Looking Beyond the Sesamoids
A recent case reminded me how easy it is to anchor on the first abnormality we find and how much a case can become complicated.
A dog presented with a few weeks history of right thoracic limb lameness and a flattened appearance of the third and fourth digits.
The lameness itself was interesting. On soft surfaces and indoors, the dog was only mildly lame. However, once the dog walked on gravel, the lameness became significantly more obvious.
We already had radiographs from before. The radiographs showed degenerative changes around the second metacarpophalangeal joint, along with sesamoid abnormalities. There were also sesamoid and osteoarthritic changes in other digits and in the contralateral limb.
At first glance, it seemed reasonable to blame the sesamoid. After all, we know that fragmented sesamoids and sesamoiditis can be painful. Metacarpophalangeal osteoarthritis can also contribute to lameness.
But there was one thing that I could not explain.
Why were the third and fourth digits flattened?
When assessing the superficial digital flexor tendon, I did not appreciate any obvious loss of structural integrity. The tendon maintained a relatively normal elastic end feel, and I did not feel anything that made me suspect a rupture.
The deep digital flexor tendon also appeared to be doing its job. The digital pad remained in contact with the ground, suggesting that the DDF was still functioning.
However, I found myself wondering why the third and fourth digits were not functioning normally despite the apparent integrity of both flexor tendons. It felt less like a structural failure and more like a functional insufficiency.
That was what made this case difficult. We had radiographic abnormalities, surface-dependent lameness with altered digit posture. And I was not convinced that the radiographs were telling the whole story.
The owner wanted a definitive answer, so we decided to pursue MRI.
What did we find from MRI?
It was amazing that we could evaluate all the soft tissue structures (e.g., SDF, DDF tendons) from MRI.
The MRI confirmed fragmentation of the sesamoid bone, but it also revealed extensive tendon sheath effusion associated with the deep digital flexor tendon of the second digit.
The effusion extended all the way to the digital pad.
Suddenly, the clinical picture became much more complicated.
Was the lameness being driven by:
Sesamoid fragmentation?
Metacarpophalangeal joint osteoarthritis?
Deep digital flexor tendon sheath pathology?
Or a combination of all three?
One of the challenges in orthopedic medicine is that abnormal imaging findings do not always identify the primary pain generator.
Interestingly, similar osteoarthritic and sesamoid changes were present in the opposite limb, yet that limb was not clinically affected.
Based on the MRI findings and clinical presentation, we felt that the inflammation and effusion associated with the tendon sheath of the second digit were likely the main contributors to the lameness, rather than the flattened third and fourth digits themselves.
And weight distribution of the forelimb digits were also very interesting.
Compared to the normal limb, this dog was using the third and fourth digits much less during weight bearing. Instead, a substantial amount of the load appeared to be shifted onto the second digit—the same digit where we identified significant tendon sheath effusion on MRI.
This made me wonder whether we were only seeing the end result of a much longer process.
Perhaps the third and fourth digits had lost function sometime in the past, leading to progressive weakness and flattening of those digits. If that was the case, the second digit may have been compensating for a long time, taking on more load than it was designed to handle. Over time, this may have contributed to overload, inflammation, and eventually clinical lameness.
I may be completely wrong.
But one thing I have learned from rehabilitation is that finding pathology is only part of the job. To develop a meaningful treatment plan, I often need to build a theory of what may have happened and how the patient arrived at its current state.
Sometimes that theory turns out to be correct. Sometimes it does not.
But understanding function, compensation, and load distribution is often just as important as identifying abnormalities on imaging.
So how did we treat this ?
After targeting the tendon sheath inflammation with a guided injection, the dog's function improved significantly.
However, that was not the end of the story.
The flattened third and fourth digits remained. There was still reduced function of the superficial digital flexor apparatus, ongoing osteoarthritis, and likely abnormal load distribution across the paw.
Managing a case like this requires more than simply controlling inflammation.
In my mind, four things were important:
Inflammation and pain control
Protection of the affected structures
Strengthening and restoring function
Long-term load management
Following tendon sheath injections and shockwave therapy, we incorporated bootie use, activity modification, and strengthening exercises.
And are we happy now?
Over time, this dog returned to the conformation show ring, and most importantly, the owner was happy with the outcome.
Does that mean the condition is cured? Probably not.
What we now have is a management plan. We have a better understanding of the condition, we know what tends to trigger flare-ups, and we have a strategy when those flare-ups occur.
For many chronic musculoskeletal conditions, that is often the goal.
To manage these patients successfully, we need to look beyond the imaging findings. We need to consider the dog's environment, daily activities, job, personality, and the expectations of the owner.
Our goal is not always to eliminate the disease. Sometimes our goal is to keep the patient comfortable, functional, and active for as long as possible.
That is also why owner education is so important. This is unlikely to be a condition that simply disappears. It is a condition that requires long-term management, and helping owners understand that is often just as important as the treatment itself.
Anyway !!
Sometimes the most important step in diagnosis is looking beyond the abnormality that first catches our attention.
In this case, that meant looking beyond the sesamoid.
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