Guest Lecture

“What if”: the use of biomechanical models for understanding and treating upper extremity musculoskeletal disorders

Dirk Jan (H.E.J.). Veeger, VU University Amsterdam, Delft University of Technology, Delft, The Netherlands

The structure of the shoulder is an ingenious compromise between stability and mobility that allows the hand to be moved within almost 2/3 of a sphere. In addition to the truly three-dimensional mobility of the upper extremity, the hand is capable of exerting forces in almost any direction. This versatility is enabled by mobile joints and controlled by mono-, bi- and tri-articular muscles. Given the 3D structure of the shoulder, muscles will not only generate joint moments to meet external forces, but will also generate considerable undesired joint moment components, which must be compensated by other muscles. Also, the mechanical effect of each muscle is highly dependent on arm posture and can even change sign completely.

We developed a musculoskeletal model of the shoulder and elbow to aid understanding the working of the upper extremity. The model comprises the thorax, scapula, clavicle, humerus and forearm and all muscles controlling these. The model uses musculoskeletal parameters from one specimen and works on the assumption of the existence of a general control principle (or cost function) based on the minimization of energy cost.

The model can, and has been used for several clinical applications, of which a selection will be discussed:

prevention of muscle overload: to be able to prevent overload injuries in wheelchair users the magnitude of muscle strains and joint loading should be quantified so that decisions on training and overuse prevention can be made (Van Drongelen et al, 2005 );
“what if”: The decision on what tendon transfer to perform to restore function is dependent on its functional gain, f.i. in terms of Activities of Daily Living (Magermans et al, 2004), on the newly constructed moment balance around a joint (Veeger et al., 2004).
understanding muscle control in pathological cases: in patients sometimes muscle activation patterns can be seen that conflict with their primary function (Steenbrink et al., 2006) Understanding this requires insight in the mechanical balance of the system, including all interactions between muscles;

Any modeling result is only as good as the model itself. Recently, the model has been validated with the use of an instrumented endoprosthesis (Asadi Nikooyan, 2008). Validation has included the effect of scaling, but still two issues remain, namely the extent to which patient data can be related to model results in which a general control principle is assumed and second, to what extent models can, or should be individualized.

References

Van Drongelen et al, Archives of Physical Medicine & Rehabilitation 2005; 1434-1440
Magermans et al, Clinical Biomechanics 2004; 116-122
Veeger et al., Journal of Hand Surgery 2004; 259-264
Steenbrink et al., Manual Therapy 2006; 231-237
Asadi Nikooyan et al, 2008, Proceedings 16th ESB Conference, Lucerne, Switzerland

Guest Lecture

“What if”: the use of biomechanical models for understanding and treating upper extremity musculoskeletal disorders

Dirk Jan (H.E.J.). Veeger, VU University Amsterdam, Delft University of Technology, Delft, The Netherlands

References

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