Transforaminal Lumbar Interbody Fusion with Double Banana Cages: Clinical Evaluations and Finite Element Model Analysis.

STUDY DESIGN: Clinical and basic study. OBJECTIVES: This study aimed to investigate whether transforaminal lumbar interbody fusion (TLIF) using 2 banana-shaped cages leads to good clinical outcomes. METHODS: First, we conducted a clinical study to compare outcomes among patients who underwent TLIF using different types or numbers of cages. Propensity matched patients in each group were reviewed. Thirty-four patients who underwent surgery with 2 bullet-shaped cages (group A), 34 with a banana-shaped cage (group B), and 34 with 2 banana-shaped cages (group C) were compared. Twelve months after the surgery, bony fusion and cage subsidence were evaluated. RESULTS: The mean amount of cage subsidence was 14.9% in group A, 19.9% in group B, and 11.8% in group C. Subsidence in group B was significantly greater than that in group C (P < .01). Radiological bony fusion was not achieved in 2 cases in group B. Second, we performed a finite element model (FEM) analysis to determine the biomechanical stress of the vertebral endplate by comparing the single-banana cage construct with a double banana-shaped cage construct. FEM analysis showed that the maximum stress of the endplate in the single-cage model was 1.72-times greater than the maximum stress in the double-cage model. Furthermore, the maximal stress in the single-cage model was significantly higher than in the double-cage model during lumbar extension and side bending. CONCLUSION: This study showed that TLIF with double banana-shaped cages led to good clinical outcomes with less cage subsidence, probably because of decreased mechanical stress on the vertebral endplate.

Alterations in axial curvature of the cervical spine with a combination of rotation and extension in the conventional anterior cervical approach.

PURPOSE: Alterations of three-dimensional cervical curvature in conventional anterior cervical approach position are not well understood. The purpose of this study was to evaluate alignment changes of the cervical spine in the position. In addition, simulated corpectomy was evaluated with regard to sufficiency of decompression and perforation of the vertebral artery canal. METHODS: Fifty patients with cervical spinal disorders participated. Cervical CT scanning was performed in the neutral and supine position (N-position) and in extension and right rotation simulating the conventional anterior approach position (ER-position). Rotation at each vertebral level was measured. With simulation of anterior corpectomy in a vertical direction with a width of 17 mm, decompression width at the posterior wall of the vertebrae and the distance from each foramen of the vertebral artery (VA) were measured. RESULTS: In the ER-position, the cervical spine was rotated rightward by 37.2° ± 6.2° between the occipital bone and C7. While the cervical spine was mainly rotated at C1/2, the subaxial vertebrae were also rotated by several degrees. Due to the subaxial rotation, the simulated corpectomy resulted in smaller decompression width on the left side and came closer to the VA canal on the right side. CONCLUSIONS: In the ER-position, the degrees of right rotation of subaxial vertebrae were small but significant. Therefore, preoperative understanding of this alteration of cervical alignment is essential for performing safe and sufficient anterior corpectomy of the cervical spine.

Incidence and characteristics of carpal fractures occurring concurrently with distal radius fractures.

PURPOSE: To investigate the incidence and characteristics of carpal fractures occurring concurrently with distal radius fractures and to determine the risk factors for this combination. METHODS: We retrospectively analyzed 161 consecutive patients with 170 distal radius fractures who were treated between 2007 and 2011. Posteroanterior, lateral, and oblique radiographs of the wrist were examined, as were computed tomography scans when available. We evaluated the incidence and characteristics of carpal fractures occurring concurrently with distal radius fractures and the patient factors of gender, age, AO/ASIF classification, and energy of the injury. RESULTS: Of the 170 distal radius fractures, 11 (7%) also had 1 or 2 carpal fractures. Of the 15 carpal fractures, 8 were scaphoid, 2 triquetrum, 2 pisiform, 1 capitate, 1 trapezium, and 1 hamate. Eleven of the 15 carpal fractures were diagnosed by computed tomography alone. Male gender, patients of lower mean age, AO/ASIF type B, and high-energy trauma significantly raised the risk of simultaneous fractures of the distal radius and carpals. CONCLUSIONS: The incidence of carpal fractures occurring concurrently with distal radius fractures was not negligible, and almost all carpal fractures had no or minimal displacement. Suspicion of carpal fractures occurring concurrently with distal radius fracture should be high, and computed tomography should be considered, in males, young patients, and those with AO/ASIF type B fractures and high energy trauma.