2017 ISAKOS Biennial Congress ePoster #1055

 

In Vivo Graft Bending Angle Can Affect Early Graft Healing after Anterior Cruciate Ligament Reconstruction

Yasutaka Tashiro, MD, PhD, Kitakyushu JAPAN
Tom Gale, MS, Pittsburgh, PA UNITED STATES
Kanto Nagai, MD, PhD, Kobe, Hyogo JAPAN
James J. Irrgang, PT, PhD, FAPTA, Pittsburgh, PA UNITED STATES
William Anderst, PhD, Pittsburgh, PA UNITED STATES
Freddie H. Fu, MD, Pittsburgh, PA UNITED STATES
Scott Tashman, PhD, Pittsburgh, PA UNITED STATES

University of Pittsburgh, Pittsburgh, PA, UNITED STATES

FDA Status Cleared

Summary

The quantitative assessment of graft healing using high-resolution MRI signal/noise quotient after anatomic ACL reconstruction showed significantly higher intensity in the proximal graft area and its high correlation with in vivo graft bending angle during dynamic knee activities 6 months postoperatively, thus suggesting higher stress between bone-graft interface at the femoral tunnel aperture.

Abstract

Introduction

It has been recently noticed that steep graft bending can occur at the femoral tunnel aperture after anatomic anterior cruciate ligament (ACL) reconstruction. But the actual influence of high graft bending angle (GBA) on graft healing in vivo is not fully understood. We aimed to clarify the association of ACL graft bending angle on the graft healing using dynamic stereo x-ray analysis and high resolution MRI. We hypothesized that the high GBA may affect graft healing after ACL reconstruction.

Methods

Anatomic single-bundle ACL reconstruction was performed on 24 patients (Avg. age 19.2 ± 3.7) using the trans-portal technique. 17 were male and 7 were female. A 10-mm quadriceps tendon autograft with a bone plug was harvested. In order to evaluate graft healing, signal/noise quotient (SNQ) was measured in 3 regions of interest (ROIs) of proximal, mid-substance and distal ACL graft using high resolution MRI (0.45 x 0.45 x 0.70 mm, 3D-DESS sequence), with decreased signals suggesting improved healing. Dynamic knee motion was examined during level walking and downhill running on an instrumented treadmill to assess in vivo GBA. The femoral and tibial tunnel aperture centers and the proximal femoral tunnel exit were identified from a high-resolution CT scan at 6 months. In vivo GBA was calculated at each motion frame from the 3D angle between the graft and femoral tunnel vectors, based on tibio-femoral kinematics determined from dynamic stereo x-ray analysis. Graft healing and GBA were assessed 6 and 24 months postoperatively. SNQ in 3 ROIs at 2 time points were compared using repeated measure ANOVA. Relationship between SNQ and average GBA during 0 to 15% gait cycle was analyzed using Pearson’s correlations.

Results

SNQ of ACL graft in the proximal area was significantly higher than that of mid-substance (p<0.05) and distal region (p<0.01) at 6 months. SNQ in the proximal area was highly correlated with GBA during standing (R=0.64, p<0.01), walking (R=0.65, p<0.01) and running (R=0.54, p<0.01) at 6 months, but not in the mid-substance or distal area (N.S.). At 24 months, SNQs in proximal and mid-substance ACL graft decreased significantly (p<0.01 for each), and there were no statistical difference across the 3 regions, although mild correlation was still residual between GBA and SNQ in the proximal region (p<0.05).

Discussion

Higher signal intensity in the proximal area at 6 months suggest that healing may progress more slowly in the proximal region of the graft. Significant correlations between higher GBA and SNQ only in the proximal area suggest that the steep graft bending angle may create higher stresses around the proximal bone-graft interface, possibly inhibiting healing. One of the limitations is that the signal intensity was assessed as a proxy for graft healing, therefore signal/noise quotient was used as a validated method. Secondly, it was a secondary analysis for a prospective study.

CLINICAL RELEVANCE:
Our findings that steeper GBA is associated with higher signal intensity suggests that the resulting higher graft-bone stress at the femoral aperture may have negative effect on early graft healing after ACL reconstruction.