Hybrid total knee arthroplasty

Hybrid total knee arthroplasty

The Journal of Arthroplasty Vol. 19 No. 7 Suppl. 2 2004 Hybrid Total Knee Arthroplasty A Retrospective Analysis of Clinical and Radiographic Outcomes...

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The Journal of Arthroplasty Vol. 19 No. 7 Suppl. 2 2004

Hybrid Total Knee Arthroplasty A Retrospective Analysis of Clinical and Radiographic Outcomes at Average 10 Years Follow-Up Richard Illgen, MD,* Jonathan Tueting, MD,* Timothy Enright,* Ken Schreibman, MD,† Andrew McBeath, MD,* and John Heiner, MD*

Abstract: Cemented total knee arthroplasty has demonstrated high success rates at 10 –12 years. Although many cementless designs have demonstrated inferior outcomes, hybrid fixation has not been studied in detail. We retrospectively reviewed 112 hybrid total knee arthroplasties (PCA– 67 and Duracon– 45) after clinical and radiographic review using the SF-12 and Knee Society Scores at an average 10-year follow-up. The revision rate was 4.5%: 4 occurred in patients with metal-backed patellae and 1 in a patient with infection. No revisions were performed for aseptic loosening of the femoral component. Hybrid total knee arthroplasty with these designs provided excellent clinical and radiographic performance at 10 years comparable to cemented series. Aseptic loosening and radiographic failure rates were 0% if patients with metal-backed patellae were excluded. The durability of hybrid fixation beyond 10 years deserves further study. Key words: total knee arthroplasty, hybrid fixation technique, Knee Society Score. © 2004 Elsevier Inc. All rights reserved.

response to this concern, cementless implants were introduced as an alternative mode of fixation. Unfortunately, many cementless implant designs have demonstrated higher rates of loosening and osteolysis when compared with cemented designs [7–10]. The failures have largely been due to problems with the cementless tibial component or the use of metal-backed patellae [11,12]. Cementless femoral fixation, in general, has been durable and has rarely been a cause of failure in previously published cementless TKA series [12–16]. Hybrid TKA was introduced in the late 1980s to gain the theoretical advantage of durable cementless femoral fixation while avoiding the problems noted with cementless tibial fixation [17]. The potential benefits of cementless femoral fixation include durable biologic fixation via bone ingrowth, decreased risk of third body wear due to cement debris, bone preservation, ease of revision, and perhaps decreased operative time [18]. Additionally,

The optimal mode of femoral fixation in total knee arthroplasty (TKA) remains controversial. Conventional TKA using cemented femoral fixation has demonstrated excellent performance with clinical success rates as high as 92% to 97% at follow-up of 10 –15 years [1– 6]. Despite the reported success of cemented TKA, long-term durability and late loosening have remained areas of controversy [2,3]. In From *the Department of Orthopedics and Rehabilitation, the Arthritis and Joint Replacement Program, Clinical Science Center, and †the Department of Musckuloskeletal Radiology, University of Wisconsin, Madison, Wisconsin. Benefits or funds were received in partial or total support of the research material described in this article. These benefits or support were received from Stryker-Howmedica-Osteonics, Allendale, NJ. Reprint requests: Richard Illgen, II, MD, The Arthritis and Joint Replacement Program, Clinical Science Center, Room K4748, Madison, WI 53792. © 2004 Elsevier Inc. All rights reserved. 0883-5403/04/1907-2017$30.00/0 doi:10.1016/j.arth.2004.06.022

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96 The Journal of Arthroplasty Vol. 19 No. 7 Suppl. 2 October 2004 Table 1. Clinical Outcomes After Hybrid TKA at Average 10 Years Follow-Up

Sex Male Female Age (y) ⱕ50 51–70 ⱖ71 Diagnosis Osteoarthritis Rheumatoid Osteonecrosis Implant Type PCA Duracon

Number of Knees

Preoperative KSS Objective

Preoperative KSS Functional

Final KSS Objective

Final KSS Functional

Good/Excellent Results (%)

Postoperative ROM

15 39

30 33

55 43

77 87

71 62

80 82

99 102

5 26 23

38 34 30

47 51 45

86 86 82

71 67 61

75 87 83

103 106 95

32 19 3

33 30 31

49 45 42

85 83 81

67 62 59

86 88 91

100 96 102

28 26

32 31

50 43

81 87

54 73

82 88

99 103

Abbreviations: KSS, Knee Society Score; ROM, range of motion.

the application of cementless femoral fixation may be advantageous when compared with cemented techniques in the setting of minimally invasive TKA. Furthermore, the outcomes beyond 10 –15 years of current TKA designs using standard cemented techniques have not been well established, and it is possible that hybrid TKA may outperform fully cemented techniques at these longer follow-up intervals. Published clinical results with hybrid TKA have been variable depending on the length of follow-up evaluation and the type of implant system used [2,7–10]. The majority of reports demonstrate excellent results in the short term [8 –10], but others have noted higher rates of failure with hybrid TKA compared with cemented TKA at intermediate follow-up intervals [7]. The purpose of this study is to review the durability of hybrid fixation in TKA at our institution with average 10-year follow-up.

Materials and Methods The authors obtained institutional review board approval for this study. Between October 1987 and July 1995, 330 primary TKAs were performed at our institution by the senior authors (AAM and JPH) using either the PCA (n ⫽ 91) or Duracon (n ⫽ 239) Total Knee System (Stryker-HowmedicaOsteonics, Allendale, NJ). The mode of fixation was based on intraoperative bone quality and component fit. The authors performed 87 cemented (cemented femur, tibia and patella), 131 cementless (uncemented femur and tibia, cemented patella), and 112 hybrid (uncemented femur, cemented tibia

and patella) TKAs. The clinical and radiographic charts of all patients with hybrid TKAs (n ⫽ 112) were subsequently reviewed. At the time of our study, 49 patients had died, 9 could not be found, and 54 patients (PCA, n ⫽ 28; Duracon, n ⫽ 26) were alive and available for follow-up. Clinical and radiographic outcomes were measured with average clinical follow-up of 10 years (range, 3–15.2 years) and average radiographic follow-up of 9.6 years (range, 3–14.1 years). The mean clinical follow-up was 11.9 years for those patients who received the PCA implant and 8.1 years for patients who received the Duracon implant; while the mean radiographic follow-up was 11.2 years for those patients who received the PCA implant and 7.6 years for patients who received the Duracon implant. Surgical technique and instrumentation were similar in all cases. Patients with a primary diagnosis of post-traumatic osteoarthritis and those patients requiring TKA secondary to tumor were excluded. Retrospective review of the office notes, hospital records, and radiographs was performed independently by two of the authors who were not the original surgeons (RLI and JLT). Demographics The mean age of the study group (n ⫽ 54) at the time of their surgery was 66.1 years (range, 29.6 – 86.8 years). The age distribution at the time of surgery was as follows: less than or equal to age 50 (n ⫽ 5), between the ages of 51 and 70 (n ⫽ 26), and greater than or equal to age 71 (n ⫽ 23). There were 15 men and 39 women who had the diagnosis

Hybrid TKA • Illgen et al.

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Prosthesis

Fig. 1. Knee Society Standard Roentgenographic Evaluation and Scoring System.

of osteoarthritis (n ⫽ 32), rheumatoid arthritis (n ⫽ 19), and osteonecrosis (n ⫽ 3) (Table 1). Clinical Evaluation The perioperative and postoperative courses of the patients were reviewed. Preoperative and postoperative clinical evaluations had been obtained on all patients. Forty-two of 54 patients were seen in the office to obtain recent clinical and radiographic evaluation. The remaining 12 patients, who were no longer living in the region, agreed to complete a phone interview to obtain relevant information regarding their clinical status and the status of their TKA implant. Clinical outcomes were measured using the Knee Society Score (KSS) and the Medical Outcomes Study Short Form (SF-12) questionnaire [19]. A KSS of ⱖ90 points was considered an excellent outcome, a score between 80 and 89 points was considered a good outcome, a score between 70 and 79 points was considered a fair outcome, and a score of less than 70 points was considered a poor outcome.

The Stryker-Howmedica-Osteonics (Allendale, NJ) PCA (porous-coated anatomic) or Duracon total knee system was used in all patients at our institution during the study interval. The PCA total knee system was used for all patients who had their TKA prior to 1991 (n ⫽ 28). The Duracon total knee system was used in all patients who had their TKA after 1991 (n ⫽ 26) when this system became available at our institution. Porous-coated and nonporous coated components were available for use with or without cement according to the surgeon’s preference. All patients received either the cruciateretaining design (n ⫽ 51) or the cruciate-substituting design (n ⫽ 3). Some differences exist between the PCA and Duracon systems. The Duracon femoral component has a deeper patellofemoral sulcus and provides more articular congruity than that seen in the PCA design. In contrast to the PCA design, the femoral lugs in the Duracon design were not porous-coated to allow for less bone loss during possible subsequent revisions. In addition, the tibial component of the Duracon design has one large, centrally located, non-porous-coated keel. The PCA tibial design has two smaller medial and lateral porouscoated lugs (Figs. 2 and 3). Surgical Technique A standard instrumentation system (StrykerHowmedica-Osteonics, Allendale, NJ) was used for implantation. Intramedullary references were used for the femoral resection, and the femoral cut was performed in 5–7 degrees of valgus. Extramedullary

Radiographic Evaluation The radiographic evaluations were performed by two of the authors (RLI and JLT) who were not the primary surgeons for all patients studied. Preoperative, first postoperative, and final postoperative radiographs were evaluated using the Knee Society Standard Roentgenographic Evaluation and Scoring System (Fig. 1) to define the assessment zones around the implants [20]. All final follow-up radiographs were weight-bearing films that included anteroposterior, lateral, and sunrise patella views. Radiographic assessment was performed in all patients to determine the rates of osteolysis, radiolucent lines, and radiographic implant failure. For those patients who completed their review by phone, radiographic review was completed using either our most recent office radiographs (9 patients) or, if more recent outside radiographs were obtained, they were sent by mail (3 patients).

Fig. 2. A photograph of a Duracon femoral component.

98 The Journal of Arthroplasty Vol. 19 No. 7 Suppl. 2 October 2004 coumadin for postsurgical deep venous thrombosis prophylaxis. Statistical Analysis Statistical analysis was performed with SAS statistical software (Release 6.12, SAS Institute, Inc., Cary, NC). Differences in rates of revision and in the incidence of radiolucent lines were evaluated using Fisher’s exact test. A P value less than .05 was considered statistically significant.

Results Overall Clinical Results Fig. 3. A photograph of a porous coated anatomic (PCA) femoral component.

references were used for the tibial resection, and the tibial cut was performed in neutral (perpendicular to the tibial mechanical axis). Fixation In all hybrid TKA patients, the tibial and patellar components were cemented with polymethylmethacrylate and the femoral components were cementless. The decision to use a cementless femoral component was not randomized, but rather an intraoperative decision by the senior surgeons based on bone quality and component fit. If adequate bone quality was noted in the patient’s femur and tibia, then a cementless TKA was used. Hybrid TKA was used in those patients who had good femoral cancellous bone but poor tibial bone quality. In those patients who had poor femoral, tibial, and patellar bone quality, a fully cemented TKA was used. All patients received cemented patellar components; and of the 112 patients who had hybrid TKAs, 13 received metal-backed patellae. Postoperative Management All patients were treated following our institutional postoperative TKA protocol. Physical therapy was begun on the first postoperative day. Quadriceps strengthening exercises, straight-leg raises, and flexion-extension exercises, including the use of a continuous passive motion machine, were instituted in a graduated fashion. All patients were allowed to be weight bearing as tolerated with use of crutches or a walker regardless of the mode of femoral and tibial fixation. All patients were given

The overall ratings for all 54 knees improved from a mean preoperative objective KSS of 32 points (range, 0 –54) to a final follow-up value of 84.5 points (range, 15–100). The mean preoperative functional KSS improved from a value of 46.7 points (range, 5– 80) to 65.6 points (range, 30 – 100). At the most recent follow-up visit, there were 44 excellent or good, 7 fair, and 3 poor results. Mean range of motion at the most recent clinical follow-up evaluation was 102 degrees (range, 84 – 125). The mean preoperative SF-12 Mental Component Score was 47.1 (range, 36.7–58.2), and the postoperative score was 53.9 (range, 34.1– 60.4). The mean preoperative SF-12 Physical Component Score was 46.0 (range, 34.2–56.6), and the postoperative score was 49.2 (range, 36.1–57.4). The data on the clinical outcomes as they relate to gender, age at the time of surgery, clinical diagnosis, implant type, and radiolucent lines are summarized in Table 1. Radiographic Results Femur: 7 of the 54 knees (13%) had a nonprogressive radiolucent line, 1–2 mm, in at least 1 zone around the femoral component: zone 1 (n ⫽ 3), zone 4 (n ⫽ 4). Four of the knees (7%) were PCA implants and three (6%) were Duracon. One PCA knee (2%) had an osteolytic lesion greater than 2 mm in zone 4 that was progressive on sequential radiographs. No femoral components were considered radiographically loose. Tibia: 7 of the 54 (13%) knees had a nonprogressive radiolucent line of 1–2 mm in at least 1 zone around the tibial component visible in the AP projection: zone 1 (n ⫽ 3, PCA ⫽ 1, Duracon ⫽ 2), zone 2 (n ⫽ 5, PCA ⫽ 4, Duracon ⫽ 1), zone 4 (n ⫽ 7, PCA ⫽ 5, Duracon ⫽ 2), zone 6 (n ⫽ 6, PCA 5, Duracon ⫽ 1). Five of the knees with tibial radiolu-

Hybrid TKA • Illgen et al.

cent lines (9%) were PCA implants and two (4%) were Duracon. Two of the PCA knees (4%) had a greater than 2-mm osteolytic lesion in zone 6 that was nonprogressive in sequential radiographs. Excluding patients with metal-backed patellae, no tibial components were considered radiographically loose. Patella: 13 of the 112 hybrid TKAs had metalbacked patellae. Four of these 13 metal-backed patellae were revised for aseptic loosening. If the metal-backed patellae were excluded, 3 of the remaining 50 (6%) knees had a nonprogressive radiolucent line in at least 1 zone of the patellar component: zone 1 (n ⫽ 3, PCA ⫽ 1, Duracon ⫽ 2), zone 2 (n ⫽ 1, PCA ⫽ 0, Duracon ⫽ 1), zone 3 (n ⫽ 2, PCA ⫽ 0, Duracon ⫽ 2), and zone 4 (n ⫽ 2, PCA ⫽ 1, Duracon ⫽ 1). Two of the knees (4%) were Duracon implants and 1 (2%) was a PCA. The last available clinic notes and radiographs for the 49 patients who died, as well as for the 9 patients who could not be found, were reviewed during the study. The average length of clinical and radiographic follow-up for these patients was 7.2 years (range, 2.1–14.5). At the time of their death or disappearance, the implants were clinically functioning well and had no evidence of osteolysis in the femoral component, though 3 knees had nonprogressive radiolucent lines in the tibial component. None of the knees in those patients who had died had been revised. Revisions At final follow-up evaluation, 5 of 112 knees (4.5%) had been revised. All 5 revisions were performed in patients who were alive and available for follow-up. Revisions were performed at a mean of 4.8 years after the index TKA (range, 3.2–7.1 years). Four revisions were performed in patients who had metal-backed patellae: 2 in patients with the PCA system, and 2 in patients with the Duracon system. All components were revised in all 4 cases. One revision was performed for infection 2 years after the index TKA and included a 2 stage exchange with antibiotic spacer and appropriate IV antibiotics. Complications Complications occurred in 4% of patients (4/ 112): 1 infection required subsequent revision; 1 deep venous thrombosis required anticoagulation; 1 patient with severe postoperative atelectasis required a prolonged hospital stay; and 1 patient with postoperative atrial fibrillation required cardioversion.

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Discussion The optimal mode of femoral fixation in TKA remains controversial. Conventional cemented TKA has demonstrated reliably good results for the treatment of arthritis at 10 –15 year follow-up analysis [1– 6]. However, several potential advantages may exist with the use of hybrid fixation compared with cemented techniques. These include the potential for decreased operative time by eliminating the need to remove excess retained cement around the femoral component and posterior femoral condyles. Avoiding the use of cement on the femoral component may also decrease the potential for polymethylmethacrylate third-body wear. Finally, hybrid total knee arthroplasty may provide a more suitable approach for minimally invasive techniques when compared with cemented fixation. Our study demonstrates that excellent clinical and radiographic performance can be achieved using hybrid TKA technique at average follow-up of 10 years. The results achieved with these hybrid TKA designs (Duracon and PCA) are comparable to cemented series at similar follow-up intervals. In our series, the overall revision rate was 4.5% (5 of 112). Four revisions were performed in patients with metal-backed patellae and 1 for infection. No revisions were performed for aseptic loosening of the femoral component and all femoral components were well fixed at the time of revision. Rates of revision, osteolysis, and radiolucent lines around the femoral, tibial, and patellar components were similar in our series compared with cemented series at similar follow-up intervals [1– 6,21]. Higher rates of failure with the use of metalbacked patellae in TKA have been noted previously [11,12]. In our study, the difference in revision rates for TKAs with metal-backed patellae (31%) compared to TKAs with non-metal-backed patellae (0.9%) was statistically significant (P ⬍ .001). If patients with metal-backed patellae were excluded, aseptic loosening and radiographic failure rates were 0%. Although our series suggests that higher rates of radiolucent lines were seen around the PCA tibial components (9%) compared to the Duracon tibial components (4%), these values were not statistically significant. The PCA tibial component was porous coated and intended for cementless use. In our hybrid TKA series, all PCA tibial components were cemented. The Duracon tibial component, in contrast, is not porous coated and was designed for cemented use. It is possible that the cemented porous coated PCA tibial components may have had

100 The Journal of Arthroplasty Vol. 19 No. 7 Suppl. 2 October 2004 higher rates of third body wear compared with the nonporous coated Duracon tibial components. Such differences in implant design may account for the observed increase in tibial radiolucent lines and osteolysis around the PCA tibial components compared with the Duracon tibial components. Further study is needed with a larger cohort of patients at longer follow-up intervals to determine whether these differences become statistically significant. Our findings suggest that hybrid total knee arthroplasty with these implant designs (PCA and Duracon) provides durable fixation with excellent clinical and radiographic performance at 10 years comparable to cemented series if metal-backed patellae were not used. In our opinion, the use of metal-backed patellae with these designs should be avoided, cemented tibial components should not be porous coated, the continued use of hybrid fixation with the Duracon knee system is warranted, and the durability of hybrid fixation beyond 10 years deserves further study.

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