Osteophytes: The product of convergent evolution

Area of Science:

• Orthopedics
• Skeletal Biology
• Pathophysiology

Background:

• Osteophytes, or bony overgrowths, on diarthrodial joints and vertebral centra are traditionally thought to share similar etiologies.
• Existing theories propose compressive forces for joint osteophytes and traction for vertebral osteophytes (enthesial derivation).
• Confirmation of differing etiologies has been lacking, hindering a complete understanding of osteophyte formation.

Purpose of the Study:

• To investigate and confirm the hypothesis that diarthrodial joint osteophytes and disc-adjacent vertebral osteophytes possess distinct pathophysiologies.
• To differentiate osteophyte origins based on microscopic surface characteristics.

Main Methods:

• Microscopic examination of osteophyte surfaces from diarthrodial joints (hip, knee, elbow, costovertebral) and vertebrae (cervical, thoracic, lumbar).
• Analysis of osteophytes from the CAL Milano Cemetery Skeletal Collection.
• Identification of transcortical channels (indicative of nutritional support) and Sharpey's fiber insertions (indicative of enthesial derivation).

Main Results:

• Examination of 22 diarthrodial joint osteophytes revealed exclusively transcortical channels.
• Microscopic analysis of 35 vertebral centra marginal osteophytes showed only the presence of inverted cones, characteristic of Sharpey's fiber insertions.
• Findings were consistent across varying ages, genders, affected joints, spinal locations, and osteophyte severity.

Conclusions:

• Diarthrodial joint osteophytes are endochondrally derived, evidenced by transcortical channels.
• Vertebral centra osteophytes are enthesially derived, characterized by Sharpey's fiber insertions.
• These distinct pathophysiologies contribute to the differing clinical presentations of these osteophyte types.