Scaphoid tuberosity excursion is minimized during a dart-throwing motion: A biomechanical study

Abstract

Purpose: The purpose of this study was to determine whether the excursion of the scaphoid tuberosity and therefore scaphoid motion is minimized during a dart-throwing motion.

Methods: Scaphoid tuberosity excursion was studied as an indicator of scaphoid motion in 29 cadaver wrists as they were moved through wrist flexion-extension, radioulnar deviation, and a dart-throwing motion.

Results: Study results demonstrate that excursion was significantly less during the dart-throwing motion than during either wrist flexion-extension or radioulnar deviation.

Conclusion: If the goal of early wrist motion after carpal ligament or distal radius injury and reconstruction is to minimize loading of the healing structures, a wrist motion in which scaphoid motion is minimal should reduce length changes in associated ligamentous structures. Therefore, during rehabilitation, if a patient uses a dart-throwing motion that minimizes his or her scaphoid tuberosity excursion, there should be minimal changes in ligament loading while still allowing wrist motion.

Study design: Bench research, biomechanics, and cross-sectional.

Level of evidence: Not applicable. The study was laboratory based.

Keywords: Dart-throwing motion; Rehabilitation after carpal injury; Scaphoid tuberosity; Scapholunate interosseous ligament injury.

Figure 1

Nine dart-throwing wrist motions studied as viewed in the transverse plane. Motion A is a pure extension to flexion motion. Motion I is a pure radial deviation to ulnar deviation. The other 7 motions were as the wrist moved from extension and radial deviation to flexion and ulnar deviation. The length of each line corresponds to the excursion of the motion. (Reprinted with permission from Werner et al. Scaphoid and Lunate Motion During a Wrist Dart Throw Motion, J Hand Surg 29A;2004;419).

Figure 2

Wrist joint motion simulator used to test each wrist. Motion of the third metacarpal and therefore the wrist was measured by an electromagnetic sensor mounted on the third metacarpal. Motion of the scaphoid (and lunate) were measured by sensors attached to posts cemented into each bone. These motions were referenced to the sensor mounted on the distal radius. Wrist motion was caused by actuators connected in series with clamps attached to the wrist flexors and extensors.

Figure 3

Excursion of the scaphoid tuberosity movement during a flexion-extension motion is shown by a series of red spheres during the wrist motion. Scaphoid (blue) and lunate (green) are located with wrist in extension.

Figure 4

Dorsal and volar scaphoid lunate interosseous ligament (SLIL) components for a right wrist in extension.

Figure 5

Absolute Magnitude of 3D Scaphoid Tuberosity Excursion During One Cycle of Flexion-Extension, Radioulnar Motion and Dart-Throwing Motions. The peak values, here in figure 5, are not the same as the peak values given in table 1, since these values are the average for all 28 arms, averaged at each degree of wrist motion. The table 1 values are the average of the largest values during each cycle for the 28 arms.

Figure 6

Scaphoid Tuberosity Excursion from the Neutral Reference Position and Length of Dorsal and Volar Components of the SLIL as a Function of Wrist Flexion Angle (Average of 28 Arms during Flexion-Extension Motion)

Figure 7

Scaphoid Tuberosity Excursion from the Neutral Reference Position and Length of Dorsal and Volar Components of the SLIL as a Function of Wrist Ulnar Deviation Angle (Average of 28 Arms during Radioulnar Deviation Motion)

Figure 8

Scaphoid Tuberosity Excursion from the Neutral Reference Position and Length of Dorsal and Volar Components of the SLIL as a Function of Wrist Flexion Angle (Average of 28 Arms during Dart-Throwing Motion)

Figure 9

Relative Excursion of Scaphoid Tuberosity for the 6 arms undergoing 9 different dart-throwing motions compared to the amount of Scaphoid motion. Here scaphoid motion is expressed as a percentage of the third metacarpal motion which by definition is the same as wrist motion. (Tuberosity excursion is amplified due here to using an ulnar coordinate based system instead of the radial coordinate system). “fe” is the planar flexion-extension motion. “ru” is the planar radioulnar deviation motion. “dart” is the same dart throw motion used in the base data set of 28 arms. The letters A, B, etc. refer to the different dart-throwing motions shown in figure 1.

Figure 10

Suggested method on how to clinically palpate the scaphoid tuberosity in an uninjured wrist. The scaphoid tuberosity of a patient be can located with the wrist in a neutral position (A, B). When the patient's wrist is moved into radial deviation (C), the tuberosity will protrude palmarly and push against the thumb of the examiner. When the wrist is moved into ulnar deviation (D), the tuberosity will move dorsally. If the wrist is moved into the radial extended position (E), or into the ulnar flexed position (F), the tuberosity will be in nearly the same position as the neutral wrist. The positions of radial extension and ulnar flexion may need to be slightly varied until the tuberosity motion is minimized.