RELIABILITY OF THE NEW MOBILITY SCORE IN HIP FRACTURE PATIENTS

Abstract

Background and Purpose: The New Mobility Score (NMS)(score from 0–9)(1) is being used to evaluate the prefracture functional level and to predict for example mortality in hip fracture patients. Previous studies have found or used a cut-off point of the NMS at 5, but reliability data of the NMS score is currently missing. Reliability refers to the consistency of a test or measurement and it can be quantified as either relative or absolute reliability. Relative reliability is often expressed by the intraclass correlation coefficients (ICC), which indicate the relationship between 2 or more measures of the same score. Absolute reliability is often expressed by the standard error of measurement (SEM). SEM quantifies the precision of individual scores on a test and gives the clinician a result in the same unit as the measurement. The aim of the study was to assess the inter-tester reliability of the NMS in acute hip fracture patients, when obtained by physicians and physiotherapists.

Subjects: Forty eight consecutive hip fracture patients at a median age of 84 (IQR, 76–89) years admitted to a specialized orthopaedic hip fracture unit at a university hospital.

Methods: The NMS, that describes the prefracture functional level, is a composite score of the patient’s ability to perform: indoor walking, outdoor walking and shopping before the hip fracture, providing a score between zero and three (0: not at all, 1: with help from another person, 2: with an aid, 3: no difficulty) for each function, resulting in a total score from 0 to 9, with nine indicating a high prefracture functional level. The NMS was assessed by physicians at the acute ward on admission and by two independent physiotherapists at different postoperative days at the stationary orthopaedic ward. Also, age, mental status on admission and residential status was recorded. The relative reliability was calculated using the ICC 1.1, while the absolute reliability was calculated using the SEM.

Results: The inter-tester reliability was higher between the two physiotherapists at the stationary ward (ICC 0.98) and (SEM 0.42) (95%CI + 0.82) compared to, between physicians at the acute ward and both physiotherapists (ICC 0.87) and (SEM 1.05) (95%CI + 2.06). No systematic between-rater bias was observed (P > 0.05). Patients with different recorded scores were significantly older (P < 0.023) and had lower NMS-scores than those with equal recorded scores.

Conclusion: The relative and absolute reliability of the NMS, when used in acute hip fracture patients, is very high, especially when the score is recorded by physiotherapists at the stationary orthopaedic ward. Ward personal should be extra careful when recording the NMS in subjects with older age and lower NMS and mental scores.