Researching an evidence-based orthosis design for the treatment of osteoarthritis of the thumb

Osteoarthritis (OA) is a degenerative joint disease characterized by the breakdown of  articular cartilage which leads to joint pain and decrease in mobility. OA is caused by multiple factors, a combination of systemic susceptibility (metabolism, a hereditary predisposition and hormonal imbalances) and mechanical factors such as bone geometry, muscle weakness and ligament laxity. This can lead to a misalignment of articular surfaces which result in a non uniform loading of the cartilage leading to peak stresses and consequential wear of the cartilage.
OA of the trapeziometacarpal (TMC) joint is a chronic and disabling disease which affects primarily the middle-aged and elderly population with prevalence of 1 in 5 people above the age of 40 and 1 in 3 people above the age of 65.
As a result, the TMC joint is considered the most common location for development of OA in the hand.
The condition strongly interferes with daily living, such as tying shoelaces, opening bottles and therefore limits the independence and self-reliance of the patient. Furthermore, when the TMC joint is affected  the more proximal scaphotrapeziotrapezoid (STT) joint is also affected in approximately  50% of the cases. 

The current treatment is mainly focussed on relieving the pain in the early  stages of the disease and joint replacement is considered in the late stages of the condition. One of the widely used conservative, and proven,  methods to relieve the pain is an orthosis. An orthosis immobilizes and stabilizes the joint. It is common practice to fit a thumb orthosis if the TMC joint is affected and a thumb-wrist orthosis if the STT joint is also affected, 
without knowing the exact impact of the orthosis on the joint dynamics. Only one study quantified the effect of different orthoses on the TMC range of motion and the impact on the joint dynamics has never been studied before.

One of the reasons  that this interaction has not yet been studied is the difficulty to measure the in vivo kinematics of the thumb joints and an absence of relevant mechanical parameters, such as cartilage and ligament properties. Recent developments in CT-based kinematic analyses without markers, now make it possible to study the in vivo movement of the carpal and metacarpal bones.