DOS BULLETIN - Dansk Ortopædisk Selskab
DOS BULLETIN - Dansk Ortopædisk Selskab DOS BULLETIN - Dansk Ortopædisk Selskab
2010-378_DOS nr. 3 2010 29/09/10 10:08 Side 102 Test-retest reliability of maximal leg muscle power and functional performance measures in patients with severe osteoarthritis (OA) Allan Villadsen, Søren Overgaard, Ewa Roos, Anders Holsgaard Larsen Institute of Sport Sciences and Clinical Biomechanics, University of Southern Denmark; Department of Orthopaedic Research, Institute of Clinical Research, University of Southern Denmark Background: Muscle power, taking both strength and velocity into account, is a more functional measure of lower extremity muscle activity compared with the traditionally used isometric and/or isokinetic muscle strength. More functional measures are preferred to determine muscle function and as outcomes in exercise studies in patients with OA. Purpose: To evaluate the reliability of single-joint and multi-joint maximal leg muscle power as well as functional performance measures in patients with severe OA. Methods: Subjects: 20 patients diagnosed with severe OA and scheduled for unilateral total hip or knee replacement (mean age: 68.7 ± 7.24). 11 knee patients (6 female) and 9 hip patients (4 female), volunteered to participate. Subjects underwent a test battery on two occasions separated by approximately one week (range 7 to 11 days). Muscle power was measured using a linear encoder during unilateral isolated single-joint knee extension and flexion and unilateral isolated single-joint hip extension and abduction. Muscle power of unilateral multi-joint knee and hip extension was obtained with a leg extension press. Three functional performance measures (20 m walk, 5 times chair stands, maximal number of knee bends/30sec) were also evaluated. Pain was measured on a VAS scale prior to and after conducting the entire test battery. Findings: For single-joint maximal peak power the observed CVws ranged from 7-25% and for multi-joint maximal peak power from 20-22%. For the three functional performance measures (20 m walk, 5 times chair stands, maximal number of knee bends/30sec) the CVws were 5%, 14%, and 17%, respectively. A systematic and significant improvement was observed for the multi- joint maximal peak power (p=.0046, CI - 28.8;-6.13), 5 times chair stands (p=.004, CI 0.96;2.66) and 20 m walk (p=.0037, CI 0.16;0.68) indicating a learning effect. A decrease in pain was found after testing (VAS change score) (p=.0005, CI -1,64; -.55). Conclusion: Familiarization sessions are needed to avoid learning effects when testing muscle function. Single-joint and multi- joint muscle power over the hip and knee, and functional performance measures, can be evaluated with moderate to good reliability in patients with severe OA. The test battery was feasible for elderly patients with severe OA as indicated by no increase in pain after testing. 102
2010-378_DOS nr. 3 2010 29/09/10 10:08 Side 103 The influence of muscle forces on the stress distribution in lumbar spine Christian Wong, John Rasmussen, Erik B. Simonsen, Lone Hansen, Mark de Zee, Sebastian Dendorfer Department of Orthopaedic Surgery, University Hospital of Hvidovre; Department of Mechanical Engineering, Aalborg University; Department of Neuroscience and Pharmacology, University of Copenhagen; Team Denmark, Idraettens hus; AnyBody Technolog A/S, Aalborg Background: Previous studies of bone stresses in the human lumbar spine have relied on simplified models when modelling the spinal musculature, even though muscle forces are likely major contributors to the stresses in the vertebral bones. Detailed musculoskeletal spine models have recently become available and show good correlation with experimental findings. Purpose: A combined inverse dynamics and finite element analysis study was conducted in the lumbar spine to investigate the effects of muscle forces on a detailed musculoskeletal finite element model of the 4th lumbar vertebral body. Methods: The muscle forces were computed with a detailed and validated inverse dynamics musculoskeletal spine model in a lifting situation, and were then applied to an orthotropic finite element model of the 4th lumbar vertebra. The muscle model consisted of roughly 1000 individually activated muscle fascicles of which about 188 are located in the lumbar spine area. The FE model consisted of 63974 volumetric elements for trabecular bone and 8886 shell elements with a thickness of 0.6 mm for cortical bone. Static analysis of the FE model was performed and the results were compared with those from a simplified load case FE model without muscles. Findings: In general inclusion of muscle forces in the FE model increased the Von Mises stress by 30 % in the superio-anterior and central part of the vertebral body and in the pedicles. Conclusion: The application of spine muscles to a finite element model shows quite clearly that muscle forces play a large and non- negligible role for the stress distribution in the vertebrae. This is especially important, when considering compression fractures in the elderly population with decreased trabecular strength, where small changes in the load axis combined with muscle forces would lead to such fractures. 103
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2010-378_<strong>DOS</strong> nr. 3 2010 29/09/10 10:08 Side 103<br />
The influence of muscle forces on the stress distribution<br />
in lumbar spine<br />
Christian Wong, John Rasmussen, Erik B. Simonsen, Lone Hansen,<br />
Mark de Zee, Sebastian Dendorfer<br />
Department of Orthopaedic Surgery, University Hospital of Hvidovre;<br />
Department of Mechanical Engineering, Aalborg University; Department<br />
of Neuroscience and Pharmacology, University of Copenhagen;<br />
Team Denmark, Idraettens hus; AnyBody Technolog A/S, Aalborg<br />
Background: Previous studies of bone stresses in the human lumbar<br />
spine have relied on simplified models when modelling the spinal musculature,<br />
even though muscle forces are likely major contributors to the<br />
stresses in the vertebral bones. Detailed musculoskeletal spine models<br />
have recently become available and show good correlation with experimental<br />
findings.<br />
Purpose: A combined inverse dynamics and finite element analysis<br />
study was conducted in the lumbar spine to investigate the effects of<br />
muscle forces on a detailed musculoskeletal finite element model of the<br />
4th lumbar vertebral body.<br />
Methods: The muscle forces were computed with a detailed and validated<br />
inverse dynamics musculoskeletal spine model in a lifting situation,<br />
and were then applied to an orthotropic finite element model of the<br />
4th lumbar vertebra. The muscle model consisted of roughly 1000 individually<br />
activated muscle fascicles of which about 188 are located in the<br />
lumbar spine area. The FE model consisted of 63974 volumetric elements<br />
for trabecular bone and 8886 shell elements with a thickness of<br />
0.6 mm for cortical bone. Static analysis of the FE model was performed<br />
and the results were compared with those from a simplified load case FE<br />
model without muscles.<br />
Findings: In general inclusion of muscle forces in the FE model<br />
increased the Von Mises stress by 30 % in the superio-anterior and central<br />
part of the vertebral body and in the pedicles.<br />
Conclusion: The application of spine muscles to a finite element model<br />
shows quite clearly that muscle forces play a large and non- negligible<br />
role for the stress distribution in the vertebrae. This is especially important,<br />
when considering compression fractures in the elderly population<br />
with decreased trabecular strength, where small changes in the load axis<br />
combined with muscle forces would lead to such fractures.<br />
103