Applied anatomy of screw placement via the posterior arch of the atlas and anatomy-based refinements of the technique.
OBJECTIVE
To present a method of posterior arch and lateral mass screw (PALMS) insertion and to prove its feasibility.


METHODS
Four formalin-fixed specimens and 40 macerated atlas vertebras were used to describe the relevant anatomy. The height of the posterior arch was measured on 42 consecutive patients using standard CT of the cervical spine. The operative technique and the special CT reconstructions used for preoperative planning are described. Eight patients underwent posterior fixation using this technique.


RESULTS
We described the relevant anatomy and important anatomical landmarks of the posterior arch of the atlas. PALMS placement was modified according to these anatomical findings. Fifteen PALMSs were placed in eight patients using this technique without vascular or neural injury.


CONCLUSIONS
It is feasible to place PALMS using the described technique. CT angiography is of crucial importance for preoperative planning using the described special reconstructions. The arch posterior to the lateral mass (APLM) is defined as the bone stock situated posterior to the lateral mass, respecting its convergence. The ideal entry point for a PALMS is on the APLM above the center of the converging lateral mass. A complete or incomplete ponticulus posticus and a retrotransverse foramen or groove can be used as an accessory landmark to refine the entry point.
Department of Orthopaedic Surgery, Klinikum Esslingen, Hirschlandstrasse 97, 73730, Esslingen a.N., Germany. gbodon@gmail.com.|Laboratory for Applied and Clinical Anatomy, Department of Anatomy, Histology and Embriology, Semmelweis University Budapest, Tuzolto u. 58, Budapest, Hungary. gbodon@gmail.com.|Clinical Anatomy Tübingen, University of Tübingen, Elfriede-Aulhorn-Str. 8, 72076, Tübingen, Germany. gbodon@gmail.com.
Gergely
G
Bodon
Laboratory for Applied and Clinical Anatomy, Department of Anatomy, Histology and Embriology, Semmelweis University Budapest, Tuzolto u. 58, Budapest, Hungary.
Andras
A
Grimm
Clinical Anatomy Tübingen, University of Tübingen, Elfriede-Aulhorn-Str. 8, 72076, Tübingen, Germany.
Bernhard
B
Hirt
Department of Radiology, Klinikum Esslingen, Hirschlandstrasse 97, 73730, Esslingen a.N., Germany.
Harald
H
Seifarth
Department of Neurosurgery, Neurocenter, Regional Hospital of Liberec, Husova Str. 10, 46063, Liberec, Czech Republic.
Pavel
P
Barsa
D000328:Adult; D001863:Bone Screws; D002102:Cadaver; D002339:Carotid Arteries / Q000000981:diagnostic imaging; D001270:Cervical Atlas / Q000033:anatomy & histology* / Q000601:surgery; D002574:Cervical Vertebrae / Q000033:anatomy & histology / Q000293:injuries / Q000601:surgery; D000072226:Computed Tomography Angiography; D005240:Feasibility Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D019919:Prosthesis Implantation / Q000379:methods; D016103:Spinal Fractures / Q000473:pathology / Q000601:surgery; D013123:Spinal Fusion / Q000295:instrumentation / Q000379:methods; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome; D014711:Vertebral Artery / Q000000981:diagnostic imaging
Atlantoaxial fixation; Atlas; Atlas anatomy; Atlas pedicle screw; Posterior arch screw