Final Exam - Patellar Luxation Flashcards by Madeleine Swindell

what dog breeds are more commonly affected by patellar luxation?

toy breeds - chihuahua, pomeranians, mini poodles, & yorkies

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T/F: toy breeds are 12x more likely to be affected by patellar luxations than large breed dogs

true

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what is surgery considered to do for dogs with patellar luxation?

improve quality of life

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what is the cause of patellar luxation?

congenital/developmental - can be acquired but congenital is more common

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what direction is luxation most common?

medial - variable for lateral luxation

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what is included in the quadriceps mechanism?

quadriceps, patella, trochlea, straight patellar tendon, & tibial tuberosity

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quadriceps function depends on what?

femoral patellar articulation & alignment

proper development of trochlear groove & tibia

proper loading of distal femur

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what happens to the pelvic limb in cases of chronic patellar luxation?

medial displacement of quadriceps mechanism

external torsion deformity of the distal femur leading to lateral bowing of the distal femur lateral torsion of distal femur

medial displacement of tibial tuberosity

distal femoral varus & distal tibial valgus

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what anatomic changes are seen in a dog with chronic patellar luxation?

lack of extension of stifle, severe deformation of the femur & tibia, & contracted & fibrotic soft tissue changes medially

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what signs may be seen on gait & standing exam on a patient with luxating patellas?

may be lame

muscle atrophy, crouched stance with weight shifting & lack of hindlimb extension

lateral recumbency - to elicit luxation

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what is grade I patellar luxation?

intermittent luxation - manual dislocation in full distension

spontaneous reduction on release

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what is grade II patellar luxation?

occasional spontaneous luxation - doesn’t always reduce on its own

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what is grade III patellar luxation?

permanent luxation, manual reduction possible

reluxation on release

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what is grade IV patellar luxation?

permanent luxation - manual reduction is impossible

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what may be seen on radiographs of a patient with luxating patellas?

medialization of tibial crest - +/- internal rotation of the proximal tibia

shallow femoral trochlea +/- hypoplastic medial trochlear ridge

quadriceps displacement

use for assessment of angular limb & other skeletal abnormalities

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why is positioning critical for radiographic assessment of patellar luxation?

need to know if the distal femur or proximal tibia needs to be surgically corrected

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what is the proper positioning for radiographs of dogs with patellar luxation?

cranial/caudal view long pelvis - V/D hip to tibia

femur as a reference - parallel to spine, no abduction or adduction

max hip extension - parallel to cassette

no external or internal rotation

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what are the requirements of radiographic positioning for evaluating a patient with luxating patellas?

symmetrical appearance of pelvis & femur

sesamoids split by femoral cortices

only tip of lesser trochanter is visible

varus measurements are repeatable

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when should you recommend surgery for a dog with luxating patellas?

huge variety - recommend when there is a loss of quality of life & pain with any degree of luxation

what are the surgical goals of luxating patellas?

restoration of limb alignment

restoration of femoropatellar articulation

soft tissue support

what are the goals of trochleoplasty surgery?

50% of patellar thickness to sit in the groove

medial & lateral ridges cradle the patella

argument for necessity in all cases

how is a trochleoplasty performed?

technique that deepens a shallow/absent/convex trochlea

articulation of patella provides physiologic pressure & retards cartilage growth - improper depth in cases with no patellar pressure & varies with degree of luxation

what is recession in terms of trochleoplasty?

preservation of the articular surface

what is resection in terms of trochleoplasty?

removal of articular cartilage & subchondral bone

what is a trochlear wedge recession technique?

diamond shaped osteochondral wedge that maintains the articular surface with smooth arcs - width is consistent with patellar width complete cut with a fine toothed saw - be conscious of depth & avoid long wedge length

where are the cuts made in a trochlear wedge recession?

distally at intercondylar notch proximally at dorsal aspect of the articular cartilage preservation of medial ridge

what is the procedure of a block recession?

similar to wedge concept but deeper placement of patella proximally often used in large breed dogs to capture patella with full extension vertical lines are consistent with patellar depth 3-4mm below the surface osteotome advanced between vertical lines proximally to create rectangular block to cradle the patella

what is the angle of the block, depth of recession, & length of recession in a block recession?

angle - parallel to femur depth - 50% of patella length - proximal margin of articular cartilage, intercondylar notch

what is a trochlear resection?

removal of articular cartilage & subchondral bone with parameters similar to recession

what is the minimum depth of a trochleoplasty?

at least 50% patella height

if the patella doesn't remain reduced through flexion/extension after transposition, what happens?

chance of luxation & revision post-surgery increases

what is the Q angle in a tibial tuberosity transposition?

angle between the direction of force of the quads, patella, straight patellar tendon, & tibial tuberosity if increased - denotes severity of medial patellar luxation

what is a normal q angle?

10.5 degrees

how is a tibial tuberosity transposition performed?

fascia is extended a few cm distally to the tuberosity - exposure is important for positioning the osteotome release the crest with the osteotome/bone cutters/oscillating saw/gigli wire place the osteotome caudal to the patellar tendon (size similar to the width of the tuberosity) & perpendicular to the bone & use the mallet to advance the osteotome distally leave the distal periosteum intact transpose adequately to assure patella in femoral trochlea & hold in place to create a bone platform use k-wires to secure & avoid the joint

what is the key to success in a tibial tuberosity transposition? what other considerations should be made?

alignment of the quadriceps mechanism k wire size, length, & number used

how is a medial release surgical procedure performed?

due to the medially luxated patella, the joint capsule & retinaculum on one side of the joint contracts & must be released to allow return to proper anatomic position tissues broken down to mobilize patella - medial joint capsule, cranial belly of the sartorius, & vastus medialis - continues proximal to femoral triangle medial parapatellar incision through full thickness tissues introducing instrument from lateral to medial - isolate the edge of the patella & straight patellar tendon prior to cutting & sharply cut over the instrument extending the incision from the patella to the proximal tibia & manually breakdown contracted tissues on the medial thigh

what is the goal of the medial release technique?

free the quadriceps mechanism until you can luxate the patella both ways - closure with simple appositional sutures

what is imbrication?

to overlay things so that they overlap in layers in a similar way to roof tiles

what is a lateral imbrication?

reinforcement to the lateral retinaculum with control of tension best done with separation of tissue layers

what is a biceps overlay?

form of imbrication - parapatellar fascia is tucked underneath lateral fascia in a vest over pants pattern - may trim excess biceps fascia to increase tension use a monofilament - gauge is the most important decision, don't under power

what should you do after every 2-3 sutures in a lateral imbrication?

check the position & movement of the patella - may require replacing sutures

what is the purpose of anti-rotational suture?

externally rotates the tibia & assists in quadriceps realignment - often done in conjunction with CCL repair

what is the procedure of lateral imbrication?

intentional overlap of the fascia lata & lateral joint capsule used on the lateral parapatellar tissues during correction of medial patellar luxation resulting in a tightening of tissues to help maintain the patella's position in the trochlear groove

what is involved in true imbrication?

using 2 separate rows of sutures to advance the biceps femoris cranially & then the fascia lata is sutured caudally

how are anti-rotational sutures placed for a medial luxation?

suture material is placed from the lateral fabella around the patella & back to the lateral fabella so when tied, the suture will help prevent medial luxation (can also place from the lateral fabella to the tibial crest)