title: Changes in patella tendon length over 5 years after different types of knee arthroplasty.
abstract: OBJECTIVE
  Post-operative shortening of the patellar tendon resulting in an abnormally low-lying patella has been described previously, but the degree of change in patella tendon length over time and extent of its progression after different types of knee arthroplasties remains unknown. This study assesses the incidence of patella tendon length change following lateral unicompartmental knee arthroplasty (UKA), medial UKA, and total knee arthroplasty (TKA), and its impact on patient-reported outcome at 5 years post-surgery.
  
  
  METHODS
  Immediate post-operative, 1- and 5-year radiographs were reviewed for 50 patients undergoing each operation (n = 150), with the Insall-Salvati ratio used as a measure of patella tendon length. Clinical outcome was assessed using the Oxford Knee Score (OKS).
  
  
  RESULTS
  At 5-year follow-up, no significant change in patella tendon length was found following medial UKA (1.07-1.05), whilst a significant shortening was found after TKA (1.02-0.96), and a significant lengthening found after lateral UKA (1.02-1.05). For the UKA groups, no further change in tendon length was observed after the first year post-surgery, whereas the TKA group continued to shorten between years one and five. OKS was significantly better in the UKA groups as compared to TKA group. Change in patella tendon length within individual groups did not correlate with OKS at 5 years.
  
  
  CONCLUSIONS
  Patella tendon length shortening is more prevalent in TKAs, whilst lengthening is more prevalent in lateral UKAs. Despite the vertical incision through the patella tendon, lateral UKAs do not cause increased tendon shortening at 5 years post-surgery. However, in the medium term, changes in patella tendon length do not affect patient-reported outcome.
  
  
  METHODS
  Retrospective, comparative study, Level III.
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK. gareth.davies@wadh.ox.ac.uk.
authors.forename: Gareth Sion
authors.initials: GS
authors.lastname: Davies
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK.
authors.forename: Ben
authors.initials: B
authors.lastname: van Duren
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK.
authors.forename: Matthew
authors.initials: M
authors.lastname: Shorthose
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK.
authors.forename: Patrick Garfjeld
authors.initials: PG
authors.lastname: Roberts
authors.affiliation: Royal Berkshire Hospital, Reading, UK.
authors.forename: John R
authors.initials: JR
authors.lastname: Morley
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Monk
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK.
authors.forename: David W
authors.initials: DW
authors.lastname: Murray
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK.
authors.forename: Hemant G
authors.initials: HG
authors.lastname: Pandit
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects* / Q000379:methods*; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000601:surgery; D008297:Male; D008875:Middle Aged; D017847:Patellar Ligament / Q000000981:diagnostic imaging* / Q000637:transplantation*; D011183:Postoperative Complications / Q000000981:diagnostic imaging*; D011859:Radiography; D012189:Retrospective Studies
keywords: Domed lateral UKA; Insall–Salvati ratio; Lateral unicompartmental knee arthroplasty; PTL; Patella alta; Patella baja; Patella infera; Patella tendon length; Total knee arthroplasty; Total knee replacement