CORR Insights®: Etiology of Above-knee Amputations in the United States: Is Periprosthetic Joint Infection an Emerging Cause?

Where Are We Now?

George and colleagues [7] reviewed the National Inpatient Sample (NIS) database and found that the incidence of above-knee amputation (AKA) due to periprosthetic joint infection (PJI) increased by 263% from 1998 to 2013. During that same 15-year period, the number of TKAs performed in the United States more than doubled [1]. George and colleagues further noted that the incidence of AKA decreased by 47% in the US, and AKAs performed for dysvascular causes likewise became less frequent.

TKA is one of the most common orthopaedic surgical procedures, and one projection suggested that approximately 3.48 million will be performed each year in the US by 2030 [11]. Assuming, conservatively, that 1% of those patients will develop an infection, this would result in 35,000 TKA PJIs annually [2]. The risk of AKA after TKA has been reported as 0.1% [5], suggesting a projected 3500 AKAs from PJI annually.

Complete elimination of PJI is not a realistically attainable goal, but continued efforts to reduce PJI are ongoing. The risk of PJI after TKA has decreased from 4.4% in 1986 to as low as 0.28% in 2016 [15].

Prior studies have identified diabetes mellitus, elevated BMI, tobacco usage, skin flora, male sex, previous surgery, and prior PJI as risk factors for PJI [9, 10, 12]. Perioperative factors found to have a role in PJI include blood conservation, operative environment factors, draping and skin preparation, antibiotic prophylaxis, operative time, use of blood transfusions, anticoagulation, and wound dressings [10, 12]. Diagnosing PJI can be challenging, but recent developments like α-defensin and micro-polymerase chain reaction have improved detection [4]. Although we are still determining how to treat TKA once PJI is identified, researchers are focusing on one-stage versus two-stage exchange arthroplasty [6, 11].

The prognosis of AKA after TKA is dire, with mortality rates of 40% at 6 years; fewer than half of these patients regain the ability to ambulate in the community [6]. The economics of revision TKA are just as staggering; an estimated USD 5 billion was spent on revision TKAs in the United States in 2015 [11]. PJI is the most common etiology of revision TKAs accounting for 25% of revision TKAs at an average cost of nearly USD 50,000 per patient [3].

We must recognize the financial aspect of preventing and treating TKA infections, but more importantly, we must pursue solutions for the long-term health of our patients.

Where Do We Need To Go?

As the authors suggest, there are numerous avenues for future study. Areas ripe for further investigation include risk stratification for PJI, perioperative medical management to decrease the risk of PJI, as well as management of PJI once it develops.

A recent review of the New Zealand Joint Registry identified male gender, increasing BMI, prior surgery, laminar airflow in the operating room, ligament reconstruction, and the use of antibiotic cement as being risk factors for PJI [15]. A number of these factors are nonmodifiable, which emphasizes the need to elucidate the best means of managing the modifiable risk factors.

Several studies have demonstrated the efficacy of single-stage revision TKA for PJI in well-selected patients with a known organism amongst other criterion [8, 13]. Further study with larger patient populations could confirm these findings, as well as potentially demonstrate expanded indications for single-stage revision.

How Do We Get There?

A large amount of research about total joint arthroplasty comes from countries with strong national joint registries, and the American Joint Replacement Registry (AJRR) can be that registry for the United States. As of 2016, the AJRR has collected data from 854 hospitals, representing nearly 270,000 of the estimated 1 million joint replacements performed in the United States annually [4].

Incentivizing participation in the AJRR would likely improve the quality of the data, and subsequently, the quality of the research. By collaborating and pooling data, researchers can potentially determine the best ways to reduce PJI rates, improve our PJI eradication rates, and minimize the number of patients who endure severe complications of a PJI such as AKA and mortality. An additional value of increased participation in the AJRR would be better implant survival data and the ability to identify poorly performing implants earlier, as the national joint registry of England and Wales as well as other national registries did when they found high early revision rates for metal-on-metal THA and hip resurfacing [14].

The AJRR and studies using that dataset as it expands may prove to be the best way to determine risk stratification for PJI after TKA. Additionally, retrospective studies using the AJRR or other databases should evaluate the characteristics of patients who develop PJI. By doing so, we can determine the relative risk ratio for individual characteristics, which will allow for more accurate individualized counseling of patients regarding their personal risk of PJI as well as identifying modifiable risk factors amenable to perioperative medical mitigation.

Large studies potentially using national databases directly comparing the PJI eradication rate and the long-term outcomes of single-stage versus two-stage revision arthroplasty should be performed to improve our treatment of confirmed PJI.

As more and more patients undergo TKA, the impetus is upon us as surgeons to minimize their risk of PJI and improve our treatment of confirmed PJIs to avoid catastrophic complications like AKA.