Preoperative prediction of autologous hamstring graft diameter in anterior cruciate ligament reconstruction

Background and objective: Currently, there is no stablished pre-operative model that helps the orthopaedic surgeon predict the final graft diameter in anterior cruciate ligament reconstruction (ACLR). The purpose of this study was to determine whether there is a correlation between semitendinosus (ST) and gracilis (GT) cross-sectional area (CSA) evaluated pre-operatively in mm² using magnetic resonance imaging (MRI) and the final intra-operative ST-GT autograft diameter in mm².

Methods: A retrospective study was designed, 89 patients undergoing ACLR with hamstring autograft participated. We analysed ST-CSA (mm²) and GT-CSA (mm²) using pre-operative MRI, intra-operative autograft diameter, age, sex, side of the injury, weight, height and body mass index (BMI).

Results: A moderate-strong correlation was identified between final autograft diameter and ST-GT CSA in MRI (Pearson correlation coefficient .6911 P<.001). We observed that, if the combination of ST-CSA and GT-STA is at least 19mm², the probability of obtaining an autograft with a diameter greater than or equal to 8mm is 91.8% or more. The ROC curve analysis demonstrated, in this model, that this predictive method on MRI correctly discriminates in over 95.6% of cases between achieving or otherwise an autograft greater than or equal to 8mm during surgery. Intra and interobserver concordance of the MRI measurements were excellent, as shown in the intraobserver intraclass correlation coefficient (CCI) of .79 and the interobserver CCI of .84 and .77 for the ST and GT respectively.

Conclusions: Preoperative determinations of ST-CSA and GT-CSA (mm²) using MRI correlate with the final autograft diameter. This method represents a reliable and reproducible model to predict the hamstring autograft diameter in ACLR.

Level of evidence: Retrospective cohort study, level IV.

Clinical relevance: A review of the available literature reveals a higher risk of ACL failure or re-rupture if the graft is smaller than 8mm in diameter. Despite being an important factor there is no established pre-operative model that predicts the final graft diameter. Knowing beforehand the possibilities of obtaining a hamstring autograft with a diameter greater than or equal to 8mm would help the orthopaedic surgeon to better plan the surgery and to anticipate the need for other graft options (such as bone-patellar-tendon-bone autograft or allografts, amongst other alternatives).