REVIEW ARTICLE Piriformis Syndrome and Endoscopic Sciatic Neurolysis Joshua S. Knudsen, MBCHB,* Omer Mei-Dan, MD,w and Mathew J. Brick, MBCHB, FRACS (Ortho)* even the existence of this syndrome.2–8 First described by Abstract: Piriformis syndrome is the compression or the irritation Yeoman9 in 1928, his remark still remains a point of view of the sciatic nerve by the adjacent piriformis muscle in the buttock held by some hip specialists: “insufficient attention has been leading to symptoms that include buttock pain, leg pain, and paid to the role of the piriformis in the causation of altered neurology in the sciatic nerve distribution. Epidemiological sciatica.” Despite advances in imaging and our ability to figures of the prevalence are unknown, but are estimated to be perform therapeutic interventions, this syndrome remains about 12.2% to 27%. There is no consensus on the diagnostic 2–8,10–13 criteria. Advancement in magnetic resonance imaging allows us to poorly defined. The reason it remains controversial observe unilateral hyperintensity and bowing of the sciatic nerve. is in itself complicated. After Yeoman published his paper, The pathophysiology of the disease includes single blunt trauma, Mixter and Barr14 produced their landmark paper that first overuse causing piriformis hypertrophy, and long-term micro- described the rupture of an intervertebral disk as being a trauma causing scarring. Treatments include physiotherapy, steroid leading cause of radicular-type pain. This led to the side- injections, and surgery. Minimally invasive techniques are emerg- lining of other causes of radicular-type pain including PS.5 ing with the hope that with less postoperative scar tissue formation, The characteristics of PS have been refined over the years, there will be less recurrence of the disease. In this chapter, senior first by Freiberg,15 then Robinson,16 who was the first to author describes his technique for endoscopic sciatic neurolysis. use the term “piriformis syndrome.”5 Despite the refine- Key Words: piriformis, piriformis syndrome, deep gluteal syn- ments, it is only with the major advancement in our clinical drome, buttock pain, sciatica, sciatic neurolysis, endoscopic understanding of the hip and the pelvis in the past decade and the advent of imaging including magnetic resonance (Sports Med Arthrosc Rev 2016;24:e1–e7) imaging (MRI) and computed tomography (CT) that we have been able to look for objective signs of this syndrome THE PROBLEM and thus begin to establish its existence. The pathophysiology is uncertain, with a number of Piriformis syndrome (PS) can be defined as the com- authors linking a hypertrophied piriformis causing the local pression or the irritation of the sciatic nerve by the adjacent irritation. Filler and colleagues proposed muscle spasms piriformis muscle in the buttock. This compression of the being another cause, their “piriformis amplifier theory” sciatic nerve leads to symptoms that include buttock and being a possible explanation.2–4,6–8,10,13,17–21 Single-episode leg pain, with altered neurology in the sciatic nerve dis- blunt trauma and repetitive use causing hypertrophy of the tribution and sitting intolerance. The definition implicitly piriformis muscle seem to be the 2 most popular explan- labels the piriformis muscle as the cause of the patient’s ations for the piriformis causing irritation of the sciatic symptoms. However, the contribution of the piriformis nerve.2,3,5,6,8,13,20,21 Scarring from repetitive microtrauma muscle in many patients is far from clear. This implication has also been described in the literature as a cause of PS, as of the piriformis muscle as the chief cause of the patients’ in competitive cyclists who spend lengthy periods on a symptoms has come about due to the intimate relationship bicycle seat causing microtrauma, or the classic example of of the piriformis muscle to the sciatic nerve, as described by having your wallet in the back pocket. In these examples Beaton and Anson.1 Deep gluteal syndrome (DGS) is a the trauma is insignificant enough to cause a problem in the more recent term that encompasses any cause of retro- short term, but the body’s adaptation to the microtrauma trochanteric pain emanating from irritation, tethering, or (ie, scarring of the piriformis muscle and the adjacent tis- compression of the sciatic nerve as it passes from the sues) is enough, in the long term, to begin to affect the greater sciatic notch to the thigh. Causes of this include sciatic nerve.17 A relatively new idea is the formation of fibrous band formation, hypertrophy of the piriformis fibrous bands (with or without a vascular component), muscle, gemelli-obturator internus syndrome, quadratus which is an emerging explanation for PS.17,21 The sciatic femoris and ischiofemoral pathology, hamstrings pathol- nerve requires up to 28 mm of excursion to accommodate ogy, and gluteal disorders, the most common being gluteal normal hip motion.17,21 It is possible that tethering by the contracture. PS is a cause of DGS, but is a pathologic entity fibrous band causes abnormal tension stress in the nerve, in itself and will be the focus of this chapter. resulting in radicular-type pain.17 Anatomic variations have Exact epidemiological figures on the prevalence of PS also been implicated, with the most common being an are unknown, but are estimated to be about 12.2% to abnormal path of the nerve through piriformis as described 27%.2 There is no consensus on the diagnostic criteria or by Beaton and Anson, or a vascular leash comprising branches of the superior gluteal artery, possibly resulting in From the *Millennium Institute of Sport and Health, Rosedale, the restriction of the sciatic nerve.17 A common observation Auckland, New Zealand; and wDepartment of Orthopedics, Divi- sion of Sports Medicine, University of Colorado School of Medi- by senior author is scarring and medial tethering of the cine, Aurora, CO. sciatic nerve to or near the ischial tuberosity, offering a Disclosure: The authors declare no conflict of interest. plausible explanation for the ubiquitous sitting intoler- Reprints: Omer Mei-Dan, MD, Department of Orthopedics, Division ance.17 This observation seems to be shared by Martin et al of Sports Medicine, University of Colorado School of Medicine, 17 12605 E 16th Ave, Aurora, CO 80045. in their paper detailing their treatment of DGS. However, Copyright r 2016 Wolters Kluwer Health, Inc. All rights reserved. despite the uncertainties, what remains well recognized is a Sports Med Arthrosc Rev Volume 24, Number 1, March 2016 www.sportsmedarthro.com | e1 Copyright r 2016 Wolters Kluwer Health, Inc. All rights reserved. Knudsen et al Sports Med Arthrosc Rev Volume 24, Number 1, March 2016 subset of patients who experience buttock pain, sitting can be performed, especially when their results are used in intolerance, and neurological symptoms, which can severely combination.21 Martin et al21 have specified that in the impact their quality of life often for many years. These workup of DGS, the physical examination should include people may benefit from prompt diagnosis and effective the Lasegue test, the Pace test, and the Seated Piriformis treatments for a cluster of symptoms and signs that fall Stretch test. Freiberg test (revisited hip abduction in the within the umbrella of PS/DGS. seated position) is also useful. Because of the conflicting results, most hip specialists including the author do not use conduction tests and instead use history, physical exami- CLINICAL EXAMINATION nation, and CT-guided lidocaine/steroid injections as part The first step is to take a thorough history. A previous of their workup of a patient with regard to PS. This heavy fall on the buttock with swelling and bruising in the involves a CT-guided injection of dilute bupivacaine, saline, past, a repetitive activity such as competitive cycling, pro- and 40 mg triamcinolone adjacent to the sciatic nerve at the longed sitting, and previous hip surgery are all rele- piriformis muscle. The patient is given a pain chart to fill vant.2–7,13,20,22,23 Patients often complain of buttock pain out over the next 2 weeks. A positive test involves either with sitting (problems with watching a movie or a car trip), reduction in symptoms on injection day (bupivacaine) and/ pain with exercise (running and cycling), burning pain, or over the next 2 weeks (triamcinolone effect). usually extending half way down the thigh, but occasionally to the foot, and less commonly numbness and tingling down the back of the leg.20,21 The patient will often sit IMAGING MODALITIES through the interview perched on the asymptomatic but- The interest in PS has only increased with our tock.20,21 A gynecologic history is important for female increasing ability to image the body. Unlike many other patients as intrapelvic conditions such as endometriosis can orthopedic issues, imaging the sciatic nerve presents several result in scarring, tethering, and restriction of the lumbo- problems as there is no definitive bony landmark that can sacral plexus within the pelvis. Symptoms fluctuating with be used to locate the sciatic nerve, and unfortunately, the menstrual cycle can be a key finding. unlike other peripheral neuropathies (carpal tunnel/cubital Unfortunately, no single test is diagnostic for PS; tunnel, etc.), the sciatic nerve is deep and surrounded by an instead, a collection of symptoms and clinical suspicion will intricate array of muscles, tendons, and blood vessels. lead to the diagnosis. Patients are often referred to the clinic Ultrasound is a more challenging investigation to find the with the provisional diagnosis of sciatica or buttock pain. nerve accurately because of its depth and often the large The physician must differentiate whether this is discogenic amount of subcutaneous fat normally found in this area of or nondiscogenic, intraspinal or extraspinal, pelvic or the body.