Tendon injuries — why healing takes months and patience carries the rehab

Tendons and ligaments connect muscle and bone and store elastic energy with every step. It is exactly this load-bearing capacity that makes them vulnerable: the superficial digital flexor tendon works close to its mechanical limit in fast gallop. If individual fibre bundles tear in the interior, a core lesion develops — the classic tendon injury of the sport horse.

The treacherous part is not the moment of injury, but the healing afterwards. Tendon tissue is cell-poor and poorly perfused, and its metabolism runs slowly. The body therefore does not repair the defect with equivalent tendon tissue, but first fills it with scar tissue — biologically a makeshift solution.

Why the repair tissue is inferior

Healthy tendon consists of thick, parallel and tautly aligned collagen type I fibres that carry tensile forces like a well-sorted rope. The fresh scar tissue, by contrast, first contains much thinner collagen type III, which is disordered and less load-bearing. Only over months does the body gradually rebuild this provisional tissue into better-aligned, more load-bearing material — the so-called remodelling. Completely, it mostly never reaches the original structure and elasticity again; the repaired site remains a weak point.

From this slow rebuilding follows the most important message for the stable: a tendon that feels clinically inconspicuous after eight weeks and looks filled on ultrasound is structurally far from matured. The outer recovery runs clearly ahead of the inner load-bearing capacity — and exactly in this gap the relapses happen.

Controlled movement instead of pure box rest

For a long time absolute rest was regarded as the safest way. Today the principle of the controlled build-up of movement — controlled exercise — is the load-bearing rehab idea. Dosed, controlled rising mechanical load gives the cells the stimulus to align new collagen along the line of pull, instead of scarring it in a disordered way. Pure, months-long box rest without a structured build-up leads to weaker, worse-aligned repair tissue; uncontrolled turnout in the paddock in turn overtaxes the immature tendon. The narrow ridge between them is the actual art of the rehab.

In practice this means a walking programme built up over many weeks, in hand or under saddle, whose duration and intensity are slowly raised on the basis of repeated ultrasound checks. The finding on the device, not the gut feeling, sets the pace. Every step of increase is awaited, every setback in the image leads back one stage.

The soberest figure of tendon healing is the recurrence risk: a considerable part of the sport and racehorses injures itself again at the same site — orders of magnitude of around 40 to 60 percent are reported in the literature depending on use. The most common cause is a too early or too fast increase of the load before the repair tissue is matured. Patience is here no soft advice, but the hardest evidence-based protection against the relapse.