title: Gap-balancing technique combined with patient-specific instrumentation in TKA.
abstract: BACKGROUND
  Combining patient-specific instrumentation (PSI) with a balancer device in total knee arthroplasty (TKA) to achieve functional femoral rotational alignment is a novel technique. The primary goal of this study was to introduce a new method to combine PSI with a gap-balancing technique and to determine the impact of the technique on rotation of the femoral component.
  
  
  METHODS
  Twenty-five primary TKAs (15 women, 10 men) were prospectively studied. All TKAs involved PSI with an associated gap-balancing device. Front plane alignment was performed intraoperatively with the PSI, followed by rectangular, symmetrical extension and creation of a flexion gap using the balancer device to set the femoral rotation.
  
  
  RESULTS
  Femoral component rotation was between 3° internal and 6° external rotation versus the transepicondylar axis. There were no postoperative signs of patellofemoral dysfunction. In no cases was the resulting joint line displacement >3 mm. The mean elevation was 1.2 ± 0.9 mm (range 0-3). The leg axis was straight in all cases (±3°), at a mean of 1.6° ± 1.0° varus (range 0°-3° varus).
  
  
  CONCLUSIONS
  PSI was with the gap-balancing technique was successfully used without affecting anatomical alignment. With the balancer device, PSI can be used more widely than techniques based solely on landmarks, as the soft-tissue tension can be taken into account, thus virtually eliminating flexion instabilities.
authors: Orthopedic Department, Hospital Märkisch Oderland, Section Wriezen, Sonnenburger Weg 3, 16269, Wriezen, Germany. H.Hommel@khmol.de.
authors: Hagen
authors: H
authors: Hommel
authors: Center for Musceloskeletal Surgery, Orthopedic Department, Charité Universitätsmedizin, Berlin, Germany.
authors: Carsten
authors: C
authors: Perka
mesh_terms: D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation* / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D011183:Postoperative Complications; D011446:Prospective Studies; D016059:Range of Motion, Articular / Q000502:physiology*
keywords: Balancer device; Extension-first technique; Gap-balancing; Patient-specific instrumentation; Total knee arthroplasty