Osteoarthritis (OA) is the leading cause of pain and disability worldwide and is characterized by the degenerative changes of articular cartilage. Joint loading is required for cartilage maintenance; however, hyper-physiologic loading is a risk factor for OA. Mechanosensitive ion channels Piezo1 and Piezo2 synergistically transduce hyper-physiologic compression of chondrocytes, leading to chondrocyte death and onset of OA. This injury response is inhibited by Piezo channel loss of function, however the mechanistic role of Piezo channels in vivo is unknown. We examined the hypothesis that deletion of Piezo in chondrocytes will protect mice from joint damage and pain-related behaviors following a surgical destabilization of the medial meniscus (DMM), investigating a key mechanistic and mechanobiological role of these channels in the pathogenesis of OA.

Aggrecan-Cre Piezo1 and Piezo1/2 knockout mice ((Agc)1-CRE^ERT2;Piezo1^fl/flPiezo2^fl/fl) were generated and given a 5-day Tamoxifen regimen at 12-weeks of age (n=6–12/group/sex). Cre-negative mice served as controls. At 16-weeks, mice received DMM surgery on the left knee. 12-weeks following DMM prior to sacrifice, activity and hyperalgesia were measured using spontaneous running wheels and a small animal algometer. Structural changes in bone, cartilage, and synovium were characterized using microCT, histology, and Modified Mankin Score criteria.

Knockout of Piezo1/2 channels was chondroprotective in both sexes following DMM surgery as demonstrated by reduced Modified Mankin Score compared to control animals. Piezo1 KO was chondroprotective in only female mice, indicating a sexually dimorphic response. Piezo1 and Piezo1/2 KO was protective against pain in male mice, while females displayed no differences compared to controls. No changes were observed in bone morphology.

Chondrocyte-specific Piezo1/2 knockout protects the knee joint from structural damage, hyperalgesia and functional deficits in a surgical model of PTOA in male and female mice, illustrating the importance of Piezo channels in response to injury in vivo. Future work aims to interrogate potential sexually dimorphic responses to cartilage damage and investigating Piezo2 KO mice.

Statement of Purpose

Meniscal tears are common knee injuries that subsequently lead to degenerative arthritis, attributed to changes in stress distribution in the knee. In such cases there is need to protect the articular cartilage by repairing or replacing the menisci. While traditionally, meniscal replacement involves implantation of allografts, problems related to availability, size matching, cost and risk of disease transmission limit their use. Another optional treatment is that of biodegradable scaffolds which are based principally on tissue engineering concepts. The variability in body response to biodegradable implants and the quality of the tissue formed still pose a problem in this respect, under intense knee loading conditions. Moreover, biological solutions are mostly limited to younger patients <40 years old. Therefore, the goal of this study was, to develop a synthetic meniscal implant which can replace the injured meniscus, restore its function, and relieve pain.

Meniscus replacement still represents an unsolved problem in orthopedics. Allograft meniscus implantation has been suggested to restore contact pressures following meniscectomy. However, graft availability, infection, and size matching still limit its use. A synthetic meniscal substitute could have significant advantages for meniscal replacement, as it could be available at the time of surgery in a substantial number of sizes and shapes to accommodate most patients. In the current study we present an optimization method for meniscal implant design and employ in the development of artificial polycarbonate-urethane (PCU) meniscus implant in an ovine model.

The construction of the gross implant structure was based on 3D interpolation of MRI scans of the native sheep meniscus in-situ. PCU-based samples based on this design were produced for testing. 35 ovine knee joints were tested. An experimental evaluation of the implants’ biomechanical performances was conducted by measuring pressure distributions on the tibial plateau (TP) during loading. Subsequently, a pressure score of 0 to 100% was calculated. The score reflects on the magnitude of peak pressure and contact area coverage with respect to the natural meniscus. Implant design was reevaluated following changes to the initial implant configuration, e.g., modification of implant geometry, adding reinforcement material, and the applying of different fixation forces during implantation. The effect of these changes on pressure distribution was assessed by additional compression tests.

The initial all-PCU implant showed limited ability to distribute pressure, The pressure score of 37% calculated for this case reflects on the small contact area (151mm2) subject to relatively high contact pressures (> 1.85MPa). The implant’s ability to distribute pressure improved significantly when circumferential reinforcement fibers were added. Applying a pretension force of 20N during fixation, improved pressure distribution and increased the contact area (273mm2). A small region of focal pressure concentration still existed in this case, but the pressure score increased markedly to 77%. Finally, it was found that optimal pressure distribution (87%) can be attained when a force of 30 to 50N is applied. In this configuration, peak pressures and coverage area (1.65MPa and 310mm2) were similar to those of the natural meniscus (1.61MPa and 373 mm2, respectively).

We conclude that peripheral reinforcement of the implant (similar to the natural meniscus microstructure), in addition to pretension of 30 to 50N can significantly improve TP pressure distributions. The results are in agreement with other studies, reported on pressure distribution improvement due to reinforcement and/or pretension. We believe that the current device can be used in future as a practical solution for patients suffering from severe meniscal injury.

Post-traumatic arthritis is a frequent consequence of articular fracture. The mechanisms leading to its development after such injuries have not been clearly delineated. A potential contributing factor is decreased viability of the articular chondrocytes. The object of this study was to characterise the regional variation in the viability of chondrocytes following joint trauma. A total of 29 osteochondral fragments from traumatic injuries to joints that could not be used in articular reconstruction were analysed for cell viability using the fluorescence live/dead assay and for apoptosis employing the TUNEL assay, and compared with cadaver control fragments.

Chondrocyte death and apoptosis were significantly greater along the edge of the fracture and in the superficial zone of the osteochondral fragments. The middle and deep zones demonstrated significantly higher viability of the chondrocytes. These findings indicate the presence of both necrotic and apoptotic chondrocytes after joint injury and may provide further insight into the role of chondrocyte death in post-traumatic arthritis.