Estimation of radiographic joint space of the trapeziometacarpal joint with computed tomographic validation.

Purpose: Joint space width (JSW) is a common metric used to evaluate joint structure on plain radiographs. For the hand, quantitative techniques are available for evaluation of the JSW of finger joints; however, such techniques have been difficult to establish for the trapeziometacarpal (TMC) joint. This study aimed to develop a validated method for measuring the radiographic joint space of the healthy TMC joint.

Approach: Computed tomographic scans were taken of 15 cadaveric hands. The location of a JSW analysis region on the articular surface of the first metacarpal was established in 3D space and standardized in a 2D projection. The standardized region was applied to simulated radiographic images. A correction factor was defined as the ratio of the CT-based and radiograph-based joint space measurements. Leave-one-out validation was used to correct the radiograph-based measurements. A t-test was used to evaluate the difference between CT-based and corrected radiograph-based measurements ($\alpha =0.05$).

Results: The CT-based and radiograph-based measurements of JSW were $3.61\pm 0.72\mathrm{mm}$ and $2.18\pm 0.40\mathrm{mm}$, respectively. The correction factor for radiograph-based joint space was $1.69\pm 0.41$. Before correction, the difference between the CT-based and radiograph-based joint space was 1.43 mm [95% CI: $0.99-1.86\mathrm{mm}$; $p<0.001$]. After correction, the difference was $-0.11\mathrm{mm}$ [95% CI: $-0.63-0.41\mathrm{mm}$; $p=0.669$].

Conclusions: Corrected measurements of radiographic TMC JSW agreed well with CT-measured JSW. With in-vivo validation, the developed methodology has potential for automated and accurate radiographic measurement of TMC JSW.