3/5/2010 Winding up with Flash

.Vet tip of the Day:  Challenging lameness
Key words: Carpus, metacarpal bones

Finally I'm back after a few down days - my apologies to those of you following daily.

Let's finish up with Flash, the gelding with the challenging lameness.  Quick review: the take home messages you should remember from following this case are: the importance of client communication, the need to treat each lame horse individually, and the importance of patience and care to do know harm when approaching a challenging lameness.

Two weeks after my initial evaluation of Flash I returned to repeat x-rays and check on his progress.  His lameness was slightly improved, but he continued to be very uncomfortable when stepping down from his stall or turning.  Repeat x-rays of his splint bone in the area of the trauma still showed no fracture.  There still was no swelling in the joints above or below the site of trauma, but there continued to be some pitting edema (soft swelling) along the length of the medial splint bone (metacarpal II) and Flash continued to show a painful response when palpated along the proximal splint and at the back of the knee where the splint bone articulates with the second carpal bone (see red arrow on diagram).

Although Flash remained very lame, I decided to performa an abaxial sesamoid nerve block, which would remove sensation to structures below the fetlock.  There was no indication that the lameness originated in the area, but because I so far had failed to identify a definitive cause for the lameness, I wanted to be sure that I wasn't making a mistake concentrating on the splint trauma.  The foot block did not change Flash's gait.  I then did a local block, injecting local anesthetic directly into the region around the focal swelling which had orignially been so painful when the trauma occurred.  Again, no change in the lameness. 
At this point I decided to examine the leg more proximally - above the site of the injury.  We took several x-rays of the knee and found that there was evidence of trauma to the second carpal bone and extensive remodelling of the proximal second metacarpal bone (the medial splint).  Again, look at the red arrow on the diagram - the second carpal bone is the bone immediately above the arrow, sitting right on top of the head of the medial splint bone.  The radiographic changes appeared chronic - in other words the character of the abnormalities suggested they had been present for more than two weeks.  I e-mailed these x-rays to my consulting surgeons, who agreed that it appeared that some trauma involving the structures of the carpus in this region probably occurred at some time in the past and this recent injury led to a flare up of an old problem. 

It is important to remember that the x-ray only shows bones.  There is a very complex system of ligaments and tendon sheaths that overlies the medial aspect of the carpus exactly where the second carpal bone meets the medial splint.  Here is a somewhat out of focus (sorry, my limited tech skills showing through) diagram of these structures.  The boney remodelling present on the x-ray very likely is accompanied by additional damage to the associated soft tissue structures.  Ultrasound or MRI would be useful in further specifying such damage.

With these changes identified radiographically, and with the recommendation of the consulting surgeons, I went ahead and did an intra-articular block (use google bar at top of blog and search for "intra-articular block" and you'll find blog entry describing this) to anesthetize the carpo-metacarpal joint and Flash's gait improved about 75%.  With an articular injury, and likely additional pain arising from soft tissue structures outside the joint, this degree of improvement is considered diagnostic.

I felt comfotable that this unusual lameness story was finally coming to a conclusion.  The treatment would be rest and slow rehabilitation.  I left instructions for Flash to remain on stall rest for 60 days, at which time radiographs and full lameness exam would be repeated.  And in fact Flash's gait improved dramatically by 21 days post injury. I'll give you an update on his progress in May.

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