SAS Bones Flashcards

Question

Describe how angular limb deformities are created and how you would counsel your clients?

Answer 1

Angular limb deformities Radius and ulna - in the pictured abnormality there has been premature closure of the distal ulnar growth plate = resulting in a shorted ulna. - as the two growth plates in the radius are unaffected they still attempt to produce a normal length in the radius - as the ulna is not growing at the normal pace - the radius starts to bow (change of shape in the radius is due to altered bone modelling during growth. - this change means weight is no longer distributed evenly across the two cortices of the radius (increased weight bearing on the concave side) Wolfs law (bone responds to the forces placed upon it) - the caudal cortex becomes thicker than the cranial cortex which becomes thinner. - This is driven by increased osteoblastic bone formation on the caudal cortex, and increased osteoclastic bone resorption on the cranial cortex - this is bone remodelling.

Answer 2

Collagen All types of collagen share a common tertiary structure - triple helix made up of three seperate polypeptide chains. The properties of collagen rish tissue are determined by; - collagen type - oreitation - packing - diameter of fibrils - Tendons have large fibrils, which are tightly packed to withstand tensile forces - collagen in joints has a small diameter in a web like layout. Collagen type one - bone, skin, dentin, cornea, blood vessels, fibrocartiliage and tendon. Collagen type two - cartilagenous tissues

Answer 3

**Diseases of growing bones** Usually acquired growth plate abnormalities; **1. Trauma / injury = abnormal growth** - growth plate cartilage is the weakest point of a growing bone. Therefore when a traumatic incident results in excessive loading of a growing bone near a joint, the growth plate will usually be disrupted before ligamentous injury occurs. - articular cartilage damage can lead to distorted epiphyseal growth. - ulna = compression, radius = shearing **2. Mechanically inuced to change = abnormal forces on the growth plate** eg Patellar luxation (Heuter Volkman law) **3. Retained Ulna cartilage cores** - cause of retarded growth in certain growth plates, especially the distal ulna - growth retardation may be partial (slow growth), or complete (no growth) - important implications for limb conformation and congruity of elbow and carpus.

Answer 4

Angular limb deformities Common in Chondrodystrophic dogs (short leg long body look) that have a genetic make up that leads to variable impairment of the growth of their appendicular skeleton. - chondrodystrophy = shortened legs and long body / Dushund Carpus Vulgus - paws turned outwards - elbows are bowed inwards Carpal varus With this condition, the elbows are often bowed out, and the paws are turned inward.

Answer 5

**The basic mechanisms of bone healing** Vascular response in fracture repair The fracture stimulates the release of growth factors that promote angiogenesis and vasodilation. - angiogenesis peaks two weeks post fracture - dependant on local muscle tissue - poorer in distal limb (tibia, radius/ulna) - vessels enter perpendicular to bone and will anastomose with periosteal vessels in early periosteal callus. This means the surgical approach must take care of the periosteum and surrounding soft tissue.

Answer 6

Primary vrs secondary fracture repair **Primary fracture repair Bone healing without a callus** - requires perfect anatomical reduction - requires rigid fixation so that the fracture site strain <2% - clinical union takes longer with primary than secondary so implants are required to work for longer. - direct haversian remodelling **Secondary bone healing Bone healing by callus formation** Sequence of events - haematoma, granulation tissue, fibrous connective tissue, fibrocartilage, cancellous / trabecular bone, cortical bone **- Callus** = functions to stabilise the fragments to allow lamellar bone to grow and fill the fracture gap - the size of the callus is related to the stability of the fracture. - callus types periosteal, medullary and endosteal.

Answer 7

Assessment and classification of fractures 1. Causal factors - direct or indirect trauma (intrinsic vrs extrinsic) - repeated stress - pathological (infection, neoplastic, metabolic) 2. Open / closed (this can not always be determined on radiographs 3. Extent - Complete vrs incomplete (greenstick) vrs fissure 4. Number and position of fracture lines 5. Configuration ie transverse, oblique 6. Localisation - which bone, which part of the bone - articular vrs non articular - anatomical location (proximal, middle, distal) 7. Forces acting upon the fracture 8. Stability - different fracture configurations have inherent stability against various forces that act upon the fracture lines - reconstructable vrs non reconstructable 9. Age of fracture

Answer 8

Fracture classifification Long oblique sinple mid - diaphyseal fracture of the femur (2.4x diameter of the bone) - probably not open due to large muscle coverage in this area.

Answer 9

Fracture classification Highly comminuted mid-diaphyseal fracture of the femur with fissuring of the proximal main fragment. Displaced fragments near skin surface mean it could be an open fracture.

Answer 10

Fracture configuration **Reconstructable** - ability to return the fragments to an anatomically correct and structurally intact state. - can bear (share) weight along with the implants. ** Non - reconstructable** Repair will have to bear all the forces - usually high energy (comminuted) fractures with more severe soft tissue injury and slower healing - decision making on type of repair more critical - race bewteen implant failure and bone union - makes post-op confinement crucial.

Answer 11

**Open fractures** A fracture in which the bone is exposed to the environment resulting from disruption of the soft tissues. **Start via classification of an open fracture** **Type one** - wound smaller than one cm - surrounding soft tissues are contused - often the wound is created by bone penetrating skin from within and retracts back into skin **Type two** - Produced from outside in by foreign object - some soft tissue injury around the skin wound (mostly viable tissue) - little if any loss of bone or soft tissue **Type three** - Most severe form with loss of tissue following penetration by an outside object has resulted - loss of skin, soft tissue and bone common - remaining soft tissue usually severely injured and requires debridement. **Management of an open fracture depends upon its classification** Type one and two open fracture; good prognosis that is managed in a similar fashion to closed fractures. Type three extensive and expensive treatment. Owners should be advised that the risk of infection and non union is high. - usually precludes internal fixation.

Answer 12

The four goals of treatment for an open fracture Open fracture = A fracture in which bone is exposed to the environment resulting from disruption of the soft tissue. 1. Prevent infection 2. Promote bony union 3. Repair soft tissue 4. Restore function

Answer 13

**Type three open fracture** Most severe form of open fracture with loss of tissue following penetration by an outside object has resulted. **Extensive and expensive treatment required** Owners should be advised that the risk of infection and non union is high. First aid - immediately stem any arterial bleed - only once the patient is assessed and stabilised, attention can be given to the wound - neurovascular integrity of the limb should be assessed. Treatment - Broad spectrum antibiotics, IV should be administered immediately (within three hours cephalosporins) - Flushing wound (even with tap water) to reduce contamination - debride any obviously devitalised tissues - cover the wound with a sterile dressing / sterile lubricant if treatment can not be administered immediately Repair should involve the simplest repair method that still allows access to the wound and preserves the integrity of surrounding tissues.

Answer 14

Physeal fractures Salter Harris classification: A descriptive term for fractures affecting growth plates of bone. Once the growth plate is closed the term Salter Harris no longer applies.

Answer 15

**Bone grafts ** Biological potential for healing can be augmented by bone grafting - cancellous or cortical - generally autografts (or allografts) - Autografts (autogenous) transferred within the same individual - Allograft (allogenic) transferred between different individuals of the same species. **The four attributes of a bone graft** 1. Osteoconduction - physical scaffolding - host bone production to bridge deficient 2. Osteoinduction - provisions of protein - stimulation of pluripotent mesenchymal cells (BMP) into osteoblasts 3. Osteosynthesis - osteocytes or undifferentiated progenitor cells that undergo mitosis and differentiation to chondrocytes and osteoblasts - the direct production of osteoid by surviving osteoblasts 4. Osteopromotion - platelets - aid in stimulation of osteogenesis

Answer 16

Fracture forces 1. Bending 2. Compression 3. Torsion 4. Shear 5. Tension 6. Combinations Different types of implants inherently resist some fracture forces better than others. - in reconstructable fractures, we need to match the type of implant to the type of fracture. - eg shear force of gluteals = pins perpendicular to the fracture plain.

Answer 17

**Bone graft** **Indication** When healing delays are anticipated; - older patient - comminuted / non reconstructable fracture - poor fracture biology - delayed / non unions - arthrodesis (surgical immobilisation of joint through fusion of bones) **Technique** Carefully select the metaphyseal site - aseptically expose the bone for harvest - broach the cortex (drill hole) - scoop out the cancellous bone - bone curette - storage = keep moist with blood ** Best sites for collection** - proximal humerous (highest yeild) - Femur - distal or proximal - proximal tibia - ilium

Answer 18

The four principles of fracture repair. 1. Reduction and fixation of fractures to restore anatomical relationships. 2. Stability of the fixation to reflect the requirements of the fracture and injury. 3. Use of gentle surgical techniques to preserve the blood supply to bone and soft tissue. 4. Early and safe mobilisation of the patient and affected bone.

Answer 19

**FAS Fracture assessment score** **Why** - Pre operative assessment and analysis of the factor for and against a successful outcome - appropriate choice of treatment based upon; stability of fracture, reconstructability, properties of available implants - Recognising important cinical factors; owner disinterest, patient young and hyperactive ** Components** - mechanical requirements of the fracture - biological factors likely to influence healing potential - assess clinical factors in context of whole animal. each component is assessed on a scaore / 10 - each component is then added together and /3 to achive an overall score.

Answer 20

**FAS fracture assessment score - mechanical** (Score out of ten). Mechanical considerations for a FAS assessment Unfavourable mechanical environment - multiple limb injury, more force applied to fracture - giant breed - communited fracture - non reducible fragments Favourable mechanical factors - single limb toy breed score 10 - simple fracture

Answer 21

FAS Fracture assessment score biological (Scored out of ten). Poor score 1 - old patient - poor health; diabetes, hypothyroidism, chronic infection - poor soft tissue envelope - cortical bone fracture - high velocity injury - extensive approach Good score = 10 - cancellous bone fracture - juvenile - excellent health - good soft tissue envelope = good blood supply - low velocity injury - closed

Answer 22

FAS fracture assessment = Clinical Poor score one - poor owner compliance eg absent owners, no cage available - poor patient compliance eg energetic dog - wimp patient - requires ongoing bandaging - high comfort level required High score ten = good prognosis - good owner compliance - good patient compliance - stoic - comfort level not a consideration

Answer 23

**Fracture repair** **Gardener approach** - closed fixation minimally invasive surgery - sacrifice load sharing for no disruption of fracture haematoma (biologcally friendly) - often increases mechanical demands on fixation system - emphasis on biological factors / assessment. **Carpenter approach** - open tissue dissection - anatomic reduction of the fracture - optimizing load sharing through cortical column restoration - often invasive, disrupts fracture haematoma - emphasis on mechanical factors / assessment.

Answer 24

Acronym definitions ORIF - open reduction internal fixation OBDT - open but do not touch MIO - Minimally invasive osteosynthesis MIPO / MINO - plate / nail

Answer 25

**MIO - Minimilly invasive osteosynthesis** A change from ORIF which lead to increases in infection and non union - MIO has become the next step **MIO** - focuses more on adequate alignment - maintenance of soft tissues and fracture haematoma then rigid fixation and anatomical reconstruction - bridging plates become more prevalent - distant manipulation of fracture ends

Answer 26

**MIO Minimilly invasive osteosynthesis** **Pros - reduced incidence of;** - non union - infection - delayed union **Cons - increased risk of** - malalignment due to poor visualistaion of the joints - joint space violation due to long plates - neurovascular injuries of the humerus - implant failure is more commonly seen as screw fracture.

Answer 27

**Strain theory and bone healing** Strain = A measure of deformation of the fracture gap in response to an applied load, expressed as a %. Calculation = magnitude of change in fracture gap when loaded / original size of fracture gap. eg 0.5mm change in a 2mm fracture gap = strain 25% - smaller fracture gaps therefore undergo more strain than larger fracture gaps - excessive strain prevents a union from forming - if fibrocartilage forms, strain is reduced further allowing bone tissue formation in the gap.

Answer 28

Stress strain theory The strain within the gap dictates which tissue can survive. - high strain enviroments >10% only fibrous tissue can survive - moderate strain <10% fibrocartilage can form - <2% strain bone can form - excessive strain will prevent a bony union. The goal of fracture fixation; too either 1. Elemenate intefragmentary strain through anatomic reconstraction, compression of bone ends and rigid fixation - cerclage wire, lag skrews - primary bone healing 2. Maintain a low strain environment, bridging techniques and implants that allow relative stability (large interfragmentary gaps to distribute strain - rod and plate, bridging plate - secondary bone healing

Answer 29

External Coaptation - external cast Often the chosen option for fracture management when costs are the driving force. **Criteria for external coaptation** Must anticipate bridging callus within four weeks as very few casts can be well maintained for longer than this. - only applicable distal to the elbow and stifle - provides good resistance to bending, but fractures are still subject to compressive forces - best for transverse fracture - simple oblique or spiral fractures that are stable following reduction may also be good candidates - juvenile: good healing potential and rapid bridging callus formation - requires a high level of compliance from the owner eg twice daily checks. Minimal displacement Minimum 50% contact at fracture line but aim for 100% reduction **When not to utilise external coaptation** - do not use for femoral or humeral fractures - do not use for growth plate injuries or articular fractures - do not utilise in unstable spiral or comminuted fractures - distal ulna and rdaius (particularly toy dogs) have a high incidence of delayed union due to a poor blood supply. - secondary health concerns eg chondrodystrophic / obeses animals

Answer 30

Major fracture fixation methods **Friction fixation Light weight fixation** - external coaptation - intra-medullary pins - cerclage wire - rush or cross pins **Threaded fixation Heavy weight fixation** - pin and tension band wire - interfragmentary screws - interlocking nail - external fixator - bone plates

Answer 31

Match fixation method to the fracture and patient ** Indications for Friction fixation;** - when time to healing is short (2-4 weeks) - with load sharing (reconstructable Fx) - young patients - low energy injury ** Indications for when threaded fixation is best;** - if longer healing time anticipated (6-8 wks or longer) - with non reconstructable Fx - older patients - high energy injury - need to maintian reduction and stability for a prolonged period.

Answer 32

**Complications of fracture repair** Aim of fracture repair = mechanical and biological. identify causes of each and actively avoid an environment for their development. **Complications of fracture repair** **Delayed union** - delayed healing - hypertrophic, oligotrophic **Non union** - dystrophic, necrotic, defect **Malunion** - Failure of mechanical reestablishment of form or function with complete healing - the bone heals but within an abnormal alignment **Osteomyelitis** Inflammatory condition usually resulting from an infectious agent - post traumatic or haematogenous spread - most commonly bacterial Staphylococcus, E.coli, Strep - Rads cortical bone resorption, lucency observed around implants - diagnosis via culture gold standard

Answer 33

**Fragment forceps** Ideal for fragment reduction, these forceps generally hold fragments in position whilst the permenant fixation is applied. Large forceps useful for when a very wide spread is required eg TTO surgery

Answer 34

**Reduction forceps** These forceps have serrated jaws and a spin lock which will provide secure incremental control.

Answer 35

**Kern bone holding forceps** Kern bone holding forceps give a very firm controllable grip on long bones, facilitating manipulation and reduction of fragments A quick release ratchet locks the jaws. Kerns are very useful in general orthopedic surgery around the hip joint, in particular; - femoral shaft fractures - triple pelvic osteotomy - hip toggle - fractures of the acetabulum

Answer 36

Arthritis A group of diseases which affect various tissues of the cartilaginous joints in the body. Osteoarthritis A group of complex diseases which result in the progressive breakdown of articular cartilage. - associated with changes in other components of the joint - currently an irreversible process Major isssue inhibiting progress - early diagnosis very difficult - large percentage of subclinical disease - aetiology / early pathogenesis still unclear

Answer 37

Unique characteristics of articular cartilage - no blood supply - no nerve supply - obtains nutrients from the surrounding synovial fluid - friction free surface (friction within a joint is less than ice). - withstands sudden changes in load - slow turnover of matrix - single cell type = chondrocytes.

Answer 38

**Normal straucture of cartilage.** **Structure** Collagen fibre arcades - loops of collagen to support structure - proteoglycans lying within the collagen arcades - lamina propria provides the friction free surface. - chondrocytes in the deeper layers of cartilage complete the structure. **Cartilage characteristics** - surrounded by pericondrium - chondroblasts (secrete matrix) - get trapped in matrix in pockets called Lacunae and become chondrocytes (maintain and repair) - collagen provides strength (type 2) - proteoglycan aggregates (cushioning).

Answer 39

**Proteoglycan aggregate** Proteoglycans lie within the collagen network. **Structure** - long chain of hyaluron (hyaluronic acid) backbone - chains of sugars attached to a core protein and attached to the HA via a core protein (Glycosaminoglycans GAGS) - proteo + glycans = core protein +GAGS Proteoglycans are proteins that are heavily glycosated. The basic glycosated unit consist of a core protein with one or more covalently attached glycosaminoglycan (GAGS) - GAG bristles act as filters to limit the diffusion of viruses and bacteria in tissues - proteoglycans attract water to form gels that; - keep cells hydrated - cushion tissues against hydrostatic pressure.

Answer 40

Pathogenesis of osteoarthritic cartilage. **Pathogenesis - inflammatory arthritis effects on synovial fluid** - haluronic acid decreases due to influx of plasma - HA molecular weight decreases due to cytokine attack - This results in a high volume, low viscosity fluid causing joint distension and pain **3 overlapping phases** - ECM degrades on a molecular level; more water and size of proteoglycans decrease and reduced stiffness - chondrocytes proliferate, increased activity - chondrocytes can't keep up repair activity, complete loss of cartilage tissue. In the short term 1-3 years anabolic increased thickness due to swelling - later cartilage loss

Answer 41

**Diagnosis of arthritis** ** Clinical examination** Physical signs of arthritis may be associated with lameness, gait abnormality, abnormal stance or no detectable clinical problem. - pain on manipulation pressure - capsule thickening / osteophytes - joint effusion - change in range of movement - crepitus on manipulation - heat ** Diagnoses ** Metrology Radiology (only shows bone) or advanced imaging scintigraphy Arthroscopy - visualisation of the joint - also allows treatment of disease (removal OCD, Meniscal damage repair, Implant positioning). - Kinematics (measure range and rate of movement) - Kinetics (plate measuring pressuring applied by foot)

Answer 42

Diagnosis by joint fluid analysis **Interpretation** **Normal joint** < 2.5 G/DL protien < 3000 total nucleated cell count > 90% mononuclear **OA osteoarthritis** WCC normal or slightly elevated <5000 total nucleated cell count <2.5 G/DL total protein <12% PMNs **Septic inflammatory** >2.5 G/DL protein >>15000 total nucleated cell count >75% neutrophils **Immune mediated** >2.5 G/DL protien >3000 total nucleated cell count >10% neutrophils Conclusion - Significant incraese in % of PMNs in joint fluid is conclusive evidence of inflammatory joint disease.

Answer 43

**Osteoarthritis** A complex of diseases which result in the progressive breakdown of articular cartilage. Pathogenesis 1. Chondrocyte metabolism is disturbed, immobilisation, biochemical poisoning and mechanical overload 2. Collagen micro-architecture breaks - the weakened collagen network allows water to be held in the cartilage matrix - cartilage nutrition decreases - cartilage loses stiffness and resiliance. It compresses easily and reshapes slowly. 3. proteoglycan synthesis is reduced; structure and organisation of the proteoglycan side chains are altered. The result of limited repair is a biochemically and biomechanically inferior joint surface.

Answer 44

Management of OA Note; aim is to manage not cure **Weight loss, exercise, treatment** - treat the clinical disease not radiographs 1. Weight - less compression and wear on the joint 2. NSAIDS **- Grapiprant** - inhibition of the enzyme cyclooxygenase (COX) - COX is required to convert arachidonic acid into thromboxanes, prostaglandins 2. Physical therapy - heat / cold massage - passive manipulation - swimming - gentle walking exercise - aim to improve blood flow and relax muscles 3. Disease modifying agents (PPS) - Gabapentin - Acetominophen (panadol mediated by serotonin) 4. Nutraceuticals - Glucosamine - Chondrotin sulphate - Omega three fatty acids 5. Stem cell therapy 6. Surgery - excision / TJR / arthrodesis - TJR total joint reconstruction Response to a particular therapeutic agent may be variable, even within a single patient - always try different agents.

Answer 45

Grapiprant Grapiprant is a small molecule drug that belongs in the piprant class Function = pain relief for mild to moderate inflammation related to osteoarthritis in dogs. MOA **- Grapipant directly and specifically blocks the EP4 receptor** - prostaglandins are key mediator of pain and inflammation - they cause inflammation by bnding to the EP4 receptor.

Answer 46

Beransa - anti nerve growth factor Highly specific immune system proteins that target and neutralise molecules involved in osteoarthritic disease. - function alike to naturally occuring antibodies - NGF and its interaction with tropomyosin receptor kinase A receptor - has been found to play a critical role in nocieception and nervous system plasticity in pain conditions.

Answer 47

**Osteochondrosis** A pathological condition in rapdly growing cartilage leading to a disturbance of endochondrial ossification. - disordered development of cartilage and bone. - may involve articular cartilage or growth plate cartilage. **Pathophysiology of OCD lesions** - cartilage matrix becomes abnormal in structure / or ischaemia - cartilage thickens - cracks and fissures develop - cartilage flap lifts - underlying bone becomes affected - degeneration / irritation of the joint

Answer 48

**Osteochondrosis** A pathological condition affecting young rapidly growing cartilage leading to a disturbance of endochondrial ossification. **Aetiology = ischaemia** - epiphyseal cartilage in growing animals receives its nutrition from blood via cartilage canals. - early failure of this blood supply results in cartilage necrosis which can lead onto osteochondrosis **Risk factors for osteochondrosis** Rapid growth - genetic factors - dietary factors Mechanical factors - trauma - weight bearing

Answer 49

**OCD Osteochondrosis** ** Osteochondrosis latens** - early microscopic lesion ** Osteochondrosis manifesta** - appearance of subclinical lesions that are macroscopically and radiologically apparent ** Osteochondrosis dissecans** - attached or loose cartilage flaps - are present and result in clinical signs. **Osteochondritis dissecans** - inflammation is not believed to be involved with the pathogenesis of this condition.

Answer 50

**OCD osteochondrosis** **Epidemiology** - usually present less than one year of age - male dogs > female dogs - large / giant breed dogs - there is likely a genetic component for each different manifestation of OC. ** Clinical signs** lameness either from synovitis or from the mechanics of a loose flap and bone trauma - 4-9 month large breed dog - assess both sides and take care not to attribute lameness to lesion too quickly (many OC manifesta arent clinical). **Diagnosis** - clinical examination and epidemiology (rapid growing large breed dog) - - radiographs - CT - arthroscopy

Answer 51

**Treatment for OCD Conservative management** Limited to young dogs <6.5 months that still have healing potential - lesions are small and mild clinical signs - no joint mice present - NSAIDS, exercise restriction, crate confimement, dietary supplyments and weight control - if signs persist surgery is indicated. **Surgery Arthrotomy or arthroscopy** debridement and lavage removing sources of irritation and inflammation. - arthroscopy allows more detailed investigation of the joint - flap excision and joint mouse retrieval is the goal of surgery - remove cartilage peripheral to lesion that is not firmly adherent to bone - the edges should be squared off and leveled to inhibit filling with fibrocartilage. **Restrorative techniques** - developed to restore focal cartilage defects with a more durable hyaline cartilage or synthetic surface.

Answer 52

The joints affected by osteochondrosis 1. Humeral head 2. medial aspect of the humeral condyle 3. lateral or medial femoral condyle 4. trichlear ridge of the talus (either medial or lateral)

Answer 53

**OCD osteochondrosis** Developed to restore focal cartilage defects with more durable hyaline cartilage or a synthetic surface. ** OATS** - osteochondral implants - cylindrical implants are harvested from the healthy patient and are implanted into the defect. **Synacart** synthetic implant - carbon fibres

Answer 54

A. Elbow dysplasia - causes forelimb lameness in large breed pups onset 5-8 months of age - male >female - very common - lameness will resolve spontaneously in some - causes OA which progresses with age regardless of how lame the dog is B. List the different pathologies involved with elbow dysplasia. - UAP, FCP and OCD incongruity - growth disturnance of radius or ulna eg trauma, retained cartilage cores - IOHC - medial compartment disease

Answer 55

Treatment options for the different pathologies of elbow dysplasia. **FCP treatment options** - conservative rest, analgesics and joint protection - Surgical arthroscopy to remove lose fragments - ulna osteotomy to reduce the pressure on the coronoid - BURP cutting of the biceps tendon to prevent compression of the radius - Subtotal coronoidectomy, removal of large fragments from the medial condyle - ulna osteotomy **UAP Ununited anconeal process** - lag screw or excison of UAP - ongoing OA management **OCD Osteochondrosis dessicans** - conservative NSAID and 6-8 weeks rest - Surgical Arthroscopy removal of joint mouse or cartilaginous flap

Answer 56

**Elbow treatment BURP** **Burp - Bicipital ulnar release procedure** - reduction of the compressive force on the radial head. Essentiall because the radius and ulna are not congruent - the added supination force from flexion and contraction of the biceps brachii and brachialis muscle = causes compression force of MCP on radial head

Answer 57

**Anatomy of muscles** Muscles are formed by bundles of fibres that are supported in connective tissue sheaths. The connective tissue contain vessels and nerves and serves to integrate muscle fibre actions as well as allow autonomous motion of various muscle components. Basic cellular unit = the sacromere - composed of actin and myosin myofibrils.

Answer 58

Mechanisms of injury and repair in muscles **Injury** 1. Contusions = blunt injury 2. Strains = direct injuries; most common musculotendinous junction. 3. Lacerations = sharp injuries 4. rupture, crushing or vascular compromise at any level. **There are three stages of muscle injury** Stage one = myositis and bruising but architecture remains intact. Stage two = myosistis and some tearing of the facial sheath. Stage three = tearing of the fascial sheath, muscle fibre disruption and haematoma formation - stage one and two are most commonly observed in the power graoup of muscles; triceps brachii, biceps femoris, tensor fascia lata - stage three is more common in the long head of the triceps brachii, gracilis, gastrocnemius.

Answer 59

**Muscle healing** injury - degeneration - regeneration or scar formation. ** Intact nerve and blood supply = regeneration** - if the muscle fibre degeneration is incomplete and an intact nerve and blood supply exists, then muscle regeneration can occur. ** Loss of blood and nerve supply** - commonly the degenerative changes occur throughout the entire muscle fibre, the fibre than becomes irreversible damaged and is replaced by fibrous tissue** = a weak point**

Answer 60

**The goal of muscle repair is to achive as litle scarring as possible.** - treat strains and contusions conservatively - immediate cold applications are indicated for the first 24 hours - injuries presented after 24hrs are treated with warm hydrotherapy, compressive bandaging and NSAIDS. **Surgical technique muscle injury** - muscle rupture typically at the musculotendinous junction. - the muscle ends should be held by skewering them with fine needles, never use crushing forceps - meticulous sutures few and fine sutures - materials should provoke a minimal inflammatory reaction, be absorbable, but maintain adequate strength for a reasonable period of time. - polyglycolic acid suture type.

Answer 61

Tendons and ligaments **Tendon** = connect muscle to bone - must be strong and resist lengthening - long tendons enable bulky muscle to be proximally located while acting distally - must be able to slide/glide over joints; tendon sheaths + seasamoid bones. - flattened **Tendon anatomy** - formed by coalescing of muscle fibres - directionally arranged type one collagen with a small amount of crimp -dense bands of collagen rich fibres that connect muscles to bone or other muscles - at points of insertion of insertion on bone tendons flare out and become more cartiliginous - seasamoid bones are found within tendons at points of maximal compression. - minimal blood supply and a low metabolic rate which has implications on their repair. **Consequence of tendon injury** - In health elongate slightly on initial loading as crimp flattens, remain a constant length under load and return to original length after load released. - damaged tendons do not return to normal length if damage has occured during load cycle.

Answer 62

**Ligaments** **Anatomy ** - Strauctures which attach bone to bone - typically span a joint and provide some stability and restriction of ROM - similar structure to tendon type one collagen with a small amount of crimp. **Function** to stabilise and guide movement of joints - important active neurosensory and proprioceptive role in locomotion **Consequence of ligament injury** - detrimental to proprioception of the joint and stability

Answer 63

**External skeletal fixation (ESF)** ESF is an apparatus comprised of transcutaneous fixation pins inserted into bone and connected by one or more connecting rods, bars or columns - can be used as aprimary or adjunctive stabilization. **ESF indications** In theory provides excellent stability against all forces so can use ESF in almost any situation. - comminuted fractures - open fractures - arthrodeses - transarticular stabilisation / fixation - tendon and ligament repair - limb deformities / corrective osteotomies

Answer 64

**External skeletal fixation** **Benefits** - allows biological healing as pins are placed in a minimally invasive fashion - maintain fracture haematoma, surrounding blood supply and soft tissue envelope - results in secondary bone healing, which is faster than primary bone healing - suitable in cases of compromised biology eg open fractures - fixation construct remains accessable and can be adjusted as necessary including mobilization - can adjust the fram post operatively - tolerated well by patients - economical for vet $ **Disadvantages** - increased risk of infection given the open skin - large bending moments placed upon pins (not suitable in cases of delayed healing). - requires high patient tolerance and owner compliance - post op care pin cleaning, bandages changed, more frequent radiographic check - connecting bar position far away from neutral axis of bone putting ESF at mechanical disadvantage.

Answer 65

**Four Types of External fixators "ESF"** ** Type one linear (half pins only)** - unilateral, uniplanar **Type two linear (full pins) ** - uniplanar, bilateral - full pins or half pins Application is more challenging - soft tissue issues - body wall for humerus and femur - careful placement of pins so that they line up with clamps on the other side. **Type three linear** - biplanar, bilateral - utilises both half and full pin splintage ** Circular and hybrid ESF** - uses tension wires through bone and attached to metal rings rather than bone pins - aluminium, stainless steel - can be complete or partial rings - multiple holes around the ring to allow connection of other elements Half pin = penetrates skin on near side only and near + far bone cortex Full pin = travels through skin, near + far cortex and excits skin far side.

Answer 66

Acrylic Use of acrylic in place of connecting bars and clamps allows pins to be placed in any configuration Advantage - pin may be placed in any configuration to position in safe corridors - can be moulded to not impede joints - no sharp edges to cause trauma - easy to claen - suitable for complex shaped bones eg mandible Disadvantage - inability to modify the frame once created - size of acrylic bars must be 3x the diameter of stainless steel bars to offer the same amount of inertia

Answer 67

Guidelines for placement and configuration of ESF framework ** Pin number and configuration** - 3-4 pins / fragment, more than four will not improve stiffness - far far near near - place pins 3/4 of bone diameter away from joints, and 1/2 bone diameter from fracture gap - pin = 25% of diameter of the bone - insertion with low drill speed Connecting bar must be 1cm away from skin - if the bar is too close to skin will cause a pressure sore - if it is too far will weaken the fixator Safe soft tissue corridors

Answer 68

**Biological osteosynthesis - open but do not touch** - less precise reconstruction and less rigid fixation will reduce iatrogenic trauma to the fracture site and encourage early formation of a callus - rapid secondary bone healing - indirect fracture reduction - bridging osteosynthesis - limited reliance on secondary implants - limited use of bone grafts **Biological osteosynthesis - open but do not touch ** 1. rigid fixation 2. less reliance on secondary implants (cerclage wire) 3. limited use of bone grafts 4. indirect fracture reduction.

Answer 69

Understand the difference between fixation methods **Friction fixation - light weight fixation** 1. External coaptation 2. intramedullar pins 3. rush pins, cross pins 4. cerclage wire When is friction fixation best - when time to healing is short 2-4 weeks - with early load shearing - young patients - low energy injury **Threaded fixation - heavy weight fixation** 1. pin and tension wire 2. interfragmentary screws 3. external fixator 4. interlocking nail 5. bone plates Threaded fixation is best; - if long healing times >6-8weeks - with non reconstructable Fx - older patients - high energy injury - maintain reduction for a prolonged time

Answer 70

**Different internal fixation options** ** Internal medullary pin** - good resistance against bending and shear forces - poor resistance against distraction, compression and rotational forces - minimally invasive use tibia, femur and humerus - Indications oblique, transverse or comminuted diaphyseal fracture **Kirschner wires (K wires)** - mostly non threaded and small - used with tension wire or in combination with other implants Especially good for growth plate injuries (small smooth implants which do not damage growth plate potential + growth plates heal quickly). **Cerclage wire** - indication oblique reducable fracture - never use alone - two wires minimum + fracture 2x diameter of bone - counteracts rotational and shear forces. - weakest point is the knot **Screws** - - Cortical skrew fine pitch indicated for diaphysis - Cancellous skrew larger diameter indicated for metaphysis and epiphysis.

Answer 71

**Intra medullary pin (Steinman pins)** 1.6-8mm in diameter - very traditional implant; sold rod circular usually with a non threaded trochar end - resist bending very well, and shear forces - NEVER USE ALONE, usually combined with cerclage wire, plates or external fixators - ideal for use in the tibia, fomur and humerus Never use in the radius or mandible Friction fixation only - light weight. **Indications** comminuted fractures in conjunction with ESF or plate and screws as part of a minimally invasive strategy. - transverse or oblique diaphyseal fractures sole implant (very few fractures meet these requirements). ** Advantgae** - resist bending forces well due to placement within neutral axis - quick + easy - little specialised equipment - inexpensive **Disadavantage** - poor resistance to compression, distraction and shear forces - rarely provide adequate stability alone - may allow wicking of bacteria along the medullary canal - iatrogenic damage - sciatic, joint, migration, surgeon.

Answer 72

**Kirschner wires (K wires)** **Solid pins 0.9-2mm diameter, mostly non threaded** Especially good for growth plate injuries - small smooth implants do not damage growth potential - growth plate injuries generally heal fast use with tension band wire temporary fixation in Sx Usually used in combination with other implants.

Answer 73

**Intermedullary pin placement** Pin must fill 60-70% of medullary canal when used as main fixation device. Fill 35% of medullary canal if it is a plate rod combination. - must consider the sahpe of the bone - select the right spot, once you create a hole/ path the pin will alawys follow it. - do not force the pin Instruments Jacobs chuck and handle power tools **Normograde technique** Difficult but preferred technique for the femur - completely control over where your pin goes proximally - can be done closed - the only way you can correctly pin a tibia **Retrograde technique** easier to get pin in the center of the medullary canal - requires an open approach to the fracture

Answer 74

**Orthopedic wire - cerclage wire** counteract rotational and shear forces Soft wire, stainless steel A greater diameter achives high yeild bending and tensile strength but is harder to work with. comes on coils or spools **Indications for cerclage wire** Full cerclage wires - encircles the bone completely - can provide interfragmentary compression in long oblique fractures - if applied correctly and reamins tight no detrimental effects on bone - NEVER USE AS A SOLE FIXATION - fractures must be fully reconstructable - use a minimum of two cerclage wires - length of fracture should be 2x the diameter of bone - wires should not be placed at fracture site or <1cm from anoth cerclage wire Atraumatically pass wire around reduced fracture, avoid blood vessels and nerves. place at 90 degress to bone axis Loose cerclage wire is very damaging to fracture healing.

Answer 75

Screws **Cortical skrews - relatively fine thread pitch** - indicated for cortical bone - designed for the diaphysis (may be used in cancellous bone. **Cancellous skrews - coarser pitch** - larger outer diameter - metaphyseal or epiphyseal bone - designed for cancellous bone only - smaller core diameter corresponding to cortical bone skrews so lower area moment of inertia.

Answer 76

**Canine hip dysplasia (CHD)** **Multipfactorial Aetiology** - most heretable orthopaedic disease - degenerative and developmental disease - complex inheritance, multifactorial - genetic - dietary - exercise factors - conformational factors - all lead to hip laxity **Pathophysiology** lag in ossification of the craniodorsal rim rapid growth asynchronus growth between muscular support and bone development This results in acetabular / femoral remodelling. - synovitis - cartilage damage - increase in synovial volume - leading to laxity/subluxation - focal forces on articular cartilage - erosion/deformation of rim - remodelling

Answer 77

**Clinical presentation of hip dysplasia** **Signalment** Two presentations - 6-9months associated with hip laxity / synovitis - mature dog associated with osteoarthritis **Presenting signs** - gait abnormality / lameness - difficulty rising - reluctance to exercise - crying in pain - inability to jump

Answer 78

**Hip Dysplasia** **Presentation** - young 6-9 months hip dysplasia - older dog hip osteoarthritis - reluctance to get up and move **General physical examination** Patient standing - check stance and assess for muscle atrophy eg symetry Second step Lateral recumbancy - palpation for range of movement and pain - palpation for joint laxity **Ortolani sign** - assessment of hip laxity and the angle of the acetabulum (open vrs closed) - requires deep sedation or anaesthesia - angle of reduction, subluxation - characteristics of 'clunk' help to assess damage to acetabular rim Hip laxity is not equivalent to hip dysplasia - but hip laxity is strongly associated with HD in young dogs.

Answer 79

Diagnosis of hip Dysplasia on rads ** PennHIP** Stress radiographic diagnostic method - three views extended, compression and distraction - Pennhip is allows for an early diagnosis at four months - advantage as treatment can be initiated early - advantages for breeders choosing pups for later breeding programs - early diagnosis in the absence of clinical signs is not an indication for surgery. **Extended distraction view** - can artificially reduce hip laxity - lack of progress in breeding programs - non functional position

Answer 80

**Puppy HD treatment options** **Young dogs** - conservative mangement - Triple pelvic osteotomy (TPO) - juvenile pubic symphysiodesis (JPS) - femoral head excision ** Conservative management** - controlled exercise - specific exercises / heat / massage / stretching - dietary management - physical therapy Grapriprant **Triple pelvic Osteotomy** The aim is to rotate the acetabular segment of the pelvis to provide more support for the femoral head **Juvenile pubic symphysiodesis** - must be carried out prior to clinical signs being evident basically a prophylactic treatment requires early diagnosis - prior to 20weeks of age - aim to rotate the acetabular segment to provide better femoral head coverage ** Femoral head excision** Aim is too remove the source of pain.

Answer 81

Hip dysplasia treatment options in a mature dog Mature dogs; - conservative management - Total hip replacement (THR) - Femoral head ostectomy (FHO) - Capsular deneravtion Conservative management** - controlled exercise - specific exercises / heat / massage / stretching - dietary management - physical therapy Grapriprant

Answer 82

Treatment options for hip dysplasia in young animals **Triple pelvic Osteotomy** - Aim is to rotate the segment of the pelvis to provide more support for the femoral head. Indications - significant CS - no signs of OA on X ray - significant hip laxity on palpation ** Juvenile pubic symphysiodesis** Aim is to rotate the acetabular segment to provide better femoral head coverage (similar to TPO) - must be performed early <3-5 months Indications - linked to early diagnosis - performed prior to the onset of clinical signs - basically a prophylactic surgery

Answer 83

**Femoral head ostectomy (FHO)** A THR must always be offered prior to FHO ** Indications** ** **- severe hip dysplasia - femoral head necrosis (terriers) - non reducable hip luxation - sever ostearthritis ** Guidelines for procedure** - early surgery before severe atrophy - craniolateral approach - free drapping - correct inscision - remove neck including the caudal shelf - palpate excision site thoroughly

Answer 84

**THR Total hip replacement** **Expensive** - can be used as a definitive treatment for a mature dog with severe pain due to OA - provides excellent functional results - surgical complications can be significant - specilised procedure - cemented and uncemented technique. ** Contraindications** - neurological dysfunction - contralateral hip disease - neoplasia - bacterial dermatitis - other local infection.

Answer 85

**Avascular necrosis of the femoral head** **Signalment and aetiology** - Avascular necrosis of te femoral head usually as a result of trauma - mostly in dogs (toy breeds terriers), so probably a genetic basis - transient loss of blood supply - femoral head becomes necrotic - as removal of dead bone occurs femoral head may collapse. **Clinical signs** - lameness and pain may be minimal if early revascularisation occurs and there is only minimal collapse and distortion of the femoral head - most cases only present after femoral head collapse

Answer 86

**Patellar luxation **Aetiology** - Most causes of patella luxation are developmental - patellar luxation in dogs is a dynamic problem involving the structure of the whole limb - abnormal direction and magnitude of forces acting upon the growing tibia and femur **Clinical signs** - hindlimb lameness - limb deformity / cannot extend the stifle - crouched stance (bilateral medial luxation) - knock kneed or crouched (bilateral lateral luxation)

Answer 87

**Grade of petella luxation** Graded from one to four depending on the tendancy of the patella to luxate and ease of manual reduction. - grades 1-4 mild - severe Grade one = Vet is able to luxate but the patellar immediately returns to correct position Grade two = patellar can sponatneously luxate and return to correct position Grade three = permenantly luxated but can be reduced to correct position Grade four = permenantly luxated and can not be reduced to correct position.

Answer 88

**Surgery option available for correction of petella luxation** - most cases of petalla luxation are developmental - abnormal direction and magnitude of forces acting on the growing tibia and femur. 1. Bilateral tibial tubercle transposition 2. Bilateral trochlear wedge recession 3. Bilateral medial desmotomy 4. Bilateral extracapsular CCL repair

SAS Bones Flashcards

(115 cards)