_________________________________________________________________________ Neck Pain in Adults
Temporomandibular Joint Disorder Temporomandibular joint disorder (TMD) is associated with whiplash injury, and TMD populations show an average 35% prevalence of whiplash trauma [42]. Chronic muscle pain in TMD is classified as localized or referred. Compared with patients with localized TMD, those with TMD and whiplash histories have greater jaw pain and dysfunction severities; more severe subjective, objective, and psychological dysfunction; and poorer treatment outcomes. Some evidence suggests TMD pain after whiplash trauma differs pathophysiologically from localized TMD pain. Whiplash trauma is a common TMD comorbidity and probably an initiating or aggravating factor. Patients with TMD and whiplash require early evaluation and multidisciplinary management [43; 44; 45]. PATHOPHYSIOLOGY This section discusses how neck pain develops and persists by examining pathologic processes in cervical spine and pain signaling structures. Discussion of normal function is presented first to assist in the understanding of pathology. CERVICAL SPINE STRUCTURE AND FUNCTION The top seven vertebrae (C1 to C7) make up the cervical spine, which provides mobility and stability to the head while connecting it to the relatively immobile thoracic spine [46]. The spine transfers force between the upper and lower extremities and generates force [47]. C1 and C2 are the upper cervical spine. C1 bears the head (“the globe”) and is called the atlas. The atlas connects above with the occiput (the atlanto-occipital joint), where 50% of all neck flexion extension occurs. The atlas connects below with C2, termed the axis, forming the atlanto-axial joint, where 50% of all neck rotation occurs [46]. The lower (subaxial) cervical spine consists of vertebrae C3 to C7, connected by facet joints and intervertebral disks, unlike the complex ligament structures that connect C1 and C2 [48]. Facet joints, also called zygapophysial joints (z-joints), stabilize and limit excessive cervical spine flexion, extension, side- bending, and rotation [49]. The medial branch of the dorsal nerve innervates the facet joint. The joint contains a fibrous capsule, synovial membrane, articular cartilage, and menisci [50]. The intervertebral disk is a functional unit connecting two vertebral bodies of the spine. The disk absorbs shock, accommodates movement, provides support, and separates vertebral bodies to lend height. Disk units have a nucleus pulposus middle, annular fibers (annulus fibrosus) surrounding the nucleus pulposus, and two cartilage end plates that separate each segment level between the C2–T1 vertebrae [51]. Annular fibers are vulnerable to rotational force injury, and nociceptors innervate the middle and outer third [46].
Risk factors for poor recovery from whiplash injury described in the medico-legal literature include [16; 34]: • High post-injury pain (>6/10) and disability (NDI >40%) • Number and severity of injury-related symptoms (e.g., post-injury headache, low back pain, neuropathic pain, radicular symptoms) • Psychological distress (e.g., post-trauma stress symptoms, pain catastrophizing) • Cervical spine cold hyperalgesia • Failure to wear seatbelt • Less than college education Cervical Radiculopathy Many patients with cervical radiculopathy secondary to acute disk herniation have a favorable clinical course. Symptom resolution occurs over weeks to months because 40% to 76% of herniated cervical disks spontaneously resorb independent of treatment. Acute neuropathic symptoms in spinal stenosis stabilize or improve in more than 50% of patients, but anatomic derangements do not generally improve without treatment [29; 35; 36]. However, patients with cervical radiculopathy and more severe acute pain or symptoms show higher risk of chronic pain. Higher pain scores and radicular symptoms are associated with chronicity and poor outcomes in both neck pain and low back pain [37; 38]. Assessment of Prognostic Factors With multiple studies showing that acute-phase risk factors can predict poor pain and disability outcomes, practice guidelines recommend that clinicians assess all patients during initial and follow-up contacts. Pain, disability, post-trauma symptoms, and pain catastrophizing are measured to quantify progress and to predict prognosis for recovery (discussed later) [39].
ASSOCIATED CONDITIONS Vertigo
Many patients experience vertigo, dizziness, unsteadiness, and other proprioceptive abnormalities following whiplash trauma. Strains to facet joint capsules, paravertebral ligaments, or cervical musculature in WAD are thought to modify proprioceptive cervical balance to produce mild but chronic vertigo [40]. Dizziness may result from injury to facet joints supplied by proprioceptive fibers; when injured, these fibers can send confused vestibular and visual inputs to the brain [41].
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