Summary

We developed a technique to virtually assess the biomechanical impact of slope changing tibial osteotomy in a computational model to aid surgeons in selecting a target tibial slope in revision ACL reconstruction on a patient-specific basis.

Abstract

Introduction

Increased posterior-inferior directed slope of the tibial plateau (i.e., tibial slope) is related to elevated risk of ACL reconstruction failure [1]. Biomechanical studies link this risk factor for ACL graft tear to increases in both anterior tibial translation (ATT) and ACL graft force [2]. Therefore, some surgeons combine ACL graft revisions with anterior closing wedge high tibial osteotomy (ACWHTO) [3]. Too small of a correction, however, may not adequately reduce ACL forces while too large of a correction may increase PCL forces and elevate risk of injury to this ligament or cause knee recurvatum [4]. Unfortunately, the relationship between tibial slope and important biomechanical outcome measures such as cruciate ligament forces and tibiofemoral kinematics remains poorly understood. Thus, we had two goals. First was to develop a technique to conduct virtual tibial osteotomy in a computational knee model. Second was to quantify sensitivity of ACL, PCL, and meniscal root forces and tibiofemoral kinematics to tibial slope changes.

Methods

A computer model of the tibiofemoral joint was developed from CT and MRI data of a right cadaveric knee of a 25-year-old female. Volumetric reconstructions of the tibia, femur, cartilage, and menisci along with the insertions of the cruciates, collaterals, capsular tissues, and peripheral and root attachments of the menisci were imported into the modeling pipeline. ACWHTO was simulated by removing a 10° wedge from the volumetric reconstruction of the tibia. The osteotomy was perpendicular to the sagittal plane and intersected the posterior-most aspect of the PCL. The computer models were loaded with 100 N compression and with loads simulating a clinical pivot shift maneuver consisting of serially applied compression (100 N), valgus (4 Nm), internal rotation (2 Nm), and an anterior force (30 N) at 15° of flexion. Outcomes measures were ATT, internal tibial rotation (ITR), and forces carried by the ACL and PCL and posterior roots of the menisci at the peak applied loads.

Results

With the simulated pivoting load, a 10° decrease in tibial slope caused a 63 N decrease and a 6 N increase in ACL and PCL force, respectively. The 10° decrease in tibial slope also decreased ATT by 7 mm and increased ITR by 2°. With isolated compression, the 10° decrease in tibial slope caused a 37 N decrease and an 8 N increase in ACL and PCL force, respectively, and a 7 mm decrease in ATT and 0.5° increase in ITR. Changes in posterior root forces of both menisci were minimal (=5.4 N).

Discussion

We developed a technique to virtually assess the biomechanical impact of slope changing tibial osteotomy in a computational model. Model predictions of decreased ACL force and increased PCL force with reduced tibial slope corroborate cadaveric studies [2, 5]. This workflow could be used to determine cruciate forces and tibiofemoral kinematics to aid surgeons in selecting a target tibial slope on a patient-specific basis.