Kaplan's cardinal line

To determine if a consensus definition exists in the literature and among hand surgeons for Kaplan's cardinal line (KCL) and to determine the relationship of the various descriptions to deep structures.

The literature contains 4 different descriptions of KCL. Members of the American Society for Surgery of the Hand were surveyed to determine which line they understand to be the correct description of KCL. The 4 variations of KCL were marked on cadavers and the lines' precision in identifying deep structures was measured.

Our survey showed that there is no consensus regarding the definition of KCL. Fifty percent of the surgeons surveyed use KCL as a surgical landmark. A line extended along the abducted thumb and a line from the apex of the interdigital fold between the thumb and the index finger to the hook of hamate most closely reproduce the location of deep structures of the hand and are the farthest from and always proximal to the superficial palmar arch. The line from the apex of the interdigital fold between the thumb and the index finger parallel to the middle crease of the palm and the line from the apex of the interdigital fold between the thumb and the index finger to a point 2 cm distal to the pisiform are the farthest from the motor branch of the median nerve and are markedly closer to the superficial palmar arch. All lines are radial and distal to the motor branch of the median nerve.

Ambiguity exists regarding the definition of KCL among hand surgeons and in the literature. Although no single line is ideal for locating all deep structures, line C is the safest line to identify hand anatomy. Kaplan's cardinal line does not locate the deep structures of the hand accurately but may assist in making palmar incisions.