Orthopedics · Part Two · The Structures and How They Heal
Lesson 13 / 44
The Big Three of Low Back Pain: Disc, Facet Joint and Sacroiliac Joint
Most persistent low back pain traces to one of three structures, and a clinician can weigh which is most likely before a single scan is ordered.
The big three sources of chronic low back pain are the intervertebral disc, the facet joints and the sacroiliac joint. In one series of 170 cases worked up with discography and dual blocks, the disc accounted for 42 percent, the facet joints 31 percent and the sacroiliac joint 18 percent. Other series using different criteria report very different shares. The Unified Model of Tone reads that disagreement as the signature of samples never sorted by tone.
Disc, facet and sacroiliac share in one dual-block series
42, 31 and 18 percent
Facet responders, screening block against confirmatory block
47 percent falling to 15 percent
Patients given a patho-anatomic diagnosis by reference-standard testing
67 percent of 216
Matched against unmatched treatment at one year
8.3 Oswestry points
What a pain generator is
A pain generator is the tissue whose stimulation reproduces a person’s familiar pain and whose anesthesia abolishes it. Three lumbar structures qualify often enough to be worth naming. The intervertebral disc sits between two vertebral bodies. The paired facet joints sit at the back of every segment. The sacroiliac joint sits where the sacrum wedges into the pelvis.
How a diagnostic block decides the question
A block places local anesthetic on one structure or on the nerve that supplies it. Relief of the familiar pain implicates that structure. One injection misleads often, because the anesthetic spreads and because relief is reported by a person who wants it. A controlled block repeats the procedure with an anesthetic of different duration and counts only the response that tracks the drug.
01Three common sources
Three structures account for most chronic low back pain
Persistent low back pain almost always traces to one of three structures, and knowing their frequency is the smartest place a clinician can begin. DePalma and colleagues reviewed 170 cases in which diagnostic procedures continued until the source was found. Internal disc disruption accounted for 42 percent, facet joint pain for 31 percent and sacroiliac joint pain for 18 percent (DePalma 2011).
Those figures rest on discography, dual facet blocks and sacroiliac injections rather than on appearance. An earlier Australian series matched them for the disc. Of 92 consecutive patients given both discography and facet blocks, 36 had a positive discogram (Schwarzer 1994a). The two ran on different continents, in Newcastle and in Virginia.
The practical value of these numbers is that they set a starting probability. Before a clinician asks a single question, the disc is already the leading candidate. Each new clinical feature then nudges that probability up or down toward one of the three.
What the guidelines still say
Guidelines continue to hold that the tissue source of low back pain cannot be specified in most patients (Hancock 2007). That describes what an ordinary consultation delivers rather than what the tissues do. Where reference-standard testing was available, 67 percent of 216 patients received a patho-anatomic diagnosis (Laslett 2005).
The rigorous block studies that followed retired the older pessimism, and left published prevalence figures a clinician can reason from.
02Findings
What the research shows
From two dual-block prevalence series, a review of 41 diagnostic studies and two randomized trials.
03Why the numbers disagree
Single-generator studies disagree because the method sets the answer
The prevalence figures for the three generators vary widely across studies, and the diagnostic procedure produces most of that variation. Schwarzer and colleagues examined 176 consecutive patients. Forty-seven percent responded to a screening facet block. Fifteen percent responded to a confirmatory block with a longer-acting anesthetic (Schwarzer 1994b).
One extra injection removed two thirds of the diagnoses. A study that stops at the first block reports the larger number. Facet Joints as Pain Generators carries the prevalence range and the false-positive rates behind it.
The disc side is sharper. Carragee and colleagues injected 24 discs in eight people with no history of low back pain, under a blinded protocol. By the usual criteria for a positive discogram, four of the eight would have been called positive (Carragee 1999).
A later review of the same procedure puts the false-positive rate at 10 percent or less when strict operational criteria are applied (Bogduk 2013). Two teams examined one test and reported error rates that differ fivefold. The criteria changed, not the tissue.
One patient, more than one source
Single-generator designs also assume each patient has one answer, and most do. Of the 92 patients given both procedures, only three had a positive discogram and a symptomatic facet joint (Schwarzer 1994a). Discogenic pain and facet pain rarely coincide.
The exceptions matter. Among 216 patients worked up against reference standards, 10 percent had more than one tissue origin (Laslett 2005). A study that tests one structure and calls the rest negative misplaces those patients.
04Age shifts the odds
Age, sex and body mass move the three probabilities before anyone touches the spine
Age reweights the three suspects before a clinician lays a hand on the spine. Patients whose pain came from internal disc disruption were significantly younger than those with facet or sacroiliac pain. As age rises, the probability of a disc source falls, while facet and sacroiliac pain rise until roughly age 70 (DePalma 2011).
A multivariable analysis of 157 cases separated the effects. Increases in age lowered the odds of internal disc disruption against every other source. Being female raised the odds of sacroiliac joint pain, and a higher body mass index raised the odds of facet pain against it (DePalma 2012). Disc pain is most prevalent in young males, and sacroiliac pain in females with a low body mass index.
So a person in their mid fifties starts to drift away from the disc and toward the posterior joints, while a person in their late thirties leans the other way. The published trend is continuous rather than a cut point. Age is never the whole answer, but it is a free and powerful first filter.
05Where the pain sits
The map of the pain narrows the three without closing the question
The map of where the pain lives is one of the richest clues a clinician has. Young, Aprill and Laslett examined 81 patients before diagnostic injections, with the examiners blinded to the result. Sacroiliac joint pain was associated with unilateral pain and the absence of lumbar pain (Young 2003).
The sacroiliac pattern sits low and to one side, below the level of the L5 spinous process. That is why a person with a sacroiliac source often reports no true lumbar pain. The Sacroiliac Joint carries the injection map and the Fortin finger test built on it.
Pain that precise is often pointed to with one finger on a single spot. The instruction is simply show me where the pain is, and the clinician watches whether one finger or a whole flat hand answers.
What location cannot settle
Location narrows the field and does not close it. In 176 patients, a positive response to facet joint injection was not associated with any single clinical feature or set of features (Schwarzer 1994b). The systematic review reached the same verdict from 41 studies, finding no informative test for facet joint pain (Hancock 2007).
The disc has exactly one clinical feature that raises its probability. Centralization during repeated movement testing produced a positive likelihood ratio of 2.8, with an interval from 1.4 to 5.3. Why MRI Misleads follows what an image can settle.
06Rising from a chair
Ordinary movements talk, and arising from a chair says the most
How the pain behaves during ordinary movement separates the three better than any special maneuver. In the same blinded series of 81 patients, discogenic pain was associated with centralization and with pain on rising from sitting. Facet joint pain was associated with the absence of pain on rising (Young 2003).
Sacroiliac joint pain sat with the disc on that item. It was associated with pain on rising, unilateral pain, absent lumbar pain and three or more positive provocation tests.
Something as simple as the way a person stands up from the waiting room chair carries real diagnostic weight. Rising loads the disc, the facet joints and the sacroiliac joint in one motion. What differs is which of them reports.
When walking is the provocateur
Pain that worsens with walking in an older adult widens the question. Spinal stenosis and vascular claudication both present that way, and Vascular Mimics and Claudication separates the load-provoked patterns.
Guarded, pain-avoidant movement is a readout of how the whole system is bracing. A clinician watching someone rise is reading a regulator rather than measuring a joint.
07Tests that confirm
No single test names the source, and a negative extension rotation test still rules the facet out
A single test never makes a diagnosis, so a clinician stacks probability by aggregating several results with the history. The extension rotation test, also called the Kemp test or quadrant test, combines lumbar extension and rotation while the person runs a hand down the back of the same leg. Disc, facet and sacroiliac pain all light it up.
Its power lies in what a negative result removes. Laslett and colleagues gave screening facet blocks to 151 patients and analyzed 120 of them. At the 75 percent relief standard, 24.5 percent responded. At the 95 percent standard, 10.8 percent did (Laslett 2006).
A negative extension rotation test and the centralization phenomenon both effectively ruled out complete relief from the block. Five prediction rules ruled out a 95 percent reduction with 100 percent sensitivity, and one carried a likelihood ratio of 9.7.
What the clusters are worth
The sacroiliac joint is the one structure with a confirmed clinical cluster. Used in combination, the manual tests produced a positive likelihood ratio of 3.2 and a negative ratio of 0.29, while single tests were uninformative (Hancock 2007). Three or more positive results out of compression, distraction, FABER, Gaenslen and thigh thrust carry that power.
Centralization, described by Robin McKenzie, uses standardized end-range movements repeated in sets, and pain that migrates toward the midline points to a disc source. Blended together, these findings let a clinician name the most probable source and choose conservative care with clear eyes.
08Claims removed
Seven claims from the earlier version were corrected or removed
The sacroiliac share was given as about 22 percent. The series those figures came from reports 18 percent (DePalma 2011). The claim that 80 percent of people with painful lumbar discs had midline or axial pain came off, because no source for it could be found.
The statement that facet pain has been recognized since 1994 as sitting laterally and sparing the midline came off as well. The 1994 series usually cited for it found no clinical feature associated with a positive facet block (Schwarzer 1994b). Two accuracy figures for the extension rotation test, 22 percent and 12 percent specificity, came off because neither could be traced to a published study.
The 50-year cut point for facet pain came off, because the published relationship between age and source is continuous (DePalma 2012). So did the claim of estimates from three continents, and the pattern that put facet pain at its best on walking and sitting. The two series carrying the figures here ran in Australia and the United States.
09The model on the three sources
What the Unified Model of Tone claims about the three generators
Everything above is established science, including the findings that came back negative. What follows is this model’s reading, stated as ours rather than drawn from the papers cited.
Our model holds that the most symptomatic site is frequently a compensation splinting a distortion elsewhere. The loudest tissue is the weakest link rather than the origin, and often the one with the least capacity left to compensate.
That changes what a prevalence figure means. It reports where a load surfaced in a population, not where the load came from. Only three of 92 patients carried both a painful disc and a painful facet joint (Schwarzer 1994a).
Why the studies disagree, in the model’s terms
Our model states the rule generally. When an outcome depends on the correspondence between an input and each person’s constraint structure, a study that delivers the same predetermined input to everyone averages a well-matched procedure and a mismatched one. The sample was never stratified by tone, so the average is a number no individual holds.
A diagnostic block is that kind of input, aimed at a fixed target in a sample sorted only by symptom. Under that reading, 47 percent falling to 15 percent is the expected result of changing the match (Schwarzer 1994b).
The same reading covers the two negative findings here. No clinical feature identified facet pain in 176 patients, and no facet test was informative across 41 studies (Hancock 2007). A test that indexes one tissue in an unsorted sample averages matched and mismatched cases.
The same input, three different results
Treatment trials show the effect directly. Childs and colleagues randomized 131 patients to manipulation plus exercise or exercise alone, then split them by a five-item rule. Rule-positive patients given manipulation had odds of success of 60.8, against 2.4 for rule-negative patients given the same manipulation (Childs 2004). A rule-positive patient had a 92 percent chance of success.
Brennan and colleagues built the same logic into a trial design. Of 123 patients classified into three subgroups then randomly assigned treatment, those whose treatment matched improved by 6.6 more Oswestry points at four weeks and 8.3 more at one year (Brennan 2006).
The prediction
From that follows a claim the prevalence literature does not make. Two people assigned the same pain generator by the same block differ measurably across the rest of their regulation, and that difference predicts who responds.
Four measures recorded together in the same people will share one underlying factor rather than varying independently. They are pressure pain threshold over the symptomatic segment, active lumbar range of motion, resting heart rate variability, and time to return to baseline after a standardized loading test.
Under an input that restores regulation, people who begin high on that threshold and people who begin low both move toward the middle, and the spread narrows. This is a claim about how low back pain is organized rather than a claim about what treatment does. If pressure pain threshold, active lumbar range of motion, resting heart rate variability and time to return to baseline are shown to move together, the unification claim is confirmed.
10The tone reading
How the three generators express tone
Every topic in this library expresses all of tone. In the three sources of low back pain three aspects carry the signature, because the same block reports one prevalence and then another.
Constraint
Where a load surfaces depends on the pattern a body already holds. Only three of 92 patients carried a painful disc and a painful facet joint at the same time.
Load
The three structures share one column and one motion. Rising from a chair loads all of them, and the response separates facet pain from the other two.
Input quality
A block is an input whose reading depends on the state it meets. A screening injection called 47 percent of patients positive and a confirmatory injection called 15 percent.
The remaining foundations run through the three generators as well. Time course: the disc leads in younger adults and the posterior joints in older ones, a shift tracked to roughly age 70. Coupling: guarding at one segment changes the load its neighbors carry, which is how a second generator is recruited. Gain: the amplifier sits above the tissue being numbed, so identical anesthetic produces different relief in different people. Set point: the resting level of protection decides how much load a segment tolerates before it reports. Prediction: a person who expects an injection to work reports relief more readily, which is why controlled blocks exist. Oscillation: pain that follows a daily rhythm is reporting the regulator rather than the joint. These are readings of one organization rather than separate systems, which is the core claim of the Unified Model of Tone.
11Across the library
How this page relates to the rest of the library
Each generator has its own page, and this one holds the ratios between them.
The prevalence range for the facet joints, the medial branch anatomy, and what the capsule reports.
The provocation test cluster, the Fortin finger test, and the map that defined the painful area.
The chemical, mechanical and vascular routes by which a disc produces pain.
What changes when leg pain enters and the three lumbar sources stop explaining it.
Why a scan raises the probability of a source without settling which structure speaks.
Why the least invasive input that can carry the message is the correct place to start.
Low back pain read as a regulatory state, with the instruments that measure it.
12Frequently asked
Questions patients ask about the sources of low back pain
What are the most common sources of low back pain?
The three leading mechanical sources are the intervertebral disc, the facet joints and the sacroiliac joint. In one series of 170 cases carried through diagnostic procedures until a source was found, the disc accounted for 42 percent, the facet joints for 31 percent and the sacroiliac joint for 18 percent. Other series report different shares, because the shares depend on which diagnostic criteria the study applied. The disc is the leading candidate in adults before any examination begins.
How does a clinician find the source of back pain?
By combining the pattern of the pain, the response to specific movements and a short cluster of targeted tests, rather than by reading a scan alone. Sacroiliac joint pain is associated with unilateral pain and the absence of lumbar pain. Discogenic pain is associated with centralization during repeated movement testing and with pain on rising from sitting. Facet joint pain is associated with the absence of pain on rising from sitting. No single finding settles the question by itself.
Does finding the exact source change treatment?
It refines it, and the refinement is measurable. In a randomized trial of 123 patients, those whose treatment matched their clinical subgroup improved by 6.6 more Oswestry points at four weeks than those given unmatched treatment. At one year the difference was 8.3 points. Identifying the main pain generator lets a clinician aim conservative care rather than guess, and all three of these sources respond to careful graded loading built around what the person can tolerate on the day.
Why do studies disagree about how common facet joint pain is?
Because the diagnostic method sets the number. Among 176 consecutive patients with chronic low back pain, 47 percent responded to a screening facet block and only 15 percent responded to a confirmatory block with a longer-acting anesthetic. One extra injection removed two thirds of the diagnoses. A study that stops at the first block reports the larger figure and a study that confirms reports the smaller one, from the same clinic and the same patients on the same day.
Does age change which source is most likely?
Yes, and the shift is continuous rather than a threshold. Patients whose pain came from the disc were significantly younger than those with facet or sacroiliac pain. As age rises, the probability of a disc source falls while the probability of facet or sacroiliac pain rises, until roughly age 70. A multivariable analysis of 157 cases added two more signals. Disc pain was more prevalent in young males, and sacroiliac pain in females with a low body mass index.
What is the extension rotation test used for?
For ruling out rather than ruling in. The test combines lumbar extension and rotation while the person runs a hand down the back of the same leg, and disc, facet and sacroiliac pain can all provoke it. Its value lies entirely in a negative result. In 120 patients given screening facet blocks, a negative extension rotation test effectively ruled out complete relief from the block, alongside the centralization phenomenon and four other prediction rules that carried 100 percent sensitivity.
What does the Unified Model of Tone say about the three sources?
That the structure which hurts is usually the one with the least capacity left to absorb a load, rather than the origin of the problem. Our model reads the disagreement between prevalence studies the same way. A fixed block delivered to a sample never sorted by tone averages a matched procedure and a mismatched one. From that the model predicts that pressure pain threshold, lumbar range of motion, heart rate variability and recovery time share one underlying factor, with compensation deciding how far each one moves.
13The sources
References
12 primary sources, each linked to its record. Figures quoted on this page were checked against the published abstract.
Related evidence