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Describes the basic principle and parts of the screw and how it has been used throughout history, along with some examples of its modern-day uses.

Background Screw loosening is a commonly reported issue following spinal screw fixation and can lead to various complications. The initial cause of screw loosening is biomechanical deterioration. Previous studies have demonstrated that modifications in screw design can impact the local biomechanical environment, specifically the stress distribution on bone-screw interfaces. There are several different designs of screw tips available for clinically used pedicle screws; however, it remains unclear whether these variations affect the local stress distribution and subsequent screw anchorage ability. Methods This study conducted comprehensive biomechanical research using polyurethane foam mechanical tests and corresponding numerical simulations to investigate this topic. Models of pedicle screw-fixed osteoporotic polyurethane foam were created with two different clinically used screw tip designs (flat and steep) featuring varying tip lengths, taper angles, and diameters, as well as identical flank overlap areas and thread designs. The anchorage ability of the different models was assessed through toggle and pull-out test. Additionally, numerical mechanical models were utilized to compute the stress distributions at the screw and bone-screw interfaces in the different models. Results Mechanical tests revealed superior anchorage ability in models utilizing flat-tipped screws. Furthermore, numerical modeling indicated improved anchorage ability and reduced stress concentration tendency in these models. Conclusion Changes in screw tip design can significantly impact the biomechanical anchoring capability of screws. Specifically, flatter tip pedicle screws may mitigate the risk of screw loosening by alleviating stress concentration on bone-screw interfaces.

Purpose S1 pedicle screws are often associated with loosening and breakage. Conventional iliac screw (CIS) or S2 alar-iliac (S2AI) techniques improve stability but have their own drawbacks. The percutaneous modified iliac screw (PMIS) technique was developed to overcome these issues with a less invasive approach. Methods This study is a retrospective case series conducted by a single surgeon. The PMIS technique uses two virtual fluoroscopic reference lines to avoid critical structures and allows percutaneous insertion of the screw into the intra-iliac cancellous corridor. Between 2014 and 2025, ten patients (2 males, 8 females; mean age 59.9 years) underwent sacropelvic fixation using the PMIS approach. Indications included spinal metastasis ( n  = 8), infection ( n  = 1), and degeneration ( n  = 1). Radiographs were used to evaluate instrumentation, complications, and spinopelvic parameters (PI, PT, SS) before surgery and at the final follow-up. Results No infection, screw prominence, or screw-related complications were noted. One revision was needed due to progression of a spinal infection unrelated to the PMIS. Radiographic measurements of PI, PT, and SS remained largely unchanged between preoperative and final follow-up. Conclusion PMIS provides a safe and minimally invasive option for sacropelvic fixation. It avoids the limitations of CIS and S2AI while reducing soft tissue dissection. Although early results are promising, larger studies are needed to validate the effectiveness and broader clinical use of this method.

\"Winding Around explores the benefits and uses of the screw. RobbO and RobbEE learn how to hold materials together using a screw, and how to use it to lift up loads and raise water.\"-- Provided by publisher.

PurposePedicle screw loosening is a common and significant complication after posterior spinal instrumentation, particularly in osteoporosis. Radiolucent carbon fiber-reinforced polyetheretherketone (CF/PEEK) pedicle screws have been developed recently to overcome drawbacks of conventional metallic screws, such as metal-induced imaging artifacts and interference with postoperative radiotherapy. Beyond radiolucency, CF/PEEK may also be advantageous over standard titanium in terms of pedicle screw loosening due to its unique material properties. However, screw anchorage and loosening of CF/PEEK pedicle screws have not been evaluated yet. The aim of this biomechanical study therefore was to evaluate whether the use of this alternative nonmetallic pedicle screw material affects screw loosening. The hypotheses tested were that (1) nonmetallic CF/PEEK pedicle screws resist an equal or higher number of load cycles until loosening than standard titanium screws and that (2) PMMA cement augmentation further increases the number of load cycles until loosening of CF/PEEK screws.MethodsIn the first part of the study, left and right pedicles of ten cadaveric lumbar vertebrae (BMD 70.8 mg/cm3 ± 14.5) were randomly instrumented with either CF/PEEK or standard titanium pedicle screws. In the second part, left and right pedicles of ten vertebrae (BMD 56.3 mg/cm3 ± 15.8) were randomly instrumented with either PMMA-augmented or nonaugmented CF/PEEK pedicle screws. Each pedicle screw was subjected to cyclic cranio-caudal loading (initial load ranging from − 50 N to + 50 N) with stepwise increasing compressive loads (5 N every 100 cycles) until loosening or a maximum of 10,000 cycles. Angular screw motion (“screw toggling”) within the vertebra was measured with a 3D motion analysis system every 100 cycles and by stress fluoroscopy every 500 cycles.ResultsThe nonmetallic CF/PEEK pedicle screws resisted a similar number of load cycles until loosening as the contralateral standard titanium screws (3701 ± 1228 vs. 3751 ± 1614 load cycles, p = 0.89). PMMA cement augmentation of CF/PEEK pedicle screws furthermore significantly increased the mean number of load cycles until loosening by 1.63-fold (5100 ± 1933 in augmented vs. 3130 ± 2132 in nonaugmented CF/PEEK screws, p = 0.015). In addition, angular screw motion assessed by stress fluoroscopy was significantly smaller in augmented than in nonaugmented CF/PEEK screws before as well as after failure.ConclusionsUsing nonmetallic CF/PEEK instead of standard titanium as pedicle screw material did not affect screw loosening in the chosen test setup, whereas cement augmentation enhanced screw anchorage of CF/PEEK screws. While comparable to titanium screws in terms of screw loosening, radiolucent CF/PEEK pedicle screws offer the significant advantage of not interfering with postoperative imaging and radiotherapy.Graphical abstractThese slides can be retrieved under Electronic Supplementary Material.

This was a prospective randomized controlled trial study. To elucidate clinical and radiographic outcomes and complications of cortical bone trajectory (CBT)-screw fixation in patients with osteoporosis at 24-month follow-up and to compare the results with those after transforaminal lumbar interbody fusion (TLIF) using traditional pedicle screw (PS) fixation. We enrolled 124 patients and randomly assigned them to two groups (each group had 62 participants). The primary outcome was fusion rate. Secondary outcomes were VAS, Oswestry Disability Index (ODI), and Japanese Orthopaedic Association (JOA) scores, operation duration, incision length, estimated blood loss, drainage volume, radiological outcomes, and complications. At the 6- and 12-month follow-up points, similar fusion rates were observed based on CT scans in both groups ( =0.583 and 0.583). CBT provided significantly better short-term functional status at 3 months postoperation on ODI and JOA scores ( =0.012 and 0) and similar improvements in pain intensity and functional status at other follow-up points. In addition, CBT resulted in significantly better surgical characteristics. Notably, CBT fixation led to lower incidence of screw loosening ( =0.006). CBT-screw fixation for single-level lumbar fusion in patients with osteoporosis provided improvement in clinical symptoms comparable to that of TLIF using PS fixation. Significantly better lumbar stability was found in the CBT group. We suggest that CBT-screw fixation is a reasonable and superior alternative to PS in TLIF in osteoporosis. ChiCTR1900022658. April 20, 2019.

PurposeTo compare the 2-year minimum postoperative results of posterior correction and spinal arthrodesis using translational correction with hybrid (sublaminar bands on concave side and pedicle screw) constructs versus correction with intermediate density pedicle screw-only constructs in the treatment of AIS (Lenke 1).MethodsA total of 37 patients with AIS at single institutions who underwent posterior spinal arthrodesis pedicle screw with sublaminar bands at the apex (19 patients) (Group A) or pedicle screw-only (18) constructs (Group B) were selected and matched according to similar age at surgery 13.8 years (Group A) and 14.3 years (Group B), similar arthrodesis area 12.3 (Group A) and 11.5 (Group B), all curves Lenke type 1 with similar pre-op curve 54° (Group A) and 57° (Group B). Patients were evaluated pre-op, immediately post-op, and at min 2-year follow-up according to radiographic curve correction, operating time, intraoperative blood loss, and f.u. loss of correction.ResultsThe average curve correction was 65.6% in sublaminar group and 68% in pedicle screw group. At 2-year follow-up, loss of the major curve correction was 2% in sublaminar group compared to 3% in pedicle screw group. Postoperative coronal and sagittal balance was similar in both groups. Operating time averaged 200 min (Group A) and 180 min (Group B). Intraoperative blood loss was significantly different in both groups 700 ± 160 cc in sublaminar group and 630 ± 150 cc in pedicle screw group. There were no neurologic complications in both groups.ConclusionThe two groups offer similar curve correction without neurologic complications in the surgical treatment of AIS (Lenke 1). The use of sublaminar bands on the apex (concave side) can be a valid fixation in the presence of hypoplastic pedicle, can reduce the thoracic hypokyphosis and derotate the vertebra but had more blood loss comparing to pedicle screws alone.Graphical abstractThese slides can be retrieved under Electronic Supplementary Material.