PIRIFORMIS SYNDROME: CADAVERIC ANALYSIS OF THE DEEP EXTERNAL ROTATOR MUSCULATURE OF THE HIP. Christopher Wise* 1. Widener University, Chester, PA; 2. Temple University, Philadelphia, PA PURPOSE: The purposes of this study are to utilize cadaveric dissection: 1.) for qualitative assessment and quantitative measurement of ten anatomic parameters related to the deep external rotators of the hip, 2.) to identify the presence of anatomic anomalies, and 3.) to review the literature on Piriformis Syndrome and to offer clinical implications based on the presented findings. BACKGROUNDS/SIGNIFICANCE: There is an estimated 40,000,000 cases of low back pain with sciatica per year. Entrapment of the sciatic nerve by the Piriformis muscle, a condition known as Piriformis Syndrome (PS), is estimated to be responsible for 6% of all cases of sciatica. PS is a highly controversial entity due to the paucity of clinical findings reported in the literature and differential diagnosis of PS remains a diagnosis of exclusion. SUBJECTS: Dissection and examination of 21 cadaver specimens using standard preservation methods was performed. METHODS AND MATERIALS: For each lower extremity specimen, 10 distinct anatomic measurements were recorded. In addition, a qualitative assessment of sciatic nerve configuration and location from its entrance into the deep gluteal region to the popliteal fossa was recorded. The principal investigator performed and recorded all measurements. The 10 measurements included the following: 1.) Greater Trochanter to Lateral Malleolus, 2.) Greater Trochanter to Lateral Femoral Condyle, 3.) Posterior Superior Iliac Spine to Sciatic Nerve, 4.) Coccyx to Sciatic Nerve, 5.) Ischial Tuberosity to Sciatic Nerve, 6.) Piriformis length and width, 7.) Superior Gemellus length and width, 8.) Obturator Internus length and width, 9.) Inferior Gemellus length and width, and 10.) Quadratus Femoris length and width. ANALYSES: For all quantative measurements both median and mode for all data was identified. Qualitative assessment pertaining to the sciatic nerve configuration and location and identification of anatomic anomalies was also included. RESULTS: The Quadratus Femoris was found to be the widest muscle observed (6.13cm avg) being more than two times wider than the next widest muscle (Piriformis, 2.55cm avg.). The Pirifomris was found to be the longest muscle (7.54 avg.) followed by the Superior Gemellus (5.27cm avg.). On average, the sciatic nerve was located at a mean distance of 2.71cm from the ischial tuberosity. The Obturator Internus was present in only 11 of the 21 specimens (52%). The sciatic nerve exited inferior to the Piriformis in all 21 specimens (100%). The nerve was undivided at the Piriformis in 18 of 21 specimens (86%). Division of the nerve occurred: 1.) at the popliteal fossa in 7 of 21 specimens (33%), 2.) at the mid thigh in 5 of 21 specimens (24%), and 3.) proximal to the popliteal fossa in 2 of 21 specimens (10%). The posterior cutaneous nerve of the thigh was observed in 14 of 21 specimens (67%). The sciatic nerve was located lateral to the posterior cutaneous nerve in 13 of 14 specimens (93%). CONCLUSIONS: No study has attempted to provide both quantitative measures and qualitative analysis of the entire deep rotator muscle group and the configuration and location of the sciatic nerve in this region. This study added to the normative data related to the size, location, and configuration of the deep rotator muscles of the hip. This data will serve as a basis for identification of aberrant structures, assist with more accurate palpation, and enhance injection and surgical procedures directed toward this region. Likewise, this study also identified normative data regarding the anatomic location of the sciatic nerve relative to easily palpable bony landmarks. This data will serve to aid clinicians in the examination and conservative or non-conservative management of those presenting with deep gluteal entrapment neuropathies of the sciatic nerve. Based on these findings, clinical studies that seek to delineate the contributions of these structures to the incidence of sciatica may translate into more efficient and efficacious intervention strategies. FUNDING SOURCE: No funding was necessary KEYWORDS: Piriformis, Low Back Pain, Sciatica Copyright 2010 by the American Physical Therapy Association. Requests for reprints should be directed to the corresponding author of the article. Educators, students, and other academic customers may receive permission to reprint copyrighted material from Physical Therapy (ISSN 1538-6724) by contacting the Copyright Clearance Center Inc, 222 Rosewood Dr, Danvers, MA 01923. Other types of customers who want permission to reprint should contact the APTA Editorial Office, Attn: Physical Therapy.