"Dinosaur spine" in ankylosing spondylitis: case illustration.

Abstract

An 89-year old man with known ankylosing spondylitis (AS) had undergone ventral corpectomy, implantation of a PEEK (polyetheretherketone) cage, and ventral fusion after suffering a dislocated compression fracture of C-7 (Fig. 1A); stabilization was subsequently achieved by dorsal C5–6 and T1–2 fusion (Fig. 1B). The patient had no neurological deficits. Eighteen months later the man presented with massive atrophy of paraspinal muscles and protrusion of spinous processes (Fig. 1C and D). Open resection of the C-7, T-1, and T-2 spinous processes was performed. The overlying skin and atrophic scar tissue were removed (Fig. 1E and F). Adaptation to the bone of paraspinal muscles was not possible due to atrophy. Six weeks after surgery, efficient wound healing was observed (Fig. 1G). Satisfactory cosmesis was achieved, and no infection developed. Neither complications of wound healing nor related to the fracture occurred within the 6-month follow-up period. The patient died 8 months after surgery, with no causal relation between the procedure and death. Atrophic changes leading to paraspinal muscle fibrosis in AS1 appeared to arise from disuse of or neurogenic damage to the posterior branches of the spinal nerves due to bony facet joint encroachment in the neural foramina. This patient with an AS-induced rigid spine had extreme atrophy of the paraspinal muscles that led to direct mechanical exposure of spinous processes. We describe a safe and simple surgical approach—so far lacking in the literature—that prevents potential complications due to wound perforation or skin infection. As ours was a single case, recommendations to prevent this condition are limited.