Chronic Low Back Pain

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Chronic low back pain is a common cause of persistent suffering and disability for the affected individual, but also has significant effects on those around them. The biomedical assessment involves determining whether they have the IASP definition of low back pain, whether it is indeed chronic, ascertaining whether they have referred pain and whether it is somatic referred pain or radicular pain, and identifying "red flag" conditions. A decision is then made about whether to go down an investigative pathway to determine the source and cause of the pain. Treatment approaches include monotherapies (e.g. physiotherapy, surgery, medication), multi-disciplinary treatments, and reductionist treatments if a precision diagnosis is made and a relevant treatment is available, efficacious, and acceptable to the patient (e.g. medial branch radiofrequency neurotomy for confirmed facet joint pain).

Definitions

Figure 1: IASP Definitions

Main article: Low Back Pain Definitions

Topography

Starting with the wrong definition of low back pain can lead to the wrong diagnosis, and so it is important to be clear here. Low back pain is not loin pain, nor is it gluteal pain. The IASP taxonomy categorises low back pain into lumbar spinal pain and sacral spinal pain. There is also an overlapping definition called lumbosacral pain. These three categories constitute the colloquial term "low back pain."

Lumbar spinal pain is pain in a region bounded superiorly by an imaginary transverse line through the tip T12, inferiorly by an imaginary transverse line through the tip of S1, and laterally by vertical lines tangential to the lateral margins of the erector spinae muscles.

Sacral Spinal Pain is pain in a region bounded superiorly by an imaginary transverse line through the tip of S1, inferiorly by an imaginary transverse line through the posterior sacrococcygeal joints, and laterally by imaginary lines passing through the posterior superior and posterior inferior iliac spines."

Lumbosacral Pain is pain perceived as arising from a region encompassing or centred over the lower third of the lumbar region as described above and the upper third of the sacral region as described above.

Acuity

Chronic pain is pain present for longer than 3 months (91 days). One pragmatic approach is to include in the definition of chronic those patients with acute low back pain who are not improving when it may not be sensible to wait until the 91 day mark, say at two months. However if they have had pain for more than two months and not had evidence based management for acute low back pain then they should have that first. Indeed, following the acute approach may still be appropriate for some patients who have had pain for longer than 3 months.

Referred Pain

Main article: Low_Back_Pain_Definitions#Referred_Pain

Referred pain is "pain perceived as arising or occurring in a region of the body innervated by nerves or branches of nerves other than those that innervate the actual source of pain"

Visceral referred pain is referred pain where the source lies in an organ or blood vessel of the body. With low back pain, the uterus and abdominal aorta are important considerations. Other viscera with higher segmental supply may cause back pain such as pancreatitis, but this may be due to irritation of the posterior abdominal wall, in which case the pain is not truly referred in nature.

Somatic referred pain is referred pain where the source originates in a tissue or structure of the body wall or limbs. A number of structures in the lumbar spine are capable of nociception including the lumbar zygapophysial joints, intervertebral discs, sacroiliac joints, and more.

Radicular pain is a subset of neuropathic pain, and refers to pain that is evoked with stimulation of the nerve roots or dorsal root ganglion of a spinal nerve. In radicular pain, the pain is felt in the peripheral innervation of the affected nerve.

Somatic referred pain and radicular pain can usually be differentiated based on the quality and spread of the pain, see the assessment section below.

Aetiology

Figure 2: Probability of CLBP sources by age and BMI for males and females. FJP = facet joint pain, SIJP = sacroiliac joint pain, IDD = internal disc disruption.

Main article: Causes and Sources of Chronic Low Back Pain

Various structures in the low back are capable of nociception as determined through noxious stimulation, including the muscles, interspinous ligaments, zygapophysial joints, sacroiliac joints, and the intervertebral discs which are the most sensitive. These constitute possible sources of pain.

As for the causes, the lumbar intervertebral discs and lumbar zygapophysial joints have the most evidence as established causes. The sacroiliac joint has the next best evidence. The prevalence is highly dependent on the age, and also the BMI and gender. Overall around 40% have disc pain, around 30% have facet joint pain, and around 20% have sacroiliac joint pain. The common aphorism that "most chronic low back pain is non-specific" is out of date and patently false, especially in those without widespread chronic pain.

Assessment

The assessment of chronic low back pain has some slight modifications to that of acute low back pain. History is still important, while physical examination still has major limitations. Imaging however now plays a greater role. The doctor must take care to avoid missing any serious causes of pain, formulate a diagnosis, instigate an investigation and treatment plan, and identify and manage any psychosocial barriers to recovery. Unlike with acute low back pain, a precise diagnosis is often possible for chronic low back pain. A decision is made whether to pursue a definitive diagnosis to enable specific targeted treatment, or apply general treatments that don't require precise source identification.

Pain History

See also: Acute Low Back Pain#Pain History, Medical History

The age of the patient is of vital importance. This is because the potential causes are dependent on age, as well as certain malignancies.

The site of pain helps to determine the taxonomy, whether they have lumbar spine pain, loin pain, gluteal pain, or abdominal pain, each of which have a different assessment and management. Abdominal pain takes priority over low back pain.

For sacroiliac joint or sacroiliac ligament pain, the site of pain tends to be over the sacroiliac region below the L5 level. So pain below L5 increases the odds of the sacroiliac complex being implicated.

The duration of illness establishes whether they have chronic pain as it is defined, and make some sort of assessment as to the likelihood of red flag conditions. The idea being that pain present for a long time without deterioration may suggest a low risk of red flags. However certain infections and tumours can develop very slowly.

The distribution of pain its quality helps distinguish between somatic referred and radicular pain. (see article on referred pain). These two entities are commonly confused, so much so that the reliability of prevalence studies on radicular pain has been called into question. Somatic referred pain is thought to be much more common than radicular pain. Patients can have combined states (e.g. radicular pain from nerve root irritation, somatic referred pain from dural sleeve irritation, and somatic back pain from internal disc disruption) which complicates assessment. In this setting each underlying feature may have separate treatment, for example discectomy only works for radicular pain, not for back pain.

Somatic Referred vs Radicular Pain

	Somatic Referred	Radicular
Pain quality	Dull, deep ache, or pressure-like, perhaps like an expanding pressure	Shooting, lancinating, or electric-shocks
Relation to back pain	Referred pain is always concurrent with back pain. If the back pain ceases then so does the referred pain. If the back pain flares then so does the leg pain intensity and spatial spread.	Not always concurrent with back pain.
Distribution	Anywhere in the lower limb, fixed in location, commonly in the buttock or proximal thigh. Spread of pain distal to the knee can occur when severe even to the foot, and it can skip regions such as the thigh. It can feel like an expanding pressure into the lower limb, but remains in location once established without traveling. It can wax and wane, but does so in the same location.	Entire length of lower limb, but below knee > above knee. In mild cases the pain may be restricted proximally.
Pattern	Felt in a wide area, with difficult to perceive boundaries, often demonstrated with an open hand rather than pointing finger. The centres in contrast can be confidently indicated.	Travels along a narrow band no more than 5-8 cm wide in a quasi-segmental fashion but not related to dermatomes (dynatomal).
Depth	Deep only, lacks any cutaneous quality	Deep as well as superficial
Neurological signs	Not characteristic	Favours radicular pain, but not required.
Neuroanatomical basis	Discharge of the peripheral nerve endings of Aδ and C fibres from the lower back converge onto second order neurons in the dorsal horn that also receive input from from the lower limb, and so the frontal lobe has no way of knowing where the pain came from.	Heterotopic discharge of Aδ, Aβ, and C fibres through stimulation of a dorsal root or dorsal root ganglion of a spinal nerve, typically in the presence of inflammation, with pain being felt in the peripheral innervation of the affected nerve

The intensity of pain can be recoded using the VAS or NRS scale. For those individuals where pain fluctuates, record the average intensity during activity, and the worst pain recently. Pain intensity is the single most significant patient factor for decision about seeking medical care, and so the pain is likely to be significant enough to them regardless of the actual figure given. Sometimes patients may indicate very high pain scores such as "12/10" and this may reflect suffering and psychological distress. The intensity of pain can be useful for recording a baseline, monitoring progress, and judging the effectiveness of treatment.

There is no association between pain intensity and how likely it is that the cause of the pain is due to a serious condition.

The periodicity refers to whether the pain is constant or intermittent. Most patients with chronic low back pain have constant pain. Intermittent can mean either the pain is constantly there but fluctuates in intensity, or can mean that it is present in between pain-free episodes. The exact meaning should therefore be clarified.

If the pain is indeed intermittent - it occurs in between pain-free episodes - then determine the periodicity, time of onset, and mode of onset of the pain. Periodicity means the frequency of episodes, and their duration. Time of onset is relevant in identifying the morning stiffness of inflammatory back pain (ankylosing spondylitis). Mode of onset is whether it is gradual or sudden in onset. Because chronic low back pain is usually constant, these parameters are not typically helpful.

Precipitating factors (what triggers episodes of pain), aggravating factors (what makes the pain worse), and relieving factors (what relieves the pain) are not helpful diagnostically, but paint a picture of the disability experienced by the patient.

Associated features are particularly relevant to red flag conditions. They are listed in the red flags section below, and discussed in more detail in the acute low back pain article.

Circumstances of onset is what they were doing when the pain started, and what the pain was like initially. The biomechanics of any particular injury with regards to the forces and posture of the patient at the time may allow a "guess" as to the injured structure. However I am not aware of any literature that has validated circumstances of onset with validated diagnostic techniques.

• Fractures: A fall for instance would raise suspicions for fracture. In the elderly fracture can occur from standing height.
• Internal disc disruption: Compression injuries are the most relevant which can occur with a single event such as a fall onto the buttocks or with repetitive compression loads over a period of time such as with repetitive heaving lifting or pulling. Internal disc disruption occurs gradually however (following endplate fracture), and initially there may only be mild discomfort, with significant pain only developing following the development of fissures, and the onset of chemical and mechanical nociception.
• Zygapophysial joint injury: Sudden severe rotation could indicate a torsional injury to the zygapophysial joints and/or the anulus fibrosus (see Torsion Injuries)
• Sacroiliac joint injury: A fall onto the buttocks or a motor vehicle accident where the lower limb is impacted.
• Spondylolysis: A stress reaction of the pars interarticularis could be considered in sportspeople where there is forceful or repetitive extension and rotation. In other people there is no association.
• Interspinous soft tissue injury: This may occur by lifting in flexion and occasionally in hyperextension. It can also occur with a fall.

In New Zealand there is a perverse incentive to link pain to an injury event because under ACC there is drastically better access to allied health, investigations, and specialist care. Without an ACC claim the patient is relegated to the far more restrictive public health system. Because of this, most patients with back pain end up with an ACC number, and trauma is the "cause" at rates far higher than seen internationally. Many sarcomas for example are diagnosed under an ACC claim. Also often injury events that occurred gradually over time may be recorded as single events, because injuries over time only have a chance of being covered under ACC if they occurred at work (called "gradual process injury")

Widespread Pain

It should be determined whether there is widespread pain, as widespread pain may indicate a more systemic condition such as rheumatological conditions, fibromyalgia, central sensitisation, or controversially some heritable connective tissue disorders. These categories of patients can still nonetheless have the standard causes and sources of chronic low back pain, but the assessment and management is made much more difficult.

Widespread pain should not be confused with somatic referred pain: the latter does not spread cranially. Another common pitfall is assuming that multiple concurrent primary nociceptive drivers can't co-exist. For example symptomatic hip osteoarthritis and lateral elbow tendinopathy are both very common conditions, and may occur simultaneously as separate primary nociceptive conditions through aleotoric processes (See article on uncertainty). A single "unifying diagnosis" of central sensitisation may not apply here. Here we see the opposing aphorisms of Occams razor ("entities should not be multiplied beyond necessity") and Hickams dictum ("patients can have as many diseases as they damn well please"). Each individual affected region should be assessed on its own merit.

In someone with multiple areas of pain, "solving" the low back pain of someone with widespread chronic pain pain may not reduce their overall pain score or improve their overall function. The clinician can end up moving around the body of the patient over years without any significant overall improvement. Some consider such patients to be best served by a multidisciplinary pain clinic, but this is not a hard and fast rule. In those where MDT is not acceptable or suitable, one approach is to address the "worst area" (patient defined) first.

Red Flags

See also: Acute Low Back Pain#Red Flags

The same red flags in acute low back pain can be used for chronic low back pain. Any red flags that are identified prompts further consideration for a serious conditions, which may include investigation. They are not diagnostic or such conditions, and are not designed to have great positive predictive power. They were developed on the basis of case reports of unusual causes that were overlooked during assessment but could have been identified if the appropriate question was asked.

If there are no positive responses then the likelihood of a serious condition is extremely low. In the presence of neurological features, this complicates the presentation, and investigating this becomes more important than investigating the cause of the back pain, as the investigations are not always the same.

Red Flags

• History of: Trauma, sports injury, fever, night sweats, recent surgery, catheterisation, venipuncture, illicit drug use, weight loss, cancer, occupational exposure, hobby exposure, overseas travel, pain severe worsening or unremitting especially at night
• Cardiovascular: Risk factors
• Respiratory: Cough in a smoker or ex-smoker
• Gentio-urinary: Infection, haematuria, retention, stream problems
• Gynaecological: abnormal uterine bleeding, dysmenorrhoea
• Haematological
• Endocrine: Diabetes, corticosteroids, parathyroid
• Musculoskeletal: pain elsewhere
• Neurologic: symptoms/signs including for cauda equina compression
• Skin: Infection, rashes
• Gastrointestinal: Diarrhoea, inflammatory bowel disease
• Demographic: Aged over 50 years with first episode, especially age over 65 years

Psychosocial Assessment

See also: Acute Low Back Pain#Psychosocial Assessment

Much of the same psychosocial assessment principles in acute low back pain apply. Of importance is that diagnoses such as "factitious disorder" and "malingering" have no valid operational criteria for diagnosis, and should not be used. A similar related concept is "secondary gain" and this too has weak scientific support. "Secondary losses" generally outweigh any "secondary gains," and so it does not constitute a diagnosis.

Various questionnaires have been developed to identify psychological features such as fear avoidance, kinesiophobia, catastrophising, depression, and anxiety. Such features can account for some of the disability a patient is experiencing as a result of their pain. Such patients may be pre-occupied with their pain, depressed, and feel unable to do anything about it, and be focused on passive therapies.

Psychological symptoms are generally a consequence of experiencing chronic pain in susceptible individuals, they are not indicative of the reverse i.e. the pain arising from psychosocial distress. In the biopsychosocial model, the biological features are essential to the experience of pain. The maladaptive response to the pain experience would not exist without the pain experience itself. However the doctor should be aware of any related psychosocial issues.

However, patients with high levels of psychological distress tend to respond poorly to conventional biomedical treatment. Identifying high levels of distress may cause pause for the doctor. Further biomedical treatments that are destined to fail can lead to cycles of hope and despair, exacerbating the patients psychological distress.

The social history includes asking about ability to work, financial distress, social supports, relationships, and functioning at home with activities of daily living. It may also include assessing for any substance abuse.

Physical Examination

See also: Lumbar Spine Examination, Sacroiliac Joint Examination

As for acute low back pain, the physical examination is not able to make a reliable patho-anatomic diagnosis in chronic low back pain due to the lack of pathognomonic signs. However, there are three main reasons for doing a physical examination

1. The first reason is that patients expect it, and doing it shows interest and caring.
2. The second reason is that if no signs of somatic dysfunction are found in the spine, then this could indicate a serious underlying visceral or vascular condition. However, due to visceral referred pain, patients with visceral pathology can still have somatic segmental dysfunction. Therefore an abdominal and vascular examination is still warranted in those at increased risk.
3. The third reason is that the doctor can provide positive reinforcement (e.g. celebrating normal findings) with the view of reducing patient fear.

The lumbar spine exam involves inspection, palpation, and movement testing.

• Inspection: posture standing and sitting (scoliosis, kyphosis, loss of lordosis), dynamic posture (antalgic gait), deformities, scars, puncture marks, swelling. The reliability reported in studies has varied. The validity is unknown.
• Palpation: altered sensitivity (hypoesthesia, hyperesthesia), tenderness and its relationship to bony landmarks, and whether localised or diffuse. The reliability is excellent for tenderness somewhere in the lumbar spine (kappa 1.0), but when the location is specified the agreement is variable. Tenderness over the iliac crest superomedial to the PSIS is good (kappa 0.66), but the validity is unknown.
• Movement testing: active, passive, and accessory movement testing. Active and passive ranges are tested in flexion and extension, side bending, and rotation. Quadrant tested can also be done (e.g. extension with rotation). The reliability is fair to moderate, but the validity is unknown.

The reliability and validity of the physical examination has been studied with regards to the three most common causes of chronic low back pain: internal disc disruption, facet joint pain, and sacroiliac joint pain.

A specialised examination sequence has been developed to detect sacroiliac joint pain (known as the cluster of Laslett) and internal disc disruption (McKenzie assessment method). This protocol can't detect zygapophysial joint pain. It also requires special training.

For internal disc disruption, a positive centralisation response under the McKenzie assessment method has a positive LR of 2.4. In a 50 year old male this increases probability from ~60% to ~80%, but in a person over 65 it rises from ~5-20% to ~10-40%.

For facet joint pain there are no diagnostic examination findings. However certain combinations of features may suggest a facet joint origin: age greater than 65; pain relieved by recumbency; and absence of aggravation of pain by coughing, forward flexion, rising from flexion, hyperextension, and extension-rotation. Five or more features has a positive LR of 3.0. In a 50 year old the pre-test probability rises from ~20% to ~40%, and in a person over 65 the pre-test probability rises from ~30% to ~55%.

The "Wadell's inorganic tests" are not appropriate for clinical use as they are neither diagnostic nor predictive. They were designed to identify patients in need of psychosocial assessment, but became abused to identify non-genuine patients. They are not a basis of denying biopsychosocial treatment. Furthermore they don't actually predict failure to return to work.

As for acute low back pain, a neurological examination is only necessary if the patient has indicated neurological symptoms. Any neurological signs indicate a neurological disorder and this should be investigated within its own merits.

Review of Previous Investigations

During the initial assessment there may be previous imaging studies on hand, as well as previous diagnostic or therapeutic procedures. Reviewing these images before formulating a clinical impression can lead the doctor down the wrong path. King and Bogduk suggest the doctor take pause and reflect on two caveats.

The first caveat is that appearances on imaging do not correlate with pain. The doctor can be mislead by irrelevant findings. The second caveat is that the reliability of radiology reports is not perfect. The quality is operator dependent and is subject to human error. It is always recommended that the doctor looks at the imaging themselves. Orthopaedic surgeons do this, and doctors in other specialties would be wise to follow suit.

Another consideration is that very often somatic referred pain is confused as radicular pain, and this leads to confusion when interpreting the report. Imaging is generally helpful in radicular pain and radiculopathy as it can often identify the cause. With somatic referred pain however, imaging is not helpful diagnostically in the majority of cases. Undertaking imaging for somatic referred pain runs the risk of false positive interpretations, as any possible nerve root compression is not relevant in this setting. This can even lead down a path towards unnecessary microdiscectomy and fusion surgery.

With previous diagnostic or therapeutic procedures, King and Bogduk suggest that they may not have been done optimally. For example the response may not have been recorded accurately. If they have had a certain procedure the technique may not have been successful. For example if they have had a previous sacroiliac intra-articular joint block, there may be no proof of intra-articular placement in the form of contrast deposition on a saved image. It can be useful to look through previous images keeping this in mind, or the doctor can ask an interventionalist if they are unsure.

Any previous investigations can otherwise assist with the assessment. Also, repeat investigations may not be needed.

Provisional Diagnosis

After the assessment and review of previous imaging (if available), a provisional diagnosis is made. It is rare to be able to make a definitive diagnosis at this point.

The doctor formulates the provisional diagnosis based on historical features, physical examination, and data from prevalence studies of the three most common causes of chronic low back pain. These are namely discogenic pain (generally internal disc disruption), zygapophysial joint pain, and sacroiliac joint pain (either the joint or ligaments). If a red flag is detected then this becomes the provisional diagnosis.

The provisional diagnosis serves as a hypothesis that can be tested with further investigations. Once a definitive diagnosis is made, targeted treatment may be available.

A definitive diagnosis is not necessary if targeted treatment is not acceptable or suitable. In this case the IASP diagnosis of "Lumbar Spinal Pain of Unknown or Uncertain Origin" can be applied, and general forms of treatment can be offered. "Nonspecific chronic low back pain" is not an IASP diagnosis and should be avoided as the term has a history of being applied to patients in a definitive sense that have not actually had appropriate investigations.

King and Bogduk suggest that if a provisional diagnosis cannot be made, then there should be no attempt at a specific treatment. This is because a specific treatment in the absence of a valid diagnosis does not tend to abolish the pain, but simply exacerbates the hope-despair cycle. If a specific treatment is still desired then they should be referred to a colleague for a second opinion.

Utility of Precision Diagnoses

Whether the cause should be diagnosed, and whether the cause can be cured are two entirely separate questions from whether it can be diagnosed. Bogduk has presented the value of making a biomedical diagnosis as being viewed from three lenses: positive therapeutic value (does making a diagnosis lead to improved outcomes), negative therapeutic value (does making a diagnosis prevent inappropriate treatment), and diagnostic utility (is making a diagnosis helpful in itself without treatment being available).

• Positive therapeutic utility: as per the treatment section of this article, there treatments proven in RCTs to work for facet joint mediated pain, sacroiliac joint pain, and discogenic pain.
• Negative therapeutic utility: Providing a diagnosis may stop a potentially inappropriate intervention. For example, if provocation discography is negative or indeterminate then it may not be appropriate to have spinal fusion.
• Diagnostic utility: Making a diagnosis provides an explanation, and reduces the fear around not knowing what is causing the pain. It also serves to inform treating clinicians that the patient doesn't have primary nociplastic pain, which otherwise may lead to the patient not being taken seriously.

Investigations

There are two possible reasons to refer for investigations: excluding red flag conditions and to test the provisional diagnosis.

For screening for serious or rare causes of chronic low back pain MRI has the best sensitivity and specificity. As well as soft tissue abnormalities, MRI can also detect fractures, and so in principle there is no point in doing plain films or CT if MRI is available.

Some consider failure to improve is a criterion for checking for red flag conditions, and suggest MRI be done. The pick up rate for this single red flag alone is very low, and so usually guidelines do not suggest MRI here.

Plain Radiography

Main article: Lumbar Spine Radiographs

Plain films can detect bone lesions such as myeloma and metastases, but may miss these if early. They also don't detect serious lesions of soft tissues. Therefore x-rays can't fully exclude serious conditions. Furthermore they have a risk of detecting issues such as spondylosis or "degenerative change" that are not causes of pain but might lead to patient misunderstanding and distress. CT has some similar issues however it may detect neurological conditions, but is not available in primary care.

MRI

Main article: Lumbar Spine MRI

MRI can visualise both bones and soft tissues. It has high sensitivity and specificity, and is safe. It is therefore the best available screening test on face value. Plain films and CT are inferior options. The major limitations are the high cost (around $1500 privately) and the low pick-up rate for serious conditions. Despite widespread availability in New Zealand the cost has not come down, unlike the situation in Australia. ACC and Southern Cross both run a scheme for GP access, but the criteria are very strict. For example low back pain with radicular pain a sensory radiculopathy does not qualify.

Like with plain films, there are many findings on MRI that do not constitute a diagnosis. These include disc bulges and degenerative changes. However high intensity zones and Modic changes (endplate changes) are relevant to chronic low back pain, in that they are indicative of internal disc disruption.

Some authors state these are not valid signs because they also occur in asymptomatic patients. The second statement is true, it is not pathognomonic, but it is more common in symptomatic patients. Many clinical tests in medicine are not pathognomonic (e.g. ANA) but still have utility. In a patient with chronic low back pain where the pre-test probability of discogenic pain is already high, they strongly indicates that the affected disc is the source of the pain. Both findings having positive LRs of around 3. The overall pretest probability of internal disc disruption is ~40%, which gives a post-test probability of ~67%. In a 35 year old, the probability rises from ~80-90% to ~90-95%; In a 50 year old it rises from ~40-65% to ~65-85%.

High Intensity Zone

High-intensity zones (HIZ) can occur in the innervated posterior anulus of lumbar intervertebral discs. They are seen on T2 weighted images as a bright signal surrounded by dark signal of surrounding fibres. It reflects a circumferential grade IV anular tear, best seen in a sagittal section, but can also correlate with a grade III tear. The brightness should be similar or exceed the brightness of the CSF, it is not just any white spot in the anulus.

The prevalence in patients with chronic low back pain is 20-30%, and they correlate with the disc being painful on provocation discography with a positive LR of greater than 3 (one pooled estimate is 3.8).

Endplate (Modic) Changes

Modic changes or lesions are changes in the spongiosa of the vertebral body above or below a disc with internal disc disruption. Type 1 lesions are dark on T1 and bright on T2 and reflect bone marrow oedema. Type 2 lesions are bright on both T1 and T2 and reflect fatty change that is usually post-inflammatory.

The prevalence amongst individuals with chronic low back pain is around 33%, and they correlate with the disc being painful on provocation discography with a positive LR of around 3 (one pooled estimate is 3.4). They also predict response to basivertebral nerve ablation, and some authors therefore subdivide patients with endplate changes and positive provocation discography as having "vertebrogenic pain".

Electrophysiology

There is no role for nerve conduction studies in the evaluation of chronic low back pain. They should only be considered if peripheral neuropathy is a possibility, but peripheral neuropathy is not in the list of differential diagnoses for chronic low back pain They also do not have any proven validity in distinguishing radicular pain from somatic referred pain.

Disc Stimluation

The gold standard test for internal disc disruption is disc stimulation (also known as provocation discography) to test for pain and post-discography CT to visualise the disruption.

A needle is placed into the nucleus pulposus and it is distended with contrast to a predetermined pressure, all under visualisation with fluoroscopy. The test is positive if the pain is reproduced at pressures of less than 50 psi (preferably less than 15 psi) and stimulation of adjacent control discs (i.e. with separate needles) doesn't reproduce the pain. With the contrast in place, CT imaging shows up any fissures and their grade.

The indications for undergoing disc stimulation is if there is a need to establish a definitive diagnosis if disc targeted therapies are being considered. In New Zealand it is not commonly done due to limited interventional options for discogenic pain available. Note however that in the basivertebral nerve ablation research, discography was not part of the inclusion criteria, Modic change was the key inclusion criteria. For intradiscal biacuplasty, disc stimulation was part of the inclusion criteria.

Medial Branch Blocks

The gold standard diagnostic test for lumbar facet joint pain are medial branch blocks. The medial branches are the nociceptive supply to the facet joints (also multifidus and the interspinous space). It is a type of diagnostic nerve block. This is preferred over intra-articular blocks because the latter have not been formally validated.

A needle is placed onto each of the two nerves that innervate the target facet joint. A tiny amount of local anaesthetic is injected (0.3-0.5mL) to achieve specificity for the target. This is visualised under fluoroscopy, however there has been more recent research using ultrasound.

The cut-off for a positive test varies, but in New Zealand we generally use 80% pain reduction, but some people use 100%. Some centres overseas use 50%. The International Spine Society procedure is that initially multiple facet joints are screened to identify those patients who don't have zygapophysial joint pain.

A single block has a high false positive rate, and so the blocks are controlled. Ideally this is done with placebo control. Due to resourcing constraints we usually do comparative blocks as the next best thing with accepting that there will still be some false positives even with two blocks. Comparative blocks involves doing one injection with lidocaine and another with bupivacaine, and blinding the patient to the agent used (single blind).

The indication for doing medial branch blocks is if radiofrequency neurotomy of the medial branches is being considered. If this isn't being considered then medial branch blocks are not indicated.

Sacroiliac Joint Blocks

The gold standard test for sacroiliac joint pain is doing controlled intra-articular local anaesthetic blocks.

This procedure is technically more challenging than medial branch blocks, especially in the elderly where osteophytosis commonly makes needle entry difficult. Access to the joint cavity is confirmed with contrast injection, and then 2mL of local anaesthetic is injected into the joint. Fluoroscopic guidance is preferred.

The cut-off for a positive test again varies. Some use 100% relief of pain, while others use 75%. Also again, a single block has a false positive rate, and so controlled blocks are necessary.

The indication for a sacroiliac joint block is if specific treatments are being considered such as sacroiliac joint fusion. Sacroiliac joint corticosteroid injections are commonly done, and it can be useful to follow the diagnostic technique while doing this in order to provide additional diagnostic value.

Sacral Lateral Branch Blocks

There is no current gold standard test for sacroiliac ligament pain, but this is emerging as a candidate. The interosseous ligament and dorsal ligamentous complex are not blocked by intra-articular sacroiliac joint injection (unless there is leak). These structures are innervated by the lateral branches of the S1-S3 dorsal rami and can be blocked with lateral branch blocks. The lateral branches emerge from the sacral foramina and pass laterally.

There are a few current limitations to this requiring further research. Firstly the prevalence of sacroiliac ligament pain is unknown. Secondly it is unknown whether sacroiliac ligament pain is a separate condition to sacroiliac joint pain or if they occur together. Thirdly the lateral branches have a variable course between people and even between sides within the same person which creates technical difficulties. There has been research into using multiple injections and using cooled radiofrequency which burns a larger area. Finally research needs to be done using controlled blocks.

The indication for sacral lateral branch blocks is to select patients for lateral branch radiofrequency neurotomy.

Management

It can be illustrative to ask the patient what their expectations are in order to establish realistic treatment goals. There is often a big difference between what patients think a worthwhile pain reduction is (median 25%, IQR 20-50), and what they hope to achieve (median 80%, IQR 60-100). There is a consistency between desired reductions in pain and disability. Note the huge difference between desired results and what is actually achieved in practice, and the low values that many studies use to define success.

King and Bogduk note that complete and enduring relief is not unrealistic, as patients may have experiences with other types of pain being effectively treated such as chronic toothache, chronic hip pain, etc. It is not surprising that patients therefore think that the source just needs to be found and then fixed.

Craft Groups

The authors continue, that the treatment literature on chronic low back pain is mired in ideology and vested interests. There are "camps" or "craft groups" with different ideologies, and this biases their approach (see Low Back Pain Treatment Strategies). What follows is my own interpretation of the craft groups:

• MDT craft group. They generally make non-specific diagnoses and provide non-specific treatments in a team. For example they may diagnose non-specific chronic low back pain with central sensitisation and provide psychological and behavioural therapy to allow better coping and reduce fear. They prioritise improving function over improving pain.
• Reductionist craft group. They generally make specific diagnoses and provide specific treatments. For example they may diagnose right L4/5 facet joint pain based on controlled medial branch blocks and provide medial branch radiofrequency neurotomy. They prioritise improving pain and view function as something that improves if the pain is fixed.
• Monotherapy craft group. They generally make non-specific diagnoses and provide specific treatments (although sometimes non-specific). For example they may diagnose mechanical low back pain and provide lumbar fusion.

Each group may state that the treatments of the other groups don't work, and each have their own literature which may not reference the literature of the other groups. There is also a lot of overlap for individual doctors and for individual specialties. Individual specialties tend to have a culture.

• Musculoskeletal medicine tends to have a bias towards reductionism (e.g. radiofrequency neurotomy following positive blocks) and monotherapies (e.g. corticosteroid injections, manual therapy, exercise prescriptions), but may also engage in MDT.
• Pain medicine have a bias towards MDT and monotherapies, and less commonly engage in reductionism. This is the newest specialty in New Zealand.
• Orthopaedic surgeons engage in both monotherapy (e.g. fusion for sagittal imbalance) and reductionism (e.g. L4/5 microdiscectomy for L5 radicular pain, or sacroiliac joint fusion following positive blocks), however generally not MDT.
• Allied health providers generally do monotherapies with some also being involved in MDT.

The patient's General Practitioner is the most important of all specialists as they can view the biases non-objectively from the outside without vested interests and tend to know the patient the best.

Conservative Approach

Laerum et al outlined what a "Good Back Consultation" entails, based on three interdisciplinary Norwedgian RCTs for chronic low back pain.

• Take them seriously
• Examination: explanation during the exam (what was being done and what was found)
• Education: Providing an understandable explanation for the pain given with conviction (exact medical diagnosis is not essential) and addressing misconceptions. He uses a disc injury explanation.
• Reassurance: given with conviction, address fears but cognitive reassurance is preferred over emotional which can create dependency.
• Psychosocial discussion: deal with possible correlation (in both directions) between daily life, job, family, coping, quality of life aspects, role function and the LBP
• Treatment: Encourage normal activity and avoiding rest. Empower the patient to take responsibility for their own rehabilitation.

Precision Treatment

For facet joint mediated pain, sacroiliac for confirmed facet joint mediated pain (two positive blocks) there is a treatment called medial branch radiofrequency neurotomy that has a good chance of working. For pure discogenic pain there is no good proven therapy. For vertebrogenic pain (modic changes), there is basivertebral nerve ablation. For proven sacroiliac joint pain and sacroiliac ligament pain, there is evidence for sacroiliac joint fusion and lateral branch cooled radiofrequency neurotomy.