Does bioresorbable cage material influence segment stability in spinal interbody fusion?

The effectiveness of biodegradable instrumentation in the treatment of spinal fractures

INTRODUCTION

A variety of biodegradable implants (screws, rods, plates and cages) are available which are composed of many different biodegradable polymers with varying characteristics. The present review of animal and clinical studies examines the efficacy and safety of biodegradable implants in spinal fracture intervention.

METHODS

A review of the literature through March 2018 was performed using PubMed and Cochrane databases. Success rates were calculated according to sufficient tissue biocompatibility, solid clinical fusion and propensity for osseointegration.

RESULTS

49 articles (24 animal and 25 human studies) were included. In animal experiments, the overall success rate for spinal fusion was 60.3%, while the mean success rate regarding the cervical spine was 51.8% compared to 68.1% for the lumbar spine (p = 0.002). In studies involving control group(s): the mean bioabsorbable implant success rate for spinal fusion was 42% compared to 57% for conventional implants (p = 0.0016). In the lumbar spine pL-lactide acid (PLLA) had 75.2% success rate compared to poly (L-lactide-co-DL-lactide) (PLDLLA) at 53.4% (p = 0.003). In clinical studies, the overall mean success rate was 89%, while the mean success rate regarding the cervical spine was 92%, as compared to 83.6% for the lumbar spine (p = 0.001). In studies involving control group(s): the mean bioabsorbable implant success rate was 75% compared to a conventional implant mean success rate of 97% (p<0.0001). In the cervical spine PLLA had a 98.7% success rate compared to 90% with PLDLLA (p = 0.015). In the lumbar spine PLDLLA had 84.7% success rate compared to 63.6% for poly-glycolic acid (PGA) (p = 0.085).

DISCUSSION

Studies combined biodegradable and conventional implants. Polymers were used in various combinations and surface modification of the implants also varied. Comparison studies were of small sample size. Animal and clinical studies diverged. The current data are not encouraging. The end-point of assessing osseointegration varies in the studies and is indeterminate. In early stages the structure comparison of osseous restoration using biodegradable implants appears inferior to utilization of conventional cages and instrumentation. There is no statistically significant evidence supporting the efficacy of biodegradable implants replacing traditional instrumentation. There is a lack of prospective clinical trials with long-term follow-up regarding utilization of biodegradable implants and the available data does not support their routine use in spinal fracture intervention.

RSA in Spine: A Review

STUDY DESIGN

Systematic review of literature.

OBJECTIVES

This systematic review was conducted to investigate the accuracy of radiostereometric analysis (RSA), its assessment of spinal motion and disorders, and to investigate the limitations of this technique in spine assessment.

METHODS

Systematic review in all current literature to invesigate the role of RSA in spine.

RESULTS

The results of this review concluded that RSA is a very powerful tool to detect small changes between 2 rigid bodies such as a vertebral segment. The technique is described for animal and human studies for cervical and lumbar spine and can be used to analyze range of motion, inducible displacement, and fusion of segments. However, there are a few disadvantages with the technique; RSA percutaneous procedure needs to be performed to implant the markers (and cannot be used preoperatively), one needs a specific knowledge to handle data and interpret the results, and is relatively time consuming and expensive.

CONCLUSIONS

RSA should be looked at as a very powerful research instrument and there are many questions suitable for RSA studies.

Two-year migration results of the ReCap hip resurfacing system-a radiostereometric follow-up study of 23 hips

There has been renewed interest for metal-on-metal hip resurfacing due to improved design and manufacturing of implants, better materials, and enhanced implant fixation. In contrast to conventional total hip replacements, only a few clinical hip resurfacing trials using radiostereometry (RSA) have been reported, and solely for the Birmingham hip resurfacing arthroplasty. The purpose of this RSA trial was to describe the migration pattern of a new hip resurfacing system (ReCap) within the first two years after primary surgery. Twenty-six patients underwent total hip replacement. The patients were followed-up for up to 24 months and were evaluated with the use of radiostereometric measurements. The prosthesis showed mean translations and rotation close to zero. Maximum translation was seen along the transverse axis in the medial direction (0.13 mm). No statistically significant translation or rotation was seen at two-years follow-up, (t-test, p <0.05, translation or rotation).

Tissue identification with micro-magnetic resonance imaging in a caprine spinal fusion model

Nonunion is a major complication of spinal interbody fusion. Currently X-ray and computed tomography (CT) are used for evaluating the spinal fusion process. However, both imaging modalities have limitations in judgment of the early stages of this fusion process, as they only visualize mineralized bone. Magnetic resonance imaging (MRI) could be of great value as it is able to discriminate between different types of tissue. A feasibility study was performed in nine animals from a goat spinal fusion study, to evaluate the detection capacity of different tissues with micro-MRI. In this study bioresorbable polylactic acid cages were used. Six- and 12-months follow-up specimens were scanned in a 6.3 T micro-MRI scanner. After scanning, the specimens were processed for histology. Different types of tissue as well as the degradable cage material were identified in the fusion zone and designated as regions of interest (ROIs). Subsequently, the location of these ROIs was determined on the corresponding micro-MRI image, and average signal intensities of every individual ROI were measured. An excellent match was seen between the histological sections and micro-MRI images. The micro-MRI images showed quantifiable differences in signal intensity between bone with adipose marrow, bone with hematopoietic marrow, fibrocartilage, fibrous tissue, and degradable implant material. In time the signal intensity of bone with adipose marrow, bone with hematopoietic red marrow, and of fibrous tissue remained relatively constant. On the other hand, the signal intensity of the degradable implant material and the fibrocartilage changed significantly in time, indicating change of structure and composition. In conclusion, in our model using bioresorbable cages the MRI provides us with detailed information about the early fusion process and may therefore, allow early diagnosis of non-union.

Twelve-Month Follow-up of Lumbar Spine Range of Motion Following Intervertebral Disc Replacement Using Radiostereometric Analysis

Background

Many clinical studies have focused on clinical pain scores and less on kinematics following intervertebral disc replacement. Although flexion and extension of the motion segment can be measured on lateral X-rays, measuring lateral bending and axial rotation of the device is extremely difficult on plain radiography. This study was designed to measure, using radiostereometric analysis (RSA), the postoperative range of motion of the spinal segment following placement of ProDisc-L interbody device (Synthes Spine, West Chester, Pennsylvania).

Methods

Twelve patients (15 discs) with a ProDisc-L intervertebral disc replacement were followed postoperatively at 1.5, 3, 6, and 12 months with both clinical and RSA examinations. For follow-up RSA analysis, 4 to 5 tantalum beads were inserted into the vertebrae adjacent to the surgical level during surgery. Standing biplanar films were collected during follow-up, and the ranges of motion (ROM) (sagittal and coronal bending) of the adjacent vertebrae were determined by RSA.

Results

Based on the clinical surveys, this group of patients had similar outcomes compared to larger clinical populations. The flexion/extension ROM with the disc replacement averaged 2.5° at 6 weeks and increased over the follow-up period to 6.6° at 6 months. The lateral bending ROM with the disc replacement remained consistent over the 4 time points and averaged 3.0°. The motion at the level of the L4-5 vertebrae following disc replacement was greater across all time points than the motion at the L5-S1 level for both sagittal (5.9° versus 2.1°) and coronal (4.2° versus 0.6°) bending.

Conclusions

In this study, the amount of RSA-measured segmental flexion/extension ROM for those with disc replacement was similar to other studies using plain radiography. In lateral bending, the amount of motion with disc replacement was less than the typical 6°–16° reported for normal ROM.

Clinical Relevance

This is the first published study evaluating the in vivo kinematics of artificial disc replacement using RSA.