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Post 88: The anatomy of the “pain in the ass”

“To better understand the medical enigma of low back pain (LBP) it is necessary to thoroughly understand all structures that could potentially refer pain to this region.”

 

This is an excellent start. Any researcher that can throw the word “enigma” into an article already has my respect. Back pain is a mystery because so many people have it and so many people have had it and yet we are no better at reducing the incidence of this problem…even with all of our modern conveniences. There are a few sources of low back pain that are spoken of in PT, the back and the sacroiliac joint (SIJ). Obviously there are other sources such as some of the vital organs, but this is for another topic.

 

TIME FOR A QUICK ANATOMY LESSON:

 

“The sacral articular (auricular area is c shaped and located on the lateral spect of this bone. During the fetal and prepubescent years, the sacral surface is flat, smooth and lines with hyaline cartilage. The articular surface of the ilium is also c shaped, but in contrast to the sacral articulating surface it is covered by firbrocartilage. The smooth and planar articular surfaces of the SIJ…permit movement in all directions…restraint by the strong inerosseous sacroiliac (SI) ligament.”

 

This is the part that we are taught in school. The SIJ can move in all directions and this could cause pain. It appears that this has changed over the years, because students are coming out of school biased that the SIJ doesn’t cause pain. I believe that the pendulum may have swung too far in the other direction. There are some therapists that believe that the SIJ causes a significant percentage of back pain (this is based on my experience and tends to be older therapists…based on what I was taught in school, I can understand their perspective). There are others that believe that the SIJ doesn’t cause back pain (I don’t believe this either, but will lean more towards it doesn’t cause pain than it causes all pain). There is some research that indicates SIJ dysfunction correlates with 7-13% of all patients with complaints of back pain.

 

Big picture from the above quote: when we are young, the SI joint is very smooth (picture two bars of wet soap on top of each other), covered in cartilage that makes it slippery (think the chewy stuff on the end of a chicken bone) and is very mobile aside from a ligament holding it in place. THIS IS ONLY WHEN WE ARE YOUNG! More on this later.

 

“As early as the third decade of life ridges and depressions begin to form, making the joint surfaces nonplaner…increases the frictional resistance to motion and imparts greater stability to the joint…taking on a coarser quality…limits movement by increasing the coefficient of frictional resistance between opposing articular sufaces”

 

Do this experiment for me. Go wash your hands. Get them very soapy and slide your palms together. How well do they slide over each other? They should slide very well. This is similar to how it is when we are younger. The SIJ slides back and forth with little resistance. Now…wash off most of the soap (this will increase the friction between the two surfaces) and then make a fist with each hand. Put your left and right knuckles together and try to rub them over each other. It’s not hard to rub back and forth, but you can feel more resistance from the knuckles making it a little harder to rub back and forth. This is what happens to the SIJ around the third decade of life. So as not to leave this example of washing the hands (I just created it, so if you don’t like it…it didn’t take much of my brainpower and I’m not offended). Now, I want you to lock your fingers together (left and right hand will be locked together (almost like when you see a child praying in the movies) and then try to move your hands left and right. They don’t move well right? Your wrists may move more than your hands if you are watching closely. SPOILER ALERT: This is what happens when we get around the 6th decade of life.

 

“The purpose of the study is to document and quantify the surface topography of the Interosseous region of the SIJ complex”

 

This article is very interesting for me to read. I typically don’t like to read cadaveric studies (studies on dead bodies), but the research for the SIJ is really limited and this one came across my desk at some point. Topographical maps: go way back to grade school for this one (As big as the word is, it was taught to most of us before high school). A map that has the contours of the earth built in is a topographical map. If you were to slide your hand over the map, you would feel the mountains, the valleys, hills etc. This same type of map can be made over a joint. It would be easier now than when this study was performed with the advent of the 3D printer.

 

“Moderate or extensive ridging of the Interosseous surfaces of the ilium and sacrum was identified in all 10 specimens with average age of 69 years. Ridging was extensive in 6 specimens (age range, 55-91 years), while moderate ridging was found in 4 specimens (age range, 58-80 years).”

 

Moderate or extensive ridging indicates that the joint has soft-fused together. This means that the joint has essentially joined together like two gears or a zipper would joint together. It would make movement of the joint, gear, zipper very difficult.

 

“In contrast, in the 20-year-old specimen only a slight ridging and depression pattern was observed on both the iliac and sacral surfaces”

 

This is more like sliding two hands together. The surfaces are relatively smooth and slide-able over each other.

 

“…there did appear to be a relationship with respect to age. Slight ridging was found in the 20-year-old specimen, while the median age of specimens with moderate ridging and extensive ridging was 58 years and 75 years, respectively”

 

This means that the older we become, the more ridges there are between the joints. These ridges serve to reduce the available movement between the two bones.

 

“…beyond their sixth decade, 6 were observed to have distinct regions within the SIJ complex where the Interosseous SI ligaments had become ossified …effectively fused the posterior aspect of the sacrum and ilium”

 

This is a big debate in PT. Does it move or doesn’t it move? The SI Joint that is. When we age, it appears based on this research study, that the SIJ loses motion over time. Any joint that can move can cause pain. If the joint is unable to move, then we hope that it is not in a painful position because the likelihood of moving it out of the painful position is unlikely. The good thing though is that it is a low prevalence of being the cause of pain, which means that if it didn’t cause pain when it moved, it may not cause pain when it doesn’t move. That’s logical, but there isn’t much research to prove or disprove it.

 

“60% of the specimens in or beyond the sixth decade of life had parial ossification…fused the ilium and sacrum posteriorly, which can be extrapolated to suggest that no movement through the SIJ complex was possible in these specimens.”

 

There you have it folks! In a majority of people over the age of 60, it doesn’t move. This means that it is still a possibility for causing pain. When a patient has pain that is in the buttock, it has to be ruled in as a cause until it is ruled out. It can be ruled out/in using Laslett’s rules. Laslett’s clinical prediction rules for the SIJ.

 

“…in all 10 specimens (100%) aged 55 years and over…more extensive ridging…reduced joint mobility”

 

The older we get, the less likely the SI joint is to move and the less likely we will find a problem that we can fix with movement of the specific joint.

 

“Mobility tests for the SIJ have been found to be unreliable and their regular use as diagnostic tools is questionable…hence the 1 to 2 mm of movement that may occur, it at all, is likely to be difficulty, if not impossible, for most clinicians to perceive.”

 

My manual skills are good, but I am not good enough to feel 1 mm of change. This is like feeling a change in position the distance of a tip of a pencil through layers of skin, adipose tissue (fat), muscle and ligaments. I readily admit that my skills suck for detecting this movement, but I think that I am in the majority on this one. With that said, in school we learned a bunch of tests to see how much movement happened in the SI joint. Needless to say, we didn’t learn much about this in school that still holds true today…aside from the anatomy.

 

I’ll finish this post with a quote that finished the article because it summarized my thoughts well.

 

“Assessing mobility in the SIJ in the older population is not likely to yield any meaningful information.”

 

Excerpts taken from:

 

Rosatelli AL, Agur AM, Chhava S. Anatomy of the Interosseous Region of the Sacroiliac Joint. JOSPT. 2006;36(4):200-208.

 

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