Radiographic and Clinical Outcomes of Transverse Process Hook Placement at the Proximal Thoracic Upper Instrumented Vertebra in Adult Spinal Deformity Surgery

Abstract

Objective: Few studies have reported radiographic and clinical outcomes of transverse process hook (TPH) placement at the proximal thoracic upper instrumented vertebra (UIV) in adult spinal deformity (ASD) surgery. This study aims to investigate radiographic and clinical outcomes of TPH placement at the UIV for ASD surgery.

Methods: This is a retrospective cohort of 56 patients with ASD (age, 59 ± 13 years; followup, 44 ± 19 months) from Johns Hopkins Hospital, who underwent long posterior spinal fusion to the proximal thoracic spine (T2-5). Visual analogue scale (VAS) for back pain, Oswestry Disability Index (ODI), 36-item Short Form health survey scores, thoracic kyphosis (TK), lumbar lordosis, sacral slope, pelvic tilt, pelvic incidence, proximal junctional kyphosis (PJK) angle, PJK incidence, pattern of PJK, grades of TPH dislodgement, revision surgery, and factors associated with high-grade TPH dislodgement were analyzed.

Results: VAS for back pain and ODI values improved significantly from preoperatively to final follow-up. Mean change in PJK angle was 12° (range, 0.5°-43°). Twenty patients (36%) developed PJK, of whom 13 had compression fractures at 1 vertebra distal to the UIV (UIV-1). Final TPH position was stable in 42 patients (75%). In most patients (86%), TPH dislodgement did not progress after 6-month postoperative follow-up. Three patients (5.3%) underwent revision surgery to extend the fusion because of symptomatic PJK. Unstable TPH position was associated only with revision surgery and TK.

Conclusion: TPH placement at the proximal thoracic UIV for long fusion showed favorable clinical and radiographic outcomes in terms of the incidence of PJK and mean PJK angle at mean 44-month follow-up. TPHs placed in the proximal thoracic UIV were in stable position in 75% of patients. Compression fracture at UIV-1 was the most common pattern of PJK. PJK angle progression was greater in revision cases and in patients with greater preoperative thoracic kyphosis.

Keywords: Adult spinal deformity; Kyphosis; Proximal junctional kyphosis; Proximal thoracic spine; Sagittal imbalance; Scoliosis; Transverse process hook.

Fig. 1.

Lateral radiographs showing the grading system used to assess transverse process hook (TPH) position. The grade of TPH position was based on 2 lines. The anterior dotted line indicates the ventral border of the transverse process, and the posterior dotted line indicates the dorsal border of the rib cage. (A) Grade 0 indicates no dislodgement or unilateral, incomplete dislodgement of the TPH (i.e., the blade of the TPH is between the transverse process and the rib cage). (B) Grade 1 indicates bilateral, incomplete dislodgement of the TPH. (C) Grade 2 indicates unilateral or bilateral complete dislodgement of the TPH (i.e., the blade of the TPH is posterior to the rib cage). Grades 0 and 1 were considered stable positions.