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gluteal nerve (weakness of the gluteus maximus), pudendal nerve (peroneal sensory loss), and posterior femoral cutaneous nerve involvement.48

Historically, imaging studies have been irrelevant. Pelvic CT scan and MRI are used primarily for detecting pathologic lesions such as space-occupying lesion, hematoma, muscle/tendon tears, and intraarticular hip problems. Occasionally, the MRI or CT scan may identify abnormalities, such as hypertrophy of the piriformis muscle, adding support to the clinical diagnosis.52,62,63 The MRI has been useful for identi fying anomalies of the piriformis muscle and variations of the sciatic nerve, but these findings have not proven to have clinical relevance.44 Nuclear medicine scintigraphy may occasionally show increased uptake within the piriformis muscle but, similar to the CT scan and MRI, it has limited diagnostic benefits.64-66 More recently, however, electrodiagnostic testing has provided reliable objective signs.53,64,65,67 Specialized electrodiagnostic studies seem to be the only diagnostic test able to objectively document functional impingement of the sciatic nerve by the piriformis muscle.64'65'67 Fishman and Zybert65 studied the prolongation of the H-reflex on 918 patients who met the criteria for piriformis syndrome. The criteria were(a) positive Lasegue's sign at 45 degrees; (b) tenderness at the sciatic notch; (c) increased pain within the distribution of the sciatic nerve with the leg in the flexion' adduction, and internal rotation (FAIR) position; and (d) electrodiagnostic tests excluding the existence of neuropathy and myopathy. They were able to document a statistically significant difference of H-reflex conductions when the affected limb was placed in the provocative (FAIR) position. Sensitivity and specificity of the FAIR test were found to be 88% and 83%, respectively. These same authors found 79% of their patients experienced 50% reduction in subjective symptoms when treated conservatively with therapy focused on reducing mechanical impingement and injections. The 28 patients who required surgery were found to have a significant improvement with the FAIR test. The FAIR test was also found to be a better predictor of successful treatment, be it physical therapy or surgery.

Last, to aid in the diagnosis and treatment, local anesthetic and steroid injections into the piriformis muscle may provide temporary relief of the symp-toms.42,54,66 When the piriformis muscle is involved, dramatic pain relief usually follows within 10 minutes of injection, supporting the diagnosis.

Differential Diagnosis

The diagnosis of piriformis syndrome remains one of exclusion. Common orthopedic and nonorthopedic etiologies should be put on the top of a differential diagnosis. In patients with atypical presentations or recalcitrant symptoms, it is also important to consider less common problems such as tumors. The differential diagnosis for patients presenting with vague gluteal and posterior thigh pain should be comprehensive. This concept cannot be overstressed in the evaluation and management of these difficult problems.

Because athletes frequently expose themselves to trauma and overstress injuries, muscular injuries and stress fractures should be an important part of the differential diagnosis. Hamstring injuries frequently present with pain in the same distribution as the piriformis muscle syndrome, but the symptoms are usually localized to the tear and readily diagnosed with an MRI. The piriformis muscle is located directly posterior to the hip joint; therefore, symptoms can also be indistinguishable from labral, chondral lesions, and loose bodies of the hip joint. Trochanteric bursitis is another common disorder causing posterior thigh pain. Both intraarticular hip problems and greater trochanteric bursitis may be diagnosed with selective anesthetic injections. In patients who present with radiculitis, more common causes such as lumbar stenosis, central spinal steno sis, lateral recess stenosis, herniated nucleus pulpo-sus, and discogenic pain should be investigated with appropriate imaging studies.

Degenerative arthritis of the hip or the sacroiliac joint may present with gluteal/posterior thigh pain and should be evaluated using imaging studies and differential injections of anesthetic. A number of peripheral nerves around the sciatic notch are prone to injury and capable of producing similar symptoms. Entrapment of the superior gluteal nerve may cause aching, claudication-type buttock pain, weakness of abduction of the affected hip, a waddling gait, and tenderness to palpation in the area of the buttock super-olateral to the greater sciatic notch.68

Additionally, masses such as hematomas, aneu-rysms/pseudoaneurysms, neoplasms, and abscesses in the gluteal or posterior thigh area are capable of pressing and injuring adjacent structures including the sciatic nerve. An MRI and CT scan of the pelvis and hip region in such instances are essential for diagnosing such entrapping lesions.

Treatment

Once the diagnosis of piriformis muscle syndrome is reached, several treatment options are available. The correct treatment is one that ideally addresses the impingement lesion in a safe and reliable manner. If the etiology is thought to be impingement from an inflamed, hypertrophied, or contracted piriformis muscle, then the treatment algorithm should begin with rest, antiinflammatory medication, muscle relaxants, and a physical therapy program aimed at stretching the piriformis muscle. Applying physical therapy modalities such as ultrasound treatment, electrical stimulation, and Fluori-Methane spray (dichlorodifluo-romethane and trichloromonofluoromethane spray) may also be helpful.69 The goal of this treatment strategy is to reduce the inflammation and contracture of the piriformis muscle. The stretching maneuvers include placing the lower extremity in the FAIR position. The patient is instructed to bring the knee into the chest and across the midline while in the supine position and in the standing position (Figure 5.7). These exercises are continued in sequential progression until maximal stretching intensity and duration is achieved. These exercises should also be executed after a piriformis muscle surgical release to prevent the reformation of contractures or adhesions. Concurrently, it is also important to address and correct abnormal biomechanical factors such as leg length discrepancies or hip flexor contractures. In cases in which the clinical progress is unacceptable or the diagnosis is unclear, a piriformis muscle anesthetic or cortico-steroid injection may be beneficial for confirming the diagnosis and as a treatment adjunct. The injections can be done with or without fluoroscopic and elec-tromyographic guidance.54,70 Often, anatomic land

FIGURE 5.7. Rehabilitation for the treatment of the piriformis muscle syndrome. A program of gradual stretching of the piriformis muscle and posterior hip musculature should be employed. The affected hip is flexed, adducted, and internally rotated (FAIR) in both the supine and the standing position.

marks are difficult to palpate, and therefore performing the injection under fluoroscopic guidance, with or without the injection of a radiographic dye to improve the accuracy, is a sensible option. No consensus exists on the type or the amount of anesthetic and steroid solution to be used. It is believed that injection of the muscle with either an anesthetic or steroid reduces the inflammation, hyperirritability, and spasm of the muscle. If properly executed and when the pir-iformis muscle is definitely involved, patients obtain immediate and sometimes long-lasting pain re-lief.69-71 Pain fiber-blocking agents such as Sarapin (aqueous distillate of Sarracenia purpuea) have also been used to a limited degree.69 Recently, Fanucci et al.72 evaluated the feasibility of CT-guided percutaneous botulinic toxin (BTX) injection for the purpose of piriformis muscle syndrome. Thirty patients with a clinical and electrophysiologic diagnosis of piri-formis muscle syndrome were treated by intramuscular injection of BTX type A under CT guidance. The follow-up (12 months) was performed with clinical examination in all cases and with MRI 3 months after the injection. In 26 cases relief of symptoms was obtained after 5 to 7 days. In 4 patients, insufficient relief of pain justified a second percutaneous treatment that was clinically successful. No complications or side effects were recorded after BTX injection. The MR examination showed a signal intensity change of the treated muscle in 7 patients, whereas in the remaining 2 cases imaged only an atrophy of the treated muscle was detected. The authors concluded that CT-guided BTX injection in the piriformis muscle is a promising and feasible technique that obtains an excellent local therapeutic effect without the risk of imprecise inoculation. Mullin and de Rosayro71 described caudal epidural injections as an alternate route for anesthetic/steroid introduction. Caudal injections are straightforward and do not place the sciatic nerve at risk from an inadvertent needle injury or anesthetic infiltration. Anesthetic solutions deposited into the caudal space would be expected to diffuse along the nerve root sleeves and along the proximal part of the sciatic nerve. The afferent innervation of the piri-formis muscle is also blocked using this method. The reports describing these conservative treatment options have been solely limited to small case reports and limited retrospective reviews. Prospective and controlled studies will ultimately determine their true effectiveness.

The length of time spent on conservative treatment should be individually based. Conservative options should have been fully optimized to the extent of performing up to three intramuscular or caudal in-jections.44,69 Surgical exploration and release of all impinging structures is recommended in recalcitrant cases. If the point of entrapment is the piriformis muscle, its surgical release has been proven effec-tive.12,52,53,56,59,61 Operative treatment consists of sectioning the muscle at its tendinous origin, release of fibrous bands or compressing vessels, and external sciatic neurolysis. The functional loss after a piriformis muscle release is minimal because there are supplementary strong external rotators of the hip remaining. The impinging lesion may not be the piriformis muscle; therefore, it is important to do a methodical exploration of the area. Symptoms usually resolve rapidly after an adequate decompression. Proper patient selection is thought to be critical for a successful outcome. Therefore, before contemplating surgery, the surgeon should review the diagnostic steps leading to the diagnosis and, if necessary, additional or repeat investigations can be performed before embarking on surgery. Surgical exploration and decompression of the piriformis muscle carries potential risks including significant injury to vascular and neural structures. Recently, Benson and Schutzer12 performed operative release of the piriformis and sciatic nerve neurolysis on 14 patients with posttraumatic piriformis muscle syndrome. Complications included a wound seroma and an infected hematoma. At an average of 2.3 months all their patients were employed, and at a minimum of 2 years postoperatively there were 11 excellent and 4 good results. Hughes et al.53 also reported on 5 cases treated successfully with surgery. Their technique included obtaining a generous exposure of the posterior gluteal area, ligation of aberrant vessels, and release and resection of the piriformis muscle overlying the sciatic nerve. The authors believed a neurolysis was not necessary. Four of the 5 patients had immediate relief of their symptoms, and all had significant long-lasting improvement.

Summary

In summary, it cannot be overemphasized that successful treatment of this syndrome depends on an accurate diagnosis and knowledge of the exact point of entrapment. The treatment algorithm begins with conservative treatment emphasizing rest, stretching, physical therapy modalities, antispasm medication, and antiinflammatory agents. If necessary, biome-chanical factors such as gait abnormalities or leg length discrepancies are addressed. If the patient ceases to make progress or plateaus, the next step should include a piriformis muscle anesthetic/steroid injection and further continuation of previous therapeutic measures. If the injection is found to be diagnostic, repeating the injections up to three times is reasonable. Surgical exploration of the sciatic nerve and release of the piriformis muscle is effective for recalcitrant cases. The key point to remember during surgery is to explore the length of the sciatic nerve path so that all impinging lesions are thoroughly addressed.

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