Interventional diagnosis of spinal pain generators
There are several common anatomical sources of back pain and or sciatica which can be accurately localised by appropriate technique.
Blocks and Provocations: In general there are two ways of telling whether a structure is painful.
- Blocks. You can anaesthetise it with local anaesthetic and see whether the pain goes away (a pain block – like a local block for dental treatment). Facet pain is diagnosed by blocks.
- Provocations. The alternative is to provoke pain. This relies on being able to reproducibly delver a stimulus or provocation which does not cause pain to a healthy tissue but which reproduces the patients usual pain when applied to a positive test tissue. This is how disc pain is diagnosed
This is the name given to pain travelling down the leg arising from irritation of the roots of the sciatic nerve within the lumbar spinal canal. The usual cause is a slipped or prolapsed intervertebral disc nucleus. In older patients the anatomy becomes more complex. In general sciatica is not too complex and may be correctly assessed by MRI alone but sometimes the source of a sciatic like pain is in doubt. Also, in certain cases it isn’t possible to be certain which of 2 possible levels (i.e. which numbered lumbar nerve) are causing the pain. The source and level can be diagnosed by a selective nerve root block (SNRB) where a restricted volume of local anaesthetic is delivers to the selected nerve root (only). If the leg pain goes away, the diagnosis s confirmed.
The same can be done in the neck, as shown below.
back pain and sciatic commonly occur together though in many cases back ache is the sole or dominant problem. The likely causes of dominant back pain are:
- Intervertebral discs: Diagnosed by pain Provocation Discography
- Modic Change Seen on MRI
- facet joints Diagnosed by medial Branch (nerve) Block
- sacro-iliac joints Diagnosed by Injection of local (and steroid)
- epidural fibrosis Diagnosed by epidural endoscopy
Each vertebra is supported by 2 facet joints to the rear. Facet joints are very similar to standard limb joints such as the knee in anatomical design and are prone to the same wear and tear problems as other joints. They are meant to stabilise the disc segment in rotation and extension. They are relatively small and are not designed for weight bearing and readily become “arthritic” (ie show the signs of osteoarthritis) if stressed. This occurs with age, especially if the patient has a tendency to OA elsewhere. Facet pain becomes more common with age rising from perhaps 15% of chronic back pain overall to 40% in the elderly. An element of facet pain is also a frequent accompaniment to disc problems since the disc and facet joints work together as a unit.
Diagnosis of Facet Joint Pain:
Clinical Examination: There are a variety of findings which suggest facet pain notably pain on extension and side flelxion from neutral. However, the latest evidence is that tenderness over the facets corresponds better to a positive response to local anaesthetic block of the joints and seems a reliable guide if it is the only feature.
Median Branch Block (MBB):
The neuro-anatomy (nerve supply) of the facet joint has been exhaustively studied by Prof Nic Bogduk and colleagues and is quite clear. The sensation from the joint is transmitted in a small nerve fibre which is a branch of the edjacent spinal nerve root called the median branch. This runs over the neck of the upper part of the adjacent facet joint (superior articular process) and can be reliably located under x-ray guidance. By placing a needle on this spot and injecting a drop 03-0.5ml) of local anaesthetic you can block the nerve and relieve pain coming from the targetted facet. Two blocks, one above and one below are needed for each facet and commonly 3 blocks are used to anaesthetise 2 joints. Lumbar 4/5 and lumbar5/sacral 1 joints are a typical combination reflecting the common wear and tear of these lower lumbar joints.
The blocks are given without sedation if possible and under X-ray screening. The test is the difference immediately before and after difference in pain at the time of the block. To check a pain diagram is made and pain on movement assessed before and then immediately after. A positive response is complete or almost complete abolition of the presenting pain. It is difficult concept to get over that this is not a treatment, the pain will return over the next few hours or days as the anaesthetic effect wears off.
L4/5 and L5/S1 facet medial branch block with the needles positioned and x-ray contrast injected to show where the block injection will go –
Sacro-Iliac Joint (SIJ)
SIJ pain as diagnosed by diagnostic block is less common, perhaps 15% of chronic spinal pain, rising with age.
The SIJs are the large very solid joints at the very bottom of the spine joining the sacrum to the pelvic bones. In health they allow a small range of quite complex rotating or gliding motion to allow leg swing in walking etc. They are very strong but can be damaged by trauma (cars, horses, trampolines) or later in life with degeneration, usually in combination with facet pain above. The SIJs are the commonest site of inflammatory pain in Ankylosing Spondylitis so in younger patients careful evaluation is required and it may be difficult to exclude inflammatory disease.
Diagnosing SIJ pain:
Clinical: – Pain below the waist level overlying the SIJ (level of the buttocks), tenderness at the top of the sacral sulcus and positive response to a variety of SIJ stress test may indicate SIJ pain.
Interventional: There are 2 approaches to diagnosing SIJ pain.
- SIJ Injection.The usual is to inject a 3mls of local anaesthetic into the joint (see below). I usually also place 1 ml (mixed in) of depo steroid on the principle that SIjs do quit well with thsteroid injection and its a difficult joint to access so sits better to do both block and inject at once.
- The second is to block the nerves which run to the joint from the nerve exit foramina (Latin for windows) in the sacral bone which lie to the midline of the joint. This is analagous to the diagnosis of facet pain but the sensory nerves are called lateral rather than median branches.
In either case, resolution of the presenting pain on before and after diagrams is accepted as diagnostic but the whole agenda of SIJ diagnosis and treatment is not as well resolved as with the facet joints.
Below is an image if an SIJ injection: the needle is visible lamost end-on and the black contrast has been injected to confirm localisation of the injected anaesthetic to the joint itself.
Grey Ramus Communicans Blocks for osteoporotic vertebral fracture:
This is a technique I learned from the American Clinician who originally described it. A lot of the pain fibres from the vertebra run with the branch of the sympathetic chain which communicates around the “waist” of the vertebra (as visualised on x-ray screening) called the grey ramus communicans. response to local anaesthetic predicts subsequent control of the pain by RF denervation.
there are a variety of techniques for blocking the sympathetic nervous system usually at the “ganglia” or hubs where the nerves join up. A useful technique for me is to bock the T12 (12th thoracic/chest nerve root), L1 and or L2 nerve bodies (also called ganglia) since the sympathetic fibres from the lower lumbar levels all coalesce to enter the spinal cord at these levels. This can useful to analyse obscure pain problems and residual symptoms after nerve root blocks. the technique is similar to GRC blocks (above).
this is an advanced technique for the visualisation of adhesions and fibrosis in the epidural space. The appearance of Inflammatory scar material in the epidural space after spinal surgery is well recognised. However, it is not well understood that the same pathology can arise in purely mechanical spinal pain, usually of very long-standing. This presumably arises from inflammation secondary to irritation and leaking inflammatory material from damaged discs but the problem is not well understood and is certainly poorly diagnosed since it does not usually show on imaging including MRI.
The epiduroscope a small (2.8mm) catheter with a very fine (1mm) fibre optic and an injection port for instillation of agents to reduce adhesion (Hyalase) and antiinflammatories (steroid). It is introduced after a small nick in the skin through the caudal hiatus, a little gap in the roof of the sacrum right down at the tail of the spine which can be felt as a slight flattening under the skin in the midline just above the coccyx (the same anatomical space is used for “Caudal” epidural steroid injection).
The instrument is used as a blunt dissector to force a plane of cleavage between the scar tissue and the spinal nerves and membranes to which it adheres and obstructs. The tissue is very painful to touch and if present or extensive the procedure is painful despite sedation and intravenous painkillers. There are also rare but significant risks to the technique. Over-pressuring of the epidural space has been reported to cause haemorrhage behind the retina with reversible loss of vision. Injury to nerves and spinal membranes can occur and injection of anaesthetic into the spinal fluid leading to spinal block (like an obstetric epidural which is intended to produce numbness and loss of power in the legs).
For all of these reasons, epiduroscopy is reserved for special situations and may need an overnight stay in hospital for observation.