Joint contact stress: a reasonable surrogate for biological processes?

Area of Science:

• Biomechanics
• Orthopedics
• Cell Biology

Background:

• Normal joint function relies on mechanical loading for articular cartilage and bone maintenance.
• Loading drives nutrient transport and provides critical signals for cellular and tissue health.
• Abnormal joint loading (too low or too high) can lead to deterioration, while specific mechanical environments may aid repair.

Purpose of the Study:

• To evaluate the role of static joint contact stresses as a surrogate for mechanical history.
• To determine if static stresses accurately reflect the dynamic loading crucial for joint health.
• To challenge the traditional view of weight-bearing versus non-weight-bearing joints.

Main Methods:

• Review of existing in vitro and in vivo studies estimating joint contact stresses across species.
• Analysis of reported ranges of static peak normal stresses in diarthrodial joints.
• Consideration of evidence linking cartilage deterioration to specific pressure ranges.

Main Results:

• Static peak normal stresses in vertebrate diarthrodial joints are consistently reported between 0.5 to 5.0 MPa across species.
• Disorders of cartilage deterioration show overlapping pressure ranges (1-20 MPa) with normal pressures.
• Static contact stresses alone do not reliably predict cartilage responses; temporal loading history is key.

Conclusions:

• Vertebrate diarthrodial joints appear to have evolved similar mechanical design criteria.
• Temporal and spatial aspects of loading history, not static stress, dictate beneficial and detrimental biological responses.
• The distinction between weight-bearing and non-weight-bearing joints is likely inaccurate, as all articular cartilage experiences similar stresses.