To the Editor:

We read with interest the article published in 2005 by Yian et al. entitled, “Radiographic and Computed Tomography Analysis of Cemented Pegged Polyethylene Glenoid Components in Total Shoulder Replacement” (2005;87:1928-36). Yian et al. demonstrated that, compared to plane X-rays, computed tomography provided a more sensitive and reproducible tool for assessment of lucencies around the glenoid component. However, they acknowledged that visualization of the glenoid fixation was severely blurred by artefacts caused by the metallic humeral head. A further disadvantage of computed tomography is the need for repeated scans if attempting to demonstrate the existence of active biologic processes, i.e. aseptic glenoid loosening. In the shoulder such repeated scans necessarily causes increased radiation exposure of sensitive organs such as breast, lungs and thyroid.

Combining computed tomography slices co-registered with tomographic images from a conventional bone scan (Tc99m HDP/ Oxidronate), namely using Tc99m HDP Bone SPECT-CT, could improve the detection of glenoid aseptic loosening without the need for possibly concerning radiation doses and may provide and important new tool in the decision making to revise the glenoid implant. We chose to test the possible value of this methodology in a patient with a suspected loose glenoid.

The patient was 63 years old when she presented to our clinic. The indication for her primary total shoulder procedure was advanced osteoarthritis. The initial procedure was performed in 1999 in another center. No information on the rotator cuff status or on the evolution of the radiolucent line on plane radiograph were available. The initial outcome was reported by the patient as excellent, with a gradual deterioration over time. The patient presented to our clinic at ten years following the index procedure with persistent and severe pain. Active movement was restricted to 90° of forward flexion and 70° of abduction. On plane X-rays, we noticed a complete radiolucent line around the glenoid component with upward migration of the humeral head (Figure 1). An ultrasound scan confirmed the integrity of the cuff. The analysis of the interface and feasibility of revision of this component was assessed by a CT-scan. The scan demonstrated a wide radiolucent line at the bone cement interface of the glenoid (Figure 2). Subsequently, a Bone SPECT/CT (GE Infinia Hawkeye 4) was performed to assess for a potentially active process around the implant. The images revealed avid tracer uptake that localised to the radiolucent zone on the CT-scan (Figure 3). Because of these observations, the diagnosis of progressive aseptic glenoid loosening was considered highly likely and it was decided to revise the glenoid. At revision surgery, the glenoid component was found to be loose and worn with granuloma formation.

Fig 1. Plane X-rays.

Fig 2. CT-scan with patient in lateral decubitus and the arm elevated: Sagittal, Coronal and Axial views of the glenoid implant and fixation.

Fig 3. Spect-CT demonstrating avid tracer uptake around the glenoid implant fixation.

Bone SPECT-CT finds more and more applications in musculo-skeletal pathology (1). Increased tracer uptake demonstrates active bone turn-over. According to previous use of bone scanning in knee or hip arthroplasty, increased uptake can be visualized for up to 2 years after joint replacement, due to bone remodelling (2). After 2 years, active process around glenoid fixation is very likely to be pathological (2) (aseptic or septic loosening), especially when associated with radiolucent zone on CT-scan. Conversely, CT evidence for lucency or cavities around the implant without increased tracer uptake are probably not of pathological origin.

In conclusion, beside the use of conventional CT-scan, Tc99m HDP-Bone SPECT-CT is an helpful tool to detect glenoid aseptic loosening of shoulder prosthesis and subsequently to aid in the decision to perform revision surgery. This application of SPECT-CT has not been reported previously.

References

1. Scharf S. SPECT/CT imaging in general orthopedic practice. Semin Nucl Med. 2009;39:293-307.

2. Rosenthall L. Hip and knee prostheses: evaluation of the natural history of periprosthetic bone changes. Semin Nucl Med. 1997;27:346-54.