Determining minimal clinically important differences in the North Star Ambulatory Assessment (NSAA) for patients with Duchenne muscular dystrophy

The North Star ambulatory assessment (NSAA) is a functional motor outcome measure in Duchenne muscular dystrophy (DMD), widely used in clinical trials and natural history studies, as well as in clinical practice. However, little has been reported on the minimal clinically important difference (MCID) of the NSAA. The lack of established MCID estimates for NSAA presents challenges in interpreting the significance of the results of this outcome measure in clinical trials, natural history studies and clinical practice. Combining statistical approaches and patient perspectives, this study estimated MCID for NSAA using distribution-based estimates of 1/3 standard deviation (SD) and standard error of measurement (SEM), an anchor-based approach, with six-minute walk distance (6MWD) as the anchor, and evaluation of patient and parent perception using participant-tailored questionnaires. The MCID for NSAA in boys with DMD aged 7 to 10 years based on 1/3 SD ranged from 2.3–2.9 points, and that on SEM ranged from 2.9–3.5 points. Anchored on the 6MWD, the MCID for NSAA was estimated as 3.5 points. When the impact on functional abilities was considered using participant response questionnaires, patients and parent perceived a complete loss of function in a single item or deterioration of function in one to two items of the assessment as an important change. Our study examines MCID estimates for total NSAA scores using multiple approaches, including the impact of patient and parent perspective on within scale changes in items based on complete loss of function and deterioration of function, and provides new insight on evaluation of differences in these widely used outcome measure in DMD.


Test Description
• The NSAA is a 17-item scale that grades performance of various functional skills on a scale from 0 (unable), 1 (completes independently but with modifications), and 2 (completed without compensation).
• NOTE: The order has been modified to enable more efficient conduct of the assessment.
• Climb and Descend stairs: climb box step is performed step up right, step down right, step up left, step down left.
• Lifts head is performed before 'gets to sitting' and 'rise from floor' to avoid fatigue.

Test Guidelines
• Performance of upright activities must not be completed if a lower limb injury exists. However, the subject may perform the head lift and gets-to-sitting items if he is able. Provide 'comments' on the source worksheet.
• Complete the NSAA in the order provided (Please note this has been modified from previous trials for a smoother administration).
• The patient should be barefoot.
• Do NOT use a mat.
• The timed 10-meter run/walk and timed rise from floor are conducted as part of the NSAA.
• For all timed function tests (10-meter run/walk, climb 4 stairs, descend 4 stairs, rise from floor), the time in seconds is rounded to the nearest tenth of a second (e.g., 5.11 to 5.14 seconds should be rounded down to 5.1 seconds, 5.15 to 5.19 should be rounded up to 5.2 seconds.
• Generally, activities are graded in the following manner: o Score of 2 = 'Normal' -no obvious modification of activity o Score of 1 = Modified method but achieves goal with no physical assistance o Score of 0 = Unable to achieve goal independently • If you think the subject is capable of a better performance, due to non-compliance or improved understanding of task, it is acceptable to ask the subject to repeat the item if appropriate. Only the best attempt will be scored and documented on the worksheet and in the database.
• If unsure if the performance on a particular item meets the higher criteria, give the subject the lower score.

10m timed run Set-Up
• Mark off a 10-metre course in a long, quiet hallway or room. Stand approximately 1 to 2 meters beyond the finish line to ensure the subject moves 'through' the 10-metre line, rather than slowing down prior to finishing.
• Ensure a clear floor space, measuring approximately 10 feet x 12 feet, is available for remaining assessments (i.e., rise from floor).

ITEM 1: STANDING
Starting position Feet must be no further than 10 cm apart and heels on the ground if possible. Arms by sides.

Instruction
Can you stand up tall for me for as long as you can and as still as you can for three seconds with your heels flat on the ground?
Scoring detail Score is based on ability to hold correct posture and placement of the heels. Score is not based on lordosis.
When counting to 3 -Use "And 1, and 2, and 3" so that three seconds is achieved on the word of 3.
Score 2 -Minimum count of 3 seconds. Hips must be in alignment with shoulders. Feet must also be pointing forwards and not turned out. Scoring detail Score is based on ability to place heels down when walking forwards. You do not score them as they are turning around.
Score 1 -If one or both heels are off the floor as they step or they need to pause to push the heel down to achieve this.

Starting position
Sitting in chair, bench or plinth with arms folded across chest with his hand up by his shoulders and with feet able to reach floor or supported on secure box. Adjust the seat height so that the hips and knees are at a 90º angle from the floor. Feet no more than shoulder width apart.

Instruction
Can you stand up from the chair keeping your arms folded?

Scoring detail
Score is based on ability to stand up without altering start position.
Score 2 -Arms must be kept crossed with the hands up by the shoulders throughout the activity. Feet must remain shoulder width apart.

Stand up from chair
Able to stand up keeping arms folded With help from thighs / push on chair / prone turn or alters starting position by widening base (moving feet apart)

Photographs/ notes
Score 2 -keeps arms folded and stands up without widening base of support Score 1 -Needs two hands to push and widens base of support Score 0 -Unable to rise from starting position without assistance.

Starting position
Standing free of support. Near a point of balance if required (evaluator or a bench)

Instruction
"Can you stand on one leg like this?" Count "And 1, and 2, and 3" Demonstrate the task especially if he lifts his leg very high.

Scoring detail
Score is based on ability to stand upright on one leg and the amount of effort to hold this position. Score is not based on arm position. We recommend arms are held at about 45 degrees of abduction but younger children may hold arms higher from a developmental perspective. If they need to hold your hand to lift their foot -you cannot score them from this effort. They must achieve stand on one leg themselves.
Score 2 -Minimum count of 3 seconds required in upright posture.
Score 1 -A trunk tilt of approximately 20º or more or lifted foot is in contact with weight-bearing leg

Instruction
Can you step onto the top of the box using your right/ left leg?

Scoring detail
Score is based on ability to get on the step without compensation.
Score 1-If they need a hand for balance only -evaluators hand should be kept relatively high or if they use a hand on their thigh. If in doubt whether this is used for balance or support offer them your hand and repeat test.
Score 0 -If they put weight through the evaluators hand (with one or two hands) or unable to climb step They should not have their hands in their pocket for a score of 2. Repeat test or counts as compensation and therefore score 1. Box step must be 15 cm high.

Instruction
Can you step down from the box using your right (or left) leg?
If they rush / skip down, stand in front of the step with space for them to step down and ask them to step down slowly.

Scoring detail
Score is based on ability to get off step without compensation or support Score 1: If they need a hand for balance only -evaluators hand should be kept relatively high.
If they use a hand on their thigh. If in doubt whether this is used for balance or support offer them your hand and repeat test. Uses method that avoids flexing supporting knee (one on the box step) Score 0: If they put weight through the evaluators hand (with one or two hands) or unable to descend step They should not have their hands in their pocket. Repeat test or counts as compensation therefore score 1. Unable without more than minimal support, or requires hands for support

Photographs/ notes
Score 2 -faces forward Score 1 -Needs hand for balance. No weight taken through hand.
Score 1 -Turning to side to descend

Starting position
Supine on a plinth or floor, arms folded across chest and the hands up by the shoulders. No pillow must be used.

Instruction
Can you lift your head and touch your chin to your chest keeping your arms folded? If they are not able, demonstrate the action by flexing their neck for them.
Scoring detail Ask patient to keep arms crossed over chest during the activity to avoid self-assistance.
Score 2 -Uses neck flexion to lift head from the beginning of the effort.
Score 1 -If they clearly use excessive protraction prior to using neck flexion or only protraction or lacks full range of neck flexion.

Lifts head from supine
In supine, full neck flexion, head must be lifted in midline. Chin moves towards chest Head is lifted through side flexion, partial neck flexion, or with protraction

Photographs / Notes
Score 2 -Chin on chest using neck flexion.
Score 1 -Does not achieve full range of flexion, mainly protraction.

Starting position
Starting position supine on the floor, or large plinth with arms by side. No pillow must be used under head.

Instruction
Can you get from lying into sitting?

Scoring detail
Aim is to move into long sitting rather than sitting over the edge of a plinth. Use of one hand or arm is acceptable to achieve a score of 2.
Score 1 -if patient turns into prone or towards the floor to work their way into sitting or if uses two arms. Also score a 1 if the child uses leg momentum/rocking to get to sitting.
*They do not sit up so their legs are over the edge of the bed

Starting position
Starting position supine with arms by sides, legs straight. No pillow to be used.

Instruction
• Give the following verbal instructions to the patient: • "When I say GO can you get up as fast as you can and stand up straight with your arms by your side like a soldier using as little support as possible". Give the command "Ready, Set, GO!" and start the stopwatch when saying "GO".
• Stop the timer when the patient assumes an upright position with his arms by his side.

Scoring detail / Diagram
Activity must be attempted without use of furniture in the first instance. Only provide a chair after the patient has attempted to stand from the floor for 30 seconds and failed.
Score 0: If the patient touches any object including another person, even if the patient does not use the object for support.
Score 1: If the patient gets to standing independently of any furniture but demonstrates any part of the maneuver described below.
• Components of Gower's maneuvers: • Turns towards the floor (into a four-point kneeling position or rolls to prone).
• Places hands on the floor to assist rising from floor and walks hands back in towards him.
• Uses one or both arms to push up on legs to achieve upright standing.
• Large base of support by abducting hips and extending knees.
Score 1 -If they get up slowly through half kneeling but lean with their chest pointing to the floor. This counts as "prone".

Rise from floor
No evidence of Gower's manoeuvre.
Exhibits at least one of the components described above -in particular rolls towards floor, and/or use hand(s) on legs (a) NEEDS to use external support object e.g. chair, wall -still record time OR (b) Unable (time must be entered as N/A if the patient scores 0)

Photographs / Note
Score 2 -Doesn't roll. Only 1 hand on floor to move into sitting Score 1 -Rolls to prone Score 1 -Uses hand on thigh Score 0 -Uses chair 1.14 ITEM 13: STANDS ON HEELS

Starting position
Standing free of support, arms by side.

Instruction
Can you stand on your heels? Count 'And 1, and 2, and 3." Helps to demonstrate item.
Do not worry how much he sticks his bottom out -does not affect score Scoring detail Score is based on ability to stand on heels for the count of three. It is NOT walking on heels.

Instruction
Can you jump?

Scoring detail
Score is based on ability to clear the floor with both feet. The item is about height, not jumping forwards although a small amount of forward travel is acceptable.
If you hold his hands in order for him to try you cannot score from this attempt.

Instruction
Can you hop on your right / left leg?

Scoring detail
Score is based on ability to clear the floor. If you hold his hands to attempt this item you cannot score from that attempt.
Score 2 -Needs obvious floor clearance. Must leave and land on one foot. If leaves floor but lands with two feet this is not a hop and scores 0.
Score 1 -Demonstrates a real effort by bending AND pushing with the knee and ankle at the same time. Real Oomph in the action.
Score 0 -If just raises heel or just bends knees.

Hop
Entire foot clears the floor Able to bend knee AND raise heel, no floor clearance Unable or only raises heel

Photographs / Notes
Score 2 -Clears foot off floor Score 1 -Bends knee and raises heel but foot does not leave floor Score 0

Instruction
Give the following verbal instructions to the patient: "When I say GO, you go as fast as you safely can all the way to me. If you can run, then run. If you can't then walk to me as fast as you can." (Encourage child to run past the 10-metre mark by placing mark or cone at 12m) by standing at least one meter behind the line. Give the command "Ready, Set -GO".
Continuously encourage the patient until he crosses the finish line.
Start the timer when you say "GO". Stop the timer when the second foot clears the finish line.

Scoring detail
Score is based on "flight" and speed A straight 12-m walkway must be clearly marked at 10-m in a quiet department or corridor. A stopwatch must be used to time the walk. They must self-select speed after being asked to go 'as fast as they can'.
Score 2 -Clear flight phase -both feet off floor at same time. It may not be normal, as there may be lots of arm movement but a run is achieved.
Score 1 -Faster than walking speed for the majority of the 10 metre test. Includes those who 'Duchenne jog' -not a true run (There is a double support phase), but it is faster than a walk. Characterized by excessive use of arms, trunk rotation, substantial 'waddle'. No real 'push-off'.
Score 0 -Unable to speed up from walking speed or can only speed up briefly. Score 1 -Picks up speed but waddles and has one foot in contact with floor at all times