Final Exam #1 - Rationale of Facts

Bonnie is a large breed dog, six years old, who is markedly overweight.  She is exhibiting acute onset lameness (first noticed less than one week ago) in the left hind leg.  Her breed and size predispose her to a variety of musculoskeletal disorders.  She has an active life style, with many opportunities for injury (such as jogging, playing fetch, chasing dogs and cats, hiking in woods).  We think her condition is primarily due to a musculoskeletal disorder because:

1. she has difficulty getting up from a sitting/lying down position
2. she has difficulty getting up and down stairs
3. she is markedly overweight
  
She also may have a systemic illness, along with a musculoskeletal abnormality.  She appears depressed (barely lifting her head and slightly wagging her tail when we walked in) which could indicate systemic illness of some sort.  However, she  is current on all vaccines and is treated regularly for heartworms, so we're keeping diseases in mind which she may not have been vaccinated for like tick paralysis or lymes disease).  Tick borne diseases are especially important to consider, because Bonnie takes walks in the forest frequently.  
Congenital abnormalities of joints or limbs could precipitate a lameness.  Reasons that we are considering congenital abnormalities are:

1. Bonnie is a large breed dog  -- predisposes her to a variety of musculoskeletal disorders
2. We don't know anything about her early history (up to six months) or her nutrition during that time  -- poor nutrition early in her development could have exacerbated problems with bone growth and development

There are some features of Bonnie's presentation that make a congenital malformation seem unlikely.  

1. she is 6 years old, so we would expect to have seen evidence of a malformation earlier
2. she's a very active dog, also suggesting that we would have seen problems sooner
3. this lesion appears to be (primarily) unilateral and a congenital defect would be likely to be bilateral

	Physical exam and orthopedic exam findings led us to hypothesize that there is problem in her left stifle joint.

1. partial weight bearing lameness of the left hind limb
2. barely toe touching on left hind leg when stands (commonly noted with stifle problems because the animal doesn't want to "load" the leg fully)
3. joint effusion of the left stifle joint
4. distension of the joint capsule on either side of the straight patellar ligament
5. pain on manipulation of left stifle
6. we noted that the left hock seemed stiff on the video - and we read that lameness of the stifle is accompanied by reduced motion in the hock. 

	She could have degenerative joint disease from the stresses of her strenuous exercise.  Osteoarthritis is a common finding in the stifle joint of dogs and seems a reasonable possibility is an older, large breed dog.  Even though hip dysplasia is a common problem with dogs of this signalment, we don't think bad hips are part of her problem.  During the orthopedic exam, there was no palpable laxity or pain when hips were run through the whole range of motion..  

	Furthur  physical and orthopedic exam findings led us to determine the problem is rupture of the cranial cruciate ligament:

1. no lateral or medial collateral damage was detected (the collateral ligaments were both intact)
2. patellas appeared to be correctly positioned and normally mobile - we ruled out medial or lateral patellar luxation
3. no evidence of bone injury (such as to distal femur or proximal tibia) was found
4. no caudal drawer sign was found - we ruled out caudal cruciate rupture
5. positive cranial drawer sign (4-5mm) on left stifle, with a cranial drawer sign also noted on the right (2mm, which is the upper limit of normal and may reflect a partial rupture.)
6. no muscular abnormalities were detected.
7. She walks well once she's up - we ruled out nerve damage

	There is potential for other factors to be involved as well.  We think that there may be a problem with the right stifle as well.  Normal cranial drawer limits are from 0 - 2 mm, and her right cranial drawer sign was 2 mm.  This may mean that's she's normal.  However, you can see a cranial drawer of 2 - 3 mm if there's a partial tear.  Because she's putting  a lot of weight on her right hind leg now and because she's quite overweight, it seems likely that the additional stresses could cause tearing of her right cranial cruciate ligament.  We also observed a marked valgus angulation on the left hind leg during ambulation.  This suggest a problem with medial stuctural support of the limb, which could be a result of simple cranial cruciate rupture but could also indicate a meniscal tear or problem with the fibrous joint capsule.  We could imagine that we saw a slight valgus angulation on the right hind leg, which might indicate poor conformation  overall.