Mosaab Alsuwaihel, MD, PGY4 Dalhousie Neurosurgery Program, Dalhousie University, Halifax, NS.
Sean Christie, MD, Professor, Department of Surgery (Neurosurgery), Faculty of Medicine, Vice-Chair and Director of Research , Division of Neurosurgery, Dalhousie University.

Abstract
Inflammatory spondyloarthropathies produce synovitis of the spinal joints in rheumatoid arthritis (RA), or enthesitis in ankylosing spondylitis (AS). In RA, progressive disease leads to synovial destruction, ligamentous laxity, pannus formation and deformity. In AS progressive enthesitis results in ascending ossification, kyphotic deformity and rigidity which increase the risk of fracture. Although pain is the common presentation, spinal cord compression can produce neurological deficits. Although the need for surgery has decreased with the advent of new disease altering drugs, there remains a number of indications when surgical consultation remains important.
Key Words: Spondyloarthropathy and spondyloarthritis, Synovium and synovitis, Enthesis and enthesitis, Pannus.

Introduction
In a general sense, the term spondyloarthropathy refers to any disease involving the joints of the spine. However, it is more commonly used in the context of certain inflammatory rheumatological disorders and, in the presence of active inflammation, is referred to as spondyloarthritis. Examples of conditions that may involve the axial skeleton, whether as a primary presentation or in association with more systemic synovial inflammation, are listed in Table 1. This article highlights the two most common and significant pathologies, rheumatoid arthritis (RA) and ankylosing spondylitis (AS). These distinct disease entities commonly present with pain and without treatment can ultimately lead to instability. This reflects progressive cartilaginous destruction and ligamentous laxity in RA, or rigidity and loss of normal supporting structures in AS. In either instance, the pathology alters the dynamic stressors and biomechanical properties of the spine potentially leading to pain, rigidity, deformity, and neurological compromise. An overview of the ligamentous and bony anatomy of the spine helps conceptualize the dynamic pathology that ensues with progressive inflammation (Figure 1). The craniovertebral junction comprises the base of the occiput, the atlas (C1), and the axis (C2). The atlas articulates with the occiput across the two horizontal condyles. The axis and atlas articulate laterally via two synovial joints. Anteriorly, the odontoid, a rostral extension of the body of C2, articulates with the anterior arch of the atlas through an intervening synovial lining. This joint is stabilized by the cruciate ligament, which limits posterior displacement of the odontoid.¹ The subaxial spine can be segmented into two columns of support. Anterior to the spinal canal, the vertebral bodies are separated by the intervertebral disc and 'braced' by the anterior longitudinal ligament (ALL) and posterior longitudinal ligament (PLL). Posterior to the spinal canal, the paired, synovial-lined facet joints interlock at each spinal level.