Intrinsic and extrinsic forces determine the distortion of the split cricoid ring.

Objective: An anterior cricoid split (ACS) causes an immediate distortion of the cricoid cartilage resulting in an anterior gap due to retraction of the cut ends. The objective of this animal study is to investigate: (1) to what extent the distortion after ACS is influenced by non-cartilaginous structures like tunica elastica, membranes, ligaments and muscles, which are connected to the cricoid; (2) how distortion is changing with further development; (3) in what way the distortion is affected by scoring of the internal surface of the cricoid; and (4) whether an immediate or late injury-induced distortion is related to age.

Methods: Surgical interventions were performed in 20 young (8 weeks of age, 1300-1600 g) and 5 adult (28 weeks of age, 3500-4000 g) New Zealand White rabbits. The immediate effects were measured, and then the animals were followed for 20 weeks to study the long-term effects of the various procedures.

Results: (1) The gap, immediately following an ACS, increased after additional transection of the cricothyroid ligament and the cricotracheal membrane, and even more when the cricovocal membrane was elevated from the inner surface of the cricoid arch. (2) The degree of distortion after various interventions in young animals appeared to increase substantially during further growth. (3) When the above-mentioned successive surgical steps were combined with scoring of the internal surface of the cricoid arch, a marked malformation of the split cricoid did develop with warping of the cut ends in lateral direction and a latero-cephalic rotation, the latter due to the action of the cricothyroid muscles. (4) The immediate distortion appeared to be similar in young and adult animals. During a follow-up of 20 weeks, a progressive distortion of the split cricoid ring was observed in the young growing rabbits. In adult animals, no significant progression of the distortion was found.

Conclusions: The immediate and long-term distortion of the split cricoid is determined by the release of intrinsic forces of the cartilage, and extrinsic forces from non-cartilaginous structures like ligaments, muscles, membranes and tunica elastica.