Amputee Mobility Predictor

Original Editor - Mariam Hashem

Top Contributors - Mariam Hashem, Jess Bell, Stacy Schiurring, Tarina van der Stockt, Simisola Ajeyalemi, Admin, Sheik Abdul Khadir, Sweta Christian, Olajumoke Ogunleye and Alexandra Stead

Objective

The Amputee Mobility Predictor (AMP) is a performance-based outcome measure designed to evaluate the functional mobility of people with lower-limb amputation, both with a prosthesis (AMPPRO) and without one (AMPnoPRO). It takes roughly 10–15 minutes to administer, requires minimal equipment, and can be used before prosthetic fitting to help predict likely mobility after fitting, as well as afterwards to track progress.

The AMP is free to use for single-users or individual clinics. However, multi-centre, commercial, or electronic medical record use (including electronic distribution, dissemination, publication, or duplication in software or any other transmission format) requires written consent from the copyright holder, Advanced Rehabilitation Therapy, Inc. (Miami, FL).

The AMP is one of the most widely used outcome measures in lower-limb amputation rehabilitation. It forms part of the International Society for Prosthetics and Orthotics' (ISPO) core recommended set for lower-limb absence (known as the ISPO lower-limb COMPASS). ISPO recommends the AMP be used alongside performance-based measures such as the Timed Up and Go, Two-Minute Walk Test, and patient-reported measures. The AMP was also named as an example instrument in the 2017 VA/DoD Clinical Practice Guideline.

Note: the AMP is easily confused with AMPREDICT, a separate statistical model for predicting prosthetic mobility outcomes after dysvascular amputation.

Medicare Functional Classification Levels (K0–K4)

The Medicare Functional Classification Level (MFCL), commonly referred to as the "K-level" system, was developed to describe the functional abilities of people who have undergone lower-limb amputation. It is widely used to guide prosthetic prescription decisions, and the AMP was specifically designed to assess the tasks identified within this system.

Table 1. K-level classification system

Level	Description	Typical ambulatory profile
K0	Does not have the ability or potential to ambulate or transfer safely with or without assistance, and a prosthesis does not enhance quality of life or mobility.	Non-ambulatory; prosthesis unlikely to add functional benefit.
K1	Has the ability or potential to use a prosthesis for transfers or ambulation on level surfaces at a fixed cadence.	Limited or unlimited household ambulator.
K2	Has the ability or potential for ambulation with the ability to traverse low-level environmental barriers such as curbs, stairs, or uneven surfaces.	Limited community ambulator.
K3	Has the ability or potential for ambulation with variable cadence; typically able to traverse most environmental barriers and may have vocational, therapeutic, or exercise demands beyond simple locomotion.	Community ambulator.
K4	Has the ability or potential for prosthetic ambulation that exceeds basic ambulation skills, exhibiting high impact, stress, or energy demands.	Child, active adult, or athlete with high-level prosthetic demands.

Intended Population

The AMP is intended to be used for people with unilateral or bilateral lower-limb amputations. People with bilateral amputation above the trans-tarsal level can only be assessed using AMPPRO, as AMPnoPRO is not feasible for them.

An adapted version, AMP-Bilateral (AMP-B), was developed for people with bilateral limb loss. It removes point deductions for using the hands to rise from a chair or for immediate standing balance, because standard AMPPRO scoring otherwise under-represents these patients' ambulatory potential.

Structure and Administration

• 21 items of increasing difficulty, progressing from sitting balance → standing balance and transfers → advanced standing balance → gait quality and obstacle negotiation → use of assistive devices.
• Most items are scored 0 (unable), 1 (partial/assisted), or 2 (independent), with a few scored differently (see scoring table).
• Higher scores indicate greater mobility potential.

Table 2. AMP structure and functional implications

Item range	Domain assessed	Approximate functional implication
1-2	Sitting balance (reach test)	Inability here suggests K0 (prosthesis unlikely to add value)
3-7	Standing balance, chair-to-chair transfers	K1 (household/limited ambulator potential)
8-13	Advanced standing balance (single-limb stance, reactive balance, nudge test)	K2 (limited community ambulator)
14-20	Gait quality, obstacle negotiation	K3/K4 (community or high-demand ambulator)
21	Assistive device use	Adjusts total score

Table 3. AMP scoring

Configuration	Maximum score without assistive device	Maximum score with assistive device
AMPnoPRO	38 (item 8, single-limb standing on prosthetic side, is not applicable)	43
AMPPRO	42	47

Psychometric Properties

Reliability

• Interrater reliability: excellent (ICC = .99) for both AMPPRO and AMPnoPRO.
• Intrarater reliability: excellent (ICC = .96–.97).
• Independent replication: test-retest reliability was found to be excellent (ICC = .88, 95% CI .79–.93) in a separate sample of 44 people with unilateral amputation, with a reported minimal detectable change (MDC90) of 3.4 points; this is a useful figure for judging whether a change in score reflects true clinical change versus measurement error.

Validity

• Concurrent validity: AMPnoPRO and AMPPRO correlated strongly with the 6-Minute Walk Test (r = .69 and .82 respectively) and the Amputee Activity Survey (r = .67 and .77).
• Predictive validity: AMPnoPRO, together with age, time since amputation, and comorbidity, significantly predicted 6-Minute Walk distance.
• Discriminative validity: distinguishes reliably between Medicare functional classification levels.
• A 2026 cross-sectional study of 63 prosthetic users found a strong inverse correlation between AMPPRO and Timed Up and Go performance (ρ = −0.603, p < .001), with each one-point increase in AMPPRO score associated with a 17% reduction in the odds of being classified at risk of falls. The authors, however, caution that the sample skewed young and trauma-related, so the findings may not generalise to older, dysvascular cohorts.

Translation/cross-cultural adaptation

A French version (AMP-F) has been cross-culturally adapted and psychometrically evaluated in 30 participants, assessing interrater and intrarater reliability alongside construct validity against the Locomotor Capabilities Index and the 6-Minute Walk Test.

Clinical Utility and Considerations

Because AMPnoPRO doesn't require an existing prosthesis, it has particular value in pre-prosthetic assessment and prescription decisions. However, a 2026 Jordan-based study noted a possible ceiling effect among younger, higher-functioning (K3–K4) ambulators, meaning that this tool may discriminate less well at the upper end of function. Additionally, as with any performance-based measure, a good AMP score doesn't rule out fall risk on its own. The authors of the 2026 study therefore recommend pairing it with balance-confidence and environmental/psychosocial screening rather than relying on functional score alone.

Additional Resources

This 10-minute video gives a demonstration on how to set-up and administer the AMP:

Assessments of the ISPO lower-limb COMPASS core set:

• AMP
• Timed Up and Go
• Two-Minute Walk Test
• Prosthetic Evaluation Questionnaire
• Trinity Amputation and Prosthesis Experience Scales (TAPES) -Revised