SPECT-CT may aid in determining which side of a revision stemmed implant problematic total knee replacement is loose when planning revision surgery

Aim: To evaluate SPECT-CT in the diagnosis of single component aseptic loosening in patients with a problematic cemented stemmed TKR (Total Knee Replacement).

Methods: SPECT-CT was performed where aseptic loosening was suspected but was not clear on plain radiography. Demographics, suspected diagnosis and intention to revise were collected prospectively before and after SPECT-CT.

Results: 30 patients were investigated. 43% (95% CI: 0.5-0.9) had clear evidence of loosening on SPECT-CT. In 23% (95% CI: 0.1-0.4) intention to perform revision surgery following SPECT-CT changed (7/30) (p = 0.0004, standard error = 42.1, z = 3.5). Intentions to perform revision surgery according to the radiologist's overall summary were: Normal SPECT-CT - 0% (95% CI: 0.0-0.8) intention to revise (0/2). Possibly abnormal SPECT-CT - 13% (95% CI: 0.0-0.4) intention to revise (2/15). Definitely abnormal SPECT-CT - 77% (95% CI: 0.5-0.9) intention to revise (10/13). We report that SPECT-CT had a test sensitivity of 90.9% (95% CI: 0.6-1.0), a specificity of 100% (95% CI: 0.9-1.0), a positive predictive value of 100% and a negative predictive value of 97.7%. In 70% (95% CI: 0.3-0.9) of cases where revision surgery was performed for aseptic loosening SPECT-CT provided information that guided pre-operative planning with regards single component or both component revision surgery (7/10).

Conclusion: When positive SPECT-CT was useful in determining single component revision. A normal SPECT-CT may have a negative predictive value; however, overall half of our series had a possibly abnormal or equivocal investigation.