The sciatic nerve, the biggest in the body, forms behind the sacrum and exits the pelvis beneath the piriformis muscle. At times the over-tight muscle, and rarely, anatomical irregularities will compress the nerve, creating severe sciatic pain that is usually worse with sitting. Some people have this extremely painful condition for years before it is diagnosed, and it can be disabling.
The usual causes are prolonged sitting at the computer or elsewhere, over-exertion in sports or working out, and trauma, such as an automobile accident or a backward fall.
At the right is the sciatic nerve exiting the pelvis just below the piriformis muscle, seenin its usual environment, the anatomy book (Clemente CD. Anatomy: A Regional Atlas of the Human Body. 3rd Ed.Urban and Schwartzenberg. Munich; 1987: fig 430.) The tightened muscle presses the nerve into the sharp edge of the ischiofemoral ligament that lies just below it.
A physical exam is the first step to diagnosing piriformis syndrome. Electrodiagnosis testing the delay of reflexes along the sciatic nerve when the piriformis muscle is stretched across it makes the diagnosis definitive and helps to monitor the efficacy of [Hypertext: treatment]. A special MRI (neural scan) is also often helpful.
We performed a controlled, double blinded, randomized crossover study designed to assess the effects of botulinum injection into the piriformis muscle after diagnosing it with the FAIR-test (described below). It proved quite successful, as per the graph that represents the patients’ response to a measure of their pain, the visual analogue scale (VAS). Level of pain was estimated every two weeks for three months following either botulinum injection (blue) or placebo (red) in a double blinded study of 58 patients.
Piriformis Syndrome Diagnostic Quiz
Just answer the questions below: the increase or decrease in odds represents the increased or decreased probability that conservatively treating the individual for piriformis syndrome will be helpful in relieving their pain at least 50%.*
Practical diagnosis: The diverse etiology of sciatica makes it necessary to be comprehensive and precise when evaluating a patient. Many clinicians rely on imaging early on in a patient’s treatment. Plain radiographs are rarely useful in the initial evaluation of non-geriatric acute back pain. They do not reveal herniated intervertebral discs nor spinal stenosis, and the findings on plain films are often unrelated to symptoms. E.g., spondylolisthesis can be seen in up to 5 percent of normal subjects. 8 Immediate X-ray of the lumbar spine should be reserved for patients with alarm symptoms suggestive of infection, cancer, violent wounds or fracture; however, a normal plain film itself does not rule out these conditions. In general, MRI or CT and EMG are required for definitive diagnosis of many spinal conditions. Nonetheless, these studies are not acutely necessary in patients with sciatica unless major neurological deficits or severe pain are present. Imaging studies may sometimes be deferred until 4-6 weeks of conservative therapy have failed.
Once obtained, there can still be an issue of misdiagnosis. One well-known study found that more than 50% of a group of pain-free subjects had serious spinal abnormalities on their MRIs. 9 If spinal pathology can be painless, it can also coexist with sciatica that has a different cause. This prompts the clinician to use EMG as an extension of the history and physical exam to confirm the diagnosis.
Treatment for Back Pain by Cause:
Herniated Nucleus Pulposus: Whether central or lateral, usual treatment begins with analgesia and McKenzie and manual medical techniques, extension exercises, paraspinal myofascial work, modalities, Alexander work, and/or Yoga. Tapering oral steroids (starting dose often dexamethasone 8-16mg) over a 6-day to 3 week period may dramatically lower a patient’s pain, enabling him or her to tolerate an effective therapy program. Translaminar or transforaminal epidural injections are sometimes beneficial, though studies demonstrating the efficacy of these common practices are lacking.
True disc-related sciatica has a very high morbidity. This makes surgery an appealing alternative to conservative treatment for some patients. Many studies support surgery as the most efficient treatment. One analysis of medication use, ability to return to work, leisure activity and pain score found that after the first year of treatment, 30% of conservatively treated patients were satisfied with their outcome, while 60% of surgically treated patients reported satisfaction. 10 Surgery continued to lead until differences became insignificant at 10 years and beyond. Another study found 99.99% identical outcomes in surgical and non-surgical patients after 10 years. It should be noted that in most studies the more severely involved patients tended to enter the surgical group.
One study followed patients hospitalized for disc-related sciatica for five years, comparing the 1/3 that refused surgery with the 2/3 that did not. At 5 years, 82% of the non-surgically treated patients still had pain in a sciatic distribution, versus 68% of the surgically treated patients. More than 13% of the surgical group required an additional operation for recurrent disc herniation. Outcome studies of this small group of patients found 84% in the WHO ‘Severe handicap’ group.
Surgery may be an appealing option for many patients given the generally more favorable outcome. However, a recent study found little risk of serious or permanent injury when surgery for simple sciatica was delayed more than 7 months. Given this information, a rational approach to treating sciatica clearly caused by a herniated disc is to attempt conservative treatment for 4-6 weeks. If intractable pain persists, a microdiscectomy or similar procedure can reasonably proceed.
Central Spinal Stenosis: although the symptoms may be literally identical, the treatment for is almost the opposite of what works for a herniated disc. There is a large ligament at the back of the actual spinal canal which buckles with extension and actually narrows the space up to 63%. What works for spinal stenosis is flexion, something that for a herniated disc would be painful and possibly harmful! We have developed electrophysiological techniques to determine whether spinal stenosis or herniated disc is really responsible for a person’s pain, invaluable tool when both conditions are present, as they frequently are. Once we found out what the main pain generator is, we can use yoga to teach people what they need you on their own, and free them from a dependence on medications and even physical therapy.
Anterior spondylolisthesis, the most common form of spondylolisthesis, in which the upper vertebra is moved forward relative to the one below, may cause radiculopathy if it truncates neuroforamina, and/or spinal stenosis if the intramedullary space is narrowed. It is graded I through IV by the quartiles of vertebral body displacement. It is often successfully treated with an abdominal binder or lumbosacral corset, abdominal strengthening and postural training (the latter by a physical therapist or Alexander therapist). Yoga and Feldenkreis are also helpful. Beyond grade II, be it antero- retro- or lateral listhesis, surgical procedures that reestablish the proper alignment often utilize hardware such as titanium cages, and usually meet with considerable, but sub-total improvement that may not last more than 4-5 years. Studies of conservative medical, chiropractic or surgical treatment of spondylolisthesis are few.
Arthritis may narrow neuroforamina to cause radiculopathy unilaterally or bilaterally at one or more levels. Often, periodic episodes of increasing severity, frequency and duration occur after age 65-70. Pain as well as motor and sensory complaints will be gradual in onset, and at least early on, are often positional. Conservative strategy reduces the attendant inflammation, lowers peripheral and central sensitization, and increases range of motion at neighboring joints to reduce compromise at the affected level(s). 14 Non-steroidal and/or steroidal anti-inflammatories, yoga, and physical therapy often accomplish these three goals, respectively. Although quite effective, steroids must be used with caution in osteoporotic patients. More advanced or complicated cases of arthritis may require surgery to remove deteriorated bone and disc material, osteophytes, or other matter impinging on the nerves. In these refractory patients, an EMG is helpful in identifying and characterizing the levels warranting treatment, and the severity of impingement.
Boney growth and/or swelling of the ligamentum flavum may narrow the lumbar intramedullary canal, causing single or multiple level spinal stenosis and resultant sciatica. The former may have genetic or arthritic pathogenesis, the latter inflammatory or traumatic. Conservative treatment aims to reduce the girth of the canal’s contents: tapered oral or epidural steroids, traction, and postural work by physical therapists, Alexander therapists and osteopathic physicians have had success.
While ligamentous swelling may subside naturally, boney narrowing will not. Surgical intervention, sometimes requiring stabilization procedures as well, should be considered when a progressive boney thickening is documented, but before emergent intervention is required. Cauda equina syndrome, a rare complication of spinal stenosis in which ascending numbness or weakness and bladder or bowel incontinence results from extreme pressure on descending rootlets within the intramedullary space, is one such surgical emergency.
In a recent study of nonemergent spinal stenosis surgery, outcome comparison of control and intervention groups at 1 and 4 years favored surgical treatment. After 8-10 years, a similar percentage of each group reported low back pain was improved but sciatica relief continued to favor the surgical group. Because it is generally progressive, surgery for spinal stenosis may wisely occur before it is utterly mandatory, since its necessity may arise after the patient is too frail for it.
Piriformis syndrome is an under-recognized cause of sciatica. This was validated when 239 patients who failed conservative or surgical treatment for the above causes underwent MR neurography. Piriformis involvement was found in more than 2/3 of them. Symptoms arise from compression of the sciatic nerve as it exits the buttock in relation to the piriformis muscle, due to spasm or tightness in the muscle. The chief environmental causes are overuse at health clubs, from running, outdoor activities, excessive sitting, trauma from auto accidents and falls. Anomalous relationships between the sciatic nerve and the inferior gluteal artery or vein at the greater sciatic foramen are uncommon but demonstrated anatomic bases for pain.
Diagnosis is made by EMG through delay of H-reflexes in flexion, adduction and internal rotation (the FAIR-test). Comparing affected with unaffected limbs helps rule out radiculopathy or spinal stenosis, and may be used in the 90% of cases that are unilateral. Neural scan imaging (NMR) will show asymmetrical development of the affected piriformis muscle, and evidence of inflammation or focal narrowing of the sciatic nerve. EMG and NMR will only be positive if piriformis syndrome is present, and not in simple SI derangement alone. However, these conditions occur together with some frequency. Since the piriformis muscle arises in part from the sacroiliac joint, it is possible that SI joint derangement causes piriformis muscle spasm in these cases.
Conservative treatment begins with EMG- or fluoroscopically-guided steroid and Lidocaine/Marcaine injection of the piriformis muscle near its lateral musculotendinous junction, as well as stretching and relaxing the muscle, using ultrasound, myofascial release and spray/stretch techniques. Appropriate home yoga therapy is often successful over time. Botulinum neurotoxin A or B, 300 or 12,500 units, respectively, in four locations throughout the muscle, are reported to significantly relieve 60% to 90% of resistant cases. Neurovascular anomalies and ventral piriformis muscle scars require surgery which appears to benefit 60-80% of cases.
While the rare vascular and neurological abnormalites have been shown to cause piriformis syndrome, the common variations in anatomy do not. Piriformis syndrome is often attributed to one or both branches of the sciatic nerve passing through the piriformis muscle, an anatomic “anomaly.” Cadaveric studies show that approximately 15% of the population has at least one branch of the sciatic nerve that travels such a course. Interestingly, in these people, the anatomy is bilateral more than 90% of the time. The “anomaly” theory comes into question in that complaints consistent with piriformis syndrome are bilateral in less than 10% of patients. Further, at surgery only 15% of patients had anatomy consistent with the “anomaly” theory, the same percentage that is seen in the gIschial tunnel syndrome:
The FAIR test is occasionally positive when entrapment is at a site other than the piriformis muscle. Four percent of sciatic nerve entrapment in the buttock is due to entrapment as the nerve passes close to the ischium. The pudendal nerve may be separately involved. Neural scan is the definitive diagnostic tool for ischial tunnel syndrome. In these cases, treatment begins with myofascial release, modalities, and postural re-training. Surgery is reported but outcome studies lack sufficient numbers to be persuasive.
There are many other causes of sciatica, ranging from tumor and fracture to gunshot wound. In all the pathogenetic mechanism and the diagnosis can be understood on the anatomical bases that we have attempted to provide. Multiple conditions can coexist in which the analytical “either – or” approach, which considers certain diagnostic entities “diagnoses of exclusion” is not recommended. Considering a condition a diagnosis of exclusion logically cannot find those cases in which more than a single condition coexist. Considering that piriformis syndrome, herniated disc and spinal stenosis, just to name three pathological entities that are independent and can occur together, it is logically impossible not to under-diagnose piriformis syndrome if it is considered a diagnosis of exclusion.