Piriformis and obturator internus morphology: A cadaveric study

Abstract

Preservation of piriformis during exposure of the hip joint via a posterior approach may result in a lower rate of dislocation following total hip arthroplasty. The aim of this study was to identify anatomical variations in the tendons of piriformis and obturator internus which could inform piriformis sparing approaches to the hip. Twenty-nine proximal femora from 15 cadavers, 5 male and 10 female aged 65-79 years, were examined. Tendon crossing angles, location and mode of insertion to the greater trochanter and the extent of fusion between tendons prior to insertion were noted. The mean (and associated standard deviation) of the vertical and horizontal widths of the piriformis tendon were 4.78 ± 1.31 mm and 7.35 ± 1.74 mm, respectively. The mean (and associated standard deviation) of the vertical and horizontal widths of the obturator internus tendon were 6.87 ± 1.61 mm and 5.72 ± 1.38 mm, respectively. The mean distances of the anterior and posterior margins of the piriformis tendon insertion from the posterior limit of the greater trochanter, defined as a percentage of the anteroposterior length of the greater trochanter, were 63.3% ± 9.4% and 43.0% ± 9.4%, respectively. Equivalent mean distances for the obturator internus insertion were 73.0% ± 6.6% and 55.9% ± 7.0%, respectively. On the basis of the relationship between the piriformis and obturator internus tendons in terms of the angle and point at which they cross, in addition to any degree of tendon fusion, four classifications were identified. This study shows that the most posterior margins of the piriformis and obturator internus attachments are located more than one-third of the way along the greater trochanter, suggesting that current osteotomies would not include these external rotators in the majority of cases.

An appraisal of the short lateral rotators of the hip joint

“…The short lateral (also referred to as external) rotators of the hip joint consist of the six deep muscles namely: piriformis, obturator internus (OI), superior gemellus (SG), inferior gemellus (IG), obturator externus (OE) and quadratus femoris (QF). These muscles, considered as the “rotator cuff” of the hip (Lockhart et al, ; Pine et al, ), are functionally important in providing support and maintaining stability during hip movements (Snijders et al, ; Solomon et al, ; Sinnatamby, ; Marieb et al, ; Sussman et al, ), thus acting as “postural muscles” rather than “prime movers” of the hip joint (Standring, ). These short lateral hip rotators contribute to joint stability by holding the femoral head in the acetabulum (Romanes, ; Moore et al, ; Giphart et al, ; Agur and Dalley, ), aided by ligamentous and capsular structures of the hip joint (Johnston and Warwick, ; Romanes, ; Roche et al, ).…”

“…Orthopaedic and surgical studies have highlighted the need for accurate and detailed anatomical understanding of the six short lateral hip rotators for improved surgical and clinical outcomes (Solomon et al, ; Pine et al, ; Ito et al, ; Roche et al, ; Tamaki et al, ). Particularly relevant to the short lateral hip rotators is the posterior approach in Total Hip Arthroplasty (THA).…”

“…Particularly relevant to the short lateral hip rotators is the posterior approach in Total Hip Arthroplasty (THA). THA requires precise identification, repair and management of the short lateral rotators ensuring the stability of the hip joint postoperatively (Solomon et al, ; Pine et al, ; Roche et al, ; Tamaki et al, ). The posterior approach for THA is one of the common approaches due to the advantages of direct exposure, minimal blood loss, short operation time and early recovery (Gibson, ; Johnsson et al, ; Anson and McVay, ; Hedley et al, ; Parks and Macaulay, ; Ko et al, ; Procyk, ).…”

Length Change of the Short External Rotators of the Hip in Common Stretch Positions: A Cadaveric Study

“…Several cadaveric studies have been performed to assess length change in order to evaluate movement of the muscles in relation to the posterior approach for total hip arthroplasty, 20,25,26 as well as peak strength and stretch as it relates to normal, gait-related movements. 21,27 These studies utilized string modeling for representation of musculature, in order to assess the excursion or lengthening of the short external rotators, respectively.…”

Bilateral Absence of Gemelli Muscles: Case Report

“…These muscles are considered short lateral rotators (Stähelin et al, 2002;Yoo et al, 2015) and together are called "rotator cuff of the hip", they act as dynamic stabilizers (Pine et al, 2011) by the positioning of the femoral head in the acetabulum (Moore et al, 2010).…”