Spinal Injuries

Potential participants had to complete a short survey outlining their medical history. If an individual had any prior symptoms of swallowing difficulties, or had a history of stroke or other neurological conditions, head or neck cancer, neck or spinal injury or a tracheostomy, he/she was excluded from the study. In total, fifty consenting healthy adults (24 males) participated in this study ranging from 18 to 65 years of age (19 participants were 18-34 years old; 9 participants were 34-44 years old; 13 participants were 45-54 years old; and 9 participants were 55-65 years old). The research ethics board of Bloorview Kids Rehab (Toronto, Ontario, Canada) approved the study protocol.
Upon the completion of the short survey, participants were seated comfortably in a chair for the rest of the experiment. To record cervical accelerometry signals (i.e., accelerometry signals without swallowing), a dual-axis accelerometer (ADXL322, Analog Devices) was placed on the neck of each participant anterior to the cricoid cartilage and secured with double-sided tape. The accelerometer has a measurement range of ± 5 g, a bandwidth of 2.5 kHz, a resonant frequency of 5.5 kHz, and sensitivity of 174 mV/g. A voltage supply (Model 1504, BK Precision) set at 5 V was used to power the acceleremoter. Furthermore, the two axes were positioned in the anterior-posterior (A-P) and superior-inferior (S-I) anatomical directions as shown in Figure 1. All participants were advised to refrain from swallowing during each task, but were permitted to swallow accumulated saliva between successive steps. No data were recorded during those swallows. Three additional sensors confirmed that the participants followed the data collection protocol properly. We collected signals from a triple-axis accelerometer (MMA7260Q, SparkFun Electronics) attached to a headband and centered on the participant's forehead to monitor head motions; a respiratory belt (1370G, Grass Technologies) secured around the participant's diaphragm to monitor breathing patterns; and a microphone placed 30 cm away from the participant's mouth to capture any vocalizations. The dual-axis accelerometer signals were filtered (passband 0.1-3000 Hz) and amplified in hardware (Grass P55 pre-amplifier). The subsequent signals were acquired at 10 kHz using a data acquisition card (NI USB-6210, National Instruments) and custom Labview software. The data were stored on a hard drive for subsequent analyses.
The data collection procedure included five primary tasks. Participants remained silent and were asked to:
1. tilt their head to the left side 10 times.
2. tilt their head to the right side 10 times.
3. tilt their head down 10 times.
4. tilt their head back 10 times.
5. rotate their head from right to left 5 times, and from left to right 5 times.
Participants performed each task only once, and the data collection did not generally last longer than 15 minutes per participant.
The participants also engaged in other tasks as part of the data collection protocol for a different study, hence, the additional sensors. For the current study, the additional sensors (head accelerometer, respiratory belt and microphone) simply served to confirm participant compliance with the experimental protocol. For example, head accelerometers were used to confirm that head motion was generated only when cued. Similarly, a microphone was used to ensure that participants did not vocalize during these tasks, while the respiratory belt was used to ensure that participants maintained normal breathing patterns during these tasks. Nevertheless, we did not engage in an extensive analysis of data collected using these sensors beyond a qualitative inspection to confirm participant compliance to the experimental protocol.

Patients age 18 to 65 who present to the ED within 24 hours after minor MVC and who are unlikely to require admission are screened for eligibility. Patients with injuries likely to require hospitalization, fractures (other than small bone fractures), major lacerations (defined as a laceration more than 20 cm in length or more than four lacerations requiring sutures), intracranial injury, or spinal injury (defined as vertebral fracture or dislocation, or new neurologic deficit) are excluded. Patients who are deemed eligible but subsequently admitted overnight to the hospital are excluded. Patients who go to an ED observation area for a brief period (e.g. "6 hour rule out") remain eligible. Patients are excluded if they are prisoners, pregnant, not alert and oriented, or unable to read and understand English. Patients are also excluded if they take β-receptor antagonist or if they take opioids on a daily basis above a total daily dose of 20 mg of oxycodone or equivalent. In addition, due to the effects of ethnicity on genetic risk factor assessment (population stratification bias [17 (link)] that may require different ethnicities to be analyzed separately) and budget restrictions limiting sample size, enrollment is limited to European Americans. After assessment for eligibility, signed informed consent is obtained from all patients enrolled in the study.

Plain radiographs and computed tomography (CT) scans were obtained before surgery, immediately after surgery, at the removal of the implants, and during the final follow-up. The segmental kyphotic angle (SKA) and anterior vertebral body height ratio (AVBHR) were measured as radiographic parameters to evaluate the indirect reduction of the vertebral body and local kyphosis. SKA was defined as the Cobb angle calculated between the cranial vertebra’s upper endplate and the caudal vertebra’s lower endplate. AVBHR was defined as the percentage of the anterior vertebral height of the fractured vertebra to the average anterior height of the two adjacent vertebrae (Fig. 1) [17 (link)].Fig. 1

Schematic diagrams of radiographic parameters. Segmental kyphotic angle (SKA) = θ, Anterior vertebral body height ratio (AVBHR) = c/(a + b)/2

The indirect reduction of fractured vertebrae and correction loss during observation were evaluated using SKA and AVBHR. In this study, correction loss was considered present if the ΔSKA was ≥10° immediately after surgery to the final examination [4 (link), 6 ].
We evaluated the degree of vertebral body involvement using the load sharing classification (LSC) scoring system [18 (link)]. The vertebral fractures were classified according to the AO classification system [19 (link)]. The severity of intervertebral disc and vertebral endplate injury were assessed using the preoperative Sander’s TIDL classification based on T2-weighted MRI (Table 1) [10 (link), 13 (link)]. In this study, TIDL was considered grade 3 when CT showed an apparent vertebral endplate fracture (Fig. 2). If both the upper and lower discs were damaged, a more severe TIDL grade was adopted.Table 1

Classification of TIDL

Grade	T2-weighted MRI	Endplate fracture	Characteristic finding
0		None	Intact
1	Hyperintense	None	Edema
2	Hypointense with perifocal hyperintense	None or mild	Disc rupture with intradiscal bleeding
3	Hypointense with perifocal hyperintense	Moderate or severe	Infraction of the disc into vertebral body, annular tears, or infraction without herniation into endplate

TIDL Traumatic intervertebral disc lesion

Fig. 2

Classification of traumatic intervertebral disc lesion (TIDL). A case of AO type A3 fracture at L3. CT shows a fracture of the cranial endplate and MRI shows infraction of the disc into the vertebral body (white triangles) which means a TIDL grade 3. The caudal disc showed a TIDL grade 2

A case with a depression of 5 mm or more on the sagittal CT slice with the greatest depression was defined to have residual endplate deformity to assess the degree of endplate deformity at follow-up (Fig. 3E).Fig. 3

A 39-year-old woman with L2 burst fracture (AO A3). CT (A) and MRI (B) showed severe damage of the cranial endplate and infraction of the disc into the vertebral body (TIDL grade 3). The fractured vertebra was reduced after surgery (C). At follow up, fractured vertebra showed bony union, however disruption of the vertebral endplate and degeneration of intervertebral disc resulted in correction loss and breakage of the pedicle screw (D, E). Panel E shows residual endplate deformity

Neurological conditions were assessed using the American Spine Injury Association (ASIA) impairment scale [15 (link)]. In addition, postoperative low back pain was classified according to the Japanese Orthopaedic Association (JOA) scoring system as follows: no pain (3 points), occasional minor back pain (2 points), constant back pain or sometimes severe back pain (1 point), and constant severe back pain (0 points) [16 (link)]. In this study, postoperative severe back pain was defined as positive in patients with zero or one point.