title: The intact posterior cruciate ligament not only controls posterior displacement but also maintains the flexion gap.
abstract: BACKGROUND
  The PCL is a strong stabilizer of the knee and provides posterior stability to the tibia. However, sagittal alignment of the PCL with the knee at 90° flexion suggests the PCL might play a role not only in posterior stabilization but also in maintaining the flexion gap.
  
  
  OBJECTIVE
  We determined whether the intact PCL helps maintain the flexion gap.
  
  
  METHODS
  We examined axial radiographs and gravity sag views of 17 patients with chronic isolated unilateral PCL injury. The flexion gap was defined as the mean value of the medial and lateral distances between the femoral and tibial bones on the axial radiograph. Increase in the flexion gap and posterior laxity were determined by comparing the patients' injured and contralateral uninjured knees.
  
  
  RESULTS
  The flexion gap of PCL injured knees (median, 7.5 mm; range, 5.3-11.5 mm; medial median, 6.2 mm; medial range, 3.7-8.3 mm; lateral median, 7.9 mm; lateral range, 5.3-11.5 mm) was larger than that seen in uninjured knees (median, 5.0 mm; range, 4.0-7.6 mm; medial median, 4.6 mm; medial range 3.4-7.1 mm; lateral median, 5.6; lateral range, 4.5-11.2 mm). The increment in the medial distance was similar to that in the lateral distance. Posterior laxity of injured knees was 9.1 (median); 5.4 to 15.2 (range) mm greater than that of uninjured knees. We found no correlation between posterior laxity and the flexion gap increment.
  
  
  CONCLUSIONS
  Our data suggest the intact PCL controls posterior displacement and maintains the flexion gap.
authors.affiliation: Osaka City General Hospital, 2-13-22, Miyakojima-hondori, Miyakojima-ku, Osaka City, Osaka, 534-0021, Japan. ichi23@js3.so-net.ne.jp
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Matsui
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Kadoya
authors.forename: Shuji
authors.initials: S
authors.lastname: Horibe
mesh_terms: D000293:Adolescent; D000328:Adult; D001182:Arthroscopy; D005260:Female; D006801:Humans; D007718:Knee Injuries / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D016119:Posterior Cruciate Ligament / Q000000981:diagnostic imaging / Q000293:injuries / Q000502:physiology*; D011859:Radiography; D012189:Retrospective Studies; D018709:Statistics, Nonparametric