Spinal injuries may be considered under three headings: 1. Injuries, mainly to non-bony tissues, in which the spine remains stable. 2. Injuries which make the spine sufficiently unstable to put the spinal cord or nerve roots at risk. 3. Injuries of the vertebral column with gross neurological damage and imminent deformity. Minor injuries in the first category far outnumber the others. This is not to imply that there is a direct relationship between the severity of musculoskeletal trauma and the amount of neurological damage. The cord can be transected without fracture or dislocation and a severely fractured spine may leave the cord unharmed, though clearly at risk (Holdsworth 1963, 1970; Roaf, 1976; Bodnar, 1977; Vigouroux et al 1978).
Fractures vary greatly in severity, some occurring without symptoms at the time of injury or later. Similarly with non-bony injuries: often the onset of pain is delayed for a day or so after injury. There are two reasons for this. First, there is an inhibitory mechanism available on the field of battle which prevents the painful stimuli from being transmitted to the cortex for recognition; and secondly, the intervertebral disc and the facets of the apophyseal joints are not supplied with nerves and can thus be injured without pain. There is another category of back or neck injury altogether in which there is an unexpected onset of the symptoms of an injury in the absence of a truly accidental occurrence, often when bent down. In these cases part of the vertebral column or its connective tissue support have become unduly susceptible to injury. This can arise because of degenerative change. It can also occur after exposure to ‘conditioning’ factors: for example, loading prolonged enough to produce ‘creep-effects’ – stiffening the spine and making it less capable of absorbing energy.
Non-bony injuries can also be severe. If the ligaments of the neural arch of the vertebra are ruptured the column is unstable even in the absence of fracture or dislocation. Moreover, one of the most common reasons for disability after a non-bony injury is the consequent mechanical irritation of the nerve roots. The reason for this wide spectrum is the proximity of nervous, bony and connective tissue in a relatively confined space (Figs. 25/1 and 25/2). This is why it may be vital to be able to distinguish between the injury which is stable and the one which is not. Any suspicion of local pain and weakness or numbness in the limbs following injury must be treated with respect. Because of the risk of converting a serious injury into a disaster, the patient must be handled with the greatest care. This caveat applies with equal force to patients who are unconscious or those with head injury because the force required to injure the head is in many cases more than enough to damage the neck at the same time.
Prevention of spinal injuries depends on an understanding of the biomechanics of the spine and of the causative mechanism; and on supervision wherever obvious dangers abound, for example at swimming baths or in contact-sports. Recovery after injury (especially where nervous tissue has been at risk) depends on the speed with which possibility of injury is appreciated, on the skill with which first aid is applied and the patient then transported, as well as on the efficiency of management of the diagnostic and therapeutic services.
The strength of the vertebral column
Stripped of its muscles and ligaments the spine is an unstable structure but the vertebral column together with its supporting tissues serve a number of mechanical functions. First of all they form a highly mobile structure. They protect the spinal cord and nerve roots from direct injury. Moreover they are able to withstand considerable compressive, tensile, shearing and torsional forces. All the tissues of the spine are plastic; that is to say they deform when stress is applied. When, therefore, the spine is subjected to impact on falling or being struck some of the energy can be dissipated safely into plastic deformation and some into intervertebral motion – provided that the spine has not been unduly stiffened by age, disease or any other cause.
The spine is relatively resistant to injury when exposed to single modes of force such as purely flexor, extensor or compressive force, but more susceptible if the modes are combined or if there is a torsional component (Roaf, 1960; Holdsworth, 1970). In addition, the strength of the spine depends very much on the time factor, being inversely proportional to the duration of the applied load (Perey, 1957).
When the compressive force exceeds the osmotic pressure of the intervertebral disc, ‘creep-effects’ take place. Tissue fluid is expelled, the disc narrows and stiffens; and the dynamic characteristics of the intervertebral joint-complex are modified accordingly (Kazarian, 1975). Creep-effects are not produced only by ‘excessive’ loading: loss of vertebral height has been recorded in healthy young male adults after loading the shoulders for 20 minutes with 9kg (Fitzgerald, 1972). Creep-effects are accelerated if the loaded spine is then exposed to vibration (Kazarian, 1972) – the phenomenon of ‘vibro-creep’.
When the applied force is of brief duration, the probability of injury is related to the magnitude of peak acceleration and to the jerk or rate of increase of acceleration (Hodgson et al, 1963). The risk of injury after a single, rapid axial loading depends on where the force is applied, on the constraints on the body after application as well as the characteristics of the individual spine. The probability of fracture after ejection from a fighter aircraft at, say, 200ms-2 may be as much as 1 in 5. The risks are less, though still far from negligible in parachuting where the deceleration on landing is of the order of 50 to 60ms’2 (Murray-Leslie et al, 1977). In parachuting such loadings are isolated. In sports such as cross-country motor-cycling or power-boat racing the frequency of impact can be expected to cause vibro-creep, susceptibility to injury increasing throughout the duration of exposure (Allen 1976).
The ‘conditioning’ factors which make back injury more likely are therefore prolonged static loading, vibratory stress and repetitive impacts and shocks. Unhappily there are too few valid data to indicate safe limits for any of these hazards, and none for the periods of recovery which should be allowed. Individual capacity for spinal stress varies greatly, depending on the size and physical characteristics of the vertebral column, on muscular strength, experience and skill and on the presence or absence of degenerative changes and other abnormalities.
The biomechanics of the spinal canal
Understanding spinal mobility entails more than a knowledge of the kinematics. In the context of spinal injuries it is important to note the effects of motion on the tissues within the spinal canal: on the spinal meninges, cord and nerve roots. The normal range of movement imposes linear and volumetric changes on the canal and the tissues within it must adapt accordingly.
On fully flexing the spine the cervical spinal canal is increased in length by 20 to 30 per cent compared with full extension, the increase being greater on the posterior than the anterior wall of the canal .
Likewise on lateral flexion, the convex side of the canal becomes longer than the concave. The spinal meninges are thereby stretched on flexion, further stretched on the convex side on lateral flexion and pulled tight by added rotation. The spinal dura mater (the outer meningeal layer forming the tube enclosing the subarachnoid space, cord and nerve roots) is relatively inextensible; on extension it is lax and when stretched by flexion tends to follow the shortest route within the canal. The cord and nerve roots are semi-fluid and readily deformable. Thus the cord becomes longer and narrower in cross-section when stretched. Similar mechanical changes in the lumbar region impose comparable changes on the lumbar spinal dura and nerve roots likewise on cord and dura in the thoracic spine though mobility there is less. The effects are not locally restricted: the increased tension in cord and dura on flexing the neck is transmitted caudally and are detectable in the lumbar region (Breig, 1978) .
Changes in the length of the canal are accompanied by changes in its lumen. The posterior part of the disc and the ligamenta flava are stretched on flexion but in extension are lax and tend to bulge into the canal, so making it narrower.
The significance of these changes is twofold. First, an injured spinal cord or nerve root may be further damaged by flexion of the neck. At the site of a fracture or dislocation there may be oedema of soft tissues, bleeding and the formation of blood clots or fragments of bone encroaching on the canal. This may be enough to restrict the blood supply to the cord. If the cord is then stretched across the site of injury by flexion and lateral flexion or rotation, additional and permanent damage can be caused. If the cord has been severed, the cut surfaces are drawn apart by flexion (Breig, 1978) allowing a blood clot to form between them . Secondly, the narrowing of the canal on extension accounts for the compressive injuries to the cord from hyperextension injuries. Full extension after injury causes further compression while added lateral flexion and rotation is likely to compress the nerve roots in the intervertebral foramina, particularly at the site of injury.
SPINAL CORD AND NERVE ROOT INJURIES
Spinal cord injuries
The cord lies in the spinal canal of the cervical and thoracic regions ending at the level of the first, or second, lumbar vertebra . The commonest sites for injury are at the fifth/sixth cervical and twelfth thoracic/first lumbar levels. In both sites the cord is relatively larger because of the origins of the great nerves of the upper and lower limbs respectively; and at both sites fractures and fracture-dislocations are common. If the spine is forcibly extended and compressed, the cord may be injured by a pincer action; while a flexion-distraction injury could lead to overstretching and rupture. Alternatively, the cord can be damaged without evidence of either fracture or dislocation.
If the patient is conscious the symptoms of injury to the cord are weakness and numbness in the limbs. In an unconscious person, bruising and laceration about the head, face or trunk are indications that the spine – and therefore the cord – may have been injured. In most cases, signs of damage to the nervous system are maximal immediately after injury, though not invariably. Later development of signs of cord damage may be due to post-traumatic oedema, to want of skill during first aid handling and transport or to haemorrhage.
First aid for spinal cord injuries (Guttmann, 1976)
Whenever a spinal cord injury is suspected, warn the patient not to move. Unless there is some overwhelming danger to compel it, the patient should never be moved without adequate help. Any handling must be slow, gentle and skilled. At least three, preferably four or five, people are needed. The danger is very great when rescuing an injured person from water after bathing and diving accidents (Kewalramani and Taylor, 1975) which are a common cause of paraplegia in sport (Steinbruck and Paeslack, 1978). Any supervisors and attendants who may find themselves responsible for first aid must be trained to prevent rough handling of the neck.
If the patient is conscious, pain at the site of injury may help to locate it. If arms and fingers can be moved but not legs, the injury could be thoracic or thoracolumbar. If there is no finger movement but the wrist can be extended and the elbow flexed but not extended, the lesion is likely to be lower or mid-cervical. Absence of all upper limb movement points to an upper cervical injury.
The patient should be moved in one piece, taking care to avoid any flexion, extension and rotation. If the breathing is satisfactory, he can be moved to a supine position, keeping the head in a straight line with the body and maintaining normal spinal curves with pads or rolled-up clothing which can be gently introduced to support the neck and lower back; with further padding each side of the head to prevent rolling. The stretcher must be rigid. Hard objects should be removed from pockets to prevent the development of pressure sores, and soft padding applied to stop rubbing of knees, ankles, elbows and hands. The patient must then be transferred to a spinal injuries unit.
In cases where there is any difficulty with breathing it may be life-saving to have the patient not supine but lying on the side, though this makes support of the spine more difficult. The whole length of the spine must be kept horizontal with padding below the neck and lower back, but maintaining the normal curvature. The main problem is to keep the limbs, pelvis and shoulders stable. They will have to be strapped to prevent rotation. It is vital in such cases to keep a clear airway but when aspirating or intubating the patient the head and neck must be kept straight and not bent back.
Nerve root injuries
Fractures of the vertebral neural arch or fractures and fracture-dislocations caused by lateral flexor, rotatory or shearing forces may be accompanied by injury to the nerve roots; either within the canal or typically, in the intervertebral foramen. In a neck injury associated with traction on the shoulder the spinal dura mater may be ruptured and the nerve root torn from the cord, though it is possible for cervical roots to be torn without injury to the dura when violence is done to the neck alone (Sunderland, 1974). In the lumbar region traction injuries to the roots are uncommon though they occur in some cases of pelvic fracture (Barnett and Connolly, 1975).
Instability of the spine may be defined as the loss of its ability to move without damage or irritation of the spinal cord or nerve roots and without the development of deformity (White et al, 1976).
After injury, stability depends mainly on the integrity of the ligaments of the neural arch and on the function of the muscles which support the spine. But it is not possible to judge from the external appearance of laceration or bruising whether a given injury is stable or not: in many disastrous injuries the skin remains unmarked and there is no visible deformity. Stability can only be established by meticulous clinical and radiological examination. In the field, the danger is that an unstable injury without initial neurological damage could be allowed to become displaced and so damage the spinal cord or nerve roots. For anyone who has fallen from a height, been thrown or violently struck and who is unconscious, the first aid care must be as for a spinal cord injury: likewise for a conscious person with a severely injured back, head or neck even in the absence of numbness and weakness of the limbs.
The actual mechanism of injury (Roaf, 1976) may prove to be valuable evidence for the surgeons and radiographers at the accident and emergency department. In many cases, for example, thoraco-lumbar fracture-dislocation caused by flexion-rotation of the trunk, there is a typical mechanism of injury. The evidence of reliable witnesses may help to speed the diagnosis.
About 1 in 10 fractures are unstable, instability occurring because of concomitant injury of the supporting ligaments and, on a longer term basis, in those cases in which the existence of a fracture makes the slow development of deformity possible because of gradual strain of the supporting ligaments.
The most unstable of all is the fracture-dislocation caused by flexion-rotation injury or by rotational shear to the trunk with accompanying rupture of the posterior ligaments and sometimes further fracture in the neural arch. The typical site for this is the thoraco-lumbar region. It is wholly unstable, deformation is imminent if not present and this type of fracture accounts for 95 per cent of the paraplegics at this spinal level (Holdsworth, 1963).
A purely flexor injury which causes a wedge fracture of the body and rupture of the posterior ligaments becomes unstable in flexion and the extensor injury with fracture of the arch and rupture of the anterior longitudinal ligament is unstable in extension .
Children are more supple than adults and their heads are proportionately larger. For these reasons, among others, they are less liable to spinal fracture in sport than young adults. However, the incidence of fractures in children differs in that they are relatively commoner in the atlas and axis – notably the odontoid process and the neural arch of the axis – and in the mid-thoracic region (Sherk et al, 1976; Hegenbarth and Ebel, 1976). A danger with children is that they may be able to get up with full use of their limbs and yet have an unstable fracture. Neck pain after a fall cannot be ignored and the problem in children is that it is often difficult to elicit a clear account of the injury.
The force on the spine which dislocates it is necessarily enough to rupture some or all of the ligaments of the neural arch, to an extent depending on the direction of dislocation and on whether it affects one or both apophyseal joints. They are commonest in the cervical region, lumbar dislocation being relatively rare, the direction of instability depending on the dislocating force. Though in some cases of unilateral dislocation, there is locking of the affected facet, it remains potentially unstable.
Dislocations also occur in combination with fractures, the most unstable being the type caused by flexion-rotation. Some fracture-dislocations remain stable in one direction depending on the ligaments left intact: for example, the extension fracture-dislocation of the neck in which it remains stable in flexion (Holdsworth 1963, 1970).
A number of spinal injuries consist in ligamentous rupture either without dislocation or with a reducible dislocation in which the vertebrae separated under strain. The latter type may be seen in some patients with lateral flexion injury of the neck (Roaf, 1963), flexion injury of cervical and lumbar vertebrae with posterior ligament rupture or extension injury with rupture of the anterior longitudinal ligament: in such cases there may be a compression fracture contralateral^ or on the opposite side to the rupture in flexion or extension injuries or the ‘tear-drop’ fracture of the vertebral body in cervical extension injuries (Holds-worth, 1963).
Rupture of the transverse ligament of the atlas allows anterior atlanto-axial subluxation which jeopardises the cord and it is almost always caused by head injury (Fielding et al, 1974) .
The majority of spinal fractures, and this includes compressive or wedge fracture of the vertebral body, are stable. It even includes the ‘burst’ fracture in which a mainly compressive force disrupts the vertebra but leaves the ligaments intact (Holdsworth 1963, 1970). Healing is seldom a problem in wedge fractures and in the young, subsequent growth may eliminate the wedg-
Back and neck injuries ing. This is not to say they should be ignored because they affect the future capacity of the spine to withstand injury (Kazarian, 1978). Experimentally it is possible to crush a vertebra to 50 per cent of its normal height and yet to see it recover (Kazarian and Graves, 1977). Not surprisingly, it is possible to miss such fractures when first x-rayed: they only become evident at a later stage when bony callus becomes visible (Crooks, 1970).
The other common type of stable fracture is that of the bony processes of the vertebra. Spinous and transverse processes can be fractured by violent muscular effort in accidental events, and this may also be true of fracture of an inferior articular process. They heal most often by fibrous union and seldom create problems: if indeed they are ever diagnosed. A comparable fracture is of the part of the neural arch between the articular processes, a defect known as spondylolysis . If it is bilateral there is a tendency for the body of the affected vertebra and the column above it to slip forward a little in relation to the one below. In some cases they heal by bony union but mostly by fibrous tissue. As the interspinous ligament and the intervertebral disc remain undamaged, the defect leaves the spine basically stable (Troup, 1977).
Like metal, bone may fracture after exposure to repeated heavy loading because jof fatigue failure. In athletes it is not uncommon for it to occur in the tibia and metatarsals, and it is one of the causes of lumbar spondylolysis (Hutton et al, 1977). It is present in three to four per cent of the adult population and appears to be commoner in gymnasts, parachutists, wrestlers, divers, weightlifters, professional dancers and other athletes (Krenz and Troup, 1973; Wiltse et al, 1975). The commonest site is at the fifth lumbar . The defect is usually trouble free, being a frequent chance finding in symptomless people; although there is a greater likelihood of irritation of a nerve root when spondylolysis is at the fourth lumbar (Jackson et al, 1978). The amount of anterior slip (spondylolisthesis) from this cause is unlikely to merit attention. Only if the defect is unstable in the sense that there appears to be neither bony nor fibrous union, or if there is nerve root irritation, is treatment likely to be needed in a patient with chronic pain.
Injuries to the muscles and ligaments of the back and neck, sprains of the synovial apophyseal joint or to the intervertebral disc in the early stages of degeneration are common.
In the healthy spine the disc itself – the nucleus pulposus and the annulus fibrosus – are relatively strong: initial damage is to the epiphyseal plates and the underlying trabecular bone of the vertebral body (Roaf 1960, 1976). In the apophyseal joints most injuries consist of sprains of the capsular ligament but the trauma may extend to the cartilaginous facets of the articular processes. It is believed that if these micro-traumata to disc and facets are repeated there will be an early onset of degenerative changes (Farfan, 1977; Hansson, 1977). Degeneration normally occurs without causing symptoms, the reason being that these same weight-bearing tissues of the spine have no nerve supply and can be injured without pain. Once the disc has begun to degenerate its dynamic behaviour changes: it responds more quickly to compressive loading and its susceptibility to injury is increased (Kazarian, 1975). The nucleus of the disc may then prolapse through the epiphyseal plate into the body, so creating a Schmorl’s node, or through the annulus postero-laterally: again, probably without immediate pain. If and when the neighbouring tissues are adversely affected by the injury, pain and muscle spasm may begin to develop.
The majority of people with non-bony injuries of the spine recover whether they are treated or not. Of the others, some fail to lose their pain, or they become liable to repeated attacks. In the latter case it may be because the spine, like some would-be-footballers’ knees, is constitutionally just not fit for the rapid motions and heavy loadings which some sports demand. In cases of persistent pain, there may be a mechanical irritation secondary to the injured apophyseal joint or disc which affects the nerve root either within the spinal canal or as it emerges through the intervertebral foramen: an occurrence which is more likely in those with small spinal canals (Porter et al, 1978). In this way symptoms of pain (though pain is not invariable), weakness or numbness may develop in those parts of the back or limb supplied by the affected nerve root. In many young people with lumbar disc prolapse irritating a nerve root, the symptoms may only be a little backache and stiffness in the leg. In the lower back the fourth and fifth lumbar and first sacral roots are commonly affected, causing symptoms referable to the sciatic nerve. Similar lesions occur in the neck, though less commonly, the lower cervical roots being liable to irritation with consequent pain, weakness or numbness in the arm.
The management of back and neck injuries
Because of the closeness of the joints of the spine and of their distance below the skin, normal clinical examination alone seldom leads to a very precise diagnosis -and spinal radiography is mainly of value in excluding serious disease or fracture. Further investigations are elaborate and costly, some entail a risk of minor complications and the full diagnostic approach is usually reserved for those who have not responded to conservative therapy.
The treatment for an acute back or neck injury is rest; most people being more comfortable on a firm bed. When moving about, a cervical collar or an ‘instant’ lumbar corset is helpful and not difficult to improvise. Food and drink should be cut down to limit the number of visits to the lavatory. If the pain spreads to the limbs, if there are urinary problems or if the pain is crippling, patients should be advised to call the doctor. Anti-inflammatory drugs are usefully prescribed at this stage, with analgesics, relaxants or sleeping pills as the situation demands.
Most acute attacks begin to abate within three or four days but symptoms are likely to persist in minor form and it is prudent to avoid any activity which exacerbates them. A truly accidental injury such as a fall may leave the back sensitive for two or three months, so it is as well to beware of any handling or postural stresses or exercises which are painful until the lesion has settled down. Mobility in the pain free ranges should, however, be maintained particularly in the lower limb after lumbo-sacral injuries for there is a risk that immobility too rigidly enforced will lead to the formation of adhesions around the nerve roots because of the locally painful irritative state. This is one of the causes of sciatic pain following a lumbar injury.
After the pain has subsided it is important to regain normal mechanical function and to retrain the supporting musculature, including all the muscles of the abdominal wall and of the hips, which may have become weak after back pain inhibited their normal usage. A satisfactory exercise programme following back injury is included in a book published by the Consumers’ Association (1978).
PREVENTION OF SPINAL INJURIES
Prevention of spinal injuries in sport is first a matter of skilled supervision and training. It can also be tackled ergonomically by improving the design of sports equipment. Finally, it may be approached by the adoption of medical screening to identify those who are susceptible to spinal injury.
Broken necks and tetraplegia due to diving into overcrowded or shallow water are avoidable if attendants know the rules and can apply them. Falls from horses, motor-cycles or the ring are difficult to prevent because the various interacting factors are less controllable-as in many competitive games. Nevertheless, the skill to adapt to the unexpected situation is partly a matter of training. This may be difficult at the beginning of the season, as in rugby (Williams and McKib-bin, 1978). Training is most likely to be fruitful in preventing non-bony injuries in situations in which the individuals at risk are in full control, as in weightlifting or for manual work in general (Charlesworth et al, 1978).
The application of ergonomics to the design of sporting equipment should be a reliable preventive method provided other dangers are not created. Head injuries, for example, can be reduced in number and severity by wearing a helmet but only provided that the physical risks remain the same. If its use leads to the development of new tactical and training methods – if the helmet is used for butting or is aggressively handled -the increased leverage may cause neck injuries which might not otherwise have happened, as in American football (Okihiro et al, 1975; Albright et al, 1976; Torg et al, 1977). Protecting the spine with special equipment is impossible without producing other effects, for example, hampering mobility, some of which may interfere with performance. Apart from the belt worn by weightlifters which conceivably augments the effects of increased intra-abdominal pressure in relieving back-stress, or the brace worn by motocross-riders to make the vibratory effects on the spine more tolerable, protective equipment for the spine in sport is of limited value.
Medical and radiological screening is considered essential in work entailing a high risk of spinal injury (Kazarian, 1978). There are those who prove to be more susceptible to injury than others and if they could be identified reliably, the incidence of spinal injuries would fall. However, this implies that certain individuals shall be deprived of their chosen sport. There is, moreover, no justification for exposing healthy, symptom free young people to the radiation needed for lumbar spinal radiography. The risks for cervical radiography are probably acceptable. For the lumbar spine, therefore, routine radiography cannot be accepted. There might be exceptions for sports such as parachuting, but only where there is a high injury rate. Medical screening which includes radiography applies mainly to those who have had a spinal injury and who need advice about the future.
PROGNOSIS AFTER SPINAL INJURY
Once an episode of back or sciatic pain has been reported in the general population, a further attack becomes three or four times more likely. And so, probably, for the neck. The reasons are not clear. The problem has a neurophysiological component arising from memory storage; there may be a psychogenic factor serving to reinforce the pain; or it may be that the first attack was inadequately treated in that spinal functions may not have been fully restored though the pain itself had been satisfactorily relieved. People who have had previous back or sciatic pain are likely to have stiffer spines and to have dynamically weaker muscles (Troup et al, 1974; Nummi et al, 1978), but these are generalisations which may not apply to an individual. There are undoubtedly many who hurt themselves at sport and simply retire from it. Those who present problems are the ones who are loath to give up their sport but are bedevilled by either successive injuries or pain which is enough to spoil their performance. Regrettably there is no body of scientific evidence on which to base advice to these people: only the rather subjective qualities of medical experience and acumen together with a biomechanical understanding of the sport.
The first thing is to be able to reassure the individual that there is no serious disease in the spine: this may mean investigations including radiography. The diagnostic problem concerns the nature of the mechanical derangement in the spine and its possible neuro- physiological effects. The prognosis depends on experience of the natural history of the condition. Pain after an old injury may require that the spine be x-rayed in extreme positions as a test of normal stability. Symptoms in the limbs can be tested electrophysiologically to record the conductivity of nerve roots if they have been damaged or irritated. The response to antiinflammatory drugs and to the various physical therapeutic methods should be assessed. Then, taking into account the personality of the patient, it is usually possible to make a prognosis, give advice and perhaps suggest further treatment. Where there is a reasonable hope of returning to training, full athletic rehabilitation should be a matter of collaboration between trainer, physical therapist and physician.
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