title: An Assessment of the Medial Angle of Inserted Subaxial Cervical Pedicle Screw during Surgery: Practical Use of Preoperative CT Scanning and Intraoperative X-rays.
abstract: The most important factor for cervical pedicle screw placement (CPS) is creating a sufficient medial angle. We aimed to know the medial angle of the inserted subaxial CPS during surgery using intraoperative AP X-rays. From March 2012 to September 2014, we performed posterior cervical fusions using CPS on 75 patients, including a total of 389 CPS insertions. Using preoperative CT scanning, we determined the θlat(i.e., an angle between a vertical line and a line to connect the planned entry point and the axial middle point of the pedicle) and θmed(i.e., an angle between a vertical line and a line to connect a new medial entry point and the axial middle point of the pedicle; this angle was regarded as minimally acceptable and a safe medial angle). The actual inserted medial angle (θins) was checked and we determined whether it was between the θmedand θlatin the accurately placed CPS, and not in the laterally violated CPS. We measured the horizontal distance of the CPS body (l; using an intraoperative AP X-ray). If the actual screw length (L) was known, we could calculate the medial angle (θAP) as sin-1l / L. We checked the θAPand θinsfor all of the same levels. Intra- and inter-observer agreement was analyzed. Among 368 accurately inserted CPSs, we found that 360 of the θinsvalues were greater than or equal to the θmedon the same level (P <0.001). The intra-observer agreements were 0.781 and 0.847. The inter-observer agreements were 0.917 and 0.949. It was important that θinswas greater than or equal to the θmed. Our suggested formula, θAP= sin-1l / L, seems to be useful for predicting the medial angle of the inserted CPS and for comparing it with θmedduring surgery based on an AP X-ray and preoperative CT scan.
authors.affiliation: Department of Neurological Surgery, Asan Medical Center, University of Ulsan College of Medicine.
authors.forename: Hong Bum
authors.initials: HB
authors.lastname: Kim
authors.affiliation: Department of Neurology, Gangneung Asan Hospital, University of Ulsan College of Medicine.
authors.forename: Moon Kyu
authors.initials: MK
authors.lastname: Lee
authors.affiliation: Department of Neurological Surgery, Gyeongsang National University School of Medicine.
authors.forename: Young-Seok
authors.initials: YS
authors.lastname: Lee
authors.affiliation: Department of Anaesthesiology, Gangneung Asan Hospital, University of Ulsan College of Medicine.
authors.forename: Jun-Young
authors.initials: JY
authors.lastname: Sohn
authors.affiliation: Department of Emergency Medicine, Gangneung Asan Hospital, University of Ulsan College of Medicine.
authors.forename: Sang Ku
authors.initials: SK
authors.lastname: Jung
authors.affiliation: Department of Neurological Surgery, Gangneung Asan Hospital, University of Ulsan College of Medicine.
authors.forename: Jin Hoon
authors.initials: JH
authors.lastname: Park
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002574:Cervical Vertebrae; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D065289:Pedicle Screws; D011859:Radiography; D013122:Spinal Diseases / Q000000981:diagnostic imaging* / Q000209:etiology / Q000601:surgery*; D013123:Spinal Fusion; D025321:Surgery, Computer-Assisted; D014057:Tomography, X-Ray Computed; D055815:Young Adult
keywords: AP X-ray; CT scan; cervical pedicle screw; cervical spine; medial angle