Keywords total knee arthroplasty - American Joint Replacement Registry - cementless total knee
- registry
Although cemented total knee arthroplasty (TKA) remains standard practice, cementless
fixation in TKA continues to be an intriguing option. Potential advantages of cementless
TKA include bone preservation in the setting of revision surgery, the elimination
of third body wear from cement debris, and a shorter operative time.[1 ] Unfortunately, this enthusiasm has been tempered by early generations of cementless
TKA designs that were plagued by a high associated risk of failure and poor clinical
outcomes.[2 ]
[3 ]
Early generations of cementless TKA failures were attributed to failure of the cementless
patellar or tibial components.[4 ]
[5 ]
[6 ] Retrieval analyses of early generation tibial components demonstrated levels of
osseointegration of less than 30%.[7 ] Improvement in the design of the patellofemoral articulation, as well as the elimination
of thin polyethylene and sharp metal borders, has led to improved results.[8 ] The decreasing popularity of patellar resurfacing as well as the introduction of
modern highly porous surfaces has tempered concerns for patellar- or tibial-related
failure. These design improvements have led to a relatively rapid increase in the
use of cementless TKA in the United States, increasing from 1.9% in 2012 to 20.5%
in 2022 in the American Joint Replacement Registry (AJRR).[9 ]
Recent prospective and retrospective investigations utilizing modern cementless TKA
have demonstrated no differences in survivorship and lower rates of aseptic loosening
in select populations when compared with cemented TKA.[1 ]
[10 ]
[11 ]
[12 ]
[13 ] Unfortunately, these studies are limited in their power to detect revision risk,
specific mechanisms of failure including mechanical loosening, and in their generalizability
to the U.S. experience. In contrast to these investigations are international registry
data that indicate an increased risk of revision for cementless TKA.[14 ]
[15 ]
[16 ] Yet these international registry analyses are limited by a lower utilization of
cementless fixation, a lack of availability of modern cementless designs, and other
confounding variables that limit their applicability to the U.S. cementless TKA experience.
In contrast, the AJRR collects data from over 1,400 sites in the United States on
greater than 2 million arthroplasty procedures with a gradually increasing use of
cementless TKA with modern tibial and patellar designs. The AJRR provides a unique
opportunity to understand the TKA experience in the United States and to evaluate
if there is evidence regarding the increased risks of revision with modern cementless
TKA. The primary aim of the present study was thus to identify if there are differences
in implant survivorship between modern cementless and cemented TKA designs using the
AJRR dataset while controlling for potential confounding variables including age,
obesity, sex, comorbidity burden, and femoral design.
Materials and Methods
We collaborated with the American Academy of Orthopaedic Surgeons Registry Analytics
Institute to perform a retrospective analysis of AJRR data on primary TKA cases in
the AJRR database from January 2012 to March 2020. We identified 1,098,792 primary
TKAs over the study period and linked cases to U.S. Centers for Medicare & Medicaid
Services (CMS) data to supplement outcome events occurring outside of AJRR reporting
institutions where available. Catalog numbers from each TKA included were identified
and recorded for the classification of cases into target component categories.
To facilitate linkage of cases to CMS data, we included only patients aged ≥65 years.
We excluded 315,507 patients with either hybrid (cemented tibial component and cementless
femoral component) or reverse hybrid (cementless tibial component and cemented femoral
component) fixation or those with missing data on cement fixation. We excluded 2,956
patients with supplemental stemmed tibial or femoral fixation, use of tibial augmentation,
or use of highly constrained implants. We only included modern generation tibial and
patellar components, defined as those with highly porous metals,[17 ]
[18 ] including those with porous tantalum,[19 ] highly porous titanium,[20 ] and those with 3D printing or electron beam melting.[21 ]
[22 ] We excluded 834 patients who received older generation tibial components, including
those with cobalt-chromium sintered beads, titanium fiber metal mesh, cancellous-structured
titanium, or titanium plasma spray. This left us with a final cohort of 442,745 cemented
TKAs and 19,841 modern cementless TKAs with a minimum of 2-year follow-up ([Fig. 1 ]).
Fig. 1 Flowchart demonstrating exclusion and allocation of primary total knee arthroplasty
(TKA) cases into cohorts, cemented versus cementless. CR, cruciate retaining; PS,
posterior stabilized.
Each identified procedure in the AJRR was assessed for a linked revision surgery in
AJRR or CMS databases. A surgery was labeled as a revision if it met four criteria:
surgical date after the index procedure, matched patient ID, matched surgical site,
and matched laterality. Codes from the 10th revision of the International Statistical
Classification of Diseases and Related Health Problems Procedure Coding System (ICD-10-PCS)
were used to infer laterality along with a discrete laterality field in the AJRR database
for older cases.
Data collected included patient age, sex, body mass index (BMI), Charlson's comorbidity
index (CCI), femoral component design (cruciate retaining [CR], or posterior stabilized
[PS]), and patellar resurfacing. Reason for revision was also recorded, and outcomes
considered were all-cause revision and revision for aseptic mechanical loosening.
Outcomes were captured through March 2022 to align with end of Medicare claims and
to allow 2-year minimal potential follow-up.
We summarized the characteristics of the two fixation groups (cemented vs. cementless)
using counts and percentages for categorical variables and mean (standard deviation
[SD]) and median (quartile 1, quartile 3) for continuous variables. We compared groups
using chi-squared test, student's t -test, and Wilcoxon rank-sum test as appropriate. Cumulative incident function (CIF)
curves and cause-specific Cox models evaluated the risk of all-cause revision and
revision for mechanical loosening, adjusting for BMI, sex, age, CR versus PS femoral
design, patellar resurfacing, and CCI, reporting hazard ratios (HRs) and their 95%
confidence intervals (CIs). Analyses were conducted using SAS Enterprise Guide v.7.15
(Cary, NC), and statistical significance evaluated at p < 0.05.
Results
Patients with cementless compared with cemented TKA were younger (mean age: 71.9 vs.
73.2 years; p < 0.001) and more likely to be aged 65 to 74 versus 75+ years (74.6 vs. 65.2%, p < 0.001). They were more likely to be male sex (48.8 vs. 39.0%, p < 0.001), and had a lower comorbidity burden with a lower CCI (mean: 2.9 vs. 3.1;
p < 0.001). Patients with cementless compared with cemented TKA had a higher mean BMI
(31.6 vs. 31.3%, p < 0.001) and were more likely to have a BMI greater than 35 (26.7 vs. 25.3%, p < 0.001). Furthermore, compared with cemented TKAs, cementless TKAs were more likely
to have a CR femoral design (81.1 vs. 45.7%, p < 0.001) and less likely to have patellar resurfacing (92.7 vs. 95.0%, p < 0.001; [Table 1 ]).
Table 1
Demographic characteristics for total knee arthroplasty with cementless and cemented
fixation
Fixation
Cemented
Cementless
Total
p value
(N = 442,745)
(N = 19,841)
(N = 462,586)
Body mass index (BMI)
Mean (SD)
31.4 (6.3)
31.6 (6.1)
31.4 (6.3)
<0.001
Median [Q1, Q3]
30.7 [27, 35]
30.9 [27.3, 35.2]
30.7 [27, 35]
<0.001
N (N missing)
187,080 (255,665)
12,050 (7,791)
199,130 (263,456)
Categories of BMI
35+
047,344 (25.31%)
003,213 (26.66%)
050,557 (10.93%)
<0.001
<35
139,736 (74.69%)
008,837 (73.34%)
148,573 (32.12%)
Missing
255,665 (57.75%)
007,791 (39.27%)
263,456 (56.95%)
Age (y)
Mean (SD)
73.3 (5.8)
71.9 (5.3)
73.2 (5.8)
<0.001
Median [Q1, Q3]
72.2 [68.5, 77.1]
70.8 [67.7, 75.1]
72.2 [68.4, 77]
<0.001
Categories of age
65–74 y
288,673 (65.2%)
014,802 (74.6%)
303,475 (65.6%)
<0.001
75+ y
154,072 (34.8%)
005,039 (25.4%)
159,111 (34.4%)
Charlson's comorbidity index (age adjusted)
Mean (SD)
3.1 (1.1)
2.9 (1.0)
3.1 (1.1)
<0.001
Median [Q1, Q3]
3 [2, 4]
3 [2, 3]
3 [2, 4]
<0.001
Femoral component design
Cruciate retaining
202,426 (45.7%)
016,087 (81.1%)
218,513 (47.2%)
<0.001
Posterior stabilized
240,319 (54.3%)
003,754 (18.9%)
244,073 (52.8%)
Patella
Resurfaced
402,962 (95.0%)
017,539 (92.7%)
420,501 (90.9%)
<0.001
Unresurfaced
021,440 (5.1%)
001,389 (7.3%)
022,829 (4.9%)
Missing
018,343 (4.1%)
0000913 (4.6%)
019,256 (4.2%)
Sex
Female
270,317 (61.1%)
010,169 (51.3%)
280,486 (60.6%)
<0.001
Male
172,428 (39.0%)
009,672 (48.8%)
182,100 (39.4%)
Abbreviation: SD, standard deviation.
We identified a total of 9,013 all-cause revisions, with 377 noted in the cementless
cohort and 8,636 in the cemented group. Of these, we identified 1,242 revisions for
mechanical loosening, with 45 noted in the cementless group and 1,197 in the cemented
group. Adjusted HRs showed no difference in associated risk for all-cause revision
(HR: 1.07; 95% CI: 0.92–1.24; p = 0.382) or revision for mechanical loosening (HR: 1.38; 95% CI: 0.9–2.12; p = 0.14) for cementless versus cemented TKA. The adjusted CIF curve showed no difference
in the associated risk of all-cause revision across the study period comparing cementless
to cemented TKA ([Fig. 2 ]). The adjusted CIF curve also showed no difference in the associated risk of mechanical
loosing across the study period comparing cementless to cemented TKA ([Fig. 3 ]).
Fig. 2 Cumulative incident function (CIF) curve comparing cemented to cementless total knee
arthroplasty (TKA) for all-cause revision, adjusting for body mass index (BMI), sex,
age, cruciate retaining (CR) versus posterior stabilized (PS) femoral design, patellar
resurfacing, and Charlson's comorbidity index (CCI) across the study period.
Fig. 3 Cumulative incident function (CIF) curve comparing cemented to cementless total knee
arthroplasty (TKA) for revision for mechanical loosening, adjusting for body mass
index (BMI), sex, age, cruciate retaining (CR) versus posterior stabilized (PS) femoral
design, patellar resurfacing, and Charlson's comorbidity index (CCI) across the study
period.
Discussion
In this analysis of data from the AJRR linked to supplementary CMS data, we found
no associated risk of all-cause revision or revision for mechanical loosening when
comparing modern cementless to cemented TKA controlling for age, BMI, sex, CCI, and
use of the CR design. This lack of associated risk was noted to be unchanged over
the 8 years of the study period despite the rapidly increasing use of cementless TKA
in the AJRR over that time. In addition, as a function of this increasing adoption,
it is important to note that our results are weighed toward more recent short-term
data as opposed to being balanced throughout the study period. Thus, although reassuring,
as cementless TKA adoption continues to increase, caution should be exercised in extrapolating
the results of this study widely across this cohort without more robust long-term
survivorship data.
Our study serves as a balancing counterpoint to existing contradictory literature
regarding the risk of revision when comparing cementless and cemented TKA. In a single-center
prospective trial, Nam et al randomized patients to cementless or cemented fixation
for TKA; this investigation was powered to evaluate the primary outcome of the Oxford
Knee Score and only evaluated loosening as a secondary outcome measure.[10 ] They found no instances of loosening in either cohort at 2 years, but this investigation
was likely underpowered to evaluate the risk of revision and lacked generalizability
as a single-center study examining only one implant design. In a separate prospective
investigation, Kamath et al evaluated 100 consecutive patients who received cementless
TKA and compared this to a control group of 312 concurrent cemented controls.[13 ] They found no failures of aseptic loosening in the cementless group and two in their
cemented cohort with an overall rate of aseptic loosening of 0.6%. This investigation
also lacked generalizability, as they only included one implant in the investigation.
In another retrospective matched case-control study of 400 TKAs comparing cementless
versus cemented TKA, Miller et al found a similar incidence of postoperative complications
with one mechanical loosening (0.5%) in the cementless group and five in the cemented
group (2.5%).[1 ] The overall rate of mechanical loosening noted in these studies is consistent with
the findings noted in our investigation of around 0.27% in both cohorts. As the overall
incidence of mechanical loosening is relatively rare, these prior investigations were
likely underpowered to detect differences between cohorts. In addition, the prior
studies included only a single implant in each, thereby limiting their generalizability.
Our investigation expands the power and generalizability of these prior results by
using the robust AJRR dataset with 19,841 modern cementless TKAs of various manufactures.
This is in contrast to international registry investigations that suggest an increased
risk of failure with cementless fixation. Most similar to the United States in terms
of the use of cementless fixation for TKA is the Australian experience with approximately
20% use in 2022.[15 ] The Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR)
2023 annual report notes increased cumulative percent revision with cementless compared
with cemented TKA when using a CR femoral component.[15 ] While the AOANJRR specifies the analyses is restricted to “modern prostheses,” only
one femoral prosthesis is noted to be excluded from analyses and there is no formal
delineation of what compromises modern prostheses. This may explain the discordant
findings compared with our study as the registry includes various older generation
tibial components including those with cobalt-chromium sintered beads, cancellous-structured
titanium, or titanium plasma spray. The National Joint Registry (NJR) of England,
Wales, Northern Ireland, the Isle of Man and Guernsey, 20th annual report Kaplan–Meier
estimates demonstrate increased cumulative revision risk for cementless compared with
the cemented TKA at 3, 5, and 10 years.[16 ] It can be difficult to contextualize the results from the NJR as the overall use
of cementless TKA represents only 2.1% of TKAs in 2022. In addition to the low overall
use of cementless fixation, the use of older generation tibial components and lack
of uniform adjusting for confounding variables may also be a contributing factor to
the differences in revision risk found in the current analyses.
Over the course of the study period, there has been a relatively rapid increase in
the use of cementless TKA in the United States. Its use has increased from 1.9% in
2012 to 20.5% in 2022 in the AJRR dataset. This is likely driven by several factors:
multiple manufactures have recently released newer designs utilizing modern highly
porous tibial and patellar components, and prospective investigations have demonstrated
equivalent patient-reported outcome measures[10 ] and noted no differences in terms of survivorship and clinical or radiographic outcomes
at midterm follow-up[23 ] when comparing modern cementless to cemented TKA. Even with evolving indications
and expanded use, it is reassuring that our CIF curves demonstrated no changing risk
of either all-cause revision or revision for mechanical loosening over the study period.
Cementless fixation can achieve osseointegration and has the potential to improve
long-term survivorship by reducing the risk of aseptic loosening. It is important
to note that the study period was only 8 years and only required a minimum of 2 years
of follow-up; thus, even though cementless TKA use has increased throughout the study
period, we cannot yet evaluate any long-term potential survivorship benefits for cementless
fixation.
There are several limitations to this study. This is a retrospective study and therefore
has the potential for selection bias. Our cementless group was younger, more likely
to be male, more likely to have a CR femoral component, and had a lower comorbidity
burden. Our comparison groups were different and we do not attempt to claim equivalence.
However, we did attempt to control for these factors in our adjusted analyses. Nevertheless,
with the selection bias present in this study, we emphasize that our conclusions are
limited in scope: with current indications, the use of cementless TKA does not appear
to be associated with an increased revision risk. Furthermore, this investigation
is potentially limited in generalizability when considering international experiences.
Despite this, the AJRR contains data representing over 2 million procedures from more
than 1,300 sites in the United States and is the largest orthopaedic registry in the
world.[24 ] Many types of practice settings are captured in this dataset. In addition to the
size and variety of institutional capture in the AJRR, a recent study found distributions
across hospital volume, age, and geography to be proportionally similar between the
AJRR and the National Inpatient Sample (NIS) database further supporting the generalizability
of AJRR data to the overall United States cohort.[24 ] Additionally, we limited our population to patients aged ≥65 years to allow linkage
to CMS data. It is possible that younger patients may have different results, and
our results may not be generalizable to a younger patient population. Despite this,
we captured over 442,745 cemented TKAs and 19,841 cementless TKAs for our analysis,
making this a very robust and encompassing group size.
Conclusion
Advancements in implant design with the availability of modern highly porous surfaces
for osseointegration into patellar and tibial components have given surgeons confidence
to increase the use of cementless TKA in the United States. It is encouraging that
despite this relatively rapid transition we found no associated risk of all-cause
revision or revision for mechanical loosening with the use of cementless TKA when
controlling for age, BMI, sex, CCI, and use of CR design. Nevertheless, we believe
caution is required prior to broad expansion of cementless TKA utilization in the
population aged ≥65 years as appropriate indications for use are established, and
future investigations demonstrating robust mid- and long-term outcomes of this relatively
new technology are established.
