University of Groningen
The Measurement and Prediction of Physical Functioning after Trauma
de Graaf, Max Willem
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Publication date: 2019
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de Graaf, M. W. (2019). The Measurement and Prediction of Physical Functioning after Trauma. Rijksuniversiteit Groningen.
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Chapter 9
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Summary
Traditionally, outcome of treatment of trauma patients has been assessed by means of objective outcome measures, such as vital parameters, labora-tory tests, mortality and bone healing assessed by radiographic imaging. The traditional clinical ways of measuring health and the effects of treatment are increasingly accompanied by patient-reported outcome measures (PROMs), which are more appropriate instruments to investigate complex domains.
The Short Musculoskeletal Function Assessment (SMFA) is a 46-item long PROM that has been designed as an instrument to measure physical functi-oning in patients with a broad range of musculoskeletal conditions. Howe-ver, the clinimetric properties of the Dutch SMFA (SMFA-NL) have not been evaluated in patients with acute traumatic injuries. Before the SMFA-NL can routinely be used in patients with acute injuries, an analysis of the clinimetric properties of the SMFA-NL is needed. In addition, an appropriate interpretabi-lity of a (change in) score is a prerequisite for the use the SMFA-NL in clinical practice. In order to make the scores of the SMFA-NL interpretable, additional information is necessary to place single scores and changes in scores within a clinical context.
The aim of this thesis was to evaluate the quality of the SMFA-NL questi-onnaire with regard to the ability to evaluate physical functioning in patients that sustained a broad range of acute traumatic injuries. This aim was divided in two parts. The first part was to evaluate the clinimetric properties of the SMFA-NL. The second part was to investigate the clinical applicability and interpretability of the SMFA-NL.
Part one of this thesis
The SMFA was originally designed to evaluate two latent constructs: patients’ physical status (Function Index) and how bothered they are by functional problems due to the musculoskeletal conditions (Bother Index). Later, it was argued that the SMFA may be better interpreted by three, four or six subscales, instead of the original two. In chapter 2 it was investigated which of the previously proposed subscale configurations provided best structural validity. By means of a confirmatory factor analysis it was shown that only the four-factor structure showed good structural validity. The SMFA-NL may therefore be used to evaluate four latent constructs using the subscales Upper Extremity Dysfunction (6 items), Lower Extremity Dysfunction (12 items),
Problems with Daily Activities (20 items) and Mental and Emotional Problems (8 items). The original two-index structure showed insufficient structural vali-dity. Clinical use of the structures that showed insufficient structural validity was discouraged.
The aim of chapter 3 was to assess test-retest reliability, construct validity and responsiveness of the four subscales of the SMFA-NL in patients that sustained acute traumatic injury. A total of 248 patients participated in a prospective longitudinal cohort study, among which 145 patients completed questionnaires 8 weeks post-injury (test retest reliability) and 160 patients completed the questionnaires 6 months post-injury (responsiveness). The SMFA-NL showed good to excellent reliability for all subscales. The smallest detectable change (SDC) is the smallest change in score that can be considered not due to measurement error. The SDC was 17.4 points for the Upper Extre-mity Dysfunction subscale, 11.0 points for the Lower ExtreExtre-mity Dysfunction subscales, 13.9 points for the Problems with Daily Activities subscale and 16.5 points for the Mental and Emotional Problems subscale. This research showed that the SMFA-NL has sufficient construct validity and adequate responsive-ness. Therefore, the SMFA-NL may be used in clinical practice and research as a measurement instrument to evaluate physical functioning at one moment, and as an instrument to evaluate change in physical functioning over time.
Part two of this thesis
One of the methods to improve interpretability of the SMFA-NL, is by investigating what is a normal score of the general population. In chapter 4 900 people of the Dutch population were invited to fill in the SMFA-NL ques-tionnaire, of which 875 participants responded. Normative data were provided for the complete population, as well as for gender and age stratified groups. A significant interaction effect was found between gender and age for the upper extremity dysfunction subscale. A larger decrease in score with increasing age was observed for women, compared to men. The SMFA-NL normative data provide an opportunity for benchmarking physical functioning of participants with musculoskeletal conditions against their age- and gender-matched peers from the Dutch population.
In chapter 5 the difference in pre-injury health status of acute traumatically injured patients and the health status of the Dutch population was evalua-ted. A broad range of patients with acute traumatic injuries completed the
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SMFA-NL, within two weeks after the injury. Differences between the norma-tive data and scores of patients with acute traumatic injurie were adjusted for patient characteristics (gender, age, educational level, relationship status and comorbidity). A total of 596 patients with acute traumatic injuries completed the questionnaires. The unadjusted difference in health state values between both groups were similar to previous studies. The differences in SMFA-NL scores were smaller after adjusting for patient characteristics, yet remained statistically sifgnificant. General characteristics explained an important part of the difference in health status between patients with acute traumatic injuries and the general population. The adjusted differences between patients with acute traumatic injuries and the general population were very small, therefore the differences were considered not clinically relevant.
In Chapter 6, minimal important change (MIC) values for the subscales of the SMFA-NL were obtained. The MIC value reflects the smallest change in score that is considered an important change by patients. A total of 225 patients completed the SMFA-NL at 6 weeks and 12 months post injury. The MIC value of the Upper Extremity Dysfunction subscale was 9 points, with a misclassification rate of 43%. In this context misclassification meant: the percentage of patients that was falsely classified as ‘importantly changed’ or ‘not-importantly changed’. The Lower Extremity Dysfunction subscale MIC value was 14 points, with a misclassification rate of 29%. The MIC value of the Problems with Daily Activities subscale was 26 points, with a misclassification rate of 33%. The MIC value of the Mental and Emotional Problems subscale was 5 points, with a misclassification rate 37%. The MIC values can be used to evaluate whether a change in physical functioning, can be considered clinically important. Due to the considerable rates of misclassification the MIC values of the Upper Extremity Dysfunction and Mental and Emotional Problems subscales should be used with caution.
In Chapter 7, the PROgnosis of functional recovery after Trauma (PRO-Trauma) prediction model was developed and internally validated. In a prospective longitudinal cohort study, 246 patients were included. Patients reported their physical functioning at 6 weeks and 12 months post-injury by means of the SMFA-NL. The predictors in the final PRO-Trauma model were: living with partner, the number of chronic health conditions, SMFA-NL Problems with Daily Activities subscale score at 6 weeks post-injury and length of stay in hospital. The model showed sufficient calibration and discrimination,
which means that the model provides acceptable predictions of gaining func-tional recovery 1 year after trauma. The PRO-Trauma prediction model can be used to obtain valid predictions of reaching functional recovery after trauma at 12 months post-injury, and may be regarded as an initial exploring step in the direction of the development of prognostic models that predict outcome after trauma, rather than mortality. Additional external validation of the PRO-Trauma prediction model with data of a different hospital is required to evaluate the validity and performance of the model.
The general discussion in Chapter 8 provided an overview and discussion of the main findings reported in this thesis. Regarding part one of this thesis, the current evidence regarding the clinimetric properties of the SMFA-NL were reviewed in a wider perspective. Based on the findings in this thesis, as well as previous research regarding the SMFA(-NL), it was concluded that the SMFA-NL can be regarded a high-quality measurement instrument with good clinimetric properties. Connotations were made about the current limitations of the PROM, which mostly concern the ceiling effects that were observed for Upper Extremity Dysfunction subscale and restrictions regarding the popu-lation in which the SMFA-NL may be applied.
In the second part of this thesis the interpretability of single scores and changes in scores of the SMFA-NL were evaluated. It was concluded that single scores of the subscales of the SMFA-NL are well-interpretable, since norma-tive data are known and the distribution scores of several groups of injured patients are known. Changes in physical functioning were more difficult to interpret, mainly due to considerable misclassification rates of the MIC values. Several clinical implications were given, such as the routine application of the SMFA-NL in individual patient care as a follow-up instrument, or as a part of a prognostic model, which was developed and internally validated.
In the last part of the general discussion it was emphasized that the domain of participation limitations of the ICF model should be investigated further. Currently, this domain is rewarded little attention. It is a not-well understood part of the ICF model and little is known how this domain can be used to improve patient care after trauma. Furthermore, suggestions were made to improve the standardization of PROMs using a more modern testing theory (item response theory). One advantage of item response theory is that it can facilitate a shift to the use of item banks rather than a widespread of individual questionnaires. Furthermore it provides an opportunity for the incorporation
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of modern technology in the administration of PROMs by the use of compu-ter-adaptive testing. Finally it was emphasized that future research is required to evaluate which of the treatment options should be preferred in terms of functional outcome after trauma.
