Computational Study on the Effects of Bone Radii and Defect Size on Subchondral Bone Contact

Articular cartilage defects in the knee can cause pain and discomfort in patients, often limiting their physical ability and leading to osteoarthritis. Fortunately, several surgical options exist to repair the cartilage. To aid in choosing the appropriate surgical procedure, surgeons use an algorithm that places a high significance on the size of the defect, with a defect size of 2 cm2 used as the threshold between microfracture surgery and autograft substitution. This algorithm, however, does not account for variations in the surface curvature of the femur and tibia, which has been found to significantly alter subchondral bone contact (SBC). We hypothesize that bone radii also affect SBC and should be considered in addition to defect size when determining the correct surgery for repair. To test this hypothesis, we developed a finite-element model of the knee with a full-thickness focal defect in the articular cartilage of the femur. This model was validated using experimental data obtained previously in our lab. We then altered tibial and femoral radii, as well as defect size, to determine the threshold at which significant SBC occurs for a given bone radii pair. Results revealed a clear trend of significant SBC occurring at a smaller defect size for smaller bone radii. These results should be confirmed with future experimental testing of various bone radii to determine if current surgical algorithms need to be altered.No embarg

Correspondence between bone mineral density and intervertebral disc degeneration across age and sex

The distribution of bone tissue within the vertebra can modulate vertebral strength independently of average density and may change with age and disc degeneration. Our results show that the age-associated decrease in bone density is spatially non-uniform and associated with disc health, suggesting a mechanistic interplay between disc and vertebra. PURPOSE: While the decline of bone mineral density (BMD) in the aging spine is well established, the extent to which age influences BMD distribution within the vertebra is less clear. Measures of regional BMD (rBMD) may improve predictions of vertebral strength and suggest how vertebrae might adapt with intervertebral disc degeneration. Thus, we aimed to assess how rBMD values were associated with age, sex, and disc height loss (DHL). METHODS: We measured rBMD in the L3 vertebra of 377 participants from the Framingham Heart Study (41-83 years, 181 M/196 F). Integral (Int.BMD) and trabecular BMD (Tb.BMD) were measured from QCT images. rBMD ratios (anterior/posterior, superior/mid-transverse, inferior/mid-transverse, and central/outer) were calculated from the centrum. A radiologist assigned a DHL severity score to adjacent intervertebral discs (L2-L3 and L3-L4). RESULTS: Int.BMD and Tb.BMD were both associated with age, though the decrease across age was greater in women (Int.BMD, - 2.6 mg/cm3 per year; Tb.BMD, - 2.6 mg/cm3 per year) than men (Int.BMD, - 0.5 mg/cm3 per year; Tb.BMD, - 1.2 mg/cm3 per year). The central/outer (- 0.027/decade) and superior/mid-transverse (- 0.018/decade) rBMD ratios were negatively associated with age, with similar trends in men and women. Higher Int.BMD or Tb.BMD was associated with increased odds of DHL after adjusting for age and sex. Low central/outer ratio and high anterior/poster and superior/mid-transverse ratios were also associated with increased odds of DHL. CONCLUSIONS: Our results indicate that the distribution of bone within the L3 vertebra is different across age, but not between sexes, and is associated with disc degeneration.Accepted manuscript2020-05-1

Wireless sensor enables longitudinal monitoring of regenerative niche mechanics during rehabilitation that enhance bone repair.

Mechanical loads exerted on the skeleton during activities such as walking are important regulators of bone repair, but dynamic biomechanical signals are difficult to measure inside the body. The inability to measure the mechanical environment in injured tissues is a significant barrier to developing integrative regenerative and rehabilitative strategies that can accelerate recovery from fracture, segmental bone loss, and spinal fusion. Here we engineered an implantable strain sensor platform and longitudinally measured strain across a bone defect in real-time throughout rehabilitation. The results showed that load-sharing permitted by a load-sharing fixator initially delivered a two-fold increase in deformation magnitude, subsequently increased mineralized bridging by nearly three-fold, and increased bone formation by over 60%. These data implicate a critical role for early mechanical cues on the long term healing response as strain cycle magnitude at 1 week (before appreciable healing occurred) had a significant positive correlation with the long-term bone regeneration outcomes. Furthermore, we found that sensor readings correlated with the status of healing, suggesting a role for strain sensing as an X-ray-free healing assessment platform. Therefore, non-invasive strain measurements may possess diagnostic potential to evaluate bone repair and reduce clinical reliance on current radiation-emitting imaging methods. Together, this study demonstrates a promising framework to quantitatively develop and exploit mechanical rehabilitation strategies that enhance bone repair