title: Tibial and Femoral Tunnel Changes After ACL Reconstruction: A Prospective 2-Year Longitudinal MRI Study.
abstract: BACKGROUND
  Tunnel widening after anterior cruciate ligament reconstruction (ACL-R) is a well-accepted and frequent phenomenon, yet little is known regarding its origin or natural history.
  
  
  OBJECTIVE
  To prospectively evaluate the cross-sectional area (CSA) changes in tibial and femoral bone tunnels after ACL-R with serial MRI.
  
  
  METHODS
  Case series; Level of evidence, 4.
  
  
  METHODS
  Patients underwent arthroscopic ACL-R with the same surgeon, surgical technique, and rehabilitation protocol. Each patient underwent preoperative dual-energy x-ray absorptiometry and clinical evaluation, as well as postoperative time zero MRI followed by subsequent MRI and clinical examination, including functional and subjective outcome tests, at 6, 12, 24, 52, and 104 weeks. Tibial and femoral tunnel CSA was measured on each MRI at tunnel aperture (ttA and ftA), midsection (ttM and ftM), and exit (ttE and ftE). Logistic regression modeling was used to examine the predictive value of demographic data and preoperative bone quality (as measured by dual-energy x-ray absorptiometry) on functional outcome scores, manual and instrumented laxity measurements, and changes in tunnel area over time.
  
  
  RESULTS
  Eighteen patients (including 12 men), mean age 35.5±8.7 years, underwent ACL-R. There was significant tunnel expansion at ttA and ftA sites 6 weeks postoperatively (P=.024 and .0045, respectively). Expansion continued for 24 weeks, with progressive tunnel narrowing thereafter. Average ttA CSA was significantly larger than ftA CSA at all times. The ttM significantly expanded after 6 weeks (P=.06); continued expansion to week 12 was followed by 21 months of reduction in tunnel diameter. The ftM and both ttE and ftE sites decreased in CSA over the 2 years. Median Lysholm and International Knee Documentation Committee scores significantly improved at final follow-up (P=.0083 and <.0001, respectively), and patients returned to preoperative activity levels. Pivot shift significantly decreased (P<.0001). Younger age (<30 years), male sex, and delayed ACL-R (>1 year from time of injury) predicted increased tunnel widening and accelerated expansion in CSA (P<.005).
  
  
  CONCLUSIONS
  Tunnel expansion after ACL-R occurs early and primarily at the tunnel apertures. Expansion may not affect clinical outcome. Younger age, male sex, and delay from injury to ACL-R may be potential risks for enlargement.
authors: Department of Orthopaedic Surgery, University of Michigan, Ann Arbor, Michigan, USA.
authors: Alexander E
authors: AE
authors: Weber
authors: Sports Medicine and Shoulder Service, Hospital for Special Surgery, New York, New York, USA.
authors: Demetris
authors: D
authors: Delos
authors: Department of Orthopaedic Surgery, University of Michigan, Ann Arbor, Michigan, USA.
authors: Hanna N
authors: HN
authors: Oltean
authors: Sports Medicine and Shoulder Service, Hospital for Special Surgery, New York, New York, USA.
authors: Katherine
authors: K
authors: Vadasdi
authors: Department of Sports Physical Therapy, Hospital for Special Surgery, New York, New York, USA.
authors: John
authors: J
authors: Cavanaugh
authors: Division of Magnetic Resonance Imaging and Department of Radiology and Imaging, Hospital for Special Surgery, New York, New York, USA.
authors: Hollis G
authors: HG
authors: Potter
authors: Sports Medicine and Shoulder Service, Hospital for Special Surgery, New York, New York, USA rodeos@hss.edu.
authors: Scott A
authors: SA
authors: Rodeo
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D000328:Adult; D016118:Anterior Cruciate Ligament / Q000601:surgery*; D000070598:Anterior Cruciate Ligament Injuries; D059549:Anterior Cruciate Ligament Reconstruction / Q000379:methods*; D001182:Arthroscopy / Q000379:methods*; D005260:Female; D005269:Femur / Q000601:surgery; D006801:Humans; D007719:Knee Joint / Q000601:surgery; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011184:Postoperative Period; D011446:Prospective Studies; D013977:Tibia / Q000601:surgery; D055815:Young Adult
keywords: ACL reconstruction; anterior cruciate ligament; arthroscopy; bone tunnels; femoral tunnel; magnetic resonance imaging; tibial tunnel; tunnel widening