POSTMORTEM STUDIES

Independent studies, in countries as respectively remote as Sweden³ and Australia,^4–6 have provided similar conclusions, which have now been systematically reviewed.⁷ Both sets of studies harvested the cervical spines of victims of fatal motor vehicle accidents. The Australian studies included victims who survived for various periods after the accident. The pathology of major head injury and suboccipital injuries was ignored. Instead, the studies focused on other lesions, which were not the cause of death, but which indicated what could happen to the cervical spine, in a motor vehicle accident.

The same spectrum of injuries was consistently observed (Fig. 53.1). They included tears of the anterior anulus fibrosus, avulsion of the anterior anulus, contusions of the posterior anulus, tears or avulsions of the capsules of the zygapophyseal joints, contusions of the meniscoids of these joints, intra-articular hemorrhage, fractures of the articular cartilage, and subchondral or greater fractures of the articular pillars. Conspicuously, virtually none of these lesions was evident on plain radiographs of the cervical spine, taken postmortem, even when read retrospectively with the knowledge that a lesion was present.^3–6

Fig. 53.1 The possible lesions after minor injuries to the cervical spine.

These lesions are consistent with the known biomechanics of whiplash injury.² Anterior separation of the vertebral bodies could cause tears or avulsions of the anterior anulus fibrosus. Posterior impaction of the zygapophyseal joints could cause articular and subarticular fractures, or contusions of the intra-articular meniscoids. Excessive separation of the zygapophyseal joints, in extension or in flexion,⁸ could cause tears of the joint capsules.

The nature of these lesions is such that they should not be evident on conventional imaging. Injuries to fibrous connective tissues will not be seen on plain radiographs or CT. They cannot be seen on conventional MRI. In the future, perhaps high-resolution MRI or spectroscopic MRI might be able to resolve them, but studies in this regard have not yet been completed.

PATHOPHYSIOLOGY

The nature of connective tissue injuries is that they are likely to be painful. Capsular tears, small fractures, and intra-articular hemorrhage are all causes of pain elsewhere in the musculoskeletal system. There is no reason why they should not be sources of pain if and when they occur in the neck.

For these lesions to be symptomatic the structures in which they occur have to be innervated. In the cervical spine, the anuli fibrosi of the intervertebral discs are innervated, and the zygapophyseal joints are innervated. The discs receive their innervation from the vertebral nerve, the sympathetic trunks, and the sinuvertebral nerves.⁹ The zygapophyseal joints are innervated by the medial branches of the cervical dorsal rami.¹⁰

Because they are innervated, these structures can become sources of pain, even though the lesions that cause that pain are effectively invisible. It is the pain that implies the presence of the injury; and the site of injury can be determined by pinpointing the source of pain.

CLINICAL STUDIES

Pinpointing a source of pain requires a diagnostic test that can be applied in patients, who cooperate by reporting if their accustomed pain is uniquely provoked by the test or is relieved by it. The available procedures differ according to the target structure. Intervertebral discs can be tested by discography. Zygapophyseal joints can be tested with medial branch blocks.