Systematic review and meta-analysis for the impact of rod materials and sizes in the surgical treatment of adult spine deformity

Validation of a new method for the radiological measurement of rod curvature in patients with spine deformity

PURPOSE

The relationship between rod curvature and postoperative radiographic results is a debated topic. One of the reasons of the heterogeneity of the observed results might reside in the lack of a validated and widely employed method to measure the curvature of the rods. Aim of this study was to present and validate a novel method for rod measurement, which is based on routine X-rays and utilizes a regression algorithm that limits manual measurements and the related errors.

METHODS

Data from 20 adolescent idiopathic scoliosis/Scheuermann kyphosis (AIS/SK) patients and 35 adult spine deformity (ASD) patients for analysis, with 112 rods in total. An orthogonal reference grid was overlaid on the lateral X-ray; seven points were then marked along each rod and their coordinates recorded in a table. Using these coordinates, a third-order polynomial regression was applied to obtain the rod curvature equation (correlation coefficients > 0.97). Three observers (one surgeon, one experienced and one inexperienced observer) independently applied the developed method to measure the rod angulation of the included patients and performed the measurements twice. The reliability of the method was evaluated in terms of intraclass correlation coefficient (ICC), Bland-Altmann plot and 2SR.

RESULTS

The intra-observer ICCs for all measurements exceed 0.85, indicating an excellent correlation. For the AIS/SK group, the surgeon showed a slightly lower reliability compared to the other two evaluators (0.93 vs 0.98 and 0.98). However, the surgeon showed a higher reliability in measurements of the rods at the lumbar level, both for L1-S1 and L4-S1 (0.98 vs 0.96 and 0.89; 0.97 vs. 0.85 and 0.91, respectively). The variability also showed excellent results, with a mean variability ranging from 1.09° to 3.76°. The inter-observer ICCs for the three measurement groups showed an excellent reliability for the AIS/SK group (0.98). The reliability was slightly lower but still excellent for the lumbar measurements in ASD patients at L1-S1 (0.89) and L4-S1 (0.83). The results of the 2SR for each measured segment were 4.4° for T5-T11, 5.4° for L1-S1 and 5.5° for L4-S1.

CONCLUSION

The described method represents a reliable and reproducible way to measure rod curvature. This method is based on routine X-rays and utilizes a regression algorithm that limits manual measurements and the related errors.

Impact of multi-rod reinforcement on rod fractures in adult spinal deformity: A retrospective case series with a minimum follow up of 5 years

BACKGROUND

This study aimed to determine the impact of the multi-rod construct on rod fractures over a minimum follow-up period of five years in comparison to that with the conventional two-rod construct using the same technique, rod composition, and rod reinforcement method.

METHODS

Data were retrospectively retrieved from a prospectively collected, single-center database. Consecutive patients >50 years of age who underwent thoracopelvic corrective fusion with planned two-stage anterior-posterior surgery and were followed up for at least five years were included in this study. The incidence of rod fracture in the conventional two-rod and multi-rod groups was investigated.

RESULTS

A total of 58 patients (mean age, 68.9 years) were included in this study (follow-up rate, 73.4 %). Rod fracture was identified in 25 patients (43.1 %), within an average period of 25.1 months. The incidence of rod fracture in the multi-rod group was significantly lower than that in the two-rod group. However, there was no significant difference in the time to rod fracture between the two groups. Reinforcement of the multi-rod to the distal portion of the connector of the iliac screw had the lowest fracture rate and no cases of reoperation.

CONCLUSIONS

The incidence of rod fracture was significantly lower using multi-rod reinforcement, but the timing of rod fracture did not differ, compared to that with the two-rod construct using the same surgical technique and rod material. Multi-rod reinforcement covering the distal portion of the iliac screw is recommended to reduce the risk of fracture and reoperation.

Patient-specific spinal rods in adult spinal deformity surgery reduce proximal junctional failure: a review of patient outcomes and surgical technique in a prospective observational cohort

Background

Spinal rods used for adult spinal deformity (ASD) correction are usually manufactured straight and bent manually during surgery. Pre-bent patient-specific spinal rods (PSSR) developed with software provide the surgeon with an intraoperative deformity correction consistent with the surgical plan. Our aim was to report clinical and radiological outcomes using PSSR. We investigated rates of junctional complications both proximally [kyphosis (PJK) and failure (PJF)] and distally [failure (DJF)].

Methods

Prospective case series of 20 consecutive patients who underwent ≥4 level ASD surgery with PSSR at a single institution between January 2019 and December 2022. Preoperative, 6-week, 6-month, 12-month, 24-month, and final follow-ups assessed patient satisfaction (Ottawa decision regret questionnaire) and patient reported outcome measures (PROMs) [visual analogue scale (VAS; Back/Leg), Oswestry disability index (ODI), and 12-Item Short Form Survey (SF-12)]. Sagittal spinopelvic parameters [sagittal vertical axis (SVA), pelvic tilt (PT), and pelvic incidence and lumbar lordosis mismatch (PI-LL)] measured by serial EOS scans were performed preoperatively then compared to planned correction and postoperative measures. Interoperative cages (narrow/wide) were placed for interbody support. PJK risk score assessed likelihood of developing kyphosis. Serial computed tomography (CT) imaging assessed complication (fusion/subsidence).

Results

The mean age of the patients (75% female) was 71.9±6.9 years, and the mean follow-up was 25.2±8.6 [7-40] months. Preoperative mean PROMs showed statistically significant overall improvement (P<0.001) postoperatively to final follow-up. Four patients without wide footprint cages at L4/5 or L5/S1, suffered DJF and reported regret undergoing surgery. Statistically significant difference (P<0.001) between preoperative and surgical plan in SVA and PI-LL but not in PT (P=0.058). No statistically significant difference in surgical plan versus the postoperative SVA, PI-LL, and PT (due to difficulty achieving the surgical plan, and also to maintaining the correction). One patient suffered PJF. There was a mean proximal kyphotic angle (PKA) of 17.8±13.0 degrees and PJK risk score of 3.7±1.0 with 40% who experienced PJK. No rod breakages were observed.

Conclusions

In this series, PSSR improved PROMs and treated ASD. Sagittal parameters planned preoperatively correlated with postoperative correction. PJF was reduced, compared to the literature (35%), but PJK was observed over time. DJF occurred and was related to the absence of interbody cages at the lumbosacral junction and decisional regret.

Rod angulation does not reflect sagittal curvature in adult spinal deformity surgery: comparison of lumbar lordosis and rod contouring

STUDY DESIGN

A retrospective study.

OBJECTIVE

Relationship between rod and spinal shape in the sagittal plane in adult spinal deformity (ASD) surgery.

BACKGROUND

Corrective surgery for adult spinal deformity (ASD) involves the use of contoured rods to correct and modify the spinal curvatures. Adequate rod bending is crucial for achieving optimal correction. The correlation between rods and spinal shape in long constructs has not been reported previously.

METHODS

We conducted a retrospective analysis of a prospective, multicenter database of patients who underwent surgery for ASD. The inclusion criteria were patients who underwent pelvic fixation and had an upper instrumented vertebra at or above T12. Pre- and post-operative standing radiographs were used to assess lumbar lordosis at the L4S1 and L1S1 levels. The angle between the tangents to the rod at the L1, L4, and S1 pedicles was calculated to determine the L4S1 and L1S1 rod lordosis. The difference between the lumbar lordosis (LL) and the rod lordosis (RL) was calculated as ΔL = LL-RL. The correlation between this difference (ΔL) and various characteristics was analyzed using descriptive and statistical methods.

RESULTS

Eighty-three patients were included in the study, resulting in 166 analyzed differences (ΔL) between the rod and spinal lordosis. The values for rod lordosis were found to be both greater and lesser than those of the spine but were mostly lower. The range for total ΔL was -24 °-30.9 °, with a mean absolute ΔL of 7.8 ° for L1S1 (standard deviation (SD) = 6.0) and 9.1 ° for L4S1 (SD = 6.8). In 46% of patients, both rods had a ΔL of over 5 °, and over 60% had at least one rod with a ΔL difference of over 5 °. Factors found to be related to a higher ΔL included postoperative higher lumbar lordosis, presence of osteotomies, higher corrected degrees, older age, and thinner rods. Multivariate analysis correlated only higher postoperative L1S1 lordosis with higher ΔL. No correlation was found between a higher ΔL and sagittal imbalance.

CONCLUSIONS

Variations between spinal and rod curvatures were observed despite the linear regression correlation. The shape of the rod does not seem to be predictive of the shape of the spine in the sagittal plane in ASD long-construct surgeries. Several factors, other than rod contouring, are involved in explaining the postoperative shape of the spine. The observed variation calls into question the fundamentals of the ideal rod concept.