Predicting infection risk in shoulder arthroplasty

Cutaneous microbiology of patients having primary shoulder arthroplasty

These authors point out that shoulder periprosthetic infections are predominantly caused by bacteria residing in the skin of healthy individuals.

They tested the hypothesis that easy-to-obtain preoperative characteristics were significantly associated with the cutaneous microbiology and the loads of specific bacteria in shoulders having joint replacement.

They identified the microbiology of the unprepared epidermal skin surface and of the dermal edge freshly incised at surgery in 332 patients having primary shoulder arthroplasty.

The load of bacteria in each sample was characterized as a value based on the laboratory report: 0 for “no growth”; 0.1 for “one colony only” or for “broth only”; and 1, 2, 3, and 4 for 1+, 2+, 3+, and 4+ growth, respectively.

Cultures of the unprepared epidermal skin surface showed positive results for a wide variety of organisms, including Cutibacterium in 72%, coagulase-negative Staphylococcus in 61%, and a spectrum of other organisms in 32%.

By contrast, cultures of the freshly incised dermal edge showed a great preponderance of Cutibacterium (34%) in comparison to low levels of coagulase-negative Staphylococcus (8%) and other organisms (2%).

An increased dermal load of Cutibacterium was significantly associated with male sex (p<.001), younger patient age (p<.001), American Society of Anesthesiologists class 1 (p 0.046), use of testosterone supplements (p 0.014), prior shoulder surgery (p 0.046, and higher Cutibacterium loads on the unprepared skin surface (p<.001)

They concluded that although the microbiology of the unprepared skin surface is diverse, the same is not true for the freshly incised dermis, where Cutibacterium is the predominant organism.

Readily available preoperative patient characteristics were significantly associated with the load of Cutibacterium in the incised dermis.

Preoperative cultures of the unprepared skin surface appear to be a new method for predicting the type and load of bacteria found in the freshly incised dermis at the time of surgery.

Comment:  Knowledge of the preoperative characteristics of patients likely to have high dermal loads of Cutibacterium may help identify those for whom extraordinary means of prophylaxis (such as Betadine lavage, in-wound topical antibiotics, extended postoperative antibiotics) may be indicated to reduce the risk of periprosthetic infection.

The relationship of male sex, young age, good health, and testosterone supplements to the dermal load of Cutibacterium is consistent with previous observations that higher levels of male sex hormones are associated with increased sebum production in dermal pilosebaceous units and a commensurate increase in the number of Cutibacterium in these dermal structures.

It is of interest that the risk factors for higher loads of Cutibacterium in the dermal incisions for elective shoulder arthroplasty are quite different from the risk factors characteristically associated with periprosthetic infections of the hip and knee, which include older age, female sex, diabetes, high ASA score, obesity, and Medicaid insurance coverage.

=====
How you can support research in shoulder surgery Click on this link.

We have a new set of shoulder youtubes about the shoulder, check them out at this link.

Be sure to visit "Ream and Run - the state of the art"  regarding this radically conservative approach to shoulder arthritis at this link and this link

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages   arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

The limited effectiveness of Vancomycin-containing spacers in treating periprosthetic infections

Vancomycin-Loaded Polymethylmethacrylate Spacers Fail to Eradicate Periprosthetic Joint Infection in a Clinically Representative Mouse Model

These authors developed a murine model of the first-stage surgery of a 2-stage revision for periprosthetic joint infection involving a 3-dimensionally printed Ti-6Al-4V tibial implant

 infected with Staphylococcus aureus and treated 2 weeks later with irrigation and debridement of the leg with revision of the implant to an articulating vancomycin-loaded PMMA spacer.

Postoperatively, mice underwent radiography and serum inflammatory-marker measurements. Following euthanasia of the mice at 6 weeks, bone and soft tissues were homogenized to quantify bacteria within periprosthetic tissues. Implants and articulating spacers were either sonicated to quantify adherent bacteria or examined under scanning electron microscopy (SEM) to characterize the biofilm.

They found that vancomycin-loaded PMMA spacers eluted vancomycin for 6 days with retained antimicrobial activity.

Control mice had elevated levels of inflammatory markers, radiographic evidence of septic loosening of the implant, and osseous destruction. Mice treated with the vancomycin-loaded PMMA spacer had significantly lower levels of inflammatory markers (p < 0.01), preserved tibial bone, and no intra-articular purulence. 

Retrieved vancomycin-loaded spacers exhibited significantly lower bacterial counts compared with implants (p < 0.001). SEM identified S. aureus encased within biofilm on control implants,

while vancomycin-loaded spacers contained no bacteria.

However, bacterial counts in periprosthetic tissue did not significantly differ between the groups.

The results suggest that the antimicrobial effects of PMMA spacers are tightly confined to the articular space and must be utilized in conjunction with thorough tissue debridement and systemic antibiotics to manage bacteria in the surrounding tissue.

Comment: This article once again demonstrates the remarkable propensity of titanium to enable biofilm formation. It also shows the effectiveness of Vancomycin spacers to resist biofilm formation and to help manage bacteria in the joint. However, it points to the relative ineffectiveness of spacers in managing infection in the tissues surrounding the joint. While they advocate "thorough tissue debridement," it is not always easy to discern what tissue needs to be debrided during surgical management of a periprosthetic infection. Hopefully a combination of debridement and systemic antibiotics will prove effective in managing bacteria in the tissues surrounding an infected prosthesis.

Interested readers may want to read these related posts:

Quantification of Peri-Implant Bacterial Load and in Vivo Biofilm Formation in an Innovative, Clinically Representative Mouse Model of Periprosthetic Joint Infection

Delayed Propionibacterium acnes surgical site infections occur only in the presence of an implant.

=====
Use the "Search" box to the right to find other topics of interest to you.

How you can support progress in shoulder surgery

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

Anaerobic biofilm conditions optimize Propionibacterium growth

Propionibacterium acnes biofilm - A sanctuary for Staphylococcus aureus?

These authors measured planktonic growth and biofilm formation of Propionibacterium acnes and Staphylococcus aureus alone and together under aerobic and anaerobic conditions.

Both P. acnes and S. aureus grew under anaerobic conditions. 

When grown under anaerobic conditions, P. acnes alone or with S. aureus formed a biofilm denser than that of S. aureus alone. 

Viable S. aureus was recovered from a 16- day old combined P. acnes and S. aureus biofilm, but not a monomicrobial S. aureus biofilm, suggesting that P. acnes biofilms may provide an ideal growth site for S. aureus.

Comment: 

Some key findings from our standpoint:

(1) planktonic growth of Propionibacterium was poor under aerobic conditions 

 (2) biofilm growth of Propionibacterium was poor under aerobic conditions

 (3) planktonic growth of Propionibacterium was slowed under anaerobic conditions

  (4) biofilm growth of Propionibacterium was robust under anaerobic conditions

These data demonstrate that anaerobic biofilm conditions optimize Propionibacterium growth.

Does a titanium implant in a relatively anaerobic medullary canal produce these conditions? See:

Infections with Propionibacterium - the necessity of a surgical implant

===

Consultation for those who live a distance away from Seattle.

Click here to see the new Shoulder Arthritis Book.

Click here to see the new Rotator Cuff Book

Information about shoulder exercises can be found at this link.

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

See from which cities our patients come.

See the countries from which our readers come on this post.

Reverse total shoulder arthroplasty - the problem of infection

Surgical management of the infected reversed shoulder arthroplasty: a French multicenter study of reoperation in 32 patients.

These authors reviewed patients who were reoperated on for infection after reversed shoulder arthroplasty between 1996 and 2011. The mean age was 71 (55-83) years. The involved implants were primary prostheses in 23 cases and revision prostheses in 9 cases. The average delay between the prosthesis implantation and the diagnosis of infection was 21 months (1-116).

Infections were largely caused by coagulase-negative staphylococci (56%) and Propionibacterium acnes (59%). The complication rate was 26%. At last follow-up, 26 patients appeared to be free of infection. After débridement with implant retention, the healing rate was only 54%. Single or two stage implant revision led to better functional results than implant removal, with superior healing rates (73% and 67%, respectively). Patients with low initial impairment (Constant score > 30) were not significantly improved by surgical treatment.

Comment: This paper does not clarify the optimal methods for diagnosing or treating infections - there was great variability in the approach in these cases. What we can take away is that (1) the presentation of infection can be long - 10 years - after the index procedure, (2) as is the case for anatomic shoulder arthroplasty infections, Propionibacterium is the most common bacterium isolated from these cases, (3) the rate of infection after reverse total shoulders is not determined, and (4) the minimum one year followup in this series is insufficient to judge whether or not the infection was eradicated.

===

Use the "Search" box to the right to find other topics of interest to you.


You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'



See from which cities our patients come.



See the countries from which our readers come on this post.

Shoulder joint replacement arthroplasty - the challenging problem of the loose glenoid

As shown in this link, glenoid component loosening always presents challenges.

Here is the instructive case of a sixty year old man who presented with shoulder pain that had been progressively increasing over the seven years after a total shoulder arthroplasty. On exam his findings included pain and stiffness.
His x-rays on presentation showed a superiorly positioned humeral component and a loose keeled glenoid component:

A revision surgery was performed eight years after his index procedure. There was no evidence of inflammation and the joint fluid was clear. The humeral stem was tightly fixed and could not be easily removed. The glenoid component was grossly loose and was removed. The humeral head was exchanged for one that was eccentric inferior to optimize its fit with the glenoid and to compensate for the superior position of the stem. Cultures were obtained and the patient discharged on oral Augmentin and standard post-arthroplasty rehabilitation. He quickly regained comfort and function in the shoulder.

At 9 days after surgery his cultures became positive as shown below.

With these results he was transitioned to IV Ceftriaxone and Rifampin through a PICC line for 6 weeks after which Augmentin was restarted. At six weeks the shoulder was doing well and the x-rays were satisfactory as shown below.

Within three weeks of discontinuance of the IV Ceftriaxone, the shoulder pain started to worsen and became severe with loss of passive and active motion and the ability to perform activities of daily living.

He is now contemplating the prospect of revision surgery to remove the incarcerated stem.

Comment: This case again illustrates the challenges for patient with a loose glenoid presenting without clinical evidence of infection. In this case the decision was made not to remove the humeral stem because of its incarceration and the absence of surgical findings suggesting infection. However, with the recurrence of symptoms after discontinuance of the IV antibiotics, there is concern about residual bacterial presence in a biofilm on the stem that can only be resolved by the removal of the incarcerated humeral prosthesis. An additional element of this case is the multiple organisms culture from this shoulder: coagulase negative staph and several colony types of Propionibacterium. Finally it is of interest that the presentation of this failed shoulder eight years after the index procedure, reinforcing the view that vigilance for infection should never stop.

===

Use the "Search" box to the right to find other topics of interest to you.


You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'



See from which cities our patients come.



See the countries from which our readers come on this post.

Propionibacteriium and Staph infection in shoulder arthroplasty - not that easy to treat.

Management of deep postoperative shoulder infections: is there a role for open biopsy during staged treatment?

The authors'  current treatment algorithm for infected shoulder arthroplasty includes explant of the infected prostheses, followed by antibiotic cement spacer placement and at least a 6-week course of antibiotic therapy before reimplantation of a new prosthesis. Even with this vigorous treatment they note that reinfection rates of between 0% and 37% have been reported after a 2-stage revision.

They reviewed 18 patients having periprosthetic shoulder infections and osteomyelitis after previous surgery who were treated with a standardized protocol of irrigation and debridement, removal of implants, antibiotic cement spacer placement (1 gram vancomycin and 1.2 grams tobramycin for every bag of polymethyl methacrylate), and pathogen-directed antibiotic therapy for 6 weeks. Open biopsies were performed in the operating room after a 4-week antibiotic holiday period. Revision arthroplasty was performed at a later date if final cultures were without evidence of infection. If evidence of infection persisted, then another course of I&D and antibiotic treatment was performed.

Four patients (22%) had evidence of persistent infection on specimens from open biopsy and required another course of formal I&D, spacer exchange, and a 6-week course of antibiotic therapy. After a second course of therapy, specimens from repeat biopsies were sterile for 3 of these 4 patients, and their prosthesis was able to be replanted. One patient had positive cultures again at his third biopsy and required a third round of surgical and antibiotic therapy according to the protocol. Results from specimens from this patient’s third open biopsy were negative, and he was replanted with a RTSA.

At the first revision, the most common pathogens isolated were Propionibacterium acnes (44%), Staphylococcus epidermidis (39%), and S aureus (22%). The infecting pathogen in 75% of patients with persistent infection was P acnes, and 38% of patients with P acnes infection had recurrence. 

Mean follow-up of 24 months showed no signs of recurrent infection in any patient and an average American Shoulder and Elbow Surgeon score of 71.

Comment: 

These authors recognize that simple needle aspirates are insufficient for excluding infection: often the organisms reside in biofilms such that tissue biopsies are necessary to recover them.

Note that the patients in this case series had obvious periprosthetic infections with deep draining sinus, purulent drainage from the wound, erythema, abnormal white blood cell, C-reactive protein, erythrocyte sedimentation rate, computed tomography, magnetic resonance imaging, and

joint aspiration.

It is indeed impressive to note the persistence of positive cultures after such a vigorous initial course of surgical and medical treatment. 

While this is a labor intensive and expensive protocol, it is rewarding to see that all 18 of these patients were free of clinical signs of infection two years after their last revision procedure.

Finally, it is important to distinguish these cases of clinically apparent periprosthetic infection with the revision arthroplasty with positive cultures but without clinical signs of infection.

===

Consultation for those who live a distance away from Seattle.

Click here to see the new Shoulder Arthritis Book

Click here to see the new Rotator Cuff Book

To see the topics covered in this Blog, click here

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

Loose glenoid components, Propionibacterium, and their management

A lady in her 70s taking insulin for her diabetes with a high BMI who uses a wheelchair presented with pain in her shoulder after a prior arthroplasty. These x-rays were taken. Showing a well fixed humeral component and a loose polyethylene and metal glenoid.

She desired surgical revision with removal of her loose glenoid. She had no clinical or laboratory evidence of infection. 

At surgery cloudy joint fluid was encountered and a frozen section showed > 5 WBC/HPF. The humeral component was well fixed. The loose glenoid was easily removed and the glenoid vault curetted to remove the reactive tissue. The wound was thoroughly irrigated and a new humeral head prosthesis with a larger diameter of curvature inserted. The well fixed ingrowth stem was not changed.  She was started on Ceftriaxone and Vancomycin via a PICC line.

The gram stain and culture results were:

*Right shoulder humeral head explant
GS: Rare PMNs, no organisms seen
C: 1+ Propionibacterium

*Right shoulder glenoid explant
GS: 2+ PMNs, 3+GPCs and 2+GPRs on gram stain
C: 1+ Propionibacterium, Dermacoccus

*Right shoulder joint fluid #1 

GS: 3+ PMNs,1+ GPCs
C: 1+ Propionibacterium type 1, 1+ Propionibacterium type 2

*Right shoulder joint fluid #2
GS: 3+ PMNs, no organisms seen
C: 1+ Propionibacterium type 1, 1+ Propionibacterium type 2

* Right shoulder glenoid membrane #1
GS: 1+ PMNs, no organisms seen
C: 1+ Propionibacterium type 1, 1+ Propionibacterium type 2

*Right shoulder glenoid membrane #2
GS: 1+ PMNs, no organisms seen
C: 1+ Propionibacterium type 1, 1+ Propionibacterium type 2, Coag neg staph (2 types)

*Right shoulder collar membrane
GS: 2+ PMNs, no organisms seen
C: 1+ Propionibacterium type 1, 1+ Propionibacterium type 2, 1+ Propionibacterium type 3

*Right shoulder capsule
GS: 2+ PMNs, no organisms seen
C: 1+ Propionibacterium type 1, 1+ Propionibacterium type 2, 1+ Propionibacterium type 3

She continues on supressive Augmentin with an improved, but imperfect shoulder.

Comment: Again it surprising how heavy a bacterial load existed in this shoulder without clinical manifestations of infection. We never know. In this case - in contrast to a prior one - we retained the humeral stem (rather than splitting the humerus to remove an ingrowth prosthesis) because of the patient's compromised health and dependency on the arm for transfers and ambulation, recognizing the risk of persistence of organisms.

This is, again, an argument against ingrowth or cemented humeral components: it is much safer to revise a humeral component fixed with impaction grafting.

3735170

===
Consultation for those who live a distance away from Seattle.

Click here to see the new Shoulder Arthritis Book

Click here to see the new Rotator Cuff Book

To see the topics covered in this Blog, click here

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

Unsuspected infection in a case of a loose glenoid component - it's not always Propionibacterium

A fifty year old gentleman presented to us with pain in his shoulder after a total shoulder arthroplasty performed elsewhere using a metal-backed glenoid. His x-rays are shown below, showing a dislocated glenoid component.

What would you do?

We performed a revision arthroplasty, removing the glenoid component, retaining the well-fixed humeral stem, smoothing the residual glenoid bone and inserting an eccentric humeral head component. There was no evidence of infection at surgery. Cultures were obtained before antibiotics were administered as is our routine in all revisions. His postoperative films are shown below. He was discharged on the yellow protocol.

His shoulder comfort and function have been dramatically improved.

At six days after surgery. His culture results were as shown below. Click on each to enlarge.

We have the advantage of very experienced infectious disease consultants to guide our approach. A PICC line was inserted and the patient was started on Ceftriaxone 2 gm IV q 24 h. Rifampin 600 mg PO q 24 h was added 8 days later.

The patient experienced diarrhea, C diff was suspected treated with oral Vancomycin X 14 days. His diarrhea resolved.

After 6 weeks of IV antibiotics, his PICC line was discontinued and he was placed on oral Doxycycline Monohydrate 100 MG Oral Cap. He experienced gastrointestinal distress without diarrhea and was switched to Sulfamethoxazole-Trimethoprim 800-160 MG Oral Tab.

His shoulder motion and comfort continue to improved, but he has some aching in his humeral area without radiographic evidence of loosening. We've elected to monitor this for now. In retrospect, perhaps we should have performed a primary exchange of his humeral component. Time will tell.

This case demonstrates the need for a standardized culture protocol for all failed shoulder arthroplasties, the need for close collaboration with experienced infectious disease consultants, and the complexities of the decision making.

===

Check out the new Shoulder Arthritis Book - click here.

Click here to see the new Rotator Cuff Book

Consultation for those who live a distance away from Seattle.

To see the topics covered in this Blog, click here

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

See from which cities our patients come.

See the countries from which our readers come on this post.

Propionibacterium is orthopaedically different from staphylococcus and can be a cause of 'aseptic' failure

Propionibacterium acnes and Staphylococcus   Cause Pyogenic Osteomyelitis in an Intramedullary Nail Model in the Rabbit

Both Propionibacterium acnes and coagulase-negative staphylococci are opportunistic pathogens implicated in prosthetic joint and fracture fixation device-related infection.

These authors isolated Propionibacterium and coagulase-negative staphylococci from ‘aseptically failed’ prosthetic hip joints and attempted to produce osteomyelitis in an established implant-related osteomyelitis model in the rabbit, in the absence of implant material wear debris.

The Propionibacterium LED2 was isolated after ultrasound treatment of a retrieved prosthetic hip joint, due to a supposed aseptic joint failure. Bacterial biofilm was also detected in the sonicate fluid by immunofluorescence microscopy (IFM) after labeling with a P. acnes-specific antibody.

This isolate belonged to the ST5 lineage within the type IB phylogenetic grouping. Isolates from this 

phylogroup are associated with healthy skin, and rarely recovered from acne vulgaris lesions. They
 have, however, been associated with soft tissue and medical device-related infections, although their
exact clinical importance in these cases has remained unclear.

The histological features of Propionibacterium infection in the in vivo rabbit model were consistent with localized pyogenic osteomyelitis, and biofilm was present on all explanted IM nails. The animals displayed no outward signs of infection, such as swelling, lameness, weight loss, or elevated white cell count. 

In contrast, infection with coagulase-negative staphylococci resulted in histological features consistent with both pyogenic osteomyelitis and septic arthritis, and all coagulase-negative staphylococci animals displayed weight loss and an elevated white cell count despite biofilm detection in only two out six rabbits.

The differences in the histological and bacteriological profiles of the two species in this rabbit model of infection are reflective of their different clinical presentations; low-grade infection in the case of Propionibacterium and acute infection for coagulase-negative staphylococci. 

These results are especially important in relation to the growing recognition of chronic Propionibacterium  biofilm infections in prosthetic joint failure and non-union of fracture fixations, which may be currently reported as ‘aseptic’ failure.

The authors conclude that: Propionibacterium has the potential to cause prosthetic joint infection and fracture non-union, in the absence of signs of classical infection and patient morbidity. Propionibacterium should therefore no longer be dismissed as an insignificant pathogen in the setting of failed retrieved implants; clinical diagnostic practice should be tailored to enable the efficient detection of P. acnes. Without this there is the risk of  an incorrect diagnosis of aseptic loosening and subsequent patient treatment may be misinformed. If a failed prosthetic joint with a mis-diagnosis of aseptic loosening is removed, and a new sterile device placed in the underlying infected site it is very possible that higher numbers of bacteria will be present, particularly if adjacent bone has been colonized.

Comment: This animal model of Propionibacterium infection nicely replicates many of the features encountered in revision arthroplasty, where the preoperative impression of 'aseptic' failure is disproven by positive cultures for Propionibacterium.

===
Consultation for those who live a distance away from Seattle.

Check out the new Shoulder Arthritis Book - click here.

Click here to see the new Rotator Cuff Book

To see the topics covered in this Blog, click here

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

See from which cities our patients come.

See the countries from which our readers come on this post.

To see other similar posts, click on the label of interest below.

Revision surgery for failed total shoulder replacement arthroplasty for infection - our approach, Part 6

We will now proceed with a discussion of some of the specific causes of failed shoulder arrthroplasty.  Surely one of the most insidious is infection. Surgical cultures obtained from shoulders requiring revision of a prior arthroplasty because of pain, stiffness, or loosening are frequently positive despite the absence of preoperative evidence of joint sepsis. Often these cultures are positive for organisms, such as Propionibacterium acnes and Coagulase-negative Staphylococci, that are less commonly recovered from revision surgery in other sites of joint replacement such as the hip or knee. These organisms are distinguished by (1) their presence on normal skin, (2) their failure to engender systemic manifestations of infection, such as elevated C reactive protein, sedimentation rate, and white blood cell count, (3) their failure to produce local clinical evidence of infection, such as redness, swelling and tenderness, (4) the low yield of cultures of joint aspiration, and (5) the difficulty in eradicating infections with these organisms. We recently completed a study regarding cultures obtained at the time of revision arthroplasty. The abstract from this as yet unpublished study is reproduced below.

Background: P. acnes is a gram-positive anaerobic bacterium not infrequently cultured at the time of revision shoulder arthroplasty, even when common clinical and laboratory signs of sepsis are absent. Because several weeks of culture incubation can be required to recover this organism, clinical decisions regarding the type of revision surgery and the post-operative antibiotic treatment program must be made before the culture results are finalized. Our goal is to seek prognostic information that would help guide necessary decision-making at the time of surgery.

Methods: The culture results from 193 consecutive shoulder arthroplasty revisions for pain or stiffness, but without clinical evidence of infection, were correlated with a host of preoperative and intraoperative observations. Univariate and multivariate logistic regression models were used to identify factors predictive of a positive culture for P. acnes or other organisms. Results: One hundred and eight of the 193 surgeries had positive cultures; 70% of the positive cultures grew P. acnes. While 97% of the P. acnes cultures were positive by 3 weeks after surgery, only 45% were positive after one week. The prognosis for a positive P. acnes culture was statistically significantly increased for male patients, shoulders with humeral loosening and osteolysis on preoperative x-ray, surgical findings of glenoid wear, osteolysis, membrane formation, and cloudy fluid

as well as cases in which there was a surgical suspicion of infection. We developed a multivariate model to predict P. acnes with 92% sensitivity and 47% specificity.

Conclusions: Preoperative and intraoperative factors can be used to prognosticate the risk of a positive culture for P. acnes. This evidence may be useful in decision making at the time of revision shoulder arthroplasty before the definitive culture results become available.

Thus the diagnosis of infection is usually made from culture at the time of revision surgery, where multiple samples are taken along with frozen sections.  This is why it is so important to avoid administering antibiotics until multiple cultures are obtained to minimize the risk of sampling errors. For this reason we do not start antibiotics after an aspiration in the office or emergency room because of the possibility that this culture may not yield a representative result (i.e., it may be falsely negative or contaminated by skin flora).  If the infection is acute, the organism sensitive to antibiotics, and the patient healthy, we may elect a vigorous debridement of soft tissue inflammation, a surgical scrub of the joint surfaces, and irrigation with copious volumes of antibiotic saline solution.  If the infection is established, we will usually remove all components and cement and then replace only an uncemented humeral component, smoothing the residual glenoid surface if needed. We no longer use antibiotic impregnated spacers, because (1) they seem no more effective in resolving infection than a primary exchange and (2) they obligate the patient to a revision procedure which is usually not necessary in a primary exchange. Culture-specific intravenous antibiotics are used for a minimum of six weeks.

Updated information on the prevalence and diagnosis of Propionibacterium can be found here.

--

Use the "Search the Blog" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including: shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery.

See the countries from which our readers come on this post.