Warren and colleagues tested whether the deep medial ligament is the main restraint to valgus and external rotation of the knee, and studied how the long superficial fibers behave in flexion.
Selective‑cutting study of 32 fresh cadaveric knees: long‑fiber length measured through flexion in all, then two cutting sequences of 10 knees each under valgus and rotational stress.
The deep medial ligament is the prime stabilizer against external rotatory and valgus stress.
Key Findings
The hypothesis was not supported. With the long superficial fibers intact, cutting the deep ligament, posterior oblique fibers and capsule allowed no significant valgus opening and never more than 1° of added external rotation.
Then cutting the long fibers allowed 5 to 7 mm of medial opening through the range tested. External rotation doubled in extension and rose to an average threefold increase at 90° of flexion.
Cutting the long fibers first, with all else intact, immediately increased valgus opening and external rotation. Cutting the deep ligament afterward added no significant opening and about 1° more rotation.
In intact knees the anterior border of the long fibers lengthened with flexion (mean 1.75 mm at 45°), while fibers 5 mm behind it shortened, by 2 mm at 90°.
The authors attribute this to the femoral origin's position relative to the instant centers, which keeps the anterior border taut from full extension to 90°. They suggest this may matter for reconstruction.
Specimens were not pressed into maximum extension, and valgus could be applied accurately only to 45° of flexion. Five specimens measured the posterior fibers.
Board pearl
Valgus laxity in extension is cruciate plus medial damage, a view the authors accept as clinically reliable. Their own specimens were not forced into full extension.
Authors' conclusion
The long fibers of the superficial medial collateral ligament are the primary stabilizers of the medial side of the knee against valgus and rotatory stress.
Warren and colleagues tested whether the deep medial ligament is the main restraint to valgus and external rotation of the knee, and studied how the long superficial fibers behave in flexion.
Selective‑cutting study of 32 fresh cadaveric knees: long‑fiber length measured through flexion in all, then two cutting sequences of 10 knees each under valgus and rotational stress.
The deep medial ligament is the prime stabilizer against external rotatory and valgus stress.
Key Findings
The hypothesis was not supported. With the long superficial fibers intact, cutting the deep ligament, posterior oblique fibers and capsule allowed no significant valgus opening and never more than 1° of added external rotation.
Then cutting the long fibers allowed 5 to 7 mm of medial opening through the range tested. External rotation doubled in extension and rose to an average threefold increase at 90° of flexion.
Cutting the long fibers first, with all else intact, immediately increased valgus opening and external rotation. Cutting the deep ligament afterward added no significant opening and about 1° more rotation.
In intact knees the anterior border of the long fibers lengthened with flexion (mean 1.75 mm at 45°), while fibers 5 mm behind it shortened, by 2 mm at 90°.
The authors attribute this to the femoral origin's position relative to the instant centers, which keeps the anterior border taut from full extension to 90°. They suggest this may matter for reconstruction.
Specimens were not pressed into maximum extension, and valgus could be applied accurately only to 45° of flexion. Five specimens measured the posterior fibers.
Board pearl
Valgus laxity in extension is cruciate plus medial damage, a view the authors accept as clinically reliable. Their own specimens were not forced into full extension.
Authors' conclusion
The long fibers of the superficial medial collateral ligament are the primary stabilizers of the medial side of the knee against valgus and rotatory stress.