Myobloc in The Treatment of Piriformis Syndrome

Figure 1. Anatomy of the Piriformis Syndrome
The sciatic nerve passes under the piriformis muscle, and above the gemellus superior in 80-­85% of legs.

Variations are generally bilateral, occurring when the posterior and anterior divisions of the lumbrosacral plexus do not unite in the pelvis, and pass separately under, through, or above the piriformis muscle. The variations do not appear to increase incidence of the syndrome.

Figure 2: Signs and Symptoms of Piriformis Syndrome
1. Fifteen-degree or greater discrepancy in straight leg raise, or less than 65-degrees in bilateral cases.

2. Tenderness in the region of intersection of the piriformis muscle and the sciatic nerve.

3. Weakened abduction of the flexed thigh.

Figure 3. The H-reflex
First investigated by Hoffmann in the early 20th Century, the H­-reflex is essentially the Achilles Tendon reflex electrically elicited by stimulating IA intrafusal fibres at the popliteal fossa, with responses recorded electronically at the soleus muscle.

Side­-to­-side variation of more than 1.25 ms (3 standard deviations beyond the mean) indicates abnormalities along the course of the L­-5 fibres.

Figure 4a. The FAIR-­Test
Placing the leg in Flexion Adduction and Internal Rotation tightens the piriformis muscle against the fibres of the sciatic nerve. In 88 normal patients, this maneuver did not prolong the H-reflex, mean prolongation = ­.01ms, standard deviation = 1.86 ms.

Figure 4b. The FAIR­-Test
Significant Prolongation of the H­-reflex with Flexion, Adduction and Internal Rotation

Our electrophysiological criterion for piriformis syndrome is H­-reflex prolongation by the FAIR­-test >1.86ms, 3 standard deviations beyond the mean.

5a. The discriminatory power of the FAIR-­test

5b. Sensitivity and Specificity of the FAIR-­test

Studies of 1014 subjects put sensitivity and specificity of the FAIR-­test at .872 and .854 respectively.

Figure 6a.

Myobloc Injections of 5,000, 7,500, 10,000 and 12,500 units were given to successive 5­-patient cohorts identified by the FAIR-­test to have piriformis syndrome.

Figure 6a. (continued)

Immediately after diagnosis each patient received four ¼ dose injections under EMG guidance at different locations in the affected piriformis muscle.

Figure 6b.
Correct needle placement required EMG activity with abduction (confirming that the needle tip was either in the piriformis or the gluteus maximus) and absence of EMG activity with extension (confirming that the needle tip was not in the gluteus maximus). The process pictured was repeated in each of the four starred locations.

7. Physical Therapy Protocol for Patient Diagnosed with Piriformis Syndrome*

Place patient in contralateral decubitus and Flexed Adducted Internally Rotated (FAIR) position:**

1. Ultrasound 2.0­2.5 Watts/square cm., applied in broad strokes longitudinally along the piriformis muscle, from the conjoint tendon to the lateral edge of the greater sciatic foramen X 10­14 minutes.**

2. Wipe off ultrasound gel.***

3. Hot packs or cold spray at the same location x 10 minutes.

4. Stretch the piriformis muscle for 10­14 minutes by manually applying horizontal pressure to the muscle's inferior border, being careful not to press downward, rather directing pressure tangentially, toward the ipsilateral shoulder.****

5. Myofascial release at lumbosacral paraspinal muscles.

6. McKenzie exercises.

7. Use lumbosacral corset when treating patient in the FAIR position.*****

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Duration: 2­3 times weekly for one to three months.

* Patients usually require 2­3 months of biweekly therapy for 60­70% improvement.

** Because it is painful, patients often subtly shift to prone. This must be avoided because it works to place the affected leg in abduction, not adduction, greatly reducing the stretch placed on the piriformis muscle.

*** Cavitation is unreported in more than 20,000 treatments.

**** Unless explicitly stated, therapists may tend to knead or massage the muscle, which is useless or worse. The muscle must be stretched perpendicular to its fibres, in a plane that is tangent to the buttock at the point of intersection of the piriformis muscle and the sciatic nerve, but approximately 1­1.5 inch deep to the buttock, (i.e., just below the gluteus maximus).

***** This is particularly important to avoid inducing lumbar hypermobility in patients with histories of laminectomy, fusion, or spondylolisthesis. Physical Therapy was given twice weekly. This protocol was available for out­of­town patients and is now at ``Sciatica.org''.

Figure 8a. Pain Relief with Myobloc and Physical Therapy

Figure 8b. Onset and Decline of Beneficial and Adverse Effects of Myobloc

Adverse effects, pain visual analogue estimates and FAIR­-tests were collected premorbidly and at weeks 2, 4, 8, and 12.

Figure a.
Dramatic pain­-reduction and FAIR­-test value reduction were strongly correlated with each other.

Figure b.
Dramatic pain-­reduction and FAIR­-test value reduction were strongly correlated with the appearance and resolution of adverse effects.

Figure 9. Clinical Course of Reinjected Patients

Reinjection of 7 patients with 10,000 units of Myobloc was more effective than the lower doses and as effective as higher doses with reduced adverse effects, suggesting that this is the optimal dosage. There were no immunological reactions of any kind.

Figure 10. Synaptic strengths

Artificial Neural Networks will make diagnostic determinations, proper dosages of Myobloc, and likely outcomes objectively available to all Internet users at ``sciatica.org''.

Conclusions
Patients diagnosed with piriformis syndrome via the FAIR­-test are successfully and innocuously treated with Myobloc and physical therapy. The present study presents optimal efficacy without adverse effects with 10,000 units given in four divided doses given at four sites in the affected piriformis muscle at the time of diagnosis, and twice weekly physical therapy. The FAIR-test provides an objective independent measure of remission of the syndrome, and is well­-correlated with visual analogue estimates of pain. For further details, please see ``sciatica.org''.