Ligament

A ligament is dense regular connective tissue running bone to bone, distinguishing it from tendon, which runs muscle to bone. Type I collagen dominates the dry mass, but ligaments carry proportionally more elastin, proteoglycan and water than tendon, and their fibre bundles are less strictly parallel because they must resist load across a range of joint angles. Embedded mechanoreceptors also feed joint position sense, which is why ligament injury degrades proprioception as well as stability.

Healing depends heavily on location. A torn medial collateral ligament sits outside the joint capsule, forms a clot, and generally recovers well without surgery. A ruptured anterior cruciate ligament sits inside the joint, where synovial fluid disperses the clot and prevents a scaffold from forming, so it usually does not heal and is reconstructed with a graft rather than repaired. Even ligaments that do heal reconstitute as scar, and the tissue remains mechanically inferior to the original for a year or more.

The practical consequence is that laxity and function separate. A knee can test stable on a clinical laxity examination while the person still lacks the proprioceptive control that prevents the next injury, and it can test lax while being entirely functional. Grading a sprain describes fibre disruption, not readiness to load.

The misreading that matters here is extrapolation. Almost all of the peptide literature offered as evidence for ligament repair is rodent tendon work, and tendon and ligament differ in matrix composition, vascularity and healing environment. There is no controlled human trial of a peptide for ligament healing, and marketing that cites tendon animal data for a ligament claim is jumping two gaps at once.