Sciatic Neuropathy

The terms lumbar radiculopathy and sciatica are used interchangeably to indicate radiating pain, numbness and weakness in a leg from a pinched nerve root in the back.

However, it is important to recognize that similar symptoms and signs can be caused by injury or compression of the sciatic nerve outside the spine, either in the buttock or thigh.

The sciatic nerve is the longest and widest nerve in the body, extending from the spine all the way to the foot, and contributes most of the nerve supply to the leg:
Sciatic-Nerve-Anatomy

Sciatic nerve injury presents with:

1. Numbness affecting the entire leg, aside from the front of the thigh.

2. Weakness of the hamstrings, and all movement at the ankle.

3. Absent ankle jerk.

http://www.youtube.com/watch?v=z2YrjAGChBw&feature=youtu.be&rel=0

Sciatic Nerve Injury in the Buttock:

The nerve can be injured by misplaced buttock injections, gunshot wounds and knife injury. Buttock injections should be given in the upper outer quadrant to avoid the sciatic nerve

Buttock injections should be given in the upper outer quadrant to avoid the sciatic nerve

The sciatic nerve injury can also be injured by prolonged sitting on a toilet seat, either from direct nerve compression or hemorrhage and compartment syndrome into the gluteal muscles.  This has been reported in cases of  severe prolonged diarrhea, or drug induced coma on the toilet, so called toilet seat neuropathy.

toilet

Sciatic Nerve Injury at the Hip:

The sciatic nerve runs behind the hip joint as it travels through the buttock.
The sciatic nerve is frequently injured by a posterior dislocation of the hip:
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Sciatic nerve injury occurs in as many as 1%–3% of patients who undergo total hip replacement surgery, usually from a stretch injury to the nerves, but occasionally from a misplaced crew, broken piece of wire, fragment of bone or cement pressing on the nerve:

Sciatic nerve injury after hip arthroplasty. (a) The skin incision for the transgluteal approach is in a continuous line. The cross on the left shows the ischium and the one on the right shows the trochanter. Between them, the skin projection of the sciatic nerve is seen. (b) The sciatic nerve was freed from all attachments. The arrows identify acrylic material from the hip arthroplasty, which was damaging the nerve

Sciatic nerve injury after hip arthroplasty. (a) The skin incision for the transgluteal approach is in a continuous line. The cross on the left shows the ischium and the one on the right shows the trochanter. Between them, the skin projection of the sciatic nerve is seen. (b) The sciatic nerve was freed from all attachments. The arrows identify acrylic material from the hip arthroplasty, which was damaging the nerve

Piriformis Syndrome:

However, symptoms of sciatic neuropathy most often result from nerve compression by the piriformis muscle at the level of the sciatic notch, so-called piriformis syndrome.

piriformis

This presents with buttock tenderness and pain, radiate down the posterior thigh.  Symptoms are made worse by prolonged sitting, bending at the waist, and activities involving hip adduction and internal rotation.  The pain can be reproduced by deep palpation over the sciatic notch.

Diagnostic modalities such as CT, MRI, ultrasound, and EMG may all be normal in piriformis syndrome, but are still useful for excluding other conditions.

Magnetic resonance neurography is a specialized imaging technique which can confirm the presence of sciatic nerve irritation or injury of the sciatic nerve in the piriformis muscle.

Magnetic resonance neurography findings in piriformis syndrome. A: Axial T1-weighted image of piriformis muscle size asymmetry (arrows indicate piriformis muscles). The left muscle is enlarged. B and C: Coronal and axial images of the pelvis (arrows indicate sciatic nerves). The left nerve exhibited hyperintensity. D: Curved reformatted neurography image demonstrating left sciatic nerve hyperintensity and loss of fascicular detail at the sciatic notch (arrows). Filler AG, Haynes J, Jordan SE, et al, "Sciatica of nondisc origin and piriformis syndrome: Diagnosis by magnetic resonance neurography and interventional magnetic resonance imaging with outcome study of resulting treatment," J Neurosurg Spine 2: 99-

MRN findings in piriformis syndrome. A: Axial T1-weighted image of piriformis muscle size asymmetry (arrows indicate piriformis muscles). The left muscle is enlarged. B and C: Coronal and axial images of the pelvis (arrows indicate sciatic nerves). The left nerve exhibited hyperintensity. D: Curved reformatted neurography image demonstrating left sciatic nerve hyperintensity and loss of fascicular detail at the sciatic notch (arrows).

Conservative treatment can include medications, physical therapy and stretching, or injection of a paralysing agent such as botulinum toxin into the piriformis muscle under ultrasound or CT control. Surgery may be necessary for recalcitrant cases.

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The Importance of Correct Positioning During Anesthesia

This post is provided courtesy of K. T. Weber, Drexel University College of Medicine Class of 2013:

When a patient goes under anesthesia, a highly trained team of people take over and monitor the body. This team controls breathing, circulation and many other processes, filling in very well for the patient’s brain… however, there is one function that cannot be replicated by the anesthesia team: movement. In order to undergo surgery, a patient must have their muscles relaxed, and therefore will not move away from sore or painful spots. It is normal for people to fidget, rearranging their weight to more comfortable positions, which helps to prevent bed sores (decubitus ulcers) as well as preventing minor nerve compression.

Decubitus (Pressure) Ulcer

Decubitus (Pressure) Ulcer

Decubitus (or “pressure”) ulcers can be a devastating complication for patients who undergo very prolonged surgeries – Superman actor Christopher Reeve actually died from complications associated with an infected pressure ulcer. Fortunately, these wounds are very rare in patients who are only temporarily relaxed for surgery, and there are many precautions in place to prevent this from occurring.

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Nerve Injury

However, minor nerve injury is still possible! One of the less commonly discussed side effects of having surgery, this minor nerve injury can be very disconcerting and affects a surprisingly large number of people

Nerve damage can occur in several forms based on the type and cause of injury:

The mildest form of nerve injury is neurapraxia, where the myelin sheath and support cells around the nerve are damaged (frequently by excessive pressure or ischemia), leading to poor signal conduction along an otherwise unharmed nerve. Neurapraxia improves on it’s own with time as the myelin sheath regenerates, and does not directly involve injury to the axon of the nerve.

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Neurotmesis, the most severe type of injury, occurs when a nerve is lacerated, over-stretched or very badly crushed, and the two ends of nerve are actually separated from each other.  These nerve injuries will not get better on their own without nerve graft repair surgery.

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Axonotmesis is an intermediate type of nerve injury, where the nerve is damaged (often by crushing) but the support cells around the nerve are intact and aid regeneration, so (slow) spontaneous recovery is possible.

The most common symptom of compressive nerve injury is numbness or pain. The tingling, pins-and-needles feeling of hitting one’s funny bone is a classic example of nerve pain.  Many patients who have undergone surgery and are held in one position for an extended period of time may wake up with areas on their skin that feel extra sensitive, like a sunburn. It is understandable to be concerned by waking up with hyperaesthesia, or pain in response to something that wouldn’t normally be painful! Weakness and uncoordination is less common, and only occurs after more severe or prolonged nerve compression during surgery.

The good news for patients who wake up with an unusually sensitive area or some numbness after having surgery is that this minor nerve damage tends to improve rapidly. Neurapraxia resolves as the swelling and bruise around the nerve decreases and the cells that help conduction recover, sometimes as quickly as a few hours, sometimes as slowly as several months. If necessary, non-steroidal anti-inflammatories, other medications for neuropathic pain and splinting can help treat the symptoms of mild nerve damage. Even more severe forms of nerve  injury can recover with time – peripheral nerves grow back around 1mm per day! In the most extreme cases, without the potential to regenerate on their own with time, nerve graft repair can be discussed as an option.

Watch a video presentation on nerve injury and repair:

Of course, an ounce of prevention is worth a pound of cure. The skilled members of the operating room staff take extensive measures to protect their patients with adequate padding and careful positioning.