A 16-year-old male adolescent presented with low back pain with progressive protrusion of the lumbar spinous process 3 years before the first visit. The protrusion in his back was not noticed from his neonatal period to early childhood by his parents, until it was discovered around the age of 13 years. After playing basketball caused his lower back pain to worsen, he visited a nearby clinic and was found to have an abnormality in the L2 vertebral body. The patient was then referred to our department. He had no medical history, including congenital diseases or spinal trauma. His chief complaint was lower back pain, which was exacerbated by exercise. He was 173 cm tall and weighed 60 kg at his first visit. The spinous process protruded in the upper lumbar spine, with tenderness in the bilateral paravertebral muscles at the same level. Neither symptoms in the lower extremities nor abnormal neurological findings were observed. The Japanese Orthopaedic Association (JOA) score for lumbar spinal disorders was 27 points out of 29.
The anteroposterior (AP) radiogram of the whole spine revealed no obvious scoliosis, with bone maturity of Risser Grade 4 (Fig. 1a). The lateral radiogram of the whole spine showed hypoplasia of the anterior portion of the L2 vertebral body with a sagittal vertical axis (SVA) of -60 mm (Fig. 1b). The AP diameters measured at the center of the L1, L2, and L3 vertebral bodies were 36 mm, 27 mm, and 41 mm, respectively. The spinal parameters measured in the lateral radiogram were as follows: Thoracic kyphosis (TK) at T5-12, 17 ; local kyphosis at L1-3, 23 ; lumbar lordosis (LL) at L1-S1, 38 ; LL at L3-S1, 59 ; and pelvic incidence (PI), 34  (Fig. 1b). In the dynamic lateral radiograms, local kyphosis at L1-3 was 23  in the extended position (Fig. 2a) and 44  in the flexed position (Fig. 2b). In addition, the facet joints at the L2-3 spinal level were subluxated in the flexed position (Fig. 2b). Computed tomography showed symmetrical hypoplasia of the anterior portion of the vertebral body of L2 (Fig. 3). Based on these radiological findings, the patient was diagnosed with L1-3 local kyphosis, with anterior column hypoplasia and subluxation of the facet joints at L2-3.
Spine-shortening osteotomy at L2 and L1-3 posterior fusion was performed for local stabilization and correction of the sagittal malalignment, using a pedicle screw and rod system with compression laminar hooks, as reported previously. This procedure is equivalent to Grade-4 osteotomy by anterior column realignment classification. First, the laminae and transverse processes of the L1-3 vertebrae were exposed. Polyaxial pedicle screws were placed bilaterally at the L1 and L3 vertebrae, parallel to each upper endplate (EXPEDIUM VERSE System , DePuy Synthes, Raynham, MA). The lower half of the L1 lamina, the L1-2 facet joints, and the upper half of the L2 lamina were resected using a high-speed burr and chisels. Then, the upper half of the L2 pedicles was removed using a high-speed burr. Subsequently, a wedge-shaped osteotomy of the upper part of the L2 vertebral body was performed together with the removal of the L1-2 intervertebral disc. The wedge-shaped osteotomy was performed with the preoperatively designed osteotomy line, with the starting point at 8 mm caudal from the posterosuperior edge of the L2 vertebral body, cutting up toward the anterosuperior endplate at an angle of 30  to the lower endplate of L1 to set local kyphosis between L1 and L3 to 0  after correction. For correction, the screws were converted from polyaxial to monoaxial screws by semi-locking the set screws. After placing bilateral temporary rods on the screws, the posterior portions of the L1 and L3 vertebral bodies were compressed gradually using a hook system (DYNACORE , Mizuho Corporation, Tokyo, Japan). The alignment and bone-on-bone contact were confirmed by fluoroscopy and the screws were connected to the final rods. Finally, autologous local bone pieces from the posterior vertebral elements were grafted between L1 and L3.
A whole-spine AP radiogram at 2-year post-operative follow-up revealed no obvious scoliosis (Fig. 4a). The lateral radiogram demonstrated that SVA improved to 9 mm, TK to 35 , local kyphosis at L1-3 to -2 , LL to 40 , and LL at L3-S1 to 34  (Fig. 4b). In addition, bone union was confirmed at L1-2 vertebral bodies by computed tomography (Fig. 4c). His lower back pain was completely relieved and his JOA score showed a maximum 29 points. Two years postoperatively, the patient had no symptoms, bony fusion was completed, and no correction loss was detected.