Abstract
Background Thumb metacarpal subsidence after trapeziectomy can affect clinical function over
time. Methods for measuring subsidence after trapeziectomy have been described, and
they rely on an intact thumb metacarpal or proximal phalanx for measurement. The authors
evaluated the reliability and reproducibility of measuring the trapezial space ratio,
using previously described methods. In addition, the authors evaluated a new method
that measures trapezial space on a posteroanterior (PA) hand/wrist radiograph that
does not rely on an intact thumb metacarpal or proximal phalanx for measurement, which
can often be altered by degenerative changes or in cases in which metacarpophalangeal
arthrodesis is performed during carpometacarpal (CMC) joint arthroplasty to correct
excessive hyperextension. The authors hypothesized that a new method of calculating
trapezial space would have comparable reliability and reproducibility to previously
proposed methods.
Methods Thirty-seven PA hand/wrist radiographs from patients who had trapeziectomy with ligament
reconstruction and tendon interposition were evaluated. Trapezial space was measured
using PACS (Picture Archiving and Communication System) digital tools as the distance
perpendicular to the tangents of the scaphoid and first metacarpal joint surfaces.
All X-rays were evaluated individually by five fellowship-trained hand surgeons, twice,
4 weeks apart. The reviewers calculated trapezial space ratios, using three different
methods, two previously described and a novel one: (1) trapezial space relative to
first metacarpal length (classic 1); (2) trapezial space relative to proximal phalanx
length (classic 2); and (3) trapezial space relative to capitate height (novel). Inter-
and intraobserver reliabilities were measured using intraclass correlation coefficients
(ICC) and limits of agreement for each method.
Results The authors identified excellent agreement between the classic 1, classic 2, and
novel methods with an ICC greater than 0.8, indicating excellent agreement. The average
trapezial space ratios for the thumb proximal phalanx, thumb metacarpal, and capitate
methods were measured as 0.19, 0.12, and 0.24, respectively. The upper and lower limits
of the 95% confidence intervals for both the inter- and intraobserver agreements of
the aforementioned trapezial space ratios were (0.17–0.26), (0.11–0.17), and (0.21–0.34)
for the interobserver rates and (0.11–0.25), (0.06–0.16), and (0.12–0.33) for the
intraobserver rates, respectively.
Conclusion Measuring trapezial space is an important diagnostic tool to assess postoperative
changes in thumb length. The trapezial space indexed to the capitate height method
(novel) provides a simple and similarly reliable method for calculating the trapezial
space ratio on a PA radiograph of the hand/wrist when other measurement techniques
are unavailable and when the thumb metacarpal or proximal phalanx is not intact. The
authors found a high degree of reproducibility and inter- and intraobserver reliability
as measured by the ICC and the 95% limits of agreement that compare with previous
agreements in the literature.
Keywords
carpometacarpal joint - intraclass correlation coefficient - trapezial space ratio
