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Influence of offset stem couplers in femoral revision knee arthroplasty: A radiographic study
The Knee 19 (2012) 112–115
Contents lists available at ScienceDirect
The Knee
Influence of offset stem couplers in femoral revision knee arthroplasty: A radiographic study Jean M. Brilhault a,⁎, Michael D. Ries b a b
Department of Orthopaedic Surgery, C.H.R.U. de Tours, Université François-Rabelais de Tours, Tours 37044, France Department of Orthopaedic Surgery, Mission Bay Orthopaedic Institute, University of California San Francisco, San Francisco, CA 94158, United States
a r t i c l e
i n f o
Article history: Received 16 September 2010 Received in revised form 4 February 2011 Accepted 8 February 2011 Keywords: Revision total knee arthroplasty Posterior femoral condylar offset Modular stem Stem alignment
a b s t r a c t We questioned whether the use of offset femoral stem would result in modifying the posterior femoral condylar offset (PFCO) in revision knee arthroplasty (RTKA). We measured both PFCO and stem alignment on lateral radiographs of two cohorts: 91 knees with straight stems and 35 knees with offset coupled stems. A higher PCOR was observed in knees with an offset stem compared to knees with straight stem. Knees with an offset stem had a better alignment within the intramedullary canal. Our conclusion is that the use of a modular offset coupler with femoral stem in RTKA compared to a modular straight stem both increases the posterior condylar offset and improves alignment of the stem within the intramedullary canal. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Posterior femoral condylar offset (PFCO) restoration in total knee arthroplasty is important to provide stability in flexion and maximize knee range of motion [1–8]. Inadequate posterior femoral offset permits posterior tibiofemoral impingement, which can limit knee flexion and also contributes to flexion instability [1,8]. Bone loss in revision total knee arthroplasty (RTKA) often necessitates the use of intramedullary stems to provide adequate implant stability. The position of a diaphyseal engaging femoral stem determines both mediolateral and antero-posterior position of the condylar portion of the femoral component [9]. Most stems are attached to the femoral component at a fixed valgus angle of 5–7° in the frontal plane and perpendicular in the lateral plane. Since the distal femur is bowed anteriorly, a straight diaphyseal engaging stem would be expected to displace the femoral component anteriorly. This can result in inadequate posterior condylar offset, which may require either the use of an oversized femoral component to fill the flexion space or the use of a smaller diameter cemented stem. A smaller diameter cemented stem does not fill the femoral intramedullary canal or restrict the sagittal positioning of the condylar component [10–12]. However, achieving low constraint RTKA requires ligament balancing through anatomical restoration of the femoral condyles. Since the anatomy of the distal femur can be quite variable, modular offset couplers have been utilized between the stem and femoral compo-
⁎ Corresponding author at: Department of Orthopaedic Surgery, C.H.R.U. de Tours, Tours 37044, Cedex 09, France. Tel.: + 33 234 389 464; fax: + 33 247 478 385. E-mail address: [email protected] (J.M. Brilhault). 0968-0160/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.knee.2011.02.005
nent to permit more versatility in orienting the position of the implant in RTKA [9,13]. We questioned whether the use of an offset femoral stem would result in modifying the PFCO in RTKA by analyzing two cohorts with different femoral stem designs: straight stems and offset coupled stems. 2. Material and methods This study is a retrospective comparative cohort radiographic analysis of 126 consecutive RTKA's in which stemmed components were used. Revision indications included wear, osteolysis, aseptic loosening, instability, arthrofibrosis, femoral component malposition and infected TKA (which were revised with a two stage procedure). Patients with prior trauma, periprosthetic fractures, or pathologic conditions associated with extra-articular bony deformity were excluded. Either Genesis II® or Legion® revision knee systems (Smith and Nephew, Memphis, TN) that share identical contour shape and stem location were used in this study (Fig. 1). The Genesis II® revision knee system provides press-fit straight stems connected directly to the condylar component. Stems are available in 100 mm, 150 mm and 200 mm lengths with a 2 mm increment in 10–24 mm diameters. The Legion® revision knee system provides press-fit straight stems that can be connected to the condylar component with or without a 2 mm, 4 mm or 6 mm offset coupler (Fig. 2). This coupler allows 360° “dial-in” positioning of the stem. Approval for this study was obtained from the committee on human research of our institution. Data from all of our TKA patients were collected prospectively and entered into a database that served as a source of information used in this study. A revision system without femoral offset couplers (Genesis II® RTKA) was used between 1998
J.M. Brilhault, M.D. Ries / The Knee 19 (2012) 112–115
Fig. 1. Image showing the Legion® condylar component in solid gray with the Genesis II® revision condylar component outlined in red.
and 2005. A revision system with offset couplers became available in 2006 (Legion® RTKA) and was subsequently used in all RTKA cases except for 3 cases during the year 2006 in which Genesis II® was used. All surgery was performed under the direction of the senior author utilizing either Genesis II® or Legion® RTKA. Both implant systems utilize a technique in which the intramedullary canal is reamed with straight reamers by power until a tight press fit is obtained in the diaphysis. The tibial cut is made perpendicular to the intramedullary canal of the tibia, and the flexion and extension gaps are assessed by applying manual traction to the tibia with the knee in full extension and at 90° of flexion. The revision cutting blocks are then fit over the femoral reamer at a fixed valgus angle and perpendicular in the lateral plane. Metal augments are used as needed on both the femoral and tibial components to address bone defects, balance the flexion and extension spaces, and restore joint line position [10]. Femoral component rotation is based on the epicondylar axis. Cement is used
Fig. 2. Image of a Legion® femoral implant showing the coupler (orange) providing offset between stem and taper of the condylar component.
113
at the metaphyseal area while the stems are inserted into the diaphysis using press-fit fixation. The length of stem is chosen so that there is adequate diaphyseal engagement past the metaphyseal–diaphyseal junction. A cross table flexion lateral radiograph with complete overlap of the medial and lateral femoral condyles was obtained prior to surgery and at each routine postoperative follow up visit [14]. Preoperative and postoperative posterior condylar offset [1] was evaluated by an independent observer (JMB) by measuring maximal thickness of the posterior condyle, projected posterior to a tangent along the posterior cortex of the femoral shaft (Fig. 3). In order to correct any magnification variations between radiographs and differences in sizes between patients, a posterior condylar offset ratio (PCOR) was determined. The PCOR was defined as the ratio between the posterior condylar offset and implant anteroposterior thickness (IAPT). The IAPT was defined as the maximal thickness from the posterior condyle to a tangent along the anterior cortex of the femoral shaft. Orientation of the intramedullary femoral stem within the femur was measured by the angle between the anterior cortex of the femoral shaft and the axis of the stem (Fig. 4). Flexion of the stem was defined as a positive value while recurvatum was defined as a negative value. All measurements were performed by a single observer (JMB) on digital eight-bit grayscale TIFF images with EazyDraw 10.4 software (Dekorra Optics, Poynette, WI). Intraobserver errors were evaluated by repeating the radiographic measurements on a single patient which resulted in standard errors of 1.46% for PCOR and 1.52° for stem angle. Once these intraobserver errors were determined, a power analysis for linear regression was performed which indicated that 30 knees in each group would allow detection of 0.77% in PCOR and 0.80° in stem angle at 0.80 power (with alpha = 0.05). P b 0.05 was considered statistically significant. Statistical analyses were performed with Chi2 test, one-way analysis of variance, one-sample t test and paired t test. Statistical significance was set at p b 0.05. All statistical analyses were performed using JMP 7.0.1 statistical software version (SAS, Cary, NC).
3. Results The series consisted of 126 cases from 122 patients (58 female, 64 male). The mean age at surgery was 57.9 years (± 12.4). The mean follow-up was 4.5 years (± 2.82). No differences were observed between the two groups in terms of demographic data except for the length of follow-up (Tables 1 and 2).
Fig. 3. Posterior condylar offset was evaluated by measuring maximal thickness of the Posterior Condyle (PC) projected posteriorly to the tangent of the posterior cortex of the femoral shaft. In order to correct magnification variations between radiographs, posterior condylar offset was divided in each case by the Implant Antero-Posterior Thickness (IAPT, maximal thickness of the posterior condyle projected posteriorly to the tangent of the anterior cortex of the femoral shaft).
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J.M. Brilhault, M.D. Ries / The Knee 19 (2012) 112–115
Fig. 4. Orientation of the intramedullary femoral stem within the femur was measured by the angle between the tangent to the anterior cortex of the femoral shaft (plain line) and the axis of the femora stem (doted line). A flexion on the stem was defined as positive while a recurvatum of the stem was defined negative.
A higher PCOR was observed in knees with an offset stem compared to knees with a straight stem in general and within the Legion group (Tables 1 and 2). Similar differences were observed when comparing Legion® knees to Genesis II® knees (Table 1). Knees with an offset stem had a lower stem angle within the intramedullary canal in every comparison: offset vs straight, Legion® vs Genesis II®, and Legion offset vs Legion straight (Tables 1 and 2). When performing one-way analysis of variance for linear regression we observed a correlation between the PCOR of the RTKA and the PCOR of the preoperative primary TKA (F ratio = 22.23, p b 0.001). Stem angle was correlated with PCOR of RTKA overall (F ratio = 5.66, p = 0.018) but more clearly in knees with straight stems (F ratio = 19.94, p b 0.001). No correlation was observed between stem angle and PCOR of RTKA when an offset stem was used (F ratio = 1.88, p = 0.179).
4. Discussion The results of this study indicate that the use of an offset femoral stem in RTKA both increased the resulting posterior condylar offset and improved alignment of the stem within the intramedullary canal.
The correlation between PCOR and stem angle in the non offset group and its absence in the offset group suggests that the use of an offset coupler substitutes for the need to flex the stem in order to achieve adequate posterior condylar offset. Restoration of adequate posterior condylar offset in RTKA is important to provide stability in flexion and minimize posterior tibiofemoral impingement in deep flexion. Posterior offset can be increased with use of an oversized component, a flexed stemmed implant that displaces the condlylar component posteriorly, or a posterior offset stem coupler. Use of an oversized component may cause soft tissue impingement resulting in pain [15]. Flexion of the stem may result in anterior bony impingement between the proximal anterior stem tip and anterior femoral cortex, which may contribute to end stem pain. However our results indicate that use of an offset coupler permits restoration of posterior condylar offset with central stem positioning within the distal femur and avoids the need for use of an oversized component. There are some limitations in this study. All measurements were performed by a single observer. Four patients had bilateral RTKA which were analyzed as independent cases. This is a retrospective radiographic review of two consecutive series of patients in which clinical outcomes between the two groups were not compared. However, both groups were treated at the same institution by the same surgical team, and the surgical technique was very similar between the two groups. Two previous studies have addressed the positioning of an offset stemmed femoral component in RTKA, although both focused primarily on AP parameters [9,13]. Nakasone et al. [13] reported a mean 2.8° (range 3.9° to 10.0°) lateral stem angle with offset stems (LCCK® Revision Knee System, Zimmer, Warsaw, IN). This is similar to the mean stem angle we observed with straight stems (2.99° ± 1.62) but higher compared to the mean value we observed with offset stems (1.23° ± 1.43). However, the study by Nakasone et al. evaluated a revision TKA with a single 4.5 mm femoral offset option and two (145 mm and 200 mm) stem lengths. A more variable series of offset options and stem lengths may allow more anatomic alignment of the stem within the intramedullary canal. Our conclusion is that the use of a modular offset coupler with femoral stem in RTKA compared to a modular straight stem both increases the posterior condylar offset and improves alignment of the stem within the intramedullary canal.
Table 1 Analysis of all cases divided according to stem design and implant design. n Straight stem Offset stem p Genesis® II Legion® p Total
91 35 65 61 126
Gender
Age at surgery (year)
FU (year)
TKA PCOR (%)
RTKA PCOR (%)
Matched pairs in PCOR (%)
Stem angle (°)
44 F/47 M 17 F/18 M 0.982 32 F/33 M 29 F/32 M 0.8605 61 F/65 M
56.7 ± 12.6 61.2 ± 11.3 0.057 56.7 ± 12.5 59.3 ± 12.2 0.2373 57.9 ± 12.4
5.4 ± 2.2 2.1 ± 0.8 b0.001 6.7 ± 2.2 2.2 ± 0.9 b0.001 4.5 ± 2.8
45.5 ± 5.5 46.3 ± 4.6 0.407 45.9 ± 5.20 45.4 ± 5.3 0.498 45.69 ± 5.26
46.0 ± 5.6 49.4 ± 4.5 0.001 44.7 ± 5.6 48.3 ± 5.1 0.008 46.96 ± 5.54
0.56 ± 5.49 3.12 ± 6.45 0.028 − 0.28 ± 5.75 2.94 ± 5.56 0.002 1.27 ± 5.86
2.99 ± 1.62 1.23 ± 1.43 b0.001 3.14 ± 1.68 1.82 ± 1.58 b0.001 2.50 ± 1.76
FU: follow up; TKA: total knee arthroplasty; RTKA: revision total knee arthroplasty; PCOR: posterior condylar offset ration; Stem Angle: angle between femoral stem and anterior femoral cortex on lateral radiograph, flexion angle is positive, extension angle negative. Data are presented by means +/− standard deviation. Matched pairs analysis is performed between TKA PCOR and RTKA PCOR.
Table 2 Analysis of Legion® cases according to stem design.
Legion® Straight stem Legion® Offset stem p Total
n
Gender
Age at surgery (year)
FU (year)
TKA PCOR (%)
RTKA PCOR (%)
Matched pairs in PCOR (%)
Stem angle (°)
35 26
17 F/18 M 12 F/14 M 0.982 29 F/32 M
56.7 ± 12.5 59.3 ± 12.2 0.237 57.9 ±12.4
2.1 ± 0.2 2.3 ± 1.1 0.535 2.2 ± 0.9
44.1 ± 6.1 46.2 ± 4.6 0.147 45.3 ± 5.3
46.8 ± 5.6 49.5 ± 4.5 0.056 48.3 ± 5.1
2.69 ± 4.19 3.22 ± 6.52 0.039 2.93 ± 5.57
1.22 ± 1.43 2.61 ± 1.44 b0.001 1.81 ± 1.58
61
FU: follow up; TKA: total knee arthroplasty; RTKA: revision total knee arthroplasty; PCOR: posterior condylar offset ration; Stem Angle: angle between femoral stem and anterior femoral cortex on lateral radiograph, flexion angle is positive, extension angle negative. Data are presented by means +/− standard deviation. Matched pairs analysis is performed between TKA PCOR and RTKA PCOR.
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5. Conflict of interest Michael Ries has received royalty income from intellectual property on Smith & Nephew hip and knee products. Jean Brilhault received funding from Smith & Nephew for participating in the study. References [1] Bellemans J, Banks S, Victor J, Vandenneucker H, Moemans A. Fluoroscopic analysis of the kinematics of deep flexion in total knee arthroplasty. Influence of posterior condylar offset. J Bone Joint Surg Br 2002;84:50–3. [2] Kim YH, Sohn KS, Kim JS. Range of motion of standard and high-flexion posterior stabilized total knee prostheses. A prospective, randomized study. J Bone Joint Surg Am 2005;87:1470–5. [3] Massin P, Gournay A. Optimization of the posterior condylar offset, tibial slope, and condylar roll-back in total knee arthroplasty. J Arthroplasty 2006;21:889–96. [4] Victor J, Bellemans J. Physiologic kinematics as a concept for better flexion in TKA. Clin Orthop Relat Res 2006;452:53–8. [5] Arabori M, Matsui N, Kuroda R, Mizuno K, Doita M, Kurosaka M, et al. Posterior condylar offset and flexion in posterior cruciate-retaining and posterior stabilized TKA. J Orthop Sci 2008;13:46–50. [6] Long WJ, Scuderi GR. High-flexion total knee arthroplasty. J Arthroplasty 2008;23(7 Suppl):6–10.
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[7] Clarke HD, Hentz JG. Restoration of femoral anatomy in TKA with unisex and gender-specific components. Clin Orthop Relat Res 2008;466:2711–6. [8] Malviya A, Lingard EA, Weir DJ, Deehan DJ. Predicting range of movement after knee replacement: the importance of posterior condylar offset and tibial slope. Knee Surg Sports Traumatol Arthrosc 2009;17:491–8. [9] Mahoney OM, Kinsey TL. Modular femoral offset stems facilitate joint line restoration in revision knee arthroplasty. Clin Orthop Relat Res 2006;446:93–8. [10] Ries MD, Haas SB, Windsor RE. Soft-tissue balance in revision total knee arthroplasty. Surgical technique. J Bone Joint Surg Am 2004;86(Suppl 1):81–6. [11] Lo CS, Wang SJ, Wu SS. Knee stiffness on extension caused by an oversized femoral component after total knee arthroplasty: a report of two cases and a review of the literature. J Arthroplasty 2003;18:804–8. [12] Vince KJ, Long W. Revision total knee arthroplasty: the limits of press fit intramedullary fixation. Clin Orthop Relat Res 1995;317:172–7. [13] Nakasone CK, Abdeen A, Khachatourians AG, Sugimori T, Vince KG. Component alignment in revision total knee arthroplasty using diaphyseal engaging modular offset press-fit stems. J Arthroplasty 2008;23:1178–81. [14] Laidlaw MS, Rolston LR, Bozic KJ, Ries MD. Assessment of Tibiofemoral Position in Total Knee Arthroplasty using the Active Flexion Lateral Radiograph. Knee 2010;17:38–42. [15] MacDonald SJ, Charron KD, Bourne RB, Naudie DD, McCalden RW, Rorabeck CH. The John Insall Award: gender-specific total knee replacement: prospectively collected clinical outcomes. Clin Orthop Relat Res 2008;466:2612–6.
Contents lists available at ScienceDirect
The Knee
Influence of offset stem couplers in femoral revision knee arthroplasty: A radiographic study Jean M. Brilhault a,⁎, Michael D. Ries b a b
Department of Orthopaedic Surgery, C.H.R.U. de Tours, Université François-Rabelais de Tours, Tours 37044, France Department of Orthopaedic Surgery, Mission Bay Orthopaedic Institute, University of California San Francisco, San Francisco, CA 94158, United States
a r t i c l e
i n f o
Article history: Received 16 September 2010 Received in revised form 4 February 2011 Accepted 8 February 2011 Keywords: Revision total knee arthroplasty Posterior femoral condylar offset Modular stem Stem alignment
a b s t r a c t We questioned whether the use of offset femoral stem would result in modifying the posterior femoral condylar offset (PFCO) in revision knee arthroplasty (RTKA). We measured both PFCO and stem alignment on lateral radiographs of two cohorts: 91 knees with straight stems and 35 knees with offset coupled stems. A higher PCOR was observed in knees with an offset stem compared to knees with straight stem. Knees with an offset stem had a better alignment within the intramedullary canal. Our conclusion is that the use of a modular offset coupler with femoral stem in RTKA compared to a modular straight stem both increases the posterior condylar offset and improves alignment of the stem within the intramedullary canal. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Posterior femoral condylar offset (PFCO) restoration in total knee arthroplasty is important to provide stability in flexion and maximize knee range of motion [1–8]. Inadequate posterior femoral offset permits posterior tibiofemoral impingement, which can limit knee flexion and also contributes to flexion instability [1,8]. Bone loss in revision total knee arthroplasty (RTKA) often necessitates the use of intramedullary stems to provide adequate implant stability. The position of a diaphyseal engaging femoral stem determines both mediolateral and antero-posterior position of the condylar portion of the femoral component [9]. Most stems are attached to the femoral component at a fixed valgus angle of 5–7° in the frontal plane and perpendicular in the lateral plane. Since the distal femur is bowed anteriorly, a straight diaphyseal engaging stem would be expected to displace the femoral component anteriorly. This can result in inadequate posterior condylar offset, which may require either the use of an oversized femoral component to fill the flexion space or the use of a smaller diameter cemented stem. A smaller diameter cemented stem does not fill the femoral intramedullary canal or restrict the sagittal positioning of the condylar component [10–12]. However, achieving low constraint RTKA requires ligament balancing through anatomical restoration of the femoral condyles. Since the anatomy of the distal femur can be quite variable, modular offset couplers have been utilized between the stem and femoral compo-
⁎ Corresponding author at: Department of Orthopaedic Surgery, C.H.R.U. de Tours, Tours 37044, Cedex 09, France. Tel.: + 33 234 389 464; fax: + 33 247 478 385. E-mail address: [email protected] (J.M. Brilhault). 0968-0160/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.knee.2011.02.005
nent to permit more versatility in orienting the position of the implant in RTKA [9,13]. We questioned whether the use of an offset femoral stem would result in modifying the PFCO in RTKA by analyzing two cohorts with different femoral stem designs: straight stems and offset coupled stems. 2. Material and methods This study is a retrospective comparative cohort radiographic analysis of 126 consecutive RTKA's in which stemmed components were used. Revision indications included wear, osteolysis, aseptic loosening, instability, arthrofibrosis, femoral component malposition and infected TKA (which were revised with a two stage procedure). Patients with prior trauma, periprosthetic fractures, or pathologic conditions associated with extra-articular bony deformity were excluded. Either Genesis II® or Legion® revision knee systems (Smith and Nephew, Memphis, TN) that share identical contour shape and stem location were used in this study (Fig. 1). The Genesis II® revision knee system provides press-fit straight stems connected directly to the condylar component. Stems are available in 100 mm, 150 mm and 200 mm lengths with a 2 mm increment in 10–24 mm diameters. The Legion® revision knee system provides press-fit straight stems that can be connected to the condylar component with or without a 2 mm, 4 mm or 6 mm offset coupler (Fig. 2). This coupler allows 360° “dial-in” positioning of the stem. Approval for this study was obtained from the committee on human research of our institution. Data from all of our TKA patients were collected prospectively and entered into a database that served as a source of information used in this study. A revision system without femoral offset couplers (Genesis II® RTKA) was used between 1998
J.M. Brilhault, M.D. Ries / The Knee 19 (2012) 112–115
Fig. 1. Image showing the Legion® condylar component in solid gray with the Genesis II® revision condylar component outlined in red.
and 2005. A revision system with offset couplers became available in 2006 (Legion® RTKA) and was subsequently used in all RTKA cases except for 3 cases during the year 2006 in which Genesis II® was used. All surgery was performed under the direction of the senior author utilizing either Genesis II® or Legion® RTKA. Both implant systems utilize a technique in which the intramedullary canal is reamed with straight reamers by power until a tight press fit is obtained in the diaphysis. The tibial cut is made perpendicular to the intramedullary canal of the tibia, and the flexion and extension gaps are assessed by applying manual traction to the tibia with the knee in full extension and at 90° of flexion. The revision cutting blocks are then fit over the femoral reamer at a fixed valgus angle and perpendicular in the lateral plane. Metal augments are used as needed on both the femoral and tibial components to address bone defects, balance the flexion and extension spaces, and restore joint line position [10]. Femoral component rotation is based on the epicondylar axis. Cement is used
Fig. 2. Image of a Legion® femoral implant showing the coupler (orange) providing offset between stem and taper of the condylar component.
113
at the metaphyseal area while the stems are inserted into the diaphysis using press-fit fixation. The length of stem is chosen so that there is adequate diaphyseal engagement past the metaphyseal–diaphyseal junction. A cross table flexion lateral radiograph with complete overlap of the medial and lateral femoral condyles was obtained prior to surgery and at each routine postoperative follow up visit [14]. Preoperative and postoperative posterior condylar offset [1] was evaluated by an independent observer (JMB) by measuring maximal thickness of the posterior condyle, projected posterior to a tangent along the posterior cortex of the femoral shaft (Fig. 3). In order to correct any magnification variations between radiographs and differences in sizes between patients, a posterior condylar offset ratio (PCOR) was determined. The PCOR was defined as the ratio between the posterior condylar offset and implant anteroposterior thickness (IAPT). The IAPT was defined as the maximal thickness from the posterior condyle to a tangent along the anterior cortex of the femoral shaft. Orientation of the intramedullary femoral stem within the femur was measured by the angle between the anterior cortex of the femoral shaft and the axis of the stem (Fig. 4). Flexion of the stem was defined as a positive value while recurvatum was defined as a negative value. All measurements were performed by a single observer (JMB) on digital eight-bit grayscale TIFF images with EazyDraw 10.4 software (Dekorra Optics, Poynette, WI). Intraobserver errors were evaluated by repeating the radiographic measurements on a single patient which resulted in standard errors of 1.46% for PCOR and 1.52° for stem angle. Once these intraobserver errors were determined, a power analysis for linear regression was performed which indicated that 30 knees in each group would allow detection of 0.77% in PCOR and 0.80° in stem angle at 0.80 power (with alpha = 0.05). P b 0.05 was considered statistically significant. Statistical analyses were performed with Chi2 test, one-way analysis of variance, one-sample t test and paired t test. Statistical significance was set at p b 0.05. All statistical analyses were performed using JMP 7.0.1 statistical software version (SAS, Cary, NC).
3. Results The series consisted of 126 cases from 122 patients (58 female, 64 male). The mean age at surgery was 57.9 years (± 12.4). The mean follow-up was 4.5 years (± 2.82). No differences were observed between the two groups in terms of demographic data except for the length of follow-up (Tables 1 and 2).
Fig. 3. Posterior condylar offset was evaluated by measuring maximal thickness of the Posterior Condyle (PC) projected posteriorly to the tangent of the posterior cortex of the femoral shaft. In order to correct magnification variations between radiographs, posterior condylar offset was divided in each case by the Implant Antero-Posterior Thickness (IAPT, maximal thickness of the posterior condyle projected posteriorly to the tangent of the anterior cortex of the femoral shaft).
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J.M. Brilhault, M.D. Ries / The Knee 19 (2012) 112–115
Fig. 4. Orientation of the intramedullary femoral stem within the femur was measured by the angle between the tangent to the anterior cortex of the femoral shaft (plain line) and the axis of the femora stem (doted line). A flexion on the stem was defined as positive while a recurvatum of the stem was defined negative.
A higher PCOR was observed in knees with an offset stem compared to knees with a straight stem in general and within the Legion group (Tables 1 and 2). Similar differences were observed when comparing Legion® knees to Genesis II® knees (Table 1). Knees with an offset stem had a lower stem angle within the intramedullary canal in every comparison: offset vs straight, Legion® vs Genesis II®, and Legion offset vs Legion straight (Tables 1 and 2). When performing one-way analysis of variance for linear regression we observed a correlation between the PCOR of the RTKA and the PCOR of the preoperative primary TKA (F ratio = 22.23, p b 0.001). Stem angle was correlated with PCOR of RTKA overall (F ratio = 5.66, p = 0.018) but more clearly in knees with straight stems (F ratio = 19.94, p b 0.001). No correlation was observed between stem angle and PCOR of RTKA when an offset stem was used (F ratio = 1.88, p = 0.179).
4. Discussion The results of this study indicate that the use of an offset femoral stem in RTKA both increased the resulting posterior condylar offset and improved alignment of the stem within the intramedullary canal.
The correlation between PCOR and stem angle in the non offset group and its absence in the offset group suggests that the use of an offset coupler substitutes for the need to flex the stem in order to achieve adequate posterior condylar offset. Restoration of adequate posterior condylar offset in RTKA is important to provide stability in flexion and minimize posterior tibiofemoral impingement in deep flexion. Posterior offset can be increased with use of an oversized component, a flexed stemmed implant that displaces the condlylar component posteriorly, or a posterior offset stem coupler. Use of an oversized component may cause soft tissue impingement resulting in pain [15]. Flexion of the stem may result in anterior bony impingement between the proximal anterior stem tip and anterior femoral cortex, which may contribute to end stem pain. However our results indicate that use of an offset coupler permits restoration of posterior condylar offset with central stem positioning within the distal femur and avoids the need for use of an oversized component. There are some limitations in this study. All measurements were performed by a single observer. Four patients had bilateral RTKA which were analyzed as independent cases. This is a retrospective radiographic review of two consecutive series of patients in which clinical outcomes between the two groups were not compared. However, both groups were treated at the same institution by the same surgical team, and the surgical technique was very similar between the two groups. Two previous studies have addressed the positioning of an offset stemmed femoral component in RTKA, although both focused primarily on AP parameters [9,13]. Nakasone et al. [13] reported a mean 2.8° (range 3.9° to 10.0°) lateral stem angle with offset stems (LCCK® Revision Knee System, Zimmer, Warsaw, IN). This is similar to the mean stem angle we observed with straight stems (2.99° ± 1.62) but higher compared to the mean value we observed with offset stems (1.23° ± 1.43). However, the study by Nakasone et al. evaluated a revision TKA with a single 4.5 mm femoral offset option and two (145 mm and 200 mm) stem lengths. A more variable series of offset options and stem lengths may allow more anatomic alignment of the stem within the intramedullary canal. Our conclusion is that the use of a modular offset coupler with femoral stem in RTKA compared to a modular straight stem both increases the posterior condylar offset and improves alignment of the stem within the intramedullary canal.
Table 1 Analysis of all cases divided according to stem design and implant design. n Straight stem Offset stem p Genesis® II Legion® p Total
91 35 65 61 126
Gender
Age at surgery (year)
FU (year)
TKA PCOR (%)
RTKA PCOR (%)
Matched pairs in PCOR (%)
Stem angle (°)
44 F/47 M 17 F/18 M 0.982 32 F/33 M 29 F/32 M 0.8605 61 F/65 M
56.7 ± 12.6 61.2 ± 11.3 0.057 56.7 ± 12.5 59.3 ± 12.2 0.2373 57.9 ± 12.4
5.4 ± 2.2 2.1 ± 0.8 b0.001 6.7 ± 2.2 2.2 ± 0.9 b0.001 4.5 ± 2.8
45.5 ± 5.5 46.3 ± 4.6 0.407 45.9 ± 5.20 45.4 ± 5.3 0.498 45.69 ± 5.26
46.0 ± 5.6 49.4 ± 4.5 0.001 44.7 ± 5.6 48.3 ± 5.1 0.008 46.96 ± 5.54
0.56 ± 5.49 3.12 ± 6.45 0.028 − 0.28 ± 5.75 2.94 ± 5.56 0.002 1.27 ± 5.86
2.99 ± 1.62 1.23 ± 1.43 b0.001 3.14 ± 1.68 1.82 ± 1.58 b0.001 2.50 ± 1.76
FU: follow up; TKA: total knee arthroplasty; RTKA: revision total knee arthroplasty; PCOR: posterior condylar offset ration; Stem Angle: angle between femoral stem and anterior femoral cortex on lateral radiograph, flexion angle is positive, extension angle negative. Data are presented by means +/− standard deviation. Matched pairs analysis is performed between TKA PCOR and RTKA PCOR.
Table 2 Analysis of Legion® cases according to stem design.
Legion® Straight stem Legion® Offset stem p Total
n
Gender
Age at surgery (year)
FU (year)
TKA PCOR (%)
RTKA PCOR (%)
Matched pairs in PCOR (%)
Stem angle (°)
35 26
17 F/18 M 12 F/14 M 0.982 29 F/32 M
56.7 ± 12.5 59.3 ± 12.2 0.237 57.9 ±12.4
2.1 ± 0.2 2.3 ± 1.1 0.535 2.2 ± 0.9
44.1 ± 6.1 46.2 ± 4.6 0.147 45.3 ± 5.3
46.8 ± 5.6 49.5 ± 4.5 0.056 48.3 ± 5.1
2.69 ± 4.19 3.22 ± 6.52 0.039 2.93 ± 5.57
1.22 ± 1.43 2.61 ± 1.44 b0.001 1.81 ± 1.58
61
FU: follow up; TKA: total knee arthroplasty; RTKA: revision total knee arthroplasty; PCOR: posterior condylar offset ration; Stem Angle: angle between femoral stem and anterior femoral cortex on lateral radiograph, flexion angle is positive, extension angle negative. Data are presented by means +/− standard deviation. Matched pairs analysis is performed between TKA PCOR and RTKA PCOR.
J.M. Brilhault, M.D. Ries / The Knee 19 (2012) 112–115
5. Conflict of interest Michael Ries has received royalty income from intellectual property on Smith & Nephew hip and knee products. Jean Brilhault received funding from Smith & Nephew for participating in the study. References [1] Bellemans J, Banks S, Victor J, Vandenneucker H, Moemans A. Fluoroscopic analysis of the kinematics of deep flexion in total knee arthroplasty. Influence of posterior condylar offset. J Bone Joint Surg Br 2002;84:50–3. [2] Kim YH, Sohn KS, Kim JS. Range of motion of standard and high-flexion posterior stabilized total knee prostheses. A prospective, randomized study. J Bone Joint Surg Am 2005;87:1470–5. [3] Massin P, Gournay A. Optimization of the posterior condylar offset, tibial slope, and condylar roll-back in total knee arthroplasty. J Arthroplasty 2006;21:889–96. [4] Victor J, Bellemans J. Physiologic kinematics as a concept for better flexion in TKA. Clin Orthop Relat Res 2006;452:53–8. [5] Arabori M, Matsui N, Kuroda R, Mizuno K, Doita M, Kurosaka M, et al. Posterior condylar offset and flexion in posterior cruciate-retaining and posterior stabilized TKA. J Orthop Sci 2008;13:46–50. [6] Long WJ, Scuderi GR. High-flexion total knee arthroplasty. J Arthroplasty 2008;23(7 Suppl):6–10.
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[7] Clarke HD, Hentz JG. Restoration of femoral anatomy in TKA with unisex and gender-specific components. Clin Orthop Relat Res 2008;466:2711–6. [8] Malviya A, Lingard EA, Weir DJ, Deehan DJ. Predicting range of movement after knee replacement: the importance of posterior condylar offset and tibial slope. Knee Surg Sports Traumatol Arthrosc 2009;17:491–8. [9] Mahoney OM, Kinsey TL. Modular femoral offset stems facilitate joint line restoration in revision knee arthroplasty. Clin Orthop Relat Res 2006;446:93–8. [10] Ries MD, Haas SB, Windsor RE. Soft-tissue balance in revision total knee arthroplasty. Surgical technique. J Bone Joint Surg Am 2004;86(Suppl 1):81–6. [11] Lo CS, Wang SJ, Wu SS. Knee stiffness on extension caused by an oversized femoral component after total knee arthroplasty: a report of two cases and a review of the literature. J Arthroplasty 2003;18:804–8. [12] Vince KJ, Long W. Revision total knee arthroplasty: the limits of press fit intramedullary fixation. Clin Orthop Relat Res 1995;317:172–7. [13] Nakasone CK, Abdeen A, Khachatourians AG, Sugimori T, Vince KG. Component alignment in revision total knee arthroplasty using diaphyseal engaging modular offset press-fit stems. J Arthroplasty 2008;23:1178–81. [14] Laidlaw MS, Rolston LR, Bozic KJ, Ries MD. Assessment of Tibiofemoral Position in Total Knee Arthroplasty using the Active Flexion Lateral Radiograph. Knee 2010;17:38–42. [15] MacDonald SJ, Charron KD, Bourne RB, Naudie DD, McCalden RW, Rorabeck CH. The John Insall Award: gender-specific total knee replacement: prospectively collected clinical outcomes. Clin Orthop Relat Res 2008;466:2612–6.