2.3 Common Causes of Hindlimb lameness: Stifle Flashcards
What are the two most common causes of stifle-based lameness in small animals?
- cranial cruciate ligament disease
- patellar luxation
Explain the anatomy of the knee ligaments.
the cranial cruciate ligament (CrCL):
- originates from the caudalmedial aspect of the lateral femoral condyle
- inserts on the cranial intercondyloid area of the tibia
one CaCL and two collateral ligaments also exist to stabilize the knee (these are less likely to be injured)
Additional anatomy references
What is the anatomy of the CrCL?
(1) intra-articular, but extra-synovial
(2) compsed of two functional bands:
- craniomedial
- caudolateral
- both bands are taut in extension, but the craniomedial is also taut in flexion “partial cruciate testing”
their role is in knee stability, craniotibial translation, and some internal rotation
What is the pathogenesis of CrCL rupture?
- degenerative weakening (most common)
- traumatic avulsion (uncommon)
- traumatic rupture (very uncommon)
the degenerative process is complex; over time, these changes cause an unstable joint which can contribute to OA and/or rupture
What are the menisci?
2 C-shaped fibrocartilage pads: medial meniscus, lateral meniscus
- they improve congruency (make the round tibial surface a flat one!)
- affect load bearing/shock absorption (collagen fiber arrangement converts compression into tension)
- blood supply on outer rim only = poor healing
- good innervation = painful
the medial meniscus is attached to the tibia, while the latteral meniscus is attaced to the femur
How does CrCL injury precipitate meniscal injury?
a degenerate or torn CrCL will allow the femoral condyle to sit back on and ‘crush’ the rear part of the meniscus; due to anatomy, the MEDIAL meniscus is the one injured following cruciate instability
- 1/3 dogs with cruciate injury have meniscal injury
- 1/2 dogs with cruciate rupture have meniscal injury
- painful on stifle extension as there is partial compression of the meniscus
- best managed by surgical resection
What are the most indicative clinical signs of CrCL disease?
- insidious or acute onset hindlimb lameness
- stifle effusion
- medial buttress (fibrous tissue proliferation on medial proximal tibia)
- positive sit test: sits with leg extended and to the side
- positive cranial drawer test (most reliable)
- positive tibial thrust test (less reliable)
What is the cranial drawer test?
the most reliable stability test for CrCL disease
- the examiner stands behind the dog and places a thumb on the femoral condylar region (caudal) with the index finger on the patella (cranial)
- the other thumb is placed on the head of the fibula (caudal) with the index finger on the tibial crest (cranial)
- the ability to move the tibia forward (cranially) with respect to a fixed femur is a positive cranial drawer sign indicative of a CCL rupture
What is the tibial thrust test?
- the examiner’s index finger is placed on the tibial tuberosity and squeezed toward the thumb that is secured behind the lateral fabella
- this maneuver shifts the tibia of the CrCL-deficient stifle caudally into its “neutral” position under the femur; the hand also holds the stifle in a standing angle (neither fully flexed, nor fully extended)
- the examiner’s other hand flexes the hock to simulate weight-bearing
- this maneuver creates cranial tibial thrust by tensing the gastrocnemius muscle
in the CrCL-deficient stifle this cranially-directed shear force palpably shifts / dislocates the tibia cranial relative to the femur
- with practice, the tibial compression test becomes an extremely reliable method to test for gross stifle instability, especially in larger breed dogs where the cranial drawer test is difficult due to muscular strength or sheer size
What radiographic findings are indicative of CrCL disease?
ligaments are not radiopaque, and therefore cannot identify the torn ligament itself, but can see the associated changes
- stifle effusion
- osteophytes (bone spurs)
- distal displacement of the popliteal sesamoid bone
(11) Normal radiograph: no degenerative changes
you know this was taken correctly because on lateral view the two heads of the femoral condyle are perfectly superimposed.
On cranial caudal view: fibellae (small sesamoid bones found in some mammals embedded in the tendon of the lateral head of the gastrocnemius muscle behind the lateral condyle of the femur) should be equally bisected by the edges of the femur. The patella should be in the middle (if not luxated).
(12) CrCL degenerative change is essentially OA change, and comes in varying levels of severity: progressing from left to right.
(10) Osteophytes: new bone remodeling on the periphery of the joints seen here and on the radiographs (Left)
How do you treat CrCL disease?
(1) conservative management
- 8 weeks: NSAIDs/other analgesia, passive ROM, physiotherapy (strengthening)
- if meniscal injury present or no response after 8 weeks -> surgery
(2) surgery (MUST inspect meniscus)
- intra-articular: proven inferior
- extra-articular: good if done correctly
- osteotomy techniques: reliable (levels tibial plateau to improve stability: TPLO, TTA)
TPLO (current best practice, and most common): “tibial plateau levelling osteotomy”
TTA: “tibial tuberosity advancement”
What is the CrCL disease prognosis?
generally good outcomes
- around 50% dogs will get bilateral rupture in 2 years
- most dogs make good recovery post surgery
- 90% dogs get to 90% of pre rupture activity
- OA will progress regardless BUT doesn’t always mean the animal will be lame
What is the patella?
- the patella is the sesamoid bone of the quadriceps muscle tendon
- it works with the trochlea to redirect the quadricep ‘pull’
- alignment is key
What is a patellar luxation?
common cause of INTERMITTENT in lameness small dogs (usually quite young)
- patellar luxations are abnormal trackings of the patella (developmental not congenital)
- usually medial in all sizes of patients but can be lateral in any size of patient
What are the most important parts of the orthopedic exam in cases of patellar luxation?
(1) rule out CrCL disease
- should have minimal effusion and a negative cranial drawer / tibial thrust
(2) check alignment of patella, patellar ligament, and tibial crest
- may be normal or abnormal
(3) if patella is NOT aligned at rest, is it:
- medial luxation: genu vara (bow legged)
-
latteral luxation: genu vulga (knock-kneed)
in both cases the stifle may be hyperflexed
(4) walk dog a few steps and repeat the exam
(5) luxate the patella (lateral reumbency)
- extend the stifle and manipulate the patella medially and laterally for laxity
- flex and extend stifle with rotation, and further manipulate the patella
- assess for pain on luxation / retropatellar pain
(6) grade luxation
How do you grade patellar luxation?
What may be seen on radiographs evaluating patellar luxation?
radiographs are best used to assess concurrent disease (e.g., CrCL-associated changes); manual palpation is the most important assessment for patellar luxation
- OA and effusion are usually mild
- patella may or may not be currently luxated
- assess for other problems / boney change
- use these for surgical planning
What is criteria for patellar luxation surgery?
tricky to assess (not simply the grade), BUT grade does influence prognosis
- make a global view on clinical impact and speak with the owner
- is there evidence of ta CLINICAL problem?
- is there evidence of OA or pain?
note: 20% complication rate with patellar luxation surgery (quite high)
