This 1999 narrative review by Frank et al. synthesizes structural, biomechanical, and molecular data on normal and healing rabbit MCL. It addresses why ligament scars fail to restore normal tissue quality despite years of remodeling. Data sources include electron microscopy, RT-PCR, and mechanical testing including creep, modulus, and stress at failure.
When a patient asks why their knee still feels loose after an MCL injury that has "fully healed," this paper provides the answer. Ligament scar is a permanently inferior tissue: it reaches only 30-40% of normal material strength and creeps more than twice as much under routine loads.
For clinical decision-making, this means that a healed MCL is biomechanically not equivalent to an intact MCL. When you see a patient with chronic medial-sided laxity after a prior MCL injury, do not assume healing failure — the healed tissue is structurally deficient by design.
This also reframes the ACL vs MCL treatment debate. The MCL heals under favorable conditions (extraarticular, vascular, low stress) and still cannot restore normal tissue. The ACL heals under worse conditions and typically does not heal at all — which is the biological rationale for ACL reconstruction rather than conservative management.
The pregnancy-laxity finding connects directly to the well-documented higher ACL injury rate in female athletes. Hormonal effects on ligament mechanics are real, measurable, and mechanistically distinct from structural differences.
This 1999 narrative review by Frank et al. synthesizes structural, biomechanical, and molecular data on normal and healing rabbit MCL. It addresses why ligament scars fail to restore normal tissue quality despite years of remodeling. Data sources include electron microscopy, RT-PCR, and mechanical testing including creep, modulus, and stress at failure.
When a patient asks why their knee still feels loose after an MCL injury that has "fully healed," this paper provides the answer. Ligament scar is a permanently inferior tissue: it reaches only 30-40% of normal material strength and creeps more than twice as much under routine loads.
For clinical decision-making, this means that a healed MCL is biomechanically not equivalent to an intact MCL. When you see a patient with chronic medial-sided laxity after a prior MCL injury, do not assume healing failure — the healed tissue is structurally deficient by design.
This also reframes the ACL vs MCL treatment debate. The MCL heals under favorable conditions (extraarticular, vascular, low stress) and still cannot restore normal tissue. The ACL heals under worse conditions and typically does not heal at all — which is the biological rationale for ACL reconstruction rather than conservative management.
The pregnancy-laxity finding connects directly to the well-documented higher ACL injury rate in female athletes. Hormonal effects on ligament mechanics are real, measurable, and mechanistically distinct from structural differences.