Validation of methods to identify knee decompensation in ACL-Deficient skeletally immature patients

Background: Anterior cruciate ligament (ACL) injuries in paediatrics have dramatically increased. Complications, such as growth disturbances and high re-injury rates of the ACL, can occur after ACL reconstruction. Non-operative treatment can be viable for skeletally immature patients without concomitant intra-articular injuries.
Decompensation of the knee has been described in failure of non-operative treatment in adults. The theory of knee decompensation is when ACL deficient knees undergo anterior tibial translation (ATT) leading to progressive structural damage soft-tissue stabilizers, e.g. meniscus. Methods have been described to define/quantify the buckling phenomenon for knee decompensation in adults: PCL-line sign, PCL angle (PCLA), PCL inclination angle (PCLIA) and the PCL-posterior cortex angle (PCL-PCA). These methods are not validated in skeletally immature, who may have different anatomical measurement because of growth. As many skeletally immature patients are treated non-operatively, identification of knee decompensation might be extra important.

Objectives: To assess and compare the reliability and accuracy of 3 different methods to assess the PCL buckling phenomenon in skeletally immature patients with and without an ACL injury. Secondarily this study assesses relation between the PCL buckling phenomenon and the degree of tibial translation and meniscal inclination, quantified as the LCL-sign, ATT and meniscal bone angle (MBA). Lastly this study identify the relation between the knee flexion angle (KFA) and the different methods.

Study Design & Methods: Design is a case-control study, consisting of skeletally immature patients with ACL injury and without ACL injury. Population size was based on the COSMIN criteria, in this study 55 case and 51 controls were included. The inter- and intra-reliability of each method was reported using intra-class correlation, using two-way mixed measured with absolute agreement. The SEM and the MDC were calculated. Independent t-tests were used to compare the methods to quantify differences in PCL angles between groups. Pearson correlation test was used to assess the relationship of the three used methods and the presence of the LCL sign and the ATT, MBA and KFA.

Results: There were no significant differences in baseline characteristics between cases and controls. The inter-observer reliability was the highest in the PCL-PCA 0.97 (95% CI 0.96-0.98) with an SEM of 2.0°, MDC of 5.0°. The intra-observer reliability of this method was 0.99 (95% CI 0.98-0.99) with an SEM 1.3°, MDC of 3.5°. The PCL-PCA and PCLA were significant different between the two groups (both p<.001). Both medial and lateral ATT were significantly different between the case and control group (medial 0.1° vs -2.6 ° , lateral 6.8° vs 2.1° both p<.001). Also both medial and lateral MBA were significantly different between the case and control group ( medial 27.5° vs 30.8°, lateral 21.6 ° vs 27.0 ° both p<.001) A significant correlation was found between the PCLA and PCL-PCLA and both medial and lateral side of both the ATT and MBA. The LCL has no significant correlation with the outcome measures of the methods.
A significant , moderate, correlation was seen between the KFA and the PCLA and PCL-PCA. The PCLIA was significant, yet poor, correlated with the KFA.

Conclusions: The PCL-PCA is the most reliable and accurate method to quantify the buckling phenomenon of the PCL and as such the proposed method to quantify decompensation of the knee in skeletally immature patients. Both the medial and lateral ATT and MBA as well as the KFA have a moderate correlation with the PCL-PCA.