Vita TU, Occupational Therapist and Project Manager
Sunshine Social Welfare Foundation
We all know safe position is the basis of good positioning in burns…
It’s common knowledge that when immobilizing the burned hand, we must position it in the safe position. The wrist in 10 to 15 degree extension, while the fingers are positioned with MP joints in 70 to 90 degree flexion, and PIP and DIP joints are in extension. The thumb’s CMC joint is in radial and palmar abduction, while the thumb’s MP joint is in extension . But have you ever wondered why this position is actually safe? In this final post, we’ll look at the wrist and thumb.
How the tenodesis effect affects the wrist and the other joints
Because of gravity, the weight of the hand and natural muscle tension, the wrist will naturally tend towards flexion. Wrist flexion will create more tension on the extrinsic extensor muscles, which will pull the MP joints into extension. On the contrary, wrist extension will cause passive flexion of the MP joints of the four digits. This is known as the tenodesis effect. To achieve safe MP flexion, we must place the wrist in extension.
As for the thumb, when the wrist is in extension, the first metacarpal will likewise fall forward into flexion. The CMC joint of the thumb is placed in the radial and palmar abduction positions, which will help maintain the arch of the hand and the first webspace of the thumb. This will in turn allow to maintain the grasping function of the thumb. This is crucial because if the thumb’s function remains intact, than over 50% of the grasping function of the hand is preserved. However, when the burn is concentrated on the volar side, we must consider the contracture direction of the scar, therefore it is possible to place the thumb in the radial abduction, but still maintain the thumb's webspace. 
Placing the wrist in extension and the thumb in radial and palmar abduction are basic to control the positioning of the hand and to prevent hand and wrist deformity.
If you’re curious to know more about “how” and “why” anatomy influences many principles behind the rehabilitation of the burned hand, don’t miss our course Rehabilitation of the Burned Hand – Introduction and Basic Concepts.
For more tips, how to's and videos about burn rehabilitation, you can also visit our Sunshine Training Youtube channel.
 M.A. Serghiou Niszczak, I. Parry, R. Richard J. Clinical practice recommendations for positioning. Burns, 42:2(2016) 267-275.
 Serghiou MA, Ott S, Whitehead C, Cowan A, McEntire S, Suman O. Comprehensive rehabilitation of the burn patient. In: Herndon DN, editor. Total burn care. 4th ed. Edinburgh: Saunders Elsevier; 2012. p. 517–49.
 Merilyn L. Moore, etc., Rehabilitation of the Burned Hand. Hand Clin 25 (2009) 529–541.