Exam 1: Lecture 6 - Patellar luxation Flashcards
what is medial patellar luxation (MPL)
displacement of patella from trochlear sulcus (aka trochlear groove)
what breed is MPL most commonly the cause of lameness in
small breed dogs…can occur in large but is uncommon
what are the associated musculoskeletal abnormalities in patients with patellar lux
- medial displacement of quadriceps muscle group (lateral torsion of distal femur or lateral bowing of distal 1/3 of femur)
- femoral epiphyseal dysplasia
- rotational instability of stifle joint
- tibial deformity
what is this picture showing
the displacement of the quadriceps apparatus and how it rotates and bows the leg
what happens with femoral deformities that have pressure on the medial aspect of distal femoral physis
greater pressure on medial aspect = less growth
what happens with femoral deformities that have pressure on the lateral aspect of distal femoral physis
decreased pressure on lateral aspect = accelerated growth
how do we get lateral bowing of distal femur
when there is decreased length of medial cortex relative to increased length of lateral cortex
Degree of lateral bowing depends on the ___1___ of patellar luxation and patients ___2____ at luxation
- severity
- age
what happens with mild luxations of quadriceps apparatus
- quadriceps rarely displaced medially
- minimal effect on distal femoral physis
what happens with severe luxations of quadriceps apparatus
- quadriceps medially displaced all times
- maximal effect on distal femoral physis to cause severe lateral bowing of distal femur in young patients
T/F: A severe luxation is extremely difficult to correct
true!
why do we see tibial deformities with medial displacement of quadriceps apparatus
because of the results of an abnormal force on proximal and distal physis of tibia
what are the 3 tibial deformities we can see with medial displacement of quadraceps
- medial displacement of tibial tuberosity
- medial bowing (varus deformity) of proximal tibia
- lateral torsion of distal tibia
T/F: Dogs with MPL do not have an abnormal development of the trochlear groove
false, they do! it does vary from near-normal to absent trochlear groove
what happens with femoral epiphyseal dysplasia
articular cartilage is the “physis” for epiphysis and responds to increased or decreases pressure as with metaphyseal physis
how does the articulation of the patella within the trochlear groove impact the articular cartilage
it puts a physiological pressure which retards cartilage growth
T/F: pressure by patella is responsible for development of normal depth of trochlear groove
true!!
what happens if the physiologic pressure exerted by the patella is not present
the trochlea fails to gain proper depth
T/F: Immature patients with mild luxation show a great loss of depth to trochlear groove
false, they show minimal loss of depth
T/F: Immature patients with severe luxations have no trochlear groove
true!! normal pressure that is responsible for growth not present
what is grade I of patellar luxation
patella in groove, can be forced out but comes back in immediately
what is grade II of patellar luxation
patella in groove, sometimes comes out but comes back in every time
what is grade III of patellar luxation
patella is NOT in groove, can be forced in but comes out again almost immediately
what is grade IV of patellar luxation
patella not in groove, cant be moved back in without sx
what is the signalment we see in patients with MPL
no age, breed, or gender predisposition….but small and toy breed dogs most often affected
T/F: lateral patellar luxation is more common than medial patellar luxation in large breed dogs
false! MPL is more common BUT large breed dogs get LPL more than small breed (small breed almost never get LPL)
what is the usual history for patellar lux
intermittent weight bearing lameness, dog occasionally holds leg in flexed position for 1-2 steps
T/F: Dogs with grade IV patellar lux have severe lameness and gait abnormalities
true!
how do we diagnose MPL
based on finding or eliciting mpl during PE
what do we see on PE for grade I patella lux
no lameness, usually incidental finding on PE
what do we see on PE for grade II patella lux
occasional skipping when walking or running and occasionally stretch lateral retinacular structures and develop NWB lameness
what do we see on PE for grade III patella lux
varying lameness with occasional skipping to weight bearing lameness
what do we see on PE for grade IV patella lux
walk with rear quarters in crouched position, patella is hypoplastic, and patella found displaced medially alongside femoral condyle
what do we see on rads with grade I or II lux
patella within trochlear sulcus or displaced medially
what do we see on rads with grade III or IV patella lux
standard craniocaudal and medial-lateral rads show patella displaced medially
what can happen with poor radiograph positioning?
can get a false positive limb deformity!!
what are the lab findings with patella lux
consistent abnormalities are not really seen
how do we decide if we treat MPL conservatively or surgically
depends on history, PE, frequency of lux, and patient age
when is sx not warranted for MPL
in asymptomatic older patients
when is sx recommended for MPL
in young animals or if lame
when is surgical treatment of MPL strongly advised
in patients with active growth plate
T/F: We should surgically treat MPLs for any age patients with lameness
true!! age is not a disease
What is important to tell owners of dogs with bilateral grade IV MPLs
they likely need multiple surgeries and probably will have continued lameness even with successful sx
what are the 4 most COMMON ways to surgically treat MPL
- tibial tuberosity transposition (TTT)
- medial restraint release
- lateral restraint reinforcement
- trochlear groove deepening
what happens during the trochlear groove deepening sx
trochlear wedge or block recession and abrasion trochleoplasty or chondroplasty
what happens during the medial retinaculum release (desmotomy)
stabilize patella in deepened trochlear groove
what happens during the tibia crest transposition
realigns mechanical forces of extensor muscles
of the 4 most common MPL procedures, what ALWAYS SHOULD be done
tibial crest transposition
what happens during lateral retinaculum reinforcement
imbricate joint capsule with sutures, place fascia lata graft fabella to parapatellar fibrocartilage, and excision of redundant retinaculum
T/F: combination of techniques are required for surgical treatment of MPL
true!!
What happens if we only do the deepening of trochlear groove, capsule and fascial release, and imbrication
correction is PRONE TO FAIL WITHOUT TTT!!!
Important!! What should we ALWAYS DO when surgically treating MPL
do the tibial tuberosity transposition!!
T/F: reinforcement techniques alone are not adequate to prevent reluxation premanently
true!! it stretches eventually
when should we do an osteotomy of the femur
when there is severe skeletal deformity
what are the deformities we should do an osteotomy of the femur for
varus bowing of distal femur and medial torsional deformity of proximal tibia
what is the goal of osteotomy of femur
to realign stifle joint in the frontal plane
what does the osteotomy of the femur require preoperatively
measurement and wedge osteotomy of the main 4!! (deepen trochlear groove, medial restraint release, transposition of tibial crest, and lateral retinacular reinforcement)
what does osteotomy of the femur REQUIRE
special equipment and training
what happens with chronic patella lux
increased stress on cranial cruciate ligament and eventual rupture
what are the extensor mechanisms of stifle joint
quadriceps muscle group, patella, trochlear groove, and straight patellar ligament
what do the quadriceps muscle group do
extend the stifle joint, aids in stabilizing stifle joint, converges as patellar tendon on proximal patella, and continues distally as straight patellar ligament
what is the patella an essential component for
a functional mechanism of extensor apparatus
T/F: alignment of quadriceps, patella, trochlea, patellar lig, and tibial tuberosity must be normal for proper function
true!!
what happens if there is mal-alignment in the quadriceps, patella, trochlea, patellar lig, or tibial tuberosity
may lead to patellar lux!
what MUST you ID before making parapatellar incision
the patellar lig!!
why is dorsal recumbency the best position for MPL correction
- allows visualization of unrestrained extensor mechanism deviation
- maximum manipulation of limb to evaluate patellar stability
what is this picture showing
trochlear wedge resection
what is being shown
trochlear block resection
what is being shown here
tibial crest transposition
T/F: For lateral patellar luxatons you transpose tibial crest the same for medial
FALSE, you transpose tibial crest medially!!
T/F: Medial joint capsule is thicker than normal and contracted with grade III or grade IV MPL
true!!!
T/F: medial joint capsule and retinaculum release does not allow lateral placement of patella
false, it does!
T/F: we want to close the tissue gap in the release of medial joint capsule
false, we do not close the tissue gap
With ___1__ luxations = redundant __2__ retinaculum
- medial lux
- lateral retinaculum
what is the suture pattern we close retinaculum with
vest-over-pants suture pattern
what type of suture pattern
vest-over-pants
what do we use to do the trochlear wedge/block recession
fine tooth saw or sagittal saw
what do we use to do the block recession
osteotome
what do we use to do the TTT
osteotome and mallet, k-wires or lag screw, orthopedic wire, and hand chuck or drill to secure tibial crest
what is the post op care for MPL correction
- activity restricted to leash walks for 6-8 weeks
- gradually returned to normal activity over 6-week period
- radiographs done 6-8 weeks to eval healing of TTT
