Predicting hospital length of stay and short-term function after hip or knee arthroplasty: are both performance and comorbidity measures useful?

PURPOSE: Variations in hospital length of stay (LOS) and function are present after hip or knee arthroplasty. Comorbidity and performance measures have been associated with post-operative outcomes. It is however not known if both independently contribute to outcome prediction. The objective of this study was to evaluate the combined predictive ability of comorbidity scores (American Society of Anesthesiologists classification system (ASA), Charlson comorbidity index (CCI), 2008 version of the CCI (CCI08)) and a performance measure (Timed-Up-and-Go (TUG)) on LOS and short-term function in patients undergoing knee or hip arthroplasty.

METHODS: One hundred eight patients undergoing hip or knee arthroplasty were assessed preoperatively with the ASA, CCI, CCI08, and TUG. LOS was determined through administrative data. The Older Americans Resources and Services ADL questionnaire (OARS) was used to assess function two and six weeks after surgery. Logistic regression was used to assess the relationship between pre-operative assessments and LOS and OARS scores.

RESULTS: Both the ASA and TUG significantly contributed to LOS prediction. Odds ratio (OR) was 3.57 (95% confidence interval (CI) 1.26-10.07) for the ASA, and 2.18 (95% CI 1.67-4.15) for a one-standard deviation (SD) increase of 4.45 s of the TUG. Only the TUG was predictive of two weeks function and trending towards significance for six weeks function. One SD TUG increase yielded an OR of 2.14 (95% CI 1.53-3.79) for two week function.

CONCLUSIONS: The TUG and ASA can be used pre-operatively in combination to predict LOS, and TUG can also be used to predict short-term post-operative function.