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52 Cards in this Set
- Front
- Back
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Valgus deformity:
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lateral deviation of the limb distal to the location of the deformity
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Varus deformity:
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medial deviation of the limb distal to the location of the deformity
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Where does most long bone growth occur?
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metaphyseal region of the physis with smaller contributions from the epiphysis growing both toward the articular surface and toward the physis
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What regulates longitudinal bone growth?
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thought to be a negative feedback loop involving parathyroid-hormone related protein and indian hedgehog protein interacting with parathyroid and parathyroid-hormone related protein receptors. Increases in IHH stimulates PTHrP release which inhibits differentiation of proliferating chondrocytes into hypertrophic chondrocytes, promoting longitudinal growth
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What regulates PTHrP-IHH feedback loop?
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signalimg molecules such as patched1, gli, and smoothend
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What perinatal factors influence development of ALD?
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incomplete ossification, laxity of periarticular structures, and aberrant intrauterine ossification
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How does incomplete ossification result in ALD?
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If allowed, uneven loading of the dysmature skeleton leads to ALD
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What regions is most affected by incomplete ossification?
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dorsal aspect of the small tarsal bones
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What occurs with loading of incompletely ossified bones?
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thinning of the precursor cartilage and development of pathologic fracture
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How does periarticular laxity result in ALD?
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allows abnormal loading of the articular surfaces
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How is Diagnosis of ALD made?
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by visual inspection, palpation & manipulation of the limb, and radiography
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How is fetlock varus detected?
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From a craniolateral position, if the carpus is pointed outward but the toes are pointed forward, a varus deviation of the fetlock exists
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When does the distal MC/MT3 physis close?
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around 3 months of age
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What does ability to straighten a carpal valgus deformity with application of pressure on the medial aspect of the carpus and lateral aspect of the fetlock indicate?
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deformity is from either incomplete ossification or preiarticular laxity. Inability to correct the valgus in this manner indicates that osseous structures are involved in the deformity
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What is offset carpi (bench knees)?
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valgus deformity of the distal radius and varus deformity in the distal MC3 of the same limb
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What is the key to successful treatment of ALD?
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early diagnosis
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Non-surgical ALD treatment:
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stall rest, splints or casts, and hoof manipulation
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When is stall rest effective?
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newborn foals with incomplete ossification and straight limbs at the time of birth, foals with adequate ossification but disproportionate growth at the physis, foals with diaphyseal deformity, and foals adequate ossification but laxity of periarticular soft tissues
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How long should foals with incomplete ossification be stall rested?
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for a maximum of a month
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How long should foals with diaphyseal deformity or disproportionate growth of the physis be stall rested?
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4 to 6 weeks
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Function of splints and casts for ALD:
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maintain the limb in proper alignment, allowing ossification and weight bearing without detrimental consequences
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Where should casts and splints end on the limb?
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end at the fetlock otherwise the flexor and extensor musculotendinous units weaken, resulting in dropped fetlock and osteopenia
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What occurs after removal of the cast or splint?
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immobilization of the flexor carpi ulnaris and ulnaris lateralis in the cast or splint results in a temporary calf-knee conformation after removal of the support but improves with time
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When are splints and casts used for ALD?
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Only ALD caused by incomplete ossification or periarticular laxity. For other types or causes of ALD, splints and casts should not be used
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How is hoof trimming used for ALD?
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The lateral aspect of the hoof should be rasped in foals with valgus deformity, causing the medial aspect of the foot to strike the ground first, and rotating the foot medially. For varus deformity, the medial wall is rasped.
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How are shoe extensions used for ALD?
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With valgus deformity, the extension is placed medially and for varus deformity, the extension is placed laterally
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What is the benefit of application of shoes with extensions?
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prevents excessive wear and may help with correction
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Types of surgical techniques for ALD:
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growth acceleration, retardation or a combination of acceleration and retardation
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Example of growth acceleration:
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periosteal transection and elevation performed on the concave surface of the affected bone
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Where is periosteal transection performed for carpal valgus?
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lateral distal radial transection
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Describe periosteal transection of distal radius:
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3 cm vertical and a 2 cm horizontal periosteal incision between the CDE and lateral DE just proximal to the distal radial physis. After creation of the T incision, the flaps of the periosteum were lifted with an elevator, or could be removed for a more prolonged effect. The SQ is closed and the skin is apposed with an intradermal pattern. If a rudimentary ulna is present, it should be removed with ronguers.
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Where is periosteal transection performed for fetlock varus:
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medial aspect of the distal aspect of the metaphysis
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Where is P1 periosteal transection performed?
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at the level of the extensor branch of the SL curvature medially or laterally, with the horizontal incision directed proximally and the vertical incision distally
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Where is periosteal transection performed for tibial deformity?
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cranial or caudal to the lateral digital extensor tendon
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How does periosteal stripping affect growth?
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upregulate IHH in the early prehypertrophic and hypertrophic zones of the growth plate, increase PTHrP receptors in all zones, and upregulate FGF and TGF in all zones
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Types of Growth retardation:
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transphyseal screws and wire, a single transphyseal screw, a single transphyseal abdorbable screw, or a 2.7mm bone plate
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When is growth retardation used?
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in foals with severe deformity or in foals with deformity that persists after the rapid growth phase is over
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When is growth retardation performed for fetlock deformity:
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after 2 months of age
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When is growth retardation performed for hock deformity?
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after 4 months of age
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When is growth retardation performed for carpal deformity?
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after 6 months of age
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Where is the implants placed for growth retardation?
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bridges the convex aspect of the bone to retard the growth on this side of the bone while allowing continued growth on the shorter aspect of the limb
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When is the single screw technique most often used?
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MC/MT3
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Advantages of single screw technique?
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more cosmetic and easier
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Disadvantages of single screw technique?
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more risk of developing physitis or metaphyseal collapse compared with the screw and wire technique
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Types of ostectomies:
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wedge or step
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When are ostectomies used for ALD?
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in foals with closed physes
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Why is the step ostectomy preferred?
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more bone length is maintained and allows placement of lag screws for interfragmentary compression through the ostectomy
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Most common location of ostectomy:
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MC/MT3
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How does the frontal plane ostectomy differ from sagittal plane?
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With a frontal plane step ostectomy, no wedge of bone is removed, but the 2 pieces of the bone can be rotated to correct rotational deformities
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Cause of ALD in mini horse:
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presence of complete ulna and complete fibula
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Disadvantage of correction of ALD in mini horses?
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must be addressed early because this breed has less growth potential and other breeds
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Correction of ALD in mini horse:
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portion of the ulna and fibula must be removed. The distal epiphysis of the fibula and tibia are not attached and after transection of the fibular, movement between the ends can cause abnormal development of the lateral trochlear ridge. To prevent this, the distal fibular styloid process is fixed to the distal tibial metaphysis or epiphysis or both with position screws
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