Effects of hip joint transverse plane range of motion with a modeled effusion and capsular tear: A cadaveric study Casey Hebert, Mark P. Smyth, Erik Woodard, Collin C. Bills, Marc J. Mihalko, William M. Mihalko ⁎ University of Tennessee-Campbell Clinic Department of Orthopaedic Surgery & Biomedical Engineering, 1211 Union Avenue, Suite 510, Memphis, TN 38104, USA abstract article info Article history: Received 12 September 2014 Accepted 19 January 2017 Background: Multiple factors contribute to range of motion of the hip joint in the transverse plane: bony anatomy, hip capsule, corresponding ligaments, articular labrum, ligamentum teres, and negative intra-articular pressure. We hypothesized that violation of the negative pressure of the hip and simulation of an effusion would increase range of motion in the transverse plane in a cadaver model. Methods: Ten hip specimens were obtained and dissected with the femur and iliac wing mounted in a custom joint-testing rig in neutral position. Specimens were tested at 0 and at 90° of flexion with 1.5 Nm internal and external rotational torque. Three conditions were assessed: (1) intact specimen, (2) an effusion modeled by a 10 ml saline infusion, and (3) a capsular tear. Findings: The modeled effusion decreased rotational range of motion limits in both 0 and 90° of flexion, with a greater effect on the specimens at 0° flexion in external rotation with 4.1° less external rotation (p = 0.009). A modeled capsular tear increased rotational motion limits in 0° of flexion in both internal and external rotation and in 90° flexion in internal rotation only (p b 0.025). Interpretation: An effusion may decrease the rotation of the hip, and a capsular tear may increase its rotation. This should be considered in hips with traumatic capsular tears or arthroscopic portals. © 2017 Elsevier Ltd. All rights reserved. Keywords: Hip joint Joint capsule Effusion Instability Capsular tear 1. Introduction The osseous structures about the hip impart a significant amount of innate stability to the hip joint; the spherical femoral head is nor- mally well constrained within the concave acetabulum. However, the contributions of the surrounding soft-tissue structures cannot be over-emphasized. The acetabulum is deepened by the surround- ing fibrocartilaginous labrum, which not only imparts mechanical stability to the joint but also forms a seal surrounding the femoral head that controls the egress of joint fluid from the peripheral compart- ment. This unique suction-effect function of the labrum stabilizes the joint by resisting distraction (Crawford et al., 2007; Dwyer et al., 2014; Polkowski and Clohisy, 2010; Shu and Safrab, 2011). The hip cap- sule, with its internal and external fibers, provides static stability by passively restraining hip motion (Hewitt et al., 2002). The internal zona orbicularis acts as a “locking ring” around the femoral neck to pre- vent distraction (Ito et al., 2009) and is thought to contribute to the “screw-home” mechanism of capsular tightening that provides stability in terminal extension (Torry et al., 2006; van Arkel et al., 2015). The external ligaments, including the iliofemoral, pubofemoral, and ischiofemoral ligaments, have been shown to restrain external rotation, external rotation in extension, and internal rotation, respectively (Bayne et al., 2014; Bedi et al., 2011; Martin et al., 2008; Myers et al., 2011; van Arkel et al., 2015). In addition, the muscles surrounding the hip, including the iliocapsularis, gluteal, and iliopsoas muscles, among others, provide dynamic stability with contraction (Bedi et al., 2011; Torry et al., 2006). Disruption of any of these can disrupt the balance among the many structures that contribute to stability and lead to pain, further damage to surrounding structures, recurrent instability, and possibly further destruction of the hip joint leading to early degeneration. Traumatic dis- location can lead to bony, capsular, or labral disruption. Moorman et al. (2003) described a classic triad of hemarthrosis, posterior acetabular lip fracture or labral tear, and iliofemoral ligament disruption in a series of dislocations in American football players demonstrating the importance of these structures to hip stability. Atraumatic instability from condi- tions of generalized laxity such as Marfan and Ehlers-Danlos syndromes, as well as microtrauma with repetitive hip twisting in certain sports, can lead to attenuation of the anterior capsular ligaments, labral injury, chondral injury, and even recurrent microinstability (Bedi et al., 2011; Philippon and Schenker, 2005; Shindle et al., 2006; Shu and Safrab, 2011; Torry et al., 2006). Clinical Biomechanics 42 (2017) 115–119 ⁎ Corresponding author. E-mail addresses: chebert5@uthsc.edu (C. Hebert), msmyth83@gmail.com (M.P. Smyth), ewoodar3@uthsc.edu (E. Woodard), colinbills@hotmail.com (C.C. Bills), mmihalko@campbellclinic.com (M.J. Mihalko), wmihalko@campbellclinic.com (W.M. Mihalko). http://dx.doi.org/10.1016/j.clinbiomech.2017.01.016 0268-0033/© 2017 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Clinical Biomechanics journal homepage: www.elsevier.com/locate/clinbiomech