Medical researchers studying osteoarthritis are exploring the use of near-infrared reflection spectroscopy to characterize bone tissue and improve standards of care for arthroscopic surgeries. There are a large number of uses for near-infrared spectroscopy in the field of biomedical research including non-invasive monitoring, blood testing, protein identification, and more. The near-infrared range is so important because it offers the best quality of reflection spectra measurements, with the least scattering and absorption between 650 nm and 1900 nm.  Spectral measurements in the near-infrared are non-invasive and non-destructive, making this particularly attractive for the potential development of clinical applications.  

The Avantes family of NIR instruments offers the best mix of sensitivity and resolution for medical applications with NIR spectroscopy. Our next-generation EVO electronics provide lowers noise and offer the latest high-speed communications options for fast data when working in vivo.

What is Osteoarthritis?

Osteoarthritis is a common degenerative condition characterized by the depletion of cartilage in the joints, causing pain and loss of mobility. A common cause of osteoarthritis is simply age; however, traumatic joint injury can cause joint degeneration in people of any age. The progression of osteoarthritis can be slowed and symptoms managed, but there is no way to reverse the underlying causes that lead to the development of this condition.

Recent research in osteoarthritis has suggested that changes to the subchondral (below the cartilage) bone structures, such as a thickening of the subchondral plate, are discernible before lesions or other symptoms become detectable in the cartilage itself.

Current standards for the diagnosis and treatment of osteoarthritis rely on radiographic imaging to detect hardening of the subchondral layer or a decrease in joint space and visual and tactile inspection during arthroscopic surgery. In recent years, advances in imaging and computing power for analysis has led to an increased interest in the use of NIR to quantify the progression of joint damage and evaluate treatment during in vivo arthroscopies.

NIR Osteoarthritis Figure 1
Bone cross-section by Pbroks13
[CC BY 3.0], via Wikimedia Commons

Evaluating the Biomechanical Properties of Bone In Vitro

Research from the University of Eastern Finland published in June 2018 in the journal Nature investigated the potential for near-infrared spectroscopy for use in characterizing human subchondral bone properties and sought a wavelength range capable of estimating human bone properties in a clinical setting.

This experiment examined several key parameters of bone integrity in bone samples harvested from human cadavers, including subchondral bone plate thickness, bone mineral density, and structural model index using near-infrared spectroscopy.

The NIR spectral data was collected using a dual-channel Avantes system that paired the AvaSpec-ULS2048L-EVO with the high-sensitivity AvaSpec-NIR256/512-2.5-HSC-EVO (the 256 pixel version). Spectra were collected across three wavelength ranges already identified for the ability to penetrate living tissue, called the biologic or therapeutic optical window. The first window covered the range 650-950 nm, the next from 1100-1350 nm, and the third biologic window examined was 1600-1870 nm. This data was correlated against micro-computed tomography results of the same bone samples using partial least squares regression multivariate technique.

This work showed that wavelength-dependent penetration of light into osteochondral samples plays a significant role in the relationship between optical response and subchondral bone properties. The first optical window, λ 650-950 nm, showed the strongest correlation and lowest error rate against the tomography results and shows the greatest potential for adaptation into arthroscopy standards of care.

NIR Osteoarthritis Figure 2
‘Gonarthrosis, medial abuse of cartilage’
by Scuba-limp [GFDLCC-BY-SA-3.0 or CC BY-SA 2.5],
via Wikimedia Commons

Developing Clinical Applications for NIRS Arthroscopy

A second group of researchers from Utrecht University in the Netherlands and the University of Eastern Finland published research in the journal Nature in September 2018 that sought to prove the reliability of NIR spectroscopy to simultaneously evaluate both articular cartilage and subchondral bone in vivo with the assistance of an artificial neural network (ANN).

Currently, there are no quantitative arthroscopic tools to evaluate both cartilage and subchondral bone. Orthopaedic surgeons use radiographic imaging and subjective scoring of injury severity relying on visual inspection and tactile probing with a metal hook during arthroscopic surgeries. While some clinical tools exist for evaluating cartilage, their use is limited by practical issues, and no clinical tool currently exists for the evaluation of the subchondral bone morphology.

Using the AvaSpec-ULS2048XL-EVO, this study first collected NIR spectral data arthroscopically from ponies 12 months after receiving experimental joint repair procedures, then collected samples from the same ponies for in vitro spectral measurements. Additional spectral data was collected in vitro from samples harvested from unaffected ponies as a control. These samples also underwent optical coherence tomography (OCT) for the complete analysis of bone morphology to serve as a reference for prediction modelling with the assistance of a shallow Artificial Neural Network (ANN).

This experiment collected spectra from a broad wavelength range covering the visible from 450nm through 2500 nm in the near-infrared but discounted wavelengths over 1900 nm due to water’s high NIR absorption properties. Additionally, the visible range between 450 and 750 nm saw interference from conventional arthroscopic light and therefore was only be used for probe orientation and positioning, but was excluded from modelling. The wavelength range between 750 and 1900 nm, which nearly spans all three therapeutic optical windows, was determined to be the optimal range for prediction of cartilage biomechanical properties including subchondral bone plate thickness, bone volume fraction and bone mineral density.

The results of the partial least squares analysis produced a prediction model capable of predicting bone integrity parameters with a 95% confidence rate. The measurements performed in vitro showed fewer prediction errors, unsurprisingly, likely because of inherent complications in achieving optimal probe placement while performing arthroscopy. There were also fewer prediction errors for analyzing the biomechanical properties of cartilage compared to analysis of the subchondral bone due to the tissue depth. Nevertheless, the researchers concluded that NIR spectroscopy was capable of simultaneous characterization of articular cartilage and subchondral bone integrity in humans with potential for augmenting conventional arthroscopy techniques in the clinical assessment of defective joints.

NIR Osteoarthritis Figure 3
Representative NIR Spectra Bone Samples
By Afara, Florea, et al.
Characterizing human subchondral bone
properties using near-infrared
(NIR) spectroscopy,
 via Scientific Reports

Light: The Medicine of the Future

In the medical field alone, light is used to monitor health status, perform diagnostic testing, assist in the treatment of chronic wounds, and detect and fight cancer, and new discoveries that advance medical science are made every day.

Avantes instruments are trusted to provide these researchers with the perfect balance between high resolution and high sensitivity and features a modular design ideal for configuring multi-channel systems. We have 25 years of experience working hand in hand with researchers and manufacturers of medical and pharmaceutical solutions designing systems and components that deliver incredible results year after year.

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Afara, Isaac O., et al. ‘Characterizing human subchondral bone properties using near-infrared (NIR) spectroscopy.’ Scientific reports 8.1 (2018): 9733.

Sarin, Jaakko K., et al. ‘Arthroscopic near-infrared spectroscopy enables simultaneous quantitative evaluation of articular cartilage and subchondral bone in vivo.’ Scientific reports 8.1 (2018): 13409. 

‘Osteoarthritis – Symptoms, and Causes – Mayo Clinic’, 14 Nov. 2018.