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SURGICAL MANAGEMENT OF TEAR DROP FRACTURES OF THE LOWER CERVICAL SPINE
F. Jacquot, F. Signoret, J-M Feron
The “ Tear-drop Injury ”
Injuries to the soft tissues
Mechanism of the injury
Burst fractures (fig 5)
Evolution and prognosis
Tear drop fractures represent 15 % of traumatic cervical spine injuries. It is a severe injury with cord involvement and tetraplegia in 60 % of cases. These fractures are highly unstable. Progressive kyphosis and neurologic deterioration may occur and require stabilization by operative means
The “ Tear-drop Injury ”
The initial accident is often caused by diving or traffic accidents. The patient is brought at the ER showing either acute neurologic involvement with a neck injury and complete or incomplete tetraplegia ; or sometimes only subtle neurologic signs are present, and may precede rapid aggravation. Some patients may come at the Emergency Department several days or weeks after the initial neck injury complaining of only neck pain or an increasing brachial pain.
The lateral X-ray shows the well known antero inferior fragment separated from the vertebral body “as a drop of tear”, and is typical (fig 1).
The fragment volume may be variable; it may be triangular or quadrangular, involving the superior vertebral endplate. The fractured vertebra is usually C5, less often C6 or C4, but the injury can occur in any lower cervical spine vertebra from C3 to C7. On the lateral views, the whole vertebral body sustains a move backward with slight rotation in kyphosis, which drives its postero inferior aspect into the spinal canal in contact with the dura and cord. This causes the neurologic involvement. Kyphosis of the sus jacent spinal segment is visible comparatively to the underlying cervical spine. This is an incomplete description since Fuentes and Lee demonstrated that the separation of the antero inferior lip of the vertebra is most often combined to an actual vertical fracture of the vertebral body in the sagittal plane, so the tear drop fracture is not a disc sprain as was stated in the past. A fracture of one or both laminae is also present. The sagittal fracture line may be difficult to see on the AP view (fig 2). When modern thin slices
computed tomograms are made, previously overlooked sagittal fractures are found with an increased frequency. This makes the tear drop fracture a three-part fracture. The backward displacement with rotation around a horizontal axis is combined to a displacement in the horizontal plane with rotation and divergence of the posterior fragments. This can be observed on the CT scan (fig 3): the articular pillars stay in continuity with the vertebral body through the pedicles, and each vertebral body unit rotates backwards in the canal (fig 4). The amount of posterior displacement is variable, from very slight to more than 7 millimeters. The diameter of the spinal canal at the C5 level is on average 17 mm, but may be less than 14 mm in congenital or acquired stenosis. The diameter of the spinal cord at C5 is 10 mm. Posterior displacement of more than 4 mm is related to a high incidence of severe neurological involvement. However, some patients suffer severe neurological injuries with slight posterior displacement on the lateral view, notwithstanding what the actual amount of displacement was at the time of injury.
Injuries to the soft tissues
The underlying disc to the fractured level is usually disrupted, as well as the posterior longitudinal ligament. Very few MRI data are available concerning the vertebral disc sus jacent to the fracture. While operating on the patients through a posterior approach, it becomes evident that the posterior articular capsules are disrupted. On the lateral view, fanning of the spinous processes is usual between the broken vertebra and the immediate lower vertebra. Less often it can be seen between the fractured level and the spinous process just above, and in these cases fractures of both laminae are seen more often with inferior displacement of the posterior elements.
Mechanism of the injury
In the original description, the injury was called an “acute flexion fracture”. Controversy arised as to the role of an axial compression mechanism. Experimental data support the fact that the cervical spine response to axial compression applied to the vertex is in anterior flexion or “buckling”, and flexion injuries have been obtained experimentally from axial load. This is consistent with the clinical circumstances of the classical diving pool accident.
Combined injuries in adjacent cervical spine vertebrae are frequent, particularly sagittal fractures of the upper and lower cervical vertebral bodies. This is an important element to look for on the AP and CT scan views. Separation-fractures of the articular pillar in an adjacent level comprises a fracture of the pedicle and a fracture of the lamina on the same side; it is responsible for toppling of the separated lateral mass that may be seen on the AP view (too much visible “squared lateral mass”) and the lateral view (loss of parallelism of the facet joints). Fractures of a superior or inferior articular process are unstable and may cause unilateral traumatic antelisthesis that can be seen on the lateral view. Discovering a combined injury at an adjacent level necessitates its adequate treatment, and may compromise the stability of the tear drop fracture fixation. One may insert a screw in an overlooked fracture line while using anterior plate fixation, or overlooking lateral mass instability while performing posterior lateral mass fixation.
Wedge fractures of the vertebral body
Wedge fractures produce a deep setting of the superior vertebral end plate into the underlying cancellous bone of the vertebral body. The posterior cortex remains untouched, and no destabilizing ligament injury is present. These fractures are considered as stable and neurologic involvement is rare.
Burst fractures (fig 5)
These are fractures that comprise numerous fracture lines through the whole vertebral body, with retropulsion of the fragments into the spinal canal. They produce numerous well separated fragments, unlike three main parts tear drop fractures, and CT scan shows no typical “ T shape ” pattern with the sagittal fracture and the anterior tear drop fragment.
The English literature makes few differences and there is a tendency to confusion between the two conditions, which are considered close siblings. Teardrops are often classified in “ burst ”, where one puts all the fractures showing several fracture lines on the vertebral body. In the clinical setting, it may be difficult faced to a given comminuted fracture to see the difference and know what is a burst and what is a tear drop fracture, because there is no consensus on a single criteria. However both conditions are different : in burst fractures the comminuted vertebral body loses connections with the articular pillars, which is not the case in tear drop fractures. The characteristics of tear drop fractures are : the typical anterior or antero-inferior fragment which may also be split by an additional fracture line, the occurrence of one single vertical fracture line on the posterior aspect of the vertebral body, the remaining continuity between the vertebral body and the articular pillar through the intact pedicle, and the backwards movement of the articular pillar being identical to the movement of the vertebral body into the canal and preserving the general architecture of the whole vertebra.
Burst fractures occur most often in a lower vertebra than real tear drop fractures, usually C7. These are unstable fractures, but neurologic involvement showing upper motor neuron syndrome is less frequent, close to 20 % of cases. Conversely, radicular signs are often present, due to protrusion of the fragments into the intervertebral foramen.
Tear-drop fracture of C2, also known as “ Extension tear-drop ”
Fractures separating the antero-inferior lip of the C2 vertebral body are well known to produce a similar aspect on the lateral X-ray (Fig 6). In these cases, there is usually no sagittal fracture line and the trauma is a hyperextension injury often combining facial trauma or combined extension injuries in the lower cervical spine. Posterior elements are intact ; there is only limited posterior displacement of the vertebral body and no ligament instability. This is thus a completely different injury, which responds well to conservative treatment.
Evolution and prognosis
Teardrop fractures are highly unstable. Progressive kyphosis and progressive neurologic involvement may occur in natural history. In the first description by Schneider and Kahn in 1956 they were related with the occurrence of immediate or delayed progressive anterior cord syndrome, showing motor palsy with sparing of the proprioceptive sensibility. In addition to this classical description, other neurologic syndromes may be encountered, such as a central cord syndrome showing motor and sensitive loss predominating in the upper limbs after partial recovery, or a true Brown-Sequard syndrome (cf. table I).
Table 1.Clinical syndromes related to cervical cord injuries
* Posttraumatic motor and sensory loss may be called “complete” only after the bulbocavernosus reflex is observable. This marks the end of the “Spinal shock”.
The generally accepted occurrence of cord involvement is close to 60% (52 à 87 %), and 30 % are complete Frankel A tetraplegics (cf. table II), whose neurological prognosis is very bad.
Tableau 2.“ ASIA impairment scale ” (modified Frankel scale) *
* International Standards for Neurological and functional Classification of Spinal Cord Injury.Spinal Cord 1997 ;35 :266-274
Considering the relative frequency of uncomplete neurological syndromes and the high risk of progressive neurological involvement, diagnosing a tear drop fracture makes surgical management very desirable. In addition, neurologic signs usually accompanies early autonomic nervous system involvement as blood pressure instability, peripheral vasodilatation and heart control instability, and respiratory insufficiency is also present due to accessory respiratory muscles palsy.
Garger in 1969 first described a case where incomplete tetraplegia fully recovered following anterior surgical excision of the fractured vertebral body and posterior arthrodesis. The most advocated treatment to date is an anterior procedure and vertebral fragment removal.
Complete excision of the vertebral body allows for cord decompression and iliac crest bone grafting is used to fill the bone gap. Anterior plate fixation is widely used to avoid the need for a posterior approach and fixation. However, Clinical studies reporting on the technique and results consistently report on mixed series including true teardrop fractures and a majority of burst fractures.
Roy-Camille, in France, widely used posterior lateral mass fixation to stabilize the underlying disrupted disc. In cases where postoperative X-rays show the decompression to be unsatisfactory, a complementary anterior approach is performed to vertebral excision and bone grafting. Fuentes stated the frequent integrity of the anterior longitudinal ligament helps reduction through a posterior approach, and this procedure is often sufficient in complete tetraplegics.
We now use routinely the posterior reduction technique described by one of us (F.S.). Whilst it has been verified on the CT scan that the two halves of the vertebral body separated by the sagittal fracture line remain in continuity with the articular pillars through the pedicles, which is constant in our experience, one can reduce the fracture fragments by dwelling antero-posteriorly onto the articular pillars (Fig 7, a and b). We operate through a conventional posterior approach with lateral mass exposure and we perform lateral mass plate fixation on both sides as described by Roy-Camille. We fix the vertebra above and the vertebra under the fracture level after careful CT scan evaluation for combined adjacent levels fractures (lateral mass separation fracture, articular fracture). In cases such fractures are present, fixation must be extended to the immediate adjacent uninvolved level. To allow the plates dwelling onto the involved articular pillars and reduce the fracture, they must be given additional bending or, alternatively, we use an additional washer secured under each plate with surgical sutures (figs 8 and 9).
The two plates are then applied onto the exposed posterior elements of the spine on each side, and lateral mass screws are inserted into the intact levels under and above the fracture site without tightening them ( Fig 10). When
screws are tightened, the washers push onto the articular pillars and reduce the fracture (Fig 11). This can be controlled on the image intensifier (fig 12, a, b and c). Persistent divergence of the fragments may occur, in which case a Müller clawed clamp may be used to bring together the both articular pillars while tightening the screws. After tightening the screws, additional screws are inserted into the lateral masses at the fractured level to secure them to the plate (fig 13). In case a combined injury at an adjacent level is present, the fixation has to be extended (fig 12). The posterior approach is closed in a conventional fashion with one or two suction drains. Postoperatively, a brace is worn until consolidation of the fracture, this usually requires as much as three months.
To date, this technique has been used in a prospective study in 10 patients who have more than twelve months follow-up. All fractures have healed and all patients experience no pain. Posterior residual displacement is consistently lower than 1 millimeter. Posterior preoperative displacement was on average 5 millimeters (2 to 6 millimeters) preoperatively. Healing of the antero-inferior fragment was obtained in all cases. No complication occurred and we had no recurrent displacement. The technique allowed clearing adequately the spinal canal in all cases with no need for a complementary anterior approach. Among the 8 patients who had neurological signs, five experienced at least partial recovery, however there is no reported statistical relation between the surgical technique and recovery rate, although one tries to clear the spinal canal as well as possible while performing the surgical procedure. We had no deceased patient in our series.
As the continuity of the pedicles and the preservation of the half vertebral body – articular pillar unit are most important, we obtain a CT scan in all patients before doing surgery to check that the fracture complies to the “ classical tear drop ” description (fig 4). In our experience, we never encountered a tear drop fracture combined to a pedicle fracture, and to our knowledge this was never described in the literature. CT scan enables us to check adjacent levels for any combined injury that may be overlooked on conventional X-rays. Reducing the fracture without bone fragment excision obviates the need for bone grafting and its non-negligible morbidity. Thus, we avoid performing an anterior cervical corpectomy in close contact with the injured cord. The posterior approach has some advantages in tetraplegic patients who need a tracheostomy. For these reasons we still support posterior surgery in cervical trauma, and the technique we use in teardrop fractures is an adaptation to a particular case.
Whatever is the surgical technique, it complies to the principles of surgery in cord injured patients, especially in incomplete tetraplegics, namely its goal is to obtain “a free cord in a stable spine” as soon as possible, and to clear the spinal canal from neurological compression as completely as feasible. Releasing the canal and stabilizing the spine is a true emergency in incomplete tetraplegics, if there is a persistent compression, if no other life-threatening combined injury is present in patients who may face polytrauma and if good haemodynamic control warrants the security conditions. In true, well examined, complete tetraplegics, haemodynamic and respiratory contingencies may preclude the pure operative emergency, to warrant control of the sympathetic dysfunction, and avoid as much as possible any preventable perioperative mortality.
Maîtrise Orthopédique n° 89 - December 1999
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