BACKGROUND: The purpose of this study was to define radiographic morphologic variations of the proximal and middle phalanges of all digits to compare these anatomic parameters with the dimensions of currently available intramedullary (IM) headless screws.
METHODS: Standardised posteroanterior (PA) and lateral (LAT) radiographs of 250 digits (125 males and 125 females) were analysed. Measurements were performed for the proximal phalanx of the thumb through little finger and for the middle phalanx of the index through little finger. Measurements included IM isthmus and cortical diameters, head and base dimensions, total bone length, and anterograde and retrograde distances from the isthmus. All dimensions were compared with specifications from commercially available headless screws.
RESULTS: On PA views, the mean IM isthmus diameter of the proximal phalanx was greatest in the thumb (4.8 mm) and smallest in the little finger (2.9 mm). On PA views the middle phalanx demonstrated isthmus diameters of 3.4 mm (middle finger) to 2.5 mm (ring finger). On LAT views, IM diameters were narrower (1.5-2.4 mm). Male participants demonstrated significantly larger osseous dimensions across most parameters. Comparative analysis with available implants demonstrated that smaller-calibre screws (≤3.0 mm) appropriately matched the IM canal of most middle and ring phalanges. In contrast, larger devices (≥3.0 mm) may be suitable for the proximal phalanges of the thumb and middle finger.
CONCLUSION: Intramedullary canal diameter and phalangeal morphology vary by digit and gender. For most digits, 2.0- to 3.0-mm IM headless screws best approximate the native canal dimensions. Awareness of these anatomic constraints is essential for preoperative planning and selecting the correct implants therby minimising the risk of iatrogenic fracture and screw jamming while optimisng intramedullary phalangeal fracture fixation.
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