Ligaments, muscles team to bolster joints

By Dr. John Aronen

Well-defined thigh and leg muscles indicate good stability in the joint.

As noted in Part I, joints were designed to allow bones to move on one another, with some joints being designed more for mobility than stability and some more for stability than mobility.

Thus, the new obstacles would be designing anatomical structures that could:

• Create motion of a joint.
• Allow mobility but provide stability.
• Maintain the alignment of the sites of articulate cartilage that are designed to articulate on each other.

  The answer? The creation of muscles and ligaments.

  It is only after one looks at the difference in the inherent makeup of muscles and ligaments that the significant difference in their contribution to overcoming these three obstacles becomes apparent.

  Ligaments are fibrous bands of fixed length that limit the extremes of distraction between bones. Because ligaments cannot actively contract, they serve as a passive stabilizer, playing the role of a check-rein.

  Muscles, because they can actively contract, serve as an active stabilizer. The motion of a joint results from active contractions by muscles.

  Ligaments are unable to contribute to motion because they cannot actively contract.

  Joints allow us mobility, but joints must have structures that provide stability. This necessitates structures that limit the degree of distraction between the bones of the joint.

  Muscles and ligaments are the primary stabilizers of every joint. Because ligaments cannot contract, they serve as a passive stabilizer. But muscles can actively contract, so they serve as an active stabilizer.

  In this role, muscles can actively limit the degrees of distraction between bones, whereas ligaments are relegated to limiting the extremes of distraction between bones. In recognizing this, one can understand why muscles are referred to as the first line of defense against instability episodes.

  Muscles protect the ligaments from forces that may challenge the stability of a joint. If the force challenging the stability of a joint is sufficient to overpower the muscles, the passive line of defense–ligaments–can be subjected to stress.

  In either instance, the stress placed on the muscles can result in a strain of the muscles, with the end result of the strain being residual weakness of the muscles. Thus becomes apparent the rationale for emphasizing regaining and maintaining the normal strength of the involved muscles in all episodes of joint instability.

  Adequate and appropriate treatment of instability in joints includes regaining and maintaining the normal strength of the involved muscles.

  Joints were designed such that specific sites of articular cartilage would be in apposition with each other during motion of a joint.

  Maintaining the alignment or tracking of these specific sites designed to be in apposition relies primarily on anatomical structures that can actively contract during motion of a joint.

  Thus, again, muscles contribute significantly to maintaining the alignment of the specific sites of articulation because they can actively contract. But ligaments contribute very little to maintaining the alignment of the sites of articulation because they cannot actively contract.

  For the muscles to maintain the designed alignment, they must have full or normal strength. Thus becomes apparent the rationale for emphasizing regaining and maintaining the normal strength of the muscles tasked with maintaining the designed alignment of joints.

  Adequate and appropriate treatment of alignment or tracking problems in joints includes regaining and maintaining the normal strength of the involved muscles.