NexGen CR Total Knee Arthroplasty: Ten Year Clinical Results

NexGen CR Total Knee Arthroplasty: Ten Year Clinical Results Authors: Sabine Mai, MD # Werner Siebert, Prof. MD # # Vitos Orthopädische Klinik Kassel, Germany Submitted to (not yet published) Argentinian Hip and Knee Society 2013 Corresponding Author: Dr. Sabine Mai Vitos Orthopädische Klinik Kassel gemeinnützige GmbH Wilhelmshöher Allee 345 34131 Kassel Tel. +49 561-30 84-821 Fax +49 561-30 84-204 sabine.mai@vitos-okk.de Keywords: Primary total knee arthroplasty, Cruciate retaining, NexGen CR, Knee Society Score, 10 year survivorship analysis

NexGen CR Total Knee Arthroplasty: Ten Year Clinical Results S. Mai, W. Siebert ABSTRACT Total Knee Arthroplasty has become a common and successful procedure in the treatment of the degenerative knee. We implanted 222 consecutive cruciate retaining third generation cemented knees as a primary procedure. Patients mean age was 71 years at surgery, 75% were women. Data were collected up to ten years postoperatively. 143 patients could be examined clinically, 76 had died and one had left the study on his own will. The mean KSS was 26.7 preoperatively, 86.8 five years and 90.8 ten years postoperatively, the mean KFS was 49.1 preoperatively, 72.2 five years and 57 ten years postoperatively. Cumulative survival with endpoint: revision for any reason was 99.1% at ten years. Six intraoperative complications occurred, two patients had infections of which one required explantation.. Thromboembolic events occurred in seven patients, one was fatal. One patient had a nerve deficit. One inlay exchange was needed for ligament laxity after repeated falls. Three patients required secondary resurfacing of the patella. One patient underwent explantation for pain due to patellar mal-tracking. This study shows very good results with the cruciate retaining NexGen implant for primary TKA in stable knees. Our findings are consistent with those of other authors. Level of evidence: IV (case series) INTRODUCTION Degeneration of joints is one of the most common diseases in orthopaedics. In the management of knees destructed by primary or secondary osteoarthritis total knee arthroplasty has become a standard treatment when conservative therapy options have been exhausted. 1

Many different implants have been developed by many different manufacturers. Today, the goals of primary total knee arthroplasty (TKA) are well defined and include the relief of pain, the restoration of function and the creation of a durable prosthetic composite. Moreover, attaining these surgical goals has created a post-operative patient population that realizes a near-complete restoration of activities of daily living (ADL), which also leads to a significant reduction in the long-term healthcare financial burden associated with the degenerative knee. The purpose of this study is to report the minimum ten year follow-up of a cruciate retaining component design used for primary TKA in a large medical teaching facility in which multiple surgeons-in-training participated performing the surgery. We hypothesize that through ten years minimum follow-up the outcome of the TKA procedures from our teaching hospital is consistent with the reported results by other studies and National Joint Registers. MATERIALS AND METHODS A series of 222 consecutive patients requiring primary TKA between November 1998 and December 1999 received the NexGen CR (Zimmer, Inc., Warsaw, IN) component and were included in the study. At the time of study initiation, no Ethics Committee approval was required by local law for quality assurance studies. For all study participants, informed consent was obtained prior to inclusion in the study. All patients were tracked continuously to minimize loss to follow-up. The tracking procedures included requesting information on the whereabouts of patients at their relatives, neighbours and at registration authorities. Patients were called in for examinations at one, two, five and ten years after surgery. Patients who did not react to our invitations or were unable to come to the hospital were visited at home but no radiographs were taken. Radiographs were taken only from patients attended at the clinic and which voluntarily agreed to it. From those, three knee images were taken: sagittal plane, coronal plane, and transverse plane (skyline 2

view). Standardized clinical assessments including the Knee Society Scoring System (KSS) ( 1 ) were performed at each follow-up visit. The KSS is divided into individual Knee and Function components. For each scoring component a maximum of 100 points can be obtained. In order to avoid bias, the data collection was performed by independent clinical observers not involved in the surgery. The data was electronically stored in an Oracle database and statistical analysis was performed using the IBM SPSS Statistics 19 software package. Besides standard descriptive statistics, data was analysed by using a two-tailed t-test for paired samples for differences between time points, or a t-test for unrelated samples for assessing differences between groups. All tests were performed two-sided. Kaplan Meier cumulative survival was calculated for revision for any reason as endpoint. Regression analysis was performed by calculating the Pearson correlation coefficient. A total of 222 consecutive knees were operated using the cruciate retaining NexGen implant from November 1998 until December 1999. The average patient age at the time of surgery was 71.0 years ±7.9 (range: 47 years 88 years). Using a Body Mass Index (BMI) of 25 as the lower threshold for overweight, only 41 (18.5%) of the patients were deemed normal, 105 (47.3%) were deemed overweight with a BMI >= 25 and < 30, 56 (25.2%) were deemed obese with a BMI >= 30 and <35, and 20 (9.0%) were deemed severely obese with a BMI of >35 (table 1). Of the total study population, 166 (74.8%) were women with a mean age of 71.6 ± 7.7 years (range: 47-88) and 56 (25.2%) were men with a mean age of 69.0 ± 7.9 years (range: 47-85). Osteoarthritis (OA) was the primary diagnosis in 202 cases (91.0%). Rheumatoid arthritis (RA was the diagnosis in 13 patients (5.9%). Four patients (1.8%) presented with post-traumatic arthritis and the remaining three patients presented with Ahlbeck disease 3

(spontaneous osteonecrosis of the knee), post-septic arthritis and psoriatic arthritis. Fixed flexion contracture was no general contraindication. The NexGen CR (Zimmer, Inc., Warsaw, IN) knee component was designed to preserve the posterior cruciate ligament (PCL) in an effort to maintain normal knee function. It is indicated for knees with intact collateral ligaments and soft tissues. The lateral and medial femoral condyles feature different radii of curvature in the sagittal plane, with the larger radius of curvature on the lateral femoral condyle. This design feature assists with axial rotation not only during rollback but through the full range of motion (ROM). In combination with the retained PCL, rotation and posterior translation are facilitated throughout the normal gait cycle. The femoral condyles feature a smaller posterior radius, supporting the rollback mechanism during flexion. With these biomechanical properties, functional ligaments are a mandatory prerequisite for this implant. Contact stresses are minimized through two independent mechanisms: In the frontal plane, the tibial plate and femoral condyles have a high congruency. This avoids point loading up to 3 of lift-off. In the sagittal plane, the large distal radius also increases the contact area, in particular during the gait phases with the highest loading. The patella shield is thin with a deep mould to improve patellar tracking and decrease stresses on the patellar-femoral compartment. The asymmetry of the femoral sulcus allows the patella to approximate physiological mediolateral translation from flexion to extension. There are eight femoral sizes, each in a left and right version. The tibial component comes in ten sizes and has a built-in posterior slope of 7. All components used in this study were stemmed, pre-coated and featured an elevated rim (cement pocket) to optimise cement fixation. Surgery was performed under spinal anaesthesia. The knee was exposed through a medial parapatellar approach with patellar eversion. The patella was resurfaced in 8 patients 4

(0.5%) who presented with patella deformation or pronounced patellar femoral pain preoperatively. In 176 patients (79.3%), no release was required. The femoral bone was cut with the aid of the 5 in 1 saw guides and intra- or extramedullary rods were used to obtain alignment. Cement mixing was always performed under vacuum. Soft tissue balancing in extension and flexion was achieved using spacer blocks. All knees were closed with 2 drains. Low molecular weight heparin (LMWH) was started the evening before surgery and, post-operatively continued in combination with compression stockings through 6-weeks. All patients started with physiotherapy on the first day after surgery and were encouraged to ambulate as tolerated. On the second day after surgery, both drains were removed and continuous passive motion (CPM) was started and continued until discharge took place, typically after 10-14 days. Whenever 90 of flexion were not achieved 14 days after surgery, manipulation under anaesthesia (MUA) was performed. This was the case in 12 patients. RESULTS At a mean Follow- up time of 10.1 ± 0.3 years (range: 9.2-11.4), 76 patients had died, one patient was no longer willing to take part in the follow-up examinations and two patients had undergone explantations, which left 143 patients available for clinical examination (table 2). Knee pain decreased over the years. Severe pain was reported in 86.0% of cases (N=191) pre-operatively, 2.4% of cases (N=5) at one year, 3.2% of cases (N=6) at five years and in no case at ten years (figure 1). 76.1% of the patients (N=108) had no pain ten years after surgery. Patello-femoral pain was reported in 68.9% (N=153) of cases pre-operatively and in 8.7% of cases (N=19) after one, in 5.9% of cases (N=11) after five and in 4.3% of cases (N=6) after ten years. 5

Pre-operatively almost every patient used the rail on the stairs or was not able to use stairs at all (95.5%, N= 212). Five years after surgery, 38.8% of patients (N=73) were able to go up and down the stairs without the use of rails. This situation deteriorated slightly ten years after surgery, when 23.2% (N=33) of the remaining patients did not need any rails to use the stairs. Walking aids were used by 53.2% of patients (N=104) preoperatively. Five years after surgery, 54.8% of patients (N=103) did not need any walking aids whereas ten years after surgery only 39.4% of patients (N=56) could walk without support. Similar results were seen with regard to walking distance. Mean pre operative flexion was 107.7 ±14.7 (range: 40-150 ), which improved minimally to 109.0 ±14.0 (range: 60-140 ) after five years and to 111.7 ±13.4 (range: 80-140 ) after ten years. Patients who had undergone a MUA in the early postoperative phase had a mean flexion of 111.3 (range 60-140) 5 years after surgery, which is comparable to the rest of the study population. The Knee Society Score (KSS) and the Knee Function-Score (KFS) were assessed preand post-operatively. A maximum of 100 points can be achieved in each. The difference between the each of the preoperative and postoperative scores at five and ten years after surgery is significant at p<0.0005 for the KFS at five years and the KSS at five and ten years and p<0.05 for the KFS at ten years (paired t-test). The Knee Score increased from preoperative 26.7 to 86.8 after five and 90.8 after ten years, the Function Score from preoperative 49.1 to 72.2 after five years and then dropped to 57 after ten years (figure 2). KFS at ten years for patients without other joints affected is 62 points whereas the mean KFS for patients with other joints deteriorated is only 53 points (p<0.05). The joints mostly affected were the spine (N=37) and the contralateral knee (N=27). Regression analysis performed at the ten year evaluation demonstrated a weak but significant correlation between increase of age at evaluation and decrease of KFS. This decrease was 1.2 points per year of age (Pearson s R 2 =0.094, p<0.001). 6

Radiographs were available from 68 knees (48%) at ten years. Three out of them (4%) showed minor radiolucent lines of 1mm around the tibial component in maximal 3 zones. No femoral or patellar radiolucencies, osteolysis, or migration of any component has been observed. Comparing the Knee Society Score of the patients with radiographic assessment with those without radiographic assessment, no significant differences between the groups for KSS (91 and 90, p=0.52), but differences in total KFS could be observed (65 and 51, p=0.007). Also a trend towards younger age could be observed in the group with radiographic assessment performed (68.3 vs. 75.5 years, p=0.09) Intraoperatively, six patients suffered complications. In one patient the femur got perforated with no further consequences. In another patient femoral cortical bone of the condyle broke off. It was treated with screw osteosynthesis and healed uneventfully. Another three patients suffered partial ruptures of (1) the medial collateral ligament, (2) the patellar tendon or (3) the quadriceps vastus muscle. The latter had been shortened preoperatively and the rupture happened upon performing a release. In one patient a complete rupture of the medial collateral ligament occurred. In the postoperative course, one patient needed secondary sutures. Superficial infections occurred in two patients, one of them developed into a deep infection and eventually required revision of the prosthesis after eight months. Another suspected deep infection could be treated successfully with ASK lavage. One patient suffered a nerve deficit. In another patient, repeated MUAs were performed until it turned out that the reason for the knee stiffness had been of neurological origin (Adenoma of the Hypophysis). Thromboembolic events occurred in seven patients during the first postoperative year. All suffered a deep vein thrombosis, one with a subsequent fatal pulmonary embolism. In one patient, ligament laxity subsequent to several falls necessitated an inlay change six years postoperatively. The same patient had a periprosthetic supracondylar fracture nine and a half years after the initial surgery and was treated with angular stable plating. The 7

prosthesis remained in situ. Another patient fractured the patella during a fall one year postoperatively and could be treated conservatively. In three patients, patellar resurfacing was performed in the course of the first postoperative year due to pronounced patellar pain. In another patient, pain caused by severe patellar mal-tracking required revision of the prosthesis three years postoperatively. The cumulative survival rate for revision for the endpoint revision for any reason was 99.1% (95% CI 97.8%-100%) after ten years (figure 3). For revision due to aseptic loosening as endpoint, the cumulative survival rate was 100% DISCUSSION This study was performed to demonstrate that the outcome of the TKA procedures from our teaching hospital is consistent with the results reported by other authors. We documented clinical results from an elderly patients group receiving standard-of-care primary TKA. The mean age of our patients was 70 years at the time of surgery. Considering their mean age was 80 years at the ten year follow-up, it is not surprising that many patients exhibited a certain degree of functional limitations. These are primarily inherent to general comorbidity and degenerative processes brought upon by old age. We could even demonstrate a statistically significant, albeit weak correlation of age and deterioration of other joints with function score at the ten year follow- up. Notwithstanding, the clinical outcome is more than satisfying and comparable to other long- term studies. ( 2 3 4 5 6 7 8 ) The radiographic assessment performed in 48% of the knees showed absence of radiographic signs of loosening at ten years. As the cohort with radiographic assessment and the cohort without assessment show very similar Knee scores, it has to be assumed, that no systematic bias in reference to the radiographic results occurred. At contrary, knee function scores were significantly lower in the cohort without radiographic assessment. This 8

demonstrates that predominately elderly patients and such with comorbidity are not willing to do a voluntary assessment at the clinic related to travel and effort. In most of our patients, the low degree of preoperative patello-femoral pain did not justify resurfacing the patella initially. Even though some patellar- femoral pain was present postoperatively in a small proportion of our patients, this decreased with time. Only in three patients postoperative patellar pain necessitated later resurfacing. This was in all cases performed during the first postoperative year. The fact that initial patellar resurfacing does not necessarily result in better clinical results has also been investigated by other researchers. Burnett et al. performed a randomised trial with patients requiring bilateral knee replacement and could demonstrate equivalent clinical results for resurfaced and non-resurfaced patellae after ten years of follow- up time.( 9 ) Moreover, the Annual Report 2008 of the Swedish Knee Arthroplasty Register analysed survival rates of TKA in patients with Osteoarthritis implanted with or without patellar button separately. In this analysis, solely the NexGen implanted without patellar button demonstrated a significantly reduced relative risk of revision.( 10 ) Survival rates with endpoint revision for any reason have recently been reported to be as high as 93-100% after similar study durations. ( 9 11 12 13 14 ). The ten-year survival rate with endpoint revision for any reason in this study is 99.1%, which is higher than what is reported for all cemented TKAs in the period 1997 2006 in the Annual Report 2008 of the Swedish Knee Arthroplasty Register, where a revision rate of slightly more than 4% after ten years is reported.( 10 ) Compared with other third generation knee replacements as well as with the predecessor of the NexGen System (Miller Galante II approx. 5%) this difference in revision rates is even more apparent. According the Annual Report 2011 of the Swedish Knee Arthroplasty Register, the reported survival rate at ten years for cemented primary TKA in osteoarthritis with endpoint revision for any reason was 96%. The same annual report mentions a more than 50% lower relative risk of revision for the NexGen implant system in both osteoarthritis and rheumatoid arthritis patients when compared to the reference implant. 9

The overall survival rate of NexGen is approximately 98% after 10 years, according the Swedish Knee Arthroplasty Register 2011 and 97% according the Norwegian Arthroplasty Register, which is the highest survival rate reported at ten years among all listed brands ( 15 ). Our own findings are consistent with these figures from the Swedish and Norwegian arthroplasty registries. The Orthopaedic Centre in Kassel is a large orthopaedic clinic and also a teaching hospital. This means that the operations were carried out by as many as 16 different surgeons, including surgeons-in-training. In all surgeries, a senior surgeon was present to supervise or perform the operation. The results presented in this publication are at least as good as those presented by other authors. Therefore, we deduce that involving surgeons-in-training in the surgeries within a controlled setting does not have a negative impact on clinical outcome. This is also supported by the results of the annual assessments executed as a part of the quality control in our institution. All data were collected in the international data base of the NexGen Clinical Outcome Multi-Center Study Registry maintained by the implants manufacturer, Zimmer. In the benchmark with this worldwide open and prospective observation our results are similar to the worldwide international group, which shows that the implant achieves consistent and favourable clinical outcomes in diverse patient populations and surgical settings. Thus, the system is able to accommodate the nuances in knee anatomy across ethnic groups and in a variety of surgical techniques used by surgeons in different countries. Limitations of this study might be the retrospective character and the resulting lack of continuous radiographic assessment, due to great distance between the clinic and the patient s home and aged patients often refuse to undergo radiographic assessment as long as they are free of discomfort. However, approximately fifty percent of knees (68) have been assessed radiographically at ten years (figure 4), and only three out of them showed minor radiolucent lines around the tibial component. 10

CONCLUSION This study shows very good clinical results with the cruciate retaining NexGen implant for primary total knee arthroplasty in stable knees. Our findings are consistent with those of other authors who have reported high rates of clinical success with third generation cemented TKAs. The philosophy of the device seems to meet the expectations. Thus this implant has continuously been further developed, now also providing gender sizes respecting the differences between men and women and providing a flex design with better conformity in flexion for patients requiring higher degrees of flexion based on their lifestyle. ACKNOWLEDGEMENTS The authors wish to thank Elke Rometsch for the medical writing support and Dieter Kaufmann for the statistical support, both Zimmer GmbH, Winterthur. CONFLICT OF INTEREST STATEMENT There is no conflict of interests. REFERENCES 1. Insall JN, Dorr LD, Scott RD, Scott WN. Rationale of the Knee Society clinical rating system. Clin.Orthop.Relat Res. 1989; 13-14 2. Barrington, Sah AP, Freiberg AA, Malchau H, Burke DW. Minimum 10-year results with a contemporary cruciate-retaining total knee arthroplasty. 1-2. 2007. San Diego, AAOS. Ref Type: Conference Proceeding 3. Bertin KC. Cruciate-retaining total knee arthroplasty at 5 to 7 years followup. Clin Orthop Relat Res. 2005; 177-183 4. Bourne RB, Laskin RS, Guerin JS. Ten-year results of the first 100 Genesis II total knee replacement procedures. Orthopedics 2007; 30: 83-85 5. Bozic KJ, Kinder J, Meneghini RM, Zurakowski D, Rosenberg AG, Galante JO. Implant survivorship and complication rates after total knee arthroplasty with a third-generation cemented system: 5 to 8 years followup. Clin Orthop Relat Res. 2005; 117-124 + erratum 11

6. Callaghan JJ, Wells CW, Liu SS, Goetz DD, Johnston RC. Cemented rotating-platform total knee replacement: a concise follow-up, at a minimum of twenty years, of a previous report. J Bone Joint Surg [Am] 2010; 92: 1635-1639 7. Rodricks DJ, Patil S, Pulido P, Colwell CW, Jr. Press-fit condylar design total knee arthroplasty. Fourteen to seventeen-year follow-up. J Bone Joint Surg [Am] 2007; 89: 89-95 8. Schwitalle M, Salzmann G, Eckardt A, Heine J. [Late outcome after implantation of the PFC modular knee system]. Z Orthop Ihre Grenzgeb 2001; 139: 102-108 9. Burnett RS, Boone JL, McCarthy KP, Rosenzweig S, Barrack RL. A prospective randomized clinical trial of patellar resurfacing and nonresurfacing in bilateral TKA. Clin Orthop Relat Res 2007; 464: 65-72 10. Annual Report 2008. The Swedish Knee Arthroplasty Register. 15-10-2008. Dept. of Orthopedics, Lund University Hospital. Ref Type: Report 11. Malin AS, Callaghan JJ, Bozic KJ, Liu SS, Goetz DD, Sullivan N, et al. Routine surveillance of modular PFC TKA shows increasing failures after 10 years. Clin Orthop Relat Res 2010; 468: 2469-2476 12. Schwartz AJ, la Valle CJ, Rosenberg AG, Jacobs JJ, Berger RA, Galante JO. Cruciate-retaining TKA using a third-generation system with a four-pegged tibial component: a minimum 10-year followup note. Clin Orthop Relat Res 2010; 468: 2160-2167 13. Aglietti P, Buzzi R, De FR, Giron F. The Insall-Burstein total knee replacement in osteoarthritis: a 10-year minimum follow-up. J Arthroplasty. 1999; 14: 560-565 14. Buehler KO, Venn-Watson E, D'Lima DD, Colwell CW, Jr. The press-fit condylar total knee system: 8- to 10-year results with a posterior cruciate-retaining design. J.Arthroplasty 2000; 15: 698-701 15 Lygre S H, Espehaug B, Havelin L I, Vollset S E, Furnes O. Failure of total knee arthroplasty with or without patella resurfacing. Acta Orthop 2011; 82 (3): 282-92. 12

Table 1: Body Mass Index of study population BMI categories Gender Total Female Male Normal <25 N 35 6 41 % within Gender 21.1% 10.7% 18.5% Overweight 25-29.99 N 81 24 105 % within Gender 48.8% 42.9% 47.3% Obese 30-34.99 N 35 21 56 % within Gender 21.1% 37.5% 25.2% Severely obese >=35 N 15 5 20 % within Gender 9.0% 8.9% 9.0% Total N 166 56 222 % within Gender 100.0% 100.0% 100.0% 13

Table 2: Patient availability preoperatively, at one, five and ten years FUP included died explanted drop-outs N % N % N % N % Preop / OP 222 100% - - - - - - 1 year 219 98.6% 2 0.9% 1 0.5% 0 0.0% 5 year 188 84.7% 32 14.4% 2 0.9% 0 0.0% 10 year 143 64.4% 76 34.2% 2 0.9% 1 0.5% 14

Captions to illustrations: Figure 1: Knee pain preoperatively, at one, five and ten years Figure 2: Knee Society Scores preoperatively, at one, five and ten years Figure 3: Kaplan Meier Survival Analysis with endpoint revision for any reason Figure 4: X-ray ten years postoperatively of the NexGen CR Knee System: a) anteroposterior, b) lateral, c) tangential projection of the patella 15

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Fig. 4 a Fig. 4 b Fig. 4 c 19