Optical coherence tomography for the identification of musculoskeletal structures of the spine: a pilot study

Er:YAG laser brain surgery with vascular specific coagulation

BACKGROUND AND OBJECTIVE

Erbium:yttrium-aluminum-garnet (Er:YAG) laser ablation can effectively resect water-bearing tissues. Application of Er:YAG resection in neurosurgery is complicated by unpredictable bleeding in surgical field. Recently, an integrated theranostic system combining a dual-wavelength laser surgery system using a thulium (Tm) fiber-laser for coagulation and Er:YAG for resection, combined with optical coherence tomography (OCT) guidance was demonstrated for the in vivo resection of tumor tissue. However, lateral thermal spread in the range of 100 seconds of micrometers is common due to lack of vascular specificity using a Tm fiber-laser for coagulation. In this study, a vascular specific ytterbium (Yb) fiber-laser is utilized for enhanced photocoagulation during in vivo neurosurgery improving the precision of Er:YAG tissue resection with minimal lateral thermal spread.

METHODS

Mice underwent stereotactic laser surgery with the proposed Yb/Er:YAG dual wavelength vascular specific neurosurgery in vivo. An OCT system (wavelength range 1310 ± 70 nm) and OCT derived angiography  images were used to record cortical images to confirm the coagulation of blood vessels and guide subsequent Er:YAG resection steps. After the laser surgery, mice were killed, and histological analysis was carried out using hematoxylin and eosin staining and Nissl staining to compare the lateral thermal spread with our previously reported Tm/Er:YAG neurosurgery where a continuous wave  Tm fiber-laser was used for coagulation.

RESULTS

Coagulation scheme using a Yb fiber-laser allowed stoppage of blood flow in disparately sized blood vessels encountered in the mice brain. Histological analysis of murine brain slices post Yb/Er:YAG laser surgery yielded lower thermal spread compared with Tm/Er:YAG laser surgery, maximizing the efficiency in both hemostasis (blood flow stoppage) and maximizing tissue ablation efficiency with minimal residual thermal damage zone.

CONCLUSION

In this study, a vascular specific coagulation scheme with Yb/Er:YAG dual-wavelength surgery is presented for neurosurgery. Additionally, Yb/Er:YAG study results are compared with that of a tissue coagulation approach in Tm/Er:YAG surgery previously reported to highlight improved coagulation, reduced nonspecific thermal damage and limited lateral thermal spread. Experimental results suggest that the developed dual-wavelength laser system can effectively resect neural tissues with high localization, minimal lateral thermal spread at the micrometer level while maintaining a bloodless surgical field.

Quality control methods in musculoskeletal tissue engineering: from imaging to biosensors

Tissue engineering is rapidly progressing toward clinical application. In the musculoskeletal field, there has been an increasing necessity for bone and cartilage replacement. Despite the promising translational potential of tissue engineering approaches, careful attention should be given to the quality of developed constructs to increase the real applicability to patients. After a general introduction to musculoskeletal tissue engineering, this narrative review aims to offer an overview of methods, starting from classical techniques, such as gene expression analysis and histology, to less common methods, such as Raman spectroscopy, microcomputed tomography, and biosensors, that can be employed to assess the quality of constructs in terms of viability, morphology, or matrix deposition. A particular emphasis is given to standards and good practices (GXP), which can be applicable in different sectors. Moreover, a classification of the methods into destructive, noninvasive, or conservative based on the possible further development of a preimplant quality monitoring system is proposed. Biosensors in musculoskeletal tissue engineering have not yet been used but have been proposed as a novel technology that can be exploited with numerous advantages, including minimal invasiveness, making them suitable for the development of preimplant quality control systems.

Novel Hemi-Staple for the Fusionless Correction of Pediatric Scoliosis: Influence on Intervertebral Disks and Growth Plates in a Porcine Model

STUDY DESIGN

In vivo porcine model utilized to evaluate the influence of an intravertebral fusionless growth modulating device (hemi-staple) on intervertebral disks and growth plates.

OBJECTIVE

To evaluate the radiographic and histologic changes in disks and growth plates with the purpose of measuring influence of the explored hemi-staple.

SUMMARY OF BACKGROUND DATA

Fusionless growth modulation for the early treatment of scoliosis should insure the long-term viability of the intervertebral disk and successfully reduce or arrest local growth. A novel hemi-staple that proved effective in the control of coronal spinal alignment warranted further analyses of its influence on the disk health and growth-plate morphology.

METHODS

A hemi-staple that inhibited local vertebral growth exclusive of the disk was introduced over T5-T8 in 4 immature pigs (16 vertebrae; experimental), whereas 3 underwent surgery without instrumentation (sham) and 2 had no intervention (control). Three-month follow-up before animal euthanasia provided radiographic (disk height and health) and histologic (growth plate morphology, disk health, and type X collagen distribution) analyses.

RESULTS

No postoperative complications were experienced. Radiographic data returned inverse disk wedging (greater disk height adjacent to device, 2.6±0.7 mm compared with the noninstrumented side, 1.8±0.5 mm) in experimental segments and suggested disk viability. Histologic data confirmed device growth modulation through significant local reduction of growth plate hypertrophic zone (125.64±16.61 μm and 61.16±8.25 μm in noninstrumented and instrumented sections, respectively) and cell height (16.14±1.87 μm and 9.22±1.57 μm in noninstrumented and instrumented sections, respectively). A variability of disk health, dependant of device insertion location, was observed. Type X collagen was consistently identified in experimental growth plates and absent from intervertebral disks.

CONCLUSIONS

Hemi-staples decreased growth plate hypertrophic zone and cell height, and, depending on device insertion site, showed positive signs of disk health sustainability. Spinal growth modulation achieved exclusive of disk compression, as practiced by this method, offers unique advantages over other fusionless techniques. This technique may provide a suitable and attractive alternative for the early treatment of idiopathic scoliosis.

Local Epiphyseal Growth Modulation for the Early Treatment of Progressive Scoliosis: Experimental Validation Using a Porcine Model

STUDY DESIGN

Experimental study of a localized device for the control of the vertebral growth using an immature porcine model.

OBJECTIVE

The aim of the study was to experimentally evaluate a localized device acting on the epiphyseal growth plates without bridging the intervertebral disc of immature hybrid pigs over 3 months of growth.

SUMMARY OF BACKGROUND DATA

Based on current published literature, fusionless devices offer promising scoliosis treatment alternatives to conventional spinal instrumentation and fusion in the growing spine. Current compression-based devices achieve growth modulation while also compressing the intervertebral discs, increasing the risk of long-term disc degeneration.

METHODS

An intravertebral staple acting on both the superior and inferior growth plates was inserted locally over T7-T9 of seven healthy immature pigs. Four age-matched animals served as controls. Radiographs were acquired monthly to assess induced spinal curvature and vertebral wedging (inverse model). Global (spinal) and local (vertebral, discal) geometric changes were evaluated over 3-months follow-up. Final left/right vertebral height differences were also quantified.

RESULTS

The only postoperative complication observed was one pig that had a persistent deep infection and was excluded from the study. No significant changes in spinal alignment were reported in control animals. Final induced Cobb angle was 25.0° ± 4.2° measured over T7-T9, with no observable sagittal profile modification. Highest vertebral wedging occurred at T9 with 18.2° ± 2.7°. Cumulative vertebral wedging over T7-T9 accounted for 45.4°, demonstrating evidence of reversed disc wedge phenomenon. Vertebral height was 3.9 ± 1.0 mm shorter on the instrumented side suggesting full growth restraint. Local and regional induced deformities significantly differed from their control counterparts (P < 0.001).

CONCLUSION

In this animal model, the local epiphyseal device achieved significant localized growth modulation over as little as three instrumented levels, with explicit vertebral wedging exclusive of the intervertebral disc. By increasing the number of instrumented levels, one may achieve higher curvature control potentially providing a unique local correction method to correct spinal deformity without affecting the intervertebral disc.

LEVEL OF EVIDENCE

5.

Using attenuation coefficients from optical coherence tomography as markers of vocal fold maturation

OBJECTIVES/HYPOTHESIS

Optical coherence tomography (OCT) is a promising technology to noninvasively assess vocal fold microanatomy. The goal of this study was to develop a methodology using OCT to identify quantifiable markers of vocal fold development.

STUDY DESIGN

In vivo study.

METHODS

A two-step process was developed to reproducibly image the midmembranous vocal fold edge of 10 patients younger than 2 years and 10 patients between 11 and 16 years of age using OCT. An image analysis algorithm was implemented to extract OCT-derived A-lines for each patient. These A-lines were divided into three zones according to apparent changes in slope. Relative attenuation coefficients, or tissue- and system-dependent parameters that describe the rate at which optical signal decays, were calculated for each zone.

RESULTS

Young patients had distinct relative attenuation coefficients in zone 1 (P < .0001), whereas zones 2 and 3 were indistinct (P = .1129). Older patients had distinct relative attenuation coefficients in zones 1, 2, and 3 (P < .0370). Between age groups, relative attenuation coefficients were different in zones 2 and 3 (P < .0001, P = .0315, respectively) and indistinct in zone 1 (P = .1438).

CONCLUSIONS

Relative attenuation coefficients can be used as markers of vocal fold development. Differences in relative attenuation coefficients likely represent changes in extracellular matrix structure within the lamina propria and may become useful for guiding treatment of voice disorders in the pediatric population.

LEVEL OF EVIDENCE

NA Laryngoscope, 126:E218-E223, 2016.

Imaging of the Rotator Cuff With Optical Coherence Tomography

This study evaluated the utility of optical coherence tomography (OCT) in imaging porcine and human rotator cuff (RTC) tissue, analyzed its effectiveness in identifying clinical pathology, and correlated these findings with histologic examination. Twelve human cadaveric and 6 porcine shoulders were evaluated. Six-millimeter-wide bone sections were harvested from the proximal humerus of each specimen, with each containing the entire enthesis of the respective RTC tendon, as well as 2 cm of tendon medial to the enthesis. Only the supraspinatus tendon was evaluated in the human specimens, whereas the enthesis of multiple RTC tendons were evaluated in the porcine model. All specimens were imaged using OCT and correlated with histologic evaluation. Optical coherence tomography evaluation of macroscopically healthy tissue consistently showed an easily identifiable banding pattern (birefringence) in contrast to a disorganized, homogeneous appearance in grossly diseased tissue. Optical coherence tomography was more effective for qualitative evaluation of RTC tissue, identification of bursal-sided RTC tears, and localization of calcific deposits, whereas intrasubstance tendon delaminations and partial articular-sided tendon avulsion lesions were relatively more difficult to identify. Optical coherence tomography correlated well with histologic evaluation in all specimens. Optical coherence tomography provides high-resolution, subsurface imaging of rotator cuff tissue in real-time to a depth of up to 4 mm with excellent correlation to histology in a cadaveric model. Optical coherence tomography could be an effective adjunctive tool for the identification and localization of rotator cuff pathology. The use of OCT in arthroscopic shoulder surgery potentially provides a minimally invasive modality for qualitative assessment of rotator cuff pathology. This may allow for a decrease in soft tissue dissection, improved qualitative assessment of cuff tissue, and improved patient outcomes.

Photothermal tomography for the functional and structural evaluation, and early mineral loss monitoring in bones

Salient features of a new non-ionizing bone diagnostics technique, truncated-correlation photothermal coherence tomography (TC-PCT), exhibiting optical-grade contrast and capable of resolving the trabecular network in three dimensions through the cortical region with and without a soft-tissue overlayer are presented. The absolute nature and early demineralization-detection capability of a marker called thermal wave occupation index, estimated using the proposed modality, have been established. Selective imaging of regions of a specific mineral density range has been demonstrated in a mouse femur. The method is maximum-permissible-exposure compatible. In a matrix of bone and soft-tissue a depth range of ~3.8 mm has been achieved, which can be increased through instrumental and modulation waveform optimization. Furthermore, photoacoustic microscopy, a comparable modality with TC-PCT, has been used to resolve the trabecular structure and for comparison with the photothermal tomography.