[Validity of bone scintigraphy for the diagnosis of periprosthetic complications in hydroxyapatite-coated total hip arthroplasty].

PURPOSE OF THE STUDY

To evaluate the efficacy and usefulness of 99Tc-MDP bone scans for the diagnosis of complications associated with hydroxyapatite- coated total hip prostheses.

MATERIAL AND METHODS

99Tc-MDP bone scans of 42 hips were taken before revision surgery in 41 patients with ABG 1 prostheses. Of these, 26 patients (27 hips) were included in our study on the basis of the following criteria: at least 23 months between the index surgery and scintigraphic examination and the availability of good quality bone scans. The average patients' age at the time of index and revision operations was 45.3 years (range, 32-57; SD, 6.02) and 50.2 years (36-61; SD, 6.01), respectively. The average time between the index surgery and bone scintigraphy was 50.3 months (23-84; SD, 15.9). Two experienced specialists in nuclear medicine, who were unaware of any clinical conclusions, participated in the study.

RESULTS

Pre- and intra-operative findings showed aseptic loosening in three cups (3/27, 11 %) and one stem (1/27, 4 %). Four hips were suspected to have an infection on the basis of the positive results of intra-operative culture. In the diagnosis of aseptic loosening, sensitivity, specificity, accuracy, and positive and negative predictive values of bone scintigraphy were 100 %, 57 %, 62 %, 23 %, and 100 %, respectively, for the ABG I cup and 100 %, 52 %, 54 %, 8 %, and 100 %, respectively, for the ABG I stem. These characteristics were 67 %, 96 %, 93 %, 67 %, and 96 %, respectively, for the ABG I cup, when plain X-ray was used for evaluation of aseptic loosening. Specificity, accuracy and negative predictive value of plain X-ray for ABG I stem aseptic loosening were 100 %, 96 %, and 96 %. Bone scintigraphy gave one false positive result of sepsis; on the other hand, none of the four hips with positive intraoperative culture was diagnosed as septic.

DISCUSSION

The fact that 99Tc-MDP bone scintigraphy as a method of diagnosing periprosthetic complications has a high sensitivity and a relatively low specificity has often been discussed in the literature. Currently, there are only a few studies on bone scintigraphy investigations of hydroxyapatite-coated prostheses. Some authors report that a slight increase in peri-prosthetic radionuclide activity may persist for up to 8 years which can explain the problematic accuracy of the technique.

CONCLUSIONS

99Tc-MDP bone scintigraphy is an intermediate useful tool for detecting complications of total hip arthroplasty with hydroxyapatite- coating. A negative bone scan almost always suggested the absence of aseptic loosening. However, the value of a positive result was regarded as controversial for the diagnosis of both aseptic and septic complications.