The Effect of Distal Location of the Volar Short Arm Splint on the Metacarpophalangeal Joint Motion

Abstract

Background: The goals of this study were to compare maximal metacarpophalangeal joint (MCPJ) flexion angles after application of a volar short arm splint at 3 different locations and verify the relations between the three different physical and radiological locations.

Methods: Forty dominant hands of healthy subjects were analyzed in the study. We defined a transverse skin folding line as a line drawn from the radial aspect of the thenar crease to the ulnar aspect of the distal transverse palmar crease. The distal end of the volar short arm splint was applied on 3 parallel locations to this line. Location A was on this transverse skin folding line; location B was 1 cm proximal to location A; and location C was 1 cm distal to location A. Two orthopedic surgeons measured the maximal MCPJ flexion angles of each finger except the thumb with the application of a volar short arm splint at 3 different locations as well as without a splint as a control. Radiological locations of the 3 different distal ends of the volar short arm splint were also assessed by anteroposterior radiographs of the wrist.

Results: When the splint was applied at location A and C, the maximal MCPJ flexion angle decreased to a mean of 83° (91% of control value) and 56° (62% of control value), respectively (compared to the control, p < 0.001). At location B, the maximal MCPJ flexion angle was a mean of 90° (99% of control value); no significant difference was observed compared to the control or without the splint (p = 0.103). On radiography, the average length from the metacarpal head to the distal end of the splint at all fingers decreased in the order of location B, A, and C (29 mm, 19 mm, and 10 mm, respectively; p < 0.001).

Conclusions: We recommend applying the distal end of a volar short arm splint at proximal 1 cm to the transverse skin folding line to preserve MCPJ motion perfectly, which is located at distal 44% of the whole metacarpal bone length radiologically.

Keywords: Joint range of motion; Metacarpophalangeal joint; Splint.

Fig. 1. The crease of midpalmar region is variable and there are diverse individual palmar crease patterns. The transverse palmar creases are of varying patterns depending on the individual as some people do not have separated proximal and distal transverse palmar creases (A) and instead have one transverse palmar crease that is called a simian crease (B).

Fig. 2. Three different locations for distal end of the volar short arm splint were tested. A transverse skin folding line was marked with dashed line between the radial border of the thenar crease and the ulnar border of the distal palmar transverse crease. Location A was marked on the transverse skin folding line, location B was defined as 1 cm vertically proximal to location A, and location C was defined as 1 cm vertically distal to location A.

Fig. 3. (A) Location A. (B) Location B. (C) Location C. The distance from the metacarpal head to the distal end of the splint (a) and the whole length of the metacarpal bone (b) were measured for every metacarpal bone except for the thumb on the wrist anteroposterior X-ray according to location A, B, and C.