There are impressive things in medicine. Heart and kidney transplants breathe life into seemingly hopeless situations. Antibiotics save lives that would have been doomed. So many wonders, yet, they share one commonality, they keep the status quo. They maintain, protect, or extend.
In our field, we also have an additional directive, to build what never was but ought to have been. There is no greater satisfaction in medicine than to carve function out of debility. Weighed against this is the fear of making a bad case worse. With this perspective, we discuss muscle transfers.
In the movie Star Trek "The Wrath of Kahn", James T. Kirk was charged with having changed the computer programming of a Star Fleet combat test simulation because it was designed to be impossible and he didn't like losing. With muscle transfers, we do likewise. There is no solace in failing when the odds seem unbeatable if that loss leaves a function-less child behind. The proper thing to do is to cheat.
But how can we cheat? "Diagnosis" is nearly useless in this arena. Descriptions of what is wrong with the child, in Latin, Greek, or ICD9 code, achieves nothing useful. The wrongness is usually overt, obvious, and easily described. What we do need, is to inventory what IS working. We need a list of what is right, what is still working, and what isn't but can be made to work. We need to know what we have, and what we can SPARE. "We'll make use of this here, so let's put this there. We can give this up, so let's use it for that instead." That is the essence, the rest is just details and knowing stuff - stretch lengths, power ratios, blood supply and nerve attachments - doctor stuff.
The key to moving muscles around is knowing if the patient has the wherewithal to actually use what is moved in the way desired. We assume that the patient does if that patient has "the moves" and if there is a sensory mechanism in place. The key to repositioning muscle is not the cutting and sewing, but the knowing - What muscle can do what and will it know to do it? Invariably, the predictive answer is not found in muscle testing, but in sensory testing. Very important is a child's quick response to subtle unexpected prods. We learn much from observing play and wrestling. Watch a child try to evade an attacking swerving tickle hand - what movements, actions does the child seem to be trying, what appears to be intact?
Muscle transfers come in two types:
1) Take a muscle and give it an entirely new function, put it somewhere else.
By taking a "bad" muscle which is naturally set up to perform several tasks and, instead, giving it a single linear action, rather than its clever multi-use capability, not only do we gain a dedicated action, we also gain sensory input. Why? Simple action provides simple feedback that demands no cross checks. If a muscle only does one thing, feedback only reflects one thing. Simplified feedback is the cheat we need to get around the complex programming impasse. Simple feedback allows surer interpretation and faster response. Speed is everything. Motions that take a pause to figure out then perform are close to useless. We fall at 32 feet per second squared. We have to beat the gravity of the situation.
It isn't an official term, but in reconstruction, a transfer that removes actions in favor of just one of the original functions is called a "recession" because of the typical way they are handled. Usually recessions recess, move a muscle attachment back from across a joint, neutralizing action on that joint.
Example: The rectus femoris is normally attached to the patella to be a knee extensor along with three other muscles doing likewise. Collectively the four are called the quadriceps (in the sense that four singers who share a single stage are called the Four Tops). They act as a unit, yet have discrete capabilities.
But what if one of those singers was also a part time auctioneer? That might screw things up. Well the rectus femoris also attaches at its other end above the hip on the pelvis. Very clever tone adjustments allow that muscle to act on behalf of the knee and the hip in one combined, ever-adjusting tension and range decision, which works as long as there is good feed back from multiple sources and fast computation.
If hip auction-calling stifles knee singing, then best drop the auction-calling activity. There are plenty of hip callers, we can spare the rectus femoris there, where it is really just a back up. By recessing that muscle off the pelvis to the femur, motion of the hip is no longer felt in that muscle nor reacted to by that muscle. Likewise, sensory information reported back from that muscle can only mean knee, and in a direct linear way
Muscles are shown cut away for visibility (we don't do that in surgery!). In the right leg, removing the lateral gastrocnemius shows that the really big unit of the calf muscle is deep - the soleus. It attaches to the tibia. The medial & lateral gastrocnemius muscles share the Achilles tendon with the soleus. Together they are also called the triceps surae. The medial & lateral heads attach above the knee to the femur.
Look at the left leg where the hamstring portions were removed for your benefit. It shows the medial gastrocnemius looping over the femur medial condyle like a string on a spool. When the knee extends this bit gets wrapped and tension develops. If overly reflexive this tug triggers a back reaction and fires the gastrocnemius in part or totally. If the muscle group is NOT short nor tight but merely prefires due to an extending knee (causing a reactive toe walk) then the inset show that moving the attachment off the spool on to the side at a neutral point will remove that reflex and not lengthen at all. That's a recession. Sometimes recessions gain length but often they can be done to remove spastic reactivity.
The tibialis posterior (a muscle named for its dwelling place, behind the tibia - the shin bone) has a complex action of helping point the foot downward and - if unopposed - inverting the heel and supinating the forefoot. It can produce a club foot posture. In a spastic situation it may be totally active nonstop making walking most difficult. But move it to a new attachment, with a single short upward-only excursion - even without any helpers - and it can be reborn, not just active in the new job but controlled. It isn't the muscle that is "bad", but the neurologic circumstances under which it acts relative to the demands, velocity, number of actions, and number of stimuli etc. Change the rules, change the outcome.
(You can click on the following images to bring up MPEG1 video.
We can move motors up or down levels by working them backward. Examples:
Muscle transfers and recessions can reduce spasticity nearly as much as selective dorsal rhizotomy (SDR) in certain cases. Why this is so is discussed in the section dealing with mechanisms of spasticity, SDR, Baclofen, and alcohol blocks.
Because his sensory mechanism was so well spared he quickly gained standing and walker supported walking skills which advanced to crutch assisted walking. Interestingly, and unexpectedly (we're not THAT smart) as his muscle mass increased (from function), the alternate pathways of metabolism inherent in muscle began to reduce his acidosis to the point where he only occasionally required his "brew".
There are so many details and requirements for muscle transfers. We can not cover them all here. The main thing is to know that they exist and that what looks bad may very well be, but occasionally there are loopholes in disease.
Muscle transfers are used more commonly in the upper extremity.