These authors illustrate that the clinical findings of detritic synovitis (the macrophage reaction to polyethylene, cement or metal debris) complicating a total shoulder arthroplasty can strongly resemble those of a ‘stealth’ periprosthetic shoulder infection with a low-virulence organism such as Propionibacterium, including a clinical presentation long after the index procedure. At present, the important differentiation between these two etiologies can only be ascertained by awaiting the results of cultures obtained at the time of revision surgery. The surgical and antibiotic treatment decisions must be made before the culture results become available.
Here is an informative case. A 76-year-old right hand dominant man presented with right shoulder pain and decreased range of motion. He had a history of bilateral total shoulder arthroplasties, his left 15 years prior and his right 14 years prior to his visit with us. Following his index surgeries he initially did well with full painless range of motion and was able to return to full activities. Eleven years after his right arthroplasty he experienced the insidious onset of worsening shoulder pain and stiffness with no known injury. He also noted painful catching and locking in his shoulder joint with certain shoulder movements. His symptoms were unresponsive to non-operative treatment, including exercises, anti-inflammatory medications and a corticosteroid injection. His left shoulder had some stiffness but was otherwise asymptomatic. The CBC, sedimentation rate and C-reactive protein were all normal.
Physical examination demonstrated a well-healed surgical scar with no erythema, drainage or evidence of infection. Both active and passive ranges of motion were decreased. There was palpable crepitus on range of motion. Rotator cuff strength was intact, as was neurologic function of the affected extremity. Radiographs demonstrated a thinned glenoid component with surrounding osteolysis, appearing grossly loose. The humeral component was well positioned with surrounding osteolysis of the medial and lateral proximal humeral bone. There were no radiolucencies around the distal stem and the prosthesis did not appear grossly loose.
There was diffuse membranous tissue around both
the humeral and glenoid components. There
was osteolysis of the proximal humerus, but the humeral component was securely
fixed ; it was removed without complication. The glenoid component was grossly loose and
easily removed. There was significant
wear of the glenoid polyethylene and osteolysis of the underlying glenoid
bone. The rotator cuff was intact.
A total of 8 samples for culture were taken from
various locations within the glenohumeral joint, including the glenoid
membrane, collar membrane between the modular humeral head and stem, humeral canal
membrane, bursa, glenoid explant, and stem explant. Due to preoperative and intraoperative
concerns of infection, including cloudy fluid, abundant membrane, glenoid
loosening and osteolysis, the patient was treated with a one-stage revision
consisting of removal of the loose glenoid and single stage exchange of the
humeral component using Vancomycin soaked cancellous allograft to secure the
stem by impaction grafting. The
remaining glenoid bone was smoothed, no bone graft was added, and no glenoid
component was reimplanted. Cultures were
grown on four types of media: blood agar, chocolate agar, Brucella agar and
brain-heart infusion broth as previously published. Postoperatively the patient was placed on IV
Ceftriaxone 2g daily and Vancomycin 1g daily via PICC line. The Vancomycin was discontinued after 2 days
when the cultures failed to grow MecA CoNS. All cultures were negative at 21 days at which
time all antibiotics were discontinued. Permanent
pathology of the deep tissues identified fibrotic tissue with chronic
inflammation, the absence of neutrophils, and a foreign body giant cell
reaction consistent with detritic synovitis
After surgery, he was placed on the standard post arthroplasty rehabilitation program focusing on range of motion in the first six weeks, followed by progressive anterior deltoid strengthening. At his six-month follow up visit, the patient was recovering well with no complaints of pain. His Simple Shoulder Test had improved from 5 out of 12 prior to his revision to 10 of 12, and radiographs showed a well-fixed humeral component.
Comment: In this case, it seems unlikely that the cultures in this were falsely negative – multiple tissue and explant specimens were obtained before antibiotic administration, the specimens were cultured on multiple media and observed for 21 days. Thus, we must consider the possibility that the detritic synovitis from polyethylene debris produced osteolysis and periprosthetic membrane formation similar to that of a Propionibacterium infection. Until better methods become available for differentiating the two conditions, our practice is to continue to treat shoulders with osteolysis and glenoid component loosening as if they were infected until cultures prove this not to be the case.
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