Lecture 6: Patellar luxation (Exam 1) Flashcards
What is a medial patellar luxation (MPL)
- Displacement of the patella from the trochlear sulcus (trochlear groove)
- Common cause of lameness in small breed dogs but can also occurs in large breed dogs
What musculoskeletal abnorms can px w/ patellar lux have
- Medial displacement of the quadriceps muscle group (lateral torsion or bowing of the distal femur) is the most common
- Femoral epiphyseal dysplasia
- Rotational instability of the stifle joint
- Tibial deformity
What doe femoral deformities w/ medial displacement of the quadriceps apparatus produce
- Pressure diffs on the distal femoral physis
- Decreased length of medial cortex w/ increased length of lateral cortex = lateral bowing of the distal femur
- Abnorm growth cont while quadriceps displaced & physes is active
> pressure on the medial aspect & < pressure on the lateral aspect leads to what
Less growth on the medial aspect & more growth on the lateral aspect
What does the degree of lateral bowing depend on
- The severity of patellar luxation
- Px age @ luxation
Describe mild luxations
- Quadriceps rarely displaced medially
- Min effect on distal femoral physis
Describe severe lux
- Quadriceps medially displaced all times
- Max effect on distal femoral physis
What causes tibial deformities
- Abnorm forces on the proximal & distal physes of the tibia
- Medial displacement of the tibial tuberosity
- Medial bowing (varus deformity) of the proximal tibia
- Lateral torsion of the distal tibia
describe femoral epiphyseal dysplasia
- Articular cartilage (AC) responds to increased or decreased pressure like the metaphyseal physis
- Dogs w/ MPLs have abnorm dev of the trochlear groove
- Articulation of the patella w/in the trochlear groove puts pressure on the AC & decreases its growth
- If pressure exerted by the patella is not present on trochlear ac the trochlea fails to gain proper depth
What is responsible for dev of norm depth of the trochlear groove
Pressure by the pattela
What is seen in immature px w/ mild lux
- Show min loss of depth to the trochlear groove
- Patella is norm positioned during dev
What is seen in immature px w/ severe lux
- No trochlear groove
- Norm pressure responsible for groove dev is not present
What are the grades of patellar lux
- I
- II
- III
- IV
Describe a grade I patellar lux
- Patella in groove
- Can be forced out but comes back in immediately
Describe a grade II patellar lux
- Patella in the groove
- Sometimes comes out but comes back in every time
Describe a grade III patellar lux
- Patella NOT in the groove
- Can be forced in but comes out again almost immed
Describe a grade IV patellar lux
- Patella not in groove
- Can’t be moved back in w/o sx
What is the typical signalment of px w/ MPL
- Small & toy breed dogs most affectd
- Large dogs higher percentage of lateral lux
What is the typical hx of px w/ MPL
- Intermittent wt bearing lameness
- Dog occasionally holds the lg in flexed position for 1 or 2 steps
- Grade IV have severe lameness & gait abnorms
How is MPL dx
Based on finding or eliciting MPL during PE
What will be seen in PE if the px has a grade I lux
- No lameness
- Dx incidental finding
What will be seen in PE if the px has a grade II lux
- Occasional “skipping” when walking or running
- Occasionally stretch lateral retinacular structures & dev NWBL
What will be seen in PE if the px has a grade III lux
- Lameness varies
- Occasional skip to wt. bearing lameness
What will be seen in PE if the px has a grade IV lux
- Walk w/ rear quarters in a crouched position (inability to extend the stifle joints fully
- Patella is hypoplastic
- Patella found displaced medially alongside the femoral condyle
What should be done during diagnostic imaging
- Full limb radiographs
- Radiographic positioning is critical (poor position leads to false pos limb deformities on radiographs)
- Special views/CT to help determine the specific type & degree if severe
When is sx not warranted for MPL
In asymptomatic older px
When is sx recommended for MPL
- Symptomatic immature/young adult px
- Any age in px w/ lameness
- Strongly advised w/ active growth plates
Techniques for growing animals should not what
Adversely affect skeletal growth
Describe Surgical tx of dogs w/ bilateral grade IV MPLs
- Likely need multi sx
- Probable continued lameness even w/ successful sx due to severity of long bone abnorms
What are some surgical tech for restraining the patella w/in the trochlear groove
- Tibial tuberosity transposition (TTT)
- Medial restraint release
- Lateral restraint reinforcement
- Trochlear groove deepening
What are the basic techs for a repair of the MPL
- Trochlear wedge or block recession
- Tibial tuberosity transposition (TTT)
- Medial fascial release (desmototmy)
- Lateral imbrication
What is done in a trochlear wedge or block recession
the trochlear groove is deepened
What is done in a medial retinaculum release (desmototmy)
Stabilizing of the patella in a deepened trochlear groove
Describe a tibial crest transposition
- should always be done
- Realigns mechanical forces of the extensor mechanism
- Unless major correction of a femoral & tibial deformity are preformed
After the patella is stable how is the lateral retinaculum reinforced
- Imbricate joint capsule w/ structures
- Place fascia lata graft fabella to parapatellar fibrocartilage
- Excision of redundant retinaculum
Describe how the surgical tx of an MPL should be done
- Combo of tech req
- Primary abnorm is biomechanical (Patella w/in quadriceps mechanism fails to align w/ trochlear groove)
- Sx prone to failure w/out TTT (Aka if only deepen the trochlear groove, capsule/fascial release, & imbrication)
T/F: Reinforcement tech alone are adequate to prevent reluxation permanently
False; they are not adequate
What eventually happens to the retinaculum even if it is reinforced
Stretches b/c of mechanical forces pulling the patella out of trochlear groove are not neutralized
Describe an osteotomy of the femur
- Use w/ severe skeletal deformities
- Done for varus bowing of the distal femur & medial torsional deformity of the proximal tibia
- Req special equipment pre op measurement & wedge osteotomy of the femur
- Req special equipment & training (trained specialist)
What is the goal of an osteotomy of the femur
- Realign the stifle joint in the frontal plane
- Make transverse axis of the femoral condyles 90 degrees to longitudinal axis of the femoral diaphysis
Describe the quadriceps mechanism
Secondary stabilizer of the stifle joint for cranial translation (cranial drawer)
What occurs due to chronic lux of the patella
Increased stress on the CCL & eventual rupture
What is a common finding particularly in small breed dogs
Combo of CCL rupture & patellar lux
What are the extensor mechanisms of the stifle jt
- Quadriceps muscle groups
- Patella
- Trochlear groove
- Straight patella lig
Describe the quadriceps muscle group
- Extends the stifle joint
- Aids in stabilizing the stifle joint (along / the entire extensor mechanism)
- Converges as a patellar tendon on the proximal patella
- Cont distally as the straight patellar lig
Why is the patella an essential component of the functional mechanism of the extensor apparatus
- Maintains even tension when the stifle is extended
- Acts as fulcrum in the lever arm (increases mechanical advantage of quad muscle group)
What needs to be norm for proper fxn? What can lead to patellar lux?
- Alignment of the quads, patella, trochlea, patellar lig, & tibial tuberosity
- Malalignment of any of these = patellar lux
what are the special anatomic considerations in an MPL
- Patellar lig need to be ID before making the parapatellar incision to enter the joing
- Lateral capsule is stretched & thin
- Medial capsule is contracted & thickened
- Medial trochlear ridge & ventral surface of the patella may be worn (must always check)
Why is the px placed in dorsal recumbency
- Allows visualization of unrestrained extensor mechanism deviation
- Max manipulation of the limb to eval patellar stability
How can the trochlear groove be deepened
- Trochlear wedge recession
- Trochlear block recession
Remove more bone from the (medial;lateral) side of groove & preserve as much (medial; lateral) ridge as poss
Lateral; medial
List the steps of a trochlear wedge resection
- Resect the osteochondral wedge from the patellar groove
- Remove bone from side of the incised groove to deepen the sulcus
- Replace the osteochondral wedge
List the steps of a trochlear block resection
- Use a thin saw blade to make 2 parallel cuts axial to both the trochlear ridges
- Use the osteotome from proximal & distal; elevate osteochondral block from the patellar groove
- Remove bone from the bottom of the incised block to deepen the sulcus
- Replace the osteochondral block
List the steps of a tibial crest transposition for a MPL
- Transpose the tibial crest laterally - lateral parapatellar incision & reflect the cranial tibial m to the long digital extensor tendon
- Place osteotome beneath the patellar lig - partly osteotomize the tibial crest & DO NOT transect the distal periosteal attachment
- Stabilize the tibial tuberosity w/ 1 or 2 small K wires
What is diff about a tibial crest transposition for a lateral patellar lux
- Transpose the tibial crest medially
- Stabilize the tibial tuberosity w/ 1 or 2 K-wires & figure 8 wire or screw
What does the medial joint capsule look like in a grade III or IV MPL
- Thicker than norm
- Contracted
Why is the medial joint capsule & retinaculum released
Allows lateral placement of the patella
How is cruciate or simple interrupted sutures placed when the patella is in the proper position
- Placed in a way that does not close the tissue gap
- Placing loose sutures prevents iatrogenic lateral lux
What is a lateral imbrication
- Lateral reinforcement of the retinaculum
- Place suture throught he femoral fabellar lig & lateral parapatellar fibrocartilage
- Place w/ leg in slight flexion
Medial luxation = redundant (medial;lateralO retinaculum)
Lateral
What is done once the patella is reduced
- Excise excess retinaculum & joint capsule allowing tight closure of the arthrotomy
- Or close the retinaculum w/ vest over pants suture pattern
What is the vest over pants suture pattern
- Interrupted horizontal mattress pattern
- Tissues sutured are overlapped
- Sutures pass through both layers
Describe the post op care & assessment for after this type of sx
- Activity restricted to physical rehab
- Leash walking for 6 to 8 W
- Gradually returned to norm activity over 6 week period
- Xrays done 6 to 8 weeks after to eval the healing of TTT
