Total knee arthroplasty (TKA) has become one of the most commonly performed orthopedic procedures. The number of TKAs performed annually is expected to continue to rise into the 2030s, at a near-exponential rate.1 Additionally, the patient population receiving TKA is expected to become younger, with patients younger than 65 years comprising well over 50% of TKA recipients by 2020.2 Younger patients tend to engage in higher levels of activity, thus placing greater stress on their joints and increasing the rate of early joint replacement failure and the need for revision.3,4 Periprosthetic joint infection is a common cause of early failure,5,6 whereas aseptic loosening, polyethylene wear, and other forms of mechanical failure are the most common causes of late revision and revision overall.6,7 Therefore, while 10- and 15-year survivorship rates have consistently been shown to be well above 90%,8–12 implant longevity remains a focus for improvement among orthopedic surgeons, especially as the surgical population becomes younger.
The optimal method of fixation for TKA is an ongoing debate. Cemented and uncemented implants are both available for use. The use of cement provides good initial stability and fixation as well as ideal hemostasis,13 but the time required for cement application and drying often leads to increased operating room time.14,15 Unfortunately, early uncemented TKAs were inferior to their cemented counterparts in terms of survivorship, complication rate, and clinical outcomes.4,11,13,16,17 As a result, cemented fixation became the gold standard.
More recently, implant manufacturers have designed newer uncemented total knee implants using highly porous tantalum or titanium metal with promising, although limited, results. The purpose of this study was to evaluate the early outcomes of a modern uncemented TKA design. The authors hypothesized that, due to the new materials, the implants would have early outcomes equivalent to those of cemented TKA and that the uncemented procedures could be performed in a cost-effective way.
Materials and Methods
This study received institutional review board approval in 2017 prior to any data collection. The Michigan Arthroplasty Registry Collaborative Quality Initiative database for all patients undergoing a primary TKA at a 2-hospital health system during a 2-year period was queried to investigate early clinical and financial outcomes of a modern uncemented TKA implant. The Michigan Arthroplasty Registry Collaborative Quality Initiative database is a validated, quality database of all total joint arthroplasty procedures from 51 participating hospitals and ambulatory surgery centers in Michigan. A total of 1400 sequential TKA procedures were reviewed from the prospectively collected data in the hospital's Michigan Arthroplasty Registry Collaborative Quality Initiative total joint registry. Patients who underwent a knee arthroplasty procedure for fracture, infection, trauma, or malignancy were excluded from the study.
Patients who received an uncemented TKA during this period were matched by age to patients who received a cemented TKA from the same manufacturer. Specific operative protocols, including the choice of performing a cemented or an uncemented TKA, were based on individual surgeon preference. A minority of these surgeons were fellowship-trained total joint arthroplasty surgeons. Inclusion criteria included the use of the Triathlon total knee arthroplasty system (Stryker, Mahwah, New Jersey). Both cruciate retaining and posterior stabilized designs were included. Patellae were resurfaced in most of the cases. There were no specific exclusion criteria. Patient demographic data, medical comorbidities, length of stay, complications, emergency department visits, discharge disposition, and 90-day outcomes were noted. The data were specifically abstracted by 2 nurse clinical data abstractors from the quality department and the Michigan Arthroplasty Registry Collaborative Quality Initiative registry.
The financial data were provided by the hospital finance team. The process was the same for all patients and implant types. Costs were determined by the relationship between individual charge codes within each hospital department. The direct costs, those associated with patient care, and the indirect costs, such as finance, information technology, and human resources, are spread similarly among departments. Departments with higher total charges have more cost allocated than departments with lower charges. Cost is spread to the department charge codes based on their relationship to each other. The charge codes were summed to determine the cost of surgery, the cost of 90-day readmissions, 90-day outpatient charges, and then the total cost.
Fisher's exact tests were used for categorical data, and paired t tests were used for continuous data. Statistical analysis was performed in Excel (Microsoft, Redmond, Washington). Statistical significance was defined as P<.05, and confidence intervals were set at 95%.
From October 4, 2014, to October 31, 2016, a total of 1400 TKAs were performed at the 2 study sites. Of these, 252 (18%) were performed with an uncemented Triathlon TKA implant. For comparison, this group of uncemented TKAs was matched by age to 252 cemented Triathlon TKAs performed during the same period.
Despite matching by age, the uncemented group had a slightly lower comorbidity burden as measured by American Society of Anesthesiologists score (Table 1). However, there were no statistically significant differences between the 2 groups in terms of age, sex, body mass index, smoking status, bleeding disorders, thromboembolic events, or incidence of diabetes (Table 1). Interestingly, despite having fewer medical comorbidities, drinking 8 or more times per week was more common among those receiving an uncemented TKA. Regarding the use of medications, cemented TKAs were found to have more preoperative medications (186 vs 151; P=.05), specifically narcotics (56 vs 35; P=.02) (Table 2).
Preoperative Medication Use
Early Outcomes, Complications, and Discharge Disposition
During the 90-day follow-up period, more uncemented knees had “no complications” (216 vs 193; P<.01) (Table 3). Cemented knees had higher returns to the operating room (19 vs 0; P<.01) and more manipulations under anesthesia (14 vs 0; P<.01) (Table 3). Uncemented knees had shorter stays (1.58 vs 1.87 days; P<.01), were more frequently discharged home (90.48% vs 68.75%; P<.0001), and used less home care or extended care facilities (6.35% vs 19.14%; P<.0001; 2.78% vs 11.72%; P=.0001). Overall, in the immediate postoperative period, 3 cemented TKAs required a transfusion of packed red blood cells (mean, 1.3 units). For uncemented TKAs, only 1 patient required a transfusion of packed red blood cells (1 unit).
90-Day Postoperative Events and Actions
For patients with reported Knee injury and Osteoarthritis Outcome Scores, uncemented TKAs scored higher than aged-matched counterparts (63.69 vs 47.10, n=85 and n=43, P<.0001). Similarly, uncemented TKAs had higher Patient-Reported Outcomes Measurement Information System (PROMIS) T-Physical and T-Mental scores (44.12 vs 39.45, n=95 and n=59, P<.0001; 51.84 vs 47.82, n=97 and n=59; P=.0018).
The use of an uncemented TKA was associated with a mean surgical episode cost savings of $1096 (direct surgical costs including implant) (Table 4) (P<.01). The number of readmissions during the 90-day global period were similar (18 uncemented and 20 cemented). As one would expect if a patient was readmitted to the hospital, the average cost of the readmission episode was not significantly different between the 2 groups. The postoperative protocols were identical for the 2 groups, and there were no significant differences between the 2 groups in terms of the costs associated with outpatient follow-up care within the 90-day global period. Overall, as a group for the 90-day bundle, the use of an uncemented TKA implant was associated with a cost savings of more than $1300 (uncemented, $7016; cemented, $8348; P<.01).
Total 90-Day Cost
Although the use of modern uncemented TKA implants has increased, data on outcomes have been limited. This study suggests that patients receiving an uncemented TKA have a shorter length of stay, a higher rate of discharge to home, better knee-specific outcome measures, fewer complications, and fewer reoperations than patients receiving a cemented TKA. In addition, the costs associated with the procedure, despite using the newer implants, were lower. These data, taken together, should alleviate fears of early failure, complications, or poor outcomes with the use of uncemented TKA in an appropriately selected group of patients. They may also encourage use of these implants for patients managed within a 90-day economic care bundle.
Uncemented fixation of TKA implants was introduced decades ago with the goal of creating a long-lasting, biologic interface for an increasingly younger1,2,18 group of patients undergoing TKA. However, use of this technique became limited after early failures were seen with early uncemented TKA implants. These failures have been attributed to design flaws that included modular tibial components, patch-porous coating,19 fatigue fracture of the femoral components,20 the use of metal-backed patellar components,21,22 lower quality polyethylene, and tibial screw osteolysis.19,23 Additionally, the osteoconductive surfaces were less efficacious than those currently available and were prone to early failures.24 Nevertheless, many authors have reported that in patients without early implant failure, excellent osseo-integration was obtained and long-term survival rates of greater than 95% were observed.25–28
More recently, science and manufacturing have led to uncemented implants corrected for past design flaws. The modern implants are now using a highly porous tantalum or titanium metal as the substrate design (in this series, cobalt-chrome–beaded femur with peri-apatite and a printed porous tritanium tibial baseplate). The changes were intended to provide a better biological interface between the bone and the implant to allow for optimal trabecular bone formation, remodeling, and adaptation.29,30 Additional design features unique to the tibial component used in this study include a press-fit tibial keel and 4 bullet-cruciform pegs on the baseplate designed to reduce early micromotion and lift off prior to osseointegration. A recent Cochrane systematic review comparing uncemented and cemented TKAs suggested that cemented implants have less micromotion and displacement in the first 2 years postoperatively.31 However, beyond 2 years, cemented implants have more than twice the risk of future aseptic loosening.31 This suggests that if early stability can be achieved in younger patients with the improved design of newer uncemented implants, they will likely benefit from the long-term stability of biologic fixation.
Because the early fixation of uncemented implants is crucial to their long-term success, particular attention should be paid to the early results of modern uncemented implants. Thus far, early results of modern uncemented TKA have indicated Knee Society Score (KSS) clinical outcome scores and rates of complication29,32–35 as good as or better than those of cemented TKA, with patient satisfaction rates of greater than 90%.10 Another study has suggested promising early outcomes for the specific TKA implant used in this study15; however, the low rate of patellar resurfacing and the relatively small number of patients included in the study limit the generalizability. The current study, performed with a greater diversity of surgeons and including a larger number of patients, showed that patients with uncemented knees had no reoperations within 90 days of surgery and had fewer complications than patients matched by age receiving a cemented TKA. Additionally, for patients with Knee injury and Osteoarthritis Outcome Scores and Patient-Reported Outcomes Measurement Information System outcome scores, the uncemented TKAs scored higher than the cemented TKAs. These results are encouraging, as by 3 months postoperatively, patients should have significant osseointegration of their implants, particularly with the improved porous coatings seen with modern uncemented implants.
The cost of arthroplasty remains an issue. Based on cost-utility analyses, TKA is at or near the top of all medical and surgical interventions.26 Nonetheless, the financial burden of TKA was $10.4 billion in the United States in 2008.3 Ideally, the decreased operative time associated with uncemented TKA14,15 would decrease cost. However, uncemented implants themselves may be as much as 30% more expensive than their cemented counterparts.30 Despite the implant costs, the current study showed that the use of an uncemented TKA was associated with decreased cost for the surgical episode and cost reduction that was maintained for the 90-day global period after surgery. It is likely that these cost savings result from decreased operative time, lack of cement cost, decreased length of stay, and decreased postoperative complications. In the modern era of bundled payments, with overall declining reimbursement for TKA and at-risk contracting, surgical and post-acute care costs are important factors to consider.
This study had some limitations. The choice of cemented or uncemented TKA was at the individual surgeon's discretion and not randomized. This introduced selection bias, which was the most likely cause of the difference in medical comorbidities between the 2 groups. Additionally, this may have been the reason for discrepancies in length of stay and rates of discharge to home and may have affected the financial data. Although this criticism is valid, this study showed that in a group of patients with few medical comorbidities, the use of uncemented TKA supported excellent early outcomes that were statistically better than those seen with cemented TKA. As the major clinical benefit of uncemented technology is thought to be long-term implant stability in those who are young and active, the authors believe that this selection bias is less concerning. The other primary limitation was the financial modeling. Although one could criticize the “accuracy” of the costs, the methodology was the same for the 2 groups, which should allow, at the least, a direct relative cost comparison.
In the short-term, modern uncemented TKA implants performed as well as or better than cemented designs and were associated with significantly decreased costs for both the acute surgical episode and the 90-day global period. These data, taken together, should alleviate fears of early failure, complications, or poor outcomes with the use of uncemented TKA in an appropriately selected group of patients.
- Kurtz S, Ong K, Lau E, Mowat F, Halpern M. 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):780–785.17403800
- Kurtz SM, Lau E, Ong K, Zhao K, Kelly M, Bozic KJ. Future young patient demand for primary and revision joint replacement: national projections from 2010 to 2030. Clin Orthop Relat Res. 2009;467(10):2606–2612. doi:10.1007/s11999-009-0834-6 [CrossRef]19360453
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- Julin J, Jämsen E, Puolakka T, Konttinen YT, Moilanen T. Younger age increases the risk of early prosthesis failure following primary total knee replacement for osteoarthritis: a follow-up study of 32,019 total knee replacements in the Finnish Arthroplasty Register. Acta Orthop. 2010;81(4):413–419. doi:10.3109/17453674.2010.501747 [CrossRef]20809740
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|Characteristic||Uncemented Group||Cemented Group||P|
|Patients, Total No.||252||252|
| Age, mean, y||65.09||65.08|
| Body mass index, mean, kg/m2||32.69||33.60||.42|
| Length of stay, mean, d||1.58||1.87||.05|
|Risk factor, No.|
| Current smoking||15||22||.30|
| Bleeding disorder||2||3||1.00|
| Thrombolic disease history||12||11||1.00|
|Preoperative ASA score, No.|
Preoperative Medication Use
|Uncemented Group||Cemented Group|
|Anticoagulant||5 (2.0%)||11 (4.4%)||.14|
|Antimicrobial||1 (0.4%)||6 (2.4%)||.12|
|Antiplatelet||109 (43.3%)||108 (43.0%)||1.00|
|Narcotic||35 (13.9%)||56 (22.2%)||.02|
|Steroid||1 (0.4%)||5 (2.0%)||.22|
|No medication||118 (46.8%)||95 (37.7%)||.05|
90-Day Postoperative Events and Actions
|Event or Action||No.||P|
|Uncemented Group||Cemented Group|
| No 90-day postoperative events||216||193||<.01|
| Emergency department visit||29||33||.69|
| Return to the operating room (other)||0||19||<.01|
| Pulmonary embolism||0||0|
| Urinary tract infection||0||0|
| Joint space infection||0||0|
| Deep venous thrombosis||0||2||.49|
| No joint-related treatment||237||216||<.01|
| Other joint-related treatment||7||15||.13|
| Antibiotic treatment||6||6|
| Removal of prosthesis||3||1||.37|
| Irrigation and debridement||0||4||.02|
| Return to the operating room (other)||1||2|
| Open reduction||1||0|
Total 90-Day Cost
|Cost Assessment||Uncemented Group||Cemented Group||P|
|Surgery cost, mean±SD||$5710.78±$37.60||$6806.43±$117.81||<.01|
|90-day readmissions, No.||18||20|
|90-day readmission cost, mean±SD||$6076.47±$893.77||$5809.04±$1006.82||.42|
|90-day outpatient, No.||86||86|
|90-day outpatient cost, mean±SD||$711.18±$165.68||$829.07±$138.15||.29|
|Total cost, mean±SD||$7016.11±$49.79||$8347.65±$131.47||<.01|