The number of patients who receive a shoulder arthroplasty is steadily increasing [11–14]. The spectrum of devices includes resurfacing techniques, and partial prosthesis up to complex inverse prosthesis types [12, 13]. Compared with other joints, the spherical component of the head causes strong beam hardening artefacts that make it difficult to analyze the images. The orthopedic point of view focuses on the following questions:

The literature regarding the use of SPECT/CT in shoulder prostheses is limited to case reports [11].

Practical recommendations:

Hip arthroplasty is currently one of the major orthopedic arthroplasty procedures. Indications are: unexplained pain in the postoperative setting (15–20% of all patients), suspicion of loosening, suspicion of infection, and detection of other/additional causes of pain such as spine pathologies. Before analyzing the images the following questions should be answered:

It is very important to differentiate between cemented and uncemented types of prosthesis. The uncemented shafts usually show a proximal or distal fixation zone where enostal thickening of the bone associated with focal higher uptake can appear. This is equivalent to a biomechanical stress reaction and physiological bone remodeling process, which should not be misinterpreted as aseptic loosening (Fig. 2). Usually — with the exception of the new hydroxyapatite-coated femoral shafts — a small boneless margin (smaller than 2 mm) around the shaft can be seen. Every focal widening or irregularity is suspicious of loosening. The cortical bone should be homogeneous. Distal periostal thickening distal is suspicious of micromotion of the shaft and can indicate loosening in cases of a proximal fixed prosthesis.

In cases of a cemented shaft, the cement layer should not show any sign of breaking, which is a clear sign of loosening. Osteopenic areas, especially in the trochanter, can indicate either cement problems (a thin layer that cannot distribute the pressure adequately) or component malposition, such as varus with high pressure in the trochanter minor (higher focal uptake) and less pressure in the trochanter major (less uptake). In cases of an uncemented cup, uptake can usually be seen in the cranial parts of the acetabulum, where the main force vectors are located. Any other uptake localization should lead to careful evaluation of the acetabular bone to exclude osteolysis/ granulomas and pathological margins >2 mm. In cases of wide margins and large granulomas, the pathology is often seen in the CT scans only, and the scinti — graphy is negative. This pathology can be missed on planar images and SPECT alone. Some cups are fixed by winding in the bone. In these cases, small focused margins and only focal missing contact between the winding and the bone is normal and is related to the operative technique. These morphological patterns do not represent any loosening. Particularly in revision surgery, the cups are often fixed with additional screws. The analysis should consider material failure. The screws should not reach far into the pelvis as this can cause muscle problems (irritation or hematoma in the iliacus muscle) or pelvic nerve irritation. For cemented cups, the same criteria used for the shaft can be applied. Subsequently, the head should be assessed to detect signs of wearing, which is usually seen as asymmetric narrowing of the joint space. It is necessary to at least have a close look at the soft tissue (is there presence of a hematoma or pseudotumor?) and ectopic ossifications, which sometimes show an inflammatory component in the early phase or can cause mechanical problems limiting the range of motion.