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Isoelastic Monoblock vs Modular Press-Fit Cup 

As the volume of total hip arthroplasty (THA) cases continues to rise, so too will the need for revision surgery. Revision THA can be complicated by insufficient bone stock on either the femoral or acetabular side, and researchers are gaining further insight into bone loss potentially related to implant design, such as loss that may occur through stress-shielding from press-fit implants.  

 In a randomized controlled trial recently reported in JBJS, Brodt et al. evaluated reduction in bone mineral density (BMD), primarily periacetabular BMD, as measured in 2 groups: patients who received a press-fit isoelastic monoblock cup (24 patients analyzed) and those who received a modular titanium press-fit cup (23 patients analyzed). At question was whether an isoelastic monoblock cup, with an elastic modulus similar to that of bone, would lead to less stress-shielding and thus less bone loss compared with a conventional modular titanium cup. 

Periprosthetic BMD was assessed at 1 week postoperatively (baseline) and at 4 years postoperatively using dual x-ray absorptiometry (DXA). The authors evaluated 4 regions of interest (ROIs) around the acetabular component and 7 ROIs around the femoral component based on regions previously described in the literature for assessing periprosthetic bone loss. 

Baseline patient characteristics, operative time, and improvement in clinical outcome scores did not differ between the groups.  A decrease in overall periacetabular BMD was found in both groups, but the difference between the groups was not significant. 

However, the researchers found a significant difference between the groups in BMD changes in certain periprosthetic regions. On the acetabular side, the group with the modular titanium cup had a 15.9% decrease in BMD in zone 2 (the superior pole of the acetabulum) compared with a decrease of 4.9% in the group with the isoelastic monoblock cup. And on the femoral side, the group with the modular titanium cup had a 15.4% decrease in BMD in zone 1 (along the greater trochanter) compared with a loss of 7% in the group with the isoelastic monoblock cup. None of the other regions differed significantly between the groups.   

Despite the relatively short follow-up and small (but adequately powered) numbers, these results are worthy of our consideration. I agree with the authors that longer follow-up is needed before conclusions can be drawn. As implant design can impact component longevity, it is critical that we evaluate differences to better understand the long-term implications. 

Matthew R. Schmitz, MD
JBJS Deputy Editor for Social Media 

 

“Normal” Ultrasound May Not Rule Out DDH Later in Childhood

Some years ago, we moved away from calling hip dysplasia “congenital” and started using the term “developmental dysplasia of the hip” (DDH). Indeed, it is developmental. As a surgeon specializing in pediatric orthopaedics and hip preservation, I see not only infants when DDH is of potential concern but also young adults with more mature manifestations of hip dysplasia not previously diagnosed or treated.

Screening protocols have successfully helped in the early identification of DDH and dislocation, but what is the likelihood that infants with risk factors for dysplasia but normal ultrasound results will go on to experience DDH in childhood? And which risk factors are predictive?

In a recent report in JBJS Open Access, Humphry et al. provide new insight into these challenging questions. This study from the UK included 1,053 children from a cohort of 2,191 children who had been assessed as newborns and had at least 1 of 9 perinatal risk factors for DDH. All had undergone ultrasound at a mean of 8 weeks and were followed clinically.

The mean age of the children in the current study was 4.4 years (range, 2.0 to 6.6 years). Thirty-seven of the participants had been treated for DDH in the postnatal period, predominantly with a harness.

Assessing the acetabular index (AI) on pelvic radiographs, the authors found that:

  • 27 of the children had “severe” hip dysplasia (an AI of >2 standard deviations above age and sex reference values). Girls were more likely to have this outcome. Only 3 of the 27 received treatment for DDH in infancy.
  • 146 (13.9%) of the children had an AI of >20°, only 12 of whom had been treated during infancy; 92% had no prior diagnosis of DDH. On multivariate analysis, female sex and breech presentation at birth were significantly predictive of this “mild” dysplasia (breech presentation demonstrated a nearly twofold increased odds of an AI of >20° at ≥3 years of age), while first-born status had a protective effect.

The findings of this study lend support to radiographic monitoring later in childhood for patients with risk factors such as breech positioning at birth. While the exact algorithm of ultrasound and radiographic workup still needs to be elucidated, it appears that a “normal” ultrasound in infancy does not necessarily rule out the development of hip dysplasia in children with select risk factors.

Matthew R. Schmitz, MD
JBJS Deputy Editor for Social Media

Functional Outcomes of Patients with Schizophrenia After Hip Fracture Surgery

Thirty-eight patients with schizophrenia were compared with 170 geriatric patients without schizophrenia who underwent a surgical procedure for a hip fracture.

Read the full article here.

The Challenges of Post-Treatment Care for Patients with Schizophrenia

The worldwide incidence of mental illness seems to be on the rise—and along with it a widespread recognition that this “epidemic” should receive at least as much attention as other health conditions. At the same time, many societies have transitioned to noninstitutionalized care for patients with severe mental health diagnoses. This parallel phenomenon has resulted in more individuals with mental and emotional challenges being cared for by their families and communities.

Orthopaedic surgeons are often asked what the prognosis is for recovery in a patient with a substantive mental health diagnosis, but only a few scholarly attempts have been made to answer that question. In the May 5, 2021 issue of JBJS, Ng et al. provide meaningful data regarding the concomitant diagnosis of schizophrenia among patients in their early 70s who experienced a hip fracture. One-year post-treatment results from this cohort study showed no differences in mortality or surgical or medical complications between patients with and matched patients without schizophrenia. These good-news findings are largely indicative of the high level of care hip fracture patients receive in the authors’ institution, which includes close collaboration among surgeons, geriatrists, physical therapists, and psychiatric clinicians.

However, the 1-year functional outcomes, as measured with the Modified Barthel Index, were worse in the cohort with schizophrenia. I think this is probably related to the difficulty of encouraging patients to participate in standardized rehabilitation processes, challenges associated with self-care, and potentially less-than-optimal social support.

We certainly need more research into determining the best peri- and post-treatment care for orthopaedic patients with severe mental health issues. Ideally, future investigations of these questions will focus on interactions between mental health professionals and surgical and rehabilitation teams. It is my hope that this study by Ng et al. will stimulate that type of research.

Click here for a downloadable Infographic summarizing this study.

Marc Swiontkowski, MD
JBJS Editor-in-Chief

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:

  1. No diabetes
  2. Controlled-uncomplicated diabetes
  3. Controlled-complicated diabetes
  4. 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:

  1. The odds of hospital readmission and complications following an elective TKA or THA are increased for Medicare beneficiaries who have diabetes.
  2. It would be reasonable to defer arthroplasty surgery for those with uncontrolled diabetes to allow them to achieve glycemic control.
  3. 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.