Increased stability due to symmetric cement volume in augmented pedicle screws? A biomechanical study.

Pedicle screw instrumentation has become "state of the art" in surgical treatment of many spinal disorders. Loosening of pedicle screws due to poor bone mineral density is a frequent complication in osteoporotic patients. As prevalence of osteoporosis and spinal disorders are increasing with an aging demographic, optimizing the biomechanical properties of pedicle screw constructions and therefore outcome after spinal surgery in osteoporotic patients is a key factor in future surgical therapy. Therefore, this biomechanical study investigated the stability of polymethylmethacrylate (PMMA)-augmented pedicle screw-rod constructions under a deviating distribution of PMMA applied to the instrumentation in osteoporotic human cadaveric vertebrae. We showed that PMMA-augmented pedicle screw-rod constructions tend to be more stable than those with non-augmented pedicle screws. Further, there appears to be a larger risk of screw loosening in unilateral augmented pedicle screws than in non-augmented, therefore a highly asymmetrically distributed PMMA should be avoided.

The impact of odontoid screw fixation techniques on screw-related complications and fusion rates: a systematic review and meta-analysis.

PURPOSE: The primary goal of this study was to conduct a systematic review and meta-analysis of articles focused on odontoid screw fixation (OSF) and screw-related complications or non-union rates. METHODS: We conducted a systematic review of the PubMed and Crossref databases between January 1982 and December 2019. Inclusion criteria comprised detailed descriptions of the surgical technique and screw-related complications (screw cut-out, loosening, breakage, malposition) or fusion rates. RESULTS: The initial selection consisted of 683 abstracts. A total of 150 full texts were chosen for detailed study, and 83 articles were included in the analysis. The point estimates for screw-related complications were as follows: 1. screw malposition frequency-4.8%; 2. screw cut-out rate-5.0%; 3. screw loosening/pull-out-3.8%; and 4. screw fracture rate-3.1%. The point estimate for the non-union rate was 9.7%. Statistical analysis of the screw-related complications rate based on surgical technique details was also performed CONCLUSIONS: Double-screw OSF performance in elder patients resulted in a higher risk of post-operative screw cut-out. In other cases, the development of screw-related complications did not depend on the method of intraoperative head fixation, selection of the implant entry point for OSF, type of the used screws, or cannulated instruments application. The outcomes of single-screw fixation through the anterior lip of the C2 vertebra were comparable to other techniques of OSF. Further, statistically reliable studies should be carried out to identify the optimal technique of OSF.

Late screw-related complications in locking plating of proximal humerus fractures: A systematic review.

Locking plating is a common surgical treatment of proximal humeral fractures with satisfactory clinical results. Implant-related complications, especially screw-related, have been reported, however, the lack of information regarding their onset, used surgical technique, complexity of the fracture, bone quality etc., prevents from understanding the causes for them. The aim of this systematic review is to identify the potential risk factors for late screw complications by gathering information about the patient characteristics, comorbidities, fracture types, surgical approaches and implant types. A PubMed search was performed using humerus, fractures, bone and locking as keywords in clinical papers written in English. All abstracts and manuscripts on distal or humerus shaft fractures, and those on proximal humerus fractures without any or with only iatrogenic complications were excluded. One hundred studies met the inclusion criteria, resulting in 33% of the reported cases having at least one complication, with 11% of all complications being screw-related. Most of the latter were secondary screw perforations and screw cut-outs, being predominantly linked to poor bone quality, while screw loosening and retraction were found less frequently as a result of locking mechanism failure. Overall, the amount of information for complications was limited and screw perforation was the most frequent screw-related complication, mostly reported in female patients older than 50 years, following four-part or AO/OTA type C fractures and detected four weeks postoperatively. The sparse information in the literature could be an indicator that the late screw complications might have been under-reported and under-described, making the understanding of the screw-related complications even more challenging.

Potential intraoperative factors of screw-related complications following posterior transarticular C1-C2 fixation: a systematic review and meta-analysis.

PURPOSE: This study aimed to evaluate the impact of several factors, including patients' intraoperative position, intraoperative visualization technique, fixation method, and type of screws and their parameters, on the frequency of intraoperative screw-associated complications in posterior transarticular C1-C2 fixation. METHODS: A systematic review of the PubMed database between January 1986 and March 2018 was performed. The key inclusion criteria comprised detailed descriptions of the surgical technique and post-operative screw-associated complications. RESULTS: The initial search resulted in 1041 abstracts, and a total of 54 abstracts were included in the present study. The overall number of operated patients was 2306. In this group, 4439 screws were inserted. The rate of screw-associated complications during the different time periods was estimated upon meta-analysis. Statistical analysis of the screw malposition rate, vertebral artery injury rate, screw breakage rate based on patients' intraoperative position, intraoperative visualization technique, fixation method, and type of implants and their parameters was also performed. CONCLUSIONS: The factors that help reduce the rate of screw-associated complications include the intraoperative application of biplanar fluoroscopy or neuronavigation system, the use of 4 mm or thicker lag screws, and screw insertion through contraincisions using cannulated ported instruments. On the other hand, the potential risk factors of screw-associated complications include inadequate intraoperative head fixation using skeletal traction, uniplanar fluoroscopy-guided screw insertion, screw insertion using the posterior midline approach, and the use of 3.5 mm or thinner full-threaded screws. These slides can be retrieved under Electronic Supplementary Material.