Advancing quantitative techniques to improve understanding of the skeletal structure-function relationship

Differential regulation of skeletal stem/progenitor cells in distinct skeletal compartments

Skeletal stem/progenitor cells (SSPCs), characterized by self-renewal and multipotency, are essential for skeletal development, bone remodeling, and bone repair. These cells have traditionally been known to reside within the bone marrow, but recent studies have identified the presence of distinct SSPC populations in other skeletal compartments such as the growth plate, periosteum, and calvarial sutures. Differences in the cellular and matrix environment of distinct SSPC populations are believed to regulate their stemness and to direct their roles at different stages of development, homeostasis, and regeneration; differences in embryonic origin and adjacent tissue structures also affect SSPC regulation. As these SSPC niches are dynamic and highly specialized, changes under stress conditions and with aging can alter the cellular composition and molecular mechanisms in place, contributing to the dysregulation of local SSPCs and their activity in bone regeneration. Therefore, a better understanding of the different regulatory mechanisms for the distinct SSPCs in each skeletal compartment, and in different conditions, could provide answers to the existing knowledge gap and the impetus for realizing their potential in this biological and medical space. Here, we summarize the current scientific advances made in the study of the differential regulation pathways for distinct SSPCs in different bone compartments. We also discuss the physical, biological, and molecular factors that affect each skeletal compartment niche. Lastly, we look into how aging influences the regenerative capacity of SSPCs. Understanding these regulatory differences can open new avenues for the discovery of novel treatment approaches for calvarial or long bone repair.

Targeting Bone Metastases Signaling Pathway Using Moringa oleifera Seed Nutri-miRs: A Cross Kingdom Approach

Moringa oleifera is a medicinally important plant that has various medical and nutritional uses. Plant miRNAs are a class of non-coding endogenous small RNAs that regulate human-specific mRNA but the mechanistic actions are largely unknown. Here, in this study, we aim to explore the mechanistic action and influence of M. oleifera seed miRNAs on vital human target genes using computer based approaches. The M. oleifera seed miRNAs sequence was taken from published data and identified its human gene targets using a psRNA target analysis server. We identified 94 miRNAs that are able to significantly regulate 47 human target genes, which has enormous biological and functional importance. Out of 47 human targeted genes, 23 genes were found to be associated with PI3K-AKT, RUNX, and MAPK1/MAPK3 signaling pathway which has shown to play key roles in bone metastases during cancer progression. The M. oleifera seed miRNAs hold a strong potential for future research that might uncover the possibility of miRNA-facilitated cross-kingdom regulation and therapeutic targets for bone metastases.

Patellofemoral Pain in Adolescents: Understanding Patellofemoral Morphology and Its Relationship to Maltracking

BACKGROUND

Developing bone is highly adaptable and, as such, is susceptible to pathological shape deformation. Thus, it is imperative to quantify if changes in patellofemoral morphology are associated with adolescent-onset patellofemoral pain, as a pathway to improve our understanding of this pain's etiology.

PURPOSE

To quantify and compare patellofemoral morphology in adolescent patients with patellofemoral pain with matched healthy adolescent controls and determine if a relationship exists between patellofemoral shape and kinematics (measured during active flexion-extension).

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Using 3-dimensional static magnetic resonance images acquired during a previous study, we measured patellar, trochlear, and lateral patellar width; trochlear and patellar depth; Wiberg index; patellar-height ratio; lateral trochlear inclination; cartilage length; and lateral femoral shaft length. Student t test was used to compare shape parameters between adolescents with patellofemoral pain and controls. Pearson correlations and stepwise linear regression models were used to explore the relationship among morphology, kinematics (medial-lateral shift/tilt), and pain.

RESULTS

Relative to controls, adolescents with patellofemoral pain had larger sulci (mean ± SD, 6.6 ± 0.7 vs 6.0 ± 1.1 mm; 95% CI, 0.6 mm; P = .043; d = 0.66), lateral patellar width (23.1 ± 2.4 vs 21.4 ± 2.6 mm; 95% CI, 1.6 mm; P = .033; d = 0.70), and patella-trochlear width ratio (1.2 ± 0.1 vs 1.1 ± 0.1; 95% CI, 0.1; P < .001; d = 1.26). Shape correlated with kinematics in both cohorts and in the entire population. In the patellofemoral pain group, lateral shaft length (r = 0.518; P = .019), Wiberg index (r = 0.477; P = .033), and patellar-height ratio (r = -0.582; P = .007) were correlated with medial shift. A moderate correlation existed between patellar-height ratio and lateral patellar tilt (r = 0.527; P = .017). Half of the variation in patellar shift in the patellofemoral pain cohort was explained by the patellar-height ratio and Wiberg index (R² = 0.487; P = .003). Linear correlations with pain were not found.

CONCLUSION

This study provides direct evidence that patellofemoral morphology is altered and influences maltracking in adolescents with patellofemoral pain, highlighting the multifactorial etiology of this pain. Neither morphology nor kinematics (measured during active flexion-extension) correlated with pain. Both increases and decreases in these parameters likely lead to pain, negating a direct linear correlation.

Fully automated patellofemoral MRI segmentation using holistically nested networks: Implications for evaluating patellofemoral osteoarthritis, pain, injury, pathology, and adolescent development

PURPOSE

Our clinical understanding of the relationship between 3D bone morphology and knee osteoarthritis, as well as our ability to investigate potential causative factors of osteoarthritis, has been hampered by the time-intensive nature of manually segmenting bone from MR images. Thus, we aim to develop and validate a fully automated deep learning framework for segmenting the patella and distal femur cortex, in both adults and actively growing adolescents.

METHODS

Data from 93 subjects, obtained from on institutional review board-approved protocol, formed the study database. 3D sagittal gradient recalled echo and gradient recalled echo with fat saturation images and manual models of the outer cortex were available for 86 femurs and 90 patellae. A deep-learning-based 2D holistically nested network (HNN) architecture was developed to automatically segment the patella and distal femur using both single (sagittal, uniplanar) and 3 cardinal plane (triplanar) methodologies. Errors in the surface-to-surface distances and the Dice coefficient were the primary measures used to quantitatively evaluate segmentation accuracy using a 9-fold cross-validation.

RESULTS

Average absolute errors for segmenting both the patella and femur were 0.33 mm. The Dice coefficients were 97% and 94% for the femur and patella. The uniplanar, relative to the triplanar, methodology produced slightly superior segmentation. Neither the presence of active growth plates nor pathology influenced segmentation accuracy.

CONCLUSION

The proposed HNN with multi-feature architecture provides a fully automatic technique capable of delineating the often indistinct interfaces between the bone and other joint structures with an accuracy better than nearly all other techniques presented previously, even when active growth plates are present.

Increased Patellar Volume/Width and Decreased Femoral Trochlear Width Are Associated With Adolescent Patellofemoral Pain

BACKGROUND

Patellofemoral pain is one of the most common forms of knee arthralgia in adolescent females. Unlike in adults, in whom the etiology of patellofemoral pain is considered to be multifactorial (eg, altered bone shape and musculoskeletal dynamics), the etiology of adolescent patellofemoral pain has been historically attributed to overuse. Although it is highly plausible that adolescent patellofemoral pain results from excessive maltracking, as suggested by recent research, an increase in patellar, relative to femoral, size could also contribute to patellofemoral pain through altered cartilage stresses/strains, resulting in overloading of the subchondral bone. Because the role of bone morphology in the genesis of patellofemoral pain in adolescent females remains largely unknown, research is needed in this area to improve our understanding of patellofemoral pain and advance diagnosis/treatment.

QUESTIONS/PURPOSES

(1) Are patellar volume and width increased, and femoral trochlear width decreased, in female adolescents with patellofemoral pain compared with asymptomatic females? (2) Are measures of patellofemoral size correlated with patellofemoral tracking?

METHODS

Twenty adolescent females with patellofemoral pain (age, 13.7 ± 1.3 years) and 20 asymptomatic female control participants (age, 13.6 ± 1.3 years) were enrolled in this case-control institutional review board-approved study. This study focused on a strict definition of patellofemoral pain, peripatellar pain in the absence of other structural pathologic conditions (eg, tendinitis, ligament injury, Osgood-Schlatter disease) or a history of dislocations/trauma. Control participants with no history of patellofemoral pain or other lower extremity pathology were matched for age (within 6 months) and body mass index (within 5 kg/m). Participants self-referred and were recruited through clinicaltrails.gov, printed advertisements, and word of mouth. Three-dimensional (3-D), static, T1-weighted, gradient recalled echo MR images were acquired, from which 3-D patellofemoral models were created. Patellar volume and width, patellar-to-femoral volume and width ratios, and femoral trochlear width were compared across cohorts. In addition, 3-D patellofemoral tracking was quantified from dynamic MR images captured during cyclical flexion-extension volitional movements of the lower extremity. The size measures and ratios were correlated to patellofemoral tracking.

RESULTS

Compared with control participants, the cohort with patellofemoral pain had greater patellar volume (13,792 ± 2256 versus 11,930 ± 1902 mm; 95% confidence interval [CI], 1336 mm; p = 0.004; d = 0.89) and width (38.4 ± 3.0 versus 36.5 ± 2.7 mm; 95% CI, 1.8 mm; p = 0.021; d = 0.67). The femoral trochlear width was smaller (32.0 ± 1.8 versus 32.9 ± 1.8 mm; p = 0.043, d = 0.54). The patellar-to-femoral volume ratio and the patellar-to-trochlear width ratio were greater in adolescents with patellofemoral pain (0.15 ± 0.02 versus 0.13 ± 0.01, p = 0.006, d = 0.83 and 1.20 ± 0.09 versus 1.11 ± 0.09, p = 0.001, d = 1.02). No correlations were found between patellar size and patellofemoral tracking (r < 0.375, p > 0.103).

CONCLUSIONS

In adolescent females with patellofemoral pain, the increased patellar volume/width and patellar-to-trochlear width ratio, along with the decreased femoral trochlear width, may initiate a pathway to pain through improper engagement of the patella within the femoral trochlea. Specifically, the mean differences between cohorts in patellar and femoral trochlear width (1.9 mm and 0.9 mm) are 58% and 37% of the mean patellar and femoral cartilage thickness in females, respectively, as reported in the literature. Further studies are needed to fully elucidate the mechanism of pain.

LEVEL OF EVIDENCE

Level III, prognostic study.