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Updated: Jun 17, 2026
Clinical Application of Microscope-Assisted Minimally Invasive Anterior Lumbar Interbody Fusion
Published on: June 16, 2023
Measurement of a posterior occipitocervical fusion angle
Ryan U Riel1, Matthew C Lee, John S Kirkpatrick
1Department of Orthopaedic Surgery, University of Florida, Shands-Jacksonville, FL 32209, USA.
Study Design:
A method for evaluating occipitocervical neutral position is described.
Objective:
To describe and measure a posterior occipitocervical angle (POCA) in normal subjects that can be used to guide contouring of fusion implants to achieve occipitocervical neutral fusion and for use in standardized testing of occipitocervical constructs.
Summary Of Background Data:
The goal of occipitocervical fusion is to fuse the head in an ideal functional position. Several methods of estimating occipitocervical neutral position have been described and tested, yet none has been proven superior. An ideal method would easily and reproducibly aid in evaluating occipitocervical position intraoperatively and potentially aid in the design and testing of implant constructs.
Methods:
Fifteen adult lateral cervical spine radiographs taken in occipitocervical neutral position and interpreted as normal by an experienced radiologist were studied. Analysis consisted of measurement of the POCA. The POCA is defined as the angle formed by the intersection of a line drawn tangential to the posterior aspect of the occipital protuberance and a line determined by the posterior aspect of the facets of the third and fourth cervical vertebrae.
Results:
The mean POCA was 109.7 degrees with a SD of 5.7 degrees. Compilation of the data revealed a normal distribution of measurements where 80% of the POCA values were between 101 and 119 degrees.
Conclusions:
POCA is a simple measurement that may be valuable as an intraoperative tool during occipitocervical fusion and may aid the design and testing of fusion implants and their application in the operating room.
