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The Change of Tibial Joint Line with The Change of Posterior Tibial Slope in Total Knee Arthroplasty
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Yoshikazu Tsuneizumi1, Tadashi Tsukeoka1, Kensuke Yoshino1
Department of Orthopedic Surgery, Chiba Rehabilitation Center, Chiba city, Japan
Disclosures: Yoshikazu Tsuneizumi (N), Tadashi Tsukeoka (N), Kensuke Yoshino (N)
INTRODUCTION: There are some reports that posterior tibial slope (PTS) affects both the flexion angle after surgery and the ligament tension in total
knee arthroplasty (TKA). As PTS increases, the quantity of bone excision of the posterior tibia increases, and joint line (JL) of the posterior tibia falls down.
And influence on flexion gap occurs. I calculated how JL of the posterior tibia changed by the change of the PTS in some kinds of manufactures and each
sizes.
METHODS: It is supposed that a stylus is put on the center part of lateral tibial plateau, and tibial osteotomy is removed surgically with a fixed quantity.
The angle of PTS will be changed as the support point at central part of lateral tibial plateau. The length between anterior border and posterior border on
tibial plate was defined as APL (figure 1). And the angle of PTS was defined θ. The change of JL at the posterior border of the plate [A] from 0 degree of
PTS is calculated in 1/2APL × sin θ, and the change of JL at plate rear 1/4 [B] is half of [A] (figure 1-a). In addition, when 2 degrees slope osteotomy was
added after first tibial osteotomy, the change of JL was calculated as in figure (figure 1-b). That 2 degrees additional osteotomy was rotated around tibial
anterior border as the support point. Four kinds of manufactures were calculated. Four models are Vanguard (V), Persona (P), FINE (F), JournyII (J). Medial
AP length of plate was defined as APL of the plate which was asymmetry.
RESULTS: In implant model V, at the posterior border of tibial plate JL were changes of 1.1-1.3mm down in 3 degrees of PTS, 2.1-2.5mm in 6 degrees of
PTS, 3.6-4.2mm in 10 degrees of PTS (fig.2). The change at rear 1/4 became half of at the posterior border of tibial plate. Results of other models at the
posterior border were as follows, P (3 degrees: 1.2-1.4mm, 6 degrees: 2.3-2.8mm, 10 degrees 3.9-4.6mm), F (3 degrees: 1.1-1.4mm, 6 degrees: 2.2-2.8mm,
10 degrees 3.6-4.6mm), J (3 degrees: 1.1-1.4mm, 6 degrees: 2.1-2.8mm, 10 degrees 3.9-4.7mm). Changes of JL were approximately 0.4mm at posterior
border, and approximately 0.2mm at rear 1/4, per PTS change 1 degree. Changes of JL at three parts on tibial plate in a 2 degrees additional osteotomy
which was rotated around tibia anterior border as the support point were as follows; model V ( center part on tibial plate: 0.7-0.8mm, rear 1/4:1.0-1.2mm,
posterior border:1.3-1.6mm), model P( center part: 0.7-0.9mm, rear 1/4:1.1-1.3mm, posterior border: 1.5-1.8mm), model F( center part: 0.7-0.9mm, rear
1/4:1.0-1.3mm, posterior border: 1.4-1.7mm), model J( center part: 0.7-0.9mm, rear 1/4:1.0-1.3mm, posterior border: 1.3-1.8mm). Changes of JL at three
parts on tibial plate in a 2 degrees additional osteotomy were approximately 0.8 mm at center part and approximately 1.2mm at rear 1/4, approximately
1.5mm at posterior border.
DISCUSSION: There are many reports that PTS increase and flexion angle increase relate to with a cruciate retaining (CR)-TKA. And some reports
described correlation between PTS and flexion gap or tension of posterior cruciate ligament. Factors such as the anteroposterior movement of the contact
point by the slope, the state of the ligaments, kinematics are related complicatedly. And, amount of flexion gap cannot be explained by PTS only, but there
is the influence by the down of rear JL caused change of PTS. Because we could not find any report about amount of change of JL caused by changing of
PTS, I showed those values. In decision of quantity of PTS and tibia excision, it is necessary to make a plan in consideration of the JL change mentioned
above in pre-surgery. And, the reference to quantity of excision mentioned above may help to confirm additional slope angle in performing additional
osteotomy.
SIGNIFICANCE: Because we could not find any report about amount of change of tibial joint line (JL) caused by changing of posterior tibial slope (PTS)
in total knee arthroplasty, we showed those values. In decision of quantity of PTS and tibia excision, it is necessary to make a plan in consideration of the JL
change mentioned above in pre-surgery. And, the reference to quantity of excision mentioned above may help to confirm additional slope angle in
performing additional osteotomy.
IMAGES AND TABLES:
ORS 2017 Annual Meeting Poster No.1001