LIMB LENGTHENING AND RECONSTRUCTION SOCIETY AIM INDEX: INTER- AND INTRARATER RELIABILITY

The Limb Lengthening and Reconstruction Society (LLRS) AIM index is designed to classify the complexity of lower limb deformities, however, it has only been validated in 10 patients, by the original authors. The aims of this study were to assess the correlation between the LLRS AIM index and disease severity; Intrarater and Interrater reliability; and identify the strengths and limitations of this scoring system across multiple clinical conditions. The LLRS AIM Index was calculated for 75 patients (aged less than 16 years) based on their status prior to their first surgery. Patients with prior surgeries were not included in this dataset. The scores were measured twice by a paediatric orthopaedic fellow who reviewed the cases three months apart in order to calculate the intra-observer reliability. A second paediatric orthopaedic fellow also completed the LLRS AIM index scoring for the same set of patients in order to determine the inter-observer reliability. A descriptive analysis of the strengths and limitations of the scoring system was also recorded for each patient. The calculated scores were compared with the severity, which was measured in the form of the total number of surgeries performed at the time of the most recent follow-up. The LLRS AIM scores of 75 patients ranged from 0 to 12 with 22 patients having moderate/ substantial complexity. The scoring system had excellent Interrater (0.88 [0.84, 9.92]) and Intrarater (0.98 [0.96, 0.99]) reliability. Out of 75, 41 underwent single or multiple surgical interventions, 23 did not require any surgical intervention and 11 have surgery planned. We found that with each unit increase in LLRS AIM Score, the chance of needing surgery increased by 17% (Rate ratio = 1.17, 95% Cl = 1.11 to 1.22, p < 0 .001). The scores calculated in certain pathologies like rotational malalignments and tibial bowing were lower relative to other limb deformity conditions and less predictive of the need for surgery. A higher LLRS-AIM index is associated with an increased need for surgery. However, the scores in rotational malalignment and tibial bowing conditions should be interpreted with caution and there may need to be modifiers to the scoring system to account for these variations. A study with a larger sample size is ongoing. This is the first independent validation of the LLRS-AIM index which confirms that it is a reliable tool to assess the severity of lower limb deformities with excellent Intrarater and Interrater reliability.