General Session: Biomechanics
Presented by: O. Kalmanson - View Audio/Video Presentation (Members Only)
O. Kalmanson(1), S. Khayatzadeh(2), A. Germanwala(2,3), R. Havey(2), L. Voronov(2,4), A. Patwardhan(2,4)
(1) Loyola University Chicago, Stritch School of Medicine, Maywood, IL, United States
(2) Edward Hines Jr. VA Hospital, Hines, IL, United States
(3) Loyola University Chicago, Neurological Surgery, Maywood, IL, United States
(4) Loyola University Chicago, Orthopaedic Surgery and Rehabilitation, Maywood, IL, United States
Introduction: Forward Head Posture (FHP) is a common postural abnormality associated with neck pain, headaches, neck disability, and poor quality of life in which the head is positioned anterior to the shoulders. The Suboccipital Triangle (SOT) is bordered medially by the Rectus Capitis Posterior major and minor (RCPmaj, RCPmin), superolaterally by the Obliquus Capitis Superior (OCS), and inferolaterally by the Obliquus Capitis Inferior (OCI) (Fig. 1). The C2 nerve root (C2nr), Greater Occipital Nerve (GON), and myodural bridges are associated with the SOT region, and their disturbance may cause pain consistent with FHP symptoms. Few studies have investigated effects of FHP on the SOT region, and we hypothesize that severe FHP risks disturbance of the associated neurological structures.
Methods: Thirteen fresh-frozen cadaveric cervical spine specimens (Occiput-T1, mean age: 54±15yrs) were tested in a validated experimental setup to investigate postural compensations needed to maintain horizontal gaze in the presence of FHP [Patwardhan 2015]. Vertebral realignments in response to increasing FHP severity were tracked with optoelectronic motion measurements, and that data was combined with three dimensional (3D) CT scans to generate specimen-specific 3D kinematic models. Fluctuations in the following musculoskeletal parameters of the SOT region were measured on the 3D models: spinal alignment, suboccipital muscle lengths, SOT area, and protective gaps surrounding the C2nr and GON. The C2nr protective gap was defined inferiorly by the superolateral point on the C2 lamina where the C2nr exits the spinal canal and the GON branches off, and superiorly by the closest point on the C1 lamina at any posture. The GON protective gap was defined inferiorly by the same superolateral point on the C2 lamina, and superiorly by the closest point on the OCI at any posture.
Results: In response to a 26mm increase in FHP, C0-C1, C1-C2, and C0-C2 segments extended by 10.7±4.6⁰ (P< 0.005), 4.6±4.3⁰ (P< 0.005), and 15.3±2.3⁰ (P< 0.005), respectively. The gaps between C0 and C1 spinous process (sp), between C1sp and C2sp, and between C0 and C2sp decreased by 5.7±2.6mm (P< 0.005), 2.4±2.8mm (P=0.01), and 7.8±1.7mm (P< 0.005), respectively. The RCPmaj, RCPmin, and OCS shortened by 20±5% (P< 0.005), 15±8% (P< 0.005), and 6±3% (P< 0.005), respectively. The OCI length did not change. The SOT area decreased by 18.7±6.4% (P< 0.005), but the protective gaps surrounding the C2nr and the GON only decreased by 1.1±1.1mm (P=0.01) and 0.2±0.18mm (P< 0.005), respectively.
Conclusions: Significant shortening of the RCPmaj and RCPmin indicate that they are persistently contracting in chronic FHP. This may establish continual tension on the myodural bridges, which is thought to be associated with headache and neck pain characteristic of FHP. The spaces surrounding the C2nr and GON did not decrease appreciably, suggesting that nerve compression may not be the cause of FHP symptoms. This study quantified the protective anatomic landscape of the cervical spine for nerves throughout postural deviations.