Delayed unions, nonunions, malunions Flashcards
What are the four tenets of bone healing?
Mechanics, scaffold, growth factors, cells (My Sad Granny Cracked).
Inadequate mechanical or biologic environment will result in delayed, non- or mal-union.
What size fracture gaps should be avoided to prevent non-union associated with too large defect size?
Defects approaching the diameter of the bone.
However, the size of defect that ultimately results in non-union likely depends on local factors of stability, width of the bone, local biologic factors, and preservation of the periosteum.
What are the two aspects of the mechanical environment that need to be optimized to ensure uncomplicated bone healing?
- Geometric configuration
- Forces and resultant motion of fracture fragments
What is the ideal strain for uncomplicated bone healing?
Varies depending on the direction (tensile strain most tolerated) and the size of the fracture gap (large fracture gaps seem less tolerant of high strain than small fracture gaps).
Limiting strain to less than 1% may result in stress protection. Strains of 5-10% are generally considered adequate for comminuted fractures or fractures with a small gap.
Mesenchymal stem cells are least tolerant of which type of forces during fracture healing?
Shear forces.
Under compression mesenchymal stem cells undergo transformation to chondroblastic lineages, under tension they undergo transformation to osteoblastic lineages.
What are the two biologic factors of bone healing?
- Growth factors
- Cells
What are some negative intrinsic factors for growth factor activity?
Diaphyseal cortical bone, decreased/compromised vascularity of the periosteum, old age, sparse soft tissue attachments
What is plate luting?
Placement of PMMA between the bone and the plate. Considered a less biologic form of repair.
What is an important source of mesenchymal stem cells during bone healing?
The periosteum.
What factors contribute to high cellular activity following fracture?
Thick periosteum, young age, metaphyseal bone, high vascularity, moderate hydrostatic tension
What is delayed union?
Prolongation in the time for fracture healing.
What are common mechanical and biologic causes of delayed union?
Mechanical: too large fracture gap, motion.
Biologic: intrinsic (patient factors), or extrinsic (surgeon factors)
What are the treatment options for delayed union?
Early intervention is preferred.
Aimed at improving the mechanical or biologic environment (introduction of BMP, demineralized bone matrix, autogenous cancellous bone graft).
What is a non-union?
A fracture that fails to progress to osteosynthesis regardless of healing time.
What are the classifications of non-unions?
Viable: Hypertrophic, oligotrophic
Non-viable: necrotic, dystrophic, atrophic, defect
What is the typical cause of viable hypertrophic non-union? How is it treated?
Inadequate mechanical environment.
Rigid fixation with dynamic compression is preferred treatment if possible, with resection of interposing fibrous tissue.
What type of non-union is shown?
What causes an oligotrophic non-union?
Combination of inadequate mechanical and biologic (inadequate cellular activity) environment.
Can be difficult to differentiate from a non-viable non-union radiographically
What is the treatment for oligotrophic non-union?
Common cause is loose implants (i.e. cerclage) in the area of the healing fracture.
Treatment therefore involves removal of the loose implants, elimination of interfragmentary motion, and reinstillation of a biologically active environment (bone grafts, growth factors).
What are the different types of non-viable non-union and their causes?
- Defect: gap at the fracture site is too large.
- Necrotic: infected section of bone.
- Dystrophic: non-viable bone on one or both sides of the fracture.
- Atrophic: resorption of the bone ends without healing or a restorative process.
How are non-viable non-unions treated?
Atrophic: requires removal of all nonviable bone and regeneration of new bone.
Defect: if stabilization is adequate may simply require regeneration of bone (bone grafts, growth factors, matrix scaffold). rhBMP-2 and 7 may be successful when used in conjunction with matrix materials.
What is the new bone that surrounds a sequestrum called?
Involucrum
What type of non-union is observed?
Oligotrophic secondary to loose cerclage wires.
What type of non-union is observed?
Necrotic due to presence of a sequestrum.
What is malunion?
Failure of mechanical reestablishment of form and function of the fracture, in which healing still occurs.
Malunion in which directions are generally tolerated?
Shortening of the limb, sagittal plane and mild translation deformities might be tolerated.
Rotational and frontal plane deformities are not tolerated.
Why is surgical correction of malunion challenging?
The absence of physical landmarks through fracture reconstruction.
Preoperative CT and use of intraoperative radiography are useful to ensure appropriate alignment is obtained.
Aside from surgical fixation, growth factors and grafts, what other methods have been described to help with non-union?
Extracorporeal shock wave therapy, pulsed electromagnetic field, low intensity pulsed ultrasonography
According to Marshall 2022 in Vet Surg, what were 5 risk factors for development of delayed or non-union?
Increasing age, comminuted fracture, use of a bone graft, surgical site infection, major implant failure.
Overall rate of delayed union was 14%, non-union was 5%.
