Bacteria and shoulder joint replacement

It is now well recognized that Cutibacterium (Propionibacterium) are the most common organisms cultured from deep tissue and explant specimens harvested at the surgical revision of a failed arthroplasty, especially in those cases revised for pain and stiffness without clinical evidence of inflammation.

It is also well recognized that the most likely source of these organisms is the sebaceous glands and hair follicles of the skin that is incised when a shoulder replacement is performed, particularly in young, healthy male patients. 

Finally, it is generally accepted that the usual surgical skin preparation and preoperative antibiotics are ineffective in lowering the amount of these organisms in the skin and in reducing the risk of Cutibacterium entering the wound at surgery.

Several questions remain unanswered.

(1) Why do Cutibacterium cause problems in some shoulders but not in others?

(2) Why does it often take months or years before the symptoms related to the Cutibacterium become evident?

(3) What can be done to prevent clinical problems associated with the presence of Cutibacterium in shoulder arthroplasty?

(4) How can the presence of Cutibacterium in a failed arthroplasty be diagnosed while the patient is still in operating room (i.e. in time to adjust the surgical plan accordingly)?

(5) What is the best medical and surgical treatment for a failed shoulder arthroplasty?

We've asked orthopaedist/artist Steve Lippitt to help us shed some light on some of these unknowns.

Most shoulder implants have bodies made of titanium, a metal that can provide a foundation for a biofilm (a film on the metal that includes bacteria, proteins, and carbohydrates). 

Cutibacterium prefer an "low oxygen" or anaerobic environment, such as that found on the inside of the humerus.

Cutibacterium can enter the wound at the time of the surgical skin incision 

Those bacteria that enter the joint are free floating or "planktonic". Because the joint has a rich blood supply, these are usually cleaned up by the body's defense system in the oxygen-rich environment.

Despite all precautions, some Cutibacterium may find their way into the humeral canal where they find an attractive environment in which to form a biofilm: the anaerobic inside of the humerus plus a titanium implant body.

Here the Cutibacterium in the biofilm (green area below) enter a semi-dormant  state of slow growth and great resistance to antibiotic therapy,

 reminding one of Sleeping Beauty or Rip Van Winkle

During this "honeymoon" period, the Cutibacteria in the biofilm can slowly multiply, but, because they do not have contact with the joint, symptoms of pain and stiffness are not apparent.

After a period of months, years or even decades, some bone resorption can occur, releasing Cutibacterium into the joint where they can give rise to pain and stiffness without the usual characteristics of inflammation. Because the number of bacteria in the joint are small, the chance of recovering them with a joint aspiration is low. Instead, identifying these bacteria requires culturing deep tissue specimens and the implants removed at revision surgery.

In some cases, bone resorption takes place to the extent that the humeral component can become loose.

The story above may seem like a "fairy tale" and is not yet robustly supported by sound research. However, this model suggests possible answers to some of our questions:

(1) Why do Cutibacterium cause problems in some shoulders but not in others?

*Some patients (female patients and older males) may have low levels of Cutibacterium in their sebaceous glands. Some patients may be better than others in terms of "cleaning up" bacteria introduced at surgery.

(2) Why does it often take months or years before the symptoms related to the Cutibacterium become evident?

*Bacteria in biofilms grow very slowly, taking a long interval between the time of the index surgery and the time that the patient presents to the surgeon with a painful stiff joint.

(3) What can be done to prevent clinical problems associated with the presence of Cutibacterium in shoulder arthroplasty?

*Our best guess at this point is copious irrigation of the wound, use of new gloves when handling the implant, placing antibiotics in the humeral canal prior to the placement of the prosthesis, and avoiding contact of the prosthesis with the skin edge.

(4) How can the presence of Cutibacterium in a failed arthroplasty be diagnosed while the patient is still in operating room (i.e. in time to adjust the surgical plan accordingly)?

*The best we have so far is to seek preoperative and intraoperative clues: young, lean, male patients, exogenous testosterone, a "honeymoon" period with the onset of symptoms without other explanation, and the intraoperative finding of synovitis. Tests of blood or joint fluid can be helpful when inflammation is present, but are less useful in the usual "stealth" presentation of Cutibacterium. 

(5) What is the best medical and surgical treatment for a failed shoulder arthroplasty?

*Our preference is to manage suspicious cases with a primary prosthesis exchange and immediate intravenous antibiotics that are continued until multiple tissue and explant cultures have been observed for three weeks.

The story above needs to be tested by many observations of many cases by many observers. It should be considered a "rough draft" ripe for editing and revision based on good clinical research.



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