Novel Customizable Fracture Fixation Technique vs. Conventional Metal Locking Plate: An Exploratory Comparative Study of Fixation Stability in an Experimental In Vivo Ovine Bilateral Phalangeal Fracture Model

Abstract

A novel composite patch osteosynthesis technique (CPT) has demonstrated promising ex vivo biomechanical performance in small tubular bones. To bridge the gap toward clinical evaluations, this study compared the stability of the CPT to a stainless-steel locking plate (LP) in an experimental in vivo ovine bilateral proximal phalanx fracture model. Eight sheep underwent a midline osteotomy with a 4.5 mm circular unicortical defect in the lateral proximal phalanx of both front limbs, treated with the CPT (n = 8) or the LP (n = 8). A half-limb walking cast, or a custom off-loading hoof shoe, was used for postoperative protection. Implant stability was assessed by post-surgery X-ray evaluations and post-euthanasia (16 weeks) dual-energy X-ray absorptiometry (DXA). At week one, all CPT implants demonstrated mechanical failure, while all LPs remained overall intact. Mean BMD was 0.45 g/cm² for CPT and 0.60 g/cm² for LP in the fracture area (p = 0.078), and 0.37 g/cm² vs. 0.41 g/cm² in the distal epiphysis (p = 0.016), respectively. In conclusion, the CPT demonstrated indications of inferior stability compared to the LP in this fracture model, which may limit its clinical applicability in weight-bearing or high-load scenarios and in non-compliant patients.

Keywords: biomechanical stability; fracture fixation; in vivo ovine fracture model.

Figure 1

Surgical procedure of the composite patch technique (CPT) and the locking plate (LP): (A) skin and soft-tissue incision and bone exposure, (B) CPT ‘2 by 2’ configuration before skin closure, (C) CPT ‘3 by 3’ configuration before skin closure, (D) LP positioning before skin closure, (E) soft-tissue envelope closed before skin closure, (F) off-loading wooden block under each medial (non-operated) toe.

Figure 2

Intra-operative X-ray images illustrating the fracture model (diaphyseal osteotomy with 4.5 mm central defect) and the implant configurations employed: (A) Composite patch technique (CPT) ‘2 by 2’ configuration, (B) CPT ‘3 by 3’ configuration, (C) Locking plate (LP) with unicortical locking head screws, and (D) LPC with bicortical locking head screws.

Figure 3

Example of post-euthanasia bone mineral density (BMD) analysis of the proximal phalangeal bone osteosynthesis with the composite patch technique (CPT), to the left, and locking plate (LP), to the right, respectively. The black arrow marks the fracture, and the grey arrow marks the distal epiphysis.

Figure 4

Examples of failure modes recorded at the 1 week mark. (A) composite patch technique (CPT) (sheep A1) showing patch breakage around screws. X-ray is taken through a cast, (B) CPT (sheep B1) showing patch breakage at midline. X-ray taken through an elastic bandage, and (C) Locking plate (LP) (sheep A3) showing the one example of screw loosening. X-ray taken through a cast.

Figure 5

Paired comparison of bone mineral density (BMD) in seven sheep treated with the composite patch technique (CPT) or conventional locking plate (LP). BMD was measured at two locations: the fracture area and the distal epiphysis. Each line represents a paired measurement from the same animal. Note that values are presented on a unified y-axis.