title: The coronal hypomochlion: a tipping point of clinical relevance when planning valgus producing high tibial osteotomies.
abstract: OBJECTIVE
  In patients undergoing medial opening wedge high tibial osteotomy (MOWHTO), soft tissue opening on the medial side of the knee is difficult to predict. When the load bearing axis is corrected beyond a certain point, the knee joint tilts open on the medial side. We therefore hypothesised that there is a tipping point and defined this as the coronal hypomochlion.
  
  
  METHODS
  In this prospective study of 150 navigated MOWHTOs (144 consecutive patients), data were collected before surgery and at three months post-operatively. In order to calculate the hypomochlion, we compared the respective changes to the joint line convergence angle (JLCA) with the post-operative axis of the leg. The change to the medial proximal tibial angle accounts for only about 80% of the change to the femorotibial angle; 20% of the correction can therefore be attributed to non-osseous, soft-tissue changes.
  
  
  RESULTS
  We were able to demonstrate a linear change of JLCA in a range of 0° to 5° of valgus which started when the post-operative long-leg axis was corrected beyond 2° of valgus.
  
  
  CONCLUSIONS
  We found that the coronal hypomochlion occurs at 2° of valgus.
  
  
  CONCLUSIONS
  It is recommended to plan realignment for medial open wedge high tibial osteotomy at a maximum of 2° valgus. Cite this article: Bone Joint J 2016;98-B:628-33.
authors.affiliation: Gelenkzentrum Rhein-Main, Wilhelmstr.30, 65193 Wiesbaden, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Heijens
authors.affiliation: Dr. Horst Schmidt Kliniken, Ludwig-Erhardt Str. 100, 65199 Wiesbaden, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Kornherr
authors.affiliation: Gelenkzentrum Rhein-Main, Wilhelmstr.30, 65193 Wiesbaden, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Meister
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000601:surgery; D010027:Osteotomy / Q000379:methods*; D011446:Prospective Studies; D013977:Tibia / Q000601:surgery*; D016474:Weight-Bearing; D055815:Young Adult
keywords: HTO; Hypomochlion; Navigation