Assessment of atlantoaxial rotation: how accurate is clinical measurement? a comparative study of cervical range of motion using MRI and standard orthopedic techniques.

PURPOSE: Measurement of neck rotation is currently reliant on radiologic imaging. Given the radiation exposure for CT imaging and the additional inconvenience for the patients, an alternative assessment is needed. Goniometers are comfortably to use and easy to access, also for private consulting. The aim of this study was the assessment of whether a handheld goniometer can be used for accurately measuring the rotation of C1-C2. METHODS: Clinical measurement of rotation was taken in flexed position of the neck. As comparison functional MRI was used. The measured rotation of C1-C2 was compared to identify the accuracy of the goniometer, in comparison to functional MRI scan. RESULTS: Analysis of accuracy using a goniometer and dynamic MRI to assess C1-2 axial rotation showed significant differences for absolute values, but not regarding the percentage of rotation compared to total neck rotation. CONCLUSION: The goniometer is exact to impartially determine the percentage contribution of C1-2 rotation to total neck rotation.

Surgical nuances and construct patterns influence construct stiffness in C1-2 stabilizations: a biomechanical study of C1-2 gapping and advanced C1-2 fixation.

PURPOSE: Stabilization of C1-2 using a Harms-Goel construct with 3.5 mm titanium (Ti) rods has been established as a standard of reference (SOR). A reduction in craniocervical deformities can indicate increased construct stiffness at C1-2. A reduction in C1-2 can result in C1-2 joint gapping. Therefore, the authors sought to study the biomechanical consequences of C1-2 gapping on construct stiffness using different instrumentations, including a novel 6-screw/3-rod (6S3R) construct, to compare the results to the SOR. We hypothesized that different instrument pattern will reveal significant differences in reduction in ROM among constructs tested. METHODS: The range of motion (ROM) of instrumented C1-2 polyamide models was analyzed in a six-degree-of-freedom spine tester. The models were loaded with pure moments (2.0 Nm) in axial rotation (AR), flexion extension (FE), and lateral bending (LB). Comparisons of C1-2 construct stiffness among the constructs included variations in rod diameter (3.5 mm vs. 4.0 mm), rod material (Ti. vs. CoCr) and a cross-link (CLX). Construct stiffness was tested with C1-2 facets in contact (Contact Group) and in a 2 mm distracted position (Gapping Group). The ROM (°) was recorded and reported as a percentage of ROM (%ROM) normalized to the SOR. A difference > 30% between the SOR and the %ROM among the constructs was defined as significant. RESULTS: Among all constructs, an increase in construct stiffness up to 50% was achieved with the addition of CLX, particularly with a 6S3R construct. These differences showed the greatest effect for the CLX in AR testing and for the 6S3R construct in FE and AR testing. Among all constructs, C1-2 gapping resulted in a significant loss of construct stiffness. A protective effect was shown for the CLX, particularly using a 6S3R construct in AR and FE testing. The selection of rod diameter (3.5 mm vs. 4.0 mm) and rod material (Ti vs. CoCr) did show a constant trend but did not yield significance. CONCLUSION: This study is the first to show the loss of construct stiffness at C1-2 with gapping and increased restoration of stability using CLX and 6S3R constructs. In the correction of a craniocervical deformity, nuances in the surgical technique and advanced instrumentation may positively impact construct stability.

Temporary treatment with magnetically controlled growing rod for surgical correction of severe adolescent idiopathic thoracic scoliosis greater than 100°.

INTRODUCTION: Correction of severe idiopathic scoliosis poses surgical challenges. Treatment options entail anterior and/or posterior release, Halo-gravity traction (HGT) and three-column osteotomies (3CO). The authors report results with a novel technique of temporary short-term magnetically controlled growing rod (MCGR) as part of a posterior-only strategy to treat severe idiopathic major thoracic curves (MTC). METHODS: Seven patients with MTC > 100° treated with temporary MCGR were included. Mean age was 15 years. Preoperative MTC was av. 118° and TC-flexibility av. 19.8%. Patients underwent posterior instrumentation, periapical release using advanced Ponte osteotomies, segmental insertion of pedicle screws and a single MCGR. After av. 14 days, the second surgery was performed with removal of MCGR and final correction and fusion. The spinal height from lowest instrumented vertebra (LIV) to T1 was measured. MTC-correction and scoliosis correction index (SCI) were calculated. RESULTS: No patient suffered a major complication or neurologic deficit. Instrumentation was from T2 to L3 or L4. This kind of staged surgery achieved a correction of postop MTC to av. 39°, MTC-correction 67% and SCI of av. 4.3. Spinal height T1-LIV increased from preoperative av. 288 mm to postoperative av. 395 mm indicating an increase of > 10 cm. CONCLUSION: This is the first series of AIS patients that had temporary MCGR to treat severe thoracic scoliosis. A staged protocol including internal temporary distraction with MCGR after posterior release and definitive correction resulted in large MTC-correction and restoration of trunk height. Results indicate that technique has the potential to reduce the necessity for HGT and high-risk 3CO for the correction of severe scoliosis.

A new nomenclature system for the surgical treatment of cervical spine deformity, developing, and validation of SOF system.

PURPOSE: To develop and assess the reliability of new nomenclature system that systematically organizes osteotomy techniques and briefly describes the surgical approach, the surgical sequence, and the fixation technique for cervical spine deformity (CSD). METHODS: We developed a new classification system (SOF system) for CSD surgery that describes the sequence of surgical approach (S), the grade of osteotomy (O), and the information of fixation (F) using alphanumeric codes. Twenty CSD osteotomies (8 anterior osteotomies, 12 posterior osteotomies) were included in this study to evaluate the inter- and intra-observer agreement based on operation records. Six observers performed independent evaluations of the operation records in random order. Each observer described 20 CSD surgeries using the SOF system twice (> 30 days between assessments) based on operation records to validate SOF system. RESULTS: Overall agreement (among all six observers at the initial assessment) on the anterior and posterior osteotomy was ICC = 0.96 and ICC = 0.91, respectively. Overall agreement (repeat observations after at least 30 days) on the anterior and posterior osteotomy was ICC = 0.96 and ICC = 0.91, respectively. This data showed that both inter- and intra-observer agreement revealed 'excellent'. CONCLUSION: This study introduces the SOF system of the CSD surgery to understand the surgical sequence, the type of osteotomy and the fixation techniques. The investigation of the inter- and intra-observer agreement revealed 'excellent agreement' for both anterior and posterior osteotomies. Thus, SOF system can provide a consistent description of the various CSD surgeries and its use will provide a common frame for CSD surgery and help communicate between surgeons.

Flexibility of thoracic kyphosis affects postoperative sagittal alignment in adult patients with spinal deformity.

PURPOSE: Proximal junctional kyphosis (PJK) in adult spinal deformity (ASD) surgery patients is a severe complication with potential need for revision surgery. While thoracic kyphosis (TK) is known to influence PJK, the role of TK flexibility is still unknown. We analyzed the influence of TK flexibility to predict postoperative sagittal alignment. METHODS: Patients with ASD, ≥ 2-year follow-up, and upper-most instrumented vertebra (UIV) including and below T10 were included in this retrospective study. TK flexibility, defined as > 10° difference of the TK in standing and supine imaging, was analyzed. Patient characteristics like age, sex, weight, total hip arthroplasty, and sagittal alignment parameters were studied. RESULTS: Sixty-five patients aged 66 ± 8 years were included in the study. Lowest instrumented vertebra was S1 or the ilium in 85% of them; the number of levels being fused averaged 7. Flexible TK was present in 31% (n = 20). These patients had a larger preoperative TK (p < 0.01), but no PJK was found (p = 0.04). In contrast, patients who underwent revision surgery had a decreased TK flexibility (p = 0.04) and increased PJK angle at follow-up (p = 0.01). In the non-flexible patients, the PJK was found in 14% of patients. CONCLUSIONS: Based on our retrospective data, TK flexibility influences the outcome of ASD surgery. In patients demonstrating no TK flexibility, a more cephalad UIV-level should be considered because spontaneous curve correction in the sagittal plane might be low in these patients. This new parameter should be included in future prediction models. These slides can be retrieved under Electronic Supplementary Material.

[Surgical challenges with spinal balance in adult spinal deformities-the forgotten coronal plane]. / Herausforderungen in der Balancierung adulter Wirbelsäulendeformitäten ­ die vergessene koronare Ebene.

This article gives a brief overview of the importance, planning and correction of coronal spinal imbalance in patients with adult and pediatric spinal deformity.

Osteotomies in ankylosing spondylitis: where, how many, and how much?

INTRODUCTION: This article presents the current concepts of correction of spinal deformity in ankylosing spondylitis (AS) patients. Untreated AS can be a debilitating disease. In a few patients, disease progression results in severe spinal deformity affecting not only the thoracolumbar, but also the cervical spine. Surgery for correction in AS patients has a long history. With the advent of modern instrumentation, standardization of surgical and anesthesiologic techniques, surgical safety and corrective results could be improved and experiences from lumbar osteotomies could be transferred to the cervical spine. METHODS: This article presents the current concepts of correction of spinal deformity in AS patients. In particular, questions regarding the localization and number of osteotomies, the optimal surgical target angle as well as planning and prediction of postoperative alignment are discussed. RESULTS: Insight into recent technical developments, current challenges with correction and geometric analysis of center of rotation (COR) in cervical 3-column osteotomies (3CO) will be presented. CONCLUSION: The article should encourage readers to improve surgical correction efficacy and provide a better understanding of correction geometry in 3CO for thoracolumbar and cervical spinal deformities.

The influence of isolated thoracoplasty on the evolution of pulmonary function after treatment of severe thoracic scoliosis.

INTRODUCTION AND PURPOSE: Isolated thoracoplasty (iTP) on the convex side is performed long time after scoliosis surgery has been performed. ITP is thought to cause a further decline in pulmonary function (PF); however, the amount of decline is ill defined. The objectives of this study were to examine the influence of iTP on the postoperative evolution of PF and rib hump reduction in patients that previously undergone scoliosis surgery. METHODS: Over an 11-year period, 75 patients underwent iTP. The authors performed a retrospective case series review. Patients with data from PF tests performed preoperatively and at the last follow-up were included. Minimum follow-up was 12 months. The PF value reported was predicted FVC (FVC%). According to the American Thoracic Society, pulmonary impairment was classified as no impairment (FVC: >80-100%), mild (FVC: >65 ≤80%), moderate (FVC: >50 ≤65), and severe (FVC ≤50%). The outcome was studied using validated measures (SRS-24 score, COMI, and the COPD Assessment Test (CAT)). The CAT is stratified into mild impairment (<10 pts), moderate impairment (10-20 pts), severe impairment (>20-30 pts), and disabled (>30 pts). RESULTS: Twenty-six patients fulfilled the inclusion criteria. The patients' average age was 28 years at surgery with iTP, and 22 were females; the average BMI was 23, and the average follow-up was 76 months. Twenty of the patients had AIS, and six had congenital scoliosis. The time between scoliosis correction and iTP averaged 39 months. The mean number of resected rib segments was 7, and the mean blood loss was 834 ml. FVC% was 66% preoperatively and 57% at follow-up, with a significant change of 9% (p < .02). Fourteen patients had a FVC% change between preoperation and follow-up that was ≥5%; this change was not dependent on the preoperative FVC%. PF showed a slight but non-significant improvement with longer follow-up. At the time of iTP, the thoracic curve averaged 67°, and thoracic kyphosis averaged 46°. Rib hump height was 34 mm before iTP and 15 mm at follow-up (p < .03). At follow-up, the SRS-24 score was 81, the COMI score was 4 points, and the CAT score was 8 points. Eight patients had a CAT >10. Two patients had a major complication. A comparison of patients with pulmonary impairment preoperation vs. follow-up found 4 vs. 1 patients had no PF impairment, 8 vs. 4 patients had mild impairment, 10 vs. 13 patients had moderate impairment, and 4 vs. 8 patients had severe impairment. CONCLUSIONS: Isolated TP was shown an effective technique for rib hump resection. Six years after iTP, the FVC% declined by an average of 9%. Several patients had long-lasting effects in terms of %FVC decline. iTP should be reserved for patients with significant rib hump deformity.

Selecting caudal fusion levels: 2 year functional and stiffness outcomes with matched pairs analysis in multilevel fusion to L5 versus S1.

PURPOSE: Controversy persists as to whether to end multilevel thoracolumbar fusions caudally at L5 or S1. Some argue that stopping at L5 may preserve greater function, but there are few data comparing functional limitations due to lumbar stiffness in patients with fusion to L5 versus S1. The aim of this study was to evaluate whether patients undergoing multilevel thoracolumbar fusions with an L5 caudal endpoint have a better lumbosacral function than patients with an S1 caudal endpoint. METHODS: Patients undergoing successful thoracolumbar fusion of 5 or more levels to L5 or S1, with solid fusion at 2 year follow-up, were examined from a single European center in addition to a multi-center North American database of 237 patients. In total, 40 patients with a distal stopping point of L5 were matched with a subset of 40 patients with a distal endpoint of S1 ± pelvic fixation. The L5 and S1 groups were matched for the final Oswestry Disability Index (ODI), Sagittal Vertical Axis (SVA C7-S1), number of fusion levels, and age. Impacts of lumbar stiffness on function as measured by the Lumbar Stiffness Disability Index (LSDI) were compared using the conditional logistic regression. RESULTS: After matching, there was no significant difference between the S1 and L5 groups for the final ODI (29.22 ± 21.6 for S1 versus 29.21 ± 21.7 for L5; p = 0.98), SVA (29.5 ± 40.3 mm for S1 versus 33.7 ± 37.1 mm for L5; p = 0.97), mean age (61.6 ± 11.0 years for S1 versus 58.3 ± 12.6 years for L5; p = 0.23), and number of fusion levels (9.7 ± 3.3 levels for S1 versus 9.0 ± 3 levels for L5; p = 0.34). The final 2-year postoperative LSDI scores were not significantly different between the S1 group (28.08 ± 21.47) and L5 group (29.21 ± 21.66) (hazard ratio 0.99, 95 % CI 0.97-1.03, p = 0.81). CONCLUSION: The analysis of patients with multilevel thoracolumbar fusions demonstrated that after minimum 2 year follow-up, self-reported functional impacts of lumbar stiffness were not significantly different between the patients with distal endpoints of L5 versus S1. The choice of distal fusion level of L5 does not appear to retain sufficient spinal flexibility to substantially affect postoperative function. LEVEL OF EVIDENCE: Level III.

Factors influencing radiographic and clinical outcomes in adult scoliosis surgery: a study of 448 European patients.

INTRODUCTION/PURPOSE: In adult scoliosis surgery (AS) delineation of risk factors contributing to failure is important to improve patient care. Treatment goals include deformity correction resulting in a balanced spine and horizontal lowest instrumented vertebra (LIV) in fusions not ending at S1. Therefore, the study objectives were to determine predictors for deformity correction, complications, revision surgery, and outcomes as well as to determine predictors of postoperative evolution of the LIV-take-off angle (LIV-TO) and symptomatic adjacent segment disease (ASD). METHODS: The authors performed a retrospective analysis of 448 patients who had AS surgery. Patients' age averaged 51 years, BMI 26, and follow-up of 40 months. According to the SRS adult scoliosis classification, 51 % of patients had major lumbar curves, 24 % each with single thoracic or double major curves. 54 % of patients had stable vertebra at L5 and 34 % of patients had fusion to S1. The mean number of posterior fusion levels was eight and implant density 73 %. Among standard radiographic measures of deformity the LIV-TO was assessed on neutral and bending/traction-films (bLIV-TO). Clinical outcomes were assessed in 145 patients with degenerative-type AS using validated measures (ODI, COMI and SF-36). Prediction analysis was conducted with stepwise multiple regression analyses. RESULTS: Preoperative thoracic curve (TC) was 53° and 33° at follow-up. Preoperative lumbar curve (LC) was 43° and 24° at follow-up. Curve flexibility was low (TC 34 %/LC 38 %). TC-correction (38 %) was predicted by preoperative TC (r = 0.9) and TC-flexibility (r = 0.8). LC-correction (50 %) was predicted by preoperative LC (r = 0.8), LC-flexibility (r = 0.8) and screw density (r = 0.7). Preoperative LIV-TO was 18.2° and at follow-up 9.4° (p < 0.01). 20 % of patients had a non-union (18 % at L5-S1). The risk for non-union at L5-S1 increased with age (p = 0.04), low screw density (p = 0.03), and postoperative sagittal imbalance [(T9-tilt (p = 0.01), C7-SVA (p = 0.01), LL (p = 0.01) and PI-LL mismatch (p = 0.01)]. 32 % of patients had revision surgery. Risk for revision was increased in fusions to S1 (p < 0.01), increased BMI (p < 0.01), sagittal imbalance (C7-SVA, p < 0.01), age (p = 0.02), and disc wedging distal to the LIV (p < 0.01). To a varying extent, clinical outcomes negatively correlated (p < 0.05) with revision, ASD, perioperative complications, age, low postoperative TC- and LC-correction, and sagittal and coronal imbalance at follow-up (C7-SVA, PT, and C7-CSVL). 59 patients had ASD, which correlated with preoperative and postoperative sagittal and coronal parameters of deformity. In a multivariate model, preoperative bLIV-TO (p < 0.01) and preoperative LIV-TO (p < 0.01) demonstrated the highest predictive strength for follow-up LIV-TO. CONCLUSION: In the current study, the magnitude of deformity correction in the sagittal and coronal planes was shown to have significant impact on radiographic and clinical outcomes as well as revision rates. Findings indicate that risks for complications might be reduced by restoration of sagittal balance, appropriate deformity correction and advanced lumbosacral fixation. The use of preoperative LIV-TO and LIV-TO on bending/traction-films were shown to be useful for surgical planning, selection of the LIV and prediction of follow-up-TO, respectively. Parameters of sagittal balance rather than coronal deformity predicted ASD.

Cervical laminectomy and instrumented lateral mass fusion: techniques, pearls and pitfalls.

INTRODUCTION: Cervical laminectomy is a reliable tool for posterior decompression in various cervical spine pathologies. Although there is increasing evidence of superior clinical, neurological and radiological outcomes when using anterior cervical decompression, laminectomy can be a valuable tool when combined with instrumented lateral mass fusion for carefully selected indications. METHODS: Literature review. RESULTS: This review article will provide decision-making guidance, technical advice and pitfalls. The technical advice for laminectomy and instrumented lateral mass fusion is illustrated. The authors review the literature on outcomes and complications and suggest indications for the safe and successful application of cervical laminectomy and lateral mass fusion.

Parameters leading to a successful radiographic outcome following surgical treatment for Lenke 2 curves.

INTRODUCTION: In Lenke 2 curves, there are conflicting data when to include the PTC into the fusion. Studies focusing on Lenke 2 curves are scant. The number of patients with significant postoperative shoulder height difference (SHD) or trunk shift (TS) is as high as 30 % indicating further research. Therefore, the purpose of the current study was to improve understanding of curve resolution and shoulder balance following surgical correction of Lenke 2 curves as well as the identification of radiographic parameters predicting postoperative curve resolution, shoulder and trunk balance in perspective of inclusion/exclusion of the proximal thoracic curve (PTC). METHODS: This is a retrospective study of a 158 Lenke 2 curves. Serial radiographs were analyzed for the main thoracic curve (MTC), PTC, and lumbar curve (LC), SHD, clavicle angle (CA), T-1 tilt, deviation of the central sacral vertical line (CSVL) off the C7 plumb line.Patients were stratified whether the PTC was included in the fusion (+PTC group, n = 60) or not (-PTC group, n = 98). Intergroup results were studied. Compensatory mechanisms for SHD were studied in detail. Adding-on distally was defined as an increase of the lowest instrumented vertebra adjacent disc angle (LIVDA) >3°. Stepwise regression analyses were performed to establish predictive radiographic parameters. RESULTS: At follow-up averaging 24 months significant differences between the +PTC and -PTC group existed for the PTC (24° vs 28°, p < .01), PTC correction (42 vs 29 %, p < .01), rate of MTC-loss >5° (27 vs 53 %, p < .01), and spontaneous LC correction in patients with a selective thoracic fusion (STF) (80/93 %, p = .04). The number of patients with a new trunk shift (CSVL > 2 cm) was 9 (6 %): 7 in the -PTC vs 2 in the +PTC group (p = .03). Utilization of compensatory mechanisms (99 vs 83 %, p < .01) and adding-on (35 vs 20 %, p < .05) occurred more often in the +PTC vs the -PTC groups. Statistics showed postoperative SHD improvement in both the +PTC and -PTC groups. There were no significant differences regarding SHD, CA and T1-Tilt between groups. However, only in the -PTC group, a significant change between postoperative and follow-up SHD existed (p = .02). Statistics identified a preoperative 'left shoulder up' (p < .01) and CSVL (p = .03) predictive for follow-up SHD ≥1.5 cm. A statistical model only for the -PTC group showed 9 parameters highly predictive for a follow-up SHD ≥1.5 cm with highest prediction strength for a PTC >40° (p = .01), a preoperative 'left shoulder up' (p < .01) and anterior fusion (p = .02). To account for baseline differences between the +PTC and -PTC groups, 49 matched-pairs were studied. Postoperative differences remained significant between the +PTC and -PTC groups for the PTC (p < .01), MTC (p = .03) and the rate of loss of MTC >5° (p < .01). CONCLUSION: Prediction of a successful surgical outcome for Lenke 2 curves depends on multiple variables, in particular a preoperative left shoulder up, preoperative PTC >40°, MTC correction, and surgical approach. Shoulder balance is not significantly different whether the PTC is included in the fusion or not. But, powerful compensation mechanisms utilized to balance shoulder in the -PTC group can impose changes of trunk alignment, main and compensatory lumbar curves.

Construct stability of an instrumented 2-level cervical corpectomy model following fatigue testing: biomechanical comparison of circumferential antero-posterior instrumentation versus a novel anterior-only transpedicular screw-plate fixation technique.

INTRODUCTION: A high rate of complications in multilevel cervical surgery with corpectomies and anterior-only screw-and-plate stabilization is reported. A 360°-instrumentation improves construct stiffness and fusion rates, but adds the morbidity of a second approach. A novel ATS-technique (technique that used anterior transpedicular screw placement) was recently described, yet no study to date has analyzed its performance after fatigue loading. Accordingly, the authors performed an analysis of construct stiffness after fatigue testing of a cervical 2-level corpectomy model reconstructed using a novel anterior transpedicular screw-and-plate technique (ATS-group) in comparison to standard antero-posterior instrumentation (360°-group). MATERIALS AND METHODS: Twelve fresh-frozen human cervical spines were mounted on a spine motion tester to analyze restriction of ROM under loading (1.5 Nm) in flexion-extension (FE), axial rotation (AR), and lateral bending (LB). Testing was performed in the intact state, and after instrumentation of a 2-level corpectomy C4 + C5 using a cage and the constructs of ATS- and 360°-group, after 1,000 cycles, and after 2,000 cycles of fatigue testing. In the ATS-group (n = 6), instrumentation was achieved using a customized C3-C6 ATS-plate system. In the 360°-group (n = 6), instrumentation consisted of a standard anterior screw-and-plate system with a posterior instrumentation using C3-C6 lateral mass screws. Motion data were assessed as degrees and further processed as normalized values after standardization to the intact ROM state. RESULTS: Specimen age and BMD were not significantly different between the ATS- and 360°-groups. After instrumentation and 2,000 cycles of testing, no specimen exhibited a ROM greater than in the intact state. No specimen exhibited catastrophic construct failure after 2,000 cycles. Construct stiffness in the 360°-group was significantly increased compared to the ATS-group for all loading conditions, except for FE-testing after instrumentation. After 2,000 cycles, restriction of ROM under loading in FE was 39.8 ± 30% in the ATS-group vs. 2.8 ± 2.3% in the 360°-group, in AR 60.4 ± 25.8 vs 15 ± 11%, and in LB 40 ± 23.4 vs 3.9 ± 1.2%. Differences were significant (p < 0.05). CONCLUSION: 360°-instrumentation resembles the biomechanical standard of reference for stabilization of 2-level corpectomies. An ATS-construct was also shown to confer high construct stiffness, significantly reducing the percentage ROM beyond that of an intact specimen after 2,000 cycles. This type of instrumentation might be a clinical valuable and biomechanically sound adjunct to multilevel anterior surgical procedures.

Criteria for successful correction of thoracolumbar/lumbar curves in AIS patients: results of risk model calculations using target outcomes and failure analysis.

INTRODUCTION: Failure to select the appropriate lowest instrumented vertebra (LIV) in selective lumbar fusion (SLF) for thoracolumbar/lumbar curves (LC) can result in adding-on in the lumbar curve (LC) or the need for fusion extension due to a decompensating thoracic curve (TC). The selection criteria that predict optimal outcomes still need to be refined. The objectives of the current study were to identify risk factors for failure of anterior scoliosis correction and fusion (ASF) as well as predictors of optimal outcomes and ASF efficacy for SLF. MATERIALS AND METHODS: A retrospective review of all patients (n = 245) with AIS who had anterior SLF at one institution was conducted. Optimal outcomes were defined as a target LC ≤ 20° and a target TC ≤ 30°. The distance from the LIV to the SV was recorded. An increase in the LIV adjacent level disc angulation (LIVDA) ≥ 5° was defined as adding-on. An increase in the TC at follow-up was defined as TC-progression. Stepwise univariate and multivariate linear and logistic regression analyses were performed to identify criteria predicting the target LC and TC. A total of 68 % of the patients had the LIV at SV-2 (=2 levels above stable vertebra). RESULTS: The patients' average age was 17 years, the average fusion length was 4.6 levels, and the average follow-up time was 32 months. The preoperative LC was 49 ± 14°, the LC-bending was 22 ± 13° (57 ± 18 %), and the follow-up LC was 25 ± 10°. LC correction was 59 ± 17% (p < 0.01). The preoperative TC was 39 ± 13°, the TC-bending was 21 ± 12°, and the follow-up TC was 29 ± 13°. The TC-correction was 32 ± 19% (p < 0.01). At follow-up, 85 patients (35%) had an LC ≤ 20°, 110 patients (45 %) had a TC ≤ 30°. The follow-up LC and an LC ≤ 20° were predicted by LC-bending (p < 0.01, r = 0.6), preoperative LC (p < 0.01, r = 0.6). The logistic regression models could define patients at risk for failing the target LC ≤ 20° or TC ≤ 30°. At follow-up, TC ≤ 30° was best predicted by the preoperative TC (p < 0.01, r = 0.8; OR 1.2) and TC-bending (p < 0.01, r = 0.8; OR 1.06), with the logistic regression model revealing a correct prediction in 84 % of all cases. Among the patients, 8 % required late posterior surgery. Patients achieving the target LC ≤ 20° had a significantly reduced risk for failure (p = 0.01). Selecting an LIV at SV-1 vs. SV-2 significantly increased the chance of achieving a target LC ≤ 20° (p = 0.01) and reduced the risk of adding-on (p < 0.01). Predictors for failure also included a high preoperative LC (p = 0.02; OR 0.97), TC-bending (p < 0.01), and preoperative TC (p = 0.01). A cut-off in the failure risk analysis was established at a TC of 38°. Additionally, a significant cut-off for risk of adding-on was established at LIVDA <3.5°. CONCLUSION: A high chance of achieving a target LC ≤ 20° and a low risk of revision was dependent on LC-bending, preoperative LC and TC, and a LIV at SV-1 with non-parallel LIVDA. Our risk model analysis may support the selection of a safe LIV to achieve the target LC.

Selective thoracic fusion in AIS curves: the definition of target outcomes improves the prediction of spontaneous lumbar curve correction (SLCC).

INTRODUCTION: The decision of when to use selective thoracic fusion (STF) and the prediction of spontaneous lumbar curve correction (SLCC) remain difficult. Using a novel methodological approach, the authors yielded for a better prediction of SLCC and analyzed the efficacy of anterior scoliosis correction and fusion (ASF). METHODS: A retrospective analysis of 273 patients treated with ASF for STF was performed. In total, 87 % of the patients showed a Lenke 1 curve pattern. The lumbar curve modifier was classified as A in 66 % of the patients, B in 21 % of the patients and C in 13 % of the patients. The fusion length averaged 6.7 levels. The analysis included an assessment of radiographic deformity and correction, surgery characteristics, complications and revisions and clinical outcomes to improve the prediction of SLCC. Patients with a Type A-L, Type B or Type C modifier were stratified into a target follow-up lumbar curve (LC) category of ≤20° or >20°. Linear regression analyses were performed to assess the accuracy of predicting LC magnitude, and a multivariate logistic regression model was built using the following preoperative (preop) predictors: main thoracic curve (MTC), LC, MTC-bending and LC-bending. The output variable indicated whether a patient had an LC >20° at follow-up. A variable selection algorithm was applied to identify significant predictors. Two thresholds (cut-offs) were applied to the test sample to create high positive and negative prediction values. The data from 33 additional patients were gathered prospectively to create an independent test sample to learn how the model performed with independent data as a test of the generalizability of the model. RESULTS: The average patient age was 17 years, and the average follow-up period was 33 months. The MTC was 53.1° ± 10.2° preoperatively, 29.8° ± 10.5° with bending and was 25.4° ± 9.7° at follow-up (p < 0.01). The LC was 35.7° ± 7.5° preoperatively, 8.9° ± 5.8° with bending, and 21.8° ± 7.0° at follow-up (p < 0.01). After applying a variable selection algorithm, the preop LC [p < 0.02, odds ratio (OR) = 1.09] and preop LC-bending (p < 0.009, OR = 1.14) remained in the model as significant predictors. The performance of the linear regression model was tested in an independent test sample, and the difference between the observed and predicted values was only 1° ± 4.5°. Based on the test sample, the lower threshold was set to 25 %, and the upper threshold was set to 75 %. Patients with prediction values of 25-75 % were identified by the model, but by definition of the model, no prediction was made. In the test sample, 87 % of the patients were correctly classified as having an LC ≤20° at follow-up, and 84 % of the patients were correctly classified as having an LC >20°. The model test in the independent test sample revealed that 100 % of the patients were correctly classified as having an LC ≤20°, and 86 % of the patients were correctly classified as having an LC >20°. CONCLUSION: After analyzing a sufficiently large sample of 273 patients who underwent ASF for STF, significant predictors for SLCC were established and reported according to the surgical outcomes. Application of the prediction models can aid surgeons in the decision-making process regarding when to perform STF. Our results indicate that with stratification of outcomes into target curves (e.g., an LC <20°), future benchmarks for STF might be more conclusive.

Surgical treatment of Scheuermann's kyphosis using a combined antero-posterior strategy and pedicle screw constructs: efficacy, radiographic and clinical outcomes in 111 cases.

INTRODUCTION: There is sparse literature on how best to correct Scheuermann's kyphosis (SK). The efficacy of a combined strategy with anterior release and posterior fusion (AR/PSF) with regard to correction rate and outcome is yet to be determined. MATERIALS AND METHODS: A review of a consecutive series of SK patients treated with AR/PSF using pedicle screw-rod systems was performed. Assessment of demographics, complications, surgical parameters and radiographs including flexibility and correction measures, proximal junctional kyphosis angle (JKA + 1) and spino-pelvic parameters was performed, focusing on the impact of curve flexibility on correction and clinical outcomes. RESULTS: 111 patients were eligible with a mean age of 23 years, follow-up of 24 months and an average of eight levels fused. Cobb angle at fusion level was 68° preoperatively and 37° postoperatively. Flexibility on traction films was 34 % and correction rate 47 %. Postoperative and follow-up Cobb angles were highly correlated with preoperative bending films (r = 0.7, p < 0.05). Screw density rate was 87 %, with increased correction with higher screw density (p < 0.001, r = 0.4). Patients with an increased junctional kyphosis angle (JKA + 1) were at higher risk of revision surgery (p = 0.049). 22 patients sustained complication, and 21 patients had revision surgery. 42 patients with ≥24 months follow-up were assessed for clinical outcomes (follow-up rate for clinical measures was 38 %). This subgroup showed no significant differences regarding baseline parameters as compared to the whole group. Median approach-related morbidity (ArM) was 8.0 %, SRS-sum score was 4.0, and ODI was 4 %. There was a significant negative correlation between the SRS-24 self-image scores and the number of segments fused (r = -0.5, p < 0.05). Patients with additional surgery had decreased clinical outcomes (SRS-24 scores, p = 0.004, ArM, p = 0.0008, and ODI, p = 0.0004). CONCLUSION: The study highlighted that AR/PSF is an efficient strategy providing reliable results in a large single-center series. Results confirmed that flexibility was the decisive measure when comparing surgical outcomes with different treatment strategies. Findings indicated that changes at the proximal junctional level were impacted by individual spino-pelvic morphology and determined by the individually predetermined thoracolumbar curvature and sagittal balance. Results stressed that in SK correction, reconstruction of a physiologic alignment is decisive to achieving good clinical outcomes and avoiding complications.

Surgical outcomes of scoliosis surgery in Marfan syndrome.

STUDY DESIGN: Retrospective review of a case series. OBJECTIVE: To present the radiologic and surgical characteristics of scoliosis treatment in patients with Marfan syndrome (MFS). SUMMARY OF BACKGROUND DATA: The treatment of scoliosis in MFS has been reported to pose unique challenges. However, the information on surgical outcomes is sparse. In clinical practice, surgery for scoliosis in MFS is reported to confer higher perioperative risks and instrumentation-related complications compared with adolescent idiopathic scoliosis because of atypical and rigid curve patterns and the underlying desmogenic disorder. METHODS: Database research identified 26 MFS patients treated surgically during 7 years at a single spine center. Three patients presented with previous failed surgeries and were excluded. The medical records, charts, and radiographs of 23 patients were analyzed focusing on curve characteristics, surgical outcomes including complications, and curve correction using modern third-generation hybrid or pedicle screw systems, and the behavior of junctional segments and compensatory curves. RESULTS: The sample included 18 female and 5 male patients with an average age of 18.2±9.2 years (13-52 y) at index surgery and 21.2±9.2 years (14-53 y) at follow-up, averaging 35.8±23.5 months (6-95 mo). According to the Lenke classification, 30% presented as type 1, 9% as type 2, 22% as type 3, 9% as type 4, 17% as type 5, and 13% of patients as type 6. Seventy-four percent of patients had a type C lumbar modifier. In total, 48% of patients underwent a posterior spinal fusion (PSF). Thirty percent had instrumented anterior spinal fusion (AISF), whereas 22% had a combined anterior release and staged PSF. Ninety-one percent of patients achieved solid fusion; there was 1 asymptomatic nonunion and 1 recalcitrant nonunion. Add-on phenomena were identified in 13% of patients (n=3) treated with AISF, indicating staged PSF once. In total, complications were encountered in 30% of patients, indicating redo surgery in 17% of patients. The cause for revision included nonunion (2x), liquor leakage (1x), and wound infection at the iliac crest (1x). We judged the outcome as excellent/good if the patient had no major redo surgery and was very satisfied/satisfied. Overall, excellent/good outcome was noted in 78% of the patients. Blood loss averaged 659 mL in AISF and 1748 mL in PSF. The surgical time was 193 minutes in AISF and 229 minutes in PSF. Preoperative, postoperative, and follow-up Cobb T4-T12 was 13, 13, and 16 degrees, respectively; the mean thoracic curves measured 66 (23-106), 36 (0-58), and 38 degrees (0-58), respectively. Lumbar curves measured 63 (23-110), 27 (0-80), and 24 degrees (0-68), respectively. Coronal plumb line measured 2.2, 2.6, and 1.2 cm, respectively, indicating good trunk balance in most patients. The flexibility rates of thoracic curves and lumbar curves were 38% and 47%, respectively. Thoracic curve correction in PSF and combined anterior release/PSF was 44%, and in AISF, it reached 57%. CONCLUSIONS: The current study highlights the potential pitfalls in scoliosis surgery for patients with MFS. Surgery was performed using third-generation pedicle screw-based and hook-based systems for PSF and second-generation and third-generation implants for AISF. We illustrated that the treatment of scoliosis in MFS, taking into account the individual challenges of the underlying desmogenic disorder, can be performed with a moderately increased risk for surgical complications compared with adolescent idiopathic scoliosis.

The potential of proximal junctional kyphosis prevention using a novel tether pedicle screw construct: an in silico study comparing the influence of standard and dynamic techniques on adjacent-level range of motion and load pattern.

OBJECTIVE: A tether pedicle screw (TPS) enables individual stepless pretensioning and is placed at one or two levels above the upper instrumented vertebra (UIV+1 and UIV+2, respectively). This study aimed to evaluate a novel customized TPS for the prevention of proximal junctional kyphosis (PJK) and to investigate the potential to generate a smoother force transition from cranial to long fusion during trunk flexion, instead of an abrupt change at the UIV, following adult spinal deformity surgery. METHODS: A finite element model was designed based on an adult patient with spinal deformity instrumented from T10 to S1. Five different sagittal balance types and implant configurations were tested. The proximal range of motion (ROM) and intervertebral stress were examined, with a special focus on their respective discontinuities. RESULTS: Tension shielding at UIV/UIV+1 by the TPS was consistent irrespective of sagittal profiles. The use of TPSs at UIV+1 and UIV+2 increased the efficacy in reducing spinal ROM discontinuity at UIV/UIV+1, as compared with the use of TPSs at UIV+1 only. Through the use of two pairs of TPSs cranial to the UIV, the optimal tension configuration could be defined to avoid a reduction effect at UIV+1. Neither the addition of transition rods to the TPSs nor the use of transition rods in combination with standard pedicle screws improved the junctional mechanics when compared with TPSs at UIV+1/UIV+2. CONCLUSIONS: A smoother motion discontinuity at the UIV can be achieved via implementation of a TPS strategy. This new technology shows favorable in silico mechanics for reducing the risk of PJK.

Lower Hounsfield Units at the Planned Lowest Instrumented Vertebra is an Independent Risk Factor for Complications Following Adult Cervical Deformity Surgery.

BACKGROUND: The association of Hounsfield units (HU) and junctional pathologies in adult cervical deformity (ACD) surgery has not been elucidated. OBJECTIVE: Assess if the bone mineral density of the LIV, as assessed by HUs, is prognostic for the risk of complications after ACD surgery. STUDY DESIGN/SETTING: Retrospective cohort study. METHODS: HUs were measured on preoperative CT scans. Means comparison test assessed differences in HUs based on the occurrence of complications, linear regression assessed the correlation of HUs with risk factors, and multivariable logistic regression followed by a conditional inference tree derived a threshold for HUs based on the increased likelihood of developing a complication. RESULTS: In all, 107 ACD patients were included. Thirty-one patients (29.0%) developed a complication (18.7% perioperative), with 20.6% developing DJK and 11.2% developing DJF. There was a significant correlation between lower LIVs and lower HUs (r=0.351, P=0.01), as well as age and HUs at the LIV. Age did not correlate with change in the DJK angle (P>0.2). HUs were lower at the LIV for patients who developed a complication and an LIV threshold of 190 HUs was predictive of complications (OR: 4.2, [1.2-7.6]; P=0.009). CONCLUSIONS: Low bone mineral density at the lowest instrumented vertebra, as assessed by a threshold lower than 190 Hounsfield units, may be a crucial risk factor for the development of complications after cervical deformity surgery. Preoperative CT scans should be routinely considered in at-risk patients to mitigate this modifiable risk factor during surgical planning. LEVEL OF EVIDENCE: Level-III.