Application of 3D-printed patient-specific skeletal implants augmented with autologous skeletal stem cells.

Joint replacements have proved a medical success providing symptomatic relief and return to mobility in many patients with arthritis. However, multiple revision surgeries due to joint failure can result in complex revision scenarios with significant bone tissue loss, in an elderly population, which poses a significant clinical challenge. Computer-aided design-computer-assisted manufacturing (CAD-CAM) prototyped bespoke implants are currently being used as an alternative and innovative approach for joint restoration in salvage cases, while the incorporation of autologous skeletal stem cells to optimize regenerative capacity can enhance implant osseointegration. We present a case series of 11 patients with severe disability and significant bone loss due to failed joint replacements. The choice of CAD-CAM prototyped joint implants enhanced with autologous skeletal stem cells resulted in significant patient-reported clinical and radiological improvements.

Local Variation in Femoral Neck Cortical Bone: In Vitro Measured Bone Mineral Density, Geometry and Mechanical Properties.

Age- and disease (osteoporotic fractured and osteoarthritic tissue)-related changes in the distribution of cortical bone were examined, using a multimodality approach, including measurement of local density, geometry and mechanical properties, where changes in these properties can give rise to instability and increasing probability of fracture. In contrast to the majority of previously reported research, this study also focuses on the characteristic non-circular femoral neck cross-sectional geometry and variation in bone mineral density (BMD) around the femoral neck. Twenty-two osteoarthritic and 7 osteoporotic femoral neck slices, collected from elective and trauma-related arthroplasty, and 16 cadaveric donor tissue controls were tested mechanically using Reference Point Indentation (BioDent™, Active Life Technologies®, Santa Barbara, CA) and then scanned with in vitro-based radiography intended to replicate the dual-energy X-ray absorptiometry technique. All parameters were measured regionally around the circumference of the femoral neck, allowing examination of spatial variability within the cortical bone. Fractured tissue was less resistant to indentation in the thinner superolateral segment compared to other segments and other groups. BMD around the fractured femoral necks appeared more consistent than that of nonfractured tissue, where BMD was reduced in the superolateral segment for the other groups. Cortical bone was thin in the superolateral segment for all groups except for the osteoarthritic group, and was thicker in the inferomedial segment for both osteoarthritic and fractured groups, resulting in the largest variation in buckling ratio (ratio of cortical bone diameter to cortical bone thickness) around the femoral neck for the fractured group. With age, healthy controls appeared to have lower inferomedial cortical thickness, whereas no significant differences in Reference Point Indentation measurements and density were observed. The study has highlighted several (both quality- and quantity-related) parameters that may be used to improve prediction of fracture risk.

Exploring inter-subject anatomic variability using a population of patient-specific femurs and a statistical shape and intensity model.

This paper is motivated by the need to accurately and efficiently measure key periosteal and endosteal parameters of the femur, known to critically influence hip biomechanics following arthroplasty. The proposed approach uses statistical shape and intensity models (SSIMs) to represent the variability across a wide range of patients, in terms of femoral shape and bone density. The approach feasibility is demonstrated by using a training dataset of computer tomography scans from British subjects aged 25-106 years (75 male and 34 female). For each gender, a thousand new virtual femur geometries were generated using a subset of principal components required to capture 95% of the variance in both female and male training datasets. Significant differences were found in basic anatomic parameters between females and males: anteversion, CCD angle, femur and neck lengths, head offsets and radius, cortical thickness, densities in both Gruen and neck zones. The measured anteversion for female subjects was found to be twice as high as that for male subjects: 13 ± 6.4° vs. 6.3 ± 7.8° using the training datasets compared to 12.96 ± 6.68 vs. 5.83 ± 9.2 using the thousand virtual femurs. No significant differences were found in canal flare indexes. The proposed methodology is a valuable tool for automatically generating a large specific population of femurs, targeting specific patients, supporting implant design and femoral reconstructive surgery.

Inter-subject variability effects on the primary stability of a short cementless femoral stem.

This paper is concerned with the primary stability of the Furlong Evolution(®) cementless short stem across a spectrum of patient morphology. A computational tool is developed that automatically selects and positions the most suitable stem from an implant system made of a total of 48 collarless stems to best match a 3D model based on a library of CT femur scans (75 males and 34 females). Finite Element contact models of reconstructed hips, subjected to physiologically-based boundary constraints and peak loads of walking mode, were simulated using a coefficient of friction of 0.4 and an interference-fit of 50 µm. Maximum and average implant micromotions across the subpopulation were predicted to be 100±7 µm and 7±5 µm with ranges [15 µm, 350 µm] and [1 µm, 25 µm], respectively. The computed percentage of implant area with micromotions greater than reported critical values of 50 µm, 100 µm and 150 µm never exceeded 14%, 8% and 7%, respectively. To explore the possible correlations between anatomy and implant performance, response surface models for micromotion metrics were constructed. Detailed morphological analyses were conducted and a clear nonlinear decreasing trend was observed between implant average micromotion and both the metaphyseal canal flare indices and average densities in Gruen zones. The present study demonstrates that the primary stability and tolerance of the short stem to variability in patient anatomy were high, reducing the need for patient stratification. In addition, the developed tool could be utilised to support implant design and planning of femoral reconstructive surgery.