BACKGROUNDRecently, increasing number of literature has identified the posterior tibial slope (PTS) as one of the risk factors of primary anterior cruciate ligament (ACL) injury. However, few studies concerning the association between failure of ACL reconstruction (ACLR) and PTS have been published. The objective of this study was to explore the association between the failure of ACLR and PTS at a minimum of two years follow-up.

METHODSTwo hundred and thirty eight eligible patients from June 2009 to October 2010 were identified from our database. A total of 20 failure cases of ACLR and 20 randomly selected controls were included in this retrospective study. The demographic data and the results of manual maximum side-to-side difference with KT-1000 arthrometer at 30° of knee flexion and pivot-shift test before the ACLR and at the final follow-up were collected. The medial and lateral PTSs were measured using the magnetic resonance imaging (MRI) scan, based on Hudek's measurement. A comparison of PTS between the two groups was performed.

RESULTSThe overall failure rate of the present study was 8.4%. Of the 40 participants, the mean medial PTS was 4.1° ± 3.2° and the mean lateral PTS was 4.6° ± 2.6°. The medial PTS of the ACLR failure group was significantly steeper than the control group (3.5° ± 2.5° vs. 6.1° ± 2.1°, P = 0.000). Similarly, the lateral PTS of the ACLR failure group was significantly steeper than the control group (2.9° ± 2.1° vs. 5.5° ± 3.0°, P = 0.006). For medial PTS ≥ 5°, the odds ratio of ACLR failure was 6.8 (P = 0.007); for lateral PTS ≥5°, the odds ratio of ACLR failure was 10.8 (P = 0.000).

CONCLUSIONBoth medial and lateral PTS were significantly steeper in failures of ACLR than the control group. Medial or lateral PTS ≥5° was a new risk factor of ACLR failure.