Association between anteroposterior laxity in mid-range flexion and subjective healing of instability after total knee arthroplasty.
OBJECTIVE
Flexion instability following total knee arthroplasty (TKA) is a common indication of early revision. The association between the objective anteroposterior (AP) laxity direction in mid-range flexion and the subjective healing of instability remains unclear; thus, this study aimed to clarify this association.


METHODS
In this study, 110 knees (74 females, 92 knees; 16 males, 18 knees) with medial pivot implants were examined with a median age of 79 (range 60-92) years for a median follow-up duration of 22 (range 6-125) months. AP laxity was measured using a KT-1000 arthrometer. Self-reported knee instability score was used for the subjective healing of instability.


RESULTS
Eighty-seven knees did not feel unstable (Group 0), whereas 23 knees felt unstable (Group 1). There was a significant difference in AP displacement [Group 0: median 6 mm; range 2-15 mm and Group 1: median 8 mm; range 4-14; p < 0.0001]. The threshold value of 7 mm was determined using the area under receiver operating characteristic curve of 0.79 [95% confidence interval (CI) 0.69-0.88, p < 0.0001]. In multivariate analysis, AP displacement of ≥7 mm was an independent risk factor for feelings of instability (odds ratio 7.695; 95% CI 2.306-25.674; p = 0.001).


CONCLUSIONS
AP laxity of ≥7 mm represents a known cause of feelings of instability. By controlling AP laxity in TKAs, without stiffness in the knee, it is possible to prevent feelings of instability. The clinical relevance is that AP laxity of <7 mm is one of the target areas in TKA.


METHODS
IV.
Department of Orthopedic Surgery, Department of Regenerative and Transplant Medicine, Graduate School of Medical and Dental Science, Niigata University, 1-757 Asahimachi-dori Chuo-ku, Niigata City, Niigata, 951-8510, Japan. tommochi121710@gmail.com.
Tomoharu
T
Mochizuki
Department of Orthopedic Surgery, Department of Regenerative and Transplant Medicine, Graduate School of Medical and Dental Science, Niigata University, 1-757 Asahimachi-dori Chuo-ku, Niigata City, Niigata, 951-8510, Japan.
Osamu
O
Tanifuji
Department of Orthopaedic Surgery, Niigata Medical Center, Niigata, Japan.
Takashi
T
Sato
Department of Orthopedic Surgery, Department of Regenerative and Transplant Medicine, Graduate School of Medical and Dental Science, Niigata University, 1-757 Asahimachi-dori Chuo-ku, Niigata City, Niigata, 951-8510, Japan.
Hiroki
H
Hijikata
Department of Orthopedic Surgery, Department of Regenerative and Transplant Medicine, Graduate School of Medical and Dental Science, Niigata University, 1-757 Asahimachi-dori Chuo-ku, Niigata City, Niigata, 951-8510, Japan.
Hiroshi
H
Koga
Department of Orthopaedic Surgery, Niigata Medical Center, Niigata, Japan.
Satoshi
S
Watanabe
Department of Orthopaedic Surgery, Tsuruoka Municipal Shonai Hospital, Niigata, Japan.
Yukimasa
Y
Higano
Department of Orthopaedic Surgery, Nagaoka Chuo General Hospital, Niigata, Japan.
Akihiro
A
Ariumi
Department of Orthopaedic Surgery, Niigata Prefectural Central Hospital, Niigata, Japan.
Takayuki
T
Murayama
Department of Orthopaedic Surgery, Saiseikai Niigata Daini Hospital, Niigata, Japan.
Hiroshi
H
Yamagiwa
Department of Orthopedic Surgery, Department of Regenerative and Transplant Medicine, Graduate School of Medical and Dental Science, Niigata University, 1-757 Asahimachi-dori Chuo-ku, Niigata City, Niigata, 951-8510, Japan.
Naoto
N
Endo
D000368:Aged; D000369:Aged, 80 and over; D053587:Arthrometry, Articular; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects*; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology* / Q000601:surgery*; D007717:Knee / Q000503:physiopathology / Q000601:surgery; D007719:Knee Joint / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000503:physiopathology / Q000601:surgery*; D016059:Range of Motion, Articular; D012307:Risk Factors; D014945:Wound Healing
Anteroposterior laxity; Mid-flexion instability; Subjective healing of instability; Total knee arthroplasty