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Why percutaneously lengthening the Achilles/gastrocsoleus in children with diplegia/quadriplegia is so harmful: a brief primer.
The soleus is, pound-for-pound, the most important muscle to keeping us upright in stance. Yes, that little muscle keeps us upright.
How?
The soleus is, pound-for-pound, the most important muscle to keeping us upright in stance. Yes, that little muscle keeps us upright.
How?
First, consider Newton's Third Law, "For every action, there is an equal and opposite reaction."
When upright, we push down on the floor, the floor pushes back up; aka, the ground reaction force (GRF). It's drawn from foot contact to center of body mass (anterior to S2).
When upright, we push down on the floor, the floor pushes back up; aka, the ground reaction force (GRF). It's drawn from foot contact to center of body mass (anterior to S2).
The little soleus muscle does important things in stance and gait.
In stance, it keeps the GRF anterior to the knee, providing a posterior vector against the knee joint, allowing for the knee to remain extended with the quads nearly completely off.
Its true, see the next tweet.
In stance, it keeps the GRF anterior to the knee, providing a posterior vector against the knee joint, allowing for the knee to remain extended with the quads nearly completely off.
Its true, see the next tweet.
An experiment:
Stand up and put your hands on your quads. Lean forward onto the balls of your feet, and feel your quads relax. Now, lean backwards onto your heel. Feel the quads turn on? With the soleus off, the quads kick in to keep your knees from buckling. The GRF moves.
Stand up and put your hands on your quads. Lean forward onto the balls of your feet, and feel your quads relax. Now, lean backwards onto your heel. Feel the quads turn on? With the soleus off, the quads kick in to keep your knees from buckling. The GRF moves.
In gait, the GRF is constantly changing depending on foot contact and body position.
The longer the GRF stays anterior to the knee, the longer we get "free" extension forces to the knee, meaning the quads don't have to work so hard.
The longer the GRF stays anterior to the knee, the longer we get "free" extension forces to the knee, meaning the quads don't have to work so hard.
This brings up the second important job of the soleus: to slow the progression of the tibia during stance phase of gait. Through eccentric muscle contraction & controlled elongation, the soleus keep the GRF anterior to the knee until terminal stance, when we're ready to pushoff.
This is another amazing video from Scott Delp that shows which muscles are on/off at different phases of gait. Amazing stuff
Every resident at some point learned the Silfverskiold test, as a way to distinguish if equinus contractures are caused by gastroc, soleus or both.
The test is done by pushing the ankle into dorsiflexion, measuring the numbers with the knee extended and flexed.
The test is done by pushing the ankle into dorsiflexion, measuring the numbers with the knee extended and flexed.
If a patient has a positive Silfverskiold test (meaning there is significantly less dorsiflexion in knee extension than in knee flexion), the gastroc is causing the equinus, not the soleus.
And that makes sense in diplegia/quadriplegia: biarticular muscles are the troublemakers.
And that makes sense in diplegia/quadriplegia: biarticular muscles are the troublemakers.
So, you have equinus in gait caused by the gastroc more than the soleus, and you want the foot flat.
BUT!!!!
You also need to keep the patient upright.
What to do, what to do???
BUT!!!!
You also need to keep the patient upright.
What to do, what to do???
You make sure that you carefully lengthen the gastrocnemius and not (excessively) the soleus.
This is best accomplished through the middle third of the calf where the gastroc is a tendon and the soluess can be lengthened over its myofascia. I do a modified Vulpius.
This is best accomplished through the middle third of the calf where the gastroc is a tendon and the soluess can be lengthened over its myofascia. I do a modified Vulpius.
At this level, you can dial in your dose. Want more gatroc than soleus? Want only gastroc? No problem.
What is the worst surgery to do?
An Achilles lengthening.
Why?
Because you lengthen both muscles equally, when one is more problematic.
What is the worst surgery to do?
An Achilles lengthening.
Why?
Because you lengthen both muscles equally, when one is more problematic.
If you lengthen them together, you've now weakened the soleus, and you get crouch gait.
Crouch gait must be avoided at all costs. It is very difficult to treat, and many kids will lose the ability to stand/walk forever.
Why?
GRF
Crouch gait must be avoided at all costs. It is very difficult to treat, and many kids will lose the ability to stand/walk forever.
Why?
GRF
The quads work constantly throughout gait. The patellar tendons stretch and lengthen over time, and require significant, painful surgeries to fix, if they can be fixed at all.
Do not EVER lengthen the Achilles on an ambulatory diplegic/quadriplegic patient.
Do not EVER lengthen the Achilles on an ambulatory diplegic/quadriplegic patient.
This is a fairly brief example of a complex subject.
But, I think it starts to explain why PERC and SPML are such bad surgeries. They do not allow for the precise lengthening surgeries these kids so desperately need. Shortcuts are always bad in surgery.
Primum non nocere
But, I think it starts to explain why PERC and SPML are such bad surgeries. They do not allow for the precise lengthening surgeries these kids so desperately need. Shortcuts are always bad in surgery.
Primum non nocere
