Orthopedics Flashcards
Name the four zones of the physis from the epiphysis to the metaphysis
RPH-PO
Reserve zone
Zone of proliferation
Zone of hypertrophy
Zone of provisional ossification
Zone of the physis where most fractures occur
Hypertrophic Zone
Tendons that contribute to the Achilles tendon
Gastrocnemius (major component), superficial digital flexor + common tendon (gracilis, semitendinosis and biceps femoris)
What is the classification system utilized for external skeletal fixators? describe
Type Ia: (Unilateral, uniplanar), composed of a single bar and clamps through which pins are introduced.
Type Ib: (unilateral, biplanar), composed of two bars located on the same side (i.e. frontal plane) with pins penetrating the bone from two different sides (i.e. craniolateral and craniomedial angles)
Type II (bilateral, uniplanar), composed of two bars on opposite sides of the limb. Further subdivided into “maximal” (all full pins) and “minimal” (full and half pins)
Type III (bilateral, biplanar), typically composed of three or more bars with pins protruding into the limb from three or more different planes.
Major factors contributing to fracture nonunions (3)
• Instability: Typically caused by poor technical judgement and/or execution on the part of the surgeon. Examples include the use of external coaptation in distal radial fractures, IM pins without added constraints against rotational and axial forces, ExFix with insufficient stiffness and loose cerclage wire.
• Poor biological environment: fracture location (small muscle envelope), extensiveness of soft tissue damage (high energy trauma) and surgical trauma may affect blood supply and prolong the debridement phase delaying healing.
• Nutrition: Adequate supply of protein, calcium, vitamin C and D are essential for bone healing and must derive from a well-balanced diet. Supplements are rarely indicated except for malnourished patents.
What are the types of a viable fracture nonunions?
• Vascular nonunion: characterized by cartilage and fibrous tissue formation within the fracture line. Radiographically characterized by a lucent line through the fracture observed on sequential radiographs.
• Hypertrophic nonunion: similar to vascular, but characterized by the presence of a prominent non-bridging callus.
Three properties of cancellus bone graft and their basic physiology
• Osteogenic property: synthesis of new bone from donor cells, which include MSC’s, osteoblasts and osteocytes.
• Osteoinductive property: MSC’s from donor site are recruited to produce chondroblasts and osteoblasts which produce new bone through endosteal ossification. The process is mediated by growth factors such as bone morphogenic proteins (BMP) ad platelet-derived growth factor (PDGF).
• Osteoconductive property: implanted scaffold passively allows ingrowth of host capillaries , perivascular tissue and MSC’s.
Describe the three phases of acceptance of a free skin graft
• Imbibition – (first 24-48 hours) thin film of fibrin and plasma separate the graft from recipient site, providing oxygenation and nutrition (although poorly). After 48 hours a fine vascular network begins to form withing the fibrin layer.
• Inosculation – (day 2 to 3 ) capillary buds interface with the deep surface of the dermis and provide more robust oxygenation and nutrition.
• Revascularization – (day 3 to 5 ) new blood vessels either directly invade the graft or anastomose with to open dermal vascular channels, establishing a permanent vascular supply.
Describe the aetiopathogenesis of Renal Secondary Hyperparathyroidism. What and where lesions are typically found?
The condition is known as Renal Secondary Hyperparathyroidism, characterized by elevated parathormone levels (PTH) secondary to Chronic Renal Disease. PTH is naturally degraded and excreted by the kidneys, and its production is limited by calcitriol (negative feedback inhibition). Calcitriol, the active form of vitamin D, is produced by renal tubular cells. The relative deficiency of Calcitriol induced by renal disease leads to persistently high PTH, which increases calcium resorption from bone and leads to osteopenia.
Bones of the skull and mandible are most commonly affected. Severe demineralization leads to softening to the point that the jaw is bendable (“rubber jaw”). Facial deformity, swelling and pain typically develop.
Most common sign of juvenile hip dysplasia
exercise intolerance
Name the five overlapping stages of secondary bone healing
- Inflammation
- Intramembranous ossification
- Soft Callus Formation (chondrogenesis)
- Hard Callus formation (endochondral ossification)
- Bone remodeling
Describe the sequence of events that take place during the Inflammatory phase of secondary bone healing, from the moment of fracture until the beginning of intramembranous ossification (second phase). State the end product of this phase.
- Inflammation: Loss of vascular integrity leads to hemorrhage and reduction of local oxygen tension. Primary hemostasis occurs and platelets release cytokines and growth factors, recruiting macrophages, neutrophils and other inflammatory cells. Fibroblast and platelet growth factors activate progenitor mesenchymal cells within periosteum, muscle and soft tissues. These progenitor cells will differentiate into osteoprogenitor cells, modulate inflammation and provide anabolic factors to encourage bone healing. Secondary hemostasis produces a hematoma composed of fibrin matrix, which provide further degranulating platelets and serves as a scaffold for mesenchymal cell infiltration as well as macrophages, endothelial cells and fibroblasts. The end result of this phase is the production of a provisional cell, growth factor and matrix-rich scaffold along the cortex, medullary cavity and periosteum into adjacent soft tissues. This scaffold is eventually remodeled into granulation tissue to form a reparative granuloma, termed external callus.
Describe the events that take place during the second stage of secondary bone healing (intramembranous ossification). State the end product of this phase.
- Intramembranous ossification: Mimics the process of skeletal development. Progenitor cells from the overlaying periosteum proliferate and differentiate into osteoblasts to start new bone production adjacent to the fracture gap, between the periosteum and cortex (no cartilaginous intermediate). This leads to the formation of an early hard callus, but is insufficient to bridge and stabilize the fracture.
Describe the events that take place during the third stage of secondary bone healing (soft callus formation/chondrogenesis).
- Soft Callus Formation (chondrogenesis): Starts as soon as a robust bed of granulation tissue is formed across the fracture gap (external callus). Granulation tissue transitions to fibrovascular tissue and finally to fibrocartilage containing collagens type I and III over several weeks. The matrix is initially avascular as resembles the proliferative zone of the physis. The persistent tissue hypoxia, presence of growth factors and cell-matrix interaction cause stem cell population to differentiate into chondrocytes. These chondrocytes produce extracellular matrix rich in collagen Type II, aggrecan and other cartilage-specific proteins. The resulting callus is termed “soft callus” and bridges the fracture gap. This callus is fragile, however, and remains insufficient to decrease strain to a level that permits osteoblast survival.
Name the four bone envelopes?
periosteal, endocortical, trabecular and intracortical
Discuss the fifth phase of secondary bone healing, explaining the role of bone multicellular units (BMU) as it pertains to the production of this phase’s final product (name and explain it).
- Bone remodeling: This final phase of bone healing lasts months to years. The abnormally large and misshapen woven bone produced during ostechondral ossification is weaker than primary bone, and therefore gradually replaced by lamellar bone. Resorption occurs withing each of the four bone envelopes (periosteal, endocortical, trabecular and intracortical). Osteoclasts and osteoblasts work together as Bone Multicellular Units (BMU) is a continuous process of activation, resorption, reversal, formation and quiescence. The end result of the formation of Osteon, a structure composed of concentric layers of bone enclosed by a cement line with a central Harversian canal.
Explain the Wolff’s Law and how it relates to mechanotransduction.
Bone remodeling is strongly influenced by Wolff’s Law, which states that bone in a healthy animal will adapt to the loads under which it is placed. This occurs through the process of mechanotransduction. Bone generates a small electrical potential when it deforms, with an electropositive environment on the concave surface (compression) and electronegative environment on the convex side (tension). Electropositivity is associated with an increase in osteoclastic activity, whereas electronegativity induces osteoblastic activity. This justifies the fact the cortical bone under compression (concave surface) typically appears osteopenic on radiographs, while bone under tension (convex side) appears sclerotic.
Define area moment of inertia
A structural property that describes a structure or material’s ability to resist deformation
How is implant compliance calculated (give formula)? Which factor can be changed with the highest degree of influence on the overall compliance of the contract? How does this apply to a juvenile bone fracture?
Compliance = L3 / I x E
L= functional length (distance between the two innermost screws), multiplied to the third power
I= Area Moment of Inertia (a material or structure’s ability to resist deformation)
E= Elastic modulus of the plate material (inherent to the type of material used in the making of the implant)
Changing the distance between screws (functional length) affects compliance the most, and is typically under the surgeon’s control.
In young patients the physes are still developing and continuously elongating. They are composed of an anastomosed network of medullary vasculature and robust periosteal blood supply with periosteum membrane that acts as an external split. The cortices remain thin and exhibit low stiffness and strength, although have high ductility compared to adult bone. Implants typically fail at the screw-bone interface because the implant is to step in comparison to the juvenile bone. This leads to high stress at the screw-bone interface and eventually implant failure. The use of more pliable constructs, term “elastic osteosynthesis”, has been proposed as a means to distribute stress along the entire plate, limiting stress at the screw-bone interface and minimizing the chance of implant failure.
Define “elastic osteosynthesis” and how it applies to juvenile bone fractures
The use of more pliable constructs, term “elastic osteosynthesis”, has been proposed as a means to distribute stress along the entire plate, limiting stress at the screw-bone interface and minimizing the chance of implant failure.
Define interfragmentary strain and how it determines the kinds of tissues that can be supported within a fracture gap
• Interfragmentary strain: The formation of various tissue types during bone healing is directly dependent on the degree of interfragmentary strain. Strain is defined as the effect of loading on a fracture gap. Practically it is calculated by dividing the resulting length of the gap after loading by the original length. Smaller fracture gaps experience greater strain (concentrate strain) than large gaps. Granulation tissue can withstand almost 100% deformation, and is therefore the tissue found it to be formed within fracture gaps undergoing significant strain. As strain is reduced, tissues region collagen can develop and form a soft callus. Specifically, fibrocartilage is capable of accommodating 10 to 15% deformation. Osteoblasts and osteocytes can only survive in a very low strange environment, and bone can only tolerate 2% deformation.
Give three possible approaches to a distal humeral intercondylar fracture (T-Y fracture) And discuss the pros and cons of each
“A variety of surgical approaches can be used to gain access for accurate fracture reduction of the articular surface. A surgical approach by osteotomy of the tuber olecrani72,81 provides good exposure,2,6,21,106 but complications with repair of the olecranon osteotomy can occur in up to 37% of cases.2,6,39,76 Alternatively, tenotomy of the tendon of the triceps brachii muscle can be performed23,100; this may be advantageous in immature animals because it avoids damage to and possible premature closure of the proximal ulnar growth plate. Intracondylar fractures can also be approached via separate lateral and medial approaches.64 Combined medial and lateral approaches enable exposure of the whole distal part of the humeral diaphysis for fractures with supracondylar comminution. The combined approach avoids risk of damage to the proximal ulnar growth plate in immature dogs.”
Excerpt From
Veterinary Surgery: Small Animal Expert Consult
Spencer A. Johnston VMD, DACVS & Karen M. Tobias DVM, MS, DACVS
https://books.apple.com/us/book/veterinary-surgery-small-animal-expert-consult/id1250368401
This material may be protected by copyright.
Classification scheme for Medial Patella Luxation, expected anatomical abnormalities and clinical signs
Grade 1: the patella can be manually luxated during stifle extension but tends to spontaneously reduce itself. Typically asymptomatic incidental finding.
Grade 2: Spontaneous luxation occurs with clinical signs ranging from non-painful “skipping” lameness to mild discomfort. Mild deformities typically exist, consisting of internal tibial rotation and abduction of the hock.
Grade 3: The patella is permanently luxated by can be manually reduced. More severe bony deformities are usually present, including marked internal tibial rotation, distal femur varus and a shallow troclear groove. The patient usually stands with a “crouched” posture due to internal rotation of the stifle.
Grade 4: The patella is luxated and cannot be manually reduced. Similar anatomical abnormalities as for Grade 3, but more severe. The tibia is internally rotated between 60 and 90 degrees relative to the sagittal plane. Severe mobility impairment present, similar to grade 3 but more severe.
Pelvic fractures: how many sites are typically fractured? In order a frequency, where are the fractures most commonly located?
 “Of 556 cases of pelvic fractures in dogs and cats, 76% of cases had fractures at three or more sites. The pubis was the most frequently fractured bone, followed, in order of frequency, by the ischium, sacroiliac joint, ilium, acetabulum, and pubic symphysis.”
Excerpt From
Veterinary Surgery: Small Animal Expert Consult
Spencer A. Johnston VMD, DACVS & Karen M. Tobias DVM, MS, DACVS
https://books.apple.com/us/book/veterinary-surgery-small-animal-expert-consult/id1250368401
This material may be protected by copyright.