## 4 Discussion  
Many recent studies highlight the ongoing relevance of predictive factors in inpatient rehabilitation, particularly following joint replacement surgery. These works emphasize the importance of understanding how demographic, clinical, and procedural variables impact rehabilitation outcomes and post-discharge care. Our investigation aligns with this growing body of literature, addressing a critically relevant topic in contemporary rehabilitation research [30; 31; 32]. The findings from our large population, single-year monocentric investigation, identify several variables that predict inpatient rehabilitation LOS and BCD. In addition, the study highlights variables that were not predictive and potentially excludes predictors that warrant further investigation in further research. The correlation between aging and osteoarthritis, widely recognized in the literature, is confirmed by the present investigation. This study also confirms that knee osteoarthritis affects women (66%) more than men, whereas this sex difference still exists but tends to diminish when considering hip osteoarthritis, with women accounting for 56% of the cases [33]. Degenerative causes overwhelmingly account for both knee and hip osteoarthritis, far surpassing traumatic and other causes, as 99% of TKRs were performed for primary osteoarthritis, while 95% of THRs were performed for secondary osteoarthritis. In our patient population, age was predictive of a longer inpatient rehabilitation both after hip and knee replacement, while sex was not. Neither age nor sex predicted a higher BCD for both conditions. Primary and secondary hip or knee osteoarthritis were not predictive of a longer inpatient rehabilitation or of a higher BCD. Early patient mobilization is associated with reduced postoperative complications such as blood clots [34; 35; 36], accelerated functional recovery [37], and improved patient-reported outcomes, at least in the short term [38]. Caution is recommended in verticalizing old and/or frail patients too early [37]. This research confirms the benefits of early patient mobilization, possibly extending this finding to elderly patients, considering that they represent the vast majority (about 69%) of the population. However, since most of these patients were admitted to surgery with a moderate ASA score in our study population, prudence remains recommended for patients at higher clinical risk. Patients living with family members tend to have a shorter inpatient rehabilitation LOS, possibly due to their readiness for a safe discharge compared to those having other living arrangements, such as living alone or with non-family members. This is in line with previous observations suggesting that inpatient rehabilitation outcomes are influenced by \begin{table}
\begin{tabular}{l l c c} \hline \hline
**Coefficient of Determination** & **Variables** & **Beta** & _p Value_ \\ \hline \multirow{8}{*}{\(\text{R}^{2}=0.16\)} & Primary hip osteoarthritis & 0.93 & 0.88 \\  & Primary knee osteoarthritis & 0.66 & 0.47 \\  & Total hip arthroplasty & 0.75 & 0.82 \\  & Total knee arthroplasty & 1.72 & 0.68 \\  & **Occupational status** & **1.33** & **0.03** \\  & **Surgical time** & **0.84** & **<0.001** \\  & Surgical ward LOS & 1.00 & 0.54 \\  & **Barthel Index at admission** & **0.96** & **<0.001** \\  & **Verticalization time** & **0.64** & **<0.001** \\  & **Barthel Index at discharge** & **0.95** & **0.02** \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Predictors of BCD after THR and TKR aggregated. levels of social support [39; 40; 41]. Unemployed and retired patients have slightly longer inpatient rehabilitation LOS. On the one side, this correlation may be explained by their older age, which would be the real predictor of a longer stay. Conversely, working patients may have more urgency to recover and return to work, possibly motivating more engagement.