Fatigue wear test comparing vitamin-E-blended crosslinked polyethylene and conventional polyethylene in a Posterior Dynamic Stabilization System of the spine in the laboratory.

BACKGROUND: Although artificial joints using polyethylene have been developed for various joints, the development of Posterior Dynamic Stabilization system of the spine using polyethylene has proceeded at a much slower pace. There are no studies which compare the abrasion resistance of vitamin-E-blended crosslinked polyethylene (VE) and conventional polyethylene (Virgin) in the spinal region. The purpose of this study was to compare the wear resistance of VE and Virgin in a Posterior Dynamic Stabilization System of the spine. METHODS: Posterior Dynamic Stabilization System of the spine uses a polyethylene ball as a sliding surface. A fatigue wear test was repeated up to 1 million cycles at a speed of ±5°, 1 Hz while the rod was being pulled at a load of 50 N. Balls were compared using VE and Virgin in 6 samples each. Ti-6AL-4 V (Ti 64) and Co-Cr-Mo (CoCr) rods were used. Abrasion loss and shape change of the polyethylene balls were compared. RESULTS: When Ti 64 was used as the rod, the average wear amount was -0.01 mg (0.02 mg, 0.01 mg, -0.06 mg) for VE, and 0.23 mg (0.18 mg, 0.13 mg, 0.38 mg) for Virgin. When CoCr was used as the rod, the average wear amount was 0.42 mg (0.71 mg, -0.06 mg, 0.61 mg) for VE, and 0.73 mg (0.72 mg, 0.70 mg, 0.76 mg) for Virgin. Most polyethylene samples showed indentations of 0.1 m or less at the contact point with the set screw. In the combination of Virgin and CoCr, a white patch was observed on the inner side of the polyethylene samples, with a maximum depression of 0.1 mm. CONCLUSIONS: A fatigue wear test showed VE to be more efficient in abrasion resistance than Virgin in a Posterior Dynamic Stabilization System of the spine in the laboratory.

The Relationship Between Global Sagittal Balance and the Incidence of Early Adjacent Vertebral Fractures Following Balloon Kyphoplasty.

BACKGROUND: Recently, it is widely known that global sagittal balance (GSB) influences the postoperative outcome of the spine. The purpose of this study was to investigate the relationship between GSB and the incidence of early adjacent vertebral fracture (AVF) following balloon kyphoplasty (BKP). METHODS: This study included 96 patients (19 males, 77 females, mean age 77.4 ± 5.5 years) who underwent BKP for osteoporotic vertebral fracture and who were over 60-years-old. We investigated the effect of GSB on early AVF within 2 months after surgery. Of the 96 patients, 76 patients (16 males, 60 females, mean age 77.0 ± 5.4) underwent BKP at the thoracolumbar junction (T11-L2) and were investigated independently. After the two-group comparison, logistic regression analysis was performed. RESULTS: During the observation period (18.3 ± 14.7 months), 27 of 96 patients (28.1%) suffered AVF after BKP, and 24 of 96 patients (25.0%) suffered early AVF. In the logistic regression analysis, spinopelvic parameters were not detected as significant risk factors. In cases of BKP at the thoracolumbar junction (T11-L2), 24 of 76 patients (31.6%) suffered AVF after BKP during the observation period (15.3 ± 19.5 months), and 21 of 76 patients (27.6%) suffered early AVF. Logistic regression analysis detected pelvic tilt (PT): odds ratio 1.087 (P = 0.046∗) and local kyphosis: 1.147 (P = 0.003∗) as risk factors for early AVF. The cutoff value was PT≥29° from the receiver operating characteristics curve. CONCLUSIONS: At the thoracolumbar junction (T11-L2), PT ≥29° is one of the risk factors of early AVF following BKP.

Preoperative Scoring System for Prediction of Early Adjacent Vertebral Body Fracture After Balloon Kyphoplasty Using X-Rays Taken in a Non-Weight-Bearing Position.

BACKGROUND: Prevention of adjacent vertebral body fracture (AVF) following balloon kyphoplasty (BKP) is a key challenge. The objective of this study was to develop a scoring system that could be more extensively and effectively used to determine the surgical indications for BKP. METHODS: The study involved 101 patients aged 60 years or older who had undergone BKP. Logistic regression analysis was used to identify risk factors for early AVF within 2 months following BKP. Scoring was based on the odds ratio for risk factors, and cut-off values were determined from the receiver operating characteristics curve. The correlation between the total scores and the incidence of early AVF, and the area under the curve for the logistic regression model predicting early AVF using the scoring system were investigated. RESULTS: 29 cases (28.7%) experienced early AVF after BKP. The scoring system was created as follows: 1) age (<75 years: 0 points (P), ≥75 years: 1P), 2) number of previous vertebral fractures (0: 0P, 1 or more: 2P), and 3) local kyphosis (<7°: 0P, ≥7°: 1P). The total scores were found to be positively correlated with the incidence of early AVF (r = 0.976, P = 0.004). The area under the curve of the scoring system for predicting early AVF was 0.796. The incidence of early AVF was 4.2% at ≤1P and 44.3% at ≥2P (P < 0.001). CONCLUSIONS: A scoring system which can be applied to a broader patient population was developed. In cases where the total score is 2P or more, alternatives to BKP should be considered.