Knee Surg Sports Traumatol Arthrosc DOI 10.1007/s00167-014-3381-y

KNEE

Decreased extension gap and valgus alignment after implantation of total knee prosthesis in primary varus knees Yukihide Minoda · Shigeru Nakagawa · Ryo Sugama · Tessyu Ikawa · Takahiro Noguchi · Masashi Hirakawa · Yoshio Matsui · Hiroaki Nakamura 

Received: 14 March 2014 / Accepted: 9 October 2014 © European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2014

Abstract  Purpose  It was hypothesised that implantation of a total knee prosthesis may change the size and shape of the joint gap. To test this hypothesis, a tensor device was used which was specifically designed to reproduce the conditions before and after implantation, including attachment of the polyethylene insert trial. This study aimed to compare the joint gaps before and after implantation of a total knee prosthesis using this new tensor device. Methods  A total of 259 primary varus knees were included in this study. Knees were exposed using a medial parapatellar approach, and the anterior and posterior

Y. Minoda (*) · H. Nakamura  Department of Orthopaedic Surgery, Osaka City University Graduate School of Medicine, 1-4-3 Asahi-machi Abeno-ku, Osaka 545-8585, Japan e-mail: [email protected] S. Nakagawa · Y. Matsui  Department of Orthopaedic Surgery, Osaka Rosai Hospital, 1179-3 Nagasone-cho Kita-ku Sakai, Osaka 591-8025, Japan R. Sugama  Department of Orthopaedic Surgery, Osaka General Hospital, 3-1-56 Mandaihigashi Sumiyoshi-ku, Osaka 558-8558, Japan T. Ikawa  Hanwa Joint Reconstruction Center, 3176 Fukaikitamachi Naka-ku Sakai, Osaka 599-8271, Japan T. Noguchi  Department of Orthopaedic Surgery, Shinbeppu Hospital, 3898 Tsurumi Beppu, Oita 874-0833, Japan M. Hirakawa  Department of Orthopaedic Surgery, Oita University Faculty of Medicine Graduate School of Medicine, 1-1 Idaigaoka Hazama-cho Yufu, Oita 879-5593, Japan

cruciate ligaments were resected. After the trial reduction, the intraoperative joint gap kinematics was measured using the tensor device. Results  Implantation of a total knee prosthesis decreased the size of the extension joint gap and made it valgus, but did not influence the size or shape of the flexion joint gap. Conclusions  The present findings suggest that the classical gap technique, which creates equal and rectangular extension and flexion joint gaps in the bone cutting surface, results in an imbalance between the extension and flexion joint gaps after implantation. To achieve equal and rectangular extension and flexion joint gaps after implantation, the prepared extension joint gap should be about 2 mm larger than the flexion joint gap and slightly varus before implantation in primary varus knees. Level of evidence  Therapeutic study, Level II. Keywords  Total knee arthroplasty · Joint gap before implantation · Joint gap after implantation

Introduction Soft tissue balancing of the knee is fundamental to the success of total knee arthroplasty (TKA) [17, 18]. Preparing equal and rectangular extension and flexion joint gaps before implantation is thought to be one of most important goals for TKA because it facilitates functional restoration of the knee [3–5, 14, 15]. However, implantation of a total knee prosthesis might change the size and shape of the joint gap. If so, the classical operative technique, which creates equal and rectangular extension and flexion joint gaps in the bone cutting surface, will result in an imbalance between the extension and flexion joint gaps after implantation. Previous studies that used a tensor device

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with femoral component trial insertion did not truly represent the joint gap after implantation because the tensor device could not be attached to the polyethylene insert and thus could not account for the shape of the articulating surface [1–3, 7–13, 19]. To address this problem, a new tensor device capable of being attached to the polyethylene insert trial was developed [6, 10]. This tensor device can reproduce the joint gap kinematics after implantation of femoral, tibial, and patellar components and has the same shape as a total knee prosthesis. The hypothesis in this study is that implantation of a total knee prosthesis changes the size and shape of the joint gap. The aim of this study was to compare the joint gaps before and after implantation of a total knee prosthesis using the new tensor device, and to reveal the joint gap before implantation that results in equal and rectangular extension and flexion joint gaps after implantation.

Materials and methods From 2009 to 2010, 280 consecutive primary TKAs were performed using a mobile-bearing posterior-stabilised TKA (Vanguard RP; Biomet Japan Inc., Tokyo, Japan). In this study, patients with primary varus osteoarthritis were included. Patients with valgus osteoarthritis (9 knees), rheumatoid arthritis (3 knees), osteonecrosis (3 knees), and incomplete intraoperative measurement data (6 knees) were excluded. A total of 259 knees were evaluated. The preoperative demographic data of the patients are shown in Table  1. Anteroposterior radiographs of the lower extremity with the subject in a standing position were taken using a long film preoperatively and within 3 weeks postoperatively. The anatomical axis and mechanical axis were measured (Table 1). Table 1  Patients’ demographic data Parameter

Mean (SD)

Age (years) Male; female Height (cm) Body weight (kg)

76.3 (6.7) 46; 213 151 (10) 60 (11)

Knee society score Knee score Function score Extension angle (°) Flexion angle (°) Preoperative anatomical axis (°) Postoperative anatomical axis (°) Preoperative mechanical axis (°)

33.5 (16.4) 41.1 (19.9) −10 (8) 125 (14) 5.5 (5.3) varus 5.3 (2.2) valgus 12.6 (5.8) varus

Postoperative mechanical axis (°)

1.0 (2.7) varus

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All procedures were performed using the same surgical technique, which was previously published as the modified gap-balancing technique [10]. The knees were exposed using a medial parapatellar approach, and the anterior and posterior cruciate ligaments were resected. After the trial reduction, the intraoperative joint gap kinematics was measured with the new tensor device (True Tensor; Biomet Japan Inc., Tokyo, Japan). The tensor device consisted of three parts: an upper seesaw plate, lower platform plate, and extra-articular main body (Fig. 1a). The upper plate contained a peg to set the mobilebearing polyethylene insert trial, which could be selected from various sizes and could freely rotate on the upper plate. The upper plate could also attach a 9-mm-thick metal block of equal thickness to the distal and posterior parts of the femoral component. The lower plate had two holes, which allowed the tensor device to be fixed to the tibia with two small-headed pins. The pin holes were located to allow fixation of the tensor device in the same position as the tibial component. Two pins and the foot of the device firmly fixed the body of the tensor device to the tibia (Fig. 1b). The arm between the plate and the main body was designed to allow for reduction of the patellofemoral joint. These design features reproduced the joint kinematics after implantation of the components. Interobserver and intraobserver variabilities with 20 subjects have previously been reported [10]. The mean absolute values of the differences between two repeated measurements by one observer were 0.2 mm (95 % confidence interval, −0.1 to 0.4 mm) and 0.1° (95 % confidence interval, −0.2° to 0.4°). The mean absolute values of the differences between two observers were 0.4 mm (95 % confidence interval, 0.1– 0.6 mm) and 0.2° (95 % confidence interval, −0.1° to 0.4°). Joint gap before implantation (bone joint gap) After the trial components were removed, the joint gap was measured at 0° of extension and 90° of flexion with 120 N of distraction force. The 9-mm-thick metal block was set on the upper plate of the tensor device. The size (mm) and tilt angle (°) of the joint gap between the lower part of the 9-mm-thick metal block and the tibial cutting surface, excluding the thickness of the femoral component (9 mm), defined the bone joint gap (Fig. 2a). The bone joint gap described the joint gap between the femoral and tibial cutting surfaces before implantation. Asao et al. [1] measured soft tissue tension after trial reduction with the relevant thickness of the insert. When the expert surgeon was sure that proper soft tissue tension was being applied, the mean distraction force was measured, giving 126.8 ± 23.6 N in extension and 120.7 ± 22.7 N in flexion. These values were similar to those in another TKA study [19]. A force of 120 N was subsequently applied to the tension device as the standard distraction force for all measurements [6].

Knee Surg Sports Traumatol Arthrosc

Fig.  1  a Photographs showing the tensor device for measurement of the implant joint gap. It consists of 3 parts: an upper plate (A), a lower platform plate (B), and an extra-articular main body (C). The upper plate has a peg to set the mobile-bearing insert trial on it. The 2 plates are connected to the extra-articular main body by the offset connection arm (D) through a medial parapatellar arthrotomy, which allows for the reduction of the patellofemoral joint while performing

measurements. The insert trial can be select from various sizes. b The lower plate has 2 pin holes to fix the tensor device to the tibia with 2 small-headed pins (arrows). This device also has a “foot” to prevent the anterior tilt due to the weight of the tensor device itself (double arrows). The length of the foot can be adjusted to fit the anterior tibial shaft. Tow pins and the foot firmly fixed the body of the tensor device to the tibia

Fig. 2  The schema of the joint was shown. a The centre size (mm) (A) and tilt angle (°) (B) of the joint gap between the femoral cutting surface and the tibial cutting surface were recorded as the bone joint gap. The 9-mm-thick metal block was set on the upper plate of the tensor device (Asterisk). Thus, the thickness of femoral component (Asterisk), which was 9 mm, has been subtracted. b The centre size (mm) (C) and tilt angle (°) (D) of the joint gap between the thinnest part of the polyethylene insert trial and tibial cutting surface were recorded as the implant joint gap

Joint gap after implantation (implant joint gap) A mobile-bearing polyethylene insert trial was set on the upper plate of the tensor device. Trials of the femoral and patellar components and the tensor device were set

in the knee joint. Subsequently, the patellofemoral joint was reduced, the quadriceps tendon was sutured with two stitches, and the joint gap was measured at 0° of extension and 90° of flexion with 120 N of distraction force. The size (mm) and tilt angle (°) of the joint gap between the upper

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Table 2  Bone joint gap (joint gap before implantation) and implant joint gap (joint gap after implantation) Status Extension Size (mm)

Bone joint gap (mean, SD)

p value

11.2 (1.4)

10.1 (1.3)

Decreased extension gap and valgus alignment after implantation of total knee prosthesis in primary varus knees.

It was hypothesised that implantation of a total knee prosthesis may change the size and shape of the joint gap. To test this hypothesis, a tensor dev...
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