title: Validation of a measurement device for instrumented quantification of anterior translation and rotational assessment of the knee.
abstract: OBJECTIVE
  A test setup for clinical use in the awake and non-anesthetized patient measuring anteroposterior translation and rotation of the knee joint is the subject of validation.
  
  
  METHODS
  A measuring device featuring fixation of the foot at 30° of knee flexion with varus/valgus stress posts for the knee was developed. Tibial rotation (external/internal) was imposed with a torque of 2 Nm on the footrest with the ankle locked in dorsiflexion. Anterior translation of the tibia in relation to the femur was measured with a commercially available arthrometer. Measurements were performed in a neutral position, internal rotation, and external rotation. Intrarater and inter-rater reliability was validated in 10 healthy volunteers (Cronbach α). We examined 10 patients with isolated anterior cruciate ligament (ACL) rupture, as well as 10 patients with ACL rupture plus medial instability and 10 patients with additional lateral instability. Side-to-side differences were used for calculation.
  
  
  RESULTS
  Comparison of healthy volunteers and subjects with isolated ACL rupture showed significant differences: internal rotation, 0.79 mm and 2.46 mm, respectively (P = .001); neutral position, 0.4 mm and 3.35 mm, respectively (P < .0001); and external rotation, 0.29 mm and 2.5 mm, respectively (P = .003). Significant differences (P = .008) were found between isolated ACL rupture and ACL rupture plus medial instability by use of the ratio of anterior translation in external rotation versus the neutral position. Inter-rater reliability was 0.948 in 10 healthy volunteers and 0.981 in 10 subjects with unilateral ACL rupture. Intrarater reliability in the volunteers was 0.829.
  
  
  CONCLUSIONS
  By use of the developed measurement device, the "Laxitester" (ORTEMA Sport Protection, Markgroeningen, Germany), objective differentiation between isolated ACL rupture and ACL rupture plus additional medial instability is possible. Values for anterior translation are reliable and reproducible by different examiners and by the same examiner at different times.
  
  
  CONCLUSIONS
  The Laxitester allows objectification of medial instability in combination with ACL injuries and provides a reference regarding the need for additional medial stabilization. Compared with the isolated measurement of anteroposterior translation, knee instability can be assessed in a more differentiated manner.
authors.affiliation: Department of Orthopedic and Trauma Surgery, Albert Ludwig University of Freiburg, Freiburg, Germany. hermann.mayr@uniklinik-freiburg.de
authors.forename: Hermann O
authors.initials: HO
authors.lastname: Mayr
authors.forename: Anna
authors.initials: A
authors.lastname: Hoell
authors.forename: Anke
authors.initials: A
authors.lastname: Bernstein
authors.forename: Robert
authors.initials: R
authors.lastname: Hube
authors.forename: Claudius
authors.initials: C
authors.lastname: Zeiler
authors.forename: Thomas
authors.initials: T
authors.lastname: Kalteis
authors.forename: Norbert P
authors.initials: NP
authors.lastname: Suedkamp
authors.forename: Amelie
authors.initials: A
authors.lastname: Stoehr
mesh_terms: D000293:Adolescent; D000328:Adult; D016118:Anterior Cruciate Ligament / Q000503:physiopathology; D000070598:Anterior Cruciate Ligament Injuries; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000175:diagnosis* / Q000503:physiopathology; D007718:Knee Injuries / Q000175:diagnosis* / Q000503:physiopathology; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D009983:Orthopedic Equipment; D015203:Reproducibility of Results; D012399:Rotation; D012421:Rupture / Q000175:diagnosis / Q000503:physiopathology; D016037:Single-Blind Method; D019415:Torque; D055815:Young Adult