Evaluation of a novel screw position in a type III distal phalanx fracture model: an ex vivo study

Bindler D, Koch C, Gendron K, Ferguson SJ3, Kaposi AD, Papp M, Bodó G. Vet Surg. 2015 Oct; 44 (7): 829-37.

OBJECTIVE: Mechanical evaluation of a novel screw position used for repair in a type III distal phalanx fracture model and assessment of solar canal penetration (SCP).

STUDY DESIGN: Experimental study.

SAMPLE POPULATION: Disarticulated equine hooves (n = 24) and 24 isolated distal phalanges.

METHODS: Hooves/distal phalanges cut in a sagittal plane were repaired with 1 of 2 different cortical screw placements in lag fashion. In group 1 (conventional screw placement), the screw was inserted halfway between the proximal border of the solar canal (SC) and the subchondral bone surface on a line parallel to the dorsal cortex, whereas in group 2, the screw was inserted more palmar/plantar, where a perpendicular line drawn from the group 1 position reached the palmar/plantar cortex. Construct strength was evaluated by 3-point bending to failure. SCP was assessed by CT imaging and macroscopically.

RESULTS: Screws were significantly longer in group 2 and in forelimbs. Group 2 isolated distal phalanges had a significantly more rigid fixation compared with the conventional screw position (maximum point at failure 31%, bending stiffness 41% higher). Lumen reduction of the SC was observed in 13/52 specimens (all from group 2), of which 9 were forelimbs.

CONCLUSIONS: More distal screw positioning compared with the conventionally recommended screw position for internal fixation of type III distal phalangeal fractures allows placement of a longer screw and renders a more rigid fracture fixation. The novel screw position, however, carries a higher risk of SCP.