title: Patient-specific positioning guides do not consistently achieve the planned implant position in UKA.
abstract: OBJECTIVE
  To investigate whether the intended preoperative planning corresponded with the postoperative component position after medial UKA using patient-specific positioning guides (PSPGs).
  
  
  METHODS
  Twenty-five consecutive UKAs performed with the PSPG technique (Signature™) were included. Two independent observers performed postoperative CT measurements. The preoperative angles for the femoral component were defined in the frontal plane as 0°. In the first eight cases, a femoral component with single peg was inserted, and the flexion of the femoral component was set to 5°. In the last 17 cases, a twin-peg component was used and flexion set to 10°. In the axial plane, the femoral component was on average set at 2.5° internal rotation. The preoperative tibial component angles in the frontal and axial plane were defined as 0° and in the sagittal plane as 4° in flexion.
  
  
  RESULTS
  The postoperative femoral component angles were on average 0.8° of valgus (SD 3.2, range 12.2° valgus to 5.1° varus, n.s., CI -2.1 to 0.6), 5.0° of flexion (SD 3.9, range 10.2° flexion to 6.0° extension, p = 0.001, CI -5.3 to -1.5) and 4.0° of internal rotation (SD 1.7, range 1.4° to 6.9° int.rot., p < 0.001, CI -4.7 to -3.4). The tibial component angles were on average 3.0° of varus (SD 1.9, range 1.3° valgus to 6.8° varus, p < 0.001, CI 2.2 to 3.8), 3.2° of flexion (SD 2.4°, 6.7° flex to 1.8° ext, n.s., CI -0.2 to 1.7) and 2.7° of internal rotation (SD 7.0, range 16.6° int.rot. to 10.7° ext.rot., n.s., CI -5.6 to 0.2).
  
  
  CONCLUSIONS
  This study showed no agreement between preoperative planning and postoperative component alignment (p < 0.05) for the femoral component angle in sagittal and axial plane and for the tibial component angle in the coronal plane. Although the results did not show significant difference for the tibial component angle in the axial plane, a considerable range of the component angles was found varying from 17° internal to 11° external rotation. This study suggests that the use of PSPGs for UKA does not lead to consistent component position.
  
  
  METHODS
  IV.
authors: Department of Orthopaedic Surgery, Betanien Hospital, Skien, Norway. justin.van.leeuwen@betanienhospital.no.
authors: Justin A M J
authors: http://orcid.org/0000-0003-1846-6768
authors: JAMJ
authors: van Leeuwen
authors: Department of Orthopaedic Surgery, Oslo University Hospital, Oslo, Norway.
authors: Stephan M
authors: SM
authors: Röhrl
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology / Q000601:surgery; D007720:Knee Prosthesis; D008297:Male; D056888:Patient Positioning; D011184:Postoperative Period; D016059:Range of Motion, Articular; D012399:Rotation; D013977:Tibia / Q000502:physiology / Q000601:surgery
keywords: Alignment; CT; Component angle; Patient-specific positioning guides; Unicompartmental knee arthroplasty