The Halo vest immobilizes the skull relative to the torso. Therefore is is ideal for controlling motion at upper cervical spine (occipitocervical junction and atlantoaxial junction. Halo immobilization allows for intercalated paradoxical motion in the subaxial cervical spine, and is therefore less ideal for lower cervical spine injuries.
Ivancic et al performed an invitro study measuring motion of cervical spine specimens with the variables of a normally applied halo, a loose vest, a loose superstructure, and an absent posterior uprights. They found that lateral bending was increased at the C6-7 level when there was a loose superstructure.
Johnson et al evaluated the ability of different cervical orthoses to control cervical range of motion at each cervical intervertebral joint. At the atlanto-axial joint, the halo vest restricted flexion-extension by 75%, which compared to only 45% by conventional cervical braces. The halo vest was less effective at controlling motion in the subaxial cervical spine below C3.
Bono et al reviews the literature and discusses the indications, contraindications, and complications for halo immobilization. They recommend the halo can be used for definitive treatment of C1 burst (Jefferson) fracture and type II and III odontoid fractures. Absolute contraindications include cranial fracture, infection, and severe soft-tissue injury at the proposed pin sites. They discuss the high mortality rate associated with using halo immobilization in the elderly population.
Illustration A shows the table from the Johnson articles that compares the effectiveness of different orthosis at controlling different types of motion (combined measurement from occiput to T1)
Answers 2,3,4,5: The halo vest is less effective at controlling motion in the subaxial cervical spine and cervicothoracic junction than at the atlanto-axial joint.
Ivancic PC, Beauchman NN, Tweardy L. Effect of halo-vest components on stabilizing the injured cervical spine. Spine (Phila Pa 1976). 2009 Jan 15;34(2):167-75.
PMID:19139667 (Link to Abstract)
Johnson RM, Hart DL, Simmons EF, Ramsby GR, Southwick WO. Cervical orthoses. A study comparing their effectiveness in restricting cervical motion in normal subjects. J Bone Joint Surg Am. 1977 Apr;59(3):332-9.
PMID:849944 (Link to Abstract)
Bono CM. The halo fixator. J Am Acad Orthop Surg. 2007 Dec;15(12):728-37. Review.
PMID: 18063713 (Link to Abstract)