Learning Issues

What are the structures in the stifle joint that could possibly show the clinical signs seen (distention of the joint capsule, 4-5 mm cranial drawer on the left stifle, toe-touching lameness)?

Structures that make up the stifle joint include the cranial cruciate ligament, the medial/lateral meniscus, the patellar ligaments, the medial and lateral collateral ligaments, the meniscofemoral ligament, the transverse ligament, the long digital extensor tendon, and the fibrous joint capsule.  In this case, the patellar ligaments and the collateral ligaments appeared intact upon physical examination.  A cranial drawer sign describes the excessive craniocaudal movement of the tibia relative to the femur as a result of cruciate ligament injury.  

What are possible causes of lameness in the left hind limb??  What grade is this lameness based on its partial weight-bearing status?

The lameness could be caused by four broad categories of injury: infectious, neoplastic, degenerative, and traumatic. Other factors like nutrition and activity level may also contribute to existing lameness by altering the stresses placed upon the joint. This lameness is a Grade 2 because there is noticeable lameness but bears weight on the limb most of the time.

Aside from trauma and neoplasia, what are some possible causes for synovial effusion?

Infectious agents could potentially cause synovial effusion, with environmental and systemic contamination possible. Possible infectious agents include Strep spp., Staph spp., C. pyogenes and others could spread hematogenously or through injury to the affected joint.

Degenerative joint disease results from damage to the articular surface, leading to the release of cytokines, interleukins (IL-1, IL-6), and other inflammatory mediators from chondrocytes. This results in damage to the collagen fibers, and it is unable to withstand normal biomechanical forces. The decreased tensile strength of the collagen leads to an inability to contrain the hydrophilic proteoglycan molecules, resulting in swelling of the cartilage. 

What are the criteria for a positive cranial drawer sign? What does a 4-5 mm or 2 mm cranial drawer sign indicate?

A cranial drawer sign describes the excessive craniocaudal movement of the tibia relative to the femur as a result of cruciate ligament injury. A positive cranial drawer sign can indicate either cranial cruciate ligament injury or medial collateral ligament injury. Any abnormal movement of the tibia cranially indicates injury to one or noth ligaments. When testing for cranial drawer sedation is necessary because anticipation of pain by the patient will cause tensing of the quadriceps preventing an accurate test. Craniocaudal movement greater than 0-2 mm indicates ligament rupture, so this patient has a negative right cranial drawer sign but a positive left cranial drawer sign (ruptured left cranial cruciate ligament).

What are Bonnie's Maintenance Energy Requirements?  Is 4 cups of Hills  Adult Maintenance too much? Could this increased feed intake lead to lameness of the left hind limb?

The average weight of a mature female Labrador Retreiver is 55-70 lbs. If we use 60 lbs. to calculate her Maintenance Energy requirement, this would be:  MER:  70 x (27.3 kg ) .75 x  1.5 (Activity) = 1253 kcal Using Small Animal Clinical Nutrition, there are 4.22 kcal / g in Hill's Adult Maintenance. This equates to 
(8 oz/cup) (30 g / oz)  (4 cups) (4.22 kcal) = 4,051 kcal Bonnie is receiving. Bonnie is receiving three times the number of kcal that she needs to meet her maintenance requirements. It has been found that grossly obese dogs have an increased prevalence of traumatic and orthopedic disorders. Although obesity might not be a primary cause of the lameness, it could increase compressive forces and exacerbate the lameness.

What are common cancers of large breed dogs?  Could neoplasia possibly be causing this hind limb lameness?

Some common primary tumors of dogs include osteosarcoma, chondrosarcoma, fibrosarcoma, hemangiosarcoma, and synovial cell sarcoma. The synovial cell sarcoma arises from the synovial lining of the joint and remained intimately associated with the joint. The stifle joint is most frequently involved with 
synovial cell sarcoma, and is capable of crossing the joint space. Osteosarcoma is the most common primary bone tumor in the canine, and is most commonly found in the distal radius and proximal humerus. It can also be found in the hindlimb with a forelimb to hindlimb ratio of 1.5:1. Hemangiosarcoma is also a possible ruleout, because it most frequently involves the proximal and distal ends of the longs bones. Chondrosarcoma is less likely in this case because flat bones are more commonly affected (ribs, nasal cavity, and pelvis). 

Can osteoarthritis cause damage to the cranial cruciate ligament, giving the cranial drawer sign noted upon physical exam?

The cranial cruciate ligament lies between the femur and tibia and within the stifle joint capsule. The inflammatory process associated with osteoarthritis starts in the synovium within the joint capsule, and inflammation could potentially interfere within the strength and range of motion of the ligament.
Osteoarthritis may not be the sole cause of cranial cruciate rupture, but inflammation and destruction of the joint structures could increase the joint laxity and lead to the positive cranial drawer sign.