Patient Specific Functional Scale (PSFS)

PSFS explained

This is a functional assessment scale that allows adult patients to quantify the impact pain and disability has on how they perform activities of daily living.

The patient needs to be instructed to choose activities that they considered are impaired by their current status or that they are not performing as they used to, because of their disability.

Because the five activities are highly customizable, the scale can address individual needs and the score result is fast to calculate and interpret.

This is a list of the patient populations in which the PSFS has been tested:

■ Neck Dysfunction and Whiplash;

■ Upper Extremity Musculoskeletal;

■ Low back pain;

■ Spinal Stenosis;

■ Pubic symphysis pain in pregnancy;

■ Joint Replacement;

■ Knee Dysfunction;

■ Lower Limb Amputees;

■ Multiple Sclerosis.

The patient specific functional scale was compared to the Roland Morris Disability Questionnaire, the severity rating scale addressed to patients with low back pain.

The PSFS shows more reliability and sensitivity than RMDQ as specific measure in cases with low levels of activity limitation, however, in cases with higher levels of daily activities limitation caused by LBP, the RMDQ is more reliable.

There are other functional models that use a visual or numerical scale, like the Bath Ankylosing Spondylitis Functional Index (BASFI).

Result interpretation

Each of the five activities needs to be rated by the patient on a scale from 0 to 10, in increments of 1. The higher the score, the less difficulty the patient encounters when performing the activity.

Activities that rate closer to 10 are likely to be very little impaired and are performed in a similar manner as they used to be before the injury occurred.

Average results closer to 0 indicate an increased loss of functionality due to the debilitating condition.

Final score = Sum of the activity scores / Number of activities registered

The minimum detectable change (90% CI) is set at 2 points for the total score and at 3 points for each activity.

This means that in order for improvement or deterioration to be considered between two subsequent evaluations, the patient must either show a difference of at least 3 points in one or more activities, or of at least 2 points between the total scores.

The following list contains some examples of activities of daily living that can be used in the evaluation:

■ Getting out of bed;

■ Dressing up / Washing up;

■ Meal preparation;

■ Walking with a particular pace;

■ Sitting down for a particular time;

■ Climbing stairs;

■ Writing on paper.

About the study

The PSFS was created by Stratford et al. in 1995 as a measure for eliciting and recording patients' problems.

The study involved a cohort of 63 out-patients, kept under monitoring for mechanical low back pain.

Each patient recorded 5 examples of activities that they considered they had difficulty with, because of their LBP problem, on a 11-point numerical scale.

Concurrent validity of the patient-specific measure was assessed by comparison to the Roland-Morris Questionnaire.

The PSFS showed moderate to excellent reliability, validity and sensitivity to change.

Original source

Stratford P, Gill C, Westway M, Binkley J. Assessing disability and change on individual patients: a report of a patient specific measure. Physiotherapy Canada. 1955; 47(4): 258-263.

Other references

1. Nicholas P, Hefford C, Tumilty S. The use of the Patient-Specific Functional Scale to measure rehabilitative progress in a physiotherapy setting. J Man Manip Ther. 2012; 20(3): 147–152.

2. Hall AM, Maher CG, Latimer J, Ferreira ML, Costa LP. The patient-specific functional scale is more responsive than the Roland Morris disability questionnaire when activity limitation is low. Eur Spine J. 2011; 20(1): 79–86.

3. Chatman AB, Hyams SP, Neel JM, Binkley JM, Stratford PW, Schomberg A, Stabler M. The Patient-Specific Functional Scale: measurement properties in patients with knee dysfunction. Phys Ther. 1997; 77(8):820-9.