Knee osteoarthritis affects hundreds of millions of people globally, and its prevalence is rising as populations age and obesity rates climb. Despite its ubiquity, diagnosing and tracking the disease remains surprisingly crude. The clinical gold standard for characterizing the soft tissue and bone changes of osteoarthritis is magnetic resonance imaging scored with detailed grading systems such as the MRI Osteoarthritis Knee Score, known as MOAKS. MRI can reveal cartilage loss, bone marrow lesions, meniscal damage, and joint effusions with remarkable detail, but it is expensive, time consuming, and impractical for repeated monitoring. Clinicians have therefore long sought cheaper, faster proxies, and the idea of listening to the joint, a technique called phonoarthrography or joint acoustic emission analysis, has circulated for decades without ever quite reaching the clinic.

The Finnish team, led by Olli Veikkola of the Research Unit of Health Sciences and Technology at the University of Oulu, together with colleagues at EPFL in Switzerland, the Basque Center for Applied Mathematics in Spain, and Oulu University Hospital, set out to test the concept rigorously. They recruited 106 participants for a single-center prospective cohort study: 66 women aged 44 to 67 years and 40 men aged 45 to 64 years. Each participant underwent knee MRI, and trained readers applied the full MOAKS grading protocol to define the osteoarthritic status of every knee. This gave the researchers a detailed, image-based ground truth against which any acoustic or kinematic signal could be validated.

To capture the joint’s sounds and movements, the team built a custom prototype device. Two non-contact air microphones were positioned just below the patella, close enough to record the subtle acoustic emissions generated inside the joint but without touching the skin, which avoids friction noise and pressure artifacts. In addition, inertial measurement unit modules, small sensor packages containing accelerometers and gyroscopes, were strapped to the thigh and shank. These recorded kinetic instability, the tiny deviations and tremors in how the leg moves during loaded tasks. Participants then performed simple physical exercises, including sit-to-stand movements performed laterally, which load the knee in controlled and repeatable ways while the sensors capture everything the joint does.

From the raw recordings, the researchers extracted a large battery of signal features. In total, 35 acoustic variables were derived, encompassing measures such as the energy distribution across frequency bands, the ratio of high-frequency click-like events to lower-frequency emissions, and statistical descriptors like skewness, which captures the asymmetry of the signal distribution. The kinematic data yielded measures of instability during the same tasks. The central analytical question was whether any of these features correlated with specific MOAKS parameters, the individual MRI findings such as bone marrow lesions, meniscal extrusion or morphology, cartilage defects, and effusion, rather than with a vague overall diagnosis of osteoarthritis.

The results, analyzed with logistic regression models, showed statistically significant associations between a subset of the acoustic variables and six relevant MOAKS parameters. The most promising signals were strikingly specific. The ratio of high-frequency emissions to click-type emissions recorded during the lateral sit-to-stand task predicted bone marrow lesions in the lateral femur. Meanwhile, the skewness of the high- and low-frequency acoustic emissions during the same movement predicted both lateral meniscal position and morphology and the presence of joint effusions. The discriminative performance of these features, quantified by the area under the receiver operating characteristic curve, ranged between 0.65 and 0.70. That is well short of the 0.90-plus values expected of a standalone diagnostic test, but it is far above chance, and it demonstrates that the sounds of a moving knee genuinely encode information about structures deep inside the joint that can otherwise only be seen on MRI.

One of the most intriguing findings emerged when the analysis was stratified by sex. Statistically significant associations appeared only among the female participants, specifically for bone marrow lesions in the lateral femur and for effusion. The male subgroup alone did not reach significance for any parameter, although including men in the combined analysis reinforced the overall associations rather than weakening them. The authors note this sex difference explicitly, and it raises questions about anatomical and biomechanical differences between male and female knees, differences in signal transmission through varying soft tissue thickness, or simply the smaller male sample size of 40 participants. Whatever the mechanism, the pattern suggests that future studies of joint acoustics will need to account for sex as a modifying variable rather than pooling all knees together.

The technical logic behind why damaged knees sound different is worth unpacking. Healthy cartilage surfaces glide over one another with minimal friction, producing little acoustic energy. As osteoarthritis progresses, the cartilage roughens, fibrillates, and eventually wears away, exposing bone and altering the lubrication of the joint. Irregular surfaces and debris generate impulsive, high-frequency vibrations during loading, and displaced menisci or inflamed, fluid-filled joint capsules change the way these vibrations propagate and how the joint moves under load. Bone marrow lesions, which represent localized edema and microdamage within the femoral or tibial bone, may alter the stiffness and damping characteristics of the structures through which the sound travels. The Finnish findings hint that different pathological features imprint different acoustic fingerprints, with high-frequency click ratios flagging bone lesions and distributional asymmetries in the emission signal tracking meniscal displacement and swelling.

The researchers are careful about what their results do and do not prove. They describe the associations as exploratory and emphasize that the diagnostic potential remains to be confirmed in larger studies. The cohort of 106 knees is modest, the AUC values indicate moderate rather than strong discrimination, and the study was conducted at a single center with a specific prototype device and a fixed set of tasks. The study was registered at clinicaltrials.gov under identifier NCT02937064, and the work received open access funding from the University of Oulu with support from the Radiological Society of Finland. One declared competing interest is worth noting: co-author Jerome Thevenot is a shareholder and CEO of Inmodi Oy, a company that could have a stake in commercializing such technology, which readers should weigh alongside the exploratory nature of the findings.

Even with those caveats, the study points toward a genuinely appealing future. If the associations hold up at scale, a knee examination could one day involve nothing more than a pair of microphones and two motion sensors, a setup costing a tiny fraction of an MRI scan and deployable in a general practitioner’s office, a physiotherapy clinic, or even a patient’s home. Such a tool would not replace MRI, whose detailed MOAKS grading remains indispensable for surgical planning and definitive characterization. Instead, the authors suggest, acoustic emissions and kinetic instability might serve as a complementary modality for characterizing knee osteoarthritis, screening patients who need imaging, and tracking disease progression over time without repeated exposure to costly scans. For a disease that will touch an ever-growing share of the aging global population, the prospect of hearing osteoarthritis before it can be seen is a quiet revolution worth listening for.

Subject of Research: Acoustic emission and kinetic instability biomarkers for detecting knee osteoarthritis changes graded by MRI

Article Title: Acoustic emissions and kinetic instability as biomarkers to detect osteoarthritic changes of knee joint according to MRI

Article References: Olli, V., Jerome, T., Tomas, T., Simo, S., & Mika, N. (2026). Acoustic emissions and kinetic instability as biomarkers to detect osteoarthritic changes of knee joint according to MRI. BioMedical Engineering OnLine. https://doi.org/10.1186/s12938-026-01632-4

Image Credits: AI Generated

DOI: 10.1186/s12938-026-01632-4

Keywords: knee osteoarthritis, acoustic emissions, kinetic instability, MRI, MOAKS, biomarkers, bone marrow lesions, meniscus, joint effusion, phonoarthrography, biomedical engineering, diagnostic markers

Researchers at Birjand University of Medical Sciences and collaborating Iranian institutions set out to solve a problem that is both biological and geopolitical. The most promising biological scaffolds for meniscus replacement have often come from pigs, whose tissue closely resembles our own. But across Iran and much of the Middle East, porcine material is culturally and religiously inaccessible, and human donor menisci are in short supply. The team therefore turned to two regionally abundant species, the sheep and the dromedary camel, and asked a deceptively simple question: if you strip the cells out of their menisci, leaving behind only the collagenous framework, how closely does the resulting scaffold match what human tissue can offer?

The answer required an unusually thorough decellularization protocol. Whole menisci from camels and sheep were collected from a local abattoir, while human specimens came from patients undergoing total knee arthroplasty. Each tissue then endured a punishing chemical gauntlet: repeated freeze-thaw cycles to rupture cell membranes, trypsin digestion, two rounds of the detergent Triton X-100, a 72-hour bath in sodium lauryl ether sulfate with EDTA, and a final treatment with peracetic acid to open pores and purge lingering cellular debris. The goal is a paradox familiar to tissue engineers: kill and remove every cell while leaving the intricate extracellular matrix, the collagen fibers and proteoglycans that give the meniscus its strength, essentially untouched.

By the standard benchmarks, the protocol succeeded. Residual DNA fell to 29.67 nanograms per milligram of dry weight in camel scaffolds, 22.33 in human, and 19.67 in sheep, all comfortably below the internationally accepted threshold of 50 nanograms per milligram that signals successful decellularization. Histological staining confirmed that cell nuclei had vanished from both the peripheral and central zones. Yet the process was not without cost. Glycosaminoglycans, the water-loving sugar chains that help the meniscus resist compression, dropped significantly in every species, a well-known vulnerability of these highly soluble molecules to detergent-based processing.

What survived, remarkably, was the architecture. Scanning electron microscopy showed that the highly aligned circumferential collagen network, the load-bearing skeleton of the meniscus, remained intact in all three species, with directionality goodness-of-fit values above 0.8. Decellularized fibers were actually thicker than native ones, swelling from roughly 1.7 to 2.4 micrometers in camel tissue, likely because removing proteoglycans released the compacted fibrils from their molecular tethers. Porosity also rose substantially, from about 20 percent to nearly 32 percent in camel scaffolds, with mean pore sizes expanding to over 129 square micrometers, changes that should ease cell migration and nutrient diffusion once the scaffold is implanted.

Mechanical testing delivered the study’s most encouraging numbers. Although decellularization softened all three tissues, the camel scaffold’s compressive modulus of 1.12 megapascals remained statistically indistinguishable from that of decellularized human meniscus at 0.86 megapascals, despite the camel’s roughly 20 percent numerical advantage. Ultimate tensile strength showed no significant decline in any species after processing, evidence that the circumferential collagen architecture retained its ability to carry tension along the meniscus’s primary load-bearing axis. The researchers attribute this resilience to two factors: the preserved network of circumferential and radial fibers that confines the tissue laterally under compression, and the camel meniscus’s inherently dense native collagen, which the protocol preserved across all groups.

The decisive test came in living tissue. The team implanted small squares of each scaffold under the skin of rats and tracked the immune response over four weeks. In the first week, all three xenogeneic materials provoked comparable acute inflammation, an expected reaction to foreign tissue. By week four, however, the paths diverged sharply. Camel scaffolds showed attenuated inflammation, vigorous migration of fibroblasts deep into the scaffold interior, and signs of active remodeling. Human scaffolds, paradoxically, retained persistent inflammatory infiltrates at their periphery with little fibroblast penetration, while sheep scaffolds showed reduced inflammation but less cellular integration than camel tissue. Quantitative histomorphometry confirmed that camel scaffolds also retained significantly more of their original area, indicating slower degradation and superior structural stability during the critical early remodeling window.

Laboratory assays reinforced the in vivo picture. NIH 3T3 fibroblasts adhered and spread on all three scaffolds, and MTT viability tests showed no cytotoxicity and no meaningful differences among the materials. Co-culture with Jurkat T-lymphocytes revealed that all xenogeneic scaffolds stimulated more T-cell proliferation than flat 2D culture, an honest reminder that animal-derived matrices are not immunologically invisible; camel scaffolds trended toward the lowest proliferation, but the differences did not reach statistical significance. Raman spectroscopy added a molecular fingerprint, detecting preserved collagen-associated peaks including amide I at 1658 and amide III at 1237 inverse centimeters, which could serve as batch-verification markers in future manufacturing. Enzymatic degradation assays told the same durability story: after 14 days in trypsin, camel scaffolds retained 84.31 percent of their mass versus 64.88 percent for human and just 45.23 percent for sheep.

The authors are careful about what these results do and do not mean. In the rat model, all three scaffolds were xenografts; in a human patient, human tissue would behave as an allograft with matched immune recognition, so camel material should be seen as a pragmatic regional alternative rather than an immunological upgrade over human transplants. The subcutaneous implantation site also cannot reproduce the biomechanical complexity of the knee, and the study lacked cyclic fatigue testing under physiological loading. Still, the work establishes the first quantitative anatomical dataset for dromedary camel menisci, showing outer circumferences of 105 to 115 millimeters that even exceed human dimensions, and demonstrates for the first time that camel, human, and sheep scaffolds can be systematically benchmarked against one another. The next milestone will be orthotopic implantation in large-animal knees under dynamic load, the true proving ground for any scaffold that hopes to keep people moving after meniscus loss.

Subject of Research: Decellularized xenogeneic meniscus scaffolds from camel and sheep as alternatives to human meniscus grafts

Article Title: Efficacy of decellularized meniscus xenogeneic substitutes from sheep and camels compared to human menisci

Article References: Khakzad, M. R., Vafaei‐Nezhad, S., Talaei‐Khozani, T., Hassanzadeh‐Taheri, M. M., Rezaeipour, M., Hashemi, H., Shadi, M., & Afshar, M. (2026). Efficacy of decellularized meniscus xenogeneic substitutes from sheep and camels compared to human menisci. Bioengineering & Translational Medicine, Article e70161. https://doi.org/10.1002/btm2.70161

Image Credits: AI Generated

DOI: 10.1002/btm2.70161

Keywords: meniscus, decellularization, tissue engineering, extracellular matrix, xenograft, camel, sheep, biocompatibility, collagen scaffold, knee injury, regenerative medicine, biomechanics