The Reliability of Kaplan’s Cardinal Line as a Potential Surface Marker for the Superficial Palmar Arch During Carpal Tunnel Release: An Anatomical Study With Surgical Perspective

Purpose Kaplan's cardinal line (KCL) provides a more accurate reference point to the superficial palmar arch (SPA). The aim was to determine the KCL-SPA distances and their relationship with the other defined superficial landmarks, such as distal wrist crease (DWC) or distal portion of the transverse carpal ligament (TCL) or DWC-TCL distance. The objective was to determine the distal limit of the incision made during carpal tunnel release (CTR). Methods Sixty hands were dissected after KCL was drawn on each hand using standard methods. The distance from KCL to the SPA was measured along the radial and ulnar borders of the ring finger and recorded as radial and ulnar KCL-SPA distance, respectively. The distance between the DWC and the distal portion of the TCL was also measured (DWC-TCL). Correlation analysis was done between the DWC-TCL and KCL-SPA distance. The ratios between the radial and ulnar KCL-SPA distance and DWC-TCL distance were calculated and mentioned as radial and ulnar Kaplan cardinal index, respectively. Results KCL-SPA distance was 6.8±3.7 mm along the radial border and 6.6±3.6 mm along the ulnar border of the ring finger. The DWC-TCL distance was 29.4±1.2 mm. The means of radial and ulnar Kaplan cardinal indices were 0.23 and 0.22, respectively. A significant correlation was found between the DWC-TCL distance and the KCL-SPA distances. Conclusion Clinically, KCL can be appraised as a predictable surface landmark in limiting the distal-most extent of the incision during CTR and protecting SPA from transection. The SPA was found to lie at a variable distance from the KCL, and the minimum distance was found to be 3.3 mm. This should be considered as the maximum permissible extension of CTR incision beyond KCL.