North Star Ambulatory Assessment

Original Editor - Eki Tunjungsari Top Contributors - Eki Tunjungsari  

Objective

The North Star Ambulatory Assessment (NSAA) is a 17-item rating scale that is used to measure functional motor abilities in ambulant children with Duchenne Muscular Dystrophy (DMD). It is usually used to monitor the progression of the disease and treatment effects.

Intended Population

Ambulant children with DMD.

Method of Use

Equipment Required:

• a size-appropriate chair or height adjustable plinth
• box step, approximately 15 cm high
• a mat
• a stopwatch
• a clear, straight, and marked 10 metres pathway

Test Details and Instruction:

The test must be completed without the use of any thoracic brace or leg orthoses. Therapist asks the patient to complete activities listed in the table below.

The activities are graded as follows:

2 - "Normal" - no obvious modification of activity

1 - Modified method but achieves goal independent of physical assistance from another

0 - Unable to achieve independently

This scale is ordinal with 34 as the maximum score indicating fully-independent function.

Activity	Instructions to patient	Starting position / test detail	Comments
1. Stand	Can you stand up tall for me for as long as you can and as still as you can?	Feet should be close together and heels on the ground if possible. Arms by sides. NO shoes should be worn.	Best done on the floor rather than on a mat. Whichever is chosen maintain consistency through repeated testing sessions. Minimum count of 3 seconds to score 2.
2. Walk	Can you walk from A to B (state to and where from) for me?	Walk without shoes/socks on. Should be enough of a distance to observe ‘normal gait’ for that subject.	A value judgement needs to be made in scoring – if the patient generally toe walks but occasionally gets heels flat, or can on request but doesn’t usually, they should score 1
3. Stand up from chair	Stand up from the chair keeping your arms folded if you can	Starting position 90º hips and knees, feet on floor/supported on a box step.	A size-appropriate chair or height adjustable plinth should be used. Arms should be kept crossed throughout the activity to score 2.
4. Stand on one leg - Right	Can you stand on your right leg for as long as you can?	Minimum count of 3 seconds to score 2. NO shoes should be worn.	Best done on the floor rather than on a mat. Whichever is chosen maintain consistency through repeated testing sessions.
5. Stand on one leg - Left	Can you stand on your left leg for as long as you can?	Minimum count of 3 seconds to score 2. NO shoes should be worn.	Best done on the floor rather than on a mat. Whichever is chosen maintain consistency through repeated testing sessions.
6. Climb box step - right	Can you step onto the top of the box using your right leg first?	Stands facing the box step. Step should be approximately 15cm high	Support may be provided by the use of a height adjustable plinth, or, if not available a ‘neutral’ hand from the therapist.
7. Climb box step - left	Can you step onto the top of the box using your left leg first?	Stands facing the box step. Step should be approximately 15cm high	Support may be provided by the use of a height adjustable plinth, or, if not available a ‘neutral’ hand from the therapist.
8. Descend box step - Right	Can you step down from the box using your right leg first?	Stands on top of the box step facing forwards. Step should be approximately 15cm high	Support may be provided by the use of a height adjustable plinth, or, if not available a ‘neutral’ hand from the therapist.
9. Descend box step - Left	Can you step down from the box using your left leg first?	Stands on top of the box step facing forwards. Step should be approximately 15cm high	Support may be provided by the use of a height adjustable plinth, or, if not available a ‘neutral’ hand from the therapist.
10. Gets to sitting	Can you get from lying to sitting?	Starting position supine on a mat. No pillow should be used under head	If patient turns into prone or towards the floor to work their way into sitting 1 should be scored
11. Rise from floor	Get up from the floor using as little support as possible and as fast as you can (from supine)	Starting position supine with arms by sides, legs straight. No pillow to be used	Activity should be attempted without use of furniture in the first instance. Do not note time if a chair has to be used.
12. Lifts head	Lift your head to look at your toes keeping your arms folded	Supine on a mat. No pillow should be used.	Ask patient to keep arms crossed over chest during the activity to avoid self-assist. Also ask to look at toes to ensure neck is flexed – should be a chin to chest manoeuvre.
13. Stands on heels	Can you stand on your heels?	Standing on the floor. No shoes to be worn.	Watch for inversion. If substantial inversion but forefeet are still lifted – score 1. If only inversion with lateral border of foot still on the ground score 0.
14. Jump	How high can you jump?	Standing on the floor, feet fairly close together.	Want height, not forward movement. Small amount of forward movement acceptable
15. Hop right leg	Can you hop on your right leg?	Starting position standing on floor on right leg. No shoes should be worn.	Needs obvious floor clearance to score 2
16. Hop left leg	Can you hop on your left leg?	Starting position standing on floor on right leg. No shoes should be worn.	Needs obvious floor clearance to score 2
17. Run (10m)	Run as fast you can to……(give point)	A straight 10m walkway should be clearly marked in a quiet department or corridor. A stopwatch should be used to time the walk. Be consistent as to whether shoes are worn or not. Ensure safety of patient. They should self select speed after being asked to go ‘as fast as they can’.	‘Duchenne jog’ - not a true run (there probably IS a double support phase), but more than a walk. Typically characterized by excessive use of arms, trunk rotation, substantial ’waddle’. No real ‘pushoff’

Rising from floor manouver that may be presented by DMD patients.

Evidence

Several studies have shown that NSAA is a quick, specific, reliable, valid, and clinically relevant method to measure the functional motor ability of ambulant children with DMD. NSAA is also considered to be suitable to be used in research and in a multicentric setting provided that adequate training is given.

Reliability

• A psychometric assessment of NSAA showed that NSAA has 0.91 Person Separation Index (i.e. a reliability statistic).
• A multicentric study showed that NSAA has a high intra-observer reliability of 0.95. It has a low inter-observer reliability ( < 0.5) when assessed after only one training but the reliability increased to 0.995 after the second training. It means that NSAA is reliable in a multicentric setting provided that adequate training is given.
• Another study showed that NSAA has a high test-retest ability. It also has a high inter-rater reliability with 0.95 consistency and more than 0.93 absolute agreement.

Validity

A psychometric assessment of NSAA showed that NSAA is valid with a good targeting (i.e. very few items measure the same level of ability) which equates to a better interpretation of results, This study also showed that NSAA has little misfit; which means that there was only a few items where the participants performed differently from the prediction. In fact, there was only one item (i.e. "lifting head from supine") where the participants performed significantly differently from the prediction.

Clinical Relevance

• A psychometric assessment of NSAA showed that the hierarchy of items within NSAA was supported by clinical expert opinion, thus increasing its clinical interpretability. The items in NSAA scale are listed based on their level of difficulty which is mostly agreed by experts (ρ = 0.80).
• A questionnaire-based study showed that clinicians considered NSAA as clinically relevant.

Miscellaneous

A revised version of NSAA was developed with items ordered according to the participants' age when they could be reliably performed. This version showed that NSAA can be used in patients starting from the age of three years.

Links

North Star Ambulatory Assessment

Registry of Outcome Measures - North Star Ambulatory Assessment