Kirsten Deruddere – Residents Forum 2014 Advanced Vetcare - Melbourne MINIMALLY INVASIVE PLATE OSTEOSYNTHESIS
Overview ⦿ Introduction ⦿ Bone healing principles and interfragmentory strain theory ⦿ ORIF vs biological osteosynthesis ⦿ Changes in plate design ⦿ MIPO principles ⦿ Important articles for exams
Plating History ⦿ Plating has been used since the 1800’s. ⦿ Common complications included infection, malunion or nonunion or poor return to function. ⦿ Steam sterilisation (1886) and xrays (1895) ⦿ 1949 – link between stability and type of bone healing was made
Bone Healing Principles
Direct Bone Healing Summary Absolute stability � Simple fractures and ⦿ osteotomies, articular fractures Accurate anatomic reduction ⦿ Open reduction with direct ⦿ visualisation of fragments Little/no callus forms ⦿ Absolute stability using: ⦿ plates and screws, lag screws, pins, etc Healing takes 2-3 months in ⦿ young animals, up to 12 months in adults
Indirect Bone Healing Summary ⦿ Comminuted fractures, Relative stability non-articular fractures ⦿ No accurate anatomic reduction ⦿ Ideally the fracture is not exposed ⦿ A large callus forms ⦿ Relative stability is achieved using: cast, bridging plates, IM pins, ESF, etc ⦿ Healing takes 4-6 weeks in young animals, or up to 12 weeks in adults
Spectrum of Stability IM Nail Ex Fix Bridge Plating Cast Compression Plating/ Lag screw Absolute Relative (Rigid) (Flexible)
Interfragmentory Strain Theory ⦿ Pluripotent cells are responsive to local deformation within a fracture gap and different tissues can withstand specific levels of deformation beyond which they are unable to survive. ⦿ Granulation tissue (100%)>cartilage (15%)>Bone (2%) ⦿ Bone resorption occurs at the fracture gap under conditions of relative stability to increase the gap, decrease strain and encourage deposition of cartilage and fibrous tissue.
The AO Principles 1962 – AO principles ⦿ (1) restoration of anatomy, ● ● (2) stable fracture fixation, (3) preservation of blood supply, ● (4) early mobilization of the limb and patient. ● � New AO Principles ⦿ Fracture reduction and fixation to restore anatomical relationships; ● ● Fracture fixation providing absolute or relative stability as the “personality” of the fracture, the patient, and the injury requires; ● Preservation of the blood supply to soft tissues and bone by gentle reduction techniques and careful handling; Early and safe mobilization and rehabilitation of the injured part and the ● patient as a whole. � Gradual change to more biological fixation ⦿ ● Plate application Plate design ●
Change from ORIF to Biological Fixation
Change from ORIF to biological osteosynthesis ⦿ Factors contributing to osteomyelitis, non-union and sequestration (Rozbruch 1998): ● Extensive soft tissue dissection ● Disruption of the fracture haematoma ● Multifocal periosteal necrosis secondary to plate compression ● Iatrogenic trauma associated with interfragmentary implants such as lag screws and cerclage wires. � ● Best predictor of success: longer plates and fewer screws ● Time to union during this study went from 20 weeks to 13 weeks as techniques shifted towards biological osteosynthesis. ● Nonunion rates dropped from 10% to 4%. ● Success rates increased despite less use of bone grafts.
ORIF to Biological Osteosynthesis ⦿ Biological osteosynthesis consists of less precise reconstruction and less rigid fixation which reduces iatrogenic trauma to the fracture site and encourages early formation of callus with rapid secondary bone healing. ⦿ Generally this requires the use of locked internal fixators which have minimal implant- to-bone contact, long-span bridging and fewer screws for fixation. ● Ie. Interlocking nails, bridge plating and internal fixator-like devices (locking plates).
Principles of Biological Osteosynthesis ⦿ Indirect reduction ⦿ Flexible fixation ⦿ Avoidance of biological damage ⦿ Less reliance on the use of bone grafts � ⦿ The aim is to produce the best biological conditions for healing rather than absolute stability of fixation. ⦿ � early solid union in both humans and animals ● Biological internal fixation is only applicable to living bone
Changes in Plate Design
Limited Contact Plates ⦿ Early temporary porosity � ● A correlation was seen between porosity and the width of contact of the implant � assumed due to damage to the periosteal blood supply ⦿ Limited contact plate ● Minimise bone contact and impingement on periosteal blood supply � minimises soft tissue necrosis
Locking plates (Internal Fixators) Screw heads lock into the plate � axial and angular ⦿ stability. Stability is not dependent on the frictional forces ⦿ generated by lagging the plate to the bone as for conventional plates. Advantages: Threads are unlikely to strip. ⦿ The plate does not need accurate contouring and sits ⦿ off the bone preserving the extraosseous blood supply. Increased strength against pull-out cf DCP ⦿ Monocortical screws can be used because the locked ⦿ head acts as a second cortex. Some locking screws have a thicker core with increased ⦿ bending stiffness.
Locking Plates ⦿ Anatomic reduction is not necessary ⦿ Iatrogenic trauma to the fracture site is minimised ⦿ Ideal for bridging osteosynthesis, comminuted fractures or fractures with large amounts of bone loss. ⦿ Achieves relative stability and secondary bone healing. � ⦿ Locking plates are ideal for MIPO!
Minimally Invasive Plate Osteosynthesis
What is MIPO? Guiot 2011 VS
Minimally Invasive Plate Osteosynthesis 1. Use of indirect, closed reduction techniques; 2. Epiperiosteal plate insertion through small incisions remote to the unexposed fracture site; and 3. Minimal reliance on secondary implants and bone grafts.
Advantages of MIPO (1) ⦿ Reduced operative time ⦿ Decreased risk of infection ● Shorter surgery time, limited soft tissue trauma, less chance of contamination. ⦿ Increased callus formation ⦿ Preservation of periosteal blood supply ○ Farouk Arch Orthop Trauma Surg 1998, J Orthop Trauma 1999, and Borrelli J Orthop Trauma 2002 showed this in humans. ○ Garfolo VS 2011 – showed this in radii in dog cadavers.
Advantages of MIPO (2) ⦿ Faster healing than ORIF, less care than ESF ● Baumgaertel Injury 1998 – sheep ● Johnson JAVMA 1998 – 35 dogs ⦿ Reduced post-op pain ⦿ More cosmetic closure
Disadvantages of MIPO ⦿ Technically challenging ⦿ Less suitable for simple and intra- articular fractures ⦿ Access to intra-op fluoro is recommended ⦿ Fluoroscopy greatly increases radiation exposure to both patient and surgeon
Case Selection Indications: Comminuted diaphyseal or metaphyseal fractures ⦿ Excellent for radial and tibial fractures (Schmokel JSAP 2007) ⦿ � Less applicable: Simple transverse fractures ⦿ Femoral and humeral fractures are more challenging to achieve alignment ⦿ Metaphyseal and epiphyseal fractures – commonly used in humans with ⦿ special plates � Contraindications: Articular fractures ⦿ If anatomic reduction is required fluoro/arthroscopy should be used ⦿ If major neurovascular bundles overly the approach ⦿ MIPO should not be used if bone is necrotic. ⦿
Indirect Fracture Reduction ⦿ The aim of the reduction is to restore length and alignment so that the joints proximal and distal to the fracture are in the correct orientation. ⦿ Vascularised fragments will be incorporated into the fracture callus. ⦿ Indirect reduction – the fracture is not exposed
Reduction – Hanging limb technique
Reduction Forceps
Circular/unilateral ESF
IM Pin
Pre-contoured plate/push-pull
Fracture Distractor
Traction Tables
Approach Minimise trauma to nerves/vessels ⦿ One distal incision and one proximal, create an ⦿ epiperiosteal tunnel and then stab incisions as needed Optimal number of screws for MIPO in dogs/cats has not ⦿ been determined Human guidelines (Gautier and Sommer) ⦿ ● Span large segments of bone at least 3X the length of the fractured segment ● Screw-to-hole ratio to less than 0.5 ● Leave at least 2-3 screw holes empty over the bone defect. ● Construct stiffness can be increased by increasing plate size, increasing the number of screws or adding an IM pin.
Articles to Read ● Perren J Bone Jt Surg 2002 – Evolution of internal fixation, interesting read and summary of conventional plating, locking internal fixators, reasons for changes in plate designs, ORIF vs MIPO, etc. ● Garfolo VS 2011 – MIPO disrupts less periosteal vasculature of the canine radius than open plating. ● Hudson VCOT 2009 – Great review article on MIPO. ● Rovesti VCOT 2006 – First article using intraoperative skeletal traction in dogs with special tables. ● Pozzi VCOT 2009 – Review of approaches to bones for MIPO – more for practical use than for exams.
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