The Intrarater and Inter-rater Reliability of Radiographic Evaluation of the Posterior Tibial Slope in Pediatric Patients.

BACKGROUND

In young athletes, an association exists between an increased posterior tibial slope (PTS) and the risk of primary anterior cruciate ligament (ACL) injury, ACL graft rupture, contralateral ACL injury, and inferior patient reported outcomes after ACL reconstruction. In spite of this, there is no consensus on the optimal measurement method for PTS in pediatric patients. The purpose of this study was to evaluate the reliability of previously described radiographic PTS measurement techniques.

METHODS

A retrospective review was performed on 130 patients with uninjured knees between the ages of 6 and 18 years. The medial PTS was measured on lateral knee radiographs by four blinded reviewers using three previously described methods: the anterior tibial cortex (ATC), posterior tibial cortex (PTC), and the proximal tibia anatomic axis (PTAA). The radiographs were graded by each reviewer twice, performed 2 weeks apart. The intrarater and inter-rater reliability were assessed using the intraclass correlation coefficient (ICC). Subgroup analyses were then performed stratifying by patient age and sex.

RESULTS

The mean PTS were significantly different based on measurement method: 12.5 degrees [confidence interval (CI): 12.2-12.9 degrees] for ATC, 7.6 degrees (CI: 7.3-7.9 degrees) for PTC, and 9.3 degrees (CI: 9.0-9.6 degrees) for PTAA (P<0.0001). Measures of intrarater reliability was excellent among all reviewers across all 3 methods of measuring the PTS with a mean ICC of 0.87 (range: 0.82 to 0.92) for ATC, 0.83 (range: 0.82 to 0.87) for PTC, and 0.88 (range: 0.79 to 0.92) for PTAA. The inter-rater reliability was good with a mean ICC of 0.69 (range: 0.62 to 0.83) for the ATC, 0.63 (range: 0.52 to 0.83) for the PTC, and 0.62 (range: 0.37 to 0.84) for the PTAA. Using PTAA referencing, the PTS was greater for older patients: 9.9 degrees (CI: 7.7-9.4 degrees) vs 8.5 degrees (CI: 9.2-10.7 degrees) (P=0.0157) and unaffected by sex: 9.5 degrees (CI: 8.8-10.1 degrees) for females and 9.0 degrees (CI: 8.0-10.0) for males (P=0.4199). There were no major differences in intrarater or inter-rater reliability based on age or sex.

CONCLUSIONS

While the absolute PTS value varies by measurement technique, all methods demonstrated an intrarater reliability of 0.83 to 0.88 and inter-rater reliability of 0.61 to 0.69. However, this study highlights the need to identify PTS metrics in children with increased inter-rater reliability.

LEVEL OF EVIDENCE

IV, Case series.