Influence of posterior instrumented correction with pedicle screw dual rod systems on thoracic kyphosis in Lenke 1 and 2 curves: minimum 2 years follow-up.

PURPOSE: Adolescent idiopathic scoliosis (AIS) often correspond with hypo thoracic kyphosis (TK) or even lordosis. The aim of this study was to analyze the influence of posterior instrumentation in thoracic AIS. METHODS: Analysis of prospectively collected AIS-data with structural thoracic curves (Lenke type 1 & 2), operated 2010-2019 with pedicle screw dual rod systems in one scoliosis center. Follow-up (FU) minimum 24 months. Coronal and sagittal angles measured based on standing long-cassette-X-rays: thoracic major (MC), proximal thoracic (PC) and lumbar curve (LC), TK, lumbar lordosis (LL). STATISTICAL ANALYSIS: values as mean ± SD, differences by student's t-test (significancy a = 0.05), Pearson's correlation, sub-analysis with sagittal modifier (-, N, +). RESULTS: A total of 127 AIS could be identified (63% type 1, 37% type 2). Mean FU 32.2 ± 16.6 months, mean age 14 ± 1.5 years. Mean Correction of MC 73 ± 12%, PC 51 ± 17%, LC 69 ± 21% with a significantly better correction of PC in Lenke 2 curves(p < 0.05). On average, TK (FU-preop) decreased by -2.1 ± 12.1°(p < 0.05) in all AIS. Whereas TK in type 1 was unchanged (p = 0.9), TK significantly decreased by - 6.0 ± 12.7°(p < 0.05) in type 2. No significant difference in LL. TK in hypokyphotic cases increased by 9.5 ± 5.5°(p < 0.05), stayed almost unchanged (- 1.4 ± 9.1°,p = 0.2) in normokyphotic, decreased by - 17.2 ± 14.2°(p < 0.05) in hyperkyphotic cases. Only hypokyphotic cases had a moderately strong correlation between correction of LC (r = 0.6) and PC (r = - 0.4) (frontal plane) and change from pre- to postoperative TK (sagittal plane) (r = 0.6). No relevant correlations for normo- and hyperkyphotic AIS. Postoperative hypokyphosis was significantly more often in Lenke 2 (16.3% vs. 2.6%, p < 0.05). Rod diameter (5,5 mm versus 6 mm) had no significant influence. CONCLUSION: Significant correction of hypo- and hyperkyphosis can be achieved with posterior spinal fusion (pedicle screw dual rod systems), whereas normokyphotic spines stay unchanged. However, Lenke 2 curves have a significantly higher risk for a postoperative thoracic hypokyphosis.

Clinical and radiological outcomes in thoracolumbar fractures using the SpineJack device. A prospective study of seventy-four patients with a two point three year mean of follow-up.

PURPOSE: The aim of this study was to assess clinical and radiological results of SpineJack on the treatment of vertebral body fractures in a continuous prospective series of patients. MATERIAL AND METHODS: Between May 2012 and April 2015, all patients operated using the SpineJack device were prospectively included in this monocentric study. Demographic data, clinical, and radiological results were recorded. Complications and surgical managements were recorded. RESULTS: At a mean follow-up of 2.3 years, 74 patients with 77 fractured vertebrae were included. The stand-alone SpineJack group comprised 60 patients with 63 fractured vertebrae (group 1) and the group with additional posterior fixation 14 patients with 14 fractured vertebrae (group 2). The average initial vertebral wedge angle was 13.3 ± 6.1 degrees for group 1 and 15.3 ± 5.7 degrees for group 2 (p = 0.25). Post-operative values were 6.5 ± 4.6 degrees for group 1 and 5.1 ± 3.9 degrees for group 2 (p = 0.31). The differences within the same group were highly significant (p < 0.0005). The loss of reduction at last follow-up was 0.8 ± 1.6 degrees in group 1 and 0.6 ± 2.0 degrees in group 2 (p = 0.77). Subjective results were considered as very good or good for 57 patients (95%) in group 1 and for 11 patients (79%) in group 2, p = 0.07. CONCLUSION: The SpineJack seems to be a promising tool in the treatment of traumatic vertebral fractures with a correction in the sagittal plane comparable with what can be found in the literature.

Rod fractures after multi-rod constructs in adult spinal deformity patients fused to the sacrum/pelvis: where do they occur and why?

PURPOSE: (1) To describe the use of multi-rod constructs (MRCs) in adult spinal deformity (ASD) surgery, (2) to report rod fractures occurring at MRC sites, and (3) to evaluate risk factors for rod fractures. METHODS: A single-center, retrospective cohort study was conducted of patients undergoing ASD surgery with these inclusion criteria: minimum 2-year follow-up, MRCs used, ≥ 10-level fusion, and fused to sacrum/pelvis. The primary outcome was rod fracture. Univariate/multivariate logistic regression was performed controlling for age, kickstand rod usage, number of rods across the lumbosacral junction (LSJ), and the amount of coronal/sagittal Cobb correction. RESULTS: Among 57 patients undergoing ASD surgery with MRCs, mean age was 60 ± 11 years. With respect to MRCs, 32 (56%) patients had 3 rods, 18 (32%) had 4, and 7 (12%) had 5. Rods crossing the LSJ were most often three (63%), followed by four (25%) and five (5%) rods. Nine (16%) patients experienced rod fractures with eight (89%) patients having no more than three rods crossing the LSJ. A coronal correction > 30 mm was more often seen in patients with rod fracture (p = 0.030), while an SVA correction > 50 mm was not significantly different (p = 0.608). Multivariate logistic regression revealed that the amount of coronal correction was significantly associated with rod fracture (OR 1.03, 95% CI 1.01-1.07, p = 0.044), as was achieving a coronal correction > 30 mm (OR 7.72, 95% CI 1.17-51.10, p = 0.034), with no association between the amount of sagittal correction obtained and rod fracture. CONCLUSION: This study found that greater coronal correction was associated with an increased odds of rod fracture. We suggest adding at least four rods across the LSJ cephalad to the interbody fusions to avoid rod fractures in these high demand areas. LEVEL OF EVIDENCE: III.

The Difference of Sagittal Correction of Adult Subaxial Cervical Spine Surgery According to Age: A Retrospective Study.

OBJECTIVE: At present, the true sagittal alignment of the cervical spine is uncertain, resulting in no standard reference for subaxial cervical surgery. So, we aimed to explore the age difference of normal cervical sagittal alignment and to further investigate the mid-and long-term changes of sagittal alignment after subaxial cervical spine surgery. MATERIALS AND METHODS: This was a retrospective study and 1223 asymptomatic volunteers and 79 patients undergoing subaxial cervical spine surgery were retrospectively reviewed in total. Asymptomatic volunteers and patients were divided into six subgroups: 20-29, 30-39, 40-49, 50-59, 60-69 and ≥70 groups. The age difference and trend with age of cervical sagittal parameters of asymptomatic volunteers were assessed by cervical lateral radiography and analyzed by ANOVA test, and the regression equation of C2-7 Cobb was established via multiple linear regression. Based on the C2-7 Cobb regression equations of different ages, the theoretical value, deviation value, loss value of the C2-7 Cobb, and JOA recovery rate of patients were calculated, and the correlation among the loss value, deviation value of the C2-7 Cobb, and JOA recovery rate of the 79 patients was evaluated by Pearson correlation analysis. RESULTS: For the asymptomatic volunteers, the C0-2 Cobb decreased gradually with increasing age. The C2-7 Cobb, C2-7 SVA, T1S, NT, and TIA increased gradually with increasing age. The CBVA fluctuated with increasing age. T1S demonstrated a moderate correlation with C2-7 Cobb (r = 0.60, p < 0.01); C0-2 Cobb, C2-7 SVA, CBVA, and TIA demonstrated a fair correlation with C2-7 Cobb (r = -0.30, -0.33, 0.41, 0.40, p < 0.01); age demonstrated a poor correlation with C2-7 Cobb (r = 0.19, p < 0.01). The regression equations of C2-7 Cobb were established using C0-2 Cobb, C2-7 SVA, CBVA, and T1S. For the patients with subaxial cervical spine surgery, the loss of C2-7 Cobb was moderately correlated with the deviation of C2-7 Cobb (r = 0.33, p < 0.01). CONCLUSION: The age difference of cervical sagittal alignment was obvious, and the C2-7 Cobb increased with age especially. The closer the postoperative C2-7 Cobb was to the theoretical value of corresponding age, the smaller the loss of correction angle was, and the better the mid- and long-term outcomes. The personalized sagittal reconstruction should be performed according to age difference for subaxial cervical spine surgery.

Laterally Placed Expandable Interbody Spacers With and Without Adjustable Lordosis Improve Radiographic and Clinical Outcomes: A Two-Year Follow-Up Study.

Introduction Interbody spacers are necessary for achieving disc height restoration when surgical intervention is used for the treatment of severe degenerative disc disease. Minimally invasive lateral lumbar interbody fusion (MIS LLIF) is a popular surgical approach that historically uses large static interbody spacers through a lateral approach. However, static spacers have been associated with iatrogenic distraction and excessive impaction forces, which may increase the risk of subsidence and loss of lordosis, compromising stability. Expandable interbody spacers with or without adjustable lordosis may help address these concerns by maximizing segmental lordosis and aiding in sagittal balance correction. This study describes the clinical and radiographic outcomes of patients treated with expandable interbody spacers with or without adjustable lordosis, for MIS LLIF. Materials and methods This is retrospective, single-surgeon Institutional Review Board-exempt chart review was of 103 consecutive patients who had undergone MIS LLIF at one to two contiguous level(s) utilizing expandable interbody spacers with or without adjustable lordosis (66/103 patients had adjustable lordosis spacers). Collection of clinical and radiographic functional outcomes occurred at preoperative and postoperative time points through 24 months. Results One-hundred and three consecutive patients were evaluated-average age, 58.2 ± 12.1 years; 42.1% (45/107) were female. There were 78.6% (81/103) one-level cases and 21.4% (22/103) two-level cases for a total of 125 levels; 44.8% (56/125) were performed at L4-5 and 34.4% (43/125) at L3-4. The average estimated blood loss was 24.6 ± 12.3cc. Mean operative time was 61.0 ± 19.1 min, and mean fluoroscopic time was 28.2 ± 14.6 sec. Visual Analog Scale (VAS) back and leg pain scores decreased significantly by an average of 7.1 ± 1.0 points at 24 months (p<0.001). Oswestry Disability Index (ODI) scores significantly decreased by a mean of 67.4 ± 8.9 points at 24 months (p<0.001). Lumbar lordosis significantly improved by a mean of 3.1 ± 8.8° at 24 months (p=0.001). Anterior, middle, and posterior disc height significantly increased at 24 months by averages of 4.7 ± 3.1, 4.0 ± 3.0, and 2.1 ± 2.2mm, respectively (p<0.001). Neuroforaminal height had significantly increased at 24 months by a mean of 3.0 ± 3.6mm (p<0.001). Segmental lordosis significantly improved by 3.7 ± 2.9° at 24 months (p<0.001). There were 51 patients with abnormal preoperative Pelvic Incidence-Lumbar Lordosis (PI-LL) measurements that significantly improved by 9.1 ± 4.9° (p<0.001) and 52 patients with normal preoperative PI-LL measurements that improved by 0.2 ± 4.6° (p=0.748) at 24 months. One-hundred percent fusion occurred at all levels, and no findings of radiolucency were observed. One case of subsidence (1/125, 0.8%) was reported at 24 months. No implanted-related complications were reported, with 0% pseudoarthrosis and no secondary surgery required at the operative levels. Conclusion Indirect decompression and sagittal correction were achieved and maintained through a 24-month follow-up. Functional clinical outcomes significantly improved based on decreased VAS pain and ODI scores at 24 months. This study resulted in positive clinical and radiographic outcomes for patients who underwent MIS LLIF with expandable interbody spacers with or without adjustable lordosis.

Does intraoperative 3D navigation improve SpineJack vertebral augmentation in thoracic and lumbar compression fracture?

INTRODUCTION: The aim of this retrospective study was to evaluate the effect of navigation on the positioning of the SpineJack implant in the treatment of thoracic and lumbar compression fractures. METHODS: Between January 2018 and December 2019, all patients operated on for thoracic or lumbar fracture using the SpineJack device in stand-alone were included in this single-center study. The positioning of the SpineJack implant was analyzed on axial CT views by measuring the angle between the axis of the pedicle and the axis of the final implant. The relationships between implant positioning and the use of navigation or fluoroscopy, pedicle dimensions and levels of injury were analyzed. Surgical time, radiation exposure, radiological findings and complications were assessed. RESULTS: One hundred patients were included, for 103 fractured vertebrae and a total of 205 implants, 148 placed under standard fluoroscopy and 57 with the Surgivisio navigation system. For pedicle diameters≥5mm (165 implants), the positioning of the implant relative to the axis of the pedicle was significantly better in the navigation group: 2°±1.4° (range, 0-7°) in the fluoroscopy group versus 1.2°±1.1° (range, 0-5°) in the navigation group (p=0.04). There were no significant differences in reduction of vertebral kyphosis angle or mean operating time. Dose area product (DAP) was significantly higher with navigation: 4.43Gy.cm2 versus 0.47Gy.cm2 (p<0.001) and dose to the surgeon significantly lower: 0.5 versus 1.6µSv (p<0.001). No difference was found regarding complications. Subgroup analysis showed significantly greater operative time and patient irradiation in the fluoroscopy group when pedicle diameter was less than 5mm. CONCLUSION: This study demonstrates the interest of navigation for positioning the SpineJack implant with respect to the pedicle axis in vertebrae with pedicle diameter≥5mm. This study also confirmed the reliability of navigation and lower radiation dose to the surgeon, regardless of the fracture level. Navigation reduced operating time and patient irradiation for vertebrae with pedicle diameter<5mm. LEVEL OF EVIDENCE: IV; retrospective study.

Comparison of Lateral Lumbar Interbody Fusion and Posterior Lumbar Interbody Fusion as Corrective Surgery for Patients with Adult Spinal Deformity-A Propensity Score Matching Analysis.

Lateral lumbar interbody fusion (LLIF) is increasingly performed as corrective surgery for patients with adult spinal deformity (ASD). This paper compares the surgical results of LLIF and conventional posterior lumbar interbody fusion (PLIF)/transforaminal lumbar interbody fusion (TLIF) in ASD using a propensity score matching analysis. We retrospectively reviewed patients with ASD who received LLIF and PLIF/TLIF, and investigated patients' backgrounds, radiographic parameters, and complications. The propensity scores were calculated from patients' characteristics, including radiographic parameters and preoperative comorbidities, and one-to-one matching was performed. Propensity score matching produced 21 matched pairs of patients who underwent LLIF and PLIF/TLIF. All radiographic parameters significantly improved in both groups at the final follow-up compared with those of the preoperative period. The comparison between both groups demonstrated no significant difference in terms of postoperative pelvic tilt, lumbar lordosis (LL), or pelvic incidence-LL at the final follow-up. However, the sagittal vertical axis tended to be smaller in the LLIF at the final follow-up. Overall, perioperative and late complications were comparable in both procedures. However, LLIF procedures demonstrated significantly less intraoperative blood loss and a smaller incidence of postoperative epidural hematoma compared with PLIF/TLIF procedures in patients with ASD.

Correction of marked sagittal deformity with circumferential minimally invasive surgery using oblique lateral interbody fusion in adult spinal deformity.

BACKGROUND: Spinal surgery performed entirely with minimally invasive surgery is referred to as circumferential MIS (cMIS). However, cMIS still has a limited sagittal correction capability for adult spinal deformity (ASD) with a marked sagittal deformity. We investigated the effectiveness of cMIS using oblique lateral interbody fusion (OLIF) and percutaneous posterior spine fixation in correcting marked sagittal deformity. METHODS: This study retrospectively evaluated 23 patients with ASD with marked sagittal deformity who underwent cMIS using OLIF without osteotomy and were followed-up for at least 24 months (whole group). The whole group was divided into the following two groups according to the type of interbody fusion at L5-S1: the OLIF51 group (n = 13) underwent OLIF at L1-L5 and L5-S1 and the TLIF51 group (n = 10) underwent OLIF at L1-L5 and transforaminal lumbar interbody fusion (TLIF) at L5-S1. RESULTS: Sagittal vertebral axis (SVA; 125.7 vs. 29.5 mm, p < 0.001), lumbar lordosis (LL; 18.2° vs. 51.7°, p < 0.001), and pelvic incidence-LL mismatch (PI-LL, 35.5° vs. 5.3°) significantly improved postoperatively in the whole group. The OLIF51 group showed significantly higher postoperative LL than the TLIF51 group (55.5° vs. 46.9°, p < 0.001). OLIF yielded a significantly greater disc angle at L5-S1 than did TLIF (18.4° vs. 6.9°, p < 0.001). Proximal junctional kyphosis occurred significantly earlier in the OLIF51 group than in the TLIF51 group (8.6 vs. 26.3 months, p < 0.001). CONCLUSION: Successful sagittal correction in ASD patients with marked sagittal deformity was achieved with cMIS using OLIF. OLIF at L5-S1 showed a synergistic effect in sagittal deformity correction by cMIS.

Anterior Column Realignment (ACR) With and Without Pre-ACR Posterior Release for Fixed Sagittal Deformity.

BACKGROUND: Multiple studies have demonstrated a strong correlation between sagittal malalignment and health-related quality of life measures. Thus, correction of sagittal vertical axis (SVA), pelvic tilt (PT), lumbar lordosis-pelvic incidence (LL-PI), and T1 spinopelvic inclination (T1SPi) have become a primary objective of adult spinal deformity surgery. Anterior column realignment (ACR) has emerged as a less invasive technique and while the addition of posterior osteotomies has shown greater correction in ACR, it is unknown if a pre-ACR posterior release is necessary for optimal correction. The purpose of this study was to determine if pre-ACR posterior release allows for greater sagittal deformity correction. METHODS: Seventeen patients were identified that underwent minimum 1-level ACR. Ten patients underwent an anterior-posterior surgical sequence without a pre-ACR posterior release, and 7 underwent a posterior-anterior-posterior (PAP) sequence with a pre-ACR posterior release. Radiographic outcomes at final follow-up and complications were compared. RESULTS: Both groups saw significant improvements in LL, LL-PI, PT, SVA, and T1SPi but the correction was not significantly different between cohorts. With the exception of PT in the PAP group, the improvements in LL-PI, PT, and SVA correlated to improvement in Scoliosis Research Society-Schwab classification. The correction achieved at the ACR level, represented by motion segment angle, was greater in the PAP group by a degree that approached statistical significance. Five patients (29%) had 6 complications. CONCLUSIONS: Both techniques achieved meaningful improvements in overall sagittal alignment. Our results suggest that a pre-ACR posterior release may allow for greater correction specifically at the ACR level but may not always be necessary to achieve clinically meaningful correction of sagittal plane deformity. LEVEL OF EVIDENCE: 3. CLINICAL RELEVANCE: We present our experience with and without pre-ACR posterior release. To our knowledge, this is the first study to show that pre-ACR posterior release may achieve greater correction at the ACR level.

Evaluation of the location of intervertebral cages during oblique lateral interbody fusion surgery to achieve sagittal correction.

INTRODUCTION: Oblique lateral interbody fusion (OLIF) can achieve recovery of lumbar lordosis (LL) in minimally invasive manner. The current study aimed to evaluate the location of lateral intervertebral cages during OLIF in terms of LL correction. METHODS: The subjects were patients who underwent OLIF for lumbar degenerative diseases, including lumbar spinal stenosis, spondylolisthesis, and discogenic low back pain. Their clinical outcome was evaluated using visual analogue scale on lower back pain (LBP), leg pain and numbness. The following parameters were retrospectively evaluated on plain radiographic images and computed tomography scans before and at 1 year after OLIF: the intervertebral height, vertebral translation, and sagittal angle. The cage position was defined by equally dividing the caudal endplate into five zones (I to V), and its association with segmental lordosis restoration was analyzed. Subjects were also evaluated for a postoperative endplate injury. RESULTS: Eighty patients (121 fused levels) with lumbar degeneration who underwent OLIF were included. There were no significant specific distribution in preoperative disc pathology such as disc angle, height, and translation. After OLIF, sagittal alignment was improved with an average correction angle of 3.8º at the instrumented segments in a level-independent fashion. All cases showed significant improvement in clinical outcomes, and had improvement in the radiological parameters (P<0.05). A detailed analysis of the cage position showed that the most significant sagittal correction and the most postoperative endplate injuries occurred in the farthest anterior zone (I). Cages with a 12-mm height were associated with more endplate injuries compared with shorter cages (8 or 10 mm). CONCLUSIONS: OLIF improves sagittal alignment with an average correction angle of 3.8º at the instrumented segments. We suggest that the optimal cage position for better lordosis correction and the fewest endplate injuries is zone II with a cage height of up to 10 mm.

Lateral interbody fusion combined with open posterior surgery for adult spinal deformity.

OBJECTIVE Lateral interbody fusion (LIF) with percutaneous screw fixation can treat adult spinal deformity (ASD) in the coronal plane, but sagittal correction is limited. The authors combined LIF with open posterior (OP) surgery using facet osteotomies and a rod-cantilever technique to enhance lumbar lordosis (LL). It is unclear how this hybrid strategy compares to OP surgery alone. The goal of this study was to evaluate the combination of LIF and OP surgery (LIF+OP) for ASD. METHODS All thoracolumbar ASD cases from 2009 to 2014 were reviewed. Patients with < 6 months follow-up, prior fusion, severe sagittal imbalance (sagittal vertical axis > 200 mm or pelvic incidence-LL > 40°), and those undergoing anterior lumbar interbody fusion were excluded. Deformity correction, complications, and outcomes were compared between LIF+OP and OP-only surgery patients. RESULTS LIF+OP (n = 32) and OP-only patients (n = 60) had similar baseline features and posterior fusion levels. On average, 3.8 LIFs were performed. Patients who underwent LIF+OP had less blood loss (1129 vs 1833 ml, p = 0.016) and lower durotomy rates (0% vs 23%, p = 0.002). Patients in the LIF+OP group required less ICU care (0.7 vs 2.8 days, p < 0.001) and inpatient rehabilitation (63% vs 87%, p = 0.015). The incidence of new leg pain, numbness, or weakness was similar between groups (28% vs 22%, p = 0.609). All leg symptoms resolved within 6 months, except in 1 OP-only patient. Follow-up duration was similar (28 vs 25 months, p = 0.462). LIF+OP patients had significantly less pseudarthrosis (6% vs 27%, p = 0.026) and greater improvement in visual analog scale back pain (mean decrease 4.0 vs 1.9, p = 0.046) and Oswestry Disability Index (mean decrease 21 vs 12, p = 0.035) scores. Lumbar coronal correction was greater with LIF+OP surgery (mean [± SD] 22° ± 13° vs 14° ± 13°, p = 0.010). LL restoration was 22° ± 13°, intermediately between OP-only with facet osteotomies (11° ± 7°, p < 0.001) and pedicle subtraction osteotomy (29° ± 10°, p = 0.045). CONCLUSIONS LIF+OP is an effective strategy for ASD of moderate severity. Compared with the authors' OP-only operations, LIF+OP was associated with faster recovery, fewer complications, and greater relief of pain and disability.

Influence of implant rod curvature on sagittal correction of scoliosis deformity.

BACKGROUND CONTEXT: Deformation of in vivo-implanted rods could alter the scoliosis sagittal correction. To our knowledge, no previous authors have investigated the influence of implanted-rod deformation on the sagittal deformity correction during scoliosis surgery. PURPOSE: To analyze the changes of the implant rod's angle of curvature during surgery and establish its influence on sagittal correction of scoliosis deformity. STUDY DESIGN: A retrospective analysis of the preoperative and postoperative implant rod geometry and angle of curvature was conducted. PATIENT SAMPLE: Twenty adolescent idiopathic scoliosis patients underwent surgery. Average age at the time of operation was 14 years. OUTCOME MEASURES: The preoperative and postoperative implant rod angle of curvature expressed in degrees was obtained for each patient. METHODS: Two implant rods were attached to the concave and convex side of the spinal deformity. The preoperative implant rod geometry was measured before surgical implantation. The postoperative implant rod geometry after surgery was measured by computed tomography. The implant rod angle of curvature at the sagittal plane was obtained from the implant rod geometry. The angle of curvature between the implant rod extreme ends was measured before implantation and after surgery. The sagittal curvature between the corresponding spinal levels of healthy adolescents obtained by previous studies was compared with the implant rod angle of curvature to evaluate the sagittal curve correction. The difference between the postoperative implant rod angle of curvature and normal spine sagittal curvature of the corresponding instrumented level was used to evaluate over or under correction of the sagittal deformity. RESULTS: The implant rods at the concave side of deformity of all patients were significantly deformed after surgery. The average degree of rod deformation Δθ at the concave and convex sides was 15.8° and 1.6°, respectively. The average preoperative and postoperative implant rod angle of curvature at the concave side was 33.6° and 17.8°, respectively. The average preoperative and postoperative implant rod angle of curvature at the convex side was 25.5° and 23.9°, respectively. A significant relationship was found between the degree of rod deformation and preoperative implant rod angle of curvature (r=0.60, p<.005). The implant rods at the convex side of all patients did not have significant deformation. The results indicate that the postoperative sagittal outcome could be predicted from the initial rod shape. CONCLUSIONS: Changes in implant rod angle of curvature may lead to over- or undercorrection of the sagittal curve. Rod deformation at the concave side suggests that corrective forces acting on that side are greater than the convex side.