The Evolution of Osteosynthesis
Biological Principles and Minimally Invasive Fracture Management
From Mechanical to Biological Fixation
Historically, the AO (Arbeitsgemeinschaft für Osteosynthesefragen) principles of the 1960s dictated that successful fracture repair required perfect anatomical reduction and absolute rigid internal fixation. While this approach dramatically advanced veterinary orthopaedics, it often came at a significant biological cost: extensive soft tissue dissection, iatrogenic stripping of the periosteum, and evacuation of the fracture hematoma.
Modern veterinary traumatology has undergone a profound paradigm shift. We have moved away from purely "mechanical osteosynthesis" toward biological osteosynthesis. Today, the overarching goal is to balance the mechanical demands of the implant with the biological imperative of preserving the local osteogenic environment, utilizing techniques like Minimally Invasive Plate Osteosynthesis (MIPO) and advanced locking constructs.
Biomechanics and Perren’s Strain Theory
To understand modern implant selection, we must look to Perren’s Strain Theory, which dictates that the type of bone healing (primary vs. secondary) is determined entirely by the mechanical strain environment at the fracture gap.
Achieved through anatomical reduction and interfragmentary compression (e.g., lag screws and dynamic compression plates). This environment permits primary (direct) bone healing, where osteoclasts form cutting cones across the fracture line, followed directly by osteoblasts. There is no cartilaginous callus. This is strictly required for articular fractures to prevent step-defects and subsequent osteoarthritis.
Achieved through bridging osteosynthesis (e.g., locking plates spanning a comminuted fracture). The implant acts as a load-sharing or load-bearing splint. This environment stimulates secondary bone healing via endochondral ossification, producing a robust periosteal callus.
In diaphyseal fractures, particularly highly comminuted ones, we actively want relative stability. Attempting to anatomically reconstruct a shattered diaphysis drains the fracture hematoma (rich in bone morphogenetic proteins) and devascularizes the bone fragments, significantly increasing the risk of delayed union, non-union, or infection.
Minimally Invasive Plate Osteosynthesis (MIPO)
The clinical application of biological osteosynthesis is best realized through MIPO. Rather than a massive lateral approach to the femur or medial approach to the tibia, MIPO utilizes small proximal and distal insertion incisions.
An epiperiosteal tunnel is bluntly created using surgical elevators or the plate itself. The plate is slid subfascially/epiperiosteally across the fracture zone, and screws are placed at the proximal and distal bone segments, leaving the fracture site completely untouched.
Key Clinical Advantages:
- Preservation of the Fracture Hematoma: The primary source of cytokines, growth factors (PDGF, TGF-β), and mesenchymal stem cells remains intact.
- Preservation of Blood Supply: Avoids disruption of the periosteal and medullary blood supply, critical since traumatized bone relies heavily on extraosseous perfusion.
- Accelerated Callus Formation: Clinical studies consistently demonstrate faster bridging callus formation and shorter times to clinical union compared to open anatomic reduction.
The Role of Locking Plate Technology
The success of biological osteosynthesis relies heavily on the evolution of implants, specifically the transition from Dynamic Compression Plates to Locking Compression Plates and similarly advanced locking plate systems.
Traditional Frictional Plates (DCP)
Traditional plates rely entirely on friction. The screws must pull the plate tightly against the bone to create stability.
- Requires perfect anatomical contouring to the bone to prevent fragment shifting during tightening.
- Inadvertently crushes the periosteum under the footprint of the plate, severely compromising cortical perfusion.
- Prone to screw toggle and pull-out in osteoporotic bone.
Locking Constructs (LCP / ALPS)
Locking plates function as internal external fixators. The screw heads lock directly into the plate via threaded or Morse taper mechanisms, creating a fixed-angle construct.
- The plate does not need to be perfectly contoured to the bone.
- Does not compress the periosteum, preserving the vital extramedullary blood supply.
- Distributes stress evenly across the implant rather than concentrating it at a single screw-bone interface, drastically reducing the risk of screw pull-out.
Orthobiologics in the Modern Theatre
Even with perfect mechanics, biology occasionally needs a catalyst, particularly in cases of severe bone loss, high-velocity trauma, or revision of a non-union.
- Autogenous Cancellous Bone Graft (ACBG): Harvested from the proximal humerus, iliac crest, or proximal tibia, ACBG remains the gold standard. It provides the trifecta of bone healing: osteogenesis (living osteoblasts), osteoinduction (growth factors), and osteoconduction (a physical scaffold).
- Allografts and Demineralized Bone Matrix (DBM): When ACBG volume is insufficient, DBM provides an excellent osteoinductive and osteoconductive alternative, recruiting local mesenchymal stem cells to differentiate into osteoblasts without donor-site morbidity.
- Advanced Cellular Therapies: Platelet-Rich Plasma (PRP) and Bone Morphogenetic Proteins (rhBMP-2) are increasingly utilized to saturate the fracture gap with heavily concentrated growth factors, accelerating endochondral ossification in challenging environments.
The BoneVet Clinical Perspective
At BoneVet Orthopaedics, our approach to trauma is dictated by the biological demands of the patient. For comminuted diaphyseal fractures, we strongly favor bridging osteosynthesis utilizing locking plate technology, often facilitated via MIPO or Open but Do Not Touch (OBDNT) approaches.
By prioritizing the vascular envelope and leveraging fixed-angle mechanics, we significantly reduce operating times, minimize soft tissue morbidity, and predictably accelerate clinical union.
For our referring primary care colleagues across Queensland, this translates to faster patient discharges, fewer implant-related complications, and a significantly smoother postoperative rehabilitation phase for the client.
Selected Clinical References
- Perren, S. M. (2002). "Evolution of the internal fixation of long bone fractures. The scientific basis of biological internal fixation: choosing a new balance between stability and biology." The Journal of Bone and Joint Surgery. British volume, 84(8), 1093-1110.
The foundational paper defining the strain theory and the paradigm shift from absolute to relative stability. - Gautier, E., & Sommer, C. (2003). "Guidelines for the clinical application of the LCP." Injury, 34(2), 63-76.
A definitive breakdown of the biomechanical differences between conventional frictional plates and fixed-angle locking constructs. - Pozzi, A., & Lewis, D. D. (2009). "Surgical approaches for minimally invasive plate osteosynthesis in dogs." Veterinary and Comparative Orthopaedics and Traumatology, 22(04), 316-320.
Details the anatomical approaches and clinical validation for applying MIPO techniques in canine patients to preserve the soft tissue envelope. - Hudson, C. C., et al. (2009). "Minimally invasive plate osteosynthesis: applications and techniques in dogs and cats." Veterinary Surgery, 38(5), 575-582.
Demonstrates the clinical efficacy, rapid callus formation, and reduced complication rates of biological osteosynthesis in veterinary trauma.