Evaluation of soft-tissue balance during total knee arthroplasty

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1 Journal of Orthopaedic Surgery 2010;18(1):26-30 Evaluation of soft-tissue balance during total knee arthroplasty Hideyuki Sasanuma, Hitoshi Sekiya, Kenzo Takatoku, Hisashi Takada, Naoya Sugimoto Department of Orthopedics, Jichi Medical University, Tochigi, Japan ABSTRACT Purpose. To evaluate soft-tissue balance during versus after total knee arthroplasty (TKA). Methods. 18 men and 7 women aged 2 to 8 (mean, 68) years who had moderate-to-severe varus deformity underwent TKAs using the Scorpio non-restrictive geometry posterior-stabilised system (Stryker Howmedica Osteonics; Allendale, [NJ], USA). All surgeries were performed by a single surgeon using the medial parapatellar approach. After the bony and soft-tissue procedures, soft-tissue balance was measured intra-operatively using a tensor/balancer device. The coronal laxity angles between the cut surfaces of the femur and tibia were measured at 0º (in extension) and 90º (in flexion). The central gap was also measured. Immediate postoperative softtissue balance was measured using an arthrometer, while anteroposterior stress radiographs were being taken. A valgus or varus force was applied just above the knee on the lateral or medial side, with the knee counter-supported and at 1º flexion. Results. Intra-operatively, the mean coronal laxity at 0º (in extension) and 90º (in flexion) was 2.1º and -1.6º, and the mean central gaps were 21.2 and 23. mm, respectively. Immediate postoperative mean coronal laxity was 2.9º, indicating that lateral laxity was greater than medial laxity. The postoperative coronal laxity was positively corrected to the intra-operative coronal laxity at 0º (r=0.304, p=0.003), but not to the intra-operative coronal laxity at 90º (r= 0.07, p=0.47). Conclusion. Slightly greater lateral laxity was observed after TKA, although equal medial-lateral balance was achieved intra-operatively. Key words: arthoroplasty, replacement, knee; knee prosthesis INTRODUCTION Knee prosthesis designs that enable deep flexion have shown good outcomes. 1 3 In a posterior-stabilised total knee arthroplasty (TKA), poor soft-tissue balance throughout the range of motion may result in postoperative instability and early implant failure. 4, At least 20% of early revision surgical procedures Address correspondence and reprint requests to: Dr Hideyuki Sasanuma, Department of Orthopedics, Jichi Medical University, Yakusjiji, Shimotsuke, Tochigi, , Japan. sasakou@pop12.odn.ne.jp

2 Vol. 18 No. 1, April 2010 Evaluation of soft-tissue balance during total knee arthroplasty 27 were related to postoperative instability. 6,7 Soft-tissue balance is mainly judged by the surgeon subjectively, and not by objective means. Intra-operative evaluation of soft-tissue balance using a quantitative technique with balancers 8 11 to equalise the medial and lateral gaps has been advocated. 4,12,13 Most TKAs for varus knees use a medial approach to dissect the medial side of fascia, patellar retinaculum, and joint capsule. The medial structures thus become less tense than lateral structures. In addition, the gaps are usually measured with the patella everted or laterally shifted. This makes the lateral structures tighter and may preclude accurate evaluation of soft-tissue balance. 14,1 Good soft-tissue balance means equal mediolateral coronal laxity and no excessive laxity after suturing the fascia and skin, and deflating the tourniquet. Because of the effect of soft-tissue repair and patellar positioning, accurate soft-tissue balance can only be measured postoperatively. We therefore aimed to correlate measurement of soft-tissue balance during TKA using a tensor/balancer versus after TKA using an arthrometer on stress radiographs. Figure 1 The tensor/balancer measures the gap in the centre of the device and inclination angle formed between 2 blades. The tension applied between the blades is controllable. MATERIALS AND METHODS From August 2004 to June 2006, 18 men and 7 women aged 2 to 8 (mean, 68) years underwent 93 TKAs for osteoarthritis (n=9) or rheumatoid arthritis (n=34) using the Scorpio non-restrictive geometry posterior-stabilised system (Stryker Howmedica Osteonics; Allendale, [NJ], USA). The mechanical axis of the knee was measured on a standing, weightbearing, anteroposterior radiograph. All patients had moderate-to-severe varus deformity, with the mean being 16º (standard deviation [SD], 7º; range, º 39º) varus. All surgeries were performed by a single surgeon under epidural or general anaesthesia with femoral nerve block and using the medial parapatellar approach. Soft-tissue release was performed based on step-by-step measurements of soft-tissue balancing. 16 The posterior cruciate ligament was removed, and then the medial collateral ligament and the semimenbranosus were separated (approximately 3 cm from the proximal tibia). The femur was osteotomised using the independent cutting manner. Rotational positioning of the femoral component was determined by the transepicondylar axis and the Whiteside line. The cutting line was parallel to the transepicondylar line and was generally perpendicular to the Whiteside line. The proximal tibia was osteotomised perpendicular to the tibial Figure 2 Measurement of intra-operative coronal laxity at 0º (extension) and (b) 90º (flexion). shaft, with the posterior tibial slope being º. After the size of the tibial component was determined, excessive medial osteophytes were resected and the soft-tissue balance measured. When the medial structures remained tight, the superficial medial collateral ligament was released in a stepwise manner. Femoral and tibial components were fixed with bone cement. Intra-operatively, the soft-tissue balance was measured using a tensor/balancer device (Fig. 1). 8,10,11 The tension applied between the blades of the tensor/

3 28 H Sasanuma et al. Journal of Orthopaedic Surgery (b) Figure 3 Measurement of immediate postoperative coronal laxity: valgus and (b) varus angle. balancer was controllable. The patella was shifted laterally and an opening force (18 kg) was applied to the cut surfaces of the femur and tibia. The coronal laxity angles between the cut surfaces of the femur and tibia were measured at 0º (in extension) and 90º (in flexion) [Fig. 2]; positive/negative angles indicated that the medial gap was smaller/greater than the lateral gap. The central gap was also measured. Immediate postoperative soft-tissue balance was measured using an arthrometer while anteroposterior stress radiographs were being taken. 7,17,18 A valgus or varus force (7 kg) was applied just above the knee on the lateral or medial side, with the knee countersupported and at 1º flexion. The coronal laxity subtraction of the angles (between the surfaces of the femoral and tibial components) under valgus and varus stress was measured (Fig. 3); positive/ negative values indicated that lateral laxity was larger/smaller than medial laxity. Correlations between intra- and post-operative coronal laxity were determined using simple correlation and linear regression analyses. A p value of <0.0 was considered statistically significant. RESULTS Intra-operatively, the mean coronal laxity at 0º (in extension) and 90º (in flexion) was 2.1º (SD, 3.7º) and -1.6º (SD, 4.9º), with the mean central gap being 21.2 (SD, 2.7) mm and 23. (SD, 3.8) mm, respectively. Immediately after the operation, the mean varus and valgus angles were.8º (SD, 3.3º) and 2.9º (SD, 2.8º), respectively, and therefore the mean coronal laxity was 2.9º (SD, 2.9º), indicating that lateral laxity was greater than medial laxity. Immediate postoperative coronal laxity (Y) correlated positively with intraoperative coronal laxity at 0º (X) [r=0.304, p=0.003, Fig. 4]. The correlation equation between the 2 variables was Y=0.421X In contrast, immediate postoperative and intra-operative coronal laxity at 90º did not correlate (r= 0.07, p=0.47, Fig. 4). DISCUSSION Good soft-tissue balance in both extension and flexion enables long-term stability after TKA. Rectangular gaps are difficult to achieve in TKA, and only 47% to 7% of TKAs achieve a mediolateral difference of 1 mm. 12,19 Slightly greater laxity in the lateral than medial side may be acceptable because even normal knees have unbalanced soft-tissue tension. 12,19 Lateral laxity of the knee joint has been demonstrated in cadaveric knees 20 and stress magnetic resonance images. 21 Greater laxity in the lateral side was important in TKAs, because equal tension on both sides impaired smooth axial tibial rotation in flexion. 22 In severely deformed knees, good intra-operative soft-tissue balance in both flexion and extension is difficult to achieve. 7 The use of a balancer is recommended for objective measurement of gaps and balance during TKA. The difference between the flexion and extension gaps should not exceed 3 mm. 8 However, measurements using such a balancer were usually performed with the patella everted or laterally shifted and the soft tissue unsutured, which may affect the accuracy of soft-tissue balance.

4 Vol. 18 No. 1, April 2010 Evaluation of soft-tissue balance during total knee arthroplasty 29 Immediate postoperative coronal laxity (Y) Intra-operative coronal laxity at 0º (X) (b) Immediate postoperative coronal laxity (Y) Intra-operative coronal laxity at 0º (X) Figure 4 Immediate postoperative coronal laxity (Y) correlates positively to intra-operative coronal laxity at 0º (extension) [X] (r=0.304, p=0.003). The correlation equation between the 2 variables is Y=0.421X (b) There is no correlation between immediate postoperative and intra-operative coronal laxity at 90º (flexion) [r= 0.07, p=0.47]. A new tensor device was developed to measure intra-operative soft-tissue balance throughout the range of motion. In flexion, the gap was smaller with the patella in a reduced position than it was in eversion. 9 Nonetheless, the measurement was not performed with the fascia and skin sutured and after tourniquet release; accurate soft-tissue balance was difficult to achieve. In a study using an arthrometer for postoperative balance, about 4º of lateral instability may be favourable, but the intra-operative balance was not mentioned. 17,18 In our study, the postoperative inclination angle on stress radiographs was positively corrected with the intra-operative inclination angle at 0º (in extension). Postoperative balance was characterised by slightly greater lateral laxity even when good medial-lateral balance was achieved intra-operatively. This may be due to the relatively tense lateral structures, the unsutured medial soft tissues, and the laterally shifted or everted patella. Although immediate postoperative lateral laxity was greater than medial laxity, this could decrease gradually in the following 3 months and result in good coronal alignment. 10 Our study has limitations. Postoperative coronal laxity was measured at 1º flexion, which was fairly close to extension. Other methods should be used to evaluate the coronal laxity in flexion. 21 Anaesthesia may have influenced the postoperative varus or

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