title: Tibial component overhang following unicompartmental knee replacement--does it matter?
abstract: As implants are made in incremental sizes and usually do not fit perfectly, surgeons have to decide if it is preferable to over or undersize the components. This is particularly important for unicompartmental knee replacement (UKR) tibial components, as overhang may cause irritation of soft tissues and pain, whereas underhang may cause loosening. One hundred and sixty Oxford UKRs were categorised according to whether they had minor (<3 mm, 70%) or major (>or=3 mm, 9%) tibial overhang, or tibial underhang (21%). One year post surgery, there was no significant difference in outcome between the groups. Five years after surgery, those with major overhang had significantly worse Oxford Knee Scores (OKS) (p=0.001) and pain scores (p=0.001) than the others. The difference in scores was substantial (OKS=10 points). There was no difference between the 'minor overhang' and the 'underhang' group. We conclude that surgeons must avoid tibial component overhang of 3 mm or more, as this severely compromises the outcome. Although this study showed no difference between minor overhang or underhang, we would advise against significant underhang because of the theoretical risk of component subsidence and loosening.
authors.affiliation: Nuffield Orthopaedic Centre, Oxford, UK.
authors.forename: R
authors.initials: R
authors.lastname: Chau
authors.forename: A
authors.initials: A
authors.lastname: Gulati
authors.forename: H
authors.initials: H
authors.lastname: Pandit
authors.forename: D J
authors.initials: DJ
authors.lastname: Beard
authors.forename: A J
authors.initials: AJ
authors.lastname: Price
authors.forename: C A F
authors.initials: CA
authors.lastname: Dodd
authors.forename: H S
authors.initials: HS
authors.lastname: Gill
authors.forename: D W
authors.initials: DW
authors.lastname: Murray
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects*; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D010146:Pain / Q000209:etiology*; D010147:Pain Measurement; D011183:Postoperative Complications / Q000209:etiology*; D011859:Radiography; D013314:Stress, Mechanical; D013977:Tibia / Q000000981:diagnostic imaging / Q000473:pathology*; D016896:Treatment Outcome; D055815:Young Adult