step down trials. The 3D marker coordinate data were captured at 240 Hz using an 8 camera motion analysis system (Motion Analysis Corporation, Santa Rosa, CA, USA). These data were smoothed at 12 Hz using a 4th order recursive Butterworth low pass filter. Hip and knee joint kinematics were calculated from the local coordinate data using Motion Monitor Software (Version 7.0, Innovative Sports Training, Chicago, IL, USA). Pelvis and femur segment kinematics were also calculated with respect to the laboratory coordinate system. The Euler sequence for segment rotations was flexioneextension, abductioneadduction, and internaleexternal rotation. A static trial was used to define joint centers of the knee and ankle. The hip joint center was determined based on pelvis coordinates (Seidel, Marchinda, Dijkers, &Soutas-Little, 1995). Segment and joint kinematics were not normalized to the static trial. Therefore, zero degrees of rotation corresponded with an erect posture at the knee and hip. For the ankle, the foot segment was positioned at a right angle to the shank. Subjects performed 5 metronome paced trials of the step down task as described. An external trigger was utilized to time stamp the 3D kinematic data at the 2-s mark during the step down to coincide with the 2D FPPA obtained previously. Custom software was used to generate the discrete variables of interest from the time series kinematic data including hip and knee joint and pelvis and femur segment angles during the step down at the time of the time stamp of the external trigger from each trial (LabView 8.6; National Instruments, Austin, TX, USA). 2.2.4. Neuromuscular training Subjects participated in a 4-week neuromuscular training program (Table 1). Previous studies that used neuromuscular training and weight bearing exercises with significant gluteus medius and maximus activation were included in our program (Chappell & Limpisvasti, 2008; Distefano, Blackburn, Marshall, & Padua, 2009; Krause, Jacobs, Pilger, Sather, Sibunka, & Hollman, 2009; Mascal, Landel, & Powers, 2003). Subjects received instruction and performance feedback from a licensed physical therapist 1 time/week including verbal and tactile feedback, plus visual feedback using a mirror for all exercises. Instructions regarding keeping the knee in line with the hip and foot in the frontal plane, the pelvis parallel with the floor, and to increase hip flexion to avoid anterior motion of the knee beyond the foot were employed. All exercises were performed independently an additional 2 times/week with Table 1 Exercise progression utilized during 4-week neuromuscular training program.
Week 0e1
Week 1e2
Weeks 2e4
Exercise
Volume
Wall or form squat Forward lunge Lateral step-down 4" step Single-leg stance with ball toss
3 3 3 3
sets sets sets sets
of of of of
10 10 10 30
repetitions repetitions repetitions s
Lateral step-down 7" step Forward step-up 7" step Single-leg deadlift Lateral shuffles with theraband
3 3 3 3
sets sets sets sets
of of of of
10 10 10 40
repetitions repetitions repetitions feet
Forward step-down 7" step Balance lunge Single-leg multidirectional deadlift Single-leg squat with theraband
3 3 3 3
sets sets sets sets
of of of of
10 repetitions 10 repetitions 5 repetitions 10 repetitions
use of a mirror. An exercise log was used to foster home exercise compliance. To standardize results from the program, all subjects followed the same exercise progression (Table 1). After the 4-week training period, subjects returned for post testing where no specific directions regarding lower extremity alignment were provided. A series of paired samples t-statistics (a ¼ 0.05) was used to compare the change in discrete 2D and 3D kinematic variables, as well as isometric hip strength measures following training. Effect sizes were calculated to illustrate the magnitude of change in these variables. Finally, Pearson correlation coefficients were used to describe pre-post training changes in 2D FPPA and changes in 3D joint kinematics. 3. Results Eighteen of 20 subjects completed all phases of the study including neuromuscular training and post testing. (Fig. 2) Exercise logs indicated all subjects who completed the study performed the exercises 3 times/week and that 85% of the exercises were performed using a mirror for alignment based lower extremity visual feedback. Post training there were changes in 2D and 3D kinematics, as well as isometric hip strength. FPPA measured less medial position of the knee during the single leg step down. Specifically, a 4.6 reduction in FPPA occurred following training (effect size ¼ 1.2, P ¼ 0.001). There was a 12% increase in hip abduction strength (P ¼ 0.18) and a 35% increase in isometric hip external rotation strength (P ¼ 0.013). (Table 2) Three dimensional results during the step down after training included decreased femoral internal rotation (effect size ¼ 0.61, P ¼ 0.008), increased contralateral pelvic drop (effect size ¼ 0.60, P ¼ 0.02), increased anterior pelvic tilt (effect size ¼ 2.1, P < 0.001), increased hip adduction (effect size ¼ 0.52, P ¼ 0.04), and increased hip flexion (effect size ¼ 1.9, P < 0.001). No differences in 3D knee abduction, knee external rotation, or hip internal rotation were identified. (Table 3) Changes in 2D FPPA were poorly correlated with 3D joint kinematic changes during the step down (range r ¼ 0.32e0.36). The relationship between the change in 2D and 3D measures with training explained only 10e12% of the variability in FPPA and each discrete 3D variable. (Table 4) 4. Discussion The main purpose of this study was to test for changes in 2D and 3D lower extremity kinematics during a single leg step down following a weight bearing neuromuscular training program among female subjects with a clinical sign of altered lower extremity kinematics. Two-dimensional methods have been reported to be moderately associated with 3D knee abduction, knee external rotation, and hip adduction angles (McLean et al., 2005; Willson & Davis, 2008a). However, to our knowledge, this 2D method has not been compared with 3D kinematic outcomes
Table 2 Two dimensional frontal plane projection angle (FPPA) and hip isometric strength values (Mean SD) for females with greatest medial knee displacement pre and post-training (n ¼ 18). * Statistically significant change (P < 0.05). Group
Pre-training
Post-training
Effect size of change
P-value of change
FPPA ( ) Hip abduction (kg) Hip external rotation (kg)
8.0 3.0 17.7 5.3 5.9 2.4
3.4 4.9 19.8 5.1 7.9 2.8
1.21 0.40 0.77
0.001* 0.18 0.01*
T.J. Olson et al. / Physical Therapy in Sport 12 (2011) 93e99 Table 3 Average ( SD) joint and segment 3D kinematics at the midpoint of the descent phase of a single leg step down among females with greatest medial knee displacement before and after training (n ¼ 18). * Statistically significant change (P < 0.05). Variable (degrees)
Pre-training
Knee flexion Knee adduction Knee external rotation Hip flexion Hip internal rotation Hip adduction Anterior pelvic tilt Contalateral pelvic drop Pelvic internal rotation Femur adduction Femur internal rotation
54.8 1.4 5.5 15.8 1.2 11.6 1.5 2.1 0.7 10.3 5.7
9.6 5.2 8.5 7.0 4.3 4.3 3.8 2.9 5.1 2.2 6.4
Post-training 55.6 0.0 6.3 31.3 0.0 14.1 7.9 4.2 3.4 7.2 1.9
7.9 4.6 7.7 9.3 4.0 5.4 5.3 4.1 4.4 6.7 6.1
Effect size of change
P-value of change
0.09 0.29 0.10 1.90 0.29 0.52 2.07 0.60 0.86 0.76 0.61
0.99 0.11 0.99 0.000 * 0.14 0.04 * 0.000 * 0.02 * 0.01 * 0.08 * 0.008 *
following a neuromuscular training program intended to minimize altered weight bearing kinematics. Therefore, the validity of this 2D method to measure 3D kinematic changes due to training response is unknown. Consistent with our hypotheses, 2D knee FPPA values increased from 8.0 to 3.4 following training. This is indicative of the knee being in a position that is less medial relative to a line from the ankle to the thigh markers during the step down. The mirror feedback and verbal cues such as “knees over toes” or “maintain neutral alignment” during the exercises in this study are representative of contemporary clinical practice for rehabilitation of individuals with PFPS or ACL reconstruction (Mascal et al., 2003; Risberg, Holm, Myklebust, & Engebretsen, 2007). These visual and verbal cues are used on the premise they promote decreased 3D transverse or frontal plane knee and hip joint rotations that may contribute to the etiology or exacerbation of such lower extremity injuries. Indeed, females with PFPS have been found to demonstrate a greater 2D medial orientation of the knee than females without during a single leg squat (Levinger et al., 2007; Willson & Davis, 2008a) as well as increased 3D hip internal rotation, hip adduction, and knee external rotation during a variety of activities (Salsich & Long-Rossi, 2010; Souza & Powers, 2009; Willson & Davis, 2008b). It is logical to conclude then that less negative 2D knee FPPA values after training would be accompanied by 3D kinematic changes believed to be beneficial for these individuals. As such, clinicians would be likely to interpret the 2D kinematic changes observed in this study as a positive rehabilitation outcome. Three dimensional joint rotation changes following the training were not consistent with our hypotheses. For example, subjects demonstrated a 2.5 increase in 3D hip adduction during the step down post-training. Interestingly, the femur of the stance leg was less adducted, i.e. oriented in a more vertical position relative to the floor, during the step down after training. Thus, this increase in hip adduction appears due to increased pelvic drop of the non weight bearing leg rather than increased femoral adduction of the stance leg. Greater contralateral pelvic drop may be related to greater hip flexion during the step down. Dostal, Soderberg, and Andrews (1986)
97
reported that the hip abduction moment arm of the gluteus medius muscle decreases with greater hip flexion. Thus, hip abduction torque may be compromised as hip flexion increases. Consequently, it may be difficult for people who participate in this program to maintain a level pelvis. Hip abductor strengthening in addition to this neuromuscular training program may increase the force output associated with a gluteus medius muscle contraction. This greater muscle force may mitigate the effect of the decreased hip abductor moment arm on a person’s ability to generate hip abductor torque. Therefore, clinicians who assert the importance of a neutral pelvis may wish to add specific gluteus medius strength exercises to a neuromuscular training program. Indeed, kinematic training in addition to a lower extremity strengthening program has recently been reported to decrease hip adduction during landing (Herman et al., 2009). Also in contrast to our hypotheses, there was no statistically significant decrease in 3D hip joint internal rotation during the step down after training. Interestingly, however, the step down was performed with less femur internal rotation of the stance leg and more pelvis internal rotation after training. Since hip joint kinematics are calculated from the orientation of the femur relative to the pelvis segment, it seems likely that these two changes would result in decreased hip internal rotation. However, our data reveal only a 1.2 decrease in hip internal rotation angle during the step down (ES ¼ 0.29, P ¼ 0 0.14). Due to a variety of factors including skin movement artifact, order of Euler angle decomposition, and errors replacing segment coordinate system markers between visits, transverse plane joint kinematics are inherently more variable than joint kinematics calculated in the frontal and sagittal plane. It is possible that a meaningful change in hip internal rotation occurred in this study but was obscured due to some combination of the above factors. However, one can also argue that the rotational change of the femur of the stance leg (relative to the lab coordinate system) following neuromuscular training is clinically meaningful despite no decrease in overall hip joint internal rotation. Cadaver and MRI studies suggest that femur internal rotation increases lateral patellar contact pressure (Lee, Anzel, Bennett, Pang, & Kim, 1994; Powers, Ward, Fredericson, Guillet, & Shellock, 2003). Therefore, this decrease in femoral internal rotation may be beneficial if the goal of treatment is to minimize retropatellar pressure thought to be associated with PFPS. The correlation between 2D FPPA changes and 3D frontal plane knee kinematic changes was low. The low correlation between 2D knee FPPA changes and 3D knee abduction kinematics in this study is consistent with a previous study using a single leg squat test movement (Willson & Davis, 2008a). However, 2D medial knee displacement has previously been moderately associated with greater 3D peak knee abduction during a running side cut in healthy athletes (McLean et al., 2005). The FPPA data in this study were recorded at the midpoint of the descent phase of a single leg squat, while McLean compared the 2D and 3D data at the time of peak knee abduction during a cut. The correlation between 2D and 3D knee abduction angles may improve if it is recorded at the point when 3D knee abduction is greatest. Additionally, it is possible that the correlation is greater during more dynamic activities than during our test movement.
Table 4 Pearson correlation coefficients (r) for the association between the change in 2D knee frontal plane projection angles (FPPA) and the change in 3D joint rotations during a single leg step down after movement training. Positive FPPA change values correspond with a less medial knee position. Positive 3D joint changes correspond with flexion, abduction, and internal rotation for the knee and hip.
Correlation of 2D FPPA change with 3D kinematic changes
r P-value (2-tailed)
Knee flexion
Knee abduction
Knee internal rotation
Hip flexion
Hip abduction
Hip internal rotation
0.26 0.30
0.20 0.42
0.12 0.65
0.32 0.19
0.34 0.17
0.15 0.57
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The correlation between 2D FPPA changes and all other 3D hip and knee joint kinematics in this study was also low. More medial 2D FPPA values are reported to have a moderate correlation with greater knee external rotation (r ¼ 0.48) and a low correlation with greater hip adduction (r ¼ 0.32) during single leg squats (Willson & Davis, 2008a). The somewhat higher correlation of the 2D FPPA with knee external rotation in this previous study was recorded among females with PFPS. Females with PFPS often demonstrate increased hip internal rotation and knee external rotation during weight bearing activities (Souza & Powers, 2009; Willson & Davis, 2008a, 2008b). These unique kinematics may facilitate a greater association between the 2D FPPA and 3D knee external rotation than observed among the female subjects in the present study. Our results indicate that the change in 2D knee FPPA following training is not strongly associated with any particular change in 3D joint kinematics. At best, the variance in 2D FPPA describes only 10e12% of the variability in any single 3D joint rotation in this study. Thus, the “clinical improvement” in knee alignment measured with the FPPA during a single step down does not appear to represent any unique change in 3D hip or knee joint rotation. Rather, the 2D change is likely a result of a combination of 3D joint kinematic changes or a change in the orientation of the subject relative to the digital camera during the step down, resulting in less femoral internal rotation of the stance leg relative to the lab coordinate system. It is important to clarify that we do not wish to imply that these 2D methods are not valuable. Indeed, there may be many uses for this clinical measure. For example, our results suggest that this 2D change during a step down may be indicative of less femoral internal rotation or adduction. Additionally, we believe 2D methods such as these may be useful in other ways including the use as a screening tool for future ACL injury (Myer et al., 2010). However, this 2D measure may not be a good choice for clinicians as a surrogate measure for 3D joint kinematic changes due to an intervention program. In order to examine the influence that neuromuscular training has on lower extremity kinematics it was necessary to minimize the potential contribution of hypertrophic muscle tissue changes during the study. Muscle strength changes up to 4 weeks are thought to be associated with increased recruitment rather than muscle hypertrophy (Moritani & deVries, 1979). Therefore, our intervention was designed as a 4-week program. Subjects demonstrated a 2.0 kg (34%) increase in isometric hip external rotation strength and a 2.1 kg (12%) increase in hip abduction strength following training. If increased isometric hip external rotation strength was not a consequence of gluteal muscle hypertrophy, it may represent a neuromuscular response such as increases in rate coding, synchronization, and/or recruitment post-training. Greater hip external rotation strength has been shown to be associated with less negative FPPA (r ¼ 0.4, p < 0.01) (Willson et al., 2006). Therefore, it is possible that neuromuscular adaptations to our training program increased force output of the hip external rotators and contributed to the smaller FPPA identified following training. Further studies using electromyography seem justified in order to substantiate this theory. To our knowledge, this is the first study to report 2D and 3D kinematic changes following an isolated neuromuscular training program among females who displayed altered kinematics during a weight bearing task. Our results provide some details on the efficacy of a 4 week training program on kinematics measured clinically and with 3D motion analysis. However, there are several notable limitations with our investigation. First, the absence of a control group with similar lower extremity alignment during the step down limits our ability to discern the effects of the neuromuscular training versus other influences such as repeated testing. Second, despite a 90% follow-up rate, 2 out of 20 subjects did not
return for post-testing which may overestimate or underestimate our findings. Third, we did not include a long term follow up. Thus, it is unknown if the neuromuscular training had a lasting effect on the lower extremity kinematic changes observed. Finally, these kinematics were recorded only during a single leg step down and only on female subjects who did not have lower extremity injury. Although this task is used routinely in clinical settings and may be an important aspect of sit to stand transitions and stair negotiation, evidence as to how well that the kinematics of a step down predict kinematics of more dynamic activities is limited. 5. Conclusion A 4-week neuromuscular training protocol to minimize transverse and frontal plane hip and knee joint excursion during weight bearing activities resulted in a more neutral 2D alignment of the leg during a single leg step down. Three-dimensional kinematic changes were also observed such as decreased femoral internal rotation, decreased femoral adduction, increased contralateral pelvic drop, increased anterior pelvic tilt, increased hip adduction, and increased hip flexion. Decreased femoral internal rotation and adduction may be beneficial changes for patients for whom increased retropatellar stress is a concern. However, 3D hip and knee transverse and frontal plane joint kinematics did not correlate well with FPPA changes. While the change in FPPA and decreased femoral internal rotation and adduction may be considered a positive clinical outcome, our results suggest this 2D change in lower extremity alignment should not be associated with any particular change in lower extremity 3D joint kinematics assessed during the step down task. Clinicians should not infer a change in any particular 3D hip or knee joint rotation based on a change in the 2D knee FPPA. Conflict of interest The authors assert that no financial or personal relationships exist that may lead to a conflict of interest for any author of this manuscript. Ethical statement The authors affirm that this research was conducted with respect to all basic ethical considerations for the protection of human participants in research. The protocol for this study was approved by the University of WisconsineLa Crosse Institutional Review Board and all subjects participated with informed consent. References Agel, J., Olson, D. E., Dick, R., Arendt, E. A., Marshall, S. W., & Sikka, R. S. (2007). Descriptive epidemiology of collegiate women’s basketball injuries: national collegiate athletic association injury surveillance system, 1988e1989 through 2003e2004. Journal of Athletic Training, 42(2), 202e210. Arendt, E. A., Agel, J., & Dick, R. (1999). Anterior cruciate ligament injury patterns among collegiate men and women. Journal of Athletic Training, 34(2), 86e92. Bohannon, R. (1997). Reference values for extremity muscle strength obtained by hand-held dynamometry from adults aged 20 to 79. Archives of Physical Medicine and Rehabilitation, 78, 26e31. Bolgla, L. A., Malone, T. R., Umberger, B. R., & Uhl, T. L. (2008). Hip strength and hip and knee kinematics during stair descent in females with and without patellofemoral pain syndrome. The Journal of Orthopaedic and Sports Physical Therapy, 38(1), 12e18. Chappell, J. D., & Limpisvasti, O. (2008). Effect of a neuromuscular training program on the kinetics and kinematics of jumping tasks. The American Journal of Sports Medicine, 36(6), 1081e1086. Claiborne, T. L., Armstrong, C. W., Gandhi, V., & Pincivero, D. M. (2006). Relationship between hip and knee strength and knee valgus during a single leg squat. Journal of Applied Biomechanics, 22(1), 41e50. de Loes, M., Dahlstedt, L. J., & Thomee, R. (2000). A 7-year study on risks and costs of knee injuries in male and female youth participants in 12 sports. Scandinavian Journal of Medicine & Science in Sports, 10(2), 90e97.
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