Download A comparison of the forces developed at the hip joints of normal

A comparison of the forces developed at the hip joints of ‘normal’ and total hip
replacement subjects
Stansfield BW, Nicol AC,
Bioengineering, Unit, University of Strathclyde, Glasgow, Scotland.
Introduction
Direct in-vivo measurement of hip joint contact forces has been performed (e.g. Bergmann et al., 1993) and
the results have provided information on the forces that act on the femoral component of the hip joint
prosthesis. However, to specify the design requirements for hip prostheses the full range of loading
conditions that might be experienced must be characterised, including those for ‘normal’ subjects. Hip joint
contact forces have been calculated in ‘normal’ subjects by a number of authors (Tsirakos et al., 1997).
However, there is limited evidence of the comparison between the hip joint contact forces in ‘normal’
subjects and those in subjects with hip replacements.
For this study the hip joint forces of normal and total hip replacement subjects were calculated using the
same protocol.
Methods
Kinematic and kinetic data were collected using a VICON motion analysis system and a Kistler force
platform.
These data were used in a computer model of the lower limb, which provided for 3D force and moment
balance at the hip, knee and ankle (Stansfield, 2000). The knee and ankle joint force bearing structures are
illustrated in Figures 1 and 2.
LCL
Knee-Z
φ
Knee-Y
MZ
FY1
PCL
FZ1
Ankle-Y
FY1
ACL
FX2
FY2
MCL
Tibial plateau
Ankle-Z
FZ1
FX3
FY2
FX1
FX4
FX1
Anterior
q
FZ2
Knee-X
Anterior
Ankle-X
L
Medial
Figure 1 The knee joint force bearing structures.
Muscles not shown.
φ=tibial long axis rotation with respect to femur.
L=distance from centre of knee to joint force location.
LCL=lateral, MCL=medial, ACL=anterior and
PCL=posterior crutiate ligaments.
FY1, FY2=joint forces.
MZ, FX1, FX2, FZ1, FZ2=joint structure effects.
FZ2
q
FX2
Medial
Figure 2 The ankle joint force bearing structures.
Muscles not shown.
q=distance from centre of ankle to joint force location.
FX1, FX2, FX3, FX4, FY1, FY2, FZ1, FZ2=joint forces.
The hip joint was treated as a ball and socket joint. At the knee and ankle joints major force bearing
structures were modelled. The knee axes were located on the tibial plateau (X pointing anteriorly, Z
laterally, Y superiorly). The variation in knee centre of contact during movement was described after Nisell
(1985). Supplementary forces were introduced at the knee to model other soft tissue structure contributions
to joint equilibrium. At the ankle the contact between the tibia, fibula and talus was effectively modelled as a
cylindrical joint with load distributed over a region ±q from the joint centre. The joint axis was defined after
Isman & Inman (1968). The ankle axes were aligned with X pointing anteriorly, Z laterally and Y superiorly
for the right foot.
47 muscle elements (Brand et al., 1982) were used in the model and wrapping procedures were used to
ensure that muscles did not pass through underlying structures.
Muscle redundancy was accommodated by the use of a linear optimisation technique minimising the
maximum muscle stress then minimising the sum of forces in the muscles and joints. Hip joint forces were
calculated from the model in a femoral co-ordinate system.
5 male ‘normal’ and 5 male total hip replacement subjects were studied for walking and
ascending/descending stair and ramp.
Results & Discussion
Subject characteristics are presented in Table 1.
Figures 3 and 4 illustrate resultant hip joint contact forces during walking and stair ascent respectively.
12
Resultant force (N/body weight)
Resultant force (N/body weight)
12
10
8
6
4
2
10
8
6
4
2
0
0
0
20
40
60
80
0
100
20
40
Figure 3A Resultant hip joint contact force during walking
for male normal subjects. All trials shown.
80
100
Figure 3B Resultant hip joint contact force during walking
for male subjects with total hip replacements. All trials shown.
8
8
7
7
Resultant force (N/body weight)
Resultant force (N/body weight)
60
Stance (%)
Stance (%)
6
5
4
3
2
1
6
5
4
3
2
1
0
0
0
20
40
60
80
100
0
20
40
60
80
100
Stance (%)
Stance (%)
Figure 4A Resultant hip joint contact force during stair ascent
for male normal subjects. All trials shown.
Figure 4B Resultant hip joint contact force during stair ascent
for male subjects with total hip replacements. All trials shown.
Table 2 details the average and standard deviation of the maximum resultant hip joint contact force
calculated for ‘normal’ subjects and subjects with prosthetic hip joints. ‘Normal’ subjects’ hip joint forces
were on average higher for all activities. The average maximum force ranged from 4.99 to 7.12 for ‘normal’
subjects and 4.28 to 5.08 times body weight for subjects with prostheses.
The relative magnitude of the resultant force during the different activities can be compared in Figure 5.
Subjects with hip replacements exhibited lower average speed, stride length and cadence than the normal
subjects (Table 3).
Age (years)
Height (cm)
Mass (kg)
Post op. (months)
Table 1
Male
normal
subjects
49.4 (5.0)
176.9 (6.8)
78.5 (5.4)
Male subjects with hip
replacements
52.6 (6.6)
170.8 (6.7)
77.8 (6.6)
18.6 (4.1)
Subject characteristics. Average and standard deviation values are illustrated
Walk
Stair A
Stair D
Ramp
A
(10°)
Ramp D
Ave.
7.12
4.99
5.59
6.82
St.dev.
1.54
0.99
1.32
1.82
Trials
30
28
24
27
Male subjects with hip
replacements
Ave. St.dev. Trials.
5.06 1.22
32
4.28 0.81
28
4.99 1.16
22
5.08 1.16
29
6.43
1.62
26
5.03
1.06
29
Table 2 Maximum resultant hip joint forces (multiples of body weight).
The number of trials includes both left and right side hips separately.
A=ascent, D=descent.
Maximum resultant hip joint force (xbody weight)
Male normal subjects
10
9
8
7
6
normal
prosthetic
5
4
3
2
1
0
walk
stair
ascent
stair
descent
ramp
ascent
ramp
descent
Figure 5 Maximum resultant hip joint contact force
for all activities. Average and standard deviation are illustrated
for both normal subjects and subjects with hip replacements.
Male normal subjects
Male subjects with hip replacements
Speed (m/s)
Stride length (m)
Cadence (strides/s)
Speed (m/s)
Stride length (m)
Cadence (strides/s)
Walk
1.65 (0.10)
1.73 (0.15)
0.95 (0.05)
1.29 (0.28)
1.45 (0.21)
0.89 (0.10)
Stair A
0.84 (0.08)
0.62 (0.09)
Stair D
1.00 (0.13)
0.65 (0.10)
Ramp A
1.42 (0.16)
1.66 (0.19)
0.86 (0.05)
1.01 (0.13)
1,42 (0.09)
0.71 (0.07)
Ramp D
1.51 (0.19)
1.64 (0.16)
0.91 (0.04)
1.01 (0.16)
1.32 (0.13)
0.76 (0.08)
Table 3 Average temporal distance parameters of the two subject groups. Average and standard deviation are illustrated.
Subjects with total hip replacements exhibited lower hip joint forces than ‘normal’ subjects. This difference
may be explained by the slower speed of activity exhibited by the subjects with hip replacements compared
to the normal subjects. Lower cadence coupled with shorter stride length would have been associated with
lower accelerations. Lower accelerations would have been associated with lower inertial and ground reaction
forces. The results indicate that this lead to lower internal forces at the hip joint contact.
The hip joint contact forces calculated for stair ascent and descent were lower than for walking and ramp
ascent and descent. The stair negotiation was performed within a controlled environment with stride length
fixed. This fact appears to have prevented the subjects developing high hip joint contact forces during stair
ascent.
The observation that normal subjects develop higher forces at their hip joints than subjects with hip
replacements suggests that using forces obtained from hip replacement subjects to define prosthesis design
requirements could compromise the long term performance of the prosthesis for subjects returning to
‘normal’ levels of activity.
References
Bergmann G et al., J. Biomech. 26, 969-990, 1993.
Brand RA et al., Trans. ASME, J. Biomech. Eng., 104, 304-310, 1982.
Isman RE, Inman VT, Anthropometric studies of the human foot and ankle, Technical Report 58,
Biomechanics Laboratory, University of California, San Francisco, Berkeley, 1968.
Nisell R, Mechanics of the knee - a study of joint and muscle loads with clinical applications, Acta. Orthop.
Scand., Vol.57 (Suppl No.216), 1-42, 1985.
Stansfield BW, ‘Hip Joint Forces’, PhD Thesis, University of Strathclyde, Glasgow, 2000.
Tsirakos D et al., Crit. Rev. Biomed. Eng., 25, 371-407, 1997.
Acknowledgement
The authors wish to thank the MRC for funding this research.