17.1 What Is Function?

Physical function has long been considered an important aspect of the individual′s quality of life; indeed, the quote “motion is life” is attributed to Hippocrates. Function, though, is not simple to define as it refers not just to motion, but the ability to perform unaided controlled voluntary and purposeful activity within a social context. This is reflected in the World Health Organization′s definition of health as a state of complete physical mental and social well-being—not merely the absence of symptoms. Functional activity encompasses the tasks and activities that a person performs, ranging from fundamental activities such as eating and locomotion through to work, recreational activities, and sport.

17.2 Assessing Function

The difficulty in assessing the function of an individual is in the breadth of the definition of function. There is really no limit to what can be tested: range of joint motion, muscle strength, time taken to perform tasks, posture, balance, proprioception, and motor skills/coordination. This can comprise assessment of walking, running, hopping, kneeling, lunging, pushing, pulling, gripping, and so on. It is vital to consider the context in which function applies to the subject or patient being tested; elderly fracture patients with multiple comorbidities and chronic diseases require a very different type of functional assessment than the young knee arthroscopy patient. It should also be recognized that in a clinical context what we really wish to measure is not function, but dysfunction—or how far removed from the patient′s “normal function” the individual is as a result of his or her condition, or indeed our treatment of it.

17.3 Measuring Function

Though there are potentially infinite physical tests, broadly speaking there are two ways in which to assess the function of a patient: Ask them or measure them.

Self-report assessments are ones in which individuals are asked to report their perceived level of functioning during daily activities described in standardized questions. 5 Broadly, these questionnaires fall into three categories: generic health assessments, disease-specific instruments, and joint-specific tools. Generic scores allow comparison across different disorders and surgeries but may not be sensitive to detect specific functional changes. Disease-specific scores may be more sensitive to change following intervention but lack generalizability across different groups. Another criticism of disease-specific scores is that they cannot isolate the function of individual joints. As such, if one wishes to assess patient function, following joint arthroplasty for example, an arthritis-specific score could be used, but this would assess the overall pain and function of the individual, and be influenced by pain and dysfunction in other joints. Joint-specific scores, then, are the most commonly employed tools following interventions to individual joints. Clearly, however, these apply only to the joint in question. A combination of these scores may then form the best outcome analysis.2, 6 Much has been written about these self-report scores, and a good review can be found in Clinical Research for Surgeons (part of this series) (see Further Reading).

Patient-reported outcome measures are commonly used as they are comparatively cheap, effective at collecting large volumes of data, and do not require follow-up clinic visits to achieve this. A disadvantage of these patient report–based scales for assessing postoperative function is that what they actually measure is the patient′s perception of their function and are thus subjective.6, 7 As a consequence, they are thought to be highly influenced by pain, which affects their content validity.5,6,7 High levels of content validity are required to evaluate biomechanical aspects of function, and generally, performance-based measures demonstrate this.

17.4 Performance Measures

Terwee et al5 define a performance measure as one in which the individual is asked to perform an activity that is evaluated in a standardized manner using predefined criteria, such as time taken. Essentially any activity can be a test of function, as long as it is conducted in a reproducible fashion with a defined start and end to the test and some way to quantify the result. Various tests have been proposed and many validated for calculating the limitations conferred by specific conditions or for assessing improvement following a particular surgery. Typical examples include simple walking or step tests (measured either in distance or time), or more demanding activity such as treadmill or cycle ergometer protocols. Composite measures that employ assessment of multiple activities are thought to be more valid than those that assess only one aspect of function such as walking tests; an example being patients with mild osteoarthritis who are unaffected during walking but may have difficulty in climbing stairs or rising from chairs.5 There are various multiactivity tests that have been validated for use in specific situations. In general, these are broadly very similar to each other and no one combination has proven more effective than another.

17.5 Activities of Daily Living

Again, a variety of measures are available to the researcher with which to assess the impact of the disease/procedure on the patient′s daily activity. A simple analysis can be conducted with tools such as the Barthel Index, which assesses the ability of the patient to complete 10 activities of daily living independently, with a score awarded out of 100 (representing complete independence). Activities of daily living include feeding, toileting, bathing, dressing, walking on a level surface, and transferring. Clearly, this is aimed at the more disabled patient, perhaps one on a protracted hospital ward stay following a hip fracture.

Walking ability and exercise tolerance can be readily measured in a laboratory or outpatient setting, but this is often not representative or realistic of the daily activity undertaken at home. Activity diaries have been widely used in a rehabilitation context to try to monitor this, though they have proven somewhat unreliable. More recently, portable accelerometers have been developed with which to record the patient′s movements. Various models are available that can assess the amount of time the patient spends walking, standing, or sitting; daily energy expenditure can be calculated from this. While relatively unobtrusive, because they are generally attached to clothing or worn against the skin with adhesive tape, these are of course more expensive and require charging and cleaning between patient uses.