title: Adolescents and female patients are at increased risk for contralateral anterior cruciate ligament reconstruction: a cohort study from the Swedish National Knee Ligament Register based on 17,682 patients.
abstract: OBJECTIVE
  The impact of different surgical techniques in index ACL reconstruction for patients undergoing contralateral ACL reconstruction was investigated.
  
  
  METHODS
  The study was based on data from the Swedish National Knee Ligament Register. Patients undergoing index ACL reconstruction and subsequent contralateral ACL reconstruction using hamstring graft under the study period were included. The following variables were evaluated: age at index surgery, gender, concomitant meniscal or cartilage injury registered at index injury, transportal femoral bone tunnel drilling and transtibial femoral bone tunnel drilling. The end-point of primary contralateral ACL surgery was analysed as well as the time-to-event outcomes using survivorship methods including Kaplan-Meier estimation and Cox proportional hazards regression models.
  
  
  RESULTS
  A total of 17,682 patients [n = 10,013 males (56.6%) and 7669 females (43.4%)] undergoing primary ACL reconstruction from 1 January 2005 through 31 December 2014 were included in the study. A total of 526 (3.0%) patients [n = 260 males (49.4%) and 266 females (50.6%)] underwent primary contralateral ACL reconstruction after index ACL reconstruction during the study period. Females had a 33.7% greater risk of contralateral ACL surgery [HR 1.337 (95% CI 1.127-1.586); (P = 0 0.001)]. The youngest age group (13-15 years) showed an increased risk of contralateral ACL surgery compared with the reference (36-49) age group [HR 2.771 (95% CI 1.456-5.272); (P = 0.002)]. Decreased risk of contralateral ACL surgery was seen amongst patients with concomitant cartilage injury at index surgery [HR 0.765 (95% CI 0.623-0.939); (P = 0.010)]. No differences in terms of the risk of contralateral ACL surgery were found between anatomic and non-anatomic techniques of primary single-bundle ACL reconstruction, comparing transportal anatomic technique to transtibial non-anatomic, anatomic and partial-anatomic.
  
  
  CONCLUSIONS
  Age and gender were identified as risk factors for contralateral ACL reconstruction; hence young individuals and females were more prone to undergo contralateral ACL reconstruction. Patients with concomitant cartilage injury at index ACL reconstruction had lower risk for contralateral ACL reconstruction. No significant differences between various ACL reconstruction techniques could be related to increased risk of contralateral ACL reconstruction.
  
  
  METHODS
  Retrospective Cohort Study, Level III.
authors.affiliation: Department of Orthopaedics, Institute of Clinical Sciences, The Sahlgrenska Academy, University of Gothenburg, Göteborg, Sweden.|Department of Orthopaedics, Sahlgrenska University Hospital, Mölndal, Sweden.
authors.forename: Thorkell
authors.initials: T
authors.lastname: Snaebjörnsson
authors.affiliation: Department of Health and Rehabilitation, Institute of Neuroscience and Physiology, The Sahlgrenska Academy, University of Gothenburg, Göteborg, Sweden.
authors.forename: Eric
authors.initials: E
authors.lastname: Hamrin Senorski
authors.affiliation: Department of Orthopaedics, Institute of Clinical Sciences, The Sahlgrenska Academy, University of Gothenburg, Göteborg, Sweden.
authors.forename: David
authors.initials: D
authors.lastname: Sundemo
authors.affiliation: Department of Orthopaedics, Institute of Clinical Sciences, The Sahlgrenska Academy, University of Gothenburg, Göteborg, Sweden.
authors.forename: Eleonor
authors.initials: E
authors.lastname: Svantesson
authors.affiliation: Department of Orthopaedics, Institute of Clinical Sciences, The Sahlgrenska Academy, University of Gothenburg, Göteborg, Sweden.|Department of Orthopaedics, Sahlgrenska University Hospital, Mölndal, Sweden.
authors.forename: Olof
authors.initials: O
authors.lastname: Westin
authors.affiliation: Department of Orthopaedic Surgery, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA.
authors.forename: Volker
authors.initials: V
authors.lastname: Musahl
authors.affiliation: Fundación García-Cugat, Barcelona, Spain.|Artroscopia GC, SL, Barcelona, Spain.|Mutualidad Catalana de Futbolistas-Delegación Cataluña, Federación Española de Fútbol, Barcelona, Spain.|Department of Orthopaedic Surgery, Mayo Clinic, Rochester, MN, USA.
authors.forename: Eduard
authors.initials: E
authors.lastname: Alentorn-Geli
authors.affiliation: Department of Orthopaedics, Institute of Clinical Sciences, The Sahlgrenska Academy, University of Gothenburg, Göteborg, Sweden. kristian@samuelsson.cc.|Department of Orthopaedics, Sahlgrenska University Hospital, Mölndal, Sweden. kristian@samuelsson.cc.
authors.forename: Kristian
authors.initials: K
authors.lastname: Samuelsson
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000070598:Anterior Cruciate Ligament Injuries / Q000453:epidemiology* / Q000209:etiology / Q000601:surgery; D059549:Anterior Cruciate Ligament Reconstruction; D015331:Cohort Studies; D005260:Female; D006801:Humans; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D012042:Registries; D012189:Retrospective Studies; D012307:Risk Factors; D012737:Sex Factors; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult
keywords: ACL; Anterior cruciate ligament; Autograft; Contralateral; Knee; Registry; Surgical predictors