Outpatient Knee/Hip Arthroplasty Yields Fewer Adverse Events
The National Surgical Quality Improvement Program (NSQIP) database contains more than a half-million records of patients who received a total knee arthroplasty (TKA), unicompartmental knee arthroplasty (UKA), or total hip arthroplasty (THA) from 2009 through 2018. Fewer than 4% of those procedures were done in an outpatient setting, but patient demand for outpatient arthroplasty is rising rapidly.
With retrospective data like that from NSQIP, the most meaningful comparisons between inpatient and outpatient procedures come through a propensity score-matched analysis. Propensity score matching pairs up patients in each group according to multiple factors thought to influence outcome. In a recent study in The Journal of Bone & Joint Surgery, Lan et al. used propensity score matching to compare inpatient and outpatient arthroplasty in terms of adverse events and readmissions.
What the Researchers Did:
- Matched each outpatient case of TKA, UKA, and THA from the database with 4 unique inpatient cases based on age, sex, ASA class, race, BMI, type of anesthesia, and history of hypertension, smoking, congestive heart failure, and diabetes
- Compared inpatient vs outpatient rates of 30-day adverse events (both minor and severe) and readmissions
- Identified risk factors for adverse events and readmissions
What the Researchers Found:
- For all 3 arthroplasty types, patients who underwent an outpatient procedure were less likely to experience any adverse event, when compared with those who underwent an inpatient procedure.
- The above adverse-event findings held true when TKAs, UKAs, and THAs were analyzed separately.
- Outpatient procedure status was an independent protective factor against the risk of adverse events.
- For all 3 procedures, readmission rates were similar among inpatients and outpatients. (The 2 most common reasons for readmission were infections and thromboembolic events.)
- Clinicians are probably (and reasonably) selecting healthier patients to undergo outpatient procedures, but 42% of the outpatient cohort had an ASA class ≥3, and 55% had a BMI ≥30 kg/m2.
In their abstract, the authors cited “increased case throughput” as one rationale for outpatient arthroplasty, but this study provides convincing evidence that adverse-event reduction is another compelling reason for certain patients to consider outpatient knee and hip procedures.
Life Expectancy Informs Choice of Hemi Implant after Femoral Neck Fracture
Predicting life expectancy is not an exact science. But estimating the remaining years of life in elderly patients with a femoral neck fracture may help orthopaedists determine whether to use unipolar or bipolar hemiarthroplasty components when surgically managing that population. So suggest Farey et al. in the February 3, 2021 issue of The Journal of Bone & Joint Surgery.
The relevant “magic number” for life expectancy after femoral neck fracture is 2.5 years. The authors arrived at that number by performing statistical analyses on nearly 63,000 cases of femoral neck fractures treated with either modular unipolar or bipolar hemiarthroplasty. Patients were in their early 80s on average at the time of surgery. The researchers focused on revision rates because reoperations in this vulnerable group of patients typically yield poor results.
There was no between-group difference in overall revision rate within 0 and 2.5 years after the procedure. However, unipolar hemiarthroplasty was associated with a higher overall revision rate than bipolar hemiarthroplasty beyond 2.5 years after surgery (hazard ratio [HR], 1.86).
Farey et al. also drilled down into reasons for revision and found that unipolar prostheses had a greater risk of revision for acetabular erosion, particularly in later postoperative time periods. Conversely, bipolar hemiarthroplasty was associated with a higher risk of revision for periprosthetic fracture, which the authors surmise might have arisen from the greater range of motion (and therefore activity levels) permitted by bipolar implants.
Although the authors did not perform a formal cost-benefit analysis related to this dilemma, they observed a nearly $1,000 USD price difference between the most commonly used bipolar and unipolar prostheses. Farey et al. therefore propose that the more expensive bipolar prosthesis may be justified for patients with a life expectancy beyond 2.5 years, but that the unipolar design is justified for patients with a postoperative life expectancy of ≤2.5 years.
Click here to listen to a 15-minute OrthoJOE podcast about this topic, featuring JBJS Editor-in-Chief Dr. Marc Swiontkowski and OrthoEvidence Editor-in-Chief Dr. Mo Bhandari.
Click here to see a 3-minute Video Summary of this study.
Click here to read a JBJS Clinical Summary comparing total hip arthroplasty with hemiarthroplasty for displaced femoral neck fractures.
Accuracy of Rapid Alpha Defensin Test Confirmed
In June 2019, OrthoBuzz reported on the FDA approval of a rapid, lateral-flow alpha defensin test that helps detect periprosthetic joint infections (PJIs) from synovial fluid. In the January 20, 2021 issue of The Journal of Bone & Joint Surgery, Deirmengian et al. report findings from the Level II diagnostic-accuracy study that led to this FDA approval.
The authors compared diagnostic sensitivity and specificity of the lateral-flow alpha defensin test with the “gold-standard” PJI diagnostic criteria endorsed by the Musculoskeletal Infection Society (MSIS) in 2013. They made the comparison with 2 groups: a prospective patient cohort of 305 patients with a failed hip or knee arthroplasty (57 of whom were determined by MSIS criteria to have a PJI) and among a “control” cohort of 462 synovial fluid samples (65 of which met MSIS criteria for PJI).
After excluding 17 patients from the prospective cohort who had grossly bloody aspirates, the authors found a sensitivity of 94.3% and a specificity of 94.5% for the lateral-flow test in that group. Among the control cohort, the lateral-flow test’s sensitivity was 98.5% and its specificity was 98.2%. Furthermore, after combining data from the 2 cohorts, Deirmengian et al. found no performance difference between the lateral-flow test (which yields results in 10 to 15 minutes) and the lab-based alpha defensin ELISA test (which typically yields results in 24 hours). Finally, in a nonstatistical descriptive comparison between the 2 alpha defensin tests and 4 other individual lab tests used in the MISI criteria to diagnose PJI (such as synovial fluid white blood cell count and erythrocyte sedimentation rate), the authors concluded that “alpha defensin tests led to the highest raw number of correct diagnoses (accuracy).”
The 2018 International Consensus Meeting on Orthopaedic Infections included alpha defensin as a minor criterion. That decision, along with these findings and the FDA approval of the lateral-flow test, should lead to increased adoption of the rapid test—and to more data being published on its clinical utility.
A Closer Look at Impingement in Ceramic-on-Ceramic THA
Total hip arthroplasty (THA) with ceramic-on-ceramic (CoC) bearings has become popular, especially in younger patients, largely because of the material’s durability. However, CoC bearings are susceptible to catastrophic failure through fracture. Although the definitive mechanistic pathway for ceramic fracture has not been elucidated, one of the proposed mechanisms is impingement between the ceramic acetabular liner and the metal neck of the femoral stem. In the January 20, 2021 issue of The Journal, Lee et al. take an illuminating radiographic dive into the patterns of impingement in CoC THA.
The authors analyzed 244 cases of CoC THAs that had ≥15 years of radiographic follow-up. They found impingement-related notches at 77 sites in 57 (23.4%) of the cases. The notches were seen either on the neck (28 cases) or on the shoulder (29 cases) of the stem. In 8 cases, notches were found in multiple locations.
All of the neck notches were found when either a medium-neck or long-neck head was used. Shoulder notches were found on the stem only when a short-neck head was used. Lee et al. observed that the use of medium-neck or long-neck heads prevents the ceramic liner from contacting the stem shoulder because the liner impinges on the neck first. The authors also noted that the mean cup inclination was significantly lower in the cases with notched stems compared to stems without notches (36.9° vs 39.8°), and that mean anteversion was higher in the cases with notches (19.9° vs 17.3°).
We have known that impingement can occur between the ceramic liner and metal stem in CoC THA, but this study suggests that it may happen in a significant proportion of patients, both along the neck and shoulder of the stem. Manufacturers should consider these findings when designing implants, and patients and surgeons considering CoC implants may want to avoid short-neck heads, if possible. Also, because impingement-related stem notching appears to occur more frequently with lower cup inclination and higher anteversion, surgical technique remains vitally important in these cases, independent of implant design and selection.
Finally, we should note that the patients in this study were young (mean age of 43 years) and Asian. Asian culture and lifestyle include frequent squatting and sitting cross-legged, which Lee et al. say “induces more impingement between the stem and liner.”
Matthew R. Schmitz, MD
JBJS Deputy Editor for Social Media
Bone-Preserving Stems in THA – Do They Work?
Total hip arthroplasty (THA) is a tried-and-true treatment for debilitating hip osteoarthritis. But as the number of patients undergoing THA continues to rise, so does the incidence of periprosthetic femoral fractures and the need for revision surgery. The increasing burden of periprosthetic fractures has led to the development of shorter-stemmed femoral components that theoretically preserve bone, decrease fracture risk, and make revision surgery easier if it is required. In the January 6, 2021 issue of The Journal, Slullitel et al. report on a randomized controlled trial that determined whether bone loss differed between patients who received a conventional stem and those who received a short, bone-preserving stem over 2 years following THA.
Forty-six patients received the short, proximally porous-coated stem (Depuy Synthes Tri-Lock bone-preservation stem), and 40 received the conventional stem (Depuy Synthes collarless Corail stem). The primary outcome–bone mineral density (BMD)–was analyzed at 12, 26, 52, and 104 weeks after surgery with dual x-ray absorptiometry region-free analysis (DXA-RFA), which revealed pixel-level resolution of BMD at the bone-implant interface.
Immediately after surgery, researchers found a similar amount of bone loss in both groups in the calcar region and the cancellous portion of the distal greater trochanter. But at all other subsequent time points, bone loss was significantly greater in patients with the bone-preserving stem (analysis of variance [ANOVA] p < 0.0001). In addition, over the full study period the small areas of bone gain that the researchers found were statistically greater in the conventional-stem group than in the Tri-Lock group. Notably, patient-reported outcomes and adverse events did not differ between the 2 groups at the 2-year follow-up.
These early results cast a shadow of doubt over whether a stem that is marketed to preserve bone actually accomplishes that objective. However, 2 years is a very short follow-up when looking at the lifetime of a hip arthroplasty, and the clinical implications of these findings will become clearer with longer-duration analysis.
Click here to read a JBJS Clinical Summary titled “Short-Stem Femoral Components in THA” by Tad Mabry, MD.
Matthew R. Schmitz, MD
JBJS Deputy Editor for Social Media
A Deeper Dive into Diabetes and Total Joint Replacement
There are many more “types” of diabetes than the pathophysiologic designations of Type 1 and Type 2. In the December 16, 2020 issue of The Journal of Bone & Joint Surgery, Na et al. delineate 4 different diabetes categories and determine their impact on 90-day complications and readmission rates after elective total joint arthroplasty (TJA) among Medicare patients. One premise for this investigation was that, although diabetes is a known risk factor for arthroplasty complications, alternative payment models such as the federally run Comprehensive Care for Joint Replacement (CJR) program adjust their payments only in diabetes cases where the comorbidity is coded as severe.
The authors stratified diabetes into 4 groups as follows:
- No diabetes
- Controlled-uncomplicated diabetes
- Controlled-complicated diabetes
- Uncontrolled diabetes
Among the >500,000 total knee arthroplasties (TKAs) and total hip arthroplasties (THAs) analyzed, the authors found the following when comparing data from the 3 diabetes groups with the no-diabetes group:
- The odds of TKA complications were significantly higher for those with uncontrolled diabetes (odds ratio [OR] = 1.29).
- The odds of THA complications were significantly higher for those with controlled-complicated diabetes (OR = 1.45).
- The odds of readmission were significantly higher in all diabetes groups for both TKA (ORs = 1.21 to 1.48) and THA (ORs = 1.20 to 1.70).
The authors come to 3 basic conclusions based on these findings:
- The odds of hospital readmission and complications following an elective TKA or THA are increased for Medicare beneficiaries who have diabetes.
- It would be reasonable to defer arthroplasty surgery for those with uncontrolled diabetes to allow them to achieve glycemic control.
- The Centers for Medicare & Medicaid Services should include less-severe diabetes and associated systemic complications in alternative-payment model adjustments.
Click here for an “Author Insight” video about this study from co-author Annalisa Na, PhD, DPT.
Eschew Standard-Sized Heads When Revising THAs for Dislocation
No consensus has emerged yet regarding the best prosthetic construct with which to manage patients who require revision surgery for dislocation after a total hip arthroplasty (THA). But in the December 2, 2020 issue of The Journal of Bone & Joint Surgery, Hoskins et al. add insight into that question by tapping the Australian Orthopaedic Association Total Joint Replacement Registry to analyze which of 4 first-revision component constructs led to the fewest second revisions.
Among the 1,275 THAs that were revised once for prosthesis dislocation, 203 hips went on to have a second revision, with dislocation being the most common cause for re-revision. The authors studied the second-revision THAs in 4 prosthetic categories: standard-sized femoral heads, large-sized femoral heads, dual-mobility heads, and constrained acetabular liners. The rate of all-cause second revision was significantly higher in the standard-head group when compared with the constrained-liner group. But in the 91 cases of second revisions for dislocation, the standard head showed significantly higher second-revision rates than any of the other 3 constructs. There was no statistically significant difference in rates of second revision between those 3 non-standard articulations
The authors discuss dual-mobility heads at some length, asserting that “caution should be exercised in their routine use, particularly in younger and active patients.” They note that the constrained liner was the “only articulation to show a difference when compared with standard-head THA for both all-cause revision and revision for a subsequent diagnosis of dislocation,” but they observe that impingement and acetabular component loosening are common concerns with constrained liners.
Despite these caveats, it seems clear from this data that the choice of articulating surface for either a first or second revision THA due to dislocation should probably exclude standard head sizes. Calling for longer-term data on all 3 alternative constructs studied here (the follow-up periods were different for all 4 articulations), the authors emphasize that “surgeons should [also] look beyond articulating surfaces”—to surgical approach, component orientation, and patient factors such as soft-tissue quality—in the effort to reduce the burden of THA dislocations.
Dashboard Depicts Surgeon-Level Value of TKA/THA
Remember when a “dashboard” referred to the display just behind a car’s steering wheel? In today’s digital universe, the word has come to mean any number of visual information displays. At the same time, the meaning of the word “value” has narrowed somewhat. In relation to health care, “value” is defined quite precisely as the quality of patient outcomes per dollar spent on healthcare services.
In the November 4, 2020 issue of The Journal of Bone & Joint Surgery, Reilly et al. explain how they created a “value dashboard” for total hip and knee arthroplasty (THA and TKA) at a tertiary-care medical center in New England. The goal: track and display the surgeon-level cost and quality of these procedures against institutional benchmarks to identify opportunities for improving value.
The 7 quality metrics that Reilly et al. used included both clinical and patient-reported outcomes, weighted by surgeons using a modified Delphi process. Average direct costs per surgeon were calculated from the medical center’s billing system, and data were collected over a 15-month period from 2017 to 2018 to ensure at least 1 year of outcomes. Six surgeons were included in the TKA value dashboard, and 5 were included in the THA dashboard.
Relative to the institutional benchmarks:
- Value for TKA by surgeon ranged from 7% below benchmark to 12% above.
- Value for THA by surgeon ranged from 12% below benchmark to 7% above.
The dashboard itself (see Figure above) displays quality, cost, and overall value so viewers can see at a glance which metrics are driving the value score for each surgeon, whose procedural volume is also depicted. The authors cite as one limitation of this study the fact that the quality metrics were weighted by local surgeons only, and they say that “ideally the weighting would be informed by a panel of national experts and several stakeholder groups,… including patients.”
Time Waits For No One—Aging Increases Costs
The cost of medical care in the United States has been shown to rise with advancing patient age, and total joint arthroplasty (TJA) is a prime example of this unsurprising phenomenon. In attempts to curtail costs and reduce variability, Medicare and other payers have introduced alternative payment models (APMs), such as the Bundled Payments for Care Improvement (BPCI) initiative. In this model’s application to TJA, when participating institutions keep the cost of the “episode” below a risk-adjusted target price, they accrue the savings as a profit, but they sustain a financial penalty if the episode costs more than the target price.
Multiple studies have suggested that APMs can negatively affect the fiscal health of institutions that care for many high-risk patients. Although increasing age has been associated with higher-cost episodes of care, age is not one of the factors that the BPCI model accounts for. Consequently, concerns have been raised that providers may practice “cost discrimination” against very old patients.
In the October 7, 2020 issue of The Journal, Petersen et al. examine how an aging population has affected a New York City orthopaedic center in terms of the BPCI model applied to TJA. The authors analyzed the relationship between patient age and cost of care among 1,662 patients who underwent primary total hip and knee arthroplasty over a 3-year period under BPCI. They then used a modeling tool to predict shifting age demographics for their local area out to the year 2040.
Petersen et al. found that under BPCI, their institution sustained a nearly $2,000-per-case loss for TJA care episodes among patients 85 to 99 years of age. Currently this loss is offset by profits realized by performing TJAs in younger patients. However, predictive modeling identified an inflection point of 2030, after which a relative increase in older patients and a decrease in younger patients will yield an overall net decrease in profits for primary TJA.
Because no one, including orthopaedic surgeons, can turn back the clock on aging, health care stakeholders must find ways either to adjust downward the cost of care for the elderly (seemingly difficult without adversely affecting outcomes) or adjust reimbursement models to account for the increased costs associated with aging. I agree with the conclusion of Petersen et al.: “The BPCI initiative and [other] novel APMs should consider age as a modifier for reimbursement to incentivize care for the more vulnerable and costly age groups in the future.”
Matthew R. Schmitz, MD
JBJS Deputy Editor for Social Media
The Importance of a “Well-Rounded” Hip
This post comes from Fred Nelson, MD, an orthopaedic surgeon in the Department of Orthopedics at Henry Ford Hospital and a clinical associate professor at Wayne State Medical School. Some of Dr. Nelson’s tips go out weekly to more than 3,000 members of the Orthopaedic Research Society (ORS), and all are distributed to more than 30 orthopaedic residency programs. Those not sent to the ORS are periodically reposted in OrthoBuzz with the permission of Dr. Nelson.
Fifty years ago, the precise etiology of hip osteoarthritis (OA) was not clear. In 1976, Solomon proposed 3 potential causes of osteoarthritis in general:1
- Failure of essentially normal cartilage subjected to abnormal or incongruous loading for long periods
- Damaged or defective cartilage failing under normal conditions of loading
- Breakup of articular cartilage due to defective subchondral bone
In 1986, Harris expanded on this concept by noting that mild acetabular dysplasia and/or pistol grip deformity were associated with 90% of patients who had “so-called primary or idiopathic” hip OA.2 Harris further claimed that “when these abnormalities are taken in conjunction with the detection of other metabolic abnormalities that can lead to osteoarthritis of the hip,…it seems clear that either osteoarthritis of the hip does not exist at all as a primary disease entity or, if it does, is extraordinarily rare.”
Subsequently, acetabular dysplasia was defined as an acetabular shape where the lateral center edge angle (LCEA) was <25°, and the cam and pincer deformities were introduced as forms of acetabular dysplasia. Acetabular retroversion, as detected by the crossover sign seen in anterolateral hip radiographs, was recognized later, and Tonnis used CT imaging to determine acetabular and femoral anteversion.3
In 2020, investigators suspected that zonal-acetabular radius of curvature (ZARC) might play a role in hip-joint shape disorders.4 ZARC is the radius of curvature of the articular contact surface (from the margin of the fovea centralis to the acetabular rim), and the authors analyzed ZARC in anterior, superior, and posterior zones in subjects with normal, borderline, and dysplastic hips. (“Normal” was defined as LCEA of 25° to <40°; “borderline” as LCEA of 20° to <25°; and “dysplastic” as LCEA of <20°.) The 3-zone ZARC findings are summarized in the table below.
Mean Zonal-Acetabular Radius of Curvature (ZARC)
| ZARC Zone | Borderline | Normal | Dysplasia |
| Anterior | 29.8 +/- 2.6 mm | 28.0 +/- 2.2 mm | 31.5 +/- 2.7 mm * |
| Superior | 25.7 +/- 3.0 mm | 25.9 +/- 2.2 mm | 25.8 +/- 2.5 mm |
| Posterior | 27.2 +/- 2.5 mm | 26.4 +/- 1.9 mm | 30.4 +/- 3.3 mm * |
* P < 0.01
In this study, the severity of lateral undercoverage affected the anterior and/or posterior zonal-acetabular curvature. The take home message is that, absent metabolic abnormalities, acetabular and femoral head congruity and orientation are the driving forces in hip OA.
References
- Solomon L. Patterns of osteoarthritis of the hip. J Bone Joint Surg Br. 1976;58(2):176-83. Epub 1976/05/01. PubMed PMID: 932079.
- Harris WH. Etiology of osteoarthritis of the hip. Clinical orthopaedics and related research. 1986(213):20-33. Epub 1986/12/01. PubMed PMID: 3780093.
- Tonnis D, Heinecke A. Acetabular and femoral anteversion: relationship with osteoarthritis of the hip. J Bone Joint Surg Am. 1999;81(12):1747-70. Epub 1999/12/23. PubMed PMID: 10608388.
- Irie T, Espinoza Orias AA, Irie TY, Nho SJ, Takahashi D, Iwasaki N, et al. Three-dimensional hip joint congruity evaluation of the borderline dysplasia: Zonal-acetabular radius of curvature. J Orthop Res. 2020;38(10):2197-205. Epub 2020/02/20. doi: 10.1002/jor.24631. PubMed PMID: 32073168.
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