Knee Surg Sports Traumatol Arthrosc (2014) 22:3127–3134 DOI 10.1007/s00167-014-3233-9

KNEE

Computer‑assisted surgery improves rotational positioning of the femoral component but not the tibial component in total knee arthroplasty Daniel Hernandez‑Vaquero · Alfonso Noriega‑Fernandez · Jose Manuel Fernandez‑Carreira · Jose Manuel Fernandez‑Simon · Jimena Llorens de los Rios 

Received: 31 March 2014 / Accepted: 11 August 2014 / Published online: 26 August 2014 © European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2014

Abstract  Purpose  Computer-assisted surgery (CAS) may facilitate better positioning of total knee arthroplasty (TKA) along the coronal and lateral axes; however, there are doubts as to its usefulness in the rotational plane. Methods  This is a prospective study of 95 TKAs comparing two groups: the CAS group and the standard equipment group. The series comprises 95 cases. A radiography of the lower limb and computer tomographies (CTs) of the femoral condylar region, the proximal end of the tibia and the ankle were performed to measure rotational angulation. A month after TKA surgery, the radiography and the CTs were repeated to analyze the position of the prosthetic components in the rotational plane. Results  In the coronal axis, both CAS and mechanical technique improved femoro-tibial alignment, but when there are preexisting deformities ≥4°, CAS obtains better results. A strong correlation (R = 0.94, p = 0.001) was observed between the mean rotational axis measured with CT in the tibial plateau and that measured from the axis of the ankle. The mean initial femoral rotation of the complete series was 6.7° and 2.7° at 1-month follow-up (p 5° in the tibial tray and 9° in the femoral component. Defective implant placements are more frequent in internal rotation, which frequently leads to severe stiffness of the knee. Although computer-assisted surgery (CAS) has not yet proven its usefulness in the long-term evolution of TKA

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[13], it does provide reliable results when it comes to coronal and lateral alignment, reducing outliers [9]. It also prevents subjective impressions at the time of implant placement, adds reliability and reproducibility to arthroplasty techniques, allows to check the orientation and thickness of bone cuts during the procedure and thus to make corrections, certifies the result and, all in all, provides the accuracy and convenience computing technologies can offer. Nevertheless, it has not been proven that CAS poses any advantage for the placement of prosthetic components in the rotational plane. At the femoral level, this may be due to the fact that epicondyle identification, as crucial as it is, is subjective and hardly reproducible [20]; at the tibial level, the problem may stem from a lack of fully validated anatomical landmarks or potential discrepancies between the rotation of the proximal region and that of the tibial axis. The present research aims to find out via computer tomography (CT) whether CAS is helpful in improving the placement of TKAs. Our specific goals were as follows: 1. To determine whether there is any correlation between tibial rotation measured in the upper tibial end and that measured following the transversal axis of the ankle. 2. To compare the final rotation achieved in both components comparing the mechanical alignment system to CAS. 3. To determine whether these results are modified in the presence of previous varus–valgus deformities. Our hypothesis is that the rotational positioning of the femoral and tibial components in TKA is improved when CAS is used. This has not been analyzed previously using CT.

Materials and methods A prospective, randomized study of radiographic results was performed. In one group, TKAs were implanted with standard equipment; in another group, CAS was used. In all cases, the original diagnosis was tricompartmental arthrosis. Patients were randomly assigned to each group by means of a random number table. Surgeons did not know to which group a patient belonged before surgery, and the radiologist who measured the angles was blinded to the technique used. The procedures were carried out by surgeons with ample experience in CAS TKAs, as each surgeon had performed over 300 cases prior to the beginning of the study. The number of patients initially enrolled in the study was 100, of which 95 were finally selected (64 women and 31 men). Two cases were lost to follow-up and another three cases were excluded because it was not possible to

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define the anatomical landmarks in the postoperative CT. In 6 cases, a bilateral TKA was implanted. The mean age of patients was 61.2 years (SD: 6.99); mean body mass index (BMI) was 29.64 kg/m2 (SD: 5.33; Range 20.68–44.00). In the “standard” group, 55.6 % of patients were woman (mean age: 60.2 years, SD: 6.92) whereas in the “navigation” group, women comprised 78 % of the total sample (mean age: 62.1 years, SD: 7.14). The implant model used in all cases was the Triathlon arthroplasty (Stryker, Kalamazoo, MI, USA). A patellar replacement was performed and all components were cemented. In the standard group, intramedullary alignment was used for the femur and extramedullary for the tibia. The femoral alignment guide was designed for use on either the left or right knee and was set at 6° of valgus with an external rotation of 3°. A posterior referencing system was used. An extramedullary guide was employed for tibial rotation, taking the patellar tendon insertion (middle 1/3 of the tubercle), the midpoint of the ankle and the axis of the second toe as references. A wireless image-free navigation system was used (Stryker Image Free Computer Navigation System, StrykerLeibinger, Freiburg, Germany). The Stryker Knee Navigation System is an active wireless nonimage-based system, which is able to track active, battery-powered instruments using light emitting diodes (LEDs) to communicate with the camera’s localization system. The active wireless localizers were placed at two locations bicortically (diaphyseal femur and tibia; separate incisions). The points and areas referenced in this navigation system are as follows: hip center, epicondyles, anterior femoral cortex mapping, femoral condyles, tibial center and tibial plateau surface mapping. The rotation within the navigation software was calculated as an average resultant of the digitized transepicondylar axis and the Whiteside line. No navigation-related complications were found. All patients received a radiography of the hip, knee and ankle in frontal and lateral position during the preoperative assessment, which was repeated a month after TKA implantation. The mechanical axis of the limb and the angulation of the femoral and tibial components were measured on the radiographies with the Impax 6.3.1.2813 (Agfa Healthcare NV, Mortsel, Belgium) and the Agfa-Orthopaedic Tools software version 2.06. Measurements were done by a radiologist that did not know what group belonged the patient. Varus deformities were considered as negative angulation and valgus as positive. A CT was performed in all patients of the femoral condylar region and the proximal tibia both preoperatively and at 1 month after surgery. The tomograph used was a Siemens AG Somatron-Volume Access, version A40A (Siemens A.G. Munich, Germany). A minimum of three cuts were made in the femur until the best view of both epicondyles and the semi-spherical shaped portion of the

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Fig. 1  Preoperative CT. The FA was determined by the angle between a line through the epicondyles and the posterior femoral condyles. TA1 was determined between a line which connected the geometric centers of the plateaus, and parallel to the patellar tendon shadow and the tangent to the posterior tibial outline. Tibial angle 2 (TA2) was defined as the angle formed by the line connecting the geometric centers of the tibial plateaus and the axis of the ankle

epicondylar tunnel was achieved. The distal metaphysis axial angulation of the femur was obtained, taking as reference the transepicondylar line and the line between the posterior condylar ridges, labeled as femoral angle (FA). In order to perform this measurement, we considered the clinical epicondyle, defined as the greatest protrusion of the lateral and medial epicondyle. As for the tibia, 3-mm interval cuts were performed. Cuts started just above the tibial joint surface and were repeated until the cut which would allow for the full visualization of the tibial plateau outline was achieved. On average, four cuts were performed, and the point closest to the articular surface was chosen. A line was traced which connected the geometric centers of the plateaus, and parallel to the patellar tendon shadow. The angle between this line and the tangent to the posterior tibial outline was found, which we labeled tibial angle 1 (TA1). In the knee, cuts were performed with the same thickness and separation at the tibial-fibular-talar articular interline (Fig. 1). At this location, the talus has a rectangular shape; thus, a line parallel to the talus axis was traced which passed through the three aforementioned bones. The angle formed by the line connecting the geometric centers of the plateaus and the axis of the ankle was labeled tibial angle 2 (TA2). After surgery, the CT studies were performed again, employing scatter-reduction software to allow visualization of the medial and lateral epicondyles and the tibial border. In the femur, a line was drawn between the two epicondyles

as the epicondylar axis. A second line was drawn across the posterior condyles of the femoral component. The angle between these represented the rotation of the femoral component. The rotational alignment of the tibial component was determined relative to the line between the geometric centers of the two circumferences which composed the outer rim of the prosthetic tray and the axis of the ankle, previously described (Fig. 2). External rotation was considered as positive angle and internal as negative. All patients filled out an informed consent form. This work was approved by the Regional Ethics Committee of Asturias, Spain. (PS09/02153). Statistical analysis A descriptive study was performed to obtain means and standard deviations for all quantitative variables. The relations between angle measurements were analyzed via Pearson’s correlation and the intraclass correlation coefficient. Chi-square and ANOVA were carried out to compare preoperative differences between groups of qualitative and quantitative variables, respectively. Paired Student’s t test was performed to assess changes in the quantitative variables between the preoperative and postoperative scenarios (paired samples). A repeated measures ANOVA (General Linear Model) was used to compare the evolution of angular variables preoperatively and postoperatively between the standard and navigated groups taking the time of

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measurement as an intra-subject factor and the study group as inter-subject factor. Statistical signification was considered when p 4°, the value was 6.47°, a difference with no statistical significance. The initial femoral rotation of the whole series measured by CT was 6.70°, and the final was 2.72° (p 11°

4°-10° Varus

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1°- 3°

0° Neutral

1°-3°

4°-10° Valgus

>11°

Knee Surg Sports Traumatol Arthrosc (2014) 22:3127–3134

Initial Final

No

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Standard CAS

a

Yes Deformity Preop

Fig. 4  Postoperative coronal mechanical axis from navigation

6.64°; postoperative: 3.18°/preoperative deformity: 6.47°; postoperative: 3.00° (n.s.).] The navigation system used in this study identified the final femoral rotation based on several measurements. When comparing the rotation as measured from the epicondyles and the final rotation, a strong correlation was found (p 

Computer-assisted surgery improves rotational positioning of the femoral component but not the tibial component in total knee arthroplasty.

Computer-assisted surgery (CAS) may facilitate better positioning of total knee arthroplasty (TKA) along the coronal and lateral axes; however, there ...
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