title: Shorter survival rate in varus-aligned knees after total knee arthroplasty.
abstract: OBJECTIVE
  One long-held tenet of total knee arthroplasty (TKA) is that post-operative neutral limb alignment promotes implant durability. Recently, the concept of generic safe zone (0° ± 3°) has been challenged. This meta-analysis aimed to evaluate whether neutral alignment was superior to malalignment in long-term survival of TKAs.
  
  
  METHODS
  The MEDLINE, Embase, Cochrane Library, China National Knowledge Infrastructure, Wan Fang Chinese Periodical, Google and reference lists of all the included studies were searched. Of the 1512 studies initially identified, ten met the eligibility criteria, including eight case-control studies and two cohort trials. Relative risks of implant failure were compared between post-operative neutrally aligned and malaligned knees.
  
  
  RESULTS
  Post-operative malalignment showed higher failure rate of knee implants compared with neutral alignment (95 % CI 1.00-1.88, P = 0.05). Failure rate in knees with varus alignment was significantly higher than with neutral alignment (95 % CI 1.07-2.55, P = 0.02). There was no significant difference in the likelihood of implant failure between knees with valgus and neutral alignment (95 % CI 0.78-2.41, n.s.). No significant difference of failure rate was noted between neutral alignment and malalignment for fixed-bearing prothesis (95 % CI 0.94-1.95, n.s.) or rotating-platform prothesis (95 % CI 0.75-2.73, n.s.). There was no significant difference of failure rate between knees with neutral alignment and malalignment for studies with a mean follow-up of more than 10 years (95 % CI 0.81-2.01, n.s.) or studies using long-leg weight-bearing radiographs (95 % CI 0.79-1.79, n.s.).
  
  
  CONCLUSIONS
  Post-operative varus alignment results in shorter survival rate after TKA. Not only neutral limb alignment but also the valgus alignment promotes implant durability. Neutral or valgus alignment rather than varus alignment is essential to achieve long-term survival of TKAs and patient satisfaction.
  
  
  METHODS
  III.
authors.affiliation: Department of Orthopaedic Surgery, Second Affiliated Hospital of Wenzhou Medical University, 109, Xueyuanxi Road, Wenzhou, 325027, China. 474827623@qq.com.
authors.forename: Hai-Xiao
authors.identifier: http://orcid.org/0000-0003-4238-9184
authors.initials: HX
authors.lastname: Liu
authors.affiliation: Department of Rehabilitation, Second Affiliated Hospital of Wenzhou Medical University, 109, Xueyuanxi Road, Wenzhou, 325027, China.
authors.forename: Ping
authors.initials: P
authors.lastname: Shang
authors.affiliation: Department of Orthopaedic Surgery, Second Affiliated Hospital of Wenzhou Medical University, 109, Xueyuanxi Road, Wenzhou, 325027, China.
authors.forename: Xiao-Zhou
authors.initials: XZ
authors.lastname: Ying
authors.affiliation: Department of Orthopaedic Surgery, Second Affiliated Hospital of Wenzhou Medical University, 109, Xueyuanxi Road, Wenzhou, 325027, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000295:instrumentation* / Q000379:methods*; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000601:surgery; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D017060:Patient Satisfaction; D011183:Postoperative Complications / Q000000981:diagnostic imaging; D011475:Prosthesis Failure; D011859:Radiography
keywords: Alignment; Meta-analysis; Survival; Total knee arthroplasty; Valgus; Varus