Occupancy Rate of Pedicle Screw Below 80% is a Risk Factor for Upper Instrumented Vertebral Fracture After Adult Spinal Deformity Surgery.

STUDY DESIGN: Retrospective study. OBJECTIVE: To determine whether an occupancy rate of a pedicle screw (ORPS) <80% in an upper instrumented vertebra (UIV) is a risk factor for UIV fracture (UIVF). SUMMARY OF BACKGROUND DATA: The ratio of the length of the pedicle screw to the anteroposterior diameter of the vertebral body at the UIV is defined as ORPS. Previous studies showed that the stress on the UIV is reduced to the greatest degree when ORPS is >80%. However, it remains unclear whether these results are clinically valid. PATIENTS AND METHODS: A total of 297 patients who had undergone adult spinal deformity surgery were included in the study. The group with an ORPS ≥80% and <80% was defined as the H (n = 198) and L (n = 99) group, respectively. Propensity score matching and logistic regression analysis were used to evaluate the association between ORPS and the development of UIVF adjusting for confounders. RESULTS: The mean age of both groups was 69 years. The average ORPS in the L and H groups was 70% and 85%, respectively. The incidence of UIVF was 30% in group L and 15% in group H ( P < 0.01). In addition, the 99 patients in group H were subdivided into 2 groups according to whether the screws penetrated the anterior wall of the vertebral body: 68 patients had no penetration (group U ), whereas 31 patients showed evidence of penetration (group B ). A total of 10% and 26% of the patients in the U and B groups, respectively, experienced UIVF ( P < 0.05). Logistic regression analysis indicated that ORPS <80% was significantly associated with UIVF ( P = 0.007, odds ratio: 3.9, 95% CI 1.4-10.5). CONCLUSION: To reduce UIVF, screw length should be set with a target ORPS of 80% or higher. If the screw penetrates the anterior wall of the vertebral body, the risk of UIVF is greater.

Effect of sagittal shape on proximal junctional kyphosis following thoracopelvic corrective fusion for adult spinal deformity: postoperative inflection vertebra cranial to T12 is a significant risk factor.

STUDY DESIGN: This was a retrospective analysis of a prospectively collected consecutive case series of patients with adult spinal deformity (ASD). OBJECTIVE: This study aimed to investigate the impact of the geometrical sagittal shape of the corrected spine on the development of proximal junctional kyphosis (PJK). Several studies have documented risk factors for PJK in ASD surgery. Geometrical assessment is vital for evaluating sagittal spinal deformity. It is essential to assess the postoperative geometrical shape of the spine and the location of the correction in the spine to decrease postoperative junctional stress and PJK. METHODS: Consecutive patients with ASD who underwent corrective fusion with long constructs to the pelvis were included. Patients with neuromuscular disease, congenital and adolescent scoliosis, infection, and spinal tumor were excluded. We investigated the spinopelvic and geometrical parameters of the whole spine. The locations of the thoracic and lumbar apical vertebrae and the inflection vertebrae (IV), where the curvature of the associated adjacent vertebral bodies changes from kyphosis to lordosis, were investigated. The subjects were divided into PJK included patients who underwent revision surgery for junctional failure or with a change in proximal junctional angle ≥ 20°, and non-PJK groups. RESULTS: A total of 139 patients (mean age, 69.6 years; range 18-82 years) were included. There were 47 and 92 patients in the PJK and non-PJK groups, respectively. The IV were located significantly cranial and posterior, the lumbar apex were located significantly posterior in the PJK group at the immediate postoperative time points. The significant risk factors for PJK on binary logistic regression were cranial IV and posterior lumbar apical vertebrae. The incidence of PJK in patients with IV at T12 or cranial tends PJK significantly higher (69%) than at L1 or caudal (26%). CONCLUSIONS: Geometrical spinal shape should be taken into account to reduce the rate of postoperative mechanical complications. LEVEL OF EVIDENCE: Level of evidence III.

Low occupancy rate of the pedicle screw in the vertebral body leads to upper instrumented vertebral fracture.

Upper instrumented vertebra (UIV) fracture in adult spinal deformity surgery leads serious complications, such as spinal cord injury in 0.5-0.8%. Although tip-apex distance is important for preventing screw cut-out in proximal femoral fracture surgery, this suggest that the screw occupancy rate for bone fragments is also important. The purpose of this study was to investigate how the occupancy rate of pedicle screws (ORPS) affects UIV fracture. Patients with UIV fracture 1 year after surgery were defined as the fracture group (F); others were defined as the no fracture group (NF). ORPS, cut-out of pedicle screw (PS), medications, and bone mineral density were evaluated. Significant differences (P < 0.05) between group F (n = 58) and group NF (n = 260) were observed in age (71 years old in group F and 65 years old in group NF), diabetes medication use (19% in group F and 4% in group NF), steroid drug use (10% in group F and 2% in group NF), and ORPS (70% in group F and 76% in group NF). The cut-off value of ORPS using receiver operator characteristic analysis was 73%. Multiple logistic regression analysis identified diabetes medication use (P = 0.026, odds ratio [OR] 4.0) and ORPS < 73% (P = 0.001, OR 3.6) as significant risk factors for UIV fracture. The surgeon can't control use of diabetes medication. However, they can replace with longer PS when ORPS < 73% is detected on radiographs taken during surgery. Further studies will be needed to better elucidate it's use.