Periosteum of the Coccyx: Tailbone Periosteal Layer and Coccygectomy.

Periosteum of the Coccyx: Tailbone Periosteal Layer and Coccygectomy.

Recently I have received a lot of questions about the periosteum and whether  the periosteum  should be left in place when ppatient undergoes a coccygectomy (surgery to amputate  or removed the coccyx, or tailbone).

What is the periosteum?
  • The periosteum is a very thin layer of fibrous tissue that surrounds almost every bone throughout the body.
  • This periosteal layer is important for bone growth and bone healing.
Plastic food wrap comparison:
  • Plastic wrap is also called, shrink wrap, cling wrap, food wrap, plastic film, Saran wrap, etc.
  • The thin layer of periosteum is essentially like a thin wrapping around the length of each bone.
  • Imagine if you have a pencil and you were to wrap it with a layer or two of plastic food wrap. Your pencil would be the bone and the plastic food wrap would represent the layer of periosteum that surrounds the bone.
How thick is the periosteum?
  • The periosteum is very very thin.
  • 100 μm thin! That’s 100 microns.
    • “Total periosteal thickness is approximately 100 μm” for both the femur (thigh bone) and tibia (shin bone). (Source:  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3969058/ )
  • What is a micron?
  • A micron is also known as a micrometre or micrometer. A micron is represented by the symbol μm.
  • (Also, note that this 100 micron measurement is for the periosteum of the thigh bone, which is the largest bone in the body. The bones of the coccyx are much smaller than that, so the periosteal layer at the coccyx is probably even thinner than what we see at the thigh.)
How thin is 100 μm?
  • 100 μm = 0.004 inches. So, the periosteal thickness is 4 thousandths of an inch.
  • Ruler comparison:
    • One way to think of this is to look at a ruler.
    • Your ruler will typically show 10 short increments to make up one inch. So, the distance between each of those small increments is 1/10 of an inch, which can also be written as 0.1 inches.
    • Now imagine if each of those small increments were to be further broken down into 10 even-smaller increments. Those even-smaller increments would each be 0.01 inches.
    • Then if you took that even-smaller-increment of 0.01 inches and split it in half, you would get 0.005 inches. And the periosteum is thinner than that.
  • As thin as a hair: Another way to think about the periosteal thickness is to compare it to a common everyday item such as human hair.
    • The thickness of a human hair is also around 100 microns. (Source: https://en.wikipedia.org/wiki/Hair%27s_breadth)
    • As noted above, 100 microns is also the thickness of the periosteal layer.
    • So, look now at an individual hair on the back of your forearm and notice how thin it is. That hair is approximately the same thickness as the layer of periosteum that surrounds your bones.
 Coccygectomy surgery and the periosteum:
  • During amputation/removal of the coccyx (coccygectomy), the surgeon has a choice:
  • Option #1: some surgeons try to take out the entire coccyx along with its’ periosteum.
  • Option #2: other surgeons try to remove the coccyx while leaving the periosteum in place within the patient.
  • Either way, typically the surgeon starts the surgery from behind the coccyx (posteriorly).
Option #1: Removing the periosteum during coccygectomy:
  • If the surgeon is removing the coccyx and also removing the periosteum, then they will try to cut and separate the muscles, tendons, and ligaments that attach to the coccyx. This allows for the coccyx (and it’s periosteum which is stuck to the coccyx bones) to all be removed together.
Option #2: Leaving the periosteum in place during coccygectomy:
  • Alternatively, if the surgeon is removing the coccyx but trying to leave the periosteum in place, then they need to attempt to separate each of the coccygeal bones from its’ periosteal film/layer.
  • To do this, the surgeon does need to cut through the periosteum to get to the coccyx. This is typically done along the back wall of the coccyx, in the midline. Then they usually use electrical cauterization to burn through the layer between the bone and the periosteum to separate at that layer.
  • Note that the periosteum is very very thin. As thin as a human hair. So it would be very very difficult, if not impossible, for a surgeon to confidently guarantee that they left all of the periosteum in place. In reality, they do their best to dissect a target layer in between the bone and the periosteum. But the tools used by the surgeon may end up cutting through or burning through the periosteal layer, in a variable fashion. It is especially challenging for the surgeon to get to the front of the coccyx (since they are approaching it from behind) and this makes it tough to reliably peel off the periosteum at the front of the coccyx.
  • Variable success at peeling off the periosteum: so, some of the periosteum may still end up still stuck to the bone, while some of the periosteum may end up being destroyed as a normal byproduct of the surgery itself, and some of the periosteum may end up still “left in place” within the pelvis [in the periosteum that is “left in place” within the pelvis will presumably remain attached to the muscles, tendons, or ligaments that have been attached to it prior to the surgery]).
  • Each individual coccygeal bone will have its own individual periosteum. (There is NOT any single continuous periosteum for the entire coccyx, unless your entire coccyx is already naturally fused together, which does happen, although it is rare.) So this means that the surgeon would need to peel the periosteal layer off of each and every individual coccygeal bone, if the goal was to leave all of the periosteum in place within the pelvis.

 

Which option is better? One Publication on Coccygectomy and the Periosteum
  • In 2010, surgeons in Turkey published a study where they tried two different techniques for performing coccygectomy. Some of the patients had their coccyx removed along with the periosteum being removed. Other patients had their coccyx removed whilst leaving the periosteum in place. They had a total of 25 patients, split unevenly between the two groups.
  • Results: “Both surgical techniques resulted in a statistically similar clinical outcome. Overall, 84% of patients who underwent coccygectomy benefited from surgery.” But the likelihood of having infection at the surgical wound site was statistically less in patients who had their periosteum left in place within the pelvis.
  • Reference:  https://www.ncbi.nlm.nih.gov/pubmed/?term=19471931
  • So, at least from this one study, leaving the periosteum in place seems to decrease the chances of infection after the surgery, but does not improve long-term outcome.
  • There were some limitations to the study: 1) there were only 25 patients total, split unevenly between the two groups. Small sample sizes make it difficult to know how reliable the statistical differences are between the two groups. 2) It was a retrospective study, instead of a prospective study. 3) The groups were not randomized. The authors do not explain what factors determined which patients went into the periosteal-sparing group. This matters. If, for example, the first group were the first coccygectomy surgeries by this surgeon, and then the surgeon switched to a different technique a year or two later for the second group, then perhaps the decreased infection rate in the second group was due to the surgeon just having become a better, more experienced surgeon over the additional years of performing coccygectomies.

 

Where can we learn more about the periosteum in general (unrelated to the coccyx)?
  • Here is a good reference article about the periosteum in general (without reference to the coccyx):  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2826636/

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- Patrick Foye, M.D., Director of the Coccyx Pain Center, New Jersey, United States.

 

 

Patrick Foye, M.D.
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Patrick Foye, M.D.

Founder and Director at Tailbone Pain Center
Dr. Foye is an expert at treating tailbone pain (coccyx pain).

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