title: The implications of mechanical alignment on soft tissue balancing in total knee arthroplasty.
abstract: OBJECTIVE
  We hypothesized that the individual bone geometry is the most important variable to achieve acceptable soft tissue balancing during total knee arthroplasty.
  
  
  METHODS
  Long-standing 3-foot films and computer navigation data from 90 patients with varus (n = 45) or valgus deformity (n = 45) were utilized who underwent navigated total knee arthroplasty. Mean age was 65 ± 8 years with 50 women and 40 men. Hip-knee-ankle angle (HKA) was measured and ranged from 23° varus to 21.5° of valgus. Three additional measurements were made: lateral distal femoral angle (DFA), the intraarticular angle (IAA), and the medial proximal tibial angle (PTA). Intra-operative computer navigation data were obtained. Knees were then stressed with both a maximum varus/valgus moment in 10° flexion. Values were compared with the angle measurements of 3-foot films. Maximum varus/valgus measurements were correlated with HKA for both varus and valgus knees.
  
  
  RESULTS
  Varus knees: Mean HKA measured 9° ± 5°, and the maximum varus stress measured intraoperatively was 12° ± 4°. The mean DFA, PTA, and IAA were 88° ± 2.5°, 84° ± 3.4°, and 4.5° ± 2.5°, respectively. If the HKA was <10°, the deformity was correctable in (16/26) 61 % of cases. Positive correlation exists between the HKA, and maximal varus stress obtained intraoperatively (r = 0.75, p < 0.0001). IAA correlated with increasing HKA (r = 0.80, p < 0.0001). Mean IAA was significantly greater in the varus than valgus group (4.5 ± 2.6 vs 3.2 ± 2.4, respectively, p = 0.01). Valgus knees: Mean HKA measured was 9.4° ± 4°. The mean DFA, PTA, and IAA were 83° ± 2°, 89.5° ± 2°, and 3.2° ± 2.4°, respectively. If the HKA was more than 10°, maximal varus stress of the knee was able to correct the valgus deformity (15/22) 68 % of the time. If the HKA was <10°, the deformity was correctable in (21/23) 91 % of cases. Positive correlation exists between the HKA and maximal valgus stress examination (r = 0.74, p < 0.0001). There was a positive correlation of IAA with increasing HKA (r = 0.61, p < 0.0001). Mean flexion contracture for varus knees was 6.3° ± 6.9° compared with 0.8° ± 7.6° in the valgus group (p = 0.0004).
  
  
  CONCLUSIONS
  These data suggest that soft tissues play more of a role in the varus knee deformity than they do in the valgus knee and that the bony contribution may be the main contributing factor to the overall deformity of the valgus knee.
  
  
  METHODS
  IV.
authors.affiliation: Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA. donaldhohman@gmail.com.
authors.forename: Donald W
authors.initials: DW
authors.lastname: Hohman
authors.affiliation: Department of Orthopaedic Surgery, SUNY at Buffalo School of Medicine and Biomedical Sciences, State University of New York at Buffalo, Buffalo, NY, USA.
authors.forename: Scott R
authors.initials: SR
authors.lastname: Nodzo
authors.affiliation: Department of Orthopaedic Surgery, SUNY at Buffalo School of Medicine and Biomedical Sciences, State University of New York at Buffalo, Buffalo, NY, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Phillips
authors.affiliation: Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Wofgang
authors.initials: W
authors.lastname: Fitz
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D005269:Femur / Q000473:pathology / Q000601:surgery; D006615:Hip / Q000473:pathology; D006801:Humans; D007719:Knee Joint / Q000473:pathology* / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000473:pathology* / Q000601:surgery*; D016059:Range of Motion, Articular; D013977:Tibia / Q000473:pathology / Q000601:surgery
keywords: Knee arthroplasty; Ligament balance varus knee; Navigation; Soft tissue balancing; Valgus knee