Journal of Orthopnedic Rcsrw-ch 10917-925 Raven Press, Ltd., New Yurk ‘C 1992 Orthopaedic Research Society
Forces and Moments on the Human Leg in the Frontal Plane During Static Bipedal Stance *+David V. Carmines and *Edward B. MacMahon *Department of Ortlzopuedic Surgery, Georgetown University; and fDepartment of Mechonical Engineering, The Catholic Univerrity of America, Washingtorr, D.C., U.S.A.
Summary: An experimental apparatus was assembled that permitted measurement of the vertical and lateral ground reaction forces as the hip is abducted, resulting in foot separations ranging from 0.25 to 71 crn, with the knee in 0” flexion. Twelve healthy volunteers (8 men and 4 women) were tested. The hip joint was located by means of center of rotation measurements on each subject’s legs, and the location of the knee joint was determined using anatomical measurements. It was observed that the mediolateral force was nonzero and directed toward the body midline, even when the subject’s feet were placed together. With the feet placed at shoulder width. the population mean mediolateral force was 3% of body weight. It was determined that simplifying assumptions based upon either “zero lateral force.“ or “zero hip moment,” produced errors, when compared with our measured values, over various ranges of foot separation, with the zero hip moment assumption providing accuracy over a broader range. The inclination of the tibial plateau, with respect to the long axis of the tibia, that would produce minimal mediolateral shear at the knee is presented. Research and clinical applications of OUT results and techniques are discussed. Key Words: Static bipedal stance-Ground reaction forces-Hip joint-Knee joint.
loading produced through realignment procedures, such as osteotomy, meniscectomy, or ligamental repair. The loading of the foot may be modulated into three categories for subsequent research and clinical analyses: static one-legged stance, dynamic loading (gait analysis), and static bipedal stance. Static one-legged stance provides a simplified means of analysis (8,9,16), but suffers from variability due to limb position (8) and pelvic tilt (8,16). Dynamic gait analysis provides peak forces during ambulation, but suffers from high cost, the need to maintain technical assistance, test-to-test and patient-to-patient variability (1,9), and masking of pathological conditions by compensatory mechanisms (2,9.20). Static bipedal stance offers a compromise between one-legged stance and dynamic gait analysis, featuring repeatability, and, hence,
The external loads applied to the foot play an important role in both research and clinical assessment of lower limb pathologies. In orthopaedic research, the loading of the foot (coupled to the body forces and inertial components) provides information necessary to model the load distributions and shear forces on the tibial plateau, stresses in the tibia and femur, soft tissue loading about the knee and hip joints, and the loads transmitted through prosthetic joints. In the clinic, the loading of the foot may be used to assess limb alignment under load support, and to approximate the changes in
Received August 16, 1991; accepted June 8. 1992. Address correspondence and reprint requests to Dr. D. V. Carmines at The Catholic University of America, Department of Mechanical Engineering, Pangborn Hall, Rm G-32, Washington, D.C. 20064, U.S.A.
917
918
D. V. CARMINES AND E. B . MACMAHON
has been used by numerous researchers as a means of analysis and modeling (8,11,12,14,15). In contrast to gait analysis, static bipedal stance may be performed with an inexpensive testing system. minimal technical support, and permits the simultaneous acquisition of forces and radiographic information. In this study we investigated the information provided by static bipedal stance. A testing apparatus was designed to provide the measured vertical and mediolateral forces on the feet for a sample population of healthy subjects. The measured ground reaction forces were altered by positioning the feet at various distances of separation in the frontal plane for each subject. In particular, our measurements are compared with two simplifications frequently employed by clinicians and researchers: (a) neglect of the mediolateral force and (b) assumption that the ground reaction vector passes from the foot through the hip joint. MATERIALS AND METHODS
A customized testing apparatus was assembled (Fig. l), that permitted the measurement of the ground reaction forces in the frontal plane. One foot plate was supported by four strain-gauged cantilever beams, providing the measured vertical ground reaction force (Fv). A second foot plate was mounted to the slider on a linear bearing track, permitting the measurement of the lateral ground reaction force (FL)by a strain-gauged load cell (proving ring). By positioning a mechanical “stop” on the
COC rIJi.crk:
$1 ~~
E ;,:!
P O 0 l‘l’l.A‘l
7C>4KllI,EYEl? I : E 2 > 1
F
\
c _
1,
I.I.Y>~II
Forces and Moments on the Human Leg in the Frontal Plane During Static Bipedal Stance *+David V. Carmines and *Edward B. MacMahon *Department of Ortlzopuedic Surgery, Georgetown University; and fDepartment of Mechonical Engineering, The Catholic Univerrity of America, Washingtorr, D.C., U.S.A.
Summary: An experimental apparatus was assembled that permitted measurement of the vertical and lateral ground reaction forces as the hip is abducted, resulting in foot separations ranging from 0.25 to 71 crn, with the knee in 0” flexion. Twelve healthy volunteers (8 men and 4 women) were tested. The hip joint was located by means of center of rotation measurements on each subject’s legs, and the location of the knee joint was determined using anatomical measurements. It was observed that the mediolateral force was nonzero and directed toward the body midline, even when the subject’s feet were placed together. With the feet placed at shoulder width. the population mean mediolateral force was 3% of body weight. It was determined that simplifying assumptions based upon either “zero lateral force.“ or “zero hip moment,” produced errors, when compared with our measured values, over various ranges of foot separation, with the zero hip moment assumption providing accuracy over a broader range. The inclination of the tibial plateau, with respect to the long axis of the tibia, that would produce minimal mediolateral shear at the knee is presented. Research and clinical applications of OUT results and techniques are discussed. Key Words: Static bipedal stance-Ground reaction forces-Hip joint-Knee joint.
loading produced through realignment procedures, such as osteotomy, meniscectomy, or ligamental repair. The loading of the foot may be modulated into three categories for subsequent research and clinical analyses: static one-legged stance, dynamic loading (gait analysis), and static bipedal stance. Static one-legged stance provides a simplified means of analysis (8,9,16), but suffers from variability due to limb position (8) and pelvic tilt (8,16). Dynamic gait analysis provides peak forces during ambulation, but suffers from high cost, the need to maintain technical assistance, test-to-test and patient-to-patient variability (1,9), and masking of pathological conditions by compensatory mechanisms (2,9.20). Static bipedal stance offers a compromise between one-legged stance and dynamic gait analysis, featuring repeatability, and, hence,
The external loads applied to the foot play an important role in both research and clinical assessment of lower limb pathologies. In orthopaedic research, the loading of the foot (coupled to the body forces and inertial components) provides information necessary to model the load distributions and shear forces on the tibial plateau, stresses in the tibia and femur, soft tissue loading about the knee and hip joints, and the loads transmitted through prosthetic joints. In the clinic, the loading of the foot may be used to assess limb alignment under load support, and to approximate the changes in
Received August 16, 1991; accepted June 8. 1992. Address correspondence and reprint requests to Dr. D. V. Carmines at The Catholic University of America, Department of Mechanical Engineering, Pangborn Hall, Rm G-32, Washington, D.C. 20064, U.S.A.
917
918
D. V. CARMINES AND E. B . MACMAHON
has been used by numerous researchers as a means of analysis and modeling (8,11,12,14,15). In contrast to gait analysis, static bipedal stance may be performed with an inexpensive testing system. minimal technical support, and permits the simultaneous acquisition of forces and radiographic information. In this study we investigated the information provided by static bipedal stance. A testing apparatus was designed to provide the measured vertical and mediolateral forces on the feet for a sample population of healthy subjects. The measured ground reaction forces were altered by positioning the feet at various distances of separation in the frontal plane for each subject. In particular, our measurements are compared with two simplifications frequently employed by clinicians and researchers: (a) neglect of the mediolateral force and (b) assumption that the ground reaction vector passes from the foot through the hip joint. MATERIALS AND METHODS
A customized testing apparatus was assembled (Fig. l), that permitted the measurement of the ground reaction forces in the frontal plane. One foot plate was supported by four strain-gauged cantilever beams, providing the measured vertical ground reaction force (Fv). A second foot plate was mounted to the slider on a linear bearing track, permitting the measurement of the lateral ground reaction force (FL)by a strain-gauged load cell (proving ring). By positioning a mechanical “stop” on the
COC rIJi.crk:
$1 ~~
E ;,:!
P O 0 l‘l’l.A‘l
7C>4KllI,EYEl? I : E 2 > 1
F
\
c _
1,
I.I.Y>~II
