title: The gap technique does not rotate the femur parallel to the epicondylar axis.
abstract: BACKGROUND
  In the analysis of painful total knee replacements, the surgical epicondylar axis (SEA) has become established as a standard in the diagnosis of femoral component rotation. It remains unclear whether the gap technique widely used to determine femoral rotation, when applied correctly, results in a rotation parallel to the SEA.
  
  
  METHODS
  In this prospective study, 69 patients (69 joints) were included who received a navigated bicondylar surface replacement due to primary arthritis of the knee joint.
  
  
  RESULTS
  In 67 cases in which a perfect soft-tissue balancing of the extension gap (<1° asymmetry) was achieved, the flexion gap and the rotation of the femoral component necessary for its symmetry was determined and documented. The femoral component was implanted additionally taking into account the posterior condylar axis and the Whiteside's line. Postoperatively, the rotation of the femoral component to the SEA was determined and this was used to calculate the angle between a femur implanted according to the gap technique and the SEA. If the gap technique had been used consistently, it would have resulted in a deviation of the femoral components by -0.6° ± 2.9° (-7.4°-5.9°) from the SEA. The absolute deviation would have been 2.4° ± 1.8°, with a range between 0.2° and 7.4°.
  
  
  CONCLUSIONS
  Even if the extension gap is perfectly balanced, the gap technique does not lead to a parallel alignment of the femoral component to the SEA. Since the clinical results of this technique are equivalent to those of the femur first technique in the literature, an evaluation of this deviation as a malalignment must be considered critically.
authors.affiliation: Orthopaedic Department, CMSC, Charité-University Medicine Berlin, Germany. Georg.Matziolis@Charite.de
authors.forename: Georg
authors.initials: G
authors.lastname: Matziolis
authors.forename: Hinrich
authors.initials: H
authors.lastname: Boenicke
authors.forename: Sascha
authors.initials: S
authors.lastname: Pfiel
authors.forename: Georgi
authors.initials: G
authors.lastname: Wassilew
authors.forename: Carsten
authors.initials: C
authors.lastname: Perka
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D005260:Female; D005269:Femur; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies