Patterns of bone tracer uptake on SPECT-CT in symptomatic and asymptomatic patients with primary total hip arthroplasty

The primary purpose of this study was to compare bone tracer uptake (BTU) on SPECT/CT in symptomatic and asymptomatic total hip arthroplasty (THA) and identify a possible relationship between BTU patterns and patient's symptoms. The secondary purpose was to investigate if the fixation methods (cemented versus uncemented) lead to different BTU patterns.

A total of 58 THAs, 31 symptomatic (group S) and 27 asymptomatic (group AS), were prospectively collected and retrospectively analyzed. All symptomatic patients underwent standardized detailed history, clinical examination, radiographs and 99mTc-HDP SPECT/CT. BTU in SPECT/CT was quantified in three dimensions and anatomically localized in a scheme of quadrants and levels using a customized previously validated software. T tests were used on both quadrants and levels inside and between groups. A Pearson correlation was performed for BTU within the quadrants. An area under receiver operating characteristic curves was drawn in order to find a BTU value that could differentiate the two groups. Within the groups, patients with cemented and uncemented stems were compared for influences on BTU intensity.

The causes of pain were identified in 61% of the patients. The most common problem was aseptic loosening (n = 12). In group AS, levels 1, 2 and 5 had similar BTUs. BTUs in these levels were significantly higher than in level 3, 4 and 6. In group S, no significant differences were seen in terms of BTU in level 1-5. However, BTU here was significantly higher than at level 6 (p < 0.001). In both groups, level 1, the superior, had a significantly higher BTU than level 2 (group AS p < 0.01, group S p < 0.05). Comparing the BTU of the two groups among levels, significant differences were found for level 4, level 5 and the entire stem areas (p < 0.05). The ROC curve calculated on the whole stem allowed identification of a BTU ratio of 3.1 that separated the 92.6% patients of group AS with BTU < 3.1 from the 54.8% of patients of group S with a BTU ≥ 3.1. With regards to the fixation technique, only the BTU at the level 6 in group S presented a significant difference between cemented and uncemented stems (p < 0.05).

Higher BTU levels significantly correlated with symptoms, but a normal BTU could not exclude a specific pathology after THA. A threshold of BTU in SPECT/CT was identified to distinguish between symptomatic and asymptomatic patients after THA.