The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 91, Issue 4

Scientific Articles | April 01, 2009

Contemporary Cruciate-Retaining Total Knee Arthroplasty with a Pegged Tibial Baseplate: Results at a Minimum of Ten Years

John W. Barrington, MD¹; Alexander Sah, MD²; Henrik Malchau, MD²; Dennis W. Burke, MD²

¹ Texas Center for Joint Replacement, 5940 West Parker Road, #100, Plano, TX 75093. E-mail address: barringtonj@tcjr.com
² Department of Orthopaedic Surgery, Massachusetts General Hospital, 55 Fruit Street, Boston, MA 02114

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Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. One or more of the authors or a member of his or her immediate family received, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provide such benefits from a commercial entity (Zimmer). Also, a commercial entity (Zimmer) paid or directed in any one year, or agreed to pay or direct, benefits in excess of $10,000 to a research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which one or more of the authors, or a member of his or her immediate family, is affiliated or associated.

Investigation performed at Massachusetts General Hospital, Boston, Massachusetts

The Journal of Bone and Joint Surgery, Inc.

J Bone Joint Surg Am, 2009 Apr 01;91(4):874-878. doi: 10.2106/JBJS.G.01609

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Abstract

Background: A total knee arthroplasty with a four-peg tibial baseplate is an uncommonly used contemporary design. Potential advantages of this baseplate include preservation of host bone, compatibility with minimally invasive techniques, and easier removal with revision techniques. The purpose of this study was to determine the long-term results of a contemporary total knee arthroplasty that included a four-peg tibial baseplate.

Methods: From February 1995 to December 1996, 127 total knee arthroplasties were performed by one surgeon in 115 patients with an average age of seventy years. Clinical and radiographic evaluations were performed with use of the Knee Society scoring system at a minimum of ten years following replacement. Complications were identified by means of chart review and screening for readmission at surrounding institutions.

Results: At the time of follow-up, at a minimum of ten years after the arthroplasty, thirty patients (with thirty-three involved knees) were documented to have died and four patients (with seven involved knees) could not be located. The next-of-kin of the patients who had died directly confirmed that the knee was unrevised at the time of death. Eighty-seven knees in eighty-one patients remained available for evaluation after a minimum of ten years of follow-up. Two knees had failed: one had a late infection at three years, and one had aseptic loosening at seven years. The rate of survival free of revision at ten years was 97%. Knee Society knee and function scores averaged 94 and 75 points, respectively. None of the remaining knees had radiographic evidence of loosening.

Conclusions: This study demonstrated excellent, durable clinical and radiographic results at a minimum of ten years after replacement with this cemented, modular, fixed-bearing, cruciate-retaining total knee prosthesis with a four-peg tibial baseplate. We believe that this design is an acceptable option for total knee arthroplasty.

Level of Evidence: Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.

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Introduction

Introduction | Materials and Methods | Results | Discussion | References

Early cruciate-retaining, cruciate-sacrificing, and posterior stabilized total knee arthroplasty designs were reported to be durable and to provide good functional outcomes^1-3. However, such first-generation designs were associated with a high rate of revision due to patellofemoral complications^4,5, a high rate of lateral release⁶, and a suboptimal range of motion⁷. Components were modified to increase the depth of the trochlea, increase patellofemoral congruence, and decrease the trochlear thickness in attempts to improve outcomes. However, even small changes in design can lead to disparate functional results.

The four-peg baseplate is one of the less commonly used tibial fixation designs in modern total knee component systems. Potential benefits of the four-peg design include removal of less bone, easier use with smaller-incision techniques, and easier removal in revision situations⁸. The major theoretical concern with this type of design is decreased resistance to torsional and shear stress with the potential for aseptic loosening⁹.

The early results of a contemporary total knee arthroplasty with a four-peg tibial baseplate have been positive^10,11, but to our knowledge this is the first retrospective study of the radiographic and clinical outcomes at a minimum of ten years. We hypothesized that a cemented, modular, fixed-bearing, cruciate-retaining total knee prosthesis with a four-peg tibial baseplate and a modern patellofemoral articulation would provide durable results, with few patellofemoral complications, at a minimum of ten years postoperatively.

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

From February 1995 to December 1996, 127 total knee arthroplasties with a four-peg tibial baseplate were implanted in 115 patients with an average age of seventy years (range, fifty to eighty-three years). All of the operations were performed by the senior author (D.W.B.). Sixty-seven of the arthroplasties were done in women, and sixty were done in men. The preoperative diagnosis was osteoarthritis in 118 knees (93%), rheumatoid arthritis in six (5%), posttraumatic or postosteotomy osteoarthritis in two (2%), and osteonecrosis in one (0.8%). During the same time frame, the surgeon performed twenty-three primary total knee arthroplasties with a posterior stabilized implant for conditions including severe flexion contracture, an absent posterior cruciate ligament, hemophilia, and pigmented villonodular synovitis as well as one primary constrained total knee arthroplasty in a patient with Charcot arthropathy.

The NexGen knee system (Zimmer, Warsaw, Indiana), with cemented, modular, fixed-bearing, cruciate-retaining components and a cemented four-peg tibial baseplate, was used for all knees. The tibial component is made of Tivanium (Ti-6Al-4V) alloy, precoated with polymethylmethacrylate, and has four undersurface pegs, two anterior and two posterior, with the posterior pegs slightly more widely spread than the anterior pegs (Fig. 1). The femoral component is made of a cobalt-chromium-molybdenum alloy and precoated with polymethylmethacrylate. All patellae were resurfaced with a three-peg, all-polyethylene implant. A midline incision, a medial parapatellar approach, and patellar eversion with medialization were used in all cases. The distal part of the femur was cut in 6° of valgus with the use of an intramedullary guide, and the finishing cuts were made to allow the femoral component to be externally rotated to meet the transepicondylar axis and the Whiteside line¹². The tibia was cut perpendicular to its long axis with use of an extramedullary guide, with 5° of posterior slope (Fig. 2). The posterior cruciate ligament was preserved on a tibial bone block and recessed as needed from the tibial side in order to obtain balancing to achieve appropriate tension. The resected osseous surfaces were lavaged and dried, and cement was manually applied to the bone and placed on the undersurface of the components. Special care was taken to resect posterior osteophytes and remove cement debris. Each knee was closed in layers over a standard medium-sized suction drain. All patients were treated with six weeks of Coumadin (warfarin) postoperatively for prophylaxis against venous thromboembolism.

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Fig. 1: Undersurface view of the NexGen cruciate-retaining four-peg tibial baseplate. (Image provided by Zimmer, Inc.)

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Fig. 2: Anteroposterior radiograph of a well-placed NexGen cruciate-retaining four-peg total knee prosthesis.

Clinical and radiographic evaluations were performed with use of the Knee Society scoring system¹³ at a minimum of ten years following replacement. Non-fluoroscopically assisted weight-bearing anteroposterior, non-weight-bearing lateral, and skyline radiographs of the knee were made and were assessed by two independent reviewers: an arthroplasty fellow and an orthopaedic senior resident, neither of whom participated in the index operations. Complications were identified by means of an exhaustive chart review and by screening for readmission at surrounding institutions.

At the time of follow-up, at a minimum of ten years postoperatively, thirty patients (with thirty-three involved knees) were documented to have died and four patients (with seven involved knees) could not be located. The date of death of the deceased patients was directly confirmed by the next-of-kin, who also reported that the knee prosthesis had not been revised at the time of death. Eighty-seven knees in eighty-one patients were available for analysis with the Knee Society knee and function scores at a minimum of ten years postoperatively. Fifteen patients (sixteen knees) were clinically examined but had incomplete radiographs; therefore, radiographic analysis was completed for seventy-one (82%) of eighty-seven knees.

Survivorship analysis was performed with the Kaplan-Meier product-limit method¹⁴. Mean survivorship was calculated and 95% confidence intervals around the curve were determined with Greenwood's formula to estimate survivorship, with an end point of freedom from revision for any reason, at five and ten years after total knee arthroplasty¹⁵. Comparative statistical analysis was performed with use of unpaired two-tailed Student t tests, with the level of significance set at p = 0.05, and 95% confidence intervals were determined.

Source of Funding

The authors received no outside funding for the study. Zimmer has contributed to the Massachusetts General Hospital Biomechanics and Biomaterials Laboratory.

Results

Introduction | Materials and Methods | Results | Discussion | References

The mean duration of follow-up of the eighty-seven knees was 11.1 years (range, ten to twelve years). The Knee Society knee score at the time of the latest follow-up averaged 94 points (95% confidence interval, ±1.7 points) out of a possible 100 points. The mean Knee Society function score was 75 points (95% confidence interval, ±5.6 points) out of a possible 100 points, with a bimodal distribution. Five elderly patients were predominantly confined to a wheelchair, and four others were affected by either stroke, Alzheimer disease, or disability from the contralateral extremity. The average range of motion at the time of the latest follow-up was 117° (95% confidence interval, ±4°; range, 100° to 130°).

Analysis of the seventy-one knees for which radiographs were available showed the femoral components to be in an average of 5.5° (95% confidence interval, ±0.6°; range, 4° to 7°) of valgus. The tibial components averaged 0.8° (95% confidence interval, ±1.3°) of varus (range, 2° of valgus to 3° of varus) and 4.4° (95% confidence interval, ±0.8°; range, 2° to 6°) of posterior slope.

The ten-year Kaplan-Meier survival rate, with revision for any reason as the end point, was 97% (95% confidence interval, 94% to 100%) (Fig. 3). Two knees required revision surgery. The first patient had a late infection three years postoperatively and was treated with two-stage reimplantation after six weeks of intravenous antibiotics and use of a temporary antibiotic spacer. The other patient had aseptic loosening of the tibial component with medial subsidence seven years postoperatively. This component had been placed in 3° of varus.

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Fig. 3: Kaplan-Meier survivorship with revision for any reason as the end point.

Sex-specific analysis showed the implant survival rate to be 100% for women and 96.7% for men. The Knee Society knee scores averaged 93 points (range, 55 to 100 points) for women and 96 points (range, 85 to 100 points) for men. The range of motion averaged 116° (range, 100° to 130°) in women and 118° (range, 100° to 130°) in men. The Knee Society function scores averaged 69 points (range, 0 to 100 points) for women and 82 points (range, 10 to 100 points) for men (p = 0.014). Five patients were wheelchair-bound, and four of them were women with a function score of <40 points (Table I).

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TABLE I Implant Survival, Range of Motion, and Knee Society Scores According to the Sex of the Patient

Outcome Measure	Women	Men	P Value
Implant survival rate	100%	96.7%	0.16
Range of motion	116°	118°	0.26
Knee Society knee score	92.5	95.5	0.07
Knee Society function score	69.2	82.2	0.014

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TABLE I Implant Survival, Range of Motion, and Knee Society Scores According to the Sex of the Patient

Outcome Measure	Women	Men	P Value
Implant survival rate	100%	96.7%	0.16
Range of motion	116°	118°	0.26
Knee Society knee score	92.5	95.5	0.07
Knee Society function score	69.2	82.2	0.014

Complications not requiring revision surgery included three cases of postoperative stiffness treated with manipulation. One case of superficial cellulitis resolved with local care and antibiotics, and one peroneal nerve palsy resolved spontaneously. Three nonfatal pulmonary emboli, two postoperative episodes of hypotension, two cases of exacerbation of congestive heart failure, and one asymptomatic deep vein thrombosis all resolved with medical treatment.

Lateral release had been performed in fourteen (12%) of the 118 knees for which the operative notes were available. There were no patellofemoral complications requiring revision or a reoperation.

Discussion

Introduction | Materials and Methods | Results | Discussion | References

This cruciate-retaining total knee design provided reliable and durable clinical and radiographic results. The overall survival of this prosthesis may, in part, be influenced by important technique and implant-related considerations. Pegged designs are not new; Hungerford and Krackow began implanting the Porous-Coated Anatomic (PCA) knee prosthesis (Stryker, Kalamazoo, Michigan), available with either screws, or pegs and screws, in 1980¹⁶. The Miller-Galante-I four-peg baseplate (Zimmer) became available in 1984, and the NexGen design used in this study, a descendant of the Miller-Galante-II implant, became available in 1995. Potential advantages of this baseplate design include avoidance of entering the tibial canal, preservation of more proximal tibial bone stock, easier removal if necessary without leaving a cavitary metaphyseal defect, and ease of placement if there is hardware or deformity at the proximal part of the tibia, such as after a high tibial osteotomy. Bertin previously showed comparable midterm results between four-peg and stemmed tibial baseplates¹¹. In that study, none of the 141 pegged or eighty-four stemmed tibial baseplates had aseptic failure. Two knee implants with a pegged baseplate were removed because of late infection, and one with a stemmed baseplate was retained during a revision of the femoral component due to a periprosthetic femoral fracture. A radiolucency was seen under only one pegged tibial baseplate, and no osteolysis was observed after five to seven years of follow-up. Miller and Pettygrow reported one aseptic failure and one failure due to late infection at a mean of 10.5 years following use of the Miller-Galante-I total knee system with a four-peg tibial baseplate in ninety-five knees¹⁷, findings that were similar to those in the current study.

No failure due to osteolysis-related complications has been reported with this particular modular tibial baseplate-polyethylene combination^3,18. We believe that the lack of revisions due to patellofemoral complications and the accompanying moderately low rate of lateral release in the present and previous studies can be attributed to changes in technique as well as implant design that increased trochlear depth and patellofemoral congruence and decreased trochlear thickness.

With regard to the performance of the implant in women compared with that in men, this design has a so-called aspect ratio that is somewhat wider in smaller sizes¹⁹ than it is in more recent "sex-specific" designs. Still, the implant showed similar survival rates, knee scores, and ranges of motion in the women, who were slightly older and in general more functionally limited than the men.

We were able to consistently and accurately reconstruct the tibiofemoral angle using anatomic landmarks and manual cutting jigs. Computer navigation was not used.

The mean Knee Society function score at the time of the latest follow-up was 75 points, with a bimodal distribution. Many patients continued to have nearly normal overall function, but some elderly patients had a decline in overall function that resulted in much lower function scores, a finding that reflects the fact that the mean age at the time of follow-up was just over eighty years old.

Weaknesses of this study include those inherent in single-surgeon retrospective series, including the question of broader applicability. However, analysis of a single implant inserted with a consistent technique allows close scrutiny of specific choices with regard to fixation, modularity, ligament handling, and bearing design. Although the four-peg tibial component can be placed with a more limited exposure, the procedures in this series were performed with a traditional approach; therefore, the results may not be applicable to minimal exposures. No comparison group was included in this study. In addition, although we recognize the importance of using patient-reported outcomes instruments²⁰, such as the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), such outcomes were not measured in this study.

At a minimum of ten years after use of this cemented, modular, four-peg fixed-bearing, cruciate-retaining total knee design, we found excellent, durable clinical and radiographic results in both women and men. Image Not Available

References

Introduction | Materials and Methods | Results | Discussion | References

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Ritter MA, Berend ME, Meding JB, Keating EM, Faris PM, Crites BM. Long-term followup of anatomic graduated components posterior cruciate-retaining total knee replacement. Clin Orthop Relat Res.2001;388:51-7.38851 2001 [CrossRef]

Rand JA. The patellofemoral joint in total knee arthroplasty. J Bone Joint Surg Am.1994;76:612-20.76612 1994

Leopold SS, Silverton CD, Barden RM, Rosenberg AG. Isolated revision of the patellar component in total knee arthroplasty. J Bone Joint Surg Am.2003;85:41-7.8541 2003

Dixon MC, Brown RR, Parsch D, Scott RD. Modular fixed-bearing total knee arthroplasty with retention of the posterior cruciate ligament. A study of patients followed for a minimum of fifteen years. J Bone Joint Surg Am.2005;87:598-603.87598 2005 [CrossRef]

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Bertin KC. Cruciate-retaining total knee arthroplasty at 5 to 7 years followup. Clin Orthop Relat Res.2005;436:177-83.436177 2005

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Topics

knee region ; knee joint ; knee replacement arthroplasty ; knee prosthesis, total ; tibial baseplate

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John W. Barrington, Alexander Sah, Henrik Malchau, Dennis W. Burke; Contemporary Cruciate-Retaining Total Knee Arthroplasty with a Pegged Tibial BaseplateResults at a Minimum of Ten Years. The Journal of Bone & Joint Surgery. 2009 Apr;91(4):874-878.

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