Objective To investigate the biomechanical properties of porous bioactive bone cement (PBC) in vivo and to observe the degradation of PBC and new bone formation histologically. Methods According to the weight percentage (W/ W, %) of polymethylmethacrylate (PMMA) to bioglass to chitosan, 3 kinds of PBS powders were obtained: PBC I (50 ︰ 40 ︰ 10), PBC II (40 ︰ 50 ︰ 10), and PBC III (30 ︰ 60 ︰ 10). The bilateral femoral condylar defect model (4 mm in diameter and 10 mm in depth) was established in 32 10-month-old New Zealand white rabbits (male or female, weighing 4.0-4.5 kg), which were randomly divided into 4 groups (n=8); pure PMMA (group A), PBC I (group B), PBC II (group C), and PBC III (group D) were implanted in the bilateral femoral condylar defects, respectively. Gross observation were done after operation. X-ray films were taken after 1 week. At 3 and 6 months after operation, the bone cement specimens were harvested for mechanical test and histological examination. Four kinds of unplanted cement were also used for biomechanical test as control. Results All rabbits survived to the end of experiment. The X-ray films revealed the location of bone cement was at the right position after 1 week. Before implantation, at 3 months and 6 months after operation, the compressive strength and elastic modulus of groups C and D decreased significantly when compared with those of group A (P lt; 0.05), but no significant difference was found between groups C and D (P gt; 0.05); the compressive strength at each time point and elastic modulus at 3 and 6 months of group B decreased significantly when compared with those of group A (P lt; 0.05). Before implantation and at 3 months after operation, the compressive strength and elastic modulus of groups C and D decreased significantly when compared with those of group B (P lt; 0.05); at 6 months after operation, the compressive strength of group C and the elastic modulus of group D were significantly lower than those of group B (P lt; 0.05). The compressive strength and elastic modulus at 3 and 6 months after operation significantly decreased when compared with those before implantation in groups B, C, and D (P lt; 0.05), but no significant difference was found in group A (P lt; 0.05). At 3 months after operation, histological observation showed that a fibrous tissue layer formed between the PMMA cement and bone in group A, while chitosan particles degraded with different levels in groups B, C, and D, especially in group D. At 6 months after operation, chitosan particles partly degraded in groups B, C, and D with an amount of new bone ingrowth, and groups C and D was better than group B in bone growth; group A had no obvious change. Quantitative analysis results showed that the bone tissue percentage was gradually increased in the group A to group D, and the bone tissue percentage at 6 months after operation was significantly higher than that at 3 months within the group. Conclusion According to the weight percentage (W/W, %) of PMMA to bioglass to chitosan, PBCs made by the composition of 40 ︰ 50 ︰ 10 and 30 ︰ 60 ︰ 10 have better biocompatibility and biomechanical properties than PMMA cement, it may reduce the fracture risk of the adjacent vertebrae after vertebroplasty.
Objective To compare the maximum pull-out strength of the upper il iac screw and lower il iac screw with and without polymethylmethacrylate (PMMA) augmentation, and to provide the experimental evidences for the rational use of il iacscrews. Methods Ten intact human il ium from 5 donated cadavers with formal in embalmed were selected. The bone mineral density (BMD) of L1-4 of each cadaver was measured with a dual energy X-ray absorptiometry. The screws placed in the upper and lower il iac column were named as the upper and lower il iac screw, respectively. Using 70 mm length and 7.5 mm diameter screws with and without PMMA augmentation, 4 il iac screw technique models were sequentially establ ished and tested as follows: upper il iac screw (group A), upper il iac screw with PMMA augmentation (group B), lower il iac screw (group C), and lower il iac screw with PMMA augmentation (group D). Each il ium was mounted on a material testing machine with its position similar to standing. Under 2 000 cycl ic compressive loadings of 100-300 N to the screw, the maximum pull-out strength of il iac screw was measured. Results The BMD value of the 5 human cadavers was (0.88 ± 0.06) g/cm2. All the il iac screws were inserted into the screw tracts accurately as expected. No screw penetrations of acetabulum or cortex was not observed through visual inspection. There was no “halo” ring sign surrounding any screw after the 2 000 cycle loading. The maximum pull-out strengths of groupsA, B, C, and D were (964 ± 250), (1 462 ± 266), (1 537 ± 279), and (1 964 ± 422) N, respectively. Group D exhibited the highest maximum pull-out strength among the 4 groups (P lt; 0.05). No significant difference was detected between groups B and C (P gt; 0.05); however, groups B, C showed higher maximum pull-out strength than group A (P lt; 0.05). Conclusion The lower il iac screw offers significantly higher fixation strength than the upper il iac screw; PMMA augmentation could effectively increase the fixation strength of il iac screws and therefore could be appl ied in the salvage of il iac screw loosening.
Objective To evaluate the effects of intraocular lenses (IOL) of silicone and polymethylmethacrylate (PMMA) on posterior capsule opacification (PCO). Methods We searched MEDLINE (1966 to 2003), EMBASE (1980 to 2003), Cochrane Central Register of Controlled Trials (Issue 1, 2003) and CBMdisc (1979 to 2003). Only randomized controlled trials (RCTs) were identified. Two reviewers independently assessed the quality of the included trial and extracted data. The following outcomes were assessed: PCO index, percentage of neodymium: YAG (Nd: YAG) laser posterior capsulotomy and visual acuity after cataract surgery. RevMan 4.2 was used for meta-analysis.Results Nine RCTs including 672 eyes were included. In patients with senile cataract, the results of meta-analysis suggested that silicone lens were better than PMMA lens on PCO index (the pooled SMD=－0.92, 95%CI －1.19 to －0.64) and percentage of Nd: YAG (the pooled OR 0.35, 95%CI 0.22 to 0.57) with a statistically significant difference, but there was no significant difference on visual acuity (the pooled OR 1.22, 95%CI 0.43 to 3.50) after cataract surgery between silicone lens and PMMA lens. However, in patients with uveitic cataract, the results of meta-analysis showed that PMMA lens were better than silicone lens in visual acuity (the pooled OR 0.38, 95%CI 0.15 to 0.91) after cataract surgery with a statistically significant difference, but there was no significant difference on PCO index (SMD 0.23, 95%CI －0.59 to 1.05) and percentage of Nd: YAG (the pooled OR 1.82, 95%CI 0.47 to 6.95) between silicone lens and PMMA lens. Conclusions Current evidence indicates that silicone lens are superior to PMMA lens in reducing PCO. Further trials with high quality on methodology are required.