Normal Range of Motion of Thumb Metacarpophalangeal Joint

Abstract

Objective: The range of motion (ROM) of the thumb metacarpophalangeal (MCP) joint varies widely among individuals. Because of this variability, the normal angles of flexion and extension of the MCP joint are difficult to determine. If the ROM of the thumb MCP joint is sufficiently similar between the right and left sides, the contralateral normal side can be used for outcome assessment in hand surgery. The purpose of this study was to define the difference between right and left ROM of the thumb MCP joint in the normal population and assess the utility of the normal side value as a normal indicator. Materials and Methods: Three hundred hands of 150 participants (75 men, 75 women; average age, 36.2 years) without a history of injuries or diseases of the thumb were included in this study. To exclude participants with degenerative joint disease, the age range was limited to 20 to 49 years. The angles of flexion and extension of the MCP joints were measured with a goniometer at an interval of 1°. Statistical analyses of flexion angle, extension angle, differences between men and women, and differences between the right and left sides of individuals were carried out. The Mann-Whitney U tests were used. A P value of < .05 was considered statistically significant. Results: The average flexion angle was 59.1° (16°-90°). The average extension angle was 7.9° (−32°-58°). Both the flexion and extension angles were greater in women than in men. The average difference in the flexion angle between right and left was 4.8°. The range was from 0° to 28°. The average difference in the extension angle between right and left was 6.4°. The range was from 0° to 38°. For a P value of .05, the one-sided 100th percentile of the flexion angle was 10.6° and that of the extension angle was 14.3°. For a P value of .01, the one-sided 100th percentile of flexion angle was 15.1° and that of the extension angle was 20.1°. Conclusions: The difference between the maximum flexion angle of 90° and the minimum flexion angle of 16° was 74°. The difference between the maximum extension angle of 58° and the minimum extension angle of −32° was 90°. Due to these large differences in the flexion and extension angles, it appeared that some angles could not be determined as normal. However, the average flexion and extension differences between the right and left sides of the same individual were 4.8° and 6.4°, respectively. These differences are small enough for the contralateral normal side to be a useful indicator of the normal ROM of the MCP joint. After rounding up the decimals to a unit, the one-sided 100th percentile results indicated that flexion loss of more than 11° and extension loss of more than 15° were suspicious for contracture of the MCP joint, and that flexion loss of more than 16° and extension loss of more than 21° strongly suggested contracture of the MCP joint.