PURPOSE: To assess osseointegration and stability of a primary cementless femoral stem, many scoring systems have been developed, but none of them have taken into account only the radiolucent line. The purposes of this study were (1) to compare the results between the Engh score to assess osseointegration and stability of the cementless stem with results of a score called the O-SS score (osseointegration-secondary stability), which takes into account the radiolucent line, (2) to verify the relationship between these two scores and the functional results, and (3) to verify if there is a relationship between the O-SS score and secondary subsidence or a pedestal. METHODS: A clinical and radiological evaluation was performed in a group of 100 hip prosthesis revisions comparing the results obtained by Engh score and O-SS score for which reproducibility was analysed. RESULTS: Inter-observer reproducibility was estimated to be average at 0.5 and intra-observer reproducibility good at 0.7. The correlation with the Engh score was good at r = 0.59 (p < 0.0001). For the 80 cases assessed O-SS score as very good/good, Harris hip score was at 83.7 versus 78.25 for the 20 cases assessed as average/poor (p = 0.07). For the 73 cases with assessed Engh score as very good/good, this score was at 82.8 versus 82.14 for the 27 cases assessed as average/poor. No correlation between the O-SS score and secondary subsidence (p = 0.2) or pedestal (p = 0.2) was noticed. CONCLUSION: The evaluation of the clear radiolucent line alone, extent and location, is a sufficient condition to assess osseointegration and secondary stability of a cementless femoral stem.