title: Patellar tendon length during knee flexion of meniscal-bearing and rotating total knee arthroplasty implants.
abstract: OBJECTIVE
  The length of the patellar tendon after total knee arthroplasty (TKA) has most commonly been compared with preoperative measurements. However, there are no reports that discuss changes in the length of the patellar tendon during knee flexion after TKA. The purpose of this study was to evaluate changes in the length of the patellar tendon during knee flexion and to clarify the impact of changes in patellar tendon strain on the length of the patellar tendon and post-operative range of motion (ROM) after TKA.
  
  
  METHODS
  Thirty-six patients undergoing sequential bilateral TKA for osteoarthritis were evaluated. Patients received a meniscal-bearing (MB) implant on one side and a rotating platform (RP) implant on the other and were followed for a median of 115 months (range 60-211 months). The lengths of the patellar tendon at maximum extension, 30°, 60°, 90° and maximum flexion were measured, and the post-operative ROM of both knees were assessed. The effects of implant design and the knee flexion angle on the length of the patellar tendon were analysed using a linear mixed-effects model. The relationship between patellar tendon strain and post-operative knee ROM was assessed using Pearson's correlation coefficients.
  
  
  RESULTS
  Post-operative clinical scores were similar for MB and RP implants. Neither the implant design nor the knee flexion angle significantly affected the length of the patellar tendon. The ROMs in the two designs at final follow-up were equivocal (114° in MB, 113° in RP). There was no correlation between patellar tendon strain and ROM in knees with either implant type.
  
  
  CONCLUSIONS
  Patellar tendon lengths after mobile-bearing TKA with implants that permitted different anteroposterior constraints were relatively constant at varying degrees of knee flexion. Differences in patellar tendon strain may not impact ROM. These results provide conclusive evidence that the quality of the patellar tendon may play a less important role in ROM after TKA.
  
  
  METHODS
  Therapeutic study, Level II.
authors: Ishii Orthopaedic and Rehabilitation Clinic, 1089 Shimo-Oshi, Gyoda, Saitama, 361-0037, Japan. ishii@sakitama.or.jp.
authors: Yoshinori
authors: Y
authors: Ishii
authors: Ishii Orthopaedic and Rehabilitation Clinic, 1089 Shimo-Oshi, Gyoda, Saitama, 361-0037, Japan.
authors: Hideo
authors: H
authors: Noguchi
authors: Ishii Orthopaedic and Rehabilitation Clinic, 1089 Shimo-Oshi, Gyoda, Saitama, 361-0037, Japan.
authors: Junko
authors: J
authors: Sato
authors: Ishii Orthopaedic and Rehabilitation Clinic, 1089 Shimo-Oshi, Gyoda, Saitama, 361-0037, Japan.
authors: Shota
authors: S
authors: Watanuki
authors: Division of Information Science and Biostatistics, Niigata University Graduate School of Medical and Dental Sciences, 1 Asahimachi Dori Niigata, Niigata, 951-8520, Japan.
authors: Shin-Ichi
authors: SI
authors: Toyabe
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology* / Q000601:surgery; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D017847:Patellar Ligament / Q000033:anatomy & histology*; D011184:Postoperative Period; D011446:Prospective Studies; D016059:Range of Motion, Articular
keywords: Bilateral total knee arthroplasty; Meniscal-bearing knee implant; Patellar tendon length; Patellar tendon strain; Postoperative range of motion; Rotating platform implant