Biomechanical Study of Distal Radioulnar Joint (DRUJ) Ballottement Test

Introduction The distal radioulnar joint (DRUJ) relies heavily on soft tissue support for stability, and dorsal and volar radioulnar ligaments are a primary stabilizer of the joint. Because of the inherently unstable and complicated soft tissue structures of the DRUJ, diagnosis and treatment of the joint instability remains a challenging problem. The instability is assessed by manual stress test in clinical hand surgery practice, but interpretation of the test is merely subjective. There is a lack of information regarding reliability and accuracy of DRUJ ballottement test. The purpose of this study was to investigate the intra- and inter-rater reliability and accuracy of the manual stress test with different techniques in intact and TFCC sectioned wrists using cadaver specimens.

Material and Methods We used six fresh-frozen cadaver upper extremities. The humerus and proximal ulna were fixed to a testing apparatus with the elbow at 90° of flexion by K-wire. The ulna was allowed to translate to palmer and dorsal directions, and the radius was allowed to move freely. Two sensors of a magnetic tracking system (3SPACE FASTRAK; Polhemus, Colchester, VT, USA) were attached directly in the distal aspect of the radius and ulna. The other two sensors were attached onto the nail of the examiner's thumbs, by which the examiner can perceive a sense of instability (Fig. 1).

Fig. 1 DRUJ ballottement tests setup.

Five examiners (two board-certified hand surgeons and three board-certified orthopedic surgeons) conducted DRUJ ballottement tests before and after sectioning of the ulnar insertion of the TFCC. We used two different techniques with and without holding the carpal bones to the radius during the testing (holding technique and nonholding technique). Each test was repeated three times, and we measured the magnitude of movement between the radius and ulna and between the examiner's nails by the electromagnetic tracking device.

We determined the intra- and inter-rater reliability of the DRUJ ballottement test by calculating the intraclass correlation coefficient (ICC) for dorsopalmer movement of the DRUJ in two different techniques of the manual testing. We compared the magnitude of the dorsopalmer (y-axis of Fig. 1) movement of the DRUJ (relative movement between the radius and ulna) with that of the dorsopalmer movement of the nails of each examiner's thumbs to determine how the nail movement approximates the bone movement. Magnitudes of the dorsopalmer movement of the DRUJ were compared before and after the TFCC sectioning, and two different techniques were compared as well between holding and nonholding technique.

Results (Reliability of manual stress test.) Intra-rater ICC of bone-to-bone (DRUJ) movement in holding and nonholding technique was 0.92 (with holding) and 0.94 (without holding). Inter-rater ICC was 0.84 (with holding) and 0.75 (without holding). Inter-rater reliability of manual stress testing in the holding technique tended to be lower than that in nonholding technique.

(Magnitude of DRUJ movement.) Magnitudes of bone-to-bone (DRUJ) and the examiner's nail-to-nail movement averaged 11.5 ± 4.6 mm and 11.9 ± 4.6 mm. In the nonholding technique, nail-to-nail movement was significantly larger than bone-to-bone movement (p < 0.01). In the holding technique, nail-to-nail movement was not significantly larger than bone to bone movement (p = 0.7).

Bone-to-bone (DRUJ) movement was significantly increased in both techniques after the TFCC sectioning. Before TFCC sectioning, bone movement in the holding and nonholding technique was 9.9 ± 4.2 mm and 10.9 ± 4.7 mm. The movement in the holding technique was significantly lower than that in the nonholding technique (p < 0.01). After TFCC sectioning, the movement was increased to 12.1 ± 4.7 mm and 12.5 ± 4.4 mm, respectively. The increase of the bone-to-bone movement during TFCC sectioning in the holding technique (average 2.5 mm) was larger than that in the nonholding technique (average 1.5 mm).

Conclusion Despite the possibility that manual stress test may overestimate instability, the test is relatively accurate to detect DRUJ instability. Intra-rater reliability of the manual stress test was almost perfect regardless of holding or nonholding of the carpal bones to the radius. However, inter-rater reliability without holding the carpal bones was lower than when holding the carpal bones. Magnitude of DRUJ movement by manual stress testing was increased significantly following TFCC sectioning, and the technique of the DRUJ ballottement test by holding the carpal bones to the radius is more accurate than the nonholding technique (Table 1).

Table 1 Comparison of the magnitude of DRUJ movement

	Holding technique	Nonholding technique
*Increase of movement from intact to TFCC sectioning.
Intact wrist	9.9 ± 4.2 mm	10.9 ± 4.7 mm	(p < 0.01)
TFCC sectioned wrist	12.1 ± 4.7 mm	12.5 ± 4.4 mm
Increase*	2.5 ± 4.2 mm	1.5 ± 2.7 mm