summary Cervical Adjacent Segment Disease is the radiographic degeneration of the disc or facets at the caudal or cephalad segment adjacent to a previous cervical surgical fusion construct. Diagnosis can be made with plain radiographs of the cervical spine. Treatment is observation and medical management for patients with mild symptoms. Surgical management is indicated in patients that have failed conservative treatment. Epidemiology Incidence studies have estimated a 1.6 to 2.4% annual incidence of clinically relevant ASD predicted 25.6% ASD rate at 10 years for patients undergoing ACDF Demographics females have a higher risk factor for the development of adjacent segment disease patients under the age of 60 have an increased risk for the development Anatomic location the lowest three segments of the subaxial spine are the most commonly affected (C4-5,C5-6, and C6-7) C5-6 has the highest risk unclear as to whether this level is more prone to natural progression of spondylosis or sensitive to adjacent segment disease C2-3 has the lowest risk Risk factors smoking is the strongest associated patient factor female sex less than 3 segments included in the fusion construct speculated that fewer motion segments remaining reduces the risk of adjacent segment degeneration C5-6 and C6-7 segments are left adjacent to the fusion construct anatomically the most mobile segments of the cervical spine with the highest rates of degeneration preoperative MRI and myelography demonstrating dura mater indentation and disc protrusion, especially at the C5-6 and C6-7 levels no decrease in risk with fusion vs. nonfusion procedures (i.e. posterior foraminotomy, anterior discectomy) Etiology Forms adjacent segment degeneration radiographic changes of degeneration at levels adjacent to a spinal fusion with or without clinical symptoms adjacent level ossification (ALOD) large anterior marginal osteophyte that forms adjacent to a fused construct unclear whether this leads to adjacent segment disease adjacent segment disease (ASD) development of clinical radiculopathy or myelopathy correlating to a motion segment adjacent to the fusion construct Pathophysiology ASD increased motion at the adjacent disc space to compensate for the rigid fused segment supraphysiologic motion, increased stress, and shear strain leads to accelerated degeneration of the disc space increase intradiscal pressure ensues from the compensatory increase in motion and stress increased disc herniation, loss of disc height, osteophyte formation results in cervical foraminal and central canal stenosis which can lead to clinical radiculopathy and myelopathy clinical data does not entirely support this as cervical disc arthroplasty, which preserves spinal segment motion, does not reduce ASD damage to the anterior longitudinal ligament and longus colli muscle at the time of surgery placement of needle marker into incorrect disc space when localizing the operative level potentially minimize ALOD etiology unclear, but speculated to be an inflammatory reaction that occurs from increased proximity of anterior cervical plate to the adjacent disc space plate place within 5 mm of the adjacent disc increases ossification risk heterotopic bone formation in the anterior longitudinal ligament Classification Park and Associates Classification of Adjacent Level Ossification Grade 0 No adjacent level ossification Grade 1 Ossification extending less than 50% of the disc space Grade 2 Ossification extending greater than 50% of the disc space Grade 3 Complete bridging of the adjacent disc space Presentation Symptoms radiculopathy pain in dermatome corresponding to adjacent motion segment to previous fusion construct motor weakness corresponding to the root level adjacent to a previous fusion construct myelopathy gait instability hand clumsiness urinary abnormalities Physical exam inspection examine surgical wound motion assess flexion-extension, side bending, and rotational motion document which portion of ROM is painful neurological exam assess fine touch sensation in dermatomal pattern patients with sensory changes should be assessed for peripheral nerve compression (e.g. cubittal tunnel and carpal tunnel syndromes) assess motor strength assess reflexes hyperreflexia may suggest myelopathy provocative tests Hoffman's test - flicking the long finger with positive finding being an involuntary ipsilateral thumb IP joint flexion, which suggests myelopathy Spurling's test - provacative test with compression applied to an extended, rotated, and bent neck to the affected side positive finding suggests radiculopathy should abduction test - lifting the arm above the head reduces or relieves symptoms, suggesting radiculopathy L'hermitte sign - forced neck flexion causes electric sensation down entire body suggesting myelopathy Imaging Radiographs recommended views AP lateral flexion-extension views findings disc space narrowing foraminal stenosis posterior osteophytes facet arthropathy anterior marginal osteophyte extending from adjacent vertebral body degenerative changes on radiographs do not always correlate with clinical symptoms CT indications assess for pseudoarthrosis assess for ossification of posterior longitudinal ligament views sagittal and axial views are most useful MRI indications determine if there is foraminal or central canal stenosis at the adjacent segment views axial and sagittal views are most useful Differential Key differential (top 5) pseudoarthrosis progressive degenerative disc disease indolent infection myelopathy at a segment not adjacent to the fused segment radiculopathy at a segment not adjacent to the fused segment Treatment Nonoperative treatment oral medications, activity modifications, physical therapy, +/- brief period of immobilization indications first line of treatment for radiculopathy and mild myelopathy without impairment modalities oral medications NSAIDs use caution in elderly patients due to risk of gastric bleeding gabapentin commonly used for nerve and associated pain narcotics should be avoided for any chronic condition brief period of immobilization some studies show it is beneficial severe myelopathy should be surgically addressed to avoid stepwise deterioration Operative extension of fusion construct to affected levels indications clinical radiculopathy consistent with the adjacent segment that have not responded well to nonoperative treatment myelopathy inclusion of C5-6 and/or C6-7 into the fusion construct highest liklihood of developing ASD place anterior plate >5 mm from the adjacent level reduces the risk of adjacent level ossification including >3 levels has a reduced risk of developing further ASD cervical total disc replacement indications single level involvement as an index procedure does not appear to have an protective effect on ASD large meta-analyses suggest possible decrease in reoperation rates for the treatment of ASD appears equivalent to ACDF reduced risk of adjacent segment ossification compared to anterior cervical plating Technique Oral medications, activity modifications, and physical therapy techniques: NSAIDs, tramadol, tylenol, and gabapentin should be first-line treatment with symptomatic ASD activity modification avoidance of exacerbating activities can reduce pain by avoiding flare ups avoiding down-gazing activities can avise patients against excessive cell phone use, excess computer use, driving with bad posture, etc. physical therapy strengthening of paraspinal muscles improved posture desensitization hot and cold therapy spinal traction manual or mechanical traction allows for expansion of the neuroforamen and reduces nerve compression temorparily Extension of fusion construct to affected levels approach anterior vs. posterior approach dictated by location of pathology (anterior vs posterior) and clinical symptoms (neck pain, unilateral arm pain, myelopathy) anterior right vs. left unless a ENT study performed to evaluation function of RLN, always assume a deficit if prior anterior surgery and use prior approach to protect contralateral nerve Cervical disc replacement technique single level disease adjacent to previous fusion construct performed through anterior approach critical to align the center of rotation in the both the sagittal and coronal planes Complications Progression of ASD following surgical treatment of ASD by extending fusion construct to affected levels further development of symptomatic degeneration of the newly adjacent segment treatment revision surgery to include affected segment Prognosis Despite a high incidence of clinically relevant ASD, the natural history of cervical spondylosis remains high studies have demonstrated radiographic degenerative findings >80% of asymptomatic unfused patients >60 years of age prevalence of radiographic adjacent segment degneration in arthrodesis patients range from 25% to 91% Increased revision surgery rates overall reoperation rates reported between 6.1 to 25.6% annual reoperation rates reported as high as 0.7 to 3.7%