Scaphotrapezoid Assessment during Thumb Carpometacarpal Arthroplasty: A Cadaveric Study

Abstract

Background Due to limited sensitivity of radiographs for scaphotrapeziotrapezoid (STT) arthritis and the high rate of concurrence between thumb carpometacarpal (CMC) and STT arthritis, intraoperative visualization of the STT joint is recommended during CMC arthroplasty. Purpose We quantified the percentage of trapezoid facet of the scaphotrapezoid (ST) joint that could be visualized during this approach, and compared it to the degree of preoperative radiographic STT arthritis. Methods We performed dorsal surgical approach to the thumb CMC joint after obtaining fluoroscopic anteroposterior, lateral, and oblique wrist radiographs of 11 cadaver wrists. After trapeziectomy, the ST joint was inspected and the visualized portion of the trapezoid articulation marked with an electrocautery. The trapezoid was removed, photographed, and the marked articular surface area and total surface area were independently measured by two authors using an image analysis software. The radiographs were analyzed for the presence of STT arthritis. Results The mean visualized trapezoid surface area during standard approach for CMC arthroplasty was 60.3% (standard deviation: 24.6%). The visualized percentage ranged widely from 16.7 to 96.5%. There was no significant correlation between degree of radiographic arthritis and visualized percentage of the joint ( p = 0.77). Conclusions: On average, 60% of the trapezoid joint surface was visualized during routine approach to the thumb CMC joint, but with very large variability. Direct visualization of the joint did not correlate with the degree of radiographic STT arthritis. Clinical Relevance A combination of clinical examination, pre- and intraoperative radiographs, and intraoperative visualization should be utilized to assess for STT osteoarthritis and determine the need for surgical treatment. Level of Evidence This is a Cadaveric Research Article.

Keywords: CMC; STT; carpometacarpal arthritis; intraoperative visualization; scaphotrapeziotrapezoid arthritis; scaphotrapezoid.

Fig. 1

Cadaver trapezoid and anatomic illustration. ( A ) Photograph of cadaver trapezoid for surface area measurement. After surgical approach to the carpometacarpal was used to visualize the scaphotrapezoid joint and marked visible articular surface with electrocautery, scaphoids were excised. To improve contrast for image analysis, electrocauterized areas were colored over with a surgical marker ( purple ink ). Photographs were taken with a ruler in frame. ( B ) Example of surface area measurement of the scaphoid articulation of the trapezoid. The marked area was outlined in the same way to allow calculation of percentage visualized. Measurement was performed by two authors independently using ImageJ software with calibration based on ruler length. ( C ) Illustration of the trapezoid.

Fig. 2

Lateral and anteroposterior radiographs showing the scaphotrapezoid and scaphotrapezium joint in a cadaver wrist. Radiographs were evaluated using White et al's classification system. While their system used a modifier for involvement of the scaphotrapezial joint, scaphotrapezoidal joint, or both, for our purposes only the scaphotrapezial joint was evaluated.

Fig. 3

Box and whiskers plot of distribution of measured percentage scaphotrapezoid joint surface. The bottom of the box represents the first quartile and the top of the box represents the third quartile. The horizontal line within the box represents the median. The vertical lines represent the minimum and maximum values.