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Comparing antegrade versus retrograde intramedullary screw fixation for extra-articular diaphyseal fractures of the proximal phalanx. A biomechanical study
Bert Vanmierlo, MD1, Bruno Vandekerckhove, MD2, Shanna Zielinski, n/a1, Joris Duerinckx, MD, PhD3, Jean Goubau, MD, PhD4 and Bert Op 't Eijnde, PhD1, (1)UHasselt, Hasselt, Limburg, Belgium, (2)AZ Delta, Roeselare, West-Vlaanderen, Belgium, (3)ZOL Genk, Genk, Limburg, Belgium, (4)UZ Brussel, Brussel, Brussels Hoofdstedelijk Gewest, Belgium

Recent literature has provided evidence supporting the efficacy and the minimally invasive nature of intramedullary headless headless compression screw (IMHCS) fixation for unstable proximal phalangeal fractures. This technique exhibits minimal complications, fast recovery, and early restoration of motion. Nevertheless, there is a lack of reports addressing fixation direction and stability in this context.
The goal of the present study was to evaluate the failure force and stability of transverse extra-articular diaphyseal proximal phalanx (P1) fractures comparing two fixation techniques: antegrade versus retrograde screw fixation. A biomechanical analysis was conducted using a cadaveric human transverse P1 fracture model.

Materials and Methods
We conducted a study involving 20 proximal phalanges of the index, middle and ring fingers from five pairs of cadaver hands. A transverse proximal cut, measuring 15 mm from the base of P1, was made in each phalanx. The phalanges were then divided into two groups: 10 were fixed using an antegrade technique, while the other 10 were fixed using a retrograde technique. In all phalanges, the same fully threaded headless compression screws (2.5mm diameter - 30mm length) were used. Subsequently, a three-point bending test was conducted to assess maximal failure force and stiffness.

The mean maximal failure force was 108.89 N in the antegrade group and 34.03 N in the retrograde group (p < 0.05, p = 0.0039). Mean stiffness was 89.68 N/mm in the antegrade group and 71.62 N/mm in the retrograde group (p < 0.05, p =0.1602).

IMHCS fixation represents a minimally invasive technique for fixation of proximal phalangeal fractures with good biomechanical properties. These fractures can be approached using different antegrade screw insertion techniques, such as the intra-articular and transmetacarpal methods, as well as the intra-articular retrograde technique. The retrograde approach, while feasible, has notable disadvantages, including a relatively smaller distal articular surface of the proximal phalanx, the need to traverse the vulnerable central slip of the extensor apparatus, and the challenge of obtaining a stable bone-screw construct due to the wider proximal metaphyseal medullary canal. Antegrade screw insertion provides distinct advantages by enabling secure insertion into the hard subchondral bone at the proximal articular surface. This facilitates a more robust and stable construct.
Consequently we concluded that the antegrade method is biomechanically superior to the retrograde method for extra-articular proximal diaphyseal fractures of the proximal phalanx, offering significantly stronger fixation.

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