Does new instrumentation improve radiologic alignment of the Oxford® medial unicompartmental knee arthroplasty?
BACKGROUND
A new instrument system has been introduced to improve the accuracy and reproducibility of implant positioning in Oxford® unicompartmental knee arthroplasty (UKA). This study aimed to determine if the new instrumentation could improve postoperative implant positioning and limb alignment, and reduce the occurrence of outliers in Oxford® UKA.


METHODS
A total of 77 cases of Oxford® UKA with the new instrumentation were included. Individual matching for the conventional instrument group was performed according to age, sex, and body mass index. Postoperative radiological variables, including the hip-knee-ankle angle and the varus/valgus and flexion/extension angles of the femoral and tibial implants, were measured and compared between the new instrumentation group and the conventional group. The outliers in implant positions and postoperative complications were also compared.


RESULTS
No significant between-group differences were observed in terms of lower limb alignment and tibial implant alignment. However, statistically significant differences were identified in the varus/valgus and flexion/extension angles of the femoral implant (P=0.01 and P<0.001, respectively). More outliers were observed in the flexion/extension angles of the femoral and tibial implants in the new instrumentation group. Eight meniscal bearing dislocations and three lateral compartmental degenerative changes were found in the conventional group, while there were two meniscal bearing dislocations in the new instrumentation group during the study period.


CONCLUSIONS
The present study did not confirm any benefit of the new instrument system in terms of postoperative limb alignment, positioning of the implant, or reducing outliers beyond the use of the conventional instruments.
Department of Orthopaedic Surgery, Anam Hospital, Korea University College of Medicine, Seoul, South Korea.
Ki-Mo
KM
Jang
Department of Orthopaedic Surgery, Seoul Barunsesang Hospital, Seoul, South Korea.
Hong Chul
HC
Lim
Department of Orthopaedic Surgery, Anam Hospital, Korea University College of Medicine, Seoul, South Korea.
Seung-Beom
SB
Han
Department of Orthopaedic Surgery, Guro Hospital, Korea University College of Medicine, Seoul, South Korea.
Chandong
C
Jeong
Department of Orthopaedic Surgery, Anam Hospital, Korea University College of Medicine, Seoul, South Korea.
Seul-Gi
SG
Kim
Department of Orthopaedic Surgery, Guro Hospital, Korea University College of Medicine, Seoul, South Korea. Electronic address: osman@korea.ac.kr.
Ji-Hoon
JH
Bae
D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation*; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000601:surgery; D007720:Knee Prosthesis; D008297:Male; D020370:Osteoarthritis, Knee / Q000601:surgery; D012189:Retrospective Studies
Knee; Medial compartmental osteoarthritis; Microplasty instrumentation; Oxford® knee replacement; Unicompartmental knee arthroplasty