The Journal of Arthroplasty 29 (2014) 2305–2308
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The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Correlation Between Knee Kinematics and Patellofemoral Contact Pressure in Total Knee Arthroplasty Takuya Konno, MD a, Tomohiro Onodera, MD, PhD a, Yusuke Nishio, MD a, Yasuhiko Kasahara, MD, PhD a, Norimasa Iwasaki, MD, PhD a, Tokifumi Majima, MD, PhD b a b
Department of Orthopaedic Surgery, Hokkaido University Graduate School of Medicine, North 15 West 7, Kita–Ku, Sapporo Japan Department of Orthopedic Surgery, International Univ. of Health and Welfare-Hospital, 537-3, Iguchi, Nasushiobara City, Japan
a r t i c l e
i n f o
Article history: Received 22 April 2014 Accepted 19 July 2014 Keywords: total knee arthroplasty medial pivot pattern patello-femoral contact stress kinematics pattern Mobile bearing insert
a b s t r a c t The aim of this study is to evaluate the relationship between patellofemoral contact stress and intraoperative knee kinematic patterns after mobile bearing total knee arthroplasty (TKA). Medial osteoarthritic knees of forty-six posterior-stabilized total knee prostheses were evaluated using a computed tomography-guided navigation system. Subjects were divided into two groups based on intraoperative knee kinematic patterns: the medial pivot group (n = 19) and the non-medial pivot group (n = 27). Mean intraoperative patellofemoral contact stress was significantly lower in the medial pivot group than in the non-medial pivot group (1.7 MPa vs. 3.2 MPa, P b 0.05). An intraoperative medial pivot pattern results in reduced patello-femoral contact stress. © 2014 Elsevier Inc. All rights reserved.
Total knee arthroplasty (TKA) has proven to be highly successful at alleviating pain and improving function in patients with advanced knee arthritis. As the indications of TKA have been widened, the demand for the procedure is increasing. Therefore, the number of revision TKAs is also rising, with a projected increase of 601% between 2005 and 2030 in The United States [1]. Patello-femoral problems are one of the common post-TKA complications and may result in revision surgery [2,3]. Several reports indicated that up to 12% of TKA revisions are due to patello-femoral dysfunction [2,4,5]. Various factors such as body mass index, patellar cartilage thickness, radiologically evident patello-femoral compartment osteoarthritis, and patellar tilt do not accurately predict patello-femoral dysfunction [6,7]. Five to 45% of post-TKA patients complain of residual anterior knee pain [8,9]. Patello-femoral complications have been attributed to errors in operative technique, inferior prosthetic design, components overstuffing, and excessive patello-femoral loads. Several in vitro patellar resurfacing studies found a decrease in the retropatellar contact area, an increase in retropatellar pressure, and an increase in shear forces after resurfacing the patella [10,11], However, the etiology of these complications with patellar resurfacing is yet to be clearly established [11,12]. Low patello-femoral pressure was considered to be advantageous because high pressures might account for anterior knee pain [12,13].
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.07.020. Reprint requests: Tokifumi Majima, MD, PhD, Department of Orthopedic Surgery, International Univ. of Health and Welfare Hospital, 537-3, Iguchi, Nasushiobara City, 329-2763, Japan. http://dx.doi.org/10.1016/j.arth.2014.07.020 0883-5403/© 2014 Elsevier Inc. All rights reserved.
Large tibiofemoral kinematic variations, including the medial pivot [14,15] and the lateral pivot [16,17], are known to exist after conventional TKA. There is a wide variation in patellar kinematics associated with patello-femoral contact stress in the normal knee as well [18,19]. However, we have found no study of the relationship between tibiofemoral kinematic patterns after TKA and patellofemoral contact stress. We hypothesized that tibiofemoral kinematic patterns after TKA will impact patello-femoral contact stress. The aim of this study was to evaluate the relationship between knee kinematics and patellofemoral contact stress in mobile bearing prosthesis with navigated TKA procedures.
Materials and Methods One hundred and fifteen consecutive patients who had medial knee osteoarthritis were enrolled in this study. All knees had a Kellgren-Lawrence grade of 4 in the medial compartment and underwent a primary posterior stabilized mobile bearing total knee arthroplasty (PFC Sigma RP-F; Depuy, Warsaw, IN, USA) between May 2007 and October 2010. A computed tomography-guided navigation system (Vector Vision 1.6, Brain LAB, Heimstetten, Germany) was used for accurate implantation with a standardized navigated TKA technique for all cases. Surgeries were performed by a single surgeon using a subvastus approach to mitigate the influence of surgical approach to producing muscle balance. No patients received a lateral retinacular release. Approval for this experiment was obtained from our institutional investigational review board.
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The patello-femoral contact stress data was obtained from 55 knees of 44 TKA patients (38%), with complete kinematics data obtained from 46 knees of 39 patients. Ultimately, thirty-nine patients (46 knees) were enrolled in the present study. The mean subject age was 73.3 years (range 55–88 years), and there were nine men and 30 women enrolled in the study. The mean body mass index was 26.6 kg/m 2 (range 18.1–36.1 kg/m 2). All knees were divided into the medial pivot group (M group, n = 19) or the non-medial pivot group (N group, n = 27). Average age at the time of surgery was 73 years (range 61–87 years) in the M group and 74 years (range 55–88 years) in the N group. Two men and 17 women were placed in the M group; eight men and 19 women were placed in the N group. The mean body mass index was 27.2 kg/m 2 (range 18.1–34.6 kg/m 2) in the M group and 26.2 kg/m 2 (range 20.6–36.1 kg/m 2) in the N group. There were no significant differences in patient demographics between the two groups (Table 1). Surgical Procedures We performed our procedures using the navigation system according to the manufacturer’s instructions. The air tourniquet was inflated with 280 mmHg in all cases during surgery and all knees were exposed with a subvastus approach. The posterior cruciate ligament was sacrificed at the beginning of the procedure. Appropriate soft tissue releases for the medial structures in the knee were completed. Next, the proximal tibial osteotomy was set on the navigation system perpendicular to the anatomical axis in the coronal plane with 3° posterior inclination in the sagittal plane. After the tibial bone resections, the femoral osteophytes were removed. Coronal plane ligament imbalance was corrected by gradual medial release following the three-step method which included: first deep MCL release, followed by semimembranosus release second and superficial MCL pie-crust release third, until the gap imbalance was fewer than 2 mm. This gap balance was checked using a ligament balancer (Endplus, Marl, Germany) at 80 N in each compartment. The flexion gap was measured by the navigation system with the CAS ligament tensionar (Depuy Inc., Warsaw, IN, USA) at 90° of knee flexion. The flexion gap was measured with a CAS ligament tensioner in order to reduce the additional tension caused by the tensioner itself pushing the patellar tendon. The amount of external rotation of the femoral component was adjusted by the navigation system with a balanced gap technique. Intraoperative Measurement The intraoperative femoral rotation assessment, patellar tracking and patello-femoral (PF) contact pressure assessment was performed with the mobile platform tibial component after all bony resections and soft tissue releases were completed. The amount of patellar bone resection measured by a vernier caliper was equal to the thickness of the patellar component. The joint capsule was temporarily sutured during the measurement, and the tourniquet remained inflated. The real-time assessment of femoral rotation, medial shift, and lateral patellar tilt from knee extension to flexion was measured using the Table 1 Patient Demographics. Variable Sex Female Male Age (years) Pre-operation knee ROM Flexion Extension BMI
Medial Pivot 17 (85%) 3 (15%) 73 (range, 61–87) 119 (range, 95–140) −5 (range, −15 to 0) 27.2
navigation system in the kinematic mode. We performed a passive range of motion from maximum extension to maximum flexion. The flexion movement began by initially supporting the foot posteriorly to record the position of full extension. While supporting the foot with an open palm, the surgeon used his opposite hand to gently lift the thigh, flexing the hip and knee. The patella tracker (Brain Lab) was fixed onto the anterior aspect of the patella by small screws. The force exerted on the patellar component was measured directly using a uniaxial ultrathin (100 μm) force transducer (FlexiForce; Nitta Corporation, Osaka, Japan) embedded between the backside of the patellar trial component and an originally developed metal plate fixed to the bony cut surface of the patella. The contact stress was calculated by dividing the total force on the sensor by the sensing area [13]. Intraoperative knee kinematics were measured using the navigation system after implantation. Cases for which all kinematic data from 0° to 90° could not be acquired were excluded. The surgical epicondylar axis connecting the medial to the lateral epicondyle was defined as the flexion axis based on previous reports [20]. Intraoperative kinematics were measured from 0° to 90° at 10° intervals. All positions of the surgical epicondylar axis were projected to the tibial axial plane. The node of the epicondylar axis of each 10° measurement was defined as the center of rotation [16]. Patients with an average medial center of rotation between 0° and 90° knee flexion were defined as belonging to the medial pivot group. Other kinematic patterns were defined as belonging to the nonmedial pivot group. The non-medial pivot group included those with a lateral pivot, parallel motion and paradoxical pivot. Although the average node did not exist in the media tibial plateau if the average center of rotation existed in medial tibial plateau or nearly parallel motion, two senior orthopedic surgeons who had no involvement with any of the operations independently evaluated all kinematic patterns before assigning groups. Details of kinematic groupings were reported previously [21]. The femoral component rotation (FCR) is defined as the span between the femoral component rotation planned for the surgical epicondylar axis before and that achieved after the operation [22]. Statistical comparison of the maximum value of femoral rotation, medial patellar shift, lateral patellar tilt and contact stress was made using an unpaired t test. All differences were considered significant at a probability level of 95% (P b .05).
Results The mean maximum patello-femoral stress in the M group was significantly lower than that of the N group (1.7 ± 1.7 MPa vs. 3.2 ± 2.7 MPa, P = 0.03). The mean medial patellar shift from knee extension to flexion demonstrated no significant difference between the M group and the N group (11.7 ± 12.4 mm vs. 8.9 ± 8.9 mm, P = 0.48). The mean lateral patellar tilt also revealed no significant difference between the M group and the N group (9.4° ± 5.2° vs. 11.6° ± 4.1°) (P = 0.33). FCR was 0.58° internal rotation in the M group and 1.97° internal rotation in the N group (P = 0.14) (Table 2). We confirmed intraobserver surgical epicondylar axis measurement consistency with the coefficient of variation (CV) when we planned femoral component rotation with the navigation. Intraobservational and interobservational CVs of these measurements were 0.8%, and 2.1%, respectively. Therefore, the same investigator performed all measurements in this study in order to reduce data variation.
Non-medial Pivot 17 (74%) 6 (26%) 74 (range, 55–88) 115 (range, 95–130) -6 (range, −20 to 0) 26.2
Table 2 Results. Variable Patella contact pressure (MPa) Patella medial shift (mm) Patella lateral tilt (degree) Condylar twist angle
Medial Pivot 1.73 11.68 9.42 −0.58
(±1.70) (±12.38) (±5.20) (±2.5)
Non-medial Pivot 3.24 8.85 11.64 −1.97
(±2.66) (±8.88) (±4.07) (±3.43)
P Value 0.03 0.48 0.33 0.14
T. Konno et al. / The Journal of Arthroplasty 29 (2014) 2305–2308
Non-medial pivot
Medial pivot
Lateral eral
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Medial
A
Lateral
Medial
B
Fig. 1. The scheme of patello-femoral stress distribution in knee flexion. Patello-femoral contact stress is homogeneously dispersed in medial pivot knee (A) whereas that is concentrated in non-medial pivot knee (B).
Discussion There is a large variation in tibiofemoral kinematics after conventional TKA including the medial pivot [14,15] and lateral pivot [16,17]. Our findings also included a large variation in tibiofemoral mechanics similar to the previous reports. We divided all samples into either a medial-pivot group or a non-medial-pivot group, finding significantly lower patello-femoral stress in the medial-pivot group than in the nonmedial pivot group. Medial-pivot kinematics reduced patello-femoral contact pressure, suggesting that restoring normal tibiofemoral kinematics possibly results in a decreased risk of patello-femoral problems such as anterior knee pain after TKA. Mobile-bearing designs were developed in an attempt to duplicate natural knee kinematics. Mobile-bearing designs allow for small mismatches of the tibial and femoral component rotational positions as well as for improved patellar tracking. In mobile bearing TKA, patello-femoral contact stress is lower than that of fixed-bearing TKA [23] with intraoperative measurement. However, the relationship between patello-femoral contact stress and kinematic patterns after TKA has not been clarified. Previous reports revealed that external rotation of femoral component alignment resulted in proper patellar tracking whereas internal femoral component rotation moves the center of the trochlear groove internally away from the patella and results in patello-femoral complications [24–26]. These results suggest that femoral component rotational alignment is an important factor in patello-femoral contact stress. In this study, the femoral component rotational alignment in the non-medial pivot group tended to be more internal rotation than that of medial pivot group, presumably suggesting that internal rotation of femoral component may induce knee kinematics to non-medial pivot pattern. Although we did not detect a significant difference between the femoral component rotational alignment in the medial pivot group and that of the non-medial pivot group, we should identify this hypothesis in the future. Medial pivot kinematics presumably disperses and equalizes patello-femoral contact stress due to direct a femoral groove at a tibial tuberosity in knee flexion (Fig. 1). We speculated that other various pre- and intraoperative factors such as soft tissue release, ligament balance and preoperative joint surface geometry, might affect the kinematics pattern. Dynamic factors during medial pivot kinematics may be the reason for reduced patello-femoral contact pressure. Further studies are required for understanding the pre- or intraoperative factors, which may predict TKA postoperative kinematics patterns. Several studies, including cadaveric studies [10,11,13,19,27–32], validated 3D computed model [33–35], and in vivo fluoroscopic investigation technique studies [36,37], have evaluated patellofemoral contact area or pressure after TKA. We have directly measured intraoperative patello-femoral contact pressure and knee kinematics in this study based on our previous report that
intraoperative kinematic measurement strongly correlates with postoperative kinematics [38]. We adopted a subvastus approach to reduce the quadriceps effect, and a mobile bearing insert to eliminate the influence of tibial component rotational variation, and used a navigation system to enhance the bone cut accuracy in an effort to eliminate the influence of other factors except knee kinematics. Our study had several limitations. First, the sample size was small. We had to exclude incomplete data from nine knees because we could not confirm whether the navigation system successfully achieved all the kinematics data from the operation. Second, knee kinematic measurements during surgery are different from measurements made on an outpatient visit due to the use of anesthesia and/or of an air tourniquet and the non-weight bearing condition of the knee. We have previously reported that intraoperative kinematic measurement strongly correlates with postoperative kinematics [38]. We believe that our intraoperative kinematic measurements in this study correlate with postoperative kinematics. Highly accurate and ethically acceptable measurement of the knee under weight bearing conditions in vivo would be ideal. In conclusion, intraoperative medial pivot kinematic patterns resulted in significant reduction of patello-femoral contact pressure compared with knees demonstrating non-medial pivot kinematic patterns. References 1. Kurtz S, Ong K, Lau E, et al. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg Am 2007;89 (4):780. 2. Boyd Jr AD, Ewald FC, Thomas WH, et al. Long-term complications after total knee arthroplasty with or without resurfacing of the patella. J Bone Joint Surg Am 1993; 75(5):674. 3. Skwara A, Tibesku CO, Ostermeier S, et al. Differences in patellofemoral contact stresses between mobile-bearing and fixed-bearing total knee arthroplasties: a dynamic in vitro measurement. Arch Orthop Trauma Surg 2009;129(7):901. 4. Harwin SF. Patellofemoral complications in symmetrical total knee arthroplasty. J Arthroplasty 1998;13(7):753. 5. Ranawat CS. The patellofemoral joint in total condylar knee arthroplasty. Pros and cons based on five- to ten-year follow-up observations. Clin Orthop Relat Res 1986; 205:93. 6. Waters TS, Bentley G. Patellar resurfacing in total knee arthroplasty. A prospective, randomized study. J Bone Joint Surg Am 2003;85-A(2):212. 7. Wood DJ, Smith AJ, Collopy D, et al. Patellar resurfacing in total knee arthroplasty: a prospective, randomized trial. J Bone Joint Surg Am 2002;84-A(2):187. 8. Armstrong AD, Brien HJ, Dunning CE, et al. Patellar position after total knee arthroplasty: influence of femoral component malposition. J Arthroplasty 2003;18 (4):458. 9. Campbell DG, Duncan WW, Ashworth M, et al. Patellar resurfacing in total knee replacement: a ten-year randomised prospective trial. J Bone Joint Surg (Br) 2006; 88(6):734. 10. Benjamin JB, Szivek JA, Hammond AS, et al. Contact areas and pressures between native patellas and prosthetic femoral components. J Arthroplasty 1998;13(6):693. 11. Xu C, Chu X, Wu H. Effects of patellar resurfacing on contact area and contact stress in total knee arthroplasty. Knee 2007;14(3):183. 12. Fuchs S, Skwara A, Tibesku CO, et al. Retropatellar contact characteristics before and after total knee arthroplasty. Knee 2005;12(1):9.
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13. Matsuda S, Ishinishi T, White SE, et al. Patellofemoral joint after total knee arthroplasty. Effect on contact area and contact stress. J Arthroplasty 1997;12(7):790. 14. Miyazaki Y, Nakamura T, Kogame K, et al. Analysis of the kinematics of total knee prostheses with a medial pivot design. J Arthroplasty 2011;26(7):1038. 15. Victor J, Van Glabbeek F, Vander Sloten J, et al. An experimental model for kinematic analysis of the knee. J Bone Joint Surg Am 2009;91(Suppl. 6):150. 16. Banks SA, Hodge WA. 2003 Hap Paul Award Paper of the International Society for Technology in Arthroplasty. Design and activity dependence of kinematics in fixed and mobile-bearing knee arthroplasties. J Arthroplasty 2004;19(7):809. 17. Dennis DA, Komistek RD, Mahfouz MR, et al. Multicenter determination of in vivo kinematics after total knee arthroplasty. Clin Orthop Relat Res 2003;416:37. 18. Lee TQ, Gerken AP, Glaser FE, et al. Patellofemoral joint kinematics and contact pressures in total knee arthroplasty. Clin Orthop Relat Res 1997;340:257. 19. Kainz H, Reng W, Augat P, et al. Influence of total knee arthroplasty on patellar kinematics and contact characteristics. Int Orthop 2012;36(1):73. 20. Asano T, Akagi M, Nakamura T. The functional flexion-extension axis of the knee corresponds to the surgical epicondylar axis: in vivo analysis using a biplanar image-matching technique. J Arthroplasty 2005;20(8):1060. 21. Nishio Y, Onodera T, Kasahara Y, et al. Intraoperative medial pivot affects deep knee flexion angle and patient-reported outcomes after total knee arthroplasty. J Arthroplasty 2014;29(4):702–6. 22. Berger RA, Rubash HE, Seel MJ, et al. Determining the rotational alignment of the femoral component in total knee arthroplasty using the epicondylar axis. Clin Orthop Relat Res 1993;286:40. 23. Sawaguchi N, Majima T, Ishigaki T, et al. Mobile-bearing total knee arthroplasty improves patellar tracking and patellofemoral contact stress: in vivo measurements in the same patients. J Arthroplasty 2010;25(6):920. 24. Berger RA, Crossett LS, Jacobs JJ, et al. Malrotation causing patellofemoral complications after total knee arthroplasty. Clin Orthop Relat Res 1998;356:144. 25. Kingsley R, Donald S, Jess H, et al. Revision surgery for patellar dislocation after primary total knee arthroplasty. J Arthroplasty 2004;19:956.
26. Rhoads DD, Noble PC, Reuben JD, et al. The effect of femoral component position on the kinematics of total knee arthroplasty. Clin Orthop Relat Res 1993;286:122. 27. Skwara A, Tibesku CO, Ostermeier S, et al. Differences in patellofemoral contact stresses between mobile-bearing and fixed-bearing total knee arthroplasties: a dynamic in vitro measurement. Arch Orthop Trauma Surg 2008;129(7):901. 28. Wurm S, Kainz H, Reng W, et al. The influence of patellar resurfacing on patellar kinetics and retropatellar contact characteristics. J Orthop Sci 2013;18(1):61–9. 29. Elias JJ, Wilson DR, Adamson R, et al. Evaluation of a computational model used to predict the patellofemoral contact pressure distribution. J Biomech 2004;37(3):295. 30. Fuchs S, Schutte G, Witte H, et al. Retropatellar contact characteristics in total knee arthroplasty with and without patellar resurfacing. Int Orthop 2000;24(4):191. 31. Li G, DeFrate LE, Zayontz S, et al. The effect of tibiofemoral joint kinematics on patellofemoral contact pressures under simulated muscle loads. J Orthop Res 2004; 22(4):801. 32. Matsuda S, Ishinishi T, Whiteside LA. Contact stresses with an unresurfaced patella in total knee arthroplasty: the effect of femoral component design. Orthopedics 2000;23(3):213. 33. Bischoff JE, Hertzler JS, Mason JJ. Patellofemoral interactions in walking, stair ascent, and stair descent using a virtual patella model. J Biomech 2009;42(11):1678. 34. Heegaard J, Leyvraz PF, Curnier A, et al. The biomechanics of the human patella during passive knee flexion. J Biomech 1995;28(11):1265. 35. Heegaard JH, Leyvraz PF, Hovey CB. A computer model to simulate patellar biomechanics following total knee replacement: the effects of femoral component alignment. Clin Biomech (Bristol, Avon) 2001;16(5):415. 36. Sharma A, Leszko F, Komistek RD, et al. In vivo patellofemoral forces in high flexion total knee arthroplasty. J Biomech 2008;41(3):642. 37. Stiehl JB, Komistek RD, Dennis DA, et al. Kinematics of the patellofemoral joint in total knee arthroplasty. J Arthroplasty 2001;16(6):706. 38. Majima T, Sawaguchi N, Kasahara Y, et al. Measurements of knee kinematics during TKA surgery using navigation system correlate with postoperative kinematics. J Bone Joint Surg (Br) 2012;94(SUPP_XXV):135.
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Correlation Between Knee Kinematics and Patellofemoral Contact Pressure in Total Knee Arthroplasty Takuya Konno, MD a, Tomohiro Onodera, MD, PhD a, Yusuke Nishio, MD a, Yasuhiko Kasahara, MD, PhD a, Norimasa Iwasaki, MD, PhD a, Tokifumi Majima, MD, PhD b a b
Department of Orthopaedic Surgery, Hokkaido University Graduate School of Medicine, North 15 West 7, Kita–Ku, Sapporo Japan Department of Orthopedic Surgery, International Univ. of Health and Welfare-Hospital, 537-3, Iguchi, Nasushiobara City, Japan
a r t i c l e
i n f o
Article history: Received 22 April 2014 Accepted 19 July 2014 Keywords: total knee arthroplasty medial pivot pattern patello-femoral contact stress kinematics pattern Mobile bearing insert
a b s t r a c t The aim of this study is to evaluate the relationship between patellofemoral contact stress and intraoperative knee kinematic patterns after mobile bearing total knee arthroplasty (TKA). Medial osteoarthritic knees of forty-six posterior-stabilized total knee prostheses were evaluated using a computed tomography-guided navigation system. Subjects were divided into two groups based on intraoperative knee kinematic patterns: the medial pivot group (n = 19) and the non-medial pivot group (n = 27). Mean intraoperative patellofemoral contact stress was significantly lower in the medial pivot group than in the non-medial pivot group (1.7 MPa vs. 3.2 MPa, P b 0.05). An intraoperative medial pivot pattern results in reduced patello-femoral contact stress. © 2014 Elsevier Inc. All rights reserved.
Total knee arthroplasty (TKA) has proven to be highly successful at alleviating pain and improving function in patients with advanced knee arthritis. As the indications of TKA have been widened, the demand for the procedure is increasing. Therefore, the number of revision TKAs is also rising, with a projected increase of 601% between 2005 and 2030 in The United States [1]. Patello-femoral problems are one of the common post-TKA complications and may result in revision surgery [2,3]. Several reports indicated that up to 12% of TKA revisions are due to patello-femoral dysfunction [2,4,5]. Various factors such as body mass index, patellar cartilage thickness, radiologically evident patello-femoral compartment osteoarthritis, and patellar tilt do not accurately predict patello-femoral dysfunction [6,7]. Five to 45% of post-TKA patients complain of residual anterior knee pain [8,9]. Patello-femoral complications have been attributed to errors in operative technique, inferior prosthetic design, components overstuffing, and excessive patello-femoral loads. Several in vitro patellar resurfacing studies found a decrease in the retropatellar contact area, an increase in retropatellar pressure, and an increase in shear forces after resurfacing the patella [10,11], However, the etiology of these complications with patellar resurfacing is yet to be clearly established [11,12]. Low patello-femoral pressure was considered to be advantageous because high pressures might account for anterior knee pain [12,13].
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.07.020. Reprint requests: Tokifumi Majima, MD, PhD, Department of Orthopedic Surgery, International Univ. of Health and Welfare Hospital, 537-3, Iguchi, Nasushiobara City, 329-2763, Japan. http://dx.doi.org/10.1016/j.arth.2014.07.020 0883-5403/© 2014 Elsevier Inc. All rights reserved.
Large tibiofemoral kinematic variations, including the medial pivot [14,15] and the lateral pivot [16,17], are known to exist after conventional TKA. There is a wide variation in patellar kinematics associated with patello-femoral contact stress in the normal knee as well [18,19]. However, we have found no study of the relationship between tibiofemoral kinematic patterns after TKA and patellofemoral contact stress. We hypothesized that tibiofemoral kinematic patterns after TKA will impact patello-femoral contact stress. The aim of this study was to evaluate the relationship between knee kinematics and patellofemoral contact stress in mobile bearing prosthesis with navigated TKA procedures.
Materials and Methods One hundred and fifteen consecutive patients who had medial knee osteoarthritis were enrolled in this study. All knees had a Kellgren-Lawrence grade of 4 in the medial compartment and underwent a primary posterior stabilized mobile bearing total knee arthroplasty (PFC Sigma RP-F; Depuy, Warsaw, IN, USA) between May 2007 and October 2010. A computed tomography-guided navigation system (Vector Vision 1.6, Brain LAB, Heimstetten, Germany) was used for accurate implantation with a standardized navigated TKA technique for all cases. Surgeries were performed by a single surgeon using a subvastus approach to mitigate the influence of surgical approach to producing muscle balance. No patients received a lateral retinacular release. Approval for this experiment was obtained from our institutional investigational review board.
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T. Konno et al. / The Journal of Arthroplasty 29 (2014) 2305–2308
The patello-femoral contact stress data was obtained from 55 knees of 44 TKA patients (38%), with complete kinematics data obtained from 46 knees of 39 patients. Ultimately, thirty-nine patients (46 knees) were enrolled in the present study. The mean subject age was 73.3 years (range 55–88 years), and there were nine men and 30 women enrolled in the study. The mean body mass index was 26.6 kg/m 2 (range 18.1–36.1 kg/m 2). All knees were divided into the medial pivot group (M group, n = 19) or the non-medial pivot group (N group, n = 27). Average age at the time of surgery was 73 years (range 61–87 years) in the M group and 74 years (range 55–88 years) in the N group. Two men and 17 women were placed in the M group; eight men and 19 women were placed in the N group. The mean body mass index was 27.2 kg/m 2 (range 18.1–34.6 kg/m 2) in the M group and 26.2 kg/m 2 (range 20.6–36.1 kg/m 2) in the N group. There were no significant differences in patient demographics between the two groups (Table 1). Surgical Procedures We performed our procedures using the navigation system according to the manufacturer’s instructions. The air tourniquet was inflated with 280 mmHg in all cases during surgery and all knees were exposed with a subvastus approach. The posterior cruciate ligament was sacrificed at the beginning of the procedure. Appropriate soft tissue releases for the medial structures in the knee were completed. Next, the proximal tibial osteotomy was set on the navigation system perpendicular to the anatomical axis in the coronal plane with 3° posterior inclination in the sagittal plane. After the tibial bone resections, the femoral osteophytes were removed. Coronal plane ligament imbalance was corrected by gradual medial release following the three-step method which included: first deep MCL release, followed by semimembranosus release second and superficial MCL pie-crust release third, until the gap imbalance was fewer than 2 mm. This gap balance was checked using a ligament balancer (Endplus, Marl, Germany) at 80 N in each compartment. The flexion gap was measured by the navigation system with the CAS ligament tensionar (Depuy Inc., Warsaw, IN, USA) at 90° of knee flexion. The flexion gap was measured with a CAS ligament tensioner in order to reduce the additional tension caused by the tensioner itself pushing the patellar tendon. The amount of external rotation of the femoral component was adjusted by the navigation system with a balanced gap technique. Intraoperative Measurement The intraoperative femoral rotation assessment, patellar tracking and patello-femoral (PF) contact pressure assessment was performed with the mobile platform tibial component after all bony resections and soft tissue releases were completed. The amount of patellar bone resection measured by a vernier caliper was equal to the thickness of the patellar component. The joint capsule was temporarily sutured during the measurement, and the tourniquet remained inflated. The real-time assessment of femoral rotation, medial shift, and lateral patellar tilt from knee extension to flexion was measured using the Table 1 Patient Demographics. Variable Sex Female Male Age (years) Pre-operation knee ROM Flexion Extension BMI
Medial Pivot 17 (85%) 3 (15%) 73 (range, 61–87) 119 (range, 95–140) −5 (range, −15 to 0) 27.2
navigation system in the kinematic mode. We performed a passive range of motion from maximum extension to maximum flexion. The flexion movement began by initially supporting the foot posteriorly to record the position of full extension. While supporting the foot with an open palm, the surgeon used his opposite hand to gently lift the thigh, flexing the hip and knee. The patella tracker (Brain Lab) was fixed onto the anterior aspect of the patella by small screws. The force exerted on the patellar component was measured directly using a uniaxial ultrathin (100 μm) force transducer (FlexiForce; Nitta Corporation, Osaka, Japan) embedded between the backside of the patellar trial component and an originally developed metal plate fixed to the bony cut surface of the patella. The contact stress was calculated by dividing the total force on the sensor by the sensing area [13]. Intraoperative knee kinematics were measured using the navigation system after implantation. Cases for which all kinematic data from 0° to 90° could not be acquired were excluded. The surgical epicondylar axis connecting the medial to the lateral epicondyle was defined as the flexion axis based on previous reports [20]. Intraoperative kinematics were measured from 0° to 90° at 10° intervals. All positions of the surgical epicondylar axis were projected to the tibial axial plane. The node of the epicondylar axis of each 10° measurement was defined as the center of rotation [16]. Patients with an average medial center of rotation between 0° and 90° knee flexion were defined as belonging to the medial pivot group. Other kinematic patterns were defined as belonging to the nonmedial pivot group. The non-medial pivot group included those with a lateral pivot, parallel motion and paradoxical pivot. Although the average node did not exist in the media tibial plateau if the average center of rotation existed in medial tibial plateau or nearly parallel motion, two senior orthopedic surgeons who had no involvement with any of the operations independently evaluated all kinematic patterns before assigning groups. Details of kinematic groupings were reported previously [21]. The femoral component rotation (FCR) is defined as the span between the femoral component rotation planned for the surgical epicondylar axis before and that achieved after the operation [22]. Statistical comparison of the maximum value of femoral rotation, medial patellar shift, lateral patellar tilt and contact stress was made using an unpaired t test. All differences were considered significant at a probability level of 95% (P b .05).
Results The mean maximum patello-femoral stress in the M group was significantly lower than that of the N group (1.7 ± 1.7 MPa vs. 3.2 ± 2.7 MPa, P = 0.03). The mean medial patellar shift from knee extension to flexion demonstrated no significant difference between the M group and the N group (11.7 ± 12.4 mm vs. 8.9 ± 8.9 mm, P = 0.48). The mean lateral patellar tilt also revealed no significant difference between the M group and the N group (9.4° ± 5.2° vs. 11.6° ± 4.1°) (P = 0.33). FCR was 0.58° internal rotation in the M group and 1.97° internal rotation in the N group (P = 0.14) (Table 2). We confirmed intraobserver surgical epicondylar axis measurement consistency with the coefficient of variation (CV) when we planned femoral component rotation with the navigation. Intraobservational and interobservational CVs of these measurements were 0.8%, and 2.1%, respectively. Therefore, the same investigator performed all measurements in this study in order to reduce data variation.
Non-medial Pivot 17 (74%) 6 (26%) 74 (range, 55–88) 115 (range, 95–130) -6 (range, −20 to 0) 26.2
Table 2 Results. Variable Patella contact pressure (MPa) Patella medial shift (mm) Patella lateral tilt (degree) Condylar twist angle
Medial Pivot 1.73 11.68 9.42 −0.58
(±1.70) (±12.38) (±5.20) (±2.5)
Non-medial Pivot 3.24 8.85 11.64 −1.97
(±2.66) (±8.88) (±4.07) (±3.43)
P Value 0.03 0.48 0.33 0.14
T. Konno et al. / The Journal of Arthroplasty 29 (2014) 2305–2308
Non-medial pivot
Medial pivot
Lateral eral
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Medial
A
Lateral
Medial
B
Fig. 1. The scheme of patello-femoral stress distribution in knee flexion. Patello-femoral contact stress is homogeneously dispersed in medial pivot knee (A) whereas that is concentrated in non-medial pivot knee (B).
Discussion There is a large variation in tibiofemoral kinematics after conventional TKA including the medial pivot [14,15] and lateral pivot [16,17]. Our findings also included a large variation in tibiofemoral mechanics similar to the previous reports. We divided all samples into either a medial-pivot group or a non-medial-pivot group, finding significantly lower patello-femoral stress in the medial-pivot group than in the nonmedial pivot group. Medial-pivot kinematics reduced patello-femoral contact pressure, suggesting that restoring normal tibiofemoral kinematics possibly results in a decreased risk of patello-femoral problems such as anterior knee pain after TKA. Mobile-bearing designs were developed in an attempt to duplicate natural knee kinematics. Mobile-bearing designs allow for small mismatches of the tibial and femoral component rotational positions as well as for improved patellar tracking. In mobile bearing TKA, patello-femoral contact stress is lower than that of fixed-bearing TKA [23] with intraoperative measurement. However, the relationship between patello-femoral contact stress and kinematic patterns after TKA has not been clarified. Previous reports revealed that external rotation of femoral component alignment resulted in proper patellar tracking whereas internal femoral component rotation moves the center of the trochlear groove internally away from the patella and results in patello-femoral complications [24–26]. These results suggest that femoral component rotational alignment is an important factor in patello-femoral contact stress. In this study, the femoral component rotational alignment in the non-medial pivot group tended to be more internal rotation than that of medial pivot group, presumably suggesting that internal rotation of femoral component may induce knee kinematics to non-medial pivot pattern. Although we did not detect a significant difference between the femoral component rotational alignment in the medial pivot group and that of the non-medial pivot group, we should identify this hypothesis in the future. Medial pivot kinematics presumably disperses and equalizes patello-femoral contact stress due to direct a femoral groove at a tibial tuberosity in knee flexion (Fig. 1). We speculated that other various pre- and intraoperative factors such as soft tissue release, ligament balance and preoperative joint surface geometry, might affect the kinematics pattern. Dynamic factors during medial pivot kinematics may be the reason for reduced patello-femoral contact pressure. Further studies are required for understanding the pre- or intraoperative factors, which may predict TKA postoperative kinematics patterns. Several studies, including cadaveric studies [10,11,13,19,27–32], validated 3D computed model [33–35], and in vivo fluoroscopic investigation technique studies [36,37], have evaluated patellofemoral contact area or pressure after TKA. We have directly measured intraoperative patello-femoral contact pressure and knee kinematics in this study based on our previous report that
intraoperative kinematic measurement strongly correlates with postoperative kinematics [38]. We adopted a subvastus approach to reduce the quadriceps effect, and a mobile bearing insert to eliminate the influence of tibial component rotational variation, and used a navigation system to enhance the bone cut accuracy in an effort to eliminate the influence of other factors except knee kinematics. Our study had several limitations. First, the sample size was small. We had to exclude incomplete data from nine knees because we could not confirm whether the navigation system successfully achieved all the kinematics data from the operation. Second, knee kinematic measurements during surgery are different from measurements made on an outpatient visit due to the use of anesthesia and/or of an air tourniquet and the non-weight bearing condition of the knee. We have previously reported that intraoperative kinematic measurement strongly correlates with postoperative kinematics [38]. We believe that our intraoperative kinematic measurements in this study correlate with postoperative kinematics. Highly accurate and ethically acceptable measurement of the knee under weight bearing conditions in vivo would be ideal. In conclusion, intraoperative medial pivot kinematic patterns resulted in significant reduction of patello-femoral contact pressure compared with knees demonstrating non-medial pivot kinematic patterns. References 1. Kurtz S, Ong K, Lau E, et al. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg Am 2007;89 (4):780. 2. Boyd Jr AD, Ewald FC, Thomas WH, et al. Long-term complications after total knee arthroplasty with or without resurfacing of the patella. J Bone Joint Surg Am 1993; 75(5):674. 3. Skwara A, Tibesku CO, Ostermeier S, et al. Differences in patellofemoral contact stresses between mobile-bearing and fixed-bearing total knee arthroplasties: a dynamic in vitro measurement. Arch Orthop Trauma Surg 2009;129(7):901. 4. Harwin SF. Patellofemoral complications in symmetrical total knee arthroplasty. J Arthroplasty 1998;13(7):753. 5. Ranawat CS. The patellofemoral joint in total condylar knee arthroplasty. Pros and cons based on five- to ten-year follow-up observations. Clin Orthop Relat Res 1986; 205:93. 6. Waters TS, Bentley G. Patellar resurfacing in total knee arthroplasty. A prospective, randomized study. J Bone Joint Surg Am 2003;85-A(2):212. 7. Wood DJ, Smith AJ, Collopy D, et al. Patellar resurfacing in total knee arthroplasty: a prospective, randomized trial. J Bone Joint Surg Am 2002;84-A(2):187. 8. Armstrong AD, Brien HJ, Dunning CE, et al. Patellar position after total knee arthroplasty: influence of femoral component malposition. J Arthroplasty 2003;18 (4):458. 9. Campbell DG, Duncan WW, Ashworth M, et al. Patellar resurfacing in total knee replacement: a ten-year randomised prospective trial. J Bone Joint Surg (Br) 2006; 88(6):734. 10. Benjamin JB, Szivek JA, Hammond AS, et al. Contact areas and pressures between native patellas and prosthetic femoral components. J Arthroplasty 1998;13(6):693. 11. Xu C, Chu X, Wu H. Effects of patellar resurfacing on contact area and contact stress in total knee arthroplasty. Knee 2007;14(3):183. 12. Fuchs S, Skwara A, Tibesku CO, et al. Retropatellar contact characteristics before and after total knee arthroplasty. Knee 2005;12(1):9.
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