A chronic flexion-distraction injury with a “fistulous wither” on the split spinous process of the L1 vertebra—a case report of a modified transpedicle wedge osteotomy

Abstract

Flexion-distraction injuries (FDIs) are caused by high-energy force and momentum on the spine. In general, the posterior column and the posterior wall of the affected vertebra have failed in distraction, and the anterior column has failed in compression based on Denis’ three column theory [1]. Hoshikawa et al. has proposed a motion axis of FDIs, which is defined as a transitional line from the anterior compression to the posterior splitting failure [2]. In terms of biomechanics, the integrity of the posterior tension band of the affected vertebrae has failed in FDIs. As a result of this loss of integrity of the posterior element, kyphotic deformity easily develops and remains unless proper treatment has been optioned in FDIs. Fresh FDIs with minimal displacement are usually treated with an extension brace or body cast, and they have a good prognosis. Meanwhile, treatment of chronic FDIs is complicated. Backache and/or gibbus, which is caused by rigid kyphosis even after bone fusion at the affected segment, is a major residual symptom in chronic FDIs. Nonoperative treatment can rarely cure rigid kyphotic deformity. Malcom et al. stated that persistent back pain in the lumbar spine and the buttocks is usually related to a compensatory hyperlordosis below the kyphotic segment [3]. Although the degree to which kyphosis should be corrected operatively is still controversial, surgical intervention is indicated for some cases with backache and/or ill cosmesis caused by rigid kyphotic deformity in chronic FDIs. LeGay et al. have proposed that a deformity of greater than 17° in kyphosis of FDIs shows a clinically poor result and an instability in vivo [4]. For surgical treatment of a rigid kyphotic deformity of chronic FDIs, access to the damaged vertebra, releasing the scar tissue, correction of the kyphosis and a stable support in the anterior and middle columns are crucial. In the anterior approach, a wide surgical field of the affected segment is obtained, but it is associated with significant pulmonary and incisional morbidity. Conversely, the posterior approach provides more limited access with less morbidity, and it also enables surgeons to directly observe the neural tissue after resection of the damaged posterior elements in FDIs. A supraspinous bursitis is described as “fistulous withers” in horses [5]. It is a mechanical inflammation caused by a poorly fitting tack on horse withers. It begins as a painless encapsulated accumulation of serum associated with the supraspinous bursa. To my best knowledge in English and Japanese literature, there is no report of a symptomatic bursitis on the lumbar spinous process in humans. The supraspinous and the interspinous ligaments are less resilient to stress than the interval disc and the capsular ligament. Thus, there is a possibility that a condition similar to “fistulous withers” in horses develops in humans, when a local post-traumatic kyphosis of chronic FDIs remains in the human thoracolumbar spine. The purpose of the current article is a case report of chronic FDIs in the L1 vertebra. The patient had developed a rigid kyphosis associated with a bursitis on the distracted spinous process. He underwent radical excision of the affected soft tissue, partial resection of the fractured spinous process, a modified transpedicle wedge osteotomy in a fractured line, and augmented with pedicle screws and titanium interbody cages. An excellent prognosis has been obtained in the current case.