Collateral Ligament Injury (MCL and LCL)

The medial collateral ligament has a rich blood supply and heals with protected motion, bracing and progressive loading. Surgery for an isolated MCL injury is rarely needed, and a patient offered it should ask why.

The lateral side is a smaller structure with a poorer blood supply, and injuries there are more often part of a wider posterolateral corner problem. Missing that produces a knee that never feels stable regardless of how well the rehabilitation is done.

Common peroneal nerve function, because it sits close to the lateral structures and foot drop after a lateral knee injury is not rare 6. Cruciate ligament integrity, because collateral injuries are often combined 1. And the growth plates in a skeletally immature patient, where a growth plate injury can mimic a ligament tear.

Protected range early with a hinged brace, weight bearing as pain allows, then progressive strengthening and gradual reintroduction of side-to-side movement. Valgus and varus stress — the directions that loaded the ligament — return last.

Return to pivoting sport is decided on measured strength and control, not on the calendar.

The medial collateral has a good blood supply and heals reliably without surgery, even in higher-grade injuries; the exceptions are few, such as a torn end caught on the wrong side of the tendons below the knee or pulled off with a piece of bone 1. The lateral side, and the structures around it, heal less reliably: complete tears of the posterolateral corner rarely heal without surgery 3.

This is why a lateral-sided injury is taken more seriously than the same grade on the inside, and why it warrants imaging rather than a bracing protocol alone.

Usually within weeks rather than months, and the grade sets the pace. In a prospective study of 130 MCL injuries in European professional football, the average time out was 24 days, and grade I sprains averaged 10 days 2. Three in four of these injuries came from contact, most often while tackling or being tackled 2. Grade II sprains averaged 31.5 days without a brace and 41.5 days with one, although the study could not show that the brace itself caused the difference 2. Early re-injury is not rare either: 8.5% of the injuries were a repeat MCL injury within two months of returning to play 2.

Most complete injuries on the outer side involve the wider posterolateral corner 4, and these rarely heal without an operation 3. The rare tear of the lateral collateral ligament alone is different: in a series of only nine professional American football players, those treated without surgery returned to play sooner, with the same chance of playing on 4. When surgery is needed for the corner, a systematic review of 134 patients found that 38% of knees treated by repairing the torn structures failed, against 9% with approaches that included reconstruction 5. The peroneal nerve is also at risk: in one surgical series, 26.2% of posterolateral corner injuries had a peroneal nerve injury 6.