A special healing pattern in stable metaphyseal fractures

Abstract

Background and purpose Metaphyseal fractures heal in a rapid fashion that is different from the bone shaft healing process. Animal studies have focused on diaphyseal fractures. We investigated the metaphyseal fracture-healing process in rabbits.Animals and methods 60 rabbits (divided into 12 groups) underwent proximal tibial osteotomy, anatomical reduction, and fixation with screws. After surgery, the proximal tibiae were harvested at different time points for histology.Results No obvious osteonecrosis or bone resorption were found 2 weeks after surgery. From day 5 to week 5, woven bone or new trabeculae formed. From week 2, remodeling into lamellar bone started and reached a peak at week 6. These 3 stages overlapped. Histomorphometry showed that the structure changed as a unimodal curve.Interpretation The healing process of metaphyseal fractures appears to differ from the commonly studied healing process in diaphyseal fractures. It is rapid, and can be divided into 4 histological stages: cellular activation and differentiation, formation of woven bone, transformation of woven bone into lamellar bone, and further remodeling.

Metaphyseal Fracture Healing

“…In human distal radius fractures, we found osteoid as early as the second week after fracture (Fig 3) [5]. Similarly fast ossification in distal radial fractures has been reported by others [6,7] and studies in human vertebrae and animal models show similar phenomena [8,9].…”

“…Inflammation is followed by mesenchymal cell condensations forming osteoid, which becomes woven bone (Fig 4). This is then remodeled into lamellar bone [4,9,11]. In our experiments osteoid formed simultaneously throughout the traumatized marrow volume rather than mostly on the surfaces of old trabeculae, which has previously been thought to dominate.…”

Inflammation, fracture and bone repair

“…It is noteworthy, however, that the classic phases of secondary fracture healing are most commonly observed during the healing of cortical bone, for example, in the case of long bone diaphyseal fractures. Fractures at the bone metaphysis characterized by a dense network of trabecular bone heal mainly via intramembranous bone formation leading directly to deposition of new bone trabeculae between the fracture ends and production of new on bone on top of the existing trabeculae in the immediate proximity of the fracture [25–27]; formation of callus and endochondral bone formation are not typically observed. This is likely due to ample vasculature, immediate proximity of the bone marrow, larger number of bone trabecula, and ultimately due to larger availability of inflammatory and osteoprogenitor cells at the trabecular compared to the cortical bone.…”

Earlier effect of alendronate in mouse metaphyseal versus diaphyseal bone healing

“…The healing of metaphyseal fractures—or rather cancellous bone—has recently attracted increasing interest. These fractures appear to heal by mechanisms that in some regards differ from those of diaphyseal bone, perhaps because of the relatively large availability of mesenchymal stem cells (MSCs) in the metaphyseal marrow, as compared to the diaphysis …”