When ACL Failed, the Knee Stayed Surprisingly Stable

After an ACL graft failed, the knee did not behave the way some might expect. In a small case series, 15 patients had ACL graft failure after a combined ACL and ALL reconstruction. The first operation was a primary procedure in 12 people and a revision surgery in 3. The ACL graft failed about 22 months after the combined surgery, with a range from 18 to 24 months.

MRI was the main clue. The reconstructed ALL graft still looked continuous in every case, which means 100% of scans showed a preserved graft path. Nine patients, or 60%, had mild signal changes in the graft. The scans were also checked for internal graft signal and nearby swelling. These findings made the graft look present even after the ACL graft had failed.

The motion tests told a similar story. Side-to-side anterior tibial translation was measured with a KT-1000 arthrometer, and pivot-shift grade was recorded. Knee looseness was measured before the first combined surgery and again after the ACL graft failure. The median front-to-back tibial movement dropped from 7 mm to 5 mm. The paired median drop was 2 mm, with an interquartile range of 1 to 3 mm. The median pivot-shift grade also fell, from 2 to 1. The paired median drop was 1 grade, with an interquartile range of 1 to 1.5. Twelve of 15 patients, or 80%, improved on both looseness measures. No patient had a high-grade pivot shift after the ACL graft failure. The comparisons used Wilcoxon signed-rank tests, and both reported p = 0.001.

This creates an important caution sign. A physical exam after ACL graft failure may show less rotational and front-to-back looseness than expected, because the ALL graft may still be helping the knee stay steadier. That raises a hard question for care: what should be trusted when the exam looks better than expected? The limits matter here. The study was retrospective, small, and mixed in patient details. It also cannot prove that the ALL graft caused the better stability. It cannot prove that an anterolateral revision should be skipped in future cases. The evidence level was Level IV.