Arch Orthop Trauma Surg DOI 10.1007/s00402-014-1938-3
Knee Arthroplasty
Effect of intraoperative weight‑bearing simulation on the mechanical axis in total knee arthroplasty M. Panzica · M. Kenawey · E. Liodakis · J. Brandes · C. Krettek · S. Hankemeier
Received: 4 April 2013 © Springer-Verlag Berlin Heidelberg 2014
Abstract Purpose Successful outcome after total knee arthroplasty (TKA) requires precise realignment of the mechanical axis. The intraoperative assessment of the mechanical axis is difficult. Intraoperatively, the effect of weight bearing on the lower limb mechanical axis is ignored. We developed a custom-made mechanical loading device to simulate weight-bearing conditions intraoperatively and analysed its effect on the mechanical axis during TKA. Methods Measurements of the mechanical axis were obtained during 30 consecutive primary TKAs in osteoarthritic patients using image-free knee navigation system. Half body weight was applied intraoperatively using our device to quantify the effect of intraoperative load application on the mechanical axis, thus receiving indirect information about soft tissue balancing. Furthermore, the intraobserver and interobserver reliability of navigated mechanical axis measurement with and without load was determined. Results Before TKA, mean mechanical axis was 4.0° ± 4.9° without load. Under loading conditions, the mean change of the mechanical axis was 2.1° ± 2.8°. Repetitive measurements of the senior surgeon and junior surgeon revealed a high intraobserver (ICC 0.997) and interobserver reliability (ICC 0.998). The registration of the mechanical axis without and with application of intraoperative loading demonstrated no significant differences during
M. Panzica (*) · M. Kenawey · E. Liodakis · J. Brandes · C. Krettek · S. Hankemeier Department of Trauma Surgery and Orthopaedic Surgery, Hannover Medical School, Carl‑Neuberg Str. 1, 30625 Hannover, Germany e-mail: panzica.martin@mh‑hannover.de
insertion of the trial components (SD 0.29 ± 0.29) and after the definitive component cementation (SD 0.63 ± 0.44). Conclusions Intraoperative quantification and analysis of the mechanical lower limb axis applying defined axial loading by our custom-made loading apparatus is reliable. Ligament stability was unbalanced before TKA and balanced after TKA. For TKA, intraoperative simulation of weight bearing may be helpful to quantify, control and correct knee stability and its influence of mechanical axis. Keywords Total knee arthroplasty · Navigation · Ligament balancing · Instability · Mechanical leg axis · Weight bearing
Introduction Soft tissue balancing and accurate restoration of mechanical limb alignment are key factors for successful implantation of TKA [1–3]. The balancing device and the use of trial components with application of varus and valgus stresses were popularised techniques for ligament balancing. Appropriate ligament balancing is strongly influenced by the surgeon’s individual feeling for knee laxity and stiffness. There is a lack of an objective definition of appropriate soft tissue balancing during implantation of TKA [4–8]. Malalignment can impair long-term results of TKA [13– 17]. Compared with conventional instrumentation of TKA, navigation systems improve the surgical accuracy at least in the frontal plane [9–11]. On the other hand, preoperative planning and the assessment of the mechanical axis are based on weight-bearing long-standing radiographs, while intraoperative implantation of TKA is performed under non-weight-bearing conditions. In a previous cadaveric
13
Arch Orthop Trauma Surg
Fig. 1 Intraoperative setting for limb alignment measurements under weight bearing using the custom-made loading device TKA
study, weight-bearing simulation was shown to influence the mechanical axis significantly [12]. To our knowledge, no study has analysed the effect of intraoperative weight bearing on the mechanical axis. A special custom-made device was built to apply an exact axial load of half body weight to the lower limb intraoperatively. The aims of this study were firstly to determine intra- and interobserver reliability of intraoperative measurement of the mechanical axis using our custom-made loading device and then to quantify the effect of intraoperative weight bearing on the mechanical axis compared with the intraoperative unloaded situation. Furthermore, knee stability in the frontal plane under simulated loading condition was compared before and after implantation of TKA.
Materials and methods This prospective study involved 30 consecutive patients who were considered for primary TKA. Radiographic evaluation included long leg standing views. Primary cruciate retaining TKA (Scorpio CR, Stryker GmbH & Co. KG, Duisburg, Germany) was performed by a single surgeon (S.H.) with the use of an infrared-based navigation system (Stryker version 3.2, Freiburg, Germany). A straight midline skin incision with a medial parapatellar arthrotomy was performed. The anchoring pins of the navigation system were fixed within the incision in the distal femur and through an additional incision in the tibial shaft. After definition of the anatomical landmarks by single point and surface digitisation, the unloaded mechanical axis was measured in extension by the navigation system.
13
A new custom-made loading device with a foot plate was used to apply an axial load of half body weight to the lower limb and the loaded mechanical axis before femoral and tibial resection was assessed (Fig. 1). A navigated resection guide was used for the distal femoral and proximal tibial cuts. A soft tissue balancing device (Stryker, Allendale, NJ, USA) was used to measure ligament tension and gap kinematics in 90° flexion and full extension and soft tissue was released until adequate ligament tension and equal gaps on the medial and lateral side were measured. After insertion of the trial components, alignment was assessed with the navigation system without and with intraoperative loading of 50 % body weight both before and after cemented implantation of the definitive prosthesis components. To assess intra- and interobserver reliability, all measurements were performed three times by the senior surgeon (S.H.) and then by a junior surgeon without visualisation of the navigation monitor showing the mechanical axis (Fig. 1). Statistical analysis Paired t tests as general linear model for repeated measures were used to compare the change among each non-load and load group. Significance was considered with p
Knee Arthroplasty
Effect of intraoperative weight‑bearing simulation on the mechanical axis in total knee arthroplasty M. Panzica · M. Kenawey · E. Liodakis · J. Brandes · C. Krettek · S. Hankemeier
Received: 4 April 2013 © Springer-Verlag Berlin Heidelberg 2014
Abstract Purpose Successful outcome after total knee arthroplasty (TKA) requires precise realignment of the mechanical axis. The intraoperative assessment of the mechanical axis is difficult. Intraoperatively, the effect of weight bearing on the lower limb mechanical axis is ignored. We developed a custom-made mechanical loading device to simulate weight-bearing conditions intraoperatively and analysed its effect on the mechanical axis during TKA. Methods Measurements of the mechanical axis were obtained during 30 consecutive primary TKAs in osteoarthritic patients using image-free knee navigation system. Half body weight was applied intraoperatively using our device to quantify the effect of intraoperative load application on the mechanical axis, thus receiving indirect information about soft tissue balancing. Furthermore, the intraobserver and interobserver reliability of navigated mechanical axis measurement with and without load was determined. Results Before TKA, mean mechanical axis was 4.0° ± 4.9° without load. Under loading conditions, the mean change of the mechanical axis was 2.1° ± 2.8°. Repetitive measurements of the senior surgeon and junior surgeon revealed a high intraobserver (ICC 0.997) and interobserver reliability (ICC 0.998). The registration of the mechanical axis without and with application of intraoperative loading demonstrated no significant differences during
M. Panzica (*) · M. Kenawey · E. Liodakis · J. Brandes · C. Krettek · S. Hankemeier Department of Trauma Surgery and Orthopaedic Surgery, Hannover Medical School, Carl‑Neuberg Str. 1, 30625 Hannover, Germany e-mail: panzica.martin@mh‑hannover.de
insertion of the trial components (SD 0.29 ± 0.29) and after the definitive component cementation (SD 0.63 ± 0.44). Conclusions Intraoperative quantification and analysis of the mechanical lower limb axis applying defined axial loading by our custom-made loading apparatus is reliable. Ligament stability was unbalanced before TKA and balanced after TKA. For TKA, intraoperative simulation of weight bearing may be helpful to quantify, control and correct knee stability and its influence of mechanical axis. Keywords Total knee arthroplasty · Navigation · Ligament balancing · Instability · Mechanical leg axis · Weight bearing
Introduction Soft tissue balancing and accurate restoration of mechanical limb alignment are key factors for successful implantation of TKA [1–3]. The balancing device and the use of trial components with application of varus and valgus stresses were popularised techniques for ligament balancing. Appropriate ligament balancing is strongly influenced by the surgeon’s individual feeling for knee laxity and stiffness. There is a lack of an objective definition of appropriate soft tissue balancing during implantation of TKA [4–8]. Malalignment can impair long-term results of TKA [13– 17]. Compared with conventional instrumentation of TKA, navigation systems improve the surgical accuracy at least in the frontal plane [9–11]. On the other hand, preoperative planning and the assessment of the mechanical axis are based on weight-bearing long-standing radiographs, while intraoperative implantation of TKA is performed under non-weight-bearing conditions. In a previous cadaveric
13
Arch Orthop Trauma Surg
Fig. 1 Intraoperative setting for limb alignment measurements under weight bearing using the custom-made loading device TKA
study, weight-bearing simulation was shown to influence the mechanical axis significantly [12]. To our knowledge, no study has analysed the effect of intraoperative weight bearing on the mechanical axis. A special custom-made device was built to apply an exact axial load of half body weight to the lower limb intraoperatively. The aims of this study were firstly to determine intra- and interobserver reliability of intraoperative measurement of the mechanical axis using our custom-made loading device and then to quantify the effect of intraoperative weight bearing on the mechanical axis compared with the intraoperative unloaded situation. Furthermore, knee stability in the frontal plane under simulated loading condition was compared before and after implantation of TKA.
Materials and methods This prospective study involved 30 consecutive patients who were considered for primary TKA. Radiographic evaluation included long leg standing views. Primary cruciate retaining TKA (Scorpio CR, Stryker GmbH & Co. KG, Duisburg, Germany) was performed by a single surgeon (S.H.) with the use of an infrared-based navigation system (Stryker version 3.2, Freiburg, Germany). A straight midline skin incision with a medial parapatellar arthrotomy was performed. The anchoring pins of the navigation system were fixed within the incision in the distal femur and through an additional incision in the tibial shaft. After definition of the anatomical landmarks by single point and surface digitisation, the unloaded mechanical axis was measured in extension by the navigation system.
13
A new custom-made loading device with a foot plate was used to apply an axial load of half body weight to the lower limb and the loaded mechanical axis before femoral and tibial resection was assessed (Fig. 1). A navigated resection guide was used for the distal femoral and proximal tibial cuts. A soft tissue balancing device (Stryker, Allendale, NJ, USA) was used to measure ligament tension and gap kinematics in 90° flexion and full extension and soft tissue was released until adequate ligament tension and equal gaps on the medial and lateral side were measured. After insertion of the trial components, alignment was assessed with the navigation system without and with intraoperative loading of 50 % body weight both before and after cemented implantation of the definitive prosthesis components. To assess intra- and interobserver reliability, all measurements were performed three times by the senior surgeon (S.H.) and then by a junior surgeon without visualisation of the navigation monitor showing the mechanical axis (Fig. 1). Statistical analysis Paired t tests as general linear model for repeated measures were used to compare the change among each non-load and load group. Significance was considered with p
