Disclosures. Background. Background

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1 Kinematic and Quantitative MR Imaging Evaluation of ACL Reconstructions Using the Mini-Two Incision Method Compared to the Anteromedial Portal Technique Drew A. Lansdown, MD Christina Allen, MD Samuel Wu Xiaojuan Li, PhD Benjamin Ma, MD Disclosures Aided by a Resident Research Grant from the Orthopaedic Research and Education Foundation. NIH/NIAMS P50-AR No other financial disclosures. Background High prevalence of ACL injury 95,000 new injuries yearly in the US 1 ACL serves as primary restraint Resists anterior displacement of the tibia 2 Controls internal rotation of the tibia 2 ACL-deficient knee at high risk of meniscal and articular cartilage injury3 1. Muneta et al. Arthroscopy Beynonn et al. AJSM Kannus et al. JBJS Several reconstruction techniques exist Open, two-incision approach Arthroscopic transtibial Arthroscopic anteromedial portal Arthroscopic mini-two incision Difference between techniques primarily related to femoral tunnel positioning Background 1

2 Background Increased risk of progression to early-onset osteoarthritis even after ACL reconstruction 1-3 Result of initial injury? Incomplete restoration of normal knee kinematics? Progressive cascade? Transtibial reconstruction restores anteroposterior stability Anteromedial reconstruction Results in improved rotational stability as compared to transtibial reconstruction Leads to stable Lachman and restoration of anterior tibial translation 4 1. Lohmander, et al. Arthritis & Rheumatism Von Porat, et al. An of Rheum Disease Andriacchi, et al. Ann of BME, Carpenter, et al. Arthroscopy Theologis, et al. Arthroscopy Mini-Two Incision Reconstruction Femoral footprint is visualized arthroscopically 1-2 cm incision over lateral femur Guide pin through lateral femoral cortex into notch Retrograde drill produces femoral tunnel 1. Lubowitz et al. Arthroscopy Theoretical Advantages 1 Direct visualization of tunnel starting and exit points may allow for improved positioning Tunnel length is longer than that created by anteromedial portal technique Minimizes risk of lateral wall blowout Procedure performed with knee flexed at 90 degrees, which may allow for improved visualization of anatomic landmarks 1. Lubowitz et al. Arthroscopy Hypotheses Tibiofemoral cartilage contact area is not significantly different between the mini-two incision reconstruction and the contralateral knee The mini-two incision reconstruction technique more closely restores the cartilage contact area as compared to the anteromedial portal technique. The mini-two incision reconstruction results in the restoration of normal translation and rotational parameters 2

3 INCLUSION CRITERIA Patient Selection EXCLUSION CRITERIA Patient Characteristics MT Reconstruction AM Reconstruction years old Associated ligamentous injury Number of patients 7 12 Mean age (Range) yrs 32 yrs Meniscal repair or debridement greater than 20% Mean time from surgery (Range) months (13-19) 12 months months post-op History of inflammatory arthropathy Graft type Hamstring autograft (7) Hamstring autograft (8) PT allograft (3) Achilles allograft (1) Mini-two incision reconstruction Previous surgery on either knee Data Acquisition 3T GE Signa MR scanner Sagittal fat-suppressed T 2 -weighted images Surgical and contralateral knees imaged Full extension flexion Imaging Parameters Repetition time (TR) Echo time (TE) Field of View 4000 ms ms 16 cm Matrix size 512 x 256 Slice thickness 1.5 mm 3

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5 Tibia ROIs registered in flexion and extension with iterative closest point algorithm Registration Femoral condyles modeled as spheres Registration Axes for femur set as central axis of spheres, defined central axis of femur and cross product of these two axes Registration Contact Area All points from defined splines are connected with a set of triangles Area is calculated as the summation of the triangles Contact centroid is the centroid of the triangles Translation defined according to tibial axis 5

6 Rotational and Translational Parameters Are Similar in MT and AM Reconstructions Cartilage Contact Area Medial Extension Medial Flexion Lateral Extension Lateral - Flexion Internal Tibial Rotation (Degrees) (Mean [SD]) MT Reconstructed 0.24 (8.2) (2.3) p = 0.55 MT Normal 3.4 (6.8) 0.01 (1.3) Anterior Tibial Translation (mm) (Mean [SD]) AM Reconstructed 3.1 (5.6) 0.7 (2.7) p = 0.36 p = 0.38 AM Normal 2.3 (5.4) 1.3 (5.4) MT = Mini-two incision method AM = Anteromedial portal technique p = 0.33 MT Recon vs MT Control AM Recon vs AM Control 90.5% (4.8%) p = % (13.1%) 86.3% (7.3%) p = % (27.1%) 101.3% (13.6%) 111.8% (29.7%) 99.4% (14.0%) 111.2% (18.9%) p = 0.03 Medial compartment contact areas are significantly lower in both flexion and extension Medial Contact Centroid Is Abnormal Shifted laterally in both flexion and extension relative to the contralateral knee 9.1 mm in flexion (p = 0.02) 8.9 mm in extension (p = 0.05) AM reconstructions show lateral contact centroid shift anteriorly in flexion and extension Conclusions MT reconstruction restores kinematic parameters Cartilage contact area in the medial compartment is significantly decreased following MT reconstruction No difference in cartilage contact area with AM reconstruction Contact centroid is shifted laterally for the medial compartment with the MT reconstruction Contact changes may be responsible for early degenerative changes despite reconstruction 6

7 Acknowledgements Christina Allen, MD Benjamin Ma, MD Xiaojuan Li, PhD Samuel Wu Will Schairer Lee Jae Morse, MD 7