These authors reviewed 14 patients with a painful total shoulder arthroplasty and suspected glenoid component loosening but inconclusive plain radiographs. They performed a CT arthrogram to access for the presence or absence of contrast material underneath the polyethylene component, followed by arthroscopy to obtain soft tissue biopsy specimens (held for 21 days) to rule out infection.
They found that CT arthrography suggested glenoid component loosening in 8 of 14 patients (57.1%), and arthroscopic inspection identified loosening in 10 of 14 patients (71.4%). In 3 of 10 patients (30%), CTA suggested a well-fixed glenoid component, but gross loosening was identified during arthroscopy. Infection, each with Propionibacterium acnes , was subsequently identified in 5 of 14 patients (35.7%).
Comment: One of the questions surfaced by this paper is the definition of glenoid component loosening. As shown in the radiographs below, bone cement used to fill in the gaps between the glenoid bone and the back of the prosthesis does not bond to the glenoid bone surface. Surface cement does not contribute to glenoid component fixation. Rather it fills in the space left when glenoid reaming did not adequately contour the bone to the back of the component - carpenter's putty. As a result it can enable the glenoid component to wobble with eccentric loading giving rise to the rocking horse phenomenon shown at the arrow. In many of these situations (as in the case below) the pegs may be securely fixed to the glenoid bone. Is that glenoid loose or not? If one defines loosening as the ability to slip a probe between the back of the component and the bone, then it is. If one defines loosening as the ability to easily lift the component off the bone, then it is not.
By contrast when there is lucency around the pegs, as shown below, there is real concern for the fixation.
Our practice is to carefully ream the glenoid bone so that it fits the back of the component so that a thin (and brittle) layer of cement on the glenoid face can be avoided. See this link.
Our practice is to carefully ream the glenoid bone so that it fits the back of the component so that a thin (and brittle) layer of cement on the glenoid face can be avoided. See this link.
The second point raised by this article is the high rate of positive cultures for Propionibacterium in these painful shoulders with inconclusive radiographs - over 1/3.
The final point is to wonder if whether CT scans or arthroscopy substantially changes the management of a painful total shoulder arthroplasty. If a patient has refractory shoulder pain after a total shoulder without obvious cause, he or she may wish to consider an open surgical exploration that includes evaluation of the capsular balance, rotator cuff, subscapularis, component fixation, and glenoid wear as well as cultures of tissue and any explanted components. We describe our approach in this link.
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