ROD DEROTATION TECHNIQUES FOR THORACOLUMBAR SPINAL DEFORMITY

Comparative Analysis of Monoaxial and Polyaxial Pedicle Screws in the Surgical Correction of Adolescent Idiopathic Scoliosis

Background: Although several biomechanical studies have been reported, few clinical studies have compared the efficacy of monoaxial and polyaxial pedicle screws in the surgical treatment of adolescent idiopathic scoliosis (AIS). This study aims to compare the radiological and clinical outcomes of mono- and polyaxial pedicle screws in the surgical treatment of AIS. Methods: A total of 46 AIS patients who underwent surgery to treat scoliosis using pedicle screw instrumentation (PSI) and rod derotation (RD) were divided into two groups according to the use of pedicle screws: the monoaxial group (n = 23) and polyaxial group (n = 23). Results: The correction rate of the main Cobb's angle was higher in the monoaxial group (70.2%) than in the polyaxial group (65.3%) (p = 0.040). No differences in the rotational correction of the apical vertebra were evident between the two groups. SRS-22 scores showed no significant differences according to the type of pedicle screws used. Conclusions: The use of polyaxial pedicle screws resulted in coronal, sagittal, and rotational correction outcomes comparable to those associated with the use of monoaxial pedicle screws for surgical treatment using PSI and RD to treat moderate cases of AIS.

Sectional Correction Technique in Dystrophic Scoliosis Secondary to Neurofibromatosis Type 1: A Comparison with Traditional 2-Rod Correction Technique

OBJECTIVE

The purpose of this study was to compare the traditional 2-rod correction technique with the sectional correction technique in terms of radiographic results and clinical outcomes for patients with dystrophic scoliosis caused by neurofibromatosis type 1 (NF1).

METHODS

From May 2015 to April 2018, 53 patients with dystrophic scoliosis caused by NF1 underwent 1-stage posterior corrective surgery. Patients were separated into 2 groups based on technique: the sectional correction technique (SC group) and the traditional 2-rod technique (TT group). Before surgery and at the final follow-up, the demographic information, radiographic parameters, and clinical outcomes were compared between the groups using independent-sample t tests.

RESULTS

The SC group consisted of 24 patients, while the TT group consisted of 29 patients. Patients in the SC group showed a higher coronal balance distance after the operation (8.3 ± 8.2 mm vs. 16.2 ± 8.8 mm, P = 0.002) and at the final follow-up (9.5 ± 9.3 mm vs. 19.3 ± 10.1 mm, P < 0.0001). At the last follow-up, the loss of correction in the SC group was 2.2 ± 0.9 and 2.1 ± 0.7 in the coronal and sagittal planes, respectively, and these values were significantly lower than those in the TT group (5.3 ± 1.6 in the coronal plane and 4.5 ± 1.9 in the sagittal plane, both P < 0.05). The SC group had better improvement based on appearance and satisfaction score at the final follow-up.

CONCLUSIONS

The sectional correction technique using a concave domino connector can restore coronal imbalance and reduce the risk of implant failure.

A 3D Parameter Can Guide Concave Rod Contour for the Correction of Hypokyphosis in Adolescent Idiopathic Scoliosis

STUDY DESIGN

Retrospective.

OBJECTIVE

To evaluate the effect of preoperative rod shape on 3D spinal deformity correction.

SUMMARY OF BACKGROUND DATA

Differential rod contouring is a surgeon-dependent process based on an estimate of 3D deformity correction sought and the flexibility of the spine. An objective measure to this otherwise subjective scoliosis correction technique is lacking.

METHODS

A series of adolescent idiopathic scoliosis (AIS) patients with right, thoracic major curves, preoperative rod contour tracings, and EOS imaging was evaluated. All patients underwent posterior spinal fusion with 5.5 mm steel rods contoured prior to insertion. 3D reconstructions were generated pre- and postoperatively using sterEOS software (EOS Imaging) and imported into MATLAB (Mathworks) for analysis. A new measurement of the maximum perpendicular distance from the preinsertion concave rod contour to the preoperative 3D sagittal spinal reconstruction was defined as rod to 3D spine distance (RSD). Linear regressions were used to identify relationships between pre and postoperative parameters, including RSD and 3D thoracic kyphosis.

RESULTS

Ninety-nine patients were included. Average preoperative concave rod angle decreased from (48 ± 10°) preoperatively to 26 ± 6° postoperatively (P < 0.001) for an average flattening of ∼20°. Average convex rod angle increased from 30 ± 6° to 34 ± 5° (P < 0.001). Average preoperative thoracic curve magnitude and apical vertebral rotation were 57 ± 8° and 16 ± 5° and decreased to 11 ± 6° and 5 ± 6° (P < 0.001). Average 2D and 3D thoracic kyphosis increased from 19 ± 14° and 2 ± 12° to 27 ± 6° and 22 ± 5° (P < 0.001). Preoperative RSD strongly correlated with 3D thoracic kyphosis change (P < 0.001, r = 0.796, R = 0.633).

CONCLUSION

On average, the concave rod flattened ∼20° after connection to the spine. Similarly, kyphosis increased ∼20° following rod insertion. A strong correlation was identified between RSD and 3D thoracic kyphosis restoration. This novel 3D parameter can guide the degree of concave rod bend necessary to achieve a desired increase in thoracic kyphosis in AIS.

LEVEL OF EVIDENCE

2.

Effect of thoracic kyphosis formation and rotational correction by direct vertebral rotation after the simultaneous double rod rotation technique for idiopathic scoliosis

OBJECTIVE

The objective of the present study was to evaluate the effect of thoracic kyphosis formation and rotational correction by direct vertebral rotation (DVR) after the simultaneous double-rod rotation technique (SDRRT) for idiopathic scoliosis (IS).

PATIENTS AND METHODS

The present study included twelve patients with IS who received SDRRT (SDRRT group) and twelve patients with IS who received DVR after SDRRT (SDRRT + DVR group). We investigated the following parameters preoperatively, postoperatively, and at postoperative 2 years: Cobb angle (PT, MT, T/L, C7-CSVL, AVT, TK (T5-12), LL(L1-S1) RSH, the angle of rotation (RAsag), percent change of RAsag and SRS22 (at postoperative 2 years only).

RESULTS

Preoperatively, the mean main thoracic curve was 58.9 ± 12.4° for the SDRRT group and 59.9 ± 16.0° for the SDRRT + DVR group, which was corrected to 14.6 ± 6.7° and 13.4 ± 4.9° postoperatively. and 14.9 ± 7.1° and 14.3 ± 4.1° at postoperative 2-year follow-up, respectively. Correction rates were 75.4 ± 10.4% and 77.2 ± 8.0 % postoperatively. Thoracic kyphosis increased postoperatively and at postoperative 2-year follow-up in both the SDRRT group and the SDRRT + DVR group. The mean preoperative TK was 11.4 ± 7.3° in the SDRRT group, and 12.8 ± 11.5° in the SDRRT + DVR group, which improved significantly to 24.8 ± 5.2° and 23.6 ± 3.5° postoperatively and 23.3 ± 3.9° and 24.2 ± 6.0° at postoperative 2-year follow-up, respectively. Correction of vertebral rotation as RAsag was significantly better in the SDRRT + DVR group than in the SDRRT group. The mean preoperative RAsag was 19.1 ± 6.7° in the SDRRT group, and 18.3 ± 7.5° in the SDRRT + DVR group, which improved to 13.3 ± 4.3° and 10.1 ± 2.9° postoperatively (P = 0.04) and 13.9 ± 4.0° and 10.6 ± 2.8° at postoperative 2-year follow-up (P = 0.02), respectively.

CONCLUSION

DVR after SDRRT for idiopathic scoliosis allowed for rotation correction without compromising kyphosis formation.

Current concepts in the surgical management of adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is a complex 3D deformity of the spine. Its prevalence is between 2% and 3% in the general population, with almost 10% of patients requiring some form of treatment and up to 0.1% undergoing surgery. The cosmetic aspect of the deformity is the biggest concern to the patient and is often accompanied by psychosocial distress. In addition, severe curves can cause cardiopulmonary distress. With proven benefits from surgery, the aims of treatment are to improve the cosmetic and functional outcomes. Obtaining correction in the coronal plane is not the only important endpoint anymore. With better understanding of spinal biomechanics and the long-term effects of multiplanar imbalance, we now know that sagittal balance is equally, if not more, important. Better correction of deformities has also been facilitated by an improvement in the design of implants and a better understanding of metallurgy. Understanding the unique character of each deformity is important. In addition, using the most appropriate implant and applying all the principles of correction in a bespoke manner is important to achieve optimum correction.

In this article, we review the current concepts in AIS surgery.

Cite this article: Bone Joint J 2018;100-B:415–24.

Quantitative analysis of a spinal surgeon’s learning curve for scoliosis surgery

Aims

The aim of this study was a quantitative analysis of a surgeon’s learning curve for scoliosis surgery and the relationship between the surgeon’s experience and post-operative outcomes, which has not been previously well described.

Patients and Methods

We have investigated the operating time as a function of the number of patients to determine a specific pattern; we analysed factors affecting the operating time and compared intra- and post-operative outcomes. We analysed 47 consecutive patients undergoing scoliosis surgery performed by a single, non-trained scoliosis surgeon. Operating time was recorded for each of the four parts of the procedures: dissection, placement of pedicle screws, reduction of the deformity and wound closure.

Results

The median operating time was 310 minutes (interquartile range 277.5 to 432.5). The pattern showed a continuous decreasing trend in operating time until the patient number reached 23 to 25, after which it stabilised with fewer patient-dependent changes. The operating time was more affected by the patient number (r =- 0.75) than the number of levels fused (r = 0.59). Blood loss (p = 0.016) and length of stay in hospital (p = 0.012) were significantly less after the operating time stabilised. Post-operative functional outcome scores and the rate of complications showed no significant differences. Take home message: We describe a detailed learning curve for scoliosis surgery based on a single surgeon’s practise, providing useful information for novice scoliosis surgeons and for those responsible for training in spinal surgery. Cite this article: Bone Joint J 2016;98-B:679–85.

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.

Surgical treatment of Lenke 1 thoracic adolescent idiopathic scoliosis with maintenance of kyphosis using the simultaneous double-rod rotation technique

STUDY DESIGN

Retrospective analysis of a prospectively collected, consecutive, nonrandomized series of patients.

OBJECTIVE

To assess the surgical outcomes of the simultaneous double-rod rotation technique for treating Lenke 1 thoracic adolescent idiopathic scoliosis (AIS).

SUMMARY OF BACKGROUND DATA

With the increasing popularity of segmental pedicle screw spinal reconstruction for treating AIS, concerns regarding the limited ability to correct hypokyphosis have also increased.

METHODS

A consecutive series of 32 patients with Lenke 1 main thoracic AIS treated with the simultaneous double-rod rotation technique at our institution was included. Outcome measures included patient demographics, radiographical measurements, and Scoliosis Research Society questionnaire scores.

RESULTS

All 32 patients were followed up for a minimum of 2 years (average, 3.6 yr). The average main thoracic Cobb angle correction rate and the correction loss at the final follow-up were 67.8% and 3.3°, respectively. The average preoperative thoracic kyphosis (T5-T12) was 11.9°, which improved significantly to 20.5° (P < 0.0001) at the final follow-up. An increase in thoracic kyphosis was significantly correlated with an increase in lumbar lordosis at the final follow-up (r = 0.42). The average preoperative vertebral rotation angle was 19.7°, which improved significantly after surgery to 14.9° (P = 0.0001). There was no correlation between change in thoracic kyphosis and change in apical vertebral rotation (r =-0.123). The average preoperative total Scoliosis Research Society questionnaire score was 3.0, which significantly improved to 4.4 (P < 0.0001) at the final follow-up. Throughout surgery and even after, there were no instrumentation failures, pseudarthrosis, infection of the surgical site, or clinically relevant neurovascular complications.

CONCLUSION

The simultaneous double-rod rotation technique for treating Lenke 1 AIS provides significant sagittal correction of the main thoracic curve while maintaining sagittal profiles and correcting coronal and axial deformities.

LEVEL OF EVIDENCE

4.

Preoperative pelvic axial rotation: a possible predictor for postoperative coronal decompensation in thoracolumbar/lumbar adolescent idiopathic scoliosis

BACKGROUND

The pelvis as the biomechanical foundation of spine, plays an important role in the balance of the stance and gait through the multi-link spinal-pelvic system. If the pelvic axial rotation (PAR) exists in adolescent idiopathic scoliosis (AIS) patients, it should theoretically have some effects on the body balance.

PURPOSE

To explore the probable effects of preoperative PAR on the spinal balance in coronal plane in AIS patients with main thoracolumbar/lumbar (TL/L) curve after posterior spinal instrumentation.

METHODS

Thirty-eight AIS patients (age: 15 ± 1.5 years) with main TL/L curve (51° ± 6.2°) were recruited retrospectively into this study. The mean follow-up period was 27 months (24-36 months). Standing full spine posteroanterior radiographs were taken preoperatively, 3 month and 1 year postoperatively, and at last follow-up. The convex/concave ratio (CV/CC ratio) of the anterior superior iliac spine laterally and the inferior ilium at the sacroiliac joint medially was measured on posteroanterior radiographs. According to the preoperative CV/CC ratios, the patients were divided into two groups: normal group (N-group: 0.95 ≤ CV/CC ≤ 1.05); and the asymmetrical group (A-group: CV/CC < 0.95, or >1.05).

RESULTS

In all the patients, the 3-month-postoperative CV/CC ratio (1.026 ± 0.087) was significantly different from the preoperative CV/CC ratio (0.969 ± 0.095, P < 0.001), indicating that the pelvis had rotated in the opposite direction of the corrective derotation load applied to the TL/L spine after surgery. No significant change was found in the CV/CC ratio from 3-month-postoperative to the last follow-up (1.013 ± 0.103, P > 0.05). There was no significant difference in the demographic, phenotypic, and treatment variables between the N- (n = 16) and A-groups (n = 22) (P > 0.05). However, more coronal decompensation occurred in the A-group after surgery (36.4 vs. 0.0 %, P = 0.013): two patients having trunk translation, three having lower instrumented vertebra (LIV) translation, and one having LIV tilt; meanwhile, one patient having both LIV translation and LIV tilt, and one having both trunk translation and LIV tilt.

CONCLUSIONS

The present study confirmed the existence of PAR in AIS patients, and indicated that the pelvis would experience an active rebalancing in the transverse plane within 3 months after spinal correction, and since then, its position would remain stable. Moreover, TL/L-AIS patients with preoperative asymmetrical PAR probably had greater risk of coronal decompensation postoperatively.

Postoperative changes in spinal rod contour in adolescent idiopathic scoliosis: an in vivo deformation study

STUDY DESIGN

Prospective case series.

OBJECTIVE

To evaluate the change in spinal rod contour from before implantation to after surgical correction of thoracic curves in patients with adolescent idiopathic scoliosis.

SUMMARY OF BACKGROUND DATA

With segmental pedicle screw spinal instrumentation and vertebral derotation, many authors have reported a loss of thoracic kyphosis postoperatively. Although surgeons anticipate some flattening of the preimplantation rod contour in the sagittal plane, the magnitude of this change in shape has not been documented.

METHODS

The concave and convex rod shapes of 5.5-mm ultrahigh-strength steel spinal rods (200 KSI) from patients with thoracic adolescent idiopathic scoliosis (n = 27), which were contoured with benders by the surgeon, were traced prior to insertion. Postoperative (average, 5 weeks) sagittal rod shape was determined from lateral 2-dimensional radiographs. Maximal rod deflection and angle of the tangents to rod end points (Cobb) were measured. Repeated measures analysis of variance assessed differences between pre- and postoperation.

RESULTS

The scoliosis of 55° ±14° was corrected 72% to 15° ± 5°. The preinsertion rod shapes were more kyphotic for the concave (45.6°) than for the convex (31.4°) rods. Following correction, the concave rods flattened, with decrease in deflection of 13 mm and reduction in angle of 21° (both P < 0.001). The convex rods increased 1.5 mm in deflection and 2° in angle (P < 0.01, P = 0.18). The sagittal profile was maintained postoperatively as measured from T5-T12: 19° ±14° versus 22° ± 6° (pre vs. post, P > 0.1).

CONCLUSION

We found a significant difference between pre- and postoperative rod contour, particularly for concave rods. Rod overcontouring (by ~20° for concave rod) resulted in high degrees of correction without loss of sagittal alignment. The resulting deformations are likely associated with substantial in vivo deforming forces.

Corrective force analysis for scoliosis from implant rod deformation

BACKGROUND

Scoliosis is a serious disease in which a human spine is abnormally deformed in three dimensions with vertebral rotation. Surgical treatment is attained when the scoliotic spine is corrected into its normal shape by implant rods and screws fixed into the vertebrae. The three-dimensional corrective forces acting at the screws deformed the implant rod during the surgical treatment of scoliosis. The objective of this study was to propose a method to analyze the three-dimensional forces acting at the rod using the changes of implant rod geometry before and after the surgical treatment.

METHODS

An inverse method based on Finite Element Analysis is proposed. The geometries of implant rod before and after the surgical treatment were measured three dimensionally. The implant rod before the surgical treatment was reconstructed using an elasto-plastic finite element model. The three-dimensional forces were applied iteratively to the rod through the screws such that the rod is deformed the same after the surgical treatment of scoliosis.

FINDINGS

The maximum force acting at the screw of each patient ranged from 198N to 439N. The magnitude of forces was clinically acceptable. The maximum forces occurred at the lowest fixation level of vertebra of each patient.

INTERPRETATION

The three-dimensional forces distribution that deformed the rod can be evaluated using the changes of implant geometry. Although the current clinical cases are still few, this study demonstrated the feasibility of measuring the forces that deformed the implant rod after the surgical treatment of scoliosis.

Pedicle screw instrumentation and spinal deformities: have we gone too far?

INTRODUCTION

Placement of pedicle screws within the thoracic and lumbar spine has become the "state of the art" for the treatment of spinal deformities. Newly trained surgeons are often trained only with the placement of pedicle screws within the thoracic and lumbar spine and not with hooks or other means of fixation. However, if the benefits of pedicle screw instrumentation in terms of correction ability cannot be questioned on some issues pertaining to their safety, their rationale for all situations as well as their long-term adverse consequence and or early or late complications start to arise.

MATERIALS AND METHODS

We therefore present four case examples that illustrate the advantages, questions and complications inherent to pedicle screw instrumentation in spinal deformities. These four cases serve as discussion supported by a review of the literature. The literature search was performed to include pedicle screws associated risks, costs and complications. Articles focusing on instrumentation of the thoracic and lumbar spine for the treatment of adult and pediatric scoliosis were reviewed.

RESULTS

Pedicle screw instrumentation in the treatment of spinal deformity is here to stay, however a fair number of issues have come up since their widespread use that started 10 years ago: these include their misplacement with the inherent risks to the vascular or neurologic structures, the rate of misplaced pedicle screw not per number of screws inserted, but per patient operated, the number of screws really necessary to achieve a satisfactory outcome while maintaining costs, their contraindications in some very challenging deformities where the risks clearly outweigh their advantage compared to hooks. At last, the use of pedicle screw instrumentation has driven many centers in increasing the safety of such procedures using intraoperative spinal cord monitoring as well as improved imaging technologies.

CONCLUSION

To answer our provocative title "Pedicle screw instrumentation have we gone too far?" Definitively we can answer that for some spinal deformities instrumented with all-pedicle-screw instrumentation, we have observed cases where the surgeons have gone way too far; in other cases, where such instrumentation was used in a comprehensive and rational manner, the answer to "Have we gone too far" is no, and such use of pedicle screw has improved outcome with minimum complications.

Simultaneous double-rod rotation technique in posterior instrumentation surgery for correction of adolescent idiopathic scoliosis

The authors present a new posterior correction technique consisting of simultaneous double-rod rotation using 2 contoured rods and polyaxial pedicle screws with or without Nesplon tapes. The purpose of this study is to introduce the basic principles and surgical procedures of this new posterior surgery for correction of adolescent idiopathic scoliosis. Through gradual rotation of the concave-side rod by 2 rod holders, the convex-side rod simultaneously rotates with the the concave-side rod. This procedure does not involve any force pushing down the spinal column around the apex. Since this procedure consists of upward pushing and lateral translation of the spinal column with simultaneous double-rod rotation maneuvers, it is simple and can obtain thoracic kyphosis as well as favorable scoliosis correction. This technique is applicable not only to a thoracic single curve but also to double major curves in cases of adolescent idiopathic scoliosis.