2015 ISAKOS Biennial Congress ePoster #1381

Graft-Tunnel Motion During Gait Persists One Year After ACL Reconstruction for Both Bone-Patellar Tendon-Bone and Hamstring Autografts

Scott Tashman, PhD, Pittsburgh, PA UNITED STATES
James Irvine, MD, Pittsburgh, PA UNITED STATES
Eric Thorhauer, BS, Seattle, WA UNITED STATES
Ermias Abebe, MD, Pittsburgh, PA UNITED STATES
Christopher D. Harner, MD, Houston, TX UNITED STATES

University of Pittsburgh, Pittsburgh, PA, USA

FDA Status Not Applicable

Summary: Motion of ACL grafts within the femoral and tibial tunnels during gait, measured with dynamic stereo X-ray imaging, ranges from 1-3 mm 6 weeks after surgical reconstruction and persisted at 1 year for both hamstrings and BTB grafts.

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Abstract:

Introduction

It has often been suggested that bone-patellar tendon-bone (BTB) grafts heal more quickly to graft tunnels than soft-tissue grafts after ACL reconstruction, due to rapid bone-to-bone healing. Little is known, however, about the motion of the grafts under functional, dynamic loads, or the actual time course for graft-tunnel healing in humans. The goal of this study was to assess the motion of both hamstrings (HS) and BTB grafts during gait at two time points (6 and 52 weeks) after surgery. It was hypothesized that there would be greater graft-tunnel motion in HS than BTB grafts, and that graft motion would decrease over time.

Methods

After IRB approval, 12 human subjects underwent anatomic single-bundle ACL reconstruction using either hamstrings (HS) or bone-patellar tendon-bone (BTB) autografts (6 in each group) and extra-cortical fixation. Six 0.8 mm tantalum beads were embedded into the grafts prior to implantation, with pairs of beads located within each bone tunnel and in the mid-substance region. Six weeks and one year after surgery, dynamic stereo X-ray (DSX) images were collected at 100 frames/s while subjects walked on an instrumented treadmill (1.3 m/s). 3D femur and tibia bone models were generated from CT scans. Tibiofemoral kinematics and graft bead positions were analyzed by combining the 3D models with DSX data. Graft-tunnel motion was assessed by determining the maximum range of motion of the most proximal femoral tunnel and most distal tibial tunnel beads along the direction of the bone tunnels during the stance phase of gait. Effects of graft type and time were assessed with a 2-factor ANOVA, with alpha = 0.05.

Results

Femoral tunnel motion (mean±s.d.) was 2.47±0.96 mm (range 0.95-3.44 mm) for BTB and 1.51±0.68 mm (range 0.88-2.41 mm) for HS grafts, decreasing slightly to 2.09±0.84 mm for BTB and 1.37±0.41 for HS grafts by one year. Tibial tunnel motion was 1.45±0.57 mm (range 0.74-2.44 mm) for BTB and 1.43±0.59 mm (range 0.89-2.30 mm) for HS grafts, and changed little by one year (1.58±0.46 mm for BTB and 1.52±0.57 for HS grafts). Across all time points, femoral graft-tunnel motion was significantly greater for BTB than HS grafts (p=0.004). There were no significant differences between graft types in the tibia, or significant changes in motion between 6 weeks and 1 year.

Discussion

Contrary to the study hypothesis, there was a greater motion relative to the femoral tunnel wall in BTB than HS grafts during walking. Significant graft-tunnel motion also persisted one year after reconstruction. These data suggest that the graft-to-tunnel healing process occurs much more slowly then widely believed, especially for BTB grafts. All subjects were asymptomatic one year after surgery, and the implications of persistent, small (1-3 mm) movements of the grafts subjects is unknown. These results, however, may have significant implications for graft choice, rehabilitation strategies and timing for return to sports.