AMERICAN SOCIETY OF BIOMECHANICS
Presented at the Twenty-First Annual Meeting
of the American Society of Biomechanics
Clemson University, South Carolina
September 24-27, 1997
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| AMERICAN SOCIETY OF BIOMECHANICS
Presented at the Twenty-First Annual Meeting |
Loss of ligamentous constraint is understood to be the sine qua non for the occurrence of malalignment of the wrist. Consequently, in theory, the displacement response of the wrist to increased compressive force could be indicative for the state of the ligaments. More importantly, this would provide a means to aid early diagnosis and intervention. To find out the practicality of this line of reasoning, this study analyzed the displacement response of juvenile arthritic wrists during grasp.
In children with juvenile chronic arthritis (JCA), the wrist joint is affected in approximately 60% of cases (Findley et al., 1983). As a result of chronic inflammation of this joint, displacement of the carpus, i.e. malalignment, occurs. In adult rheumatoid arthritis (RA), the development of ulnar carpal displacement is understood as the result of loss of radiocarpal ligamentous constraint in combination with the compressive forces of the forearm muscles acting across the wrist, and the inclination angle of the distal radial articular surface (Linscheid, 1986). Consequently, given loss of ligamentous constraint, increasing the compressive force (i.e. the tangential force vector) could provoke ulnar displacement of the carpus.
A way to increase the compressive force in vivo is by grasping. Schuind et al. (1992) described the changes in wrist and forearm configuration during grasp in a study involving 15 healthy adults. During grasp they found proximal migration of the radius, buckling of the carpal bones with capitate angulation and decrease in carpal height. Most interestingly, ulnar translation of the carpus was also found.
If JCA wrists act in accordance with the pathokinesiological concept for adult RA wrists, ulnar displacement should be found during grasp, and the loss of ligamentous constraints would result in a more pronounced displacement of the carpus. However, wrist involvement per se does not necessarily lead to the same extent of loss of ligamentous constraint (Viegas et al., 1995; Melvin, 1989). Consequently, it would be interesting to know if all JCA wrists displace to the same extent during grasp. If not, the effect of increased loading on the carpus could be indicative for the state of the ligaments, and thus aid early diagnosis and intervention.
Of 30 consecutive children with a clinical diagnosis of JCA according to EULAR criteria, x-rays of the wrist were made on clinical indication only. Visual comparisons were made regarding similarity in wrist position (deviation) of the two x-rays per child. From this it was determined that 12 wrists of 11 children were suitable for assessment (mean age: 10.4 years, sd 3.3, range 4.5-16.9; mean age at onset 5.8 years, sd 3.7; range 1.5-12.8: mean age at onset of wrist involvement 7.0 years, sd 3.2, range 2.0-12.8).
For each child, a set of two PA x-rays was made, including the metacarpals, the wrist and ± 7 cm of the distal radius, using a standardized technique. The first x-ray was taken with the wrist resting in neutral position, the second with the child grasping the rolled armcuff of a sphygmomanometer with maximum strength. A rigid dorsal splint was used to ensure that the wrist did not extend during grasp.
On the digitized x-rays osseous landmarks were identified, angles measured and lengths calculated from x- and y-coordinates. The displacement response of the carpus was obtained as the uncovered portion of the lunate (UPL) and the carpal-ulnar distance (CUD) (Youm et al. 1978). Because the position of the lunate changes with deviation, the wrist position on both x-rays was verified to be equal regarding the third metacarpal-ulna angle. Ratios were calculated for the CUD to the intermetacarpal width. Buckling of the capitate was assessed by visual observation. If the shape of the capitate had changed during grasp, CUD was not measured. Carpal narrowing (CN) and ulnar variance (UV) were assessed to analyze if grasping had produced the expected effects of loss of carpal height (Schuind et al., 1992) and proximal migration of the radius (Schuind et al., 1992; Linscheid, 1992), respectively. The standard t-test and analysis of variance techniques were used to analyze the results. The level of significance was at p < 0.05.
Because of probable extension during grasp, despite the splint, two wrists were further excluded from the results. Change in shape of the capitate was observed in seven of the remaining ten wrists. Therefore, CUD measurements were not included in the results. The change in the third metacarpal-ulna angle ranged from 8.9¡ radial deviation to 4.0¡ ulnar deviation and was not statistically significant (p = 0.4). The shape of the lunate did not change during grasp, as shown by a statistical insignificant difference (p = 0.5) between lunate width in resting position and during grasp. During grasp a statistically significant increase in UPL (p = 0.004), as well as in CN (p = 0.05) was found, and a decrease in UV (p = 0.05). The mean change in UPL was an increase of 10.0% (sd: 8.4%; range: -1.2%-22.5%). The displacement responses of individual wrists are shown in figure 1, including change in CN and UV. In two cases a slight radial displacement of the lunate was found. In the other eight, ulnar lunate displacement was found, ranging from 3.1% to 22.5%.
Figure 1: Change in uncovered portion of the lunate (ÆUPL), carpal narrowing (ÆCN), and ulnar variance (ÆUV), in mm, from resting position to grasp in 10 juvenile arthritic wrists.
It is the general understanding that the pattern of wrist malalignment in JCA is different from RA. How and to what extent the underlying pathokinesiology of these patterns is different and/or similar, is still unclear. In this study, ulnar displacement of the lunate, loss of carpal height (increase in UPL and CN, respectively) and proximal migration of the radius (decrease in UV) were found during grasp. These changes are similar to those found in healthy wrists (Schuind et al., 1992). Furthermore, they suggest that on the whole the juvenile arthritic wrists act in accordance with the explanation for the development of malalignment of the wrist in adult RA wrists. However, not all wrists responded the same. Radial displacement of the lunate and varying amounts of ulnar displacement were found. The amount of ulnar displacement varied substantially (3.1% to 22.5%).
The development and course of malalignment is a complex interaction of, changes in, bone geometry and configuration, ligamentous constraint and muscle performance. In view of treatment it is imperative to understand why the carpus may respond differently in terms of displacement mode and direction. This means analyzing the different factors and their influence and interaction. Analyzing the displacement response during grasp in juvenile arthritic wrists has proved not to be easy. However, further research along this line is warranted, using biomechanical modeling along with in vivo studies.
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Viegas S.F. et al. J Hand Surg, 20A, 312-8, 1995.
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This work is supported, in part, by the Royal Dutch Association of Physiotherapy and the University Hospital Utrecht.
