title: Tibial tubercle-posterior cruciate ligament distance: a new measurement to define the position of the tibial tubercle in patients with patellar dislocation.
abstract: BACKGROUND
  In patients with patellar instability, a pathological tibial tubercle-trochlear groove (TT-TG) distance is a risk factor. However, the TT-TG distance gives no information about the location of the malformation.
  
  
  OBJECTIVE
  Not all patients with a pathological TT-TG distance (≥20 mm) had lateralization of the tibial tubercle.
  
  
  METHODS
  Cohort study (diagnosis); Level of evidence, 2.
  
  
  METHODS
  Fifty-eight knees in 49 patients with 2 or more patellar dislocations and 60 knees in 30 volunteers with no history of dislocation were analyzed using magnetic resonance imaging (MRI). The tibial tubercle-posterior cruciate ligament (TT-PCL) distance was defined as the mediolateral distance between the tibial tubercle midpoint and the medial border of the posterior cruciate ligament. The distance was measured parallel to the dorsal aspect of the proximal tibia (dorsal tibia condylar line). Three observers performed the measurements. Significant differences in the TT-PCL distance between the patient and the control group were estimated using an unpaired t test. The inter- and intraobserver variability of the measurement was performed.
  
  
  RESULTS
  The intraclass correlation coefficients for inter- and intraobserver variability of the TT-PCL distance were higher than 0.74 and 0.93, respectively. A statistically significant difference (P < .05) was found between the TT-PCL distance in the control group (mean [SD], 18.4 [3.35] mm) and in patients (21.9 [4.30] mm). The mean (SD) TT-TG was 18.9 (5.16) mm in the patient group and 11.9 (4.67) mm in the control group (P < .05). In the control group, 95% had a TT-PCL distance <24 mm. In the patient group, 22 of 58 knee joints (38%) had a TT-PCL distance ≥24 mm. Seventeen of 40 knee joints (43%) with a TT-TG distance ≥20 mm had a TT-PCL distance <24 mm.
  
  
  CONCLUSIONS
  Only 57% of the patients with a pathological TT-TG distance (≥20 mm) had lateralization of the tibial tubercle in relation to the posterior cruciate ligament. The TT-PCL distance is an alternative method for determining the position of the tibial tubercle.
authors.affiliation: General Hospital Oberndorf, Department of Orthopaedic Surgery, Stolzalpe, Austria. dr.seitlinger@aon.at
authors.forename: Gerd
authors.initials: G
authors.lastname: Seitlinger
authors.forename: Georg
authors.initials: G
authors.lastname: Scheurecker
authors.forename: Richard
authors.initials: R
authors.lastname: Högler
authors.forename: Luc
authors.initials: L
authors.lastname: Labey
authors.forename: Bernardo
authors.initials: B
authors.lastname: Innocenti
authors.forename: Siegfried
authors.initials: S
authors.lastname: Hofmann
mesh_terms: D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D002648:Child; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D031222:Patellar Dislocation / Q000473:pathology*; D016119:Posterior Cruciate Ligament / Q000473:pathology*; D012008:Recurrence; D012189:Retrospective Studies; D016037:Single-Blind Method; D013977:Tibia / Q000473:pathology*; D014102:Torsion Abnormality / Q000473:pathology; D055815:Young Adult