Experimental study Anatomic considerations in headaches associated with cervical sagittal imbalance: A cadaveric biomechanical study Olivia A. Kalmanson a , Saeed Khayatzadeh b , Anand Germanwala b,c , Matthew Scott-Young d , Robert M. Havey b,e , Leonard I. Voronov b,e , Avinash G. Patwardhan b,e,⇑ a Loyola University Stritch School of Medicine, Maywood, IL, USA b Edward Hines Jr. VA Hospital, Hines, IL, USA c Loyola University Medical Center Dept. of Neurologic Surgery, Maywood, IL, USA d Gold Coast Spine, Southport, Queensland, Australia e Loyola University Medical Center Dept. of Orthopaedic Surgery, Maywood, IL, USA article info Article history: Received 6 October 2018 Accepted 20 February 2019 Available online xxxx Keywords: Greater Occipital Nerve Cervical spine Biomechanics Sagittal imbalance Cervicogenic headache Tension-type headache abstract Chronic Forward Head Posture is associated with headaches, neck pain, and disability, though few studies have investigated the effects it has on the suboccipital triangle. The objective of this study was to quan- titatively assess whether the biomechanical changes in the suboccipital triangle help explain the clinical manifestations of Forward Head Posture. Specifically, this study aimed to identify whether the Greater Occipital Nerve or C2 nerve root may be compressed in Forward Head Posture. Three-dimensional, specimen-specific computer models were rendered from thirteen cadaveric cervical spine specimens. The spines transitioned from neutral to Forward head posture while motion data was collected. This data was synced with the computer models to make precise measurements. In Forward Head Posture, occiput- C1, C1-C2, and occiput-C2 segments extended by 10.7 ± 4.6 deg, 4.6 ± 4.3 deg, and 15.3 ± 2.3 deg, respec- tively. The Rectus Capitis Posterior Major and Minor and Obliquus Capitis Superior muscles shortened by 20.0 ± 4.6%, 15.0 ± 7.6%, and 6.6 ± 3.3%, respectively. The Obliquus Capitis muscle inferior length did not change. The suboccipital triangle area decreased by 18.7 ± 6.4%, but the protective gaps surrounding the C2 nerve root and the Greater Occipital Nerve did not reveal clinically significant impingement. The C2 nerve root gap decreased by 1.0 ± 1.3 mm and the Greater Occipital Nerve gap by 0.2 ± 0.18 mm. These results demonstrate that the C2 nerve root and the Greater Occipital Nerve are protected by the bony landscape of the cervical spine. However, there is likely persistent contraction of the rectus muscles in Forward Head Posture, which suggests a secondary tension-type etiology of the associated headache. Ó 2019 Published by Elsevier Ltd. 1. Introduction Cervical sagittal imbalance is a deviation from neutral posture within the sagittal plane. Forward Head Posture (FHP) is one of the most common forms of cervical sagittal imbalance in which the head is positioned anterior to the plane of the shoulders [1–6]. FHP may result from poor posture over time, degenerative disc disease, excessive thoracic kyphosis, or post-surgical cervical kyphosis [1,2,4–6,7–10]. It is associated with headaches [11,12,13,14] and neck pain [1,2,15–18], resulting in significant morbidity and disability [2,7,19–21] that increases with the severity of FHP [19]. Headaches associated with FHP are estimated to have up to a 13.8% prevalence, contribute to significant health- care cost, and can significantly impact the health-related quality of life of many patients [22]. However, the underlying pathophysiol- ogy of the headaches associated with FHP is poorly understood and is likely multifactorial. One possible component may be compres- sion of the Greater Occipital Nerve (GON) or C2 nerve root (C2nr) within the Suboccipital Triangle (SOT). This would liken the head- ache of FHP to a cervicogenic headache, defined as a nontraumatic disorder of the neck, including the cervical spine, discs, and/or soft tissues [23]. This definition encompasses the degenerative changes seen in FHP. The goal of this study is to evaluate the likelihood of GON and C2nr compression as a possible etiology of headache associated with FHP using cadaveric spines and biomechanical modeling. https://doi.org/10.1016/j.jocn.2019.02.003 0967-5868/Ó 2019 Published by Elsevier Ltd. ⇑ Corresponding author at: Department of Orthopaedic Surgery and Rehabilita- tion, Loyola University Medical Center, 2160 S. First Avenue, Maywood, IL 60153, USA. E-mail address: apatwar@lumc.edu (A.G. Patwardhan). Journal of Clinical Neuroscience xxx (xxxx) xxx Contents lists available at ScienceDirect Journal of Clinical Neuroscience journal homepage: www.elsevier.com/locate/jocn Please cite this article as: O. A. Kalmanson, S. Khayatzadeh, A. Germanwala et al., Anatomic considerations in headaches associated with cervical sagittal imbalance: A cadaveric biomechanical study, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2019.02.003