SUMMARY: Needles may be directed outside or inside the spinal canal, or into the cerebrospinal fluid that bathes the spinal cord. Substandard care may Cause some of the adverse outcomes of such diagnostic or therapeutic procedures. Injections that are intended to be placed outside the spinal canal but are misdirected do most harm in the cervical (neck) region. Inadvertently entering the subarachnoid space during epidural injections is a predictable complication and not de facto evidence of substandard technique. The factors that Cause occasional injury after entering the subarachnoid space are poorly understood.
Needles are inserted into the spine for a variety of diagnostic and therapeutic purposes.
These procedures can occasionally result in serious adverse effects, some of which are Caused by medical negligence.
The needle-tip may be directed into the back muscles, a facet joint, an intervertebral disc, the epidural space or, most deeply, the subarachnoid space.
Some adverse effects result from the needle-tip missing the mark, some by Causing temporary or permanent physical injury, others through somatoform response and yet others by unknown mechanisms.
Adverse Effects
Injections that are intended to be placed outside the spinal canal but are misdirected do most harm in the cervical (neck) region. In the lumbar (lower back) region, adverse effects are rare and are generally restricted to temporary worsening of pain, or inadvertent puncture of the coverings of the spinal cord, Causing spinal anesthesia (see below INSIDE THE SPINAL CORD)(1) or chemical meningitis(2).
In the cervical (neck) region, inadvertent puncture of the vertebral artery is more common with injections into the facet joints and may have serious consequences, including stroke.
Cervical injections are more likely to Cause injury to the nerve roots, sometimes resulting in sensory and motor deficits(3).
Anatomy and Physiology
Local anesthetic agents may be injected for diagnostic purposes into spinal muscles that are suspected of triggering pain.
If the anesthetic temporarily abolishes the pain, subsequent injections, usually combined with corticosteroid medication, may be administered for therapeutic effect.
Although the exact cause of most "mechanical" back pain is unknown, certain features, particularly worsening when arching the back (hyperextension), may suggest facet joint origin.
The facet joints are paired protrusions from the upper and lower surfaces of the bony laminae that, with the vertebral bodies in front, encircle the spinal canal.
Local anesthetic, with or without corticosteroid, may be injected into the suspect facet joint itself or into the region of its nerve supply.
This procedure can provide relief of pain, for diagnostic or therapeutic purposes.
Medical malpractice counsel should be aware that there is a wide range of evidence-based opinion on the efficacy of this form of treatment(4,5).
Practice PointSerious injury following misplaced injections in the neck may be actionable on grounds that the intended procedure was of doubtful benefit |
Adverse Effects
Inadvertently entering the subarachnoid space during epidural injections is a predictable complication and not de facto evidence of substandard technique.
Unintentional puncture of the subarachnoid space may Cause headache, that may persist if there is a continued leakage of cerebrospinal fluid.
Such low pressure headache is routinely treated by blood patch, the injection of blood freshly-drawn from the patient into the region of the leak, with a view to creating a small blood clot and thereby sealing the leak.
Not all headaches that persist after puncture of the subarachnoid space are Caused by cerebrospinal fluid leak(6,7).
Compression of the spinal cord by iatrogenic hematoma (blood clot) or abscess is extremely rare(8).
Practice PointAdverse effects of inadvertently entering the subarachnoid space may not have been disclosed or appropriately monitored |
Permanent neurological injury from placement of needle or catheter is similarly rare(9), and is usually heralded by numbness, tingling or pain during needle insertion or during delivery of local anesthetic by catheter(10).
However, such abnormal sensations are relatively common during placement of needles and catheters for spinal (see below) and epidural anesthesia and analgesia(11) so standard care does not require that the procedure be discontinued because of such symptoms.
Neurological injury can also be Caused by compromise to the blood supply to the spinal cord because of prolonged low blood-pressure, a common and treatable consequence of epidural anesthesia. Failure to monitor blood-pressure has been the basis of a successful Canadian Action(12) for medical malpractice.
Anatomy and Physiology
This largely outmoded diagnostic procedure involves the injection of inert fluid under pressure into the substance of an intervertebral disc that is suspected of being the origin of back pain.
In theory at least, such injection into a pathologically abnormal disc will mimic or worsen the pain, and thereby predict benefit from neurosurgical removal of the disc ( discectomy).
Local anesthetic injected precisely in the region of a single spinal root precedes the operation of rhizotomy (neurosurgical interruption of a sensory nerve root).
If the preliminary injection temporarily abolishes the otherwise intractable pain, such permanent destruction of the root can be undertaken with greater confidence of success.
Epidural anesthesia provides temporary abolition of pain without impairing consciousness.
Local anesthetic is injected into the spinal canal outside the spinal cord to interrupt sensation from the lower body.
The object is to bathe the spinal roots with anesthetic fluid as they enter the spinal cord.
The spinal cord itself is not affected, and the intent is not to enter the subarachnoid space that contains the cerebrospinal fluid.
Although sometimes administered as a single shot through a needle itself, the local anesthetic fluid is more usually delivered by narrow catheter that is introduced through the hollow needle.
Inadvertent puncture of the subarachnoid space is not always avoidable. However, drawing back the plunger of the syringe and giving a small test dose of local anesthetic are standard precautions to minimise the risk of unintentional spinal anesthesia.
Failure to observe those precautions may result in serious and permanent injury.
Narcotic such as morphine may replace local anesthetic, typically for continuous postoperative pain relief.
In Patient Controlled Analgesia, increments of narcotic are delivered by catheter, triggered by the patient according to need.
Failure of the various built-in and procedural safety mechanisms can result in respiratory arrest and the consequent brain-damage has been the subject of both an unsuccessful Canadian Action(13) and substantial settlements.
Adverse Effects
The factors that Cause occasional injury after entering the subarachnoid space are poorly understood.
Both temporary and permanent neurological injury occur more frequently than when needle or catheter are placed outside the spinal cord.
In experimental rats, placement of catheters into the subarachnoid space can cause inflammation and permanent injury to the insulation ( demyelination) of spinal roots and spinal cord(14).
However, this is an extremely rare adverse effect in humans.
Although spinal cord injury is well recognised and not de facto evidence of substandard technique, failure to disclose has been successful as medical malpractice litigation strategy(15,16).
Practice PointSerious iatrogenic needle injury to the spinal cord is rare and idiosyncratic but must be disclosed for informed consent |
Anatomy and Physiology
The dura mater and arachnoid mater (2 outer linings of the spinal cord) are intentionally pierced for spinal anesthesia, in which the volume of local anesthetic agent required is much less than for epidural anesthesia.
The subarachnoid space is also intentionally entered, usually for the purpose of testing the cerebrospinal fluid for infection (meningitis) or blood ( SubArachnoid Hemorrhage, SAH).
Antibiotics, or chemotherapy for cancer of the brain and spinal cord, may be administered by this route if adequate concentrations of the drugs cannot be achieved through the bloodstream without causing unacceptable toxic effects.
Dye that is opaque to xrays is introduced into the cerebrospinal fluid in the subarachnoid space to delineate the anatomy of the spinal cord and spinal canal.
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