2015 ISAKOS Biennial Congress ePoster #1208

Stress Distribution at the Femoral Tunnel Aperture During the Lachman Test After Anatomic ACL Reconstruction.

Yuichi Hoshino, MD, PhD, Kobe, Hyogo JAPAN
Ryosuke Kuroda, MD, PhD, Kobe, Hyogo JAPAN
Yuichiro Nishizawa, MD. PhD, Kobe, Hyogo JAPAN
Naoki Nakano, MD, Kobe, Hyogo JAPAN
Kanto Nagai, MD, PhD, Kobe, Hyogo JAPAN
Daisuke Araki, MD, PhD, Kobe, Hyogo JAPAN
Shinya Oka, MD, PhD, Nishinomiya, Hyogo JAPAN
Shogo Kawaguchi, MS, Fukui, Fukui JAPAN
Kouki Nagamune, PhD, Fukui, Fukui JAPAN
Masahiro Kurosaka, MD, Kobe, Hyogo JAPAN

Kobe University, Kobe, Hyogo, JAPAN

FDA Status Not Applicable

Summary: The stress around the femoral tunnel aperture was measured during the Lachman test after anatomic ACL reconstruction using a hamstrings graft. The stress from the graft was differently distributed and the distal part of the femoral tunnel had the largest stress. The position of the distal part of the tunnel should be carefully determined when performing the ACL reconstruction.

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Abstract:

Introduction

A great attention has been paid to the tunnel location in the anterior cruciate ligament (ACL) reconstruction. However, the tensile load of the ACL graft is not supposed to be equally distributed in the whole area of the tunnel aperture especially when a soft tissue graft is used, since a soft tissue graft moves inside the tunnel when it is pulled diagonally to the tunnel. Therefore, it is quite important which part of the tunnel aperture carries a major load from the ACL graft while the ACL serves its function. The Lachman test is commonly used to evaluate the function of the ACL which is to restrain the anterior translation of the tibia. The purpose of this study was to measure the stress in different areas of the tunnel aperture during the Lachman test. It was hypothesized that the stress from the graft would be differently distributed around the tunnel.

Methods

Seven cadaveric knees were used. Single bundle ACL reconstruction was performed using a hamstrings graft. The guide pin was inserted at the center of the ACL footprint through the far antero-medial portal, and the tunnel was over-drilled up to 13mm diameter. A 13mm outside diameter and 7mm inside diameter aluminum cylinder with four tiny pressure sensors all around was inserted into the femoral tunnel, simulating an anatomic 7mm diameter femoral tunnel. 7mm diameter tibial tunnel was then created at the center of the ACL footprint. 7mm hamstrings graft with a micro force sensor was inserted and fixed using a suspensory button on the femoral side and a suture post on the tibial side. After fixing the graft with 20N at 20degrees of knee flexion, the Lachman test was performed while monitoring the tunnel aperture pressure and the ACL graft tension simultaneously. The pressures of four different directions on the femoral tunnel aperture at the time of peak ACL graft tension were recorded. The difference of the pressures between four different directions was tested by Kruskal-Wallis test. P<0.05 was considered as statistically significant.

Results

The ACL graft tension reaches its peak (54±34N) during the Lachman test. Pressure at the femoral tunnel aperture was different between different directions (p<0.01). Distal direction bore significantly larger pressure (33.8±36.5N) compared to the other directions (p<0.01). Second largest pressure was carried in the anterior direction (7.9±4.2N), followed by proximal and posterior directions (2.7±1.9N, 1.0±1.0N respectively).

Discussion

The Lachman test assesses the ACL function against the anterior tibial loading. The ACL graft suspends onto the edge of the femoral tunnel, and the distal part of the femoral tunnel has the largest pressure when the ACL serves its function. The stress from the graft onto the edge of the tunnel could mechanically induce the tunnel enlargement and further compromising the stability. Therefore, the distal part of the femoral tunnel seems to be quite important when considering the tunnel position and should be located well inside the anatomical footprint.