Morbidity following hip and knee arthroplasty has previously been poorly recorded. This is the first time the Post-Operative Morbidity Survey (POMS) has been used for this purpose. The POMS identifies clinically significant morbidity using indicators of organ system dysfunction rather than traditional diagnostic categories. The most common types of morbidity following hip and knee arthroplasty are infection and renal morbidity. Pulmonary, pain and gastro-intestinal morbidity are less common. Cardiovascular, wound, neurological and haematological morbidity are least common. Many arthroplasty patients remain in hospital without morbidity. The POMS identifies these patients and thus has potential as a prospective bed utilisation tool. To be used for this purpose, the POMS must identify all clinically significant morbidity. Mobility is an important factor for safe discharge of arthroplasty patients. Addition of a ‘mobility’ domain could improve the utility of POMS as a bed utilisation tool following orthopaedic surgery. This study showed no association between post-operative morbidity defined by the POMS and longer-term patient-reported outcome measures (PROMs). This study does not support the POMS as an early surrogate marker of long-term PROMs in orthopaedic patients. The wound domain of the POMS has a high specificity, reasonable sensitivity, high negative predictive value and low positive predictive value compared to the inpatient ASEPSIS (Additional treatment, Serous discharge, Erythema, Purulent exudate, Separation of deep tissues, Isolation of bacteria, inpatient Stay over 14 days) score. The wound domain of POMS could be replaced with a validated definition of wound infection such as ASEPSIS. On the same series of orthopaedic patients, surgical site infection (SSI) rate according to the Centres for Disease Control (CDC) definition was 15.45%, according to the Nosocomial Infection National Surveillance Scheme (NINSS) definition was 11.32% and according to the ASEPSIS definition was 8.79%. This highlights the need for a consistent definition of SSI
