Distal Phalanx Depth Variation and Implications for Zone I Flexor Tendon Anchor Repairs: A CT and X-Ray Comparative Study

Abstract

Background:

Suture anchors in Zone I flexor tendon repairs risk dorsal cortex penetration and nail bed disruption. Preoperative measurements guide safe anchor-drill selection, yet the accuracy of radiograph-based measurements and optimal safety thresholds remain unclear. This study quantified distal phalanx depths, verified radiograph measurements with computed tomography (CT) scans, and assessed compatibility with commercially available anchor systems.

Methods:

Thirty adult subjects (120 digits) with paired lateral radiographs and CT scans of the same hand were retrospectively reviewed. Oblique and perpendicular depths at the distal phalanx base were measured independently by 2 reviewers on both imaging modalities and statistically analyzed. Safe depth thresholds were calculated and compared with specifications for 5 commercially available anchor systems. Male and female digits were compared.

Results:

Radiographs slightly overestimated CT (mean bias ≤ 0.6 mm) but showed a largely linear and predictable relationship. Maximum safe depths ranged from 3.8 mm in the little finger to 4.9 mm in the index, increasing to 4.6 to 5.9 mm with oblique drilling. Several anchor systems exceeded these limits, particularly in ring and little fingers.

Conclusions:

Digital radiographs provide sufficiently accurate measurements for most clinical scenarios with the use of a modest safety margin. Distal phalanx size varies by digit and gender, warranting added caution in female patients and in ring and little fingers. Our findings support routine consideration of retrograde oblique drilling techniques to optimize bone purchase and reduce the risk of dorsal cortex penetration.