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Table 3 Accuracy rate classifications for screw insertion

From: Accuracy and safety of C2 pedicle or pars screw placement: a systematic review and meta-analysis

Name of classification Year Description Studies used the classification
Gertzbein and Robbins [88] 1990 Grade 0, when a screw was placed inside the bone; grade I, screw perforation of the cortex within 2 mm; grade II, screw perforation from 2 to 4 mm; and grade III, screw perforation of more than 4 mm. In some of articles, this classification was modified [28, 56]. Grade 0 is considered the accuracy of in C2 screw placement [28]. [17, 28, 29, 50, 52, 56, 59, 63, 67, 68, 75, 82, 84, 87]
Laine et al. [89] 2000 Based on CT images, in this classification, screw position was staged as screw inside the pedicle or perforation of the pedicle cortex by up to 2 mm, from 2 to 4 mm, from 4 to 6 mm, or by more than 6 mm. Type I and type II were categorized as acceptable placement. [83]
Rao et al. [90] 2002 Each screw position was assigned a grade from 0 to 3, as follows: grade 0 reflected no perforation of the pedicle; grade 1 indicated less than 2 mm of perforation of the pedicle; grade 2 represented 2–4 mm of perforation of the pedicle; and grade 3 reflected perforation greater than 4 mm. Grades 2 and 3 insertions were judged to be major perforations. Overall, it is considered a perforation of less than 2 mm to be satisfactory. [62]
Neo et al. [91] 2005 Screw positions were classified into four grades: grade 0, no perforation, and the screw was completely contained in the pedicle; grade 1, perforation < 2 mm (that is, less than half of the screw diameter); grade 2, perforations ≥ 2 mm but < 4 mm; and grade 3, perforation ≥ 4 mm(complete perforation). The screw was classified as grade 0 be acceptable. [27, 34, 40, 43, 45, 46, 48, 53, 54]
Upendra et al. [92]. It was modified by Park et al. [79] 2008 Type I, ideal placement—screw threaded completely within bony cortex; type IIa, acceptable placement—< 50% of the diameter of the screw violating surrounding cortex and screw protrusion of < 1 mm from the anterior cortex for pedicle and pars screws; type IIb, relatively acceptable placement—screw violating < 33% of the diameter of the C2 transverse foramen (TF); type IIc, relatively unacceptable placement—screw violating ≥ 33% of the diameter of the C2 TF or ≥ 50% of diameter of screw violating surrounding cortex; type III, unacceptable placement—clear violation of TF or spinal canal; regardless of clinical neurovascular complications. Overall, types I, IIa, and IIb were categorized as acceptable placement and types IIc and III as unacceptable placement. [33, 77, 79]
Sciubba et al. [19] 2009 It is described by location (lateral, medial, inferior, and superior) and percentage of screw diameter over cortical edge (0 = none; grade I = < 25% of screw diameter; grade II = 26–50%; grade III = 51–75%; and grade IV = 76–100%). Type 0 was categorized as acceptable placement. [5, 19, 47, 73]
Yukawa et al. [21] 2009 The accuracy of the placement of the pedicle screws into the medial/lateral pedicle walls was evaluated on axial CT scans (2 mm slices), whereas superior/inferior pedicle wall screw location was examined on oblique radiographs. Incorrect screw placement was classified as either screw exposure or pedicle perforation. A screw was exposed if it broke the pedicle wall, but more than 50% of the screw diameter remained within the pedicle. A pedicle perforation occurred if a screw breached the pedicle wall, and more than 50% of the screw diameter was outside the pedicle. [21]
Wang et al. [85] 2010 This classification was based on axial plane, para-sagittal plane, and coronal plane. The grading has been described elsewhere in detail [85]. [85]
Kawaguchi et al. [40] 2012 Grade 0, the screw was completely located in the vertebral pedicle; grade I, the screw penetrated the pedicle bone cortex < 2 mm without complications; grade II, the screw penetrated the pedicle bone cortex > 2 mm without complications; and grade III, complications related to screw placement occurred, such as nerve and vertebral artery injuries. Grade 0 was considered to be the correct location of pedicle screws and safe placement. [70, 71]
Uehara et al. [49]. 2014 The screw insertion status was classified as grade 1 (no perforation), indicating that the screw was accurately inserted in pedicle; grade 2 (minor perforation), indicating perforation of less than 50% of the screw diameter; and grade 3 (major perforation), indicating perforation of 50% or more of the screw diameter. The screw was classified as grade 1 be acceptable. [49, 62]
Smith et al. [93] 2016 On postoperative CT scans, type I was defined as ideal placement without cortical violation; type II was an acceptable placement with less than half the diameter of the screw violating the surrounding cortex and less than 1 mm protrusion from the anterior cortex; and type III is an unacceptable placement with clear violation of the transverse foramen or spinal canal. [80]
Hlubek et al. [7] 2018 Grade A, screw completely confined within cortical surfaces; grade B, transverse foramen violation with the screw obstructing 1–25% of the foramen; grade C, transverse foramen violation with the screw obstructing 26–50% of the foramen; grade D, transverse foramen violation with the screw obstructing 51–75% of the foramen; grade E, transverse foramen violation with the screw obstructing 76–100% of the foramen; grade M, medial breach into the spinal canal. Grades A and B were determined to be acceptable placement, and Grades C–E and M were determined to be unacceptable. [81]