Radical débridement following removal of an infected primary total knee arthroplasty. The Academy’s new SLR offers guidance for reducing risk of SSIs and for managing those that occur. Reproduced from Maale G: Débridement for orthopaedic infection (pp. 121-155). In: Hsu WK, McLaren AC, Springer BD (Eds.), Let’s Discuss: Surgical Site Infections. Rosemont, IL: American Academy of Orthopaedic Surgeons; 2015.


Published 8/1/2018
Terry Stanton

Academy Approves Guidelines for SSIs and Imaging Before Referral to an Oncologist

The Academy’s Board of Directors has approved two systematic literature reviews (SLRs): Management of Surgical Site Infections (SSIs) and Use of Imaging Prior to Referral to a Musculoskeletal Oncologist.

The latter SLR was a product of the Musculoskeletal Tumor Society (MSTS) and was developed through the Academy’s Clinical Practice Guideline (CPG) process by the AAOS Evidence-Based Quality and Value Unit, with funding provided by both organizations. AAOS endorsement allows the SLR to be listed on the OrthoGuidelines web platform and mobile app.

An SLR is equivalent in format to a CPG but with a narrower focus and a smaller set of questions deliberated by the work group.

MSTS guideline for referral

In the introduction to its SLR on imaging prior to oncologist referral, the MSTS work group wrote that the intent was to provide guidance to orthopaedic surgeons regarding imaging options for musculoskeletal tumors of unknown biological significance. “These investigations demonstrated that many of the choices regarding musculoskeletal imaging are made prior to referral to cancer specialists,” the guideline authors wrote. They identified three studies that found that advanced imaging studies, ordered in an effort to pin down the diagnosis before a tumor referral is made, often lead to additional tests that can been avoided if some of the advanced studies are left to the treating oncologist to order.

With this SLR, they wrote, “The goal is not to diminish the use of advanced imaging techniques and modalities, but rather to propose a clinically meaningful approach to ensure that the correct studies are done for appropriate indications. Although diminishing the use of costly imaging is an important consequence of this project, these guidelines will also provide (good) support” for the images necessary for the best treatment in these cases.

As with CPGs, recommendations are characterized by the strength of evidence in support of them—strong, moderate, or limited. Those with no supporting evidence are labeled consensus, meaning that in the absence of reliable evidence, the guideline-development group is making a recommendation based on clinical opinion.

The chair of the work group for the MSTS SLR, Benjamin J. Miller, MD, MS, of the University of Iowa, who is also a member of the AAOS Committee on Evidence-Based Quality and Value, explained that the group had two main goals in writing the guideline: (1) to reduce costly imaging and (2) to help justify use of advanced imaging when clinically necessary. Dr. Miller explained that the SLR’s recommendations are intended for orthopaedic generalists and specialists without oncology training at the initial visit stage and “are not meant to comment on definitive imaging that is required for oncology patients—which can be patient-specific and difficult to generalize.” In regard to unnecessary testing, he said, “I would also note that prior studies have shown that orthopaedic surgeons obtain inappropriate imaging at a similar rate of other nonorthopaedic–trained practitioners. Diffusion of guidelines is challenging, and we encourage everyone to use these when talking to residents, medical students, and other colleagues.”

The SLR offers recommendations for the primary modalities of imaging. For plain radiographs, it states, “moderate evidence supports using conventional radiographs in the initial evaluation of a bone tumor of unknown etiology.” For soft-tissue tumor, the consensus recommendation states, “conventional radiographs are a reasonable diagnostic test and may be considered during the initial evaluation.”

For MRI imaging, “strong evidence supports that contrast enhancement on MRI can assist in determining if a soft-tissue tumor is benign or malignant,” the SLR advises. The consensus recommendations provide guidance on considerations for magnet strength and on areas to visualize with MRI and CT scans.

For ultrasound, the SLR states that moderate evidence “supports that ultrasound helps to distinguish benign from malignant soft-tissue tumors.” The work group came to a consensus opinion that “ultrasounds in small (< 5 cm), superficial soft-tissue tumors can help distinguish between benign lipomas, vascular malformations, cystic structures, and solid tumors that require further characterization.”

For patients with a history of pain, the SLR cites moderate evidence to support that “both radiographs and MRI have weak sensitivity in determining malignancy but moderate to strong specificity in determining benignity of bone tumors.” In patients with suspected soft-tissue tumor recurrence, moderate evidence shows that MRI of the tumor site can reliably identify neoplastic tissue and differentiate between solid and cystic areas. Moderate evidence also supports the use of MRI (or CT if MRI is not available) for evaluation of cortical irregularity or periosteal reaction in a bone tumor.

Dr. Miller said the takeaway for orthopaedic surgeons is: “Often radiographs are enough, while advanced imaging should be considered in soft-tissue tumors that are large (> 5 cm), growing, deep to the muscle fascia, or painful, and in bone tumors that are painful or aggressive-appearing on X-ray (with cortical destruction, periosteal reaction, permeative borders).”

Dr. Miller said that further studies beyond MRI are not required prior to referral. “Other studies are occasionally required but should be left to the oncology specialists,” he said. Ultrasounds are relatively ineffective in large and deep soft-tissue tumors, he added. “Beware of false reassurance. We were worried about the possibility of false reassurance if the study were misinterpreted. However, ultrasound is relatively inexpensive, and we felt there is utility for specific questions and distinguishing between superficial cysts, lipomas, hematomas, and other entities that require further evaluation.”

The work group’s findings point to areas in need of further research and evidence. “Specifically, the role of contrast in MRI and staging CT scans of the chest/abdomen/pelvis is not well defined, and it is unclear if it is required or can be used selectively,” Dr. Miller said. “We also agreed that imaging decisions would be enhanced by engaging musculoskeletal-trained radiologists or orthopaedic oncologists when making decisions regarding the type of imaging that is best, which is theoretically sound but not supported by any evidence of cost-effectiveness or diagnostic efficiency.”

Management of SSIs

The chair of the work group for the SLR on SSIs, Douglas W. Lundy, MD, MBA, of Resurgens Orthopaedics, commented that the final product, although in the shorter SLR format, emerged from a review of “an incredible amount of literature” addressing SSIs. “We are very proud of this work and extremely appreciative of all of the efforts delivered by the AAOS staff to get it done,” he said. “This work accurately reflects the current literature on SSI. Do not be disappointed that it wasn’t a CPG!”

Among the recommendations backed by strong evidence is one advising that synovial fluid and tissue cultures are strong rule-in tests for diagnosis of infection and that negative synovial fluid and tissue cultures do not reliably exclude infection. Strong evidence also supports that C-reactive protein is a strong rule-in and rule-out marker for patients with suspected SSI.

The work group found that moderate evidence supports that clinical examination (for pain, drainage, and fever) is a moderate to strong rule-in test (i.e., high probability of infection if test is positive) for patients with suspected SSI but that it is a weak rule-out test.

Moderate evidence also supports that patients who meet one of the following criteria are at increased risk of infection after hip or knee arthroscopy:

  • chronic kidney disease
  • diabetes (conflicting evidence)
  • tobacco use (conflicting evidence)
  • malnutrition (conflicting evidence)

The evidence was deemed limited to support that patients having cancer, hypertension (conflicting evidence), and/or liver disease (conflicting evidence) are at increased risk of infection after hip or knee arthroplasty.

The work group found moderate evidence supporting that rifampin, as a second antimicrobial, increases the probability of treatment success for staphylococcal infections in the setting of retained orthopaedic implants. Also in that setting, moderate evidence indicates that antibiotic protocols of eight weeks do not result in significantly different outcomes compared with protocols of three to six months.

Dr. Lundy commented that “one clear message from the SLR is that the diagnosis of SSI is often derived from a constellation of findings and that physicians should avoid being dogmatic on one point. This is true in medical imaging, in that SSIs are often complex and difficult to diagnose, and that the orthopaedic surgeon should consider the whole clinical picture, while remaining extremely vigilant.” Although overtreatment is not a stated goal, orthopaedic surgeons must guard against missing SSIs and avoid undertreatment.

He said that given the continual emergence of new technologies for diagnosing SSIs, “I would implore every orthopaedic surgeon to read the SLR and carefully consider how their practice could benefit from these recommendations.”

The SLRs may be accessed at www.orthoguidelines.org or from the OrthoGuidelines app.

Terry Stanton is the senior science writer for AAOS Now. He can be reached at tstanton@aaos.org.