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Project

Looking beyond the image: biomechanics & anatomy of thumb function and instability

The modern human thumb can be seen as a hallmark of human evolution. The unique anatomy of the human thumb makes it possible to carefully manipulate tools, powerfully grasp objects and even throw items with precision. These apparent contradictory functions of the thumb, high mobility for manual dexterity vs. high stability during forceful grasping, imply that daily activities impose a high strain on a relative instable joint. This makes the thumb susceptible to joint disorders such as osteoarthritis.

 

Both systemic (e.g. genetics, hormones, obesity) and mechanical factors (e.g. joint loading) are important in the development of osteoarthritis, but the precise pathomechanism remains largely unknown. In this project, we focus on the mechanical factors in the disease process and use a multidisciplinary approach to develop, refine and apply a toolset that helps to further investigate the link between structure and (dys)function of the human thumb.

 

First of all, we developed and validated a dynamic CT protocol that allows accurate quantification of 3D bone motion using a limited radiation dose. This validated dynamic CT technique was then used to analyze thumb motion in patients with an unstable and painful trapeziometacarpal (TMC) joint. We compared the thumb base kinematics from patients before and after a dorsal ligament shortening operation. These kinematics were compared with age-and-sex-matched healthy controls. In addition, changes in contact patterns between the articular facets during the motion cycle were mapped to assess the impact of the surgery on joint mechanics.

 

As mechanical loading of the TMC joint is largely generated by contraction of thumb muscles, we also investigated thumb muscle activations during functional tasks using fine-wire electromyography. We found subject-specific muscle recruitment patterns which remained largely unchanged between tasks.

 

Finally we expand on the anatomy in general. By using 7T MRI, CT and detailed dissection, a 3D digital model of the forearm and hand of a single, un-embalmed, specimen was created with full quantification of the muscle architecture, bone and cartilage geometry.

 

This multifaceted approach has led to profound insights in the relation between form and function of the human thumb, as well as in the involvement of distinct anatomical and mechanical factors in the onset and development of osteoarthritis of the thumb joint.

Date:1 Oct 2011 →  22 Nov 2017
Keywords:function, hand structure, biomechanics, Evolution
Disciplines:Orthopaedics, Human movement and sports sciences, Rehabilitation sciences
Project type:PhD project