On the development of the patella

Area of Science:

• Skeletal biology
• Developmental biology
• Biomechanical engineering

Background:

• Sesamoid bones, embedded within tendons, have a poorly understood developmental origin.
• Current models suggest mechanical signals from muscles drive sesamoid formation within tendons.

Purpose of the Study:

• To investigate the developmental mechanisms of sesamoid bone formation, specifically the patella.
• To challenge the existing model of sesamoid development and propose an alternative pathway.

Main Methods:

• Embryonic mouse models were used to observe patella development.
• Analysis of cellular progenitors using Sox9 and Scx markers.
• Investigated the roles of TGFβ and BMP4 signaling pathways.

Main Results:

• The patella initially forms as an outgrowth of the femur, not directly within the tendon.
• Joint formation, regulated by mechanical load, separates the patella from the femur.
• Patella progenitors are Sox9- and Scx-positive, with TGFβ and BMP4 signaling controlling specification and differentiation.
• The patella becomes embedded in the quadriceps tendon after joint formation.

Conclusions:

• An alternative model for patella development is proposed, involving initial femoral outgrowth and subsequent joint formation.
• Mechanical load and specific molecular pathways (TGFβ, BMP4) are crucial for patella development.
• Joint formation programs can influence skeletal patterning, offering insights into bone evolution and plasticity.