Throughout my career as an anatomy teacher at the university, my students have asked me several times about muscles that I did not know existed. Since I have been engaged in anatomy for more than thirty years, after each such question I re-read a huge amount of materials to get to the bottom of the truth. The human body is unique – it consists of a great many diverse structures. However, if this diversity goes beyond the scope of classical textbooks on anatomy, many experts refuse to recognize it. On the other hand, many experienced surgeons and anatomists are faced with different variants of the norm literally every day.
One of these “new muscles” that my students told me about is the so-called “sphenoid-mandibular” muscle. It was described in several journals in the late 90s of the last century as a hitherto unknown chewing muscle. In classical textbooks, the medial part of the temporal muscle is located in place of this muscle.
These articles are not widely distributed. The authors were convinced that problems with this muscle underlie the etiology of some varieties of headaches, such as pain caused by trigeminal neuralgia. Already in our century, two researchers – Ibarra and Bauer – published in the journal Clinical Anatomy a clear and concise refutation of this article and explained what kind of “new muscle” it is .1
The temporal muscle is a much more complex structure than textbooks tell us. Moreover, a complex structure always manifests itself in functional versatility. The first detailed description of the medial part of the temporal muscle dates from the beginning of the 19th century. Ibarra and Bauer in their article examined some other descriptions of this part of the temporal muscle. After anatomical analysis of several samples and describing in great detail all the difficulties of the onset and attachment of the medial head of the temporal muscle, the anatomists examined the possible clinical consequences of various impaired functionality of this muscle. They paid special attention to the difficulties of attaching this part of the temporal muscle to the sphenoid bone. The authors describe the possibility of a connection between the pinched lateral part of the middle branch of the trigeminal nerve (maxillary nerve, V2) with pain in the face. They indicate that differences in the structure of the pterygo-palatine fossa may be a factor contributing to various manifestations of this pain syndrome.
Some of its manifestations, which are musculoskeletal in nature, may be confused with neuralgia, that is, with pain caused by problems with the nervous system. Despite the fact that different authors may not agree on whether the medial part of the temporal muscle should be distinguished as a separate muscle or not, they nevertheless agree that problems with it can cause headaches.
Muscles, problems with which can be the causes of various types of headaches, can actually be more difficult than we think. Travel and Simons2 have described many of these muscles. In addition, sometimes only some parts of the muscle may be associated with the etiology of some types of headache.
We have already mentioned that the muscular system of the human body is very diverse in nature and, importantly, varied – and these variations can cause pain. Such standard options can confuse the specialist or, even worse, lead to a diagnostic or clinical error.
For example, one of the most common variations of this kind is the absence of a long palmar muscle. 10-15 percent of people do not have this muscle. This leads to the fact that the part of the median nerve, located directly proximal to the entrance to the carpal tunnel, is less protected. You can easily check if you have a long palmar muscle by performing an isometric contraction of the flexors of the wrist with resistance (for example, place the hand palm up under the edge of the table and try to bend the brush in the wrist). If you have this muscle, it will protrude anteriorly, passing through the carpal tunnel.
Other common variants of the norm, such as the presence or absence of a third peroneal muscle, do not (of course, as far as the author knows) have functional and clinical significance.
Another type of muscle variability is hypertrophy, intentional (achieved through training) or arising due to lifestyle characteristics. One of the most interesting examples of functional muscle hypertrophy is the increase in the volume of a round pronator in the serving players (pitcher) in soft-feed with a quick feed. Players in the pitcher position in this game actively use the round pronator when throwing the ball. As a result of long workouts, this muscle hypertrophies, squeezing the median nerve, passing in the forearm between the two proximal heads of the round pronator. As a result of this, the player develops symptoms resembling carpal tunnel syndrome, however, the use of treatment methods for SZK when compressing the median nerve between the heads of the round pronator does not contribute to recovery.