Abstract
Increased tibial slope may be associated with anterior cruciate ligament (ACL) injuries,
although potential confounding effects from various patient characteristics and radiographic
quantification methods have not been rigorously studied. The association of the slope
of the lateral plateau with recurrent ACL injury after primary ACL reconstruction
has recently been reported, but the role of medial slope is less well defined. The
purpose of this study was to (1) assess medial tibial slope measurement reliability
among examiners, (2) compare medial tibial slope values between patients undergoing
primary ACL reconstruction, reinjured patients undergoing revision ACL reconstruction,
and a control cohort with an intact ACL, (3) analyze if the medial tibial slope is
an independent risk factor for noncontact ACL injury, and (4) assess how different
anatomical references affect medial tibial slope values. A total of 206 patients were
enrolled into one of three groups: (1) ACL-intact controls (CONTROL, n = 83), (2) first-time ACL-injured patients (PRIMARY, n = 77), and (3) patients undergoing revision ACL reconstruction (REVISION, n = 46). Three fellowship-trained sports medicine surgeons performed repeated measurements
of plain lateral radiographs. The medial tibial slope was determined by three anatomical
references: anterior tibial cortex (anterior tibial slope [ATS]), posterior tibial
cortex (posterior tibial slope [PTS]), and the anatomical long axis of the tibia (composite
tibial slope [CTS]). Substantial intra- and interobserver reliabilities were established
by the intraclass correlation coefficient of 0.73 to 0.89. There was no difference
in CTS, ATS, or PTS comparing the CONTROL, PRIMARY, and REVISION groups upon univariate
analyses. Multivariable logistic regression model showed that none of the slope values
was independently associated with ACL injury. The mean ATS for all 206 subjects was
4 and 8 degrees greater than the mean CTS and PTS, respectively. ATS correlated only
moderately to PTS. We concluded that medial tibial slope measured on radiographs is
not associated with primary or recurrent ACL injury, and has substantial variation
and suboptimal correlation when using different anatomical references despite good
inter- and intraobserver reliabilities.
Keywords
anterior cruciate ligament - ACL injury - revision ACL - knee biomechanics - tibial
slope
