Anatomy is not engineering — it’s wetter and sloppier. Strange, wonderful, and problematic anatomical variations occur in humans all the time. My father, a US Navy corpsman (the navy equivalent of an army medic) has told me stories about the surprising number of minor and major birth defects he witnessed while working in a maternity ward in a Naval Hospital in Japan: webbings, large skin tags, extra digits, and so on.
Other interesting (and clinically significant) examples:
The line between “normal variation” and “defect” is blurry. For every visible, superficial oddity, there may be an invisible internal one. Surgeon Sherwin Nuland writes:
Of the many hundreds of appendectomies I have done during a career of thirty-five years, no two were the same. … Although the configurations of human innards do not vary nearly as much as do those of our outards (a word that exists in no dictionary but should), they nevertheless reveal unmistakable variations among individuals — and only surgeons ever find out about them.
See below for a longer excerpt from Nuland’s fantastic book.
And for every striking variation, there are probably a dozen minor ones. Any of them have the potential to be involved in musculoskeletal problems. In 2004, Hislop and Tierney wrote in the Journal of Science and Medicine in Sport:
… anatomical variations may be present, such as supernumerary [extra] muscles, thickened fascial bands or variant courses of nerves and blood vessels, which can themselves manifest as acute or chronic conditions that lead to significant morbidity or limitation of activity.
Hislop M, Tierney P. Anatomical variations within the deep posterior compartment of the leg and important clinical consequences. Journal of Science & Medicine in Sport. 2004;7:392–399.
For example, consider this story, reported by Costa et al. Its concerns a cyst (which isn’t strictly an “anatomical variation” — it’s more of a straightforward abnormality, a “growth”). But the exact same thing could have happened with a cyst-like anatomical variation:
We present the case of a 28-year-old competitive runner with iliotibial band syndrome associated with a synovial cyst … open exploration revealed a large cyst beneath the ITB arising from the capsule of the knee proximal to the lateral meniscus. The cyst disappeared on extension. The preoperative MRI scan may have revealed the cyst, if it had been taken with the knee flexed.
Costa ML, Marshall T, Donell ST, Phillips H. Knee synovial cyst presenting as iliotibial band friction syndrome. Knee. 2004;11(3):247–248.
So the cyst basically created an atypical case of knee pain that defied diagnosis without surgical exploration. This person could easily have gone through a dozen doctors and therapists before finally getting some answers … and with no one really to blame. The body is just a weird place.
The word ‘normal’ is probably an inappropriate word to apply to the human body.
Choosing Running Shoes: The Evidence Behind the Recommendations, Griffiths (Sportspodiatryinfo.wordpress.com)
Therapists and doctors will routinely make a great fuss over visible anatomical variations, often concocting elaborate treatment plans based on them — expensive orthotics for your feet, tedious exercises to get you “aligned,” and so on. All the while, there could easily be invisible anatomical variations that are actually more important.
It’s a classic and chronic clinical error: paying attention only to that which is easy to pay attention to, looking for your lost keys only where the light is good. It’s obviously foolish, and yet difficult to avoid. Out of sight really is out of mind.
Such cases often join the “X-files” of therapy. The most important clinical implication of all this is:
Here are some other considerations:
I’m a freak! I have an extra pair of floating ribs! And I’ve only realized it just now (early 2016). Turns out my tenth ribs are “false” — that is, they don’t merge with the costal cartilage of the 8th and 9th ribs, like well-behaved 10th ribs. This anatomical jiggery-pokery is reputedly common in the Japanese, a fact mentioned (without support) in several sources.11
Most humans have a dozen ribs, with the occasional extra one at the top of bottom. Stubby little 13th ribs are almost common, about 1% of the population — so there’s enough 13th ribbers out there to populate several megacities. But floating 10th ribbers? There is exactly zero data on our prevalence. (Rule of thumb: if you can barely Google it, it’s rare.)
But the real marvel is that I didn’t know. That wouldn’t be so surprising for most people, but I’ve been professionally keen on anatomy, massage, and self-massage for 15 years. I’ve worked on myself a lot. And it’s not like I haven’t noticed the tips of my floating ribs before: they’re pretty obvious. How could I possibly have missed this? How could literally dozens of massage therapists?
It sounds like it should be obvious, in practice it was surprisingly difficult to confirm.12
I am a science writer, former massage therapist, and I was the assistant editor at ScienceBasedMedicine.org for several years. I have had my share of injuries and pain challenges as a runner and ultimate player. My wife and I live in downtown Vancouver, Canada. See my full bio and qualifications, or my blog, Writerly. You might run into me on Facebook or Twitter.
The following excerpt is from the first chapter of Sherwin Nuland’s superb book, The Mysteries within: A surgeon explores myth, medicine, and the human body, “The Stomach: A Little Boy’s Big Secret.” I could not ask for a better passage to explain how strange and diverse “normal” anatomy can be:
No matter how often a surgeon performs the same operation, it is different each time. Any operating room nurse can tell you that. The sequential precision of predictable steps so exactingly depicted in manuals of surgical technique resembles the real thing about as much as a diagram of human anatomy looks like a human being.
To take something simple: Of the many hundreds of appendectomies I have done during a career of thirty-five years, no two were the same. Even such a straightforward operative procedure for a straightforward disease, divisible into a short series of straightforward technical maneuvers that were standardized almost one hundred years ago, done by an operator of long experience — even under such circumstances every case is a novelty. And some of those novelties can be daunting tests of skill and confidence.
On bedside rounds one day during the period of my training, the senior attending surgeon, a man highly respected for his dexterity and judgment, was asked to name the half-dozen most difficult operative cases he had encountered in his career. After a moment’s thought, he replied that three of them had been appendectomies. His answer surprised no one in the group of interns and residents who were crowded around him. In the few years of our embryonic surgical experience, every one of us had already seen enough to appreciate what he meant.
Although the configurations of human innards do not vary nearly as much as do those of our outards (a word that exists in no dictionary but should), they nevertheless reveal unmistakable variations among individuals — and only surgeons ever find out about them. The way in which an organ is attached by ligaments and folds of tissue to its surroundings, for example, is in general predictable, and yet just enough personal difference occurs that an operator never knows beforehand whether the viscus he is approaching will come up easily into his seeking hands or require deep dissection to free it. Friend appendix, in fact, epitomizes this kind of anatomical uncertainty. Being attached to the large intestine only at one narrow end of its wormlike body, the appendix is free to turn upward toward the liver, downward toward the pelvis, sideward toward the center of the abdomen, forward toward the abdominal wall, or even retrocecal, which means it has tucked itself up behind the bowel into a hidden location. The appendix may be as short as a stumpy inch or as willowy as five or six times that length. There is no telling where its tip may be found. Other organs, though not as variable, have unpredictabilities of their own.
And then there is the problem of fat. The copiousness of the cushions of fatty tissue lying between internal structures depends in general on an individual’s station along the spectrum between leanness and obesity. Thin people are a great deal easier to operate upon than are the chubbies, who hide vital structures deep within thick, greasy blankets of adiposity. Among those concealed vital structures are blood vessels, which have an obnoxious tendency to make uncharted course changes now and then, obstinately refusing to reach their destination via the route assigned to them by anatomy books. Lying in wait for the unwary, or perhaps lurking within a fatty bolster, an unanticipated artery or vein — and nerves are known to do this too — can affect the entire plan of a surgeon’s work, and sometimes its outcome.
Beyond even these considerations, the occasional occurrence of a congenital variation of structure must be taken into account. The operating team always has to be on guard for such an abnormality, especially because it may involve blood vessels or the slender ducts that carry secretions and other vital fluids to their destinations. Some of these inborn irregularities can present major challenges, or at least major surprises. From time to time, for example, one or another viscus or a part of it must be sought in an area of the body where it seems not to belong. I am not at all unique among surgeons to have removed thyroid tissue from the chest, found the right colon on the left side of the abdomen, and taken an ovary or appendix out of a hernia bulging into the uppermost part of the thigh.
Just to promote Nuland’s excellent book, I will continue the excerpt a little longer, even though the topic changes. He goes on to explain many more things that make every operation unique, even the common ones. But then he introduces an exotic case …
I have been referring here to operations done with relative frequency. For the reasons given or others, some cases will be so unusual that they stand out in a surgeon’s mind for the rest of his life. But in addition to that list, there exists a special category within even less commonly done procedures — these are the real rarae aves. By this I mean the one-and-onlies. These are the operations of such a unique type that the members of the team will regale one another with their details when they meet at reunions or conventions decades later, even in farflung parts of the world. Some of these procedures are firsts, or at least firsts in a given hospital — the first organ transplant, the first use of the heart-lung machine, the first video-controlled gallbladder operation — but some are memorable because no member of the team has ever seen their like before or since. Like all surgeons, I have a few of those once-in-a-lifetime adventures tucked away in the back of my mind, ready to be pulled out and relived at a moment's notice.
One of them involves the stomach.
My patient had been an independent citizen for all of six weeks, the first two of which were spent in the preemie unit …
It’s a great story!
Sometimes the sacrum is fused to the lowest lumbar vertebra: a lumbosacral transition vertebra. “LSTV is the most common congenital anomaly of the lumbosacral spine.” In about a thousand patients studied, it was about twice as common in patients who had sought spinal surgery as it was in patients with no spinal complaint (about 14-16% of patients, instead of 8%). The study also identified a “definite causal relationship” with degeneration of the disc above the LSTV.BACK TO TEXT
There is a fairly common spinal deformity, a “transitional vertebra,” in which the lowest vertebrae of the spine is partially merged with the sacrum. It is not quite a vertebra, and not quite sacrum — thus, “transitional.” This study looked at how common transitional vertebrae are, and if they correlate with low back pain. Not that we needed it, but the results give us yet more evidence that structure is nowhere near the most important factor in pain. Simply put, this study found that this common spinal deformity is not much more common in people with pain (maybe no more common at all): “Although LSTV's role in low back pain remains controversial, our study has shown that, when the same criteria are used for classification, prevalence among the general population and symptomatic patients may be similar.”
As always, this kind of finding is strongly at odds with an entire industry of therapy based on trying to fix subtle alleged biomechanical problems because they are supposedly painful. And yet here we have a vertebral birth defect that is found in pain-free people about as often as it is found in cases of back pain. Something is wrong with this picture.BACK TO TEXT
This dissection study of 275 dead buttocks found that 6.4% of them had variations of sciatic nerve and piriformis muscle anatomy, with considerable variety in the variation. They found several different arrangements, and concluded: “Some rare, unclassified variations of the sciatic nerve should be expected during surgical intervention of the region.” Prepare to be surprised, surgeons!
All of these differences are potentially clinically significant, probably especially in the cases where the nerve (or part of it) passes right through the muscle. For a couple case studies, see Arooj 2014 and Kraus 2015.BACK TO TEXT