The global end-ranges of neck flexion and extension do not represent the maximum rotational ranges of the cervical intervertebral joints in healthy adults - an observational study

Abstract

Background: In clinical diagnosis, the maximum motion of a cervical joint is thought to be found at the joint's end-range and it is this perception that forms the basis for the interpretation of flexion/extension imaging studies. There have however, been representative cases of joints producing their maximum motion before end-range, but this phenomenon is yet to be quantified.

Purpose: To provide a quantitative assessment of the difference between maximum joint motion and joint end-range in healthy subjects. Secondarily to classify joints into type based on their motion and to assess the proportions of these joint types.

Study design: This is an observational study.

Subject sample: Thirty-three healthy subjects participated in the study.

Outcome measures: Maximum motion, end-range motion and surplus motion (the difference between maximum motion and end-range) in degrees were extracted from each cervical joint.

Methods: Thirty-three subjects performed one flexion and one extension motion excursion under video fluoroscopy. The motion excursions were divided into 10% epochs, from which maximum motion, end-range and surplus motion were extracted. Surplus motion was then assessed in quartiles and joints were classified into type according to end-range.

Results: For flexion 48.9% and for extension 47.2% of joints produced maximum motion before joint end-range (type S). For flexion 45.9% and for extension 46.8% of joints produced maximum motion at joint end-range (type C). For flexion 5.2% of joints and for extension 6.1% of joints concluded their motion anti-directionally (type A). Significant differences were found for C2/C3 (P = 0.000), C3/C4 (P = 0.001) and C4/C5 (P = 0.005) in flexion and C1/C2 (P = 0.004), C3/C4 (P = 0.013) and C6/C7 (P = 0.013) in extension when comparing the joint end- range of type C and type S. The average pro-directional (motion in the direction of neck motion) surplus motion was 2.41° ± 2.12° with a range of (0.07° -14.23°) for flexion and 2.02° ± 1.70° with a range of (0.04°-6.97°) for extension.

Conclusion: This is the first study to categorise joints by type of motion. It cannot be assumed that end-range is a demonstration of a joint's maximum motion, as type S constituted approximately half of the joints analysed in this study.

Keywords: Cervical vertebrae; Fluoroscopy; Maximum motion; Neck; Range of motion.

Fig. 1

Joint motion types. Three types of cervical joint motion 1) C 2) S and 3) A. The joint motion type C illustrates the common perception of joint motion from upright along the purple line to end-range. Type C joint motion has no pro-directional surplus motion. This type of motion is documented in almost half of all cervical joints. Type S joint motion is illustrated by the red line, and beyond end-range by the green line. Almost half of the joint motion in this study was type S. The green returning arrow illustrates that the motion passes the point of end-range, before the end of neck motion, and continues to the point of maximum surplus joint motion. It then moves anti-directionally towards the end-range position. Type A joint motion terminates in the opposite direction to that of head motion. This type of joint motion is demonstrated by approximately 6% of all cervical joints and is illustrated by the blue line

Fig. 2

Cervical extension motion for an individual subject. C0/C1, C4/C5 and C5/C6 are type C joints, producing maximum motion at end-range. C1/C2, C2/C3 and C3/C4 is are type S joints, reaching maximum motion in the 7th, 5th and 8th epochs respectively. C6/C7 is a type A joint, terminating its motion anti-directionally

Fig. 3

Average flexion and extension joint ROM. * Indicates a significant difference when comparing average flexion and extension. ¤ indicates a significant difference in the end-range motion of type S and type C