Arch Orthop Trauma Surg (2014) 134:571–576 DOI 10.1007/s00402-014-1944-5
Knee Arthroplasty
The effect of femoral component design on patellar tracking in total knee arthroplasty: Genesis II prosthesis versus Vanguard prosthesis Chae‑Gwan Kong · Se‑Wook Park · Hyo Yang · Yong In
Received: 10 August 2013 / Published online: 11 February 2014 © Springer-Verlag Berlin Heidelberg 2014
Abstract Introduction The Genesis II knee system incorporates 3° of external rotation into the femoral component and the femoral component is implanted in neutral rotation to the femur. The purpose of this study was to compare patellar tracking of the Genesis II knee system with that of the Vanguard knee system, in which the femoral component is routinely implanted in a 3° externally rotated position to the posterior condylar axis (PCA) of the femur. Materials and methods One hundred consecutive knees scheduled to undergo total knee arthroplasty (TKA) were enrolled. Fifty knees underwent TKA with the posteriorstabilized (PS) Genesis II prosthesis and 50 knees underwent TKA with the PS Vanguard prosthesis. Rotation of the femoral component was calculated by measuring the acute angle between the transepicondylar axis (TEA) and the PCA on axial computed tomography (CT) images. The postoperative patellar tilt and displacement were compared between groups. The range of motion and Knee Society scores were also compared. Results Forty-eight knees in each group were followed up for 2 years. There was no difference in the angle between the PCA and the TEA on postoperative CT scans between the two designs. There was also no difference in patellar tracking between groups. Both the Genesis II and Vanguard knee systems showed good clinical results at 2 years postoperatively. Conclusion The patellar tracking of the Genesis II prosthesis was comparable to that of the Vanguard prosthesis. Level of evidence Prospective cohort study, Level II. C.-G. Kong · S.-W. Park · H. Yang · Y. In (*) Department of Orthopaedic Surgery, The Catholic University of Korea, 222 Banpodaero, Seocho‑Gu, Seoul 137‑701, Korea e-mail: [email protected]
Keywords Total knee arthroplasty · Patellar tracking · Genesis II · Vanguard
Introduction Optimizing patellar tracking in total knee arthroplasty (TKA) is a surgical priority [1]. Many studies have demonstrated that rotational alignment of the femoral component affects patellar tracking [2–6]. External rotation of the femoral component has been advocated to balance the flexion gap and improve patellar tracking [2, 3, 5–8]. Knee implant manufacturers emphasize on improved patellar tracking in their design rationale of newly developed implants. The Genesis II knee system (Smith & Nephew, Memphis, TN) incorporates 3° of external rotation into the femoral component, and the femoral component is implanted in neutral rotation to the femur (Fig. 1). Developers explain that the Genesis II system offers the benefits of femoral external rotation without possible adverse effects, such as patellar medialization in deep flexion, rotational malalignment between the femur and tibia in flexion, or notching the lateral anterior cortex of the femur (http://www.smithnephew.com/key-products/orthopaedic-reconstruction/ genesis-ii-knee-system/). They also explain that a deeper, more lateralized trochlear groove of the Genesis II femoral component improves patellar contact and tracking. Femoral component design can be a determinant of patellar tilt or subluxation [9, 10]. The major difference between the Genesis II prosthesis and the other knee systems is in the amount of femoral component rotation. The kinematic superiority of one design over the other has not been shown. The Vanguard knee system (Biomet, Warsaw, IN) was designed with a more forgiving track, which allows the
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572
Fig. 1 Asymmetric posterior femoral condyles of the Genesis II prosthesis (Smith & Nephew, Memphis, TN) with thicker lateral femoral condyle than medial femoral condyle do not allow for external rotation of the implant
knee to achieve motion without sacrificing healthy bone during surgery (http://www.biomet.com/patients/vanguard_ complete.cfm). Although the amount of external rotation of the femoral component is the surgeon’s decision, the femoral component of the Vanguard system is usually implanted with traditional 3° external rotation to the posterior condylar axis (PCA) of the femur. The purpose of this study was to compare the patellar tracking of the Genesis II prosthesis with that of the Vanguard prosthesis. In this study, we hypothesized that the Genesis II prosthesis would have worse patellar tracking characteristics than those of the Vanguard prosthesis, in which the femoral component is implanted in a routine 3° externally rotated position to the PCA.
Materials and methods Between February 2009 and December 2009, we carried out a prospective, consecutive, non-randomized, comparative clinical trial to determine if the component design can be a determinant of patellar tracking. This study was approved by the institutional review board of our hospital. All patients were adequately informed and they signed an informed consent form. Patients with osteoarthritis were selected as potential candidates for the study. The exclusion criteria were patients with severe deformity (valgus or varus angulation of more than 15° or a flexion contracture of more than 20°), rheumatoid arthritis, a history of previous high tibial osteotomy, or other previous knee surgeries.
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Arch Orthop Trauma Surg (2014) 134:571–576
One hundred knees were included in this study. Fifty knees (30 patients) underwent TKA using the posterior-stabilized (PS) Vanguard prosthesis and 50 knees (34 patients) underwent TKA using the PS Genesis II prosthesis. Both prostheses were implanted alternately without using any randomization process. Preoperative patient data including age, sex, body mass index (BMI), range of motion, and Knee Society scores were recorded. Lower extremity alignment was measured using standing anteroposterior (AP) radiographs. The axial images of the patellofemoral joint were taken with the knee in ~45° of flexion using the Merchant’s technique [11]. The preoperative patellar tilt and displacement were measured using the axial radiographs as described by Aglietti et al. [12]. Patellar tilt was defined as the angle between the equatorial line of the patella and the intercondylar line. The patellar displacement was defined as the distance to the median ridge of the patella, which is deepest point of the patella in relation to the equatorial line of the patella, from the intercondylar sulcus. Lateral patellar tilt or displacement was presumed to be positive. All operations were done with a uniform approach and technique by one surgeon using the subvastus approach without patellar eversion. A tourniquet was used for all knees. The subvastus approach was done through a midline skin incision, as described by Hofmann et al. [13]. The same surgical technique was used in both the groups including superomedialization of the patellar component. The only difference in the surgical procedure was in the femoral component rotation. The femoral component of the Vanguard knee system was implanted with 3° external rotation to the posterior femoral condylar axis. The femoral component of the Genesis II knee system was implanted in neutral femoral rotation. All the patellae were resurfaced using the same eyeball technique, and efforts were made to cut the same thickness with the patellar component. All components were cemented. A final evaluation of patellar tracking was performed, using both the so-called the nothumb test and the towel clip test after the tourniquet was deflated. A towel clip test was performed if the patella did not track centrally with the no-thumb test. A lateral retinacular release was considered if the towel clip test was positive. No knee in either group underwent lateral retinacular release. All patients of both the groups received the same rehabilitation programs. On the first postoperative day, all patients began full weight-bearing walking with the use of a walker. They started active range of motion exercises. The closed suction drain was removed 48 h after operation. We did not use a continuous passive motion machine, but we encouraged the patients to perform active range of motion exercise under our supervision. We used the oral medication, celecoxib 200 mg q day, in all patients for pain control for a period of 6 weeks.
Arch Orthop Trauma Surg (2014) 134:571–576
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Table 1 Patient demographics Vanguard group (N = 48) Preoperative alignment (°) (valgus,−; varus,+) Age (years) Sex ratio (f:m) Preoperative patellar tilt (°) Preoperative patellar displacement (mm) Preoperative BMI (kg/m2) Preoperative range of motion (°)
2.2 ± 5.6 (range −4.9 to 13.2) 64.6 ± 7.4 (range 52 to 82) 47:1 10.7 ± 4.6 (range −7.9 to 33.0) 2.4 ± 1.5 (range −7.3 to 17.2) 27.3 ± 2.9 (range 21.1 to 37.8) 120.6 ± 16.2 (range 85 to 145)
All patients underwent computed tomography (CT) scans of the knee at 10 days after operation. Rotation of the femoral component was calculated by measuring the acute angle between the transepicondylar axis (TEA) and the PCA on axial CT images. The TEA was created by connecting the medial and lateral femoral epicondyles, which were defined as the most prominent bony landmark at the medial and lateral condyles of the femur. The PCA was created by connecting the lowest points between the posterior condyles. Negative value represents internal rotation of the PCA compared to the TEA. Patients were followed up at 6 weeks, 3 months, 6 months, and 1 year after operation and then yearly thereafter. The postoperative patellar tilt and displacement were measured as described by Gomes et al. [14]. The postoperative patellar tilt and displacement were compared between both the groups. The range of motion and Knee Society scores were also recorded and compared. Extensor mechanism function was evaluated using a chair rise test [15]. Patients were asked to rise from a 40-cm high chair while keeping their arms folded across their chest. If the patient failed to perform the test independently, then the test was rated as negative. Statistical comparison of the clinical results was done using SPSS version 13.0 software (SPSS Inc., Chicago, IL). Means and standard deviation were used to describe the data. The differences between groups were calculated using a parametric test for independent samples (Student’s t test). Paired t tests were used for comparison between the preoperative data and the 2-year follow-up data. Chi-square tests were used to compare the sex ratio. Statistical significance was defined as P
Knee Arthroplasty
The effect of femoral component design on patellar tracking in total knee arthroplasty: Genesis II prosthesis versus Vanguard prosthesis Chae‑Gwan Kong · Se‑Wook Park · Hyo Yang · Yong In
Received: 10 August 2013 / Published online: 11 February 2014 © Springer-Verlag Berlin Heidelberg 2014
Abstract Introduction The Genesis II knee system incorporates 3° of external rotation into the femoral component and the femoral component is implanted in neutral rotation to the femur. The purpose of this study was to compare patellar tracking of the Genesis II knee system with that of the Vanguard knee system, in which the femoral component is routinely implanted in a 3° externally rotated position to the posterior condylar axis (PCA) of the femur. Materials and methods One hundred consecutive knees scheduled to undergo total knee arthroplasty (TKA) were enrolled. Fifty knees underwent TKA with the posteriorstabilized (PS) Genesis II prosthesis and 50 knees underwent TKA with the PS Vanguard prosthesis. Rotation of the femoral component was calculated by measuring the acute angle between the transepicondylar axis (TEA) and the PCA on axial computed tomography (CT) images. The postoperative patellar tilt and displacement were compared between groups. The range of motion and Knee Society scores were also compared. Results Forty-eight knees in each group were followed up for 2 years. There was no difference in the angle between the PCA and the TEA on postoperative CT scans between the two designs. There was also no difference in patellar tracking between groups. Both the Genesis II and Vanguard knee systems showed good clinical results at 2 years postoperatively. Conclusion The patellar tracking of the Genesis II prosthesis was comparable to that of the Vanguard prosthesis. Level of evidence Prospective cohort study, Level II. C.-G. Kong · S.-W. Park · H. Yang · Y. In (*) Department of Orthopaedic Surgery, The Catholic University of Korea, 222 Banpodaero, Seocho‑Gu, Seoul 137‑701, Korea e-mail: [email protected]
Keywords Total knee arthroplasty · Patellar tracking · Genesis II · Vanguard
Introduction Optimizing patellar tracking in total knee arthroplasty (TKA) is a surgical priority [1]. Many studies have demonstrated that rotational alignment of the femoral component affects patellar tracking [2–6]. External rotation of the femoral component has been advocated to balance the flexion gap and improve patellar tracking [2, 3, 5–8]. Knee implant manufacturers emphasize on improved patellar tracking in their design rationale of newly developed implants. The Genesis II knee system (Smith & Nephew, Memphis, TN) incorporates 3° of external rotation into the femoral component, and the femoral component is implanted in neutral rotation to the femur (Fig. 1). Developers explain that the Genesis II system offers the benefits of femoral external rotation without possible adverse effects, such as patellar medialization in deep flexion, rotational malalignment between the femur and tibia in flexion, or notching the lateral anterior cortex of the femur (http://www.smithnephew.com/key-products/orthopaedic-reconstruction/ genesis-ii-knee-system/). They also explain that a deeper, more lateralized trochlear groove of the Genesis II femoral component improves patellar contact and tracking. Femoral component design can be a determinant of patellar tilt or subluxation [9, 10]. The major difference between the Genesis II prosthesis and the other knee systems is in the amount of femoral component rotation. The kinematic superiority of one design over the other has not been shown. The Vanguard knee system (Biomet, Warsaw, IN) was designed with a more forgiving track, which allows the
13
572
Fig. 1 Asymmetric posterior femoral condyles of the Genesis II prosthesis (Smith & Nephew, Memphis, TN) with thicker lateral femoral condyle than medial femoral condyle do not allow for external rotation of the implant
knee to achieve motion without sacrificing healthy bone during surgery (http://www.biomet.com/patients/vanguard_ complete.cfm). Although the amount of external rotation of the femoral component is the surgeon’s decision, the femoral component of the Vanguard system is usually implanted with traditional 3° external rotation to the posterior condylar axis (PCA) of the femur. The purpose of this study was to compare the patellar tracking of the Genesis II prosthesis with that of the Vanguard prosthesis. In this study, we hypothesized that the Genesis II prosthesis would have worse patellar tracking characteristics than those of the Vanguard prosthesis, in which the femoral component is implanted in a routine 3° externally rotated position to the PCA.
Materials and methods Between February 2009 and December 2009, we carried out a prospective, consecutive, non-randomized, comparative clinical trial to determine if the component design can be a determinant of patellar tracking. This study was approved by the institutional review board of our hospital. All patients were adequately informed and they signed an informed consent form. Patients with osteoarthritis were selected as potential candidates for the study. The exclusion criteria were patients with severe deformity (valgus or varus angulation of more than 15° or a flexion contracture of more than 20°), rheumatoid arthritis, a history of previous high tibial osteotomy, or other previous knee surgeries.
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Arch Orthop Trauma Surg (2014) 134:571–576
One hundred knees were included in this study. Fifty knees (30 patients) underwent TKA using the posterior-stabilized (PS) Vanguard prosthesis and 50 knees (34 patients) underwent TKA using the PS Genesis II prosthesis. Both prostheses were implanted alternately without using any randomization process. Preoperative patient data including age, sex, body mass index (BMI), range of motion, and Knee Society scores were recorded. Lower extremity alignment was measured using standing anteroposterior (AP) radiographs. The axial images of the patellofemoral joint were taken with the knee in ~45° of flexion using the Merchant’s technique [11]. The preoperative patellar tilt and displacement were measured using the axial radiographs as described by Aglietti et al. [12]. Patellar tilt was defined as the angle between the equatorial line of the patella and the intercondylar line. The patellar displacement was defined as the distance to the median ridge of the patella, which is deepest point of the patella in relation to the equatorial line of the patella, from the intercondylar sulcus. Lateral patellar tilt or displacement was presumed to be positive. All operations were done with a uniform approach and technique by one surgeon using the subvastus approach without patellar eversion. A tourniquet was used for all knees. The subvastus approach was done through a midline skin incision, as described by Hofmann et al. [13]. The same surgical technique was used in both the groups including superomedialization of the patellar component. The only difference in the surgical procedure was in the femoral component rotation. The femoral component of the Vanguard knee system was implanted with 3° external rotation to the posterior femoral condylar axis. The femoral component of the Genesis II knee system was implanted in neutral femoral rotation. All the patellae were resurfaced using the same eyeball technique, and efforts were made to cut the same thickness with the patellar component. All components were cemented. A final evaluation of patellar tracking was performed, using both the so-called the nothumb test and the towel clip test after the tourniquet was deflated. A towel clip test was performed if the patella did not track centrally with the no-thumb test. A lateral retinacular release was considered if the towel clip test was positive. No knee in either group underwent lateral retinacular release. All patients of both the groups received the same rehabilitation programs. On the first postoperative day, all patients began full weight-bearing walking with the use of a walker. They started active range of motion exercises. The closed suction drain was removed 48 h after operation. We did not use a continuous passive motion machine, but we encouraged the patients to perform active range of motion exercise under our supervision. We used the oral medication, celecoxib 200 mg q day, in all patients for pain control for a period of 6 weeks.
Arch Orthop Trauma Surg (2014) 134:571–576
573
Table 1 Patient demographics Vanguard group (N = 48) Preoperative alignment (°) (valgus,−; varus,+) Age (years) Sex ratio (f:m) Preoperative patellar tilt (°) Preoperative patellar displacement (mm) Preoperative BMI (kg/m2) Preoperative range of motion (°)
2.2 ± 5.6 (range −4.9 to 13.2) 64.6 ± 7.4 (range 52 to 82) 47:1 10.7 ± 4.6 (range −7.9 to 33.0) 2.4 ± 1.5 (range −7.3 to 17.2) 27.3 ± 2.9 (range 21.1 to 37.8) 120.6 ± 16.2 (range 85 to 145)
All patients underwent computed tomography (CT) scans of the knee at 10 days after operation. Rotation of the femoral component was calculated by measuring the acute angle between the transepicondylar axis (TEA) and the PCA on axial CT images. The TEA was created by connecting the medial and lateral femoral epicondyles, which were defined as the most prominent bony landmark at the medial and lateral condyles of the femur. The PCA was created by connecting the lowest points between the posterior condyles. Negative value represents internal rotation of the PCA compared to the TEA. Patients were followed up at 6 weeks, 3 months, 6 months, and 1 year after operation and then yearly thereafter. The postoperative patellar tilt and displacement were measured as described by Gomes et al. [14]. The postoperative patellar tilt and displacement were compared between both the groups. The range of motion and Knee Society scores were also recorded and compared. Extensor mechanism function was evaluated using a chair rise test [15]. Patients were asked to rise from a 40-cm high chair while keeping their arms folded across their chest. If the patient failed to perform the test independently, then the test was rated as negative. Statistical comparison of the clinical results was done using SPSS version 13.0 software (SPSS Inc., Chicago, IL). Means and standard deviation were used to describe the data. The differences between groups were calculated using a parametric test for independent samples (Student’s t test). Paired t tests were used for comparison between the preoperative data and the 2-year follow-up data. Chi-square tests were used to compare the sex ratio. Statistical significance was defined as P
