In Vivo Scaphoid Motion During Thumb and Forearm Motion in Casts for Scaphoid Fractures

Purpose In nonsurgical treatment for acute undisplaced or minimally displaced scaphoid waist fractures, immobilization of both wrist and thumb can be an option. However, in vivo scaphoid motion during forearm and thumb motion with the wrist immobilized in a cast has not been measured. Therefore, we examined the in vivo kinematics of the scaphoid during forearm and thumb motion with cast immobilization. Methods Ten healthy right wrists of 10 male volunteers were included. These wrists were immobilized in a short-arm spica cast with the thumb in a position of volar abduction and then were scanned with the forearm in supination, neutral rotation, and pronation using computed tomography. Next, these wrists were scanned with a forearm gauntlet cast in place with the thumb abducted radially and opposed with the forearm positioned in neutral rotation. From these data, the 3-dimensional position of the third metacarpal and scaphoid was analyzed. Results From forearm supination to pronation, the scaphoid showed 0.2° radial deviation, 0.4° pronation, and 8.3° extension. The third metacarpal showed 14.6° ulnar deviation, 6.5° pronation, and 1.6° flexion. During thumb opposition from radial abduction, the scaphoid showed 2.9° radial deviation, 0.4° supination, and 7.2° extension and the third metacarpal showed 4.5° ulnar deviation, 2.8° pronation, and 5.5° extension. Conclusions The scaphoid was not completely immobilized by either cast. However, the scaphoid motion during forearm and thumb motion was not significant. Clinical relevance Several high-quality studies have shown that undisplaced or minimally displaced scaphoid waist fractures can be successfully treated with casts. Movement of scaphoid and wrist during forearm rotation or thumb motion with a cast may not be sufficient to have a negative impact on the outcome of scaphoid fracture using a cast.