Results
Group 11-Final case

Physical Exam

Bonnie has a partial weight bearing left hind limb lameness. She has difficulty getting up, but can walk quite well once she is up. When she stands still she is barely toe touching on the left hind leg. There is effusion of the left stifle joint with a distention of the joint capsule on either side of the straight patella ligament. There is pain on manipulation of the stifle. Bonnie is quite overweight but she has no other abnormalities. 

Interpretation:  The unilateral partial weight bearing lameness is consistent with a cranial cruciate ligament (CrCL) rupture.  It has been nearly a week since the actual event, so while initially with an acute full rupture of the ligament a non-weight bearing lameness would be expected, this usually evolves into a partial weight bearing lameness with time.  Joint effusion is a normal finding with CrCL rupture due to the influx of inflammatory mediators resulting in leaky capillaries. The immune system releases chemical mediators like histamine that cause vasodilation (redness and heat) and vascular permeability .  Serous exudate rich in protein seeps out of the leaky capillaries (swelling).  The histamine and other chemotactic factors attract phagocytes such as neutrophils and later monocytes to the area of inflammation (further swelling) to clean up the waste.  The chemical mediators also irritate nerve endings in the joint capsule (pain and loss of function).  Lysosomal enzymes from leukocytes can begin to digest the debris with in the joint.  Obesity is important in this case because it increases load and stress on the supporting structures of the stifle.  Therefore if there is a traumatic event or the CrCL is weakened, obesity increases  the chances of rupture.


Orthopedic Exam

There is joint effusion in the left stifle joint. A joint tap was performed. While awake, no cranial drawer can be palpated in the stifle joints. While under sedation a 4 - 5 mm cranial drawer can be palpated in the left stifle, with less than 2 mm palpable in the right. The patellae appear correctly positioned and normally mobile. The collateral ligaments are intact. The hip joints do not have any palpable laxity or pain when run through a full range of motion. No other abnormalities could be found.

Interpretation:  All results of the orthopedic exam are consistent with CrCL rupture. The function of the CrCL is to constrain the stifle joint so as to limit the normal internal rotation and cranial displacement of the tibia relative to the femur, and to prevent hyperextension of the stifle.  Therefore a rupture of the CrCL will present as a cranial drawer sign or cranial displacement of the tibia in relation to the femur when shearing force is applied to the stifle.  When awake, reflexive tightening of muscles, tendons, and external ligaments in response to pain provide enough stability n to eliminate a cranial drawer sign.  Under sedation, these structures relax and a cranial drawer sign can be elicited in the presence of a partial or full CrCL rupture.  In this case, a 4-5mm cranial drawer sign was elicited under sedation indicating a complete rupture.  The rest of the findings of the orthopedic exam localize the cause of the lameness to the stifle and rule out patellar and collateral ligament involvement in the etiology of the lameness.

Specialty Exam