Kimberly-Anne Tan

How the spine differs in standing and in sitting—important considerations for correction of spinal deformity

BACKGROUND CONTEXT The current prevailing school of thought in spinal deformity surgery is to restore sagittal balance with reference to the alignment of the spine when the patient is standing. This strategy, however, likely accounts for increased rates of proximal junctional failure. PURPOSE The purpose of this study was to investigate the differences between the spine in standing and sitting positions as these may elucidate reasons for deformity correction failure. STUDY DESIGN/SETTING A prospective, comparative study of 58 healthy patients presenting to a tertiary hospital over a 6-month period was carried out. PATIENT SAMPLE All patients presenting with a less than 3-month history of first episode lower back pain were included. Patients who had radicular symptoms, red flag symptoms, previous spine surgery, or visible spinal deformity during forward bending test were excluded. Pregnant patients were also excluded. OUTCOME MEASURES Radiographic measurements including sagittal vertical axis (SVA), lumbar lordosis (LL), thoracolumbar angle (TL), thoracic kyphosis (TK), cervical lordosis (CL), pelvic incidence (PI), and pelvic tilt (PT) were collected. The sagittal apex and end vertebrae of all radiographs were also recorded. METHODS Basic demographic data (age, gender, and ethnicity) was recorded. Lateral standing and sitting radiographs were obtained using EOS technology. Statistical analysis was performed to compare standing and sitting parameters using chi-square tests for categorical variables and paired t tests for continuous variables. RESULTS Taking the standing position as the reference point, forward displacement of the SVA occurred during sitting by a mean of 6.39±3.87 cm (p<.001). This was accompanied by a reduction of LL and TK by a mean of 24.63±12.70° (p<.001) and 8.56±7.21°(p<.001), respectively. The TL became more lordotic by a mean of 3.25±7.30° (p<.001). The CL only reached borderline significance (p=.047) for increased lordosis by a mean of 3.45±12.92°. The PT also increased by 50% (p<.001). Despite relatively constant end vertebrae, the apex vertebra moved inferiorly for the thoracic curve (p<.006) and superiorly for the lumbar curve (p<.001) by approximately one vertebral level each. CONCLUSIONS Sagittal spinal alignment changes significantly between standing and sitting positions. Understanding these differences is crucial to avoid overcorrection of LL, which may occur if deformity correction is based solely on the spines standing sagittal profile.

Cervical Alignment Variations in Different Postures and Predictors of Normal Cervical Kyphosis - A New Understanding.

Study Design. Comparative study of prospectively collected radiographic data. Objective. To predict physiological alignment of the cervical spine and study its morphology in different postures. Summary of Background Data. There is increasing evidence that normal cervical spinal alignment may vary from lordosis to neutral to kyphosis, or form S-shaped or reverse S-shaped curves. Methods. Standing, erect sitting, and natural sitting whole-spine radiographs were obtained from 26 consecutive patients without cervical spine pathology. Sagittal vertical axis (SVA), global cervical lordosis, lower cervical alignment C4-T1, C0-C2 angle, T1 slope, C0-C7 SVA and C2-7SVA, SVA, thoracic kyphosis, thoracolumbar junctional angle, lumbar lordosis, sacral slope, pelvic tilt, and pelvic incidence were measured. Statistical analysis was performed to elucidate differences in cervical alignment for all postures. Predictive values of T1 slope and SVA for cervical kyphosis were evaluated. Results. Most patients (73.0%) do not have lordotic cervical alignment (C2-C7) upon standing (mean −0.6, standard deviation 11.1°). Lordosis increases significantly when transitioning from standing to erect sitting, as well as from erect to natural sitting (mean −17.2, standard deviation 12.1°). Transition from standing to natural sitting also produces concomitant increases in SVA (−8.8–65.2 mm) and T1-slope (17.4°–30.2°). T1 slope and SVA measured during standing significantly predicts angular cervical spine alignment in the same position. SVA < 10 mm significantly predicts C4-C7 kyphosis (P < 0.001), and to a lesser extent, C2-C7 kyphosis (P = 0.02). T1 slope <20° is both predictive of C2-C7 and C4-7 kyphosis (P = 0.001 and P = 0.023, respectively). For global cervical Cobb angle, T1 slope seems to be a more significant predictor of kyphosis than SVA (odds ratio 17.33, P = 0.001 vs odds ratio 11.67, P = 0.02, respectively). Conclusion. The cervical spine has variable normal morphology. Key determinants of its alignment include SVA and T1 slope. Lordotic correction of the cervical spine is not always physiological and thus correction targets should be individualized. Level of Evidence: 3

Lumbar Spine Alignment in Six Common Postures: An Rom Analysis With Implications for Deformity Correction

Study Design. A cross-sectional study of prospectively collected data. Objective. To compare lumbar spine alignment in six common postures, and estimate loss in range of motion (ROM) relative to standing. Summary of Background Data. Ideal position for fusion of lumbar spine remains unknown. Although surgical fusion is necessary for deformity correction and symptom relief, the final position in which the vertebrae are immobilized should provide maximum residual function. Methods. Data were collected prospectively from 70 patients with low back pain recruited over a year. All subjects had x-rays performed in slump sitting, forward bending, supine, half squatting, standing, and backward bending postures. ROM quantified in terms of sagittal global and segmental Cobb angles was measured from L1 to S1. Loss of ROM relative to standing was calculated for each posture. Analysis of variance and unpaired t tests were used to identify differences in alignment between postures. Results. Slump sitting gives the greatest lumbar flexion followed by forward bending, and supine postures (P < 0.001). Backward bending produces greater lumbar extension than standing (P = 0.035). Half-squatting and standing postures were not significantly different (P = 0.938). For all postures, L4–5 and L5-S1 segments remained in lordosis, with L4–5 having greater ROM than L5-S1. L1–2 turns kyphotic in lying supine, L2–3 at forward bending, and L3–4 at slump sitting in the form of a “kyphosing cascade.” Should the entire lumbar spine be fused in standing position from L1-S1, there would likely be a mean loss of 47.6° of lumbar flexion and 5.9° of lumbar extension. Conclusion. The present study demonstrates the extent of flexibility required of the lumbar spine in assuming various postures. It also enables comparison of the differences in degree of motion occurring in the lumbar spine, both across postures and across segments. Significant loss in ROM, particularly flexion, is anticipated with fusion modeled after the lordotic standing lumbar spine. Level of Evidence: 2

T9 versus T10 as the upper instrumented vertebra for correction of adult deformity—rationale and recommendations

BACKGROUND CONTEXT Adult spinal deformity correction sometimes involves long posterior pedicle screw constructs extending from the lumbosacral spine to the thoracic vertebra. As fusion obliterates motion and places supraphysiological stress on adjacent spinal segments, it is crucial to ascertain the ideal upper instrumented vertebra (UIV) to minimize risk of proximal junctional failure (PJF). The T10 vertebra is often chosen to allow bridging of the thoracolumbar junction into the immobile thoracic vertebrae on the basis that it is the lowest immobile thoracic vertebra strut by the rib cage. PURPOSE This study aimed to characterize the range of motion (ROM) of each vertebral segment from T7 to S1 to determine if T10 is truly the lowest immobile thoracic vertebra. STUDY DESIGN/SETTING This is a prospective, comparative study. PATIENT SAMPLE Seventy-nine adults (mean age of 45.4 years) presenting with low back pain or lower limb radiculopathy or both, without previous spinal intervention, metastases, fractures, infection, or congenital deformities of the spine, were included in the study. OUTCOME MEASURES A ROM >5° across two vertebral segments as determined by the Cobb method from radiographs. METHODS Lumbar flexion-extension and neutral erect radiographs were obtained in randomized order using a slot scanner. Segmental ROM was measured from T7-T8 to L5-S1 and analyzed for significant differences using t tests. Age, gender, radiographical indices such as standard spinopelvic parameters, sagittal vertical axis (SVA), C7-T12 SVA, T1 slope, thoracic kyphosis (TK), and lumbar lordosis (LL) were studied via multivariate analysis to identify predictive factors for >5° change in ROM at the various segmental levels. There were no sources of funding and no conflicts of interest associated with this study. RESULTS In the thoracolumbar spine, significant decreases in ROM when compared with the adjacent caudad segment occurs up to T9-T10, with mean total ROM of 1.98±1.47° (p<.001) seen in T9-T10, 2.19±1.67° (p<.001) in T10-T11, and 3.92±3.21°(p<.001) in T11-T12. The total ROM of T8-T9 (2.53±1.79°) was not significantly different from that of T9-T10 (p=.261). At the thoracolumbar junction, absence of scoliosis (OR 11.37, p=.020), high pelvic incidence (OR 1.14, p=.046), and low T1 slope (OR 1.45, p=.030) were predictive of ROM >5°. CONCLUSIONS Lumbar spine flexion-extension ROM decreases as it approaches the thoracolumbar junction. T10 is indeed the lowest immobile thoracic vertebra strut by the rib cage, and the last significant decrease in ROM is observed at T9-T10, in relation to T10-T11. However, because this also implies that a UIV of T10 would mean there is only one level of fixation above the relatively mobile segment, while respecting other factors that influence UIV selection, we propose the T9 vertebra as a more ideal UIV to fulfill the biomechanical concept of bridge fixation. However, this decision should still be taken on a case-by-case basis.

Evaluation of scoring systems and prognostic factors in patients with spinal metastases from lung cancer

Study Design. A retrospective study of 180 patients with lung cancer spinal metastases, wherein prognostic score-predicted survival was compared with actual survival. Objective. To evaluate and compare the accuracy of prognostic scoring systems in lung cancer spinal metastases. Summary Of Background Data. The modified Tokuhashi, Tomita, modified Bauer, and Oswestry scores are currently used to guide decisions regarding operative treatment of patients with spinal metastases. The best system for predicting survival in patients with lung cancer spinal metastases remains undetermined. The high incidence of spinal metastases from lung cancer and improved survival of patients treated with systemic therapy warrants evaluation of these scoring systems in this particular context. Methods. Patients with lung cancer spinal metastases treated at our institution between May 2001 and August 2012 were studied. Fifty-one patients were treated surgically. The primary outcome measure was survival from the time of diagnosis. Scoring-predicted survival was compared with actual survival. Potential prognostic factors were investigated using Cox regression analyses. Predictive values of each scoring system for 3- and 6-month survival were measured via receiver operating characteristic (ROC) curves. Results. Histological subtype (P = 0.015), sex (P = 0.001), Karnofsky performance scale (P = 0.001), extent of neurological palsy (P = 0.002), and visceral metastases (P = 0.037) are significant predictors of survival. Besides the Oswestry spinal risk index, no significant differences were found between different prognostic subgroups within the individual scoring systems. Although the modified Bauer score was most accurate, all four scoring systems had areas under the ROC curve 0.5 or less. Conclusion. Although better prognostic scores correlated with longer survival, all four scoring systems are inaccurate in prognosticating patients with lung cancer spinal metastases. Specific lung cancer histology appears prognostic and should be considered, especially given the increased survival of patients receiving new targeted therapies appropriate to their disease. Level of Evidence: 3

Using spinopelvic parameters to estimate residual lumbar lordosis assuming previous lumbosacral fusion—a study of normative values

BACKGROUND CONTEXT Pelvic incidence (PI)=pelvic tilt (PT)+sacral slope (SS) is an established trigonometric equation which can be expanded from studying the fixed pelvis with the spine to a fixed spinopelvic complex with the remnant spine, in scenarios of spinopelvic fusion or ankylosis. For a fixed spinopelvic complex, we propose the equation termed: lumbar incidence (LI)=lumbar tilt (LT)+lumbar slope (LS). PURPOSE This study aimed to establish reference values for LI, LT, and LS at each lumbar vertebral level, and to show how LI can be used to determine residual lumbar lordosis (rLL). STUDY DESIGN This is a cross-sectional study of prospectively collected data, conducted at a single academic tertiary health-care center. PATIENT SAMPLE The study included 53 healthy patients aged 19-35 with first episode mechanical low back pain for a period of <3 months. Patients with previous spinal intervention, those with known or suspected spinal pathologies, and those who were pregnant, were excluded. OUTCOME MEASURES Radiological measurements of LI, LT, LS, and rLL. METHODS All patients had full-body lateral standing radiographs obtained via a slot scanner. Basic global and regional radiographic parameters, spinopelvic parameters, and the aforementioned new parameters were measured. LI was correlated with rLL at each level by plotting LI against rLL on scatter plots and drawing lines-of-best-fit through the datapoints. RESULTS The mean value of L5I was 22.82°, L4I was 6.52°, L3I was -0.92°, L2I was -5.56°, and L1I was -5.95°. LI turns negative at L3, LS turns negative at the L3/L4 apex, and LT remains positive throughout the lumbar spine. We found that the relationship of LI with its corresponding rLL follows a parabolic trend. Thus, rLL can be determined from the linear equations of the tangents to the parabolic lumbar spine. We propose the LI-rLL method for determining rLL as the LI recalibrates via spinopelvic compensation post instrumentation, and thus the predicted rLL will be based on this new equilibrium, promoting restoration of harmonized lordosis. The rLL-to-LI ratio is a simplified, but less accurate, method of deriving rLL from LI. CONCLUSIONS This study demonstrates the extended use of PI=PT+SS proposed as LI=LT+LS. These new spinopelvic reference values help us better understand the position of each vertebra relative to the hip. In situations when lumbar vertebrae are fused or ankylosed to the sacrum to form a single spinopelvic complex, LI can be used to determine rLL, to preserve spinal harmony within the limits of compensated body balance.

Prevalence and Predictors of Pressure Injuries From Spine Surgery in the Prone Position: Do Body Morphological Changes During Deformity Correction Increase the Risks?

Study Design. Review of data and prospective study. Objective. To investigate the prevalence and predictive factors of pressure injuries in spine surgery performed in the prone position, and to determine whether morphological changes and truncal shifts occurring during deformity correction predispose to this complication. Summary of Background Data. Spine surgery performed in the prone position presents the risk of developing pressure injuries. This risk is potentially increased in deformity correction, because it tends to involve more extensive procedures, with associated longer operating times. Methods. Cases of pressure injuries after spine surgery in the prone position were reviewed to ascertain prevalence and determine risk factors. Data including patient factors (age, sex, height, weight, body mass index, American Society of Anesthesiologists grade, comorbidities, Braden scale, neurological status, spinal pathology) and surgical factors (approach, procedure type, number of screws, operated levels, operative time) were collected. Independent risk factors were identified via multivariate analysis. A subsequent prospective analysis of all patients undergoing spinal deformity correction was conducted by performing intraoperative measurements of body morphological changes and shifts in truncal positions. Statistical correlation was performed to determine whether positional shifts cause pressure injuries. Results. The prevalence of pressure injuries was 23.0%. Previous skin problems (P = 0.034), myelopathy (P = 0.013), operative time >300 minutes (P = 0.005), and more than four operated levels (P = 0.006) were independent predictors of pressure injuries. Being a spinal deformity patient was also an independent risk factor for developing pressure injuries (odds ratio 3.31, P = 0.010). Significant changes in body measurements during deformity correction were predictive of pressure injuries. Conclusion. Pressure injuries are prevalent in patients undergoing spine surgery while prone. Future studies should investigate strategies to prevent this complication based on the multiple risk factors identified in the present study. Patients undergoing spinal deformity correction surgery are particularly at risk due to intraoperative body morphological changes. Improved padding methods should be trialed in future studies. Level of Evidence: 3

Bone bridge formation across the neuroforamen 14 years after instrumented fusion for isthmic spondylolisthesis—a case report

This case report describes the first case of a bone bridge formation across the left L5/S1 neuroforamen after instrumented posterolateral fusion for L5/S1 isthmic spondylolisthesis. Our patient was a 70-year-old lady who had grade 2, L5/S1 isthmic spondylolisthesis and bilateral S1 nerve root compression. She suffered from mechanical low back pain and neurogenic claudication, with radicular pain over both S1 dermatomes. She underwent in-situ, instrumented, posterolateral fusion and was asymptomatic for more than 13 years before developing progressive onset of left radicular pain over the L5 dermatome. Imaging revealed a bisected left L5/S1 neuroforamen secondary to a bone bridge formation resulting in stenosis. The pars defect in this case may have had sufficient osteogenic and osteoinductive factors to heal following spinal stabilization. Although in-situ posterolateral fusion is an accepted surgical treatment for isthmic spondylolisthesis, surgeons should consider reduction of the spondylolisthesis and excision of the pars defects to avoid this possible long-term complication.

Distal junctional failure secondary to L5 vertebral fracture—a report of two rare cases

Distal junctional failure (DJF) with fracture at the last instrumented vertebra is a rare occurrence. In this case report, we present two patients with L5 vertebral fracture post-instrumented fusion of the lumbar spine. The first patient is a 78-year-old female who had multi-level degenerative disc disease, spinal stenosis and degenerative scoliosis involving levels T12 to L5. She underwent instrumented posterolateral fusion (PLF) from T12 to L5, and transforaminal lumbar interbody fusion (TLIF) at L2/3 and L4/5. Six months after her operation, she presented with a fracture of the L5 vertebral body necessitating revision of the L5 pedicle screws, with additional TLIF of L5/S1. The second patient is a 71-year-old female who underwent decompression and TLIF of L3/4 and L4/5 for degenerative spondylolisthesis. Six months after the surgery, she developed a fracture of the L5 vertebral body with loosening of the L5 screws. The patient declined revision surgery despite being symptomatic. DJF remains poorly understood as its rare incidence precludes sufficiently powered studies within a single institution. This report aims to contribute to the currently scarce literature on DJF.