Orthopedics

Feature Article 

Early Clinical Outcomes of a New Cementless Total Knee Arthroplasty Design

Russell G. Cohen, MD; Nathan C. Sherman, MBA; Sheridan L. James, BS

Abstract

Cementless fixation design failures led to low use of this alternative technology. A cementless total knee arthroplasty addressed these design flaws. The single radius knee design incorporated additive manufacturing to produce the tibial and patellar implants. Both implants have enhanced porous substrates, optimizing initial bony ingrowth. A nonrandomized prospective review was conducted of 72 cementless knees followed for a minimum of 2 years (mean, 37 months). Surgical time, estimated blood loss, and range of motion at 6 weeks were compared with those of a matched cohort of 70 cemented knees performed by the same surgeon. Knee Society Score and Oxford Knee Score were recorded for the cementless group. Radiographs were evaluated for change in implant position, subsidence, and radiolucent and sclerotic lines. Operative time was statistically shorter in the cementless group (40 vs 45 minutes), but there was no significant difference in postoperative estimated blood loss (557 vs 355 mL). Range of motion at 6 weeks averaged 118° in the cementless group vs 114° in the cemented group. Knee Society Score improved from 53.9 preoperatively to 85.0 at 6 weeks and 91.6 at most recent follow-up. Oxford Knee Score improved from 23.9 preoperatively to 31.7 at 6 weeks and 43.4 at most recent follow-up. No implants aseptically loosened or migrated. There were 2 early infections in the cemented group requiring revision. This cementless total knee arthroplasty revealed excellent clinical results at 3-year follow-up and resulted in shortened operative times. Biologic fixation was achieved in 100% of patients with improved functional and objective scores. Early results are encouraging, and this cementless total knee arthroplasty appears to provide an excellent alternative to cemented total knee arthroplasty. [Orthopedics. 201x; xx(x):xx–xx.]

Abstract

Cementless fixation design failures led to low use of this alternative technology. A cementless total knee arthroplasty addressed these design flaws. The single radius knee design incorporated additive manufacturing to produce the tibial and patellar implants. Both implants have enhanced porous substrates, optimizing initial bony ingrowth. A nonrandomized prospective review was conducted of 72 cementless knees followed for a minimum of 2 years (mean, 37 months). Surgical time, estimated blood loss, and range of motion at 6 weeks were compared with those of a matched cohort of 70 cemented knees performed by the same surgeon. Knee Society Score and Oxford Knee Score were recorded for the cementless group. Radiographs were evaluated for change in implant position, subsidence, and radiolucent and sclerotic lines. Operative time was statistically shorter in the cementless group (40 vs 45 minutes), but there was no significant difference in postoperative estimated blood loss (557 vs 355 mL). Range of motion at 6 weeks averaged 118° in the cementless group vs 114° in the cemented group. Knee Society Score improved from 53.9 preoperatively to 85.0 at 6 weeks and 91.6 at most recent follow-up. Oxford Knee Score improved from 23.9 preoperatively to 31.7 at 6 weeks and 43.4 at most recent follow-up. No implants aseptically loosened or migrated. There were 2 early infections in the cemented group requiring revision. This cementless total knee arthroplasty revealed excellent clinical results at 3-year follow-up and resulted in shortened operative times. Biologic fixation was achieved in 100% of patients with improved functional and objective scores. Early results are encouraging, and this cementless total knee arthroplasty appears to provide an excellent alternative to cemented total knee arthroplasty. [Orthopedics. 201x; xx(x):xx–xx.]

Total knee arthroplasty (TKA) is one of the most commonly performed orthopedic procedures.1 In 2012, more than 700,000 TKAs were performed in the United States,2 and it is projected that this number will increase to approximately 3.48 million in the United States alone by 2030.3 In the Western world, the lifetime risk for TKA has been calculated as 8.1% for men and 10.8% for women.4 In response to the growing demand for TKA, particularly among younger, more active patients, it is necessary to reevaluate the efficacy and perioperative outcomes of TKA device fixation modalities to continually improve patient care and clinical outcomes.

Several studies have reported inferior outcomes of cemented fixation in TKA in younger patients. McCalden et al5 reported decreased survivorship and increased aseptic loosening in patients younger than 55 years. Meehan et al6 reported a 4.7 times greater risk of revision within 1 year for patients younger than 50 years compared with those older than 65 years. It is also well established that obesity has a negative impact on survivorship of TKA. Bagsby et al7 reported an 89% survivorship in morbidly obese patients compared with a 99% survivorship in a matched cohort of obese patients with cementless implants. Abdel et al8 reported similar results in obese patients with increased aseptic loosening.

Multiple successful results have been reported for TKA with cementless technology. In one study of cementless (hydroxyapatite-coated) knees conducted by Watanabe et al,9 the cohort of young, active patients younger than 45 years had no implant failures at the latest follow-up, as far as 11 years out. Melton et al10 studied long-term outcome for an uncemented, hydroxyapatite-coated total knee replacement, reporting 96% survival at 18 years. Epinette et al11 reported survivorship of 97% at 20 years using a hydroxyapatite-coated cementless total knee replacement.

However, specific features of previous designs have been flawed, leading to inferior outcomes compared with cemented designs in select studies. Inferior and patchy porous coating, less wear-resistant polyethylene with suboptimal locking mechanisms, and thin polyethylene in metal-backed patella have all caused failures that affected the adoption of this alternative fixation option. An understanding of these modes of failure along with new additive manufacturing techniques led to the development of a new cementless tibial baseplate and patellar component. Strategic placement of the pure titanium 3-dimensional porous ingrowth surface along with 4 cruciform pegs and a press-fit keel provide the necessary initial stability to allow bone ingrowth.

Materials and Methods

This nonrandomized prospective review reports the early results of a new cementless knee design (Triathlon Tritanium cementless total knee system; Stryker, Mahwah, New Jersey) (Figure 1). All research was performed at Tucson Orthopaedic Institute Research Center and was approved by the Tucson Medical Center Human Research Committee. All surgeries were performed by a single surgeon (R.G.C.) at Tucson Medical Center through a subvastus approach using a tourniquet that was released following skin closure. Patients received a Triathlon cementless posterior cruciate-sparing implant, and all patellae were resurfaced using the Tritanium metal-backed patellar component. A retrospective chart review of a matched cohort of cemented knee replacements performed by the same surgeon using the Triathlon cemented TKA with a cemented all-polyethylene patellar component was performed to evaluate intraoperative and perioperative parameters.

The Triathlon Tritanium cementless total knee system (Stryker, Mahwah, New Jersey).

Figure 1:

The Triathlon Tritanium cementless total knee system (Stryker, Mahwah, New Jersey).

Seventy-two cementless Triathlon TKAs were implanted in 70 patients between November 2014 and May 2015 and were compared with 70 knee replacement procedures between January and July 2013 in 66 age- and sex-matched patients who had the same implant geometry placed using cement fixation (Figures 23). Patients were recruited sequentially and were included in the study if they were not pregnant, were between the ages of 18 and 75 years, and maintained a diagnosis of non-inflammatory degenerative joint disease. Patients with a body mass index of 40 kg/m2 or greater or those with inflammatory arthritis, avascular necrosis, or latent infection were excluded from the study.

Lateral view of the knee after total knee arthroplasty with the Triathlon Tritanium cementless total knee system (Stryker, Mahwah, New Jersey).

Figure 2:

Lateral view of the knee after total knee arthroplasty with the Triathlon Tritanium cementless total knee system (Stryker, Mahwah, New Jersey).

Anteroposterior view of the knee after total knee arthroplasty with the Triathlon Tritanium cementless total knee system (Stryker, Mahwah, New Jersey).

Figure 3:

Anteroposterior view of the knee after total knee arthroplasty with the Triathlon Tritanium cementless total knee system (Stryker, Mahwah, New Jersey).

The cementless cohort included 27 men and 43 women with a mean age of 66.1 years (SD, 6.7 years) and a mean body mass index of 30.1 kg/m2 (SD, 3.8 kg/m2) (Table 1). The cemented group included 24 men and 42 women with a mean age of 63.5 years (SD, 7.1 years) and a mean body mass index of 30.1 kg/m2 (SD, 4.9 kg/m2). The cementless group was then followed prospectively for a minimum of 2 years to evaluate the early outcomes, survivorship, and radiographic appearance of the implants at this time interval. The mean follow-up was 37 months (range, 31–39 months).

Demographics of the 2 Patient Groups

Table 1:

Demographics of the 2 Patient Groups

The intraoperative efficiency of a cementless TKA was evaluated by comparing its operative times with those of the matched cohort of patients undergoing cemented fixation with all other surgical parameters being identical. In addition, immediate outcomes were compared with the well-established outcomes of the surgeon's cemented TKA.

Secondary parameters were compared to ascertain whether cementless knees have increased blood loss due to exposed porosity of the bone that is otherwise covered by cement. All knees were drained with a medium Hemovac drain, and output measurements were recorded during the first 24 hours. All drains were removed 24 hours postoperatively by nursing staff. Therefore, an accurate comparison of postoperative blood loss could be made between the 2 groups.

In addition, early range of motion was compared between the 2 cohorts at 6 weeks to establish whether the cementless patients might have stiffer knees if they endured greater pain in the early postoperative time frame. The groups were then evaluated at the minimum 2-year follow-up to establish their most recent range of motion as well. The senior author (R.G.C.) used a standard goniometry technique to examine all patients.

Knee Society Scores and Oxford Knee Scores were established preoperatively for the cementless cohort and followed until the most recent evaluation. Interval scores were recorded at each follow-up visit, including 6 weeks, 1 year, and most recent.

Staged bilateral TKAs were performed for 4 patients (8 knees) in the cemented group and 2 patients (4 knees) in the cementless group. Selection for the study was sequential. Exclusion for the cementless group included osteoporotic bone that was deemed inadequate to support cementless fixation and was decided on at the time of surgery following completion of all bone cuts. All 66 cemented knees were operated on immediately prior to release of the cementless design and were not subject to selection bias based on deformity, age, sex, diagnosis, or any other clinical concern. This cohort was used as a perioperative baseline comparison for blood loss, operative time, and range of motion. Knee Society Scores and Oxford Knee Scores were not prospectively collected for these patients.

Radiographs were evaluated by the senior author (R.G.C.) and included standing anteroposterior, lateral, and skyline views obtained 6 weeks postoperatively and at annual follow-up. Comparisons were made with the baseline 6-week radiograph to evaluate change in implant position, subsidence of the tibial tray, radiolucent lines (progressive or nonprogressive), and reactive or sclerotic lines and the presence of radiographic signs of loosening.

Statistical analysis was performed with the use of Revolution Analytics Software R 3.2.0 (Microsoft, Redmond, Washington) and Excel (Microsoft) and through analysis of covariance. Statistical significance was set at P<.05.

Results

Operative time was significantly increased for cemented vs cementless TKA application (mean, 45.6 minutes [SD, 7.2 minutes] vs 40.8 minutes [SD, 6.0 minutes]; P=.0006) (Table 2). Operative time was recorded as the time from incision to placement of surgical dressing. An observation was made that there was a trend to decreased operative time with increasing age (P=.0173) and slightly longer operative time with male sex (P=.0211) (Table 3). Tourniquet time was significantly increased in the cemented group (P=.0001) and in male patients of both groups (P=.0356).

Perioperative Outcomes of the 2 Patient Groups

Table 2:

Perioperative Outcomes of the 2 Patient Groups

Perioperative Outcomes According to Sex

Table 3:

Perioperative Outcomes According to Sex

Overall drain output was not significantly different (355 mL for cemented vs 557 mL for cementless; P=.2676); however, when stratified by sex, males in the cementless cohort had the highest drain output compared with those in the cemented group (820 mL vs 453 mL; P=.0105). There was no significant difference among females when comparing drain output in the cemented and cementless groups. There was a higher overall drain output in all males compared with females, regardless of implant fixation (643.1 mL vs 343.7 mL, P=.3035). No transfusions were performed for either cohort of patients.

Six-week postoperative flexion was slightly increased in the cementless cohort but did not meet statistical significance (cemented group: mean, 114.2°; range, 70°–135°; SD, 13.5°; vs cementless group: mean, 118.2°; range, 90°–140°; SD, 9.9°; P=.0586). There were no statistically significant differences in sequential range of motion outcomes at the intervals recorded. The 2 groups continued to improve their range of motion until the 2-year evaluation, with both achieving a mean of greater than 120° of flexion (Figure 4). Arthrofibrosis requiring manipulation under anesthesia occurred in 5 patients, 1 in the cementless group and 4 in the cemented cohort. Two of the 4 patients in the cemented group required revision because of infection. One underwent a washout and polyethylene exchange, whereas the other required a 2-stage revision. The infection was eventually eradicated in both patients.

Average flexion range of motion to 2-year follow-up.

Figure 4:

Average flexion range of motion to 2-year follow-up.

Knee Society Scores were obtained prospectively for the cementless group and showed an improvement in functional scores from 43.9 (SD, 16.1) to 59.2 (SD, 15.4) at 6 weeks and 83.0 (SD, 13.6) at most recent follow-up (Table 4, Figure 5). The objective scores improved from 53.9 (SD, 21.9) to 85.0 (SD, 6.8) at 6 weeks and 91.6 (SD, 4.5) at most recent follow-up. The Oxford Knee Score was also collected and recorded, showing improvement from 23.9 (SD, 1.2) preoperatively to 31.7 (SD, 6.9) at 6 weeks and 43.4 (SD, 4.7) at most recent follow-up (Figure 6). Scores were not available for the cemented cohort because they were not included in a prospective clinical study.

Knee Society Scores and Oxford Knee Scoresa

Table 4:

Knee Society Scores and Oxford Knee Scores

Knee Society Score (KSS) improvement.

Figure 5:

Knee Society Score (KSS) improvement.

Oxford Knee Score improvement.

Figure 6:

Oxford Knee Score improvement.

Evaluation of most recent radiographs at an average of 37 months postoperatively revealed that no implants showed signs of migration or change in position. Both femoral and tibial implants remained in their original orientation compared with the baseline postoperative radiograph. A nonprogressive radiolucent line in 1 or 2 locations on either the anteroposterior or the lateral view was present in 4 tibial trays (5%) at the 6-week interval. All lucencies were less than 1 mm, nonprogressive (did not increase in size and did not diverge with time), and not thought to represent loosening. The lucent lines were present on the medial margin of the tibial tray in 3 knees and laterally at the margin in 1 knee. There were no radiolucent lines around any of the keels or below the central portion of the tray in any circumstance. Reactive or sclerotic lines were noted on the most recent radiographs of 3 tibial components, 2 at the medial margin and 1 laterally, and all were noted for the same patients who had a lucent line at 6 weeks.

No femoral components appeared loose or had progressive lucencies that were considered significant. All patellar components appeared to have well-ingrown margins along each of the 3 pegs, with a less than 1-mm lucent line present under the baseplate on 5 (6.9%) of the components. This lucency did not increase in width or length in any of the patients and covered less than 20% of the measured width of the component. All patellar implants appeared well ingrown on most recent radiographs.

Discussion

Total knee arthroplasty provides an excellent treatment option for patients with end-stage arthritis. Implant design features have evolved during the past 50 years, and improved polyethylene has facilitated favorable long-term outcomes. However, as the need for knee arthroplasty reaches younger, heavier, and more active patients, the demands on the cement interfaces increase as well. Many studies have shown that TKAs in these subgroups of patients do not have the same long-term results as those in older patients with lower body mass indexes.12–16 As such, improved cementless designs that can provide biological fixation are important to avoid early aseptic loosening.

Many surgeons have been reluctant to consider using cementless fixation in knee arthroplasty because of poor designs in earlier generation implants.17,18 Ingrowth surfaces were less predictable, and relying on screws to provide initial stability was not always ideal. In addition to the inconsistency of screw fixation, those screw holes provided a direct path for less wear-resistant polyethylene that was secured to the baseplate in a less efficient manner than is provided by current designs. This combination of suboptimal design features created baseplate loosening and, in some instances, massive osteolysis of the tibia19 and femur.20 For these reasons, tibial component stability has remained a concern,18,21,22 despite advances in cementless designs. The patellar component failed because of the polyethylene properties and the resultant metal-on-metal destruction of the femoral component. Kwong et al,23 however, showed that new technology in cementless designs has decreased the number of patellar component failures. Recent evidence has suggested that such technological innovations have made survivorship outcomes in cementless fixation similar to those in cemented fixation.21,24–32

Additive manufacturing 3-dimensional printing using pure titanium provided the ability to design a new tibial baseplate and patellar component that have an ideal pore size for bone ingrowth. Four cruciform pegs were carefully placed using the Stryker Modeling and Analytics System database information33 and provide the ideal geometry to resist movement and pullout forces. In addition, a press-fit keel provides initial anterior–posterior as well as torsional stability. To address the earlier patellar failures previously described, the polyethylene thickness was enhanced and the transition zone for the unsupported polyethylene around the margins was optimized. The necessity for an implant to provide initial implant stability is paramount so as to promote bone ingrowth for long-term survivorship. Once a cementless implant is biologically incorporated to the surrounding bone, it is highly unlikely that it will ever loosen.

Miller et al34 recently reported excellent clinical outcomes at minimum 2-year follow-up using the Triathlon cementless implant with a mix of cruciate-sparing and cruciate-substituting knees. Aseptic loosening was reported as 0.5%, compared with 2.5% in the cemented cohort. Nam et al35 reported outcomes similar to those of the current study, including no significant difference in blood loss and a decrease in operative time.

Conclusion

The encouraging clinical and radiographic results of this new cementless technology suggest that these implants achieve consistent early bone ingrowth. Given the excellent long-term results of the Triathlon design on which the joint biomechanics of this implant are based, perhaps this platform will provide more consistent long-term outcomes for younger, more active, and heavier patients. Studies reporting longer-term results are necessary to reach definitive conclusions; however, the short-term results are encouraging.

References

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  35. Nam D, Kopinski JE, Meyer Z, Rames RD, Nunley RM, Barrack RL. Perioperative and early postoperative comparison of a modern cemented and cementless total knee arthroplasty of the same design. J Arthroplasty. 2017;32(7):2151–2155. doi:10.1016/j.arth.2017.01.051 [CrossRef]

Demographics of the 2 Patient Groups

DemographicCement GroupCementless Group
Patients, No.6670
Total knee arthroplasty, No.7072
Bilateral total knee arthroplasty, No.42
Agea, mean (SD) [range], y63.5 (7.1) [41–74]66.1 (6.7) [48–75]
Body mass index, mean (SD) [range], kg/m230.1 (4.9) [19.3–38.4]30.1 (3.8) [22.6–39.1]
Sex, No.
  Male2427
  Female4243
Side, No.
  Right4037
  Left3035
Dates of operation, start and end1/30/2013 and 7/1/201311/3/2014 and 5/6/2015

Perioperative Outcomes of the 2 Patient Groups

Perioperative MeasureCement GroupCementless GroupP
Operative time, mean (SD), min45.6 (7.2)40.8 (6.0).0006
Operative time—male, mean (SD), min48.8 (8.7) [n=26]44.0 (5.6) [n=28].7124
Tourniquet time, mean (SD), min43.2 (6.9)38.5 (5.7).0001
Tourniquet time—male, mean (SD), min45.3 (8.5) [n=26]41.9 (5.3) [n=28].1699
Drain output, mean (SD), mL354.8 (276.1)557.4 (409.1).2676
Drain output—male, mean (SD), mL453.3 (316.6) [n=26]819.5 (481.5) [n=28].0105
Flexion 6-week range of motion, mean (SD)114.2 (13.5) [n=69]118.2 (9.9) [n=71].0586
Adverse events, No.51.1442

Perioperative Outcomes According to Sex

Perioperative MeasureMean (SD)P

Male (n=54a)Female (n=88a)
Operative time, min46.4 (7.6)41.3 (5.9).0211
Tourniquet time, min43.6 (7.2)39.2 (5.9).1781
Drain output, mL643.1 (446.6)343.7 (240.2).3035

Knee Society Scores and Oxford Knee Scoresa

Outcome MeasureMean (SD)P


Preoperative6 WeeksMost RecentPreoperative to 6 Weeks6 Weeks to Most Recent
Knee Society Score functional (maximum score, 100)43.9 (16.1)59.2 (15.4)83.0 (13.6)<.0005<.0005
Knee Society Score objective (maximum score, 100)53.9 (21.9)85.0 (6.8)91.6 (4.5)<.0005<.0005
Oxford Knee Score (maximum score, 50)23.9 (1.2)31.7 (6.9)43.4 (4.7)<.0005<.0005
Authors

The authors are from Tucson Orthopaedic Institute (RGC) and the University of Arizona College of Medicine–Tucson (NCS, SLJ), Tucson, Arizona.

Mr Sherman and Ms James have no relevant financial relationships to disclose. Dr Cohen is a paid consultant for and has received grants from Stryker.

The authors thank Nebojsa Skrepnik, MD, PhD, for project management and Annie Phinizy for clinical support.

Correspondence should be addressed to: Russell G. Cohen, MD, Tucson Orthopaedic Institute, 5301 E Grant Rd, Tucson, AZ 85712 ( russgc@aol.com).

Received: March 20, 2018
Accepted: May 17, 2018

10.3928/01477447-20180828-05

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