Identifying bum knees before injury with laser light

 Collagen Orientation Probed by Polarized Raman Spectra Can Serve as Differential Diagnosis Indicator between Different Grades of Meniscus Degeneration
Authors: Prokopi, N.; Andrikopoulos, K. S.; Beobide, A. S.; Voyiatzis, G. A.; Papachristou, D. J.
Journal: Scientific Reports
Year: 2021
Featured image licensed under Creative Commons Attribution-Share Alike 4.0

Our knees can carry a heavy burden, and healthy menisci are key to our comfort. Menisci are the cushions of cartilage that separate our femur from our tibia in our knees. Damaged menisci can disrupt normal knee function and eventually lead to osteoarthritis in the knee. Although it is straightforward to diagnose a damaged meniscus when an injury occurs, small lesions – which can develop into serious problems later – frequently go unnoticed. If diagnosed soon enough, interventions can reverse cartilage degeneration, so it is vital to detect damage as early as possible for patient health. Recently, a team of researchers published a new technology for detecting meniscus degeneration in Scientific Reports that may aid in early detection and diagnosis.

Meniscus cartilage is primarily composed of collagen type I, a protein that looks like a twisted cable, which is flexible with a bit of stretch. As the meniscus degrades, the matrix of collagen fibers becomes disordered, like a frayed cable, and loses the elasticity and structural integrity vital for joint comfort. 

Figure 1. The triple helix of collagen type 1 losing structural integrity over time which will eventually lead to joint disease. Adapted from Hwang et al. (CC BY 4.0). 

Cartilage damage is most commonly diagnosed through CT and MRI scans, which can differentiate between healthy and diseased tissue. However, their limited resolution and artifacts, or “shadows”, on scan images make it difficult to diagnose early cartilage degeneration. Prokopi and their team established a new protocol that uses laser light to bypass these issues.

Raman spectroscopy is a technique that allows researchers to determine information about a material by measuring how laser light scatters. The scattered light gives insight to specific bonds in a molecule, molecular environment, and other nanoscopic characteristics. This allows researchers to identify different proteins and ensure that they are only analyzing collagen. These researchers took this analytical technique a step further by introducing polarization to the laser light.

Figure 2. Scattering that occurs when light interacts with a molecule, in this case, methane. Rayleigh scattering is elastic and at the same energy as the incident light, Stokes shift is inelastic and lower energy than the incident light, and anti-Stokes is also inelastic but higher energy than the incident light. Created by Fionna Samuels.
Figure 3. Unpolarized light going through a filter that selects for one specific polarization. Credit to Bob Mellish (CC BY-SA 3.0).

To polarize the laser, a filter selects light waves only oscillating in one direction – either up and down, or side to side. When combined with Raman spectroscopy, researchers can learn even more about a material’s structural integrity. In this case, healthy and diseased collagen scatter the laser light differently depending on polarization because the collagen fibers become frayed when damaged. This allows these researchers to diagnose how diseased the tissue is. This technique has higher resolution than CT or MRI scans and does not suffer from imaging artifacts like shadows, giving it potential to flag damage earlier.

Raman spectrum of thin slices of collagen type I collected on a traditional Raman microscope. Prokopi et al. collected Raman spectra of both cartilage and glass and identified peaks that were unique to each to differentiate between the sample (cartilage) and the sample holder (a glass slide). The highlighted peak is particularly strong when cartilage is thinly sliced. Adapted from Prokopi et al. (CC BY 4.0). 
Raman spectra associated with healthy and degenerated meniscus tissue. Three samples ranging from healthy (bottom) to highly degenerated (top). The yellow line shows the primary direction of collagen within the sample, with the small grey box in the middle of each microscopy image indicating the frame.  Adapted from Prokopi et al. (CC BY 4.0).

The results of this methodology are promising for future diagnostic tests. The researchers suggest that this technique can be applied to any disease that is characterized by a change in structural morphology. This can range from skin diseases that impact collagen to muscle degeneration which would change the morphology of the tissue. With further development, this technique may end-up at doctors’ offices and aid in preventing bum knees before they’re too damaged to be fixed.

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