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More Data on Periprosthetic Hip Infections

Among >100,000 total hip arthroplasty (THA) patients ≥55 years of age whose data resides in a Canadian arthroplasty database, the 15-year cumulative incidence of periprosthetic joint infection (PJI) was 1.44%, according to a study by the McMaster Arthroplasty Collaborative in the March 18, 2020 issue of JBJS.

In addition to finding that the overall risk of developing PJI after THA has not changed over the last 15 years in this cohort, the authors found the following factors associated with increased risk of developing a PJI:

  • Male sex (absolute increased risk of 0.48% at 10 years)
  • Type 2 diabetes (absolute increased risk of 0.64% at 10 years)
  • Discharge to a convalescent-care facility (absolute increased risk of 0.46% at 10 years)

The authors view the third bulleted item above as “a surrogate marker of frailty and poorer general health.”

Patient age, surgical approach, surgical setting (academic versus rural), use of cement, and patient income were not associated with an increased risk of PJI. Nearly two-thirds of PJI cases occurred within 2 years after surgery, and 98% occurred within 10 years postoperatively.

The authors conclude that these and other substantiated findings about PJI risk factors “should be reviewed with the patient during preoperative risk counseling.”

THA in the Very Young: Midterm Results

Orthopaedic surgeons work hard to find good alternatives to total hip arthroplasty (THA) in patients <50 years old. That’s because the high functional demands and longer remaining lifespan in these patients can result in excessive wear of the bearing surfaces and loosening of the components—both of which have been documented in multiple publications. But what happens when THA is the most viable solution for a posttraumatic or congenital hip problem in a very young patient because arthrodesis or other osteotomies are not feasible?

In the March 18, 2020 issue of The Journal, Pallante et al. report medium-term outcomes of THA in 78 patients who were ≤20 years of age at the time of surgery, with follow-ups ranging from 2 to 18 years. The findings included the following:

  • 10-year survivorship for reoperation of 95.0%
  • 10-year survivorship for revision of 97.2%
  • 10-year survivorship for complications of 89.5%

Overall, the linear articular wear averaged 0.019 mm/yr in the ceramic-on-ceramic, ceramic-on-highly cross-linked polyethylene, and metal-on-highly cross-linked polyethylene bearings studied, and the average modified Harris hip score in the cohort was 92.

However, despite these impressive clinical and survivorship outcomes, I advise orthopaedists not to lower their resistance to performing THA on these very young patients, many of whom present with hip problems caused by deforming conditions such as Legg-Calve-Perthes disease. We really need 30 to 40 years of outcome data to truly  understand what happens with function, revision rates, and wear characteristics in this population. Having said that, I am confident that this group from Mayo will continue reporting on this patient cohort at 5- to 10-year intervals, so that the worldwide orthopaedic community can keep learning from this experience.

Marc Swiontkowski, MD
JBJS Editor-in-Chief

Are Tantalum Hip Implants Safe?

I have been told that daytime TV is punctuated by a continual stream of ads for personal-injury lawyers asking if you have been injured by a particular medication or medical device.  Since 2002, billions of dollars have been paid out in lawsuits over metal-on-metal hip replacements containing cobalt and/or chromium, the “loose” ions of which increase the risk for aseptic lymphocyte-dominated vasculitis-associated lesions (ALVAL)—which are sometimes referred to as “pseudotumors.” So orthopaedic surgeons understandably want to know more about the potential long-term implications of newer metal technologies such as tantalum.

“Trabecular Metal” is a trade name for tantalum-based bone-ingrowth material that is now quite common in acetabular cups and revision shells used for total hip arthroplasty (THA). In the March 4, 2020 issue of the The Journal, Brüggemann et al. investigated the safety of these tantalum components. They retrospectively reviewed blood tantalum levels in 30 patients who underwent primary THA with no tantalum components, 30 patients who received a tantalum cup during a primary THA, and 84 patients who received a tantalum shell during a revision. Tantalum levels in 59 blood-donor volunteers served as controls. The authors also measured subsets of lymphocytes (CD8+ and CD4+ T-cells) that are thought to be associated with the immunologic cascade causing ALVAL.

At an average follow-up of 4 years, Brüggemann et al. found that median tantalum concentrations were 0.051 µg/L  in those receiving primary tantalum implants and 0.05 µg/L in those receiving primary implants without tantalum. (The “detection limit” for tantalum used in this study was 0.05 µg/L.) Patients receiving revision tantalum shells had median serum tantalum levels of 0.091 µg/L.  Time since surgery did not affect tantalum levels.

The authors also found a weak negative correlation between increased tantalum concentration and lower concentrations of CD8+ T-cells. Clinically, none of the hips in this series was deemed loose, and the Harris hip scores among all subjects were good to excellent.

It seems that with stable tantalum implants, any increase in serum concentrations of tantalum is small, but we don’t yet know the longer-term implications of these small increases. While it’s also reassuring that the lymphocyte activation associated with ALVAL does not seem to occur with these tantalum implants, I agree with the authors’ conclusion that this study “cannot exclude the possibility that even low tantalum concentrations confer a risk to patients’ health.”  Clearly, longer-term studies are needed.

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

Implant Prices are Main Cost Driver in Joint Replacements

Orthopaedic surgeons have long been aware of the role that implant prices play in the total cost of care for arthroplasty procedures, but methodical breakdowns of implant costs in relation to the cost of other aspects of care have generally been lacking. In the March 4, 2020 issue of The Journal, Carducci et al. detail the impact of implant costs on the total cost of care in a study of 6 lower- and upper-extremity arthroplasty types performed at a single, high-volume orthopaedic specialty hospital.

Using a uniform method called time-driven activity-based costing, the authors calculated the total costs of >22,200 inpatient primary total joint arthroplasties, and then broke down those total costs by categories, including implant price and personnel costs. It was no surprise that, as a percentage of total cost, implant costs were highest for low-volume surgeries (as high as 65% for total ankle arthroplasty) and lowest for high-volume procedures (e.g., 40% for total knee arthroplasty). Nevertheless, across the board, implant price was the most expensive component of total cost.

Implant prices are individually negotiated between a hospital and an implant supplier and are usually protected by nondisclosure agreements, so the data from this investigation may not match up with data from any other institution. Unfortunately, the future of implant-cost research will be tied to the complex issue of return-on-investment for implant-manufacturer stockholders as it relates to negotiations with individual hospitals and health systems.

The profound impact of implant price on the total cost of all the joint arthroplasties studied by Carducci et al. also begs the questions as to how “generic” implants (those not manufactured by the major orthopaedic producers) will ultimately influence the market—and whether “branded” implants, with their 30% to 50% markups, provide any functional benefit for patients. We will need further well-designed research to address those questions.

Marc Swiontkowski, MD
JBJS Editor-in-Chief

So Far, Bundled Payments Not Affecting Patient Selection for Joint Replacement

Many people predicted that the mandatory “bundling” of payments for knee and hip arthroplasty by the Centers for Medicare and Medicaid Services (CMS) that began on April 1, 2016 in several US metropolitan areas would lead to  “cherry-picking” and ”lemon-dropping.” In other words, hospitals and surgeons wouldn’t take on more complex and sicker patients for joint replacement for fear that the bundled payment would be insufficient (lemon-dropping), and would instead select the healthier patients (cherry-picking). See related OrthoBuzz post.

In the February 19, 2020 issue of The Journal, Humbyrd et al. compare the characteristics of patients who underwent hip and knee replacement (HKR) from April to December 2015 with those of HKR patients during the same period in 2016, after CMS mandated the bundled-payment program in 67 metropolitan statistical areas (MSAs). The patients were matched so that those treated in bundled and non-bundled settings had similar socioeconomic backgrounds.

The matched groups included 12,388 HKR episodes in 40 bundled MSAs and 20,288 HKRs in 115 nonbundled MSAs. The authors also evaluated pre- and post-policy case-mix changes among 1,549 hip hemiarthroplasties, which are not subject to bundling, in the bundled MSAs.

Among patients who underwent HKR, Humbyrd et al. found no significant differences in patient characteristics—including race, dual Medicare-Medicaid eligibility, tobacco use, obesity, diabetes, and Charlson Comorbidity Index (CCI)—after the bundled-payment policy was implemented. Also, they found that patients in bundled MSAs undergoing hemiarthroplasty had significantly higher CCI values and were more likely to have diabetes than those who underwent HKR. This suggests that some surgeons opt for hemiarthroplasty over total hip replacement in less-healthy patients to avoid treating such patients under a bundled program.

From the MSA perspective, these results suggest that cherry picking and lemon dropping are not occurring in the short term. But we would do well as a profession to ensure that those controversial patient-selection practices are not happening at the individual surgeon level, and that the short-term results demonstrated here by Humbyrd et al. persist over the longer term. Even our sickest joint replacement patients deserve the best surgical care.

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

MRI Can Detect “Invisible” Femoral Neck Fractures in Patients with Shaft Fractures

For more than 40 years, orthopaedic trauma surgeons have been interested in this fairly common fracture combination, which is often seen in polytrauma patients. We have long hypothesized that much of the energy that fractures the femoral shaft is dissipated, leaving many ipsilateral neck fractures nondisplaced and difficult to recognize on plain radiographs.

But the consequences of missing a femoral neck fracture can be devastating. For example, because the neck fracture pattern is often vertical (Pauwels type III), the risk of displacing the neck fracture during intramedullary nailing is very high. Achieving reduction and fixation of a displaced neck fracture near an intramedullary nail—either intraoperatively or postoperatively—is extremely challenging.

Because of these issues, some authors recommend a thin-cut CT series to identify nondisplaced ipsilateral neck fractures preoperatively, and this protocol has been shown to significantly reduce the delay in identifying such fractures. In the February 19, 2020 issue of The Journal, Rogers et al. from UTHealth in Houston show that even with thin-cut CT, the crack can be missed. These authors added to the protocol limited-sequence MRI that identifies these fractures with very high sensitivity and takes <10 minutes to perform.

In this study, among 39 acute, high-energy femoral shaft fractures, the authors identified 4 ipsilateral neck fractures with MRI that were not seen on CT. Despite exhibiting polytrauma, 89% of all indicated patients in this study were evaluated preoperatively with the limited-sequence MRI protocol, including those in traction and those treated initially with external fixation.

The findings from this study should prompt trauma surgeons practicing in high-volume centers to develop similar MRI protocols. It may also be possible to develop such protocols in lower-volume centers, but in those settings it is especially incumbent on the surgical team to recognize that this fracture combination occurs in a fairly high percentage of cases and to carefully scrutinize plain radiographs and consider thin-cut CT scanning of the ipsilateral hip. In addition, the potential for an ipsilateral nondisplaced femoral neck fracture should trigger increased use of fluoroscopy during intramedullary nailing of shaft fractures, so that concomitant neck fractures can be recognized and stabilized with screws before they become displaced.

Marc Swiontkowski, MD
JBJS Editor-in-Chief

Safe Retractor Placement during Direct Anterior THA

One of my residency mentors always stressed that orthopaedic surgeons should be “masters of musculoskeletal anatomy.” During his first lecture each July, he would grill the junior residents on muscle origins and insertions, along with innervations. Knowing safe surgical planes helps us avoid complications from neural or vascular injury and increases the likelihood of a successful orthopaedic procedure. With the increased popularity of the direct anterior approach (DAA) for total hip arthroplasty (THA), it is crucial that orthopaedists understand the anatomical implications of that technique.

One key to a successful DAA hip replacement is adequate visualization, which is aided by retractors. However, malpositioned retractors can cause femoral nerve palsy, a potentially serious neurological complication that can delay postoperative rehabilitation. In the January 15, 2020 issue of The Journal, Yoshino et al. report on a cadaveric study that quantifies the distance between the femoral nerve and the acetabular rim at varying points along the rim. Knowing these precise distances could help surgeons make safer decisions about where—and where not—to place retractors.

The authors dissected 84 cadaveric hips from 44 formalin-embalmed cadavers and measured the distance from the femoral nerve to various points along the acetabular rim by using a reference line drawn from the anterior superior iliac spine (ASIS) to the center of the acetabulum. They found the femoral nerve was closest to the rim (only 16.6 mm away) at the 90° point.

In addition, at 90°, the thickness of the iliopsoas muscle and the femoral length (a probable proxy for size of the patient) were positively associated with increased distance to the nerve. Other anatomic factors such as inguinal ligament length, femoral head diameter, and thickness of the capsule were not associated with the nerve-rim distance.

The degree nomenclature used by Yoshino et al. can be correlated to a clock-face representation of the acetabulum, with the 60° point at the 3 o’clock (anterior) position; the 30° point represents a relatively safe  location for placement of the anterior inferior iliac spine retractor (see Figure above).

This important anatomic study can help us improve our mastery of musculoskeletal anatomy—and avoid, if possible, placement of retractors at 90° relative to a line drawn from the ASIS to the center of the acetabulum.

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

Revisiting INR Targets Prior to THA

In March 2019, OrthoBuzz covered a JBJS study by Rudasill et al. that found a progressively increasing risk of bleeding requiring transfusion among total knee arthroplasty (TKA) patients who had a preoperative International Normalized Ratio (INR) >1. (INR is a standardized measure of how long it takes blood to clot—the higher the number, the longer the clotting time.) These authors also found a significantly increased risk of infection in TKA patients with INR >1.5. and an increased risk of mortality within 30 days of surgery among those with an INR >1.25 to 1.5.

In the January 2, 2020 issue of JBJS, the same team of researchers report findings from a similarly designed NSQIP-based study of patients undergoing total hip arthroplasty (THA). The authors evaluated data from >17,500 patients who underwent a primary THA between 2005 and 2016 and who also had an INR value documented within 2 days prior to joint replacement. Rudasill et al. stratified these patients into 4 groups based on preoperative INRs: ≤1, >1 to <1.25, 1.25 to <1.5, and ≥1.5).

After adjustment, the authors found a significant, independent effect between increased preoperative INR and increased bleeding requiring transfusion and mortality. Specifically, bleeding risk became evident at INR ≥1.25, and patients with INR ≥1.5 were at a significantly increased risk of mortality. The length of hospital stay also increased significantly as INR class increased.

The authors suggest that “current INR targeting [INR <1.5 for elective orthopaedic surgery] may not be strict enough to minimize adverse outcomes for patients undergoing primary total hip arthroplasty.” While admitting that these findings are not likely to change the day-to-day practice of orthopaedic surgeons, the authors say they “may influence preoperative risk stratification for those patients with elevated INR.”

Whence SCFE? More Hints Here

Pediatric orthopaedists have long been searching for anatomic, mechanical, and metabolic causes of slipped capital femoral epiphysis (SCFE). Adolescent obesity has been a recognized SCFE risk factor for 50 years. (Interestingly, high BMI is a consistent risk factor in males, but females who experience SCFE are often thin.) Possible racial risk factors have been examined as well, with no clear conclusions.

Because the incidence of SCFE is relatively low (1 in 10,000 children according to this JBJS Clinical Summary) and the risk of bilaterality is high (in the range of 30% to 40%), it seems likely that anatomic risk factors are at play. In the January 2, 2020 issue of The Journal, Novias et al. home in on the 3-D anatomy of the epiphyseal tubercle (a small, round protuberance thought to stabilize the epiphysis) and peripheral “cupping” of the epiphysis in patients with and without SCFE.

They found a smaller epiphyseal tubercle and more extensive epiphyseal cupping in patients with SCFE compared with normal hips. The authors encourage further investigation of the first finding to determine whether smaller tubercles are a consequence of the slip process or an anatomic variant that predisposes the epiphysis to slip.

A major strength of this study is that all measurements were made by a single observer blinded to the diagnosis of SCFE and other potentially confounding clinical and demographic data. Also, the measurement processes used in this study have been previously validated.

Investigation into the anatomic features of this disease should continue, along with development of minimally invasive, safe, and inexpensive ways to screen for possible anatomic risk factors. The most pertinent clinical goals are to  continue evolving minimally invasive methods of epiphyseal stabilization to prevent and/or treat SCFE and to more accurately identify hips at risk of SCFE.

Marc Swiontkowski, MD
JBJS Editor-in-Chief

Predicting ‘Fast,’ ‘Slow Starters’ and ‘Late Dippers’ after THA

Based on ample published data and experience, today’s hip surgeons can give patients who are considering total hip arthroplasty (THA) a good general idea of outcomes to expect. But what if orthopaedists could provide more tailored predictions of THA outcome, and thus help patients more realistically manage expectations?

That is essentially what Hesseling et al. set out to do in their database analysis of 6,030 THA patients gleaned from the Dutch Arthroplasty Register; the findings appear in the December 18, 2019 issue of JBJS. Using the patients’ Oxford Hip Scores (OHS) collected up to 1 year postoperatively and a sophisticated statistical technique called latent class growth modeling, the authors categorized outcome trajectories into 3 categories:

  1. Fast Starters (n = 5,290)—steep improvement in OHS during the first 3 postoperative months, after which the OHS leveled out
  2. Late Dippers (n = 463)—more modest improvement in OHS initially, followed by subsequent decline toward the 1-year mark
  3. Slow Starters (n = 277)—virtually no change at the 3-month mark, followed by an improvement in OHS at 1 year postoperatively

Although the authors were unable to tease out factors that clearly distinguished between late dippers and slow starters, they did identify several factors associated with less-than-fast-starter outcomes:

  • Female sex
  • Smoking
  • Age >75 years
  • Obesity
  • Anxiety and depression
  • American Society of Anesthesiologist (ASA) grade III or IV
  • Hybrid fixation (cemented acetabular implant)
  • Direct lateral surgical approach

Emphasizing that all 3 subgroups experienced functional improvement after THA, Hesseling et al. nevertheless provide useful information that can help surgeons more accurately estimate which patients might be at risk of a less favorable recovery.