Realignment surgery in adult spinal deformity

Gravity Line-Hip Axis Offset as a Guide for Global Alignment to Prevent Recurrent Proximal Junctional Kyphosis/Failure

BACKGROUND AND OBJECTIVES

Proximal junctional kyphosis/failure (PJK/F) is a potentially serious complication after adult spinal deformity (ASD) corrective surgery. Recurrent PJK/F is especially troublesome, necessitating fusion extension and occasionally resulting in irreversible neurological deficits. The gravity line (GL) offers valuable insights into global sagittal balance. This study aims to examine the postoperative GL-hip axis (GL-HA) offset as a critical risk factor for recurrent PJK/F.

METHODS

We retrospectively reviewed patients with ASD who had undergone revision surgery for initial PJK/F at a single academic center. Patients were categorized into 2 groups: nonrecurrent PJK/F group and recurrent PJK/F group. Demographics, surgical characteristics, preoperative and postoperative parameters of spinopelvic and global alignment, and the Scoliosis Research Society-22 scores were assessed. We examined these measures for differences and correlations with recurrent PJK/F.

RESULTS

Our study included 32 patients without recurrent PJK/F and 28 patients with recurrent PJK/F. No significant differences were observed in baseline demographics, operative characteristics, or Scoliosis Research Society-22 scores before and after surgery. Importantly, using a cutoff of -52.6 mm from logistic regression, there were considerable differences and correlations with recurrent PJK/F in the postoperative GL-HA offset, leading to an odds ratio of 7.0 (95% CI: 1.94-25.25, P = .003).

CONCLUSION

Postoperative GL-HA offset serves as a considerable risk factor for recurrent PJK/F in patients with ASD who have undergone revision surgery. Overcorrection, with GL-HA offset less than -5 cm, is associated with recurrent PJK/F. The instrumented spine tends to align the GL near the HA, even at the cost of proximal junction.

Proprioceptive reliance on trunk muscles for maintaining postural stability decreases in older patients with sagittal imbalance

BACKGROUND

Control of postural adjustments requires tight regulation of the spinal alignments. Sagittal imbalance may cause balance impairment and proprioceptive decline in older adults. However, the evidence on the proprioceptive mechanisms is limited, although it is known that poor proprioceptive inputs may induce spinal deformities. Thus, this study aimed to measure proprioceptive control quantifiers in older adults with sagittal imbalance to clarify the characteristic postural adjustments during proprioceptive inputs.

RESEARCH QUESTION

What are the specific proprioceptive postural adjustments required to maintain balance in older adult patients with lumbar spondylosis?

METHODS

This was a cross-sectional, observational study. The participants were classified according to the sagittal vertical axis (SVA) lengths with 50 mm as the cut-off value. The pressure displacement center was determined in 36 patients without sagittal imbalance and 68 patients with sagittal imbalance during an upright stance on a balance board with eyes closed. Vibratory stimulations of 27-272 Hz were applied to the gastrocnemius (GS) and lumbar multifidus (LM) muscles to measure the relative contributions and center of pressures of different relative proprioceptive weighting ratios (RPWs) used on postural adjustments.

RESULTS

The RPWs of older adults with sagittal imbalance were higher than that in those without sagittal imbalance (56-100 Hz; p = 0.013). Logistic regression analysis showed that older patients with sagittal imbalance had a significant ankle proprioception control of advantage (odds ratio: 1.1, 95% confidence interval: 1.01-1.1, p = 0.012).

SIGNIFICANCE

In older patients with sagittal imbalance, the reliance on hip strategy during balance control (RPW 56-100 Hz) decreases. A quantitative assessment of postural stability during proprioceptive inputs is crucial to identify dependence on proprioception signals, including postural strategy, in older patients with sagittal imbalance. Interventions to improve proprioception can improve the postural stability and strategy of older patients with sagittal imbalance.

Junctional Kyphosis after Correction with Long Instrumentation for Late Posttraumatic Thoracolumbar Kyphosis: Characteristics and Risk Factors

OBJECTIVE

Junctional kyphosis is a common complication after corrective long spinal fusion for adult spinal deformity. Whereas there is still a paucity of data on junctional kyphosis, specifically among late posttraumatic thoracolumbar kyphosis (LPTK) patients. Thus, the aim of this study was to investigate the characteristics and risk factors of junctional kyphosis in LPTK patients receiving long segmental instrumented fusion.

METHODS

We retrospectively reviewed a cohort of LPTK patients who had received long segmental instrumented fusion (>4 segments) in our center between January 2012 and January 2019. Radiographic assessments included the sagittal alignment, pelvic parameters, bone quality on CT images, and measurements of the cross-sectional area (CSA, cross-sectional area of muscle-vertebral body ratio × 100) and fat saturation fraction (FSF, cross-sectional area of fat-muscle body ratio × 100) of paraspinal muscles. Patients in this study were divided into those with junctional kyphosis or failure (Group J) and those without (Group NJ) during follow-up. Group J included patients with junctional kyphosis (Group JK) and patients with junctional failure (Group JF).

RESULTS

A total of 65 patients (16 males and 49 females, average age 56.5 ± 23.4 years) were enrolled in this study. After (32.7 ± 8.5) months follow-up, 15 patients (23.1%) experienced junctional kyphosis, and four of them deteriorated into junctional failure. Eighty percent (12/15) of junctional kyphosis was identified within 6 months after surgery. In comparison with Group NJ, Group J were older (P = 0.026), longer fusion levels (P < 0.001), greater thoracic kyphosis (P = 0.01), greater global kyphosis (P = 0.023), lower bone quality (P < 0.001), less CSA (P = 0.005) and higher FSF (P <0.001) of paraspinal muscles. Preoperative global kyphosis more than 48.5° (P = 0.001, odds ratio 1.793) and FSF more than 48.4 (P = 0.010, odds ratio 2.916) were identified as independent risk factors of junctional kyphosis. Based on the statistical differences among Group NJ, Group JK and Group JF (P < 0.001), Group JF had lower bone quality than Group NJ (P < 0.001) and Group JK (P = 0.015). In terms of patient-reported outcomes, patients in Group JF had worse outcomes in ODI and VAS scores, and PCS and MCS of SF-36 than Group NJ and group JK CONCLUSION: The prevalence of junctional kyphosis was 23.1% in LPTK patients after long segmental instrumented fusion. Preoperative hyperkyphosis and advanced fatty degeneration of paraspinal muscles were independent risk factors of junctional kyphosis. Patients with lower bone quality were more likely to develop junctional failure.

Stereophotogrammetric approaches to multi-segmental kinematics of the thoracolumbar spine: a systematic review

BACKGROUND

Spine disorders are becoming more prevalent in today's ageing society. Motion abnormalities have been linked to the prevalence and recurrence of these disorders. Various protocols exist to measure thoracolumbar spine motion, but a standard multi-segmental approach is still missing. This study aims to systematically evaluate the literature on stereophotogrammetric motion analysis approaches to quantify thoracolumbar spine kinematics in terms of measurement reliability, suitability of protocols for clinical application and clinical significance of the resulting functional assessment.

METHODS

Electronic databases (PubMed, Scopus and ScienceDirect) were searched until February 2022. Studies published in English, investigating the intersegmental kinematics of the thoracolumbar spine using stereophotogrammetric motion analysis were identified. All information relating to measurement reliability; measurement suitability and clinical significance was extracted from the studies identified.

RESULTS

Seventy-four studies met the inclusion criteria. 33% of the studies reported on the repeatability of their measurement. In terms of suitability, only 35% of protocols were deemed suitable for clinical application. The spinous processes of C7, T3, T6, T12, L1, L3 and L5 were the most widely used landmarks. The spine segment definitions were, however, found to be inconsistent among studies. Activities of daily living were the main tasks performed. Comparable results between protocols are however still missing.

CONCLUSION

The literature to date offers various stereophotogrammetric protocols to quantify the multi-segmental motion of the thoracolumbar spine, without a standard guideline being followed. From a clinical point of view, the approaches are still limited. Further research is needed to define a precise motion analysis protocol in terms of segment definition and clinical relevance.

Characteristics of patients undergoing revision surgery for proximal junctional failure after adult spinal deformity surgery: revalidation of the Hart-International Spine Study Group proximal junctional kyphosis severity scale

OBJECTIVE

Score on the proximal junctional kyphosis severity scale (PJKSS) has been validated to show good correlations with likelihood of revision surgery for proximal junctional failure (PJF) after surgical treatment of adult spinal deformity (ASD). However, if the patient has progressive neurological deterioration, revision surgery should be considered regardless of severity based on PJKSS score. This study aimed to revalidate the correlation of PJKSS score with likelihood of revision surgery in patients with PJF but without neurological deficit. In addition, the authors provide the cutoff score on PJKSS that indicates need for revision surgery.

METHODS

A retrospective study was performed. Among 360 patients who underwent fusion of more than 4 segments including the sacrum, 83 patients who developed PJF without acute neurological deficit were included. Thirty patients underwent revision surgery (R group) and 53 patients did not undergo revision surgery (NR group). All components of PJKSS and variables other than those included in PJKSS were compared between groups. The cutoff score on PJKSS that indicated need for revision surgery was calculated with receiver operating characteristic curve analysis. Multivariate analysis with logistic regression was performed to identify which variables were most predictive of revision surgery.

RESULTS

The mean patient age at the time of index surgery was 69.4 years, and the mean fusion length was 6.1 segments. All components of PJKSS, such as focal pain, instrumentation problem, change in kyphosis, fracture at the uppermost instrumented vertebra (UIV)/UIV+1, and level of UIV, were significantly different between groups. The average total PJKSS score was significantly greater in the R group than in the NR group (6.0 vs 3.9, p < 0.001). The calculated cutoff score was 4.5, with 70% sensitivity and specificity. There were no significant between-group differences in patient, surgical, and radiographic factors (other than the PJKSS components). Three factors were significantly associated with revision surgery on multivariate analysis: instrumentation problem (OR 8.160, p = 0.004), change in kyphosis (OR 4.809, p = 0.026), and UIV/UIV+1 fracture (OR 6.462, p = 0.002).

CONCLUSIONS

PJKSS score positively predicted need for revision surgery in patients with PJF who were neurologically intact. The calculated cutoff score on PJKSS that indicated need for revision surgery was 4.5, with 70% sensitivity and specificity. The factor most responsible for revision surgery was bony failure with > 20° focal kyphotic deformity. Therefore, early revision surgery should be considered for these patients even in the absence of neurological deficit.

Instrumentation Techniques to Prevent Proximal Junctional Kyphosis and Proximal Junctional Failure in Adult Spinal Deformity Correction: A Systematic Review of Clinical Studies

STUDY DESIGN

Systematic review.

OBJECTIVES

To summarize the results of clinical studies investigating spinal instrumentation techniques aiming to reduce the postoperative incidence of proximal junctional kyphosis (PJK) and/or failure (PJF) in adult spinal deformity (ASD) patients.

METHODS

EMBASE and Medline® were searched for articles dating from January 2000 onward. Data was extracted by 2 independent authors and methodological quality was assessed using ROBINS-I.

RESULTS

18 retrospective- and prospective cohort studies with a severe or critical risk of bias were included. Different techniques were applied at the upper instrumented vertebra (UIV): tethers in various configurations, 2-level prophylactic vertebroplasty (2-PVP), transverse process hooks (TPH), flexible rods (FR), sublaminar tapes (ST) and multilevel stabilization screws (MLSS). Compared to a pedicle screw (PS) group, significant differences in PJK incidence were found using tethers in various configurations (18% versus 45%, P = 0.001, 15% versus 38%, P = 0.045), 2-PVP (24% vs 36%, P = 0.020), TPH (0% vs. 30%, P = 0.023) and FR (15% versus 38%, P = 0.045). Differences in revision rates for PJK were found in studies concerning tethers (4% versus 18%, P = 0.002), 2-PVP (0% vs 13%, P = 0.031) and TPH (0% vs 7%, P = n.a.).

CONCLUSION

Although the studies are of low quality, the most frequently studied techniques, namely 2-PVP as anterior reinforcement and (tensioned) tethers or TPH as posterior semi-rigid fixation, show promising results. To provide a reliable comparison, more controlled studies need to be performed, including the use of clinical outcome measures and a uniform definition of PJF.

Postoperative and Intraoperative Cement Augmentation for Spinal Fusion

OBJECTIVE

To review outcomes of patients undergoing spinal fusion with prophylactic cement augmentation (CA) of pedicle screws and adjacent levels.

METHODS

In a retrospective case-control study, 59 patients underwent CA of pedicle screws for spinal fusion between 2003 and 2018. Most patients (83%) underwent postoperative CA, while 17% underwent intraoperative CA. Outcomes of CA techniques were compared, and patients undergoing CA for a thoracolumbar fusion (n = 51) were compared with a cohort not undergoing CA (n = 39). Mean follow-up was 3 years.

RESULTS

In patients receiving CA, survivorship free of proximal junctional kyphosis (PJK) was 94%, 60%, and 20% at 2, 5, and 10 years postoperatively. Survivorship free of revision was 95%, 83%, and 83% at 2, 5, and 10 years postoperatively. Development of PJK (P = 0.02, odds ratio [OR] 24.44) was associated with revision surgery. There were 4 (7%) cardiopulmonary complications. Patients who received CA for thoracolumbar fusion were older (70 years vs. 65 years) and were more likely to have osteoporosis (53% vs. 5%) than patients who did not receive CA. CA was associated with a decreased risk of PJK (P = 0.009, OR 0.16), while osteoporosis (P = 0.05, OR 4.10) and fusion length ≥8 levels (P = 0.06, OR 2.65) were associated with PJK. PJK was associated with revision surgery (P = 0.006, OR 12.65).

CONCLUSIONS

CA allows for substantial rates of radiographic PJK; however, this typically does not result in a need for revision surgery and leads to revision and PJK rates that are comparable to patients undergoing long segment fusions without osteoporosis.

Correlation between lordosis distribution index, lordosis tilt, and occurrence of proximal junctional kyphosis following surgery for adult degenerative scoliosis

PURPOSE

This study aimed to evaluate the effect of postoperative reciprocal progression of Lordosis tilt (LT), Lordosis distribution index (LDI) and occurrence of Proximal junctional kyphosis (PJK) following surgery for Degenerative lumbar scoliosis (DLS).

METHODS

A total of 122 consecutive patients with ADS were treated with correction of deformity and followed up for a minimum of 2 years. Spinopelvic parameters were measured preoperatively, postoperatively, and at the latest follow-up. The Japanese Orthopaedic Association score, Oswestry Disability Index, and visual analog scale scores were measured at the latest follow-up. Associations between LT, LDI, and PJK were analyzed using receiver operating characteristic analyses.

RESULTS

The prevalence of PJK in the present study was 24.6%. The outcomes of patients with PJK were significantly worse than those of patients without PJK. Postoperative reciprocal progression in LT and LDI with lumbar lordosis restorative surgery was observed. Preoperative risk factors for PJK were older age, larger LT, and larger Cobb angle of the curves. Postoperative risk factors for PJK included postoperative LT and postoperative Cobb angle of the curves, which were smaller than those preoperatively. We found a strong correlation between postoperative LT and Cobb angle of the curves resulting in PJK. Patients with LT < - 8° were at a higher risk of PJK.

CONCLUSIONS

LT can be used to predict the occurrence of PJK in patients undergoing surgery for DLS. Appropriate postoperative LT is crucial for preventing the progression of PJK.

Multilevel Stabilization Screws Prevent Proximal Junctional Failure and Kyphosis in Adult Spinal Deformity Surgery: A Comparative Cohort Study

BACKGROUND

Proximal junctional kyphosis (PJK) and proximal junctional failure (PJF) occurred in up to 40% of patients with adult spinal deformity (ASD) who underwent open thoracolumbar fusion. Proximal stabilization techniques have been investigated to prevent PJK/PJF without conclusive results.

OBJECTIVE

To demonstrate reductions in PJK/PJF with multilevel stabilization screws (MLSSs).

METHODS

This observational longitudinal cohort study compares MLSSs with standard instrumentation. We reviewed the charts of consecutive patients with ASD undergoing open thoracolumbar fusion (>3 levels, extending cranially above T6 and caudally below L1) from 2009 to 2017 and were followed for >2 yr postoperatively. We defined PJF using the International Spine Study Group criteria and PJK as a Cobb angle increase >10°. We defined the upper instrumented vertebra as the most cephalad vertebral body with bilateral MLSSs. Confounders, MLSS-specific complications, and radiographic outcomes were collected. We evaluated comparability between groups using univariate analyses. We adjusted for covariates by using multivariable regressions modeling PJF and PJK separately with a P-value < .00625 considered significant after the Bonferroni correction. Sensitivity analysis accounted for those lost to follow-up.

RESULTS

Seventy-six patients (50 MLSS vs 26 controls) were included. MLSS patients were significantly older (64.5 ± 8.9 vs 54.8 ± 19.9 yr, P = .024) and had significantly lower PJF incidence (10.0% vs 30.8%, P = .023) and less kyphosis (1.3° ± 5.3° vs 5.2° ± 6.3°, P = .014). Multivariable analysis demonstrated a significant independent association between MLSSs and decreased odds of PJF (odds ratio: 0.11, 0.02-0.53, P = .006). Perioperative complications did not significantly differ between cohorts.

CONCLUSION

MLSSs are safe and efficacious in reducing PJF/PJK in patients with ASD undergoing open thoracolumbar fusion.

Indications for early revision surgery for material failure in spinal instrumentation: experience at a level 1 center for spinal surgery - a single-center study

Posterior instrumentation is an established treatment for a range of spinal disorders. Material failure is not uncommon, and the indications for a revision are very heterogeneous. This study aimed to evaluate the indications and timing for early revision spinal surgery due to material failure.In this retrospective, single-center cohort study, patients underwent spinal posterior instrumentation between January 2017 and July 2019. They were followed up at 3, 12, and 18 months postoperatively. The time of onset of material failure which led to revision surgery was analyzed. In addition, the relationship between the indications for revision surgery and independent variables was examined using a multivariate logistic regression model.A total of one hundred thirty-five patients were enrolled. Radiolucent zones were found in 30 patients (20%) after 3 months, whereas 48 patients (31%) had radiolucent zones after 12 months. Revision surgery was performed in 13 patients (8.5%). The peak time for revision due to instability was within the first four months of the primary surgery. Multivariate analysis revealed that location, pathology, ASA score, and smoking had no significant impact on the indication for revision surgery, and neither did BMI (P = .042). Non-fusion (P = .007) and radiolucent zones (P = .004), in combination with increased pain (P = .006), were predictors for revision.Our data show that the peak time for early revision of material failure after posterior instrumentation was within the first 4 months of primary surgery. The abnormalities (e.g., radiolucent zones) surrounding the screws without fusion, including persistence of pain, were predictors for revision surgery.

Posterior instrumented fusion on lumbar stenosis syndrome can bring benefit to proximal degenerative kyphosis: A CONSORT-compliant article

ABSTRACT

The effect on degenerative thoracolumbar kyphosis (DTLK) after short-segment instrument for lumbar spinal stenosis syndrome (LSS) remains controversial. Based on the biomechanics and compensatory of the global spino-pelvic alignment, it was assumed that the interference on the lumbar spine, instead of the thoracolumbar segment, could still make a difference on the proximal spine.To explore whether DTLK could improve with only surgery for LSS and identify influencing factors on postoperative TLK.The study was performed from January 2016 to December 2018. Sixty-nine participants (25 male) diagnosed LSS with DTLK were enrolled and surgery was only for LSS. Radiological parameters included TLK, lumbar lordosis, pelvic incidence, pelvic tilt, sacral slope, and osteoporosis. Clinical outcomes were visual analogue scale and Oswestry disability index. According to lower instrumented vertebrae (LIV) on L5 or S1, inter-group comparisons were performed between LIV on L5 (L5 group) and S1 (S1 group).Demographics were well-matched between L5 and S1 group with a mean follow-up of 24.3 ± 12.1 (m). TLK improved with a mean of 16.2 ± 7.6 (°) (P < .001). There was no significance on radiological and clinical parameters between L5 and S1 groups except for a larger pelvic tilt in S1 group (P = .046). Visual analogue scale (P = .787) and Oswestry disability index (P = .530) were both indifferent between normal TLK and DTLK at last (P > .05). Postoperative TLK was affected by osteoporosis and sacral slope, the latter was dominated by pelvic incidence and pelvic rotation. Osteoporosis was the risk factor for TLK correction (P = .001, odd risk = 9.58).DTLK decreased if instrument only performed for LSS, where TLK and clinical outcomes are comparably affected whether L5 or S1 is selected as LIV. This study supplements the compensatory mechanism of spino-pelvic alignment, especially for cases with severe osteoporosis.

Compensatory mechanisms recruited against proximal junctional kyphosis by patients instrumented from the thoracolumbar junction to the iliac

PURPOSE

The compensatory mechanisms recruited by un-instrumented patients against sagittal imbalance are well documented. However, there is a lack of information regarding instrumented patients.

MATERIAL AND METHODS

We performed a retrospective analysis of data collected prospectively in a multicenter adult spinal deformity database. We included patients suffering PJK/PJF after (T8-L2) to iliac instrumentation with minimum two-year follow-up. We measured quantitative sagittal spinopelvic and qualitative sagittal distribution parameters in the immediate postoperative period (6w) and at the time of PJK/PJF appearance. We analyzed how these parameters changed comparing these two time points with univariate and multivariate logistic regression analyses.

RESULTS

A total of 69 patients were included. Two different patterns at PJK/PJF were found: 36 patients activated compensation (defined as an increase in pelvic retroversion (ΔRPV > 5º), and 33 did not (ΔRPV < 5º). The difference in behavior relied mostly on the amount of not surgically restored pelvic rotation at 6w (OR: 0.6; CI95%: 0.4-9.2; P = 0.017). Non-compensators had less rotation reserve (PTx100/PI = 33.9% vs 47.8%;P < 0.001) associated with worse 6w relative pelvic version and lower lumbar arc restoration, worse 6w relative sagittal alignment and GAP-score, compared with compensators (P < 0.001). Compensators' response was based on pelvic retroversion, causing lower lumbar arc decrease, lumbar apex caudal migration, and upper lumbar arc posterior inclination. Despite compensation, a thoracic kyphosis increase in both upper and lower arches gradually evolved into a PJK/PJF. Non-compensators did not react to PJK/PJF, which forced them into kyphosis from the lumbar apex and extending cranially, mainly throughout the upper thoracic arc.

CONCLUSIONS

In patients fused from the TL junction to the iliac, those having greater postoperative pelvic rotation reserve showed greater capacity to recruit compensatory mechanisms against PJK/PJF.

Osteoporosis and Spine Surgery: A Critical Analysis Review

Despite being part of the aging process, early and adequate management of osteoporosis mitigates adverse outcomes associated with low bone mineral density. Although the health-care burden of osteoporosis is on the rise, screening and management of osteoporosis are not yet an integral part of preoperative patient evaluation in spine surgery. Patients with osteoporosis should undergo multidisciplinary evaluation and management, including lifestyle modifications and initiation of multiple therapeutic modalities. Integrating osteoporosis in preoperative optimization and surgical planning for patients undergoing spine surgery has the potential to mitigate osteoporosis-related postoperative complications.

Estimation and assessment of sagittal spinal curvature and thoracic muscle morphometry in different postures

Spine models are typically developed from supine clinical imaging data, and hence clearly do not fully reflect postures that replicate subjects' clinical symptoms. Our objectives were to develop a method to: (i) estimate the subject-specific sagittal curvature of the whole spine in different postures from limited imaging data, (ii) obtain muscle lines-of-action in different postures and analyze the effect of posture on muscle fascicle length, and (iii) correct for cosine between the magnetic resonance imaging (MRI) scan plane and dominant fiber line-of-action for muscle parameters (cross-sectional area (CSA) and position). The thoracic spines of six healthy volunteers were scanned in four postures (supine, standing, flexion, and sitting) in an upright MRI. Geometry of the sagittal spine was approximated with a circular spline. A pipeline was developed to estimate spine geometry in different postures and was validated. The lines-of-action for two muscles, erector spinae (ES) and transversospinalis (TS) were obtained for every posture and hence muscle fascicle lengths were computed. A correction factor based on published literature was then computed and applied to the muscle parameters. The maximum registration error between the estimated spine geometry and MRI data was small (average RMSE∼1.2%). The muscle fascicle length increased (up to 20%) in flexion when compared to erect postures. The correction factor reduced muscle parameters (∼5% for ES and ∼25% for TS) when compared to raw MRI data. The proposed pipeline is a preliminary step in subject-specific modeling. Direction cosines of muscles could be used while improving the inputs of spine models.

Instrumentation techniques to prevent proximal junctional kyphosis and proximal junctional failure in adult spinal deformity correction-a systematic review of biomechanical studies

BACKGROUND CONTEXT

Correction of adult spinal deformity (ASD) by long segment instrumented spinal fusion is an increasingly common surgical intervention. However, it is associated with high rates of complications and revision surgery, especially in the elderly patient population. The high construct stiffness of instrumented thoracolumbar spinal fusion has been postulated to lead to a higher incidence of proximal junctional kyphosis (PJK) and failure (PJF). Several cadaveric biomechanical studies have reported on surgical techniques to reduce the incidence of PJF/PJK. As yet, no overview has been made of these biomechanical studies.

PURPOSE

To summarize the evidence of all biomechanical studies that have assessed techniques to reduce PJK/PJF following long segment instrumented spinal fusion in the ASD patient population.

STUDY DESIGN

A systematic review.

METHODS

EMBASE and MEDLINE databases were searched for human and animal cadaveric biomechanical studies investigating the effect of various surgical techniques to reduce PJK/PJF following long segment instrumented thoracolumbar spinal fusion in the adult patient population. Studied techniques, biomechanical test methods, range of motion (ROM), intervertebral disc pressure (IDP) and other relevant outcome parameters were documented.

RESULTS

Twelve studies met the inclusion criteria. Four of these studies included non-human cadaveric material. One study investigated the prophylactic application of cement augmentation (vertebroplasty), whereas the remaining studies investigated semi-rigid junctional fixation techniques to achieve a gradual transition zone of forces at the proximal end of a fusion construct, so-called topping-off. An increased gradual transition zone in terms of ROM compared to pedicle screw constructs was demonstrated for sublaminar tethers, sublaminar tape, pretensioned suture loops, transverse hooks and laminar hooks. Furthermore, reduced IDP was found after the application of sublaminar tethers, suture loops, sublaminar tapes and laminar hooks. Finally, two-level prophylactic vertebroplasty resulted in a lower incidence of vertebral compression fractures in a flexion-compression experiment.

CONCLUSIONS

A variety of techniques, involving either posterior semi-rigid junctional fixation or the reinforcement of vertebral bodies, has been biomechanically assessed. However, the low number of studies and variation in study protocols hampers direct comparison of different techniques. Furthermore, determination of what constitutes an optimal gradual transition zone and its translation to clinical practice, would aid comparison and further development of different semi-rigid junctional fixation techniques. Even though biomechanics are extremely important in the development of PJK/PJF, patient-specific factors should always be taken into account on a case-by-case basis when considering to apply a semi-rigid junctional fixation technique.

Who Will Require Revision Surgery Among Neurologically Intact Patients with Proximal Junctional Failure After Surgical Correction of Adult Spinal Deformity?

STUDY DESIGN

Retrospective study.

OBJECTIVE

To identify the risk factors for revision surgery among neurologically intact patients with proximal junctional failure (PJF) after adult spinal deformity (ASD) surgery.

SUMMARY OF BACKGROUND DATA

PJF following long fusion for ASD is a well-recognized complication that negatively affects clinical outcomes. However, revision surgery is not required for every patient with PJF especially if the patient does not present with neurologic deficit. Identifying the risk factors of revision surgery is necessary to determine who will need revision surgery as well as when is the right time for the revision surgery.

METHODS

Sixty-nine neurologically intact patients with PJF following ASD surgery were followed up with more than 2 years after PJF development or until undergoing revision surgery. PJF was divided into ligamentous failure (proximal junctional angle [PJA] of more than 20°) and bony failure. According to the conduct of revision surgery, two groups (revision and no revision) were created. Risk factors for revision surgery were analyzed in univariate and multivariate analysis with regard to patient, surgical and radiographic variables.

RESULTS

The mean age at the time of PJF development was 70.9 years. There were 45 patients with bony failure and 24 with ligamentous failure. Revision surgery was performed for 23 patients (33.3%). Multivariate analysis revealed that bony failure (odds ratio: 10.465) and PJA (odds ratio: 1.131) were significant risk factors. For those with bony failure, the cutoff value of PJA for performing revision surgery was calculated as 22°. The revision rate was significantly highest in patients (63.6%) with bony failure + PJA 22° or higher followed by patients (26.1%) with bony failure + PJA less than 22° and patients (12.5%) with ligamentous failure (P = 0.002).

CONCLUSION

Bony failure with PJA of greater than 22° increased the likelihood for revision surgery. Therefore, early surgical intervention should be considered in these patients.Level of Evidence: 4.

Postural Sway in Older Patients with Sagittal Imbalance and Young Adults during Local Vibratory Proprioceptive Stimulation

This study aimed to assess differences in somatosensory control strategies between older patients with sagittal imbalance and young adults during postural tasks. The center of pressure displacement in 27 older patients with sagittal imbalance and 27 young adults was determined upon standing blindfolded on a balance board. Vibratory stimulation at 56 to 100 Hz was applied bilaterally to the gastrocnemius and soleus muscles (GS) and lumbar multifidus to evaluate the contributions of proprioceptive signals to postural control. Data of older patients and young adults were compared using the Mann–Whitney U-test or independent sample t-tests. Compared with the young adults, the older patients were significantly more reliant on the GS (p < 0.005) for their postural control and showed a higher relative proprioceptive weighting ratio (RPW) (p = 0.038). The postural strategy adopted by the older patients depended on the level of proprioceptive stimulation applied to the GS, and the postural control strategy of the ankle correlated with RPW. Overall, this study identifies RPW as a novel measure of postural strategy in older patients with sagittal imbalance and provides an understanding of strategies used to maintain balance, which may assist in developing preventative measures to reduce the risk of falls.

Should Thoracolumbar Junction Be Always Avoided as Upper Instrumented Vertebra in Long Instrumented Fusion for Adult Spinal Deformity?: Risk Factor Analysis for Proximal Junctional Failure

STUDY DESIGN

Retrospective study.

OBJECTIVE

The aim of this study was to investigate the risk factors for proximal junctional failure (PJF) following long instrumented fusion stopping at thoracolumbar junction (TLJ) in adult spinal deformity (ASD) and to determine which cases are suitable for TLJ stop without increasing the risk for PJF.

SUMMARY OF BACKGROUND DATA

PJF following long fusion for ASD is a well-recognized complication that negatively affects clinical outcomes. Generally, the uppermost instrumented vertebra (UIV) at the TLJ is associated with the risk of PJF. Little is known about the risk factors for PJF in case with the UIV at TLJ.

METHODS

Radiographic and clinical data of 63 consecutive patients who underwent instrumented fusion from sacrum to TLJ (T11, T12, and L1) for the treatment of ASD with a minimum 2-year follow-up were analyzed to identify the risk factors for PJF, which was defined as proximal junctional angle (PJA) ≥20°, fracture at UIV or UIV+1, failure of UIV fixation, myelopathy, or 'need for proximal extension of fusion.

RESULTS

During the average follow-up duration of 51.7 months, PJF developed in 23 patients (36.5%) at a mean of 9.3 months after surgery. Multivariate analysis revealed that age >70 years (odds ratio [OR]: 1.119), osteoporosis (OR: 4.459), and preoperative kyphotic PJA (OR: 1.138) were significant risk factors for the development of PJF. No PJF occurred in 14 patients lacking any risk factors. The last follow-up clinical results were significantly inferior in the PJF group than in the non-PJF group in terms of Oswestry Disability Index and Scoliosis Research Society-22 score.

CONCLUSION

Age >70 years, osteoporosis, and PJA greater 0° were identified as significant risk factors for PJF. Therefore, the TLJ level can be considered as UIV selectively for patients younger than 70 years without osteoporosis and with lordotic preoperative PJA.

LEVEL OF EVIDENCE

3.

The Dubousset Functional Test is a Novel Assessment of Physical Function and Balance

BACKGROUND

Currently, the functional status of patients undergoing spine surgery is assessed with quality-of-life questionnaires, and a more objective and quantifiable assessment method is lacking. Dr. Jean Dubousset conceptually proposed a four-component functional test, but to our knowledge, reference values derived from asymptomatic individuals have not yet been reported, and these are needed to assess the test's clinical utility in patients with spinal deformities.

QUESTIONS/PURPOSES

(1) What are the reference values for the Dubousset Functional Test (DFT) in asymptomatic people? (2) Is there a correlation between demographic variables such as age and BMI and performance of the DFT among asymptomatic people?

METHODS

This single-institution prospective study was performed from January 1, 2018 to May 31, 2018. Asymptomatic volunteers were recruited from our college of medicine and hospital staff to participate in the DFT. Included participants did not report any musculoskeletal problems or trauma within 5 years. Additionally, they did not report any history of lower limb fracture, THA, TKA, or patellofemoral arthroplasty. Patients were also excluded if they reported any active medical comorbidities. Demographic data collected included age, sex, BMI, and self-reported race. Sixty-five asymptomatic volunteers were included in this study. Their mean age was 42 ± 15 years; 27 of the 65 participants (42%) were women. Their mean BMI was 26 ± 5 kg/m. The racial distribution of the participants was 34% white (22 of 65 participants), 25% black (16 of 65 participants), 15% Asian (10 of 65 participants), 9% subcontinental Indian (six of 65 participants), 6% Latino (four of 65 participants), and 10% other (seven of 65 participants). In a controlled setting, participants completed the DFT after verbal instruction and demonstration of each test, and all participants were video recorded. The four test components included the Up and Walking Test (unassisted sit-to-stand from a chair, walk forward/backward 5 meters [no turn], then unassisted stand-to-sit), Steps Test (ascend three steps, turn, descend three steps), Down and Sitting Test (stand-to-ground, followed by ground-to-stand, with assistance as needed), and Dual-Tasking Test (walk 5 meters forwards and back while counting down from 50 by 2). Tests were timed, and data were collected from video recordings to ensure consistency. Reference values for the DFT were determined via a descriptive analysis, and we calculated the mean, SD, 95% CI, median, and range of time taken to complete each test component, with univariate comparisons between men and women for each component. Linear correlations between age and BMI and test components were studied, and the frequency of verbal and physical pausing and adverse events was noted.

RESULTS

The Up and Walking Test was completed in a mean of 15 seconds (95% CI, 14-16), the Steps Test was completed in 6.3 seconds (95% CI, 6.0-6.6), the Down and Sitting Test was completed in 6.0 seconds (95% CI, 5.4-6.6), and the Dual-Tasking Test was performed in 13 seconds (95% CI, 12-14). The length of time it took to complete the Down and Sitting (r = 0.529; p = 0.001), Up and Walking (r = 0.429; p = 0.001), and Steps (r = 0.356; p = 0.014) components increased with as the volunteer's age increased. No correlation was found between age and the time taken to complete the Dual-Tasking Test (r = 0.134; p = 0.289). Similarly, the length of time it took to complete the Down and Sitting (r = 0.372; p = 0.005), Up and Walking (r = 0.289; p = 0.032), and Steps (r = 0.366; p = 0.013) components increased with increasing BMI; no correlation was found between the Dual-Tasking Test's time and BMI (r = 0.078; p = 0.539).

CONCLUSIONS

We found that the DFT could be completed by asymptomatic volunteers in approximately 1 minute, although it took longer for older patients and patients with higher BMI.

CLINICAL RELEVANCE

We believe, but did not show, that the DFT might be useful in assessing patients with spinal deformities. The normal values we calculated should be compared in future studies with those of patients before and after undergoing spine surgery to determine whether this test has practical clinical utility. The DFT provides objective metrics to assess function and balance that are easy to obtain, and the test requires no special equipment.

Paraspinal muscle size as an independent risk factor for proximal junctional kyphosis in patients undergoing thoracolumbar fusion

OBJECTIVE

Proximal junctional kyphosis (PJK) is a structural complication of spinal fusion in 5%–61% of patients treated for adult spinal deformity. In nearly one-third of these cases, PJK is progressive and requires costly surgical revision. Previous studies have suggested that patient body habitus may predict risk for PJK. Here, the authors sought to investigate abdominal girth and paraspinal muscle size as risk factors for PJK.

METHODS

All patients undergoing thoracolumbosacral fusion greater than 2 levels at a single institution over a 5-year period with ≥ 6 months of radiographic follow-up were considered for inclusion. PJK was defined as kyphosis ≥ 20° between the upper instrumented vertebra (UIV) and two supra-adjacent vertebrae. Operative and radiographic parameters were recorded, including pre- and postoperative sagittal vertical axis (SVA), sacral slope (SS), lumbar lordosis (LL), pelvic tilt, pelvic incidence (PI), and absolute value of the pelvic incidence–lumbar lordosis mismatch (|PI-LL|), as well as changes in LL, |PI-LL|, and SVA. The authors also considered relative abdominal girth and the size of the paraspinal muscles at the UIV.

RESULTS

One hundred sixty-nine patients met inclusion criteria. On univariate analysis, PJK was associated with a larger preoperative SVA (p < 0.001) and |PI-LL| (p = 0.01), and smaller SS (p = 0.004) and LL (p = 0.001). PJK was also associated with more positive postoperative SVA (p = 0.01), ΔSVA (p = 0.01), Δ|PI-LL| (p < 0.001), and ΔLL (p < 0.001); longer construct length (p = 0.005); larger abdominal girth–to-muscle ratio (p = 0.007); and smaller paraspinal muscles at the UIV (p < 0.001). Higher postoperative SVA (OR 1.1 per cm), smaller paraspinal muscles at the UIV (OR 2.11), and more aggressive reduction in |PI-LL| (OR 1.03) were independent predictors of radiographic PJK on multivariate logistic regression.

CONCLUSIONS

A more positive postoperative global sagittal alignment and smaller paraspinal musculature at the UIV most strongly predicted PJK following thoracolumbosacral fusion.