In vivo distraction force and length measurements of growing rods: which factors influence the ability to lengthen?

STUDY DESIGN: Prospective, intraoperative force measurement in consecutive lengthening procedures in a series of growing-rod patients undergoing lengthening. OBJECTIVE: The purpose of this study was to measure the forces and amount of distraction over time in early onset scoliosis patients treated with growing rods. SUMMARY OF BACKGROUND DATA: Growing rods are one of the current techniques used in the treatment of early onset scoliosis, and the goal of the growing-rod technique is to achieve deformity correction, maintaining spinal growth at the same time. Gradual stiffening or spontaneous fusion of the spine can interfere with the ability to lengthen. In addition, diminished acquired length with serial distraction are common observations and need to be evaluated and quantified. METHODS: Distraction forces were measured prospectively during 60 consecutive lengthening procedures in 26 patients. All patients had single submuscular rod constructs with side-to-side connectors. For each measurement, output from a transducer on a dedicated pair of distraction calipers was recorded at zero load status and the force was then recorded at every 1 mm lengthening; length was obtained at each event and was recorded in millimeters. RESULTS: The force required to distract the spine doubled at the 5th lengthening procedure (mean 368 N ± 54 N), and the distraction force was significantly higher at the fifth lengthening compared with the previous lengthening (P <0.01). Mean length achieved at each distraction decreased over time such that by the fifth lengthening, consistently 8 mm or less was achieved. CONCLUSION: Distraction forces increase significantly after repeated lengthening of growing-rod constructs, and the length obtained at each procedure exhibits a decreasing trend.

Minimizing complications with single submuscular growing rods: a review of technique and results on 88 patients with minimum two-year follow-up.

STUDY DESIGN: Retrospective clinical and radiologic review of consecutive series of patients treated with single submuscular growing rods from a single center with a minimum of 2-year follow-up. OBJECTIVES: To describe the surgical technique and methods used to minimize complications and to report on the outcomes of a large consecutive series of patients treated with single submuscular growing rods for scoliosis in the immature spine from a single center. SUMMARY OF BACKGROUND DATA: Previous studies have reported on the safety and efficacy of single and dual growing-rod constructs; however, these studies have been of small patient numbers with varying results. METHODS: Between 1999 and 2007, 88 patients underwent the insertion of a single, submuscular growing-rod construct for scoliosis. A clinical and radiologic review of these 88 consecutive patients with a minimum of 2-year follow-up was conducted. Diagnoses include idiopathic, neuromuscular, syndromic, and congenital. Data include Cobb angle measurements, T1-S1 heights, number, and frequency of lengthening as well as complications. RESULTS: The patients underwent single submuscular growing-rod insertion at an average age of 7.0 years. The mean follow-up period was 42 months. Twenty-eight patients had a simultaneous apical fusion. Growing-rod lengthening was performed on an average at 9-month intervals. The average initial Cobb angle was 73° (range: 40-117) and improved to 44° (range: 9-90) at final follow-up. T1-S1 height gain was 3.37 cm; this translates to 1.04 cm growth/yr. No significant difference was noted between those who had undergone apical fusion and those without. Complications noted in this series include 8 incidences of superficial infection and 3 of deep infection, proximal junctional kyphosis in 2 patients requiring early fusion, 31 rod fractures, 10 cases of proximal anchor failure, and 6 distal anchor failures. Thirty patients within study group have reached definitive fusion. CONCLUSION: Favorable outcomes have been demonstrated in this large single-center series of growing-rod constructs used to treat scoliosis in the growing spine. Their safety and efficacy in controlling spinal deformity and allowing spinal growth along with an acceptable rate of complications would support the continued use of single growing-rod constructs as a scoliosis management option.

Can vertebroplasty restore normal load-bearing to fractured vertebrae?

STUDY DESIGN: Cadaver motion segments were used to evaluate the effects of vertebroplasty on spinal loading following vertebral fracture. OBJECTIVES: To determine if vertebroplasty reverses fracture-induced changes in the distribution of compressive stress in cadaver motion segments. SUMMARY OF BACKGROUND DATA: Vertebroplasty involves reinforcement of vertebrae by injection of cement and is now being used increasingly to treat osteoporotic vertebral fractures. However, its effects on spinal load-bearing are largely unknown. We hypothesize that vertebroplasty, following vertebral fracture, helps to equalize stress acting on the intervertebral disc and adjacent vertebral bodies. METHODS: Nineteen cadaver thoracolumbar motion segments (age 64-90 years) were induced to fracture by compressive overload. Specimens were then subjected to vertebroplasty, and subsequently creep loaded for 1 hour at 1.5 kN. The compressive stress acting on the intervertebral disc was measured before and after fracture, after vertebroplasty, and after creep, by pulling a pressure transducer mounted in a 1.3-mm needle across the disc's midsagittal diameter. This information was then used to calculate neural arch load-bearing. At each time point, measurements were also made of compressive stiffness. RESULTS: Vertebral fracture reduced motion segment compressive stiffness, decompressed the adjacent nucleus, increased stress concentrations in the posterior anulus, and increased neural arch load-bearing, all by a significant amount. Vertebroplasty partially, but significantly, reversed all of these fracture-induced changes. CONCLUSIONS: Vertebroplasty reduces stress concentrations in the anulus and neural arch resulting in a more even distribution of compressive stress on the intervertebral disc and adjacent vertebral bodies.

"Does size matter?"A comparison of balloon-assisted less-invasive vs conventional retroperitoneal approach for anterior lumbar interbody fusion.

This is a case-series comparison of two approaches to anterior lumbar interbody fusion. A conventional open approach (COA) was compared with a balloon-assisted minimally invasive approach (BMI). Outcome measures included operating time, blood loss and complications. Secondary outcome measures included analgesia requirements, time to mobilization and inpatient stay. There were 17 females (7 COA, 10 BMI) and 18 males (9 COA and 9 BMI). Forty-five discs (21 COA, 24 BMI) in total were fused in 35 patients. There were significant differences (in favour of the BMI) in the overall operating time between the COA and the BMI, and the single level COA and the BMI. There was no inter-group difference in the PCA requirements either overall or between one or two-level operations. The less invasive approach did have a benefit in earlier mobilization of the single-level fusions.