Objective: To compare the diagnostic value of ^99mTc-MDP SPECT/CT and MSCT in detecting thoracic wall and rib involvement in lung adenocarcinoma. Methods: A retrospective analysis was conducted on the imaging data of 78 thoracic wall and rib lesions from 66 patients, a total of 32 males and 34 females, aged (53.2 ± 5.6) years old with pathologically confirmed lung adenocarcinoma who underwent both ^99mTc-MDP SPECT/CT and MSCT examinations from March 2017 to September 2023. The diagnostic efficacy of the two imaging modalities was compared using pathological confirmation or clinical follow-up as the gold standard. Results: Pathological confirmation or clinical follow-up revealed 74 lesions with thoracic wall bone involvement in lung adenocarcinoma (20 lesions confirmed by surgical pathology and 54 lesions confirmed by clinical follow-up) and 4 lesions without thoracic wall or rib involvement (2 lesions confirmed by surgical pathology and 2 lesions confirmed by clinical follow-up). The diagnostic sensitivity, specificity, and accuracy of ^99mTc-MDP SPECT/CT were 97.3%, 50.0%, and 94.9%, respectively. Its diagnostic sensitivity and accuracy were higher than those of MSCT (72.3% and 74.4%, respectively), with statistically significant differences (P < 0.05). The specificity of ^99mTc-MDP SPECT/CT was lower than that of MSCT (100.0%), but the difference was not statistically significant (P < 0.05). There were no statistically significant differences in the positive predictive value and negative predictive value between ^99mTc-MDP SPECT/CT and MSCT (P > 0.05). ^99mTc-MDP SPECT/CT examination revised the MSCT tumor staging in 14 patients [21.2% (14/66)] with lung adenocarcinoma. Conclusion: ^99mTc-MDP SPECT/CT imaging demonstrates superior diagnostic efficacy compared to MSCT in detecting thoracic wall and rib involvement in lung adenocarcinoma. It offers more accurate tumor staging than MSCT, and an accurate diagnosis aids in clinical treatment decision-making.