title: Joint line position in revision total knee arthroplasty: the role of posterior femoral off-set stems.
abstract: BACKGROUND
  Elevation of the joint line frequently occurs in revision total knee arthroplasty (RTKA) because of a wider flexion space than extension space. One solution to balance this flexion-extension space involves the introduction of couplers between the stem and femoral components, and the use of posteriorly offset femoral stems that we hypothesized would improve gap balancing and facilitate joint line restoration.
  
  
  METHODS
  We retrospectively reviewed a selected series of 43 RTKA. Postoperative joint line height was subtracted from intended height using postoperative lateral radiographs. The value was negative if the joint line position was lowered, and positive if raised.
  
  
  RESULTS
  Forty knees were followed for a mean of 3.5years. Mean postoperative joint line position change from intended position was 1.5mm (range -2.5-7.5mm). In 28 knees (70%), the joint line position was restored to within ±2mm of the intended position; in eight knees (20%), from 2-4mm; and in four knees (10%), >4mm. Joint line position was raised in 32 knees (80%) and lowered in eight (20%). In the offset stem knees, the intended joint line position was 0.9mm (range -1.2-3.4mm) as compared with 3.2mm (range -2.5-7.5mm) for the straight stem knees.
  
  
  CONCLUSIONS
  A coupler system between the femoral stem and femoral component restored the joint line in 70% of cases. The posterior offset stem provided increased posterior condylar offset, addressed the wider flexion space, provided better positioning of the stem, and restored the joint line.
  
  
  METHODS
  Therapeutic Study Level IV.
authors.affiliation: First Orthopedic Clinic, Department of Special Surgical Science, University of Florence, CTO-Largo Palagi 1, 50139 Florence, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Innocenti
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Matassi
authors.forename: Christian
authors.initials: C
authors.lastname: Carulli
authors.forename: Stefano
authors.initials: S
authors.lastname: Soderi
authors.forename: Marco
authors.initials: M
authors.lastname: Villano
authors.forename: Roberto
authors.initials: R
authors.lastname: Civinini
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects* / Q000379:methods; D017760:Bone Malalignment / Q000209:etiology* / Q000601:surgery; D015331:Cohort Studies; D005260:Female; D005270:Femur Head / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D005500:Follow-Up Studies; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000503:physiopathology; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D011474:Prosthesis Design; D011475:Prosthesis Failure; D011859:Radiography; D016059:Range of Motion, Articular / Q000502:physiology*; D012086:Reoperation / Q000009:adverse effects / Q000379:methods; D012189:Retrospective Studies; D018570:Risk Assessment; D013997:Time Factors; D016896:Treatment Outcome
keywords: Femoral stem; Joint Line; Offset stem; Total knee revision