Advances in Dynamization of Plate Fixation to Promote Natural Bone Healing

Abstract

The controlled dynamization of fractures can promote natural fracture healing by callus formation, while overly rigid fixation can suppress healing. The advent of locked plating technology enabled new strategies for the controlled dynamization of fractures, such as far cortical locking (FCL) screws or active plates with elastically suspended screw holes. However, these strategies did not allow for the use of non-locking screws, which are typically used to reduce bone fragments to the plate. This study documents the first in vivo study on the healing of ovine tibia osteotomies stabilized with an advanced active plate (AAP). This AAP allowed plate application using any combination of locking and non-locking screws to support a wide range of plate application techniques. At week 9 post-surgery, tibiae were harvested and tested in torsion to failure to assess the healing strength. The five tibiae stabilized with an AAP regained 54% of their native strength and failed by spiral fracture through a screw hole, which did not involve the healed osteotomy. In comparison, tibiae stabilized with a standard locking plate recovered 17% of their strength and sustained failure through the osteotomy. These results further support the stimulatory effect of controlled motion on fracture healing. As such, the controlled dynamization of locked plating constructs may hold the potential to reduce healing complications and may shorten the time to return to function. Integrating controlled dynamization into fracture plates that support a standard fixation technique may facilitate the clinical adoption of dynamic plating.

Keywords: axial dynamization; callus; fracture healing; interfragmentary motion; plate; screw.

Figure 1

Two screw-based and three plate-based strategies for early and controlled dynamization of fractures: (A) far cortical locking; (B) dynamic locking screw; (C) active plate; (D) bi-phasic plate; and (E) axial micromotion locked plate (AMLP).

Figure 2

(A) Advanced active plate with (B) six PEEK anvils that are elastically suspended inside rectangular plate pockets by means of silicone bumpers. (C) Stiffness evaluation of the advanced active plating construct. (D) Post-operative fluoroscopies, showing plate application with two compression screws and four locking screws to stabilize the 3 mm osteotomy gap.

Figure 3

(A) Early fixation failure in two sheep due to overloading. Rectangular pockets in the plate are clearly visible since the PEEK anvils are radiolucent. (B) Week 9 radiographs of the remaining five tibiae with consistent bridging callus at the lateral cortex opposite the plate.

Figure 4

Consistent formation of periosteal callus formation and bridging at the anterior and posterior aspects at week 9 post-op.

Figure 5

(A) Consistent formation of periosteal callus on the medial aspect adjacent to the plate. (B) In two out of the five specimens, the medial callus extended partially onto the plate surface but did not adhere to the plate surface.

Figure 6

(A) All 5 specimens failed by spiral fracture involving a distal screw hole, as depicted by the white arrows. (B) The 5 mm diameter screw hole comprised approximately 30% of the diaphyseal diameter.