Amputee Mobility Predictor
Original Editor - Mariam Hashem
Amputee mobility predictor (AMP) is a quick and easily administered assessment tool designed to measure the functional status of lower-limb amputees with (AMPPRO) and without (AMPnoPRO) the use of a prosthesis.
The test was also designed to be clinically feasible in that it takes less than 10 to 15 minutes to administer and requires very little equipment.
AMP can be used before prosthetic ﬁtting to predict functional mobility after prosthetic ﬁtting. Although the AMP can be administered both with (AMPPRO) and without (AMPnoPRO) a prosthesis, the AMPnoPRO has the greatest potential to assist in prosthetic prescription.
The AMP was also designed to assess the speciﬁc tasks identiﬁed in the 5-level Medicare functional classification system (MFCL). MFCL was developed in 1995 by the US Health Care Financing Administration (HCFA) to describe the functional abilities of persons who had undergone lower-limb amputation. (K0, K1, K2, K3, K4)
|K-Level 0||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.|
|K-Level 1||Has the ability or potential to use a prosthesis for transfers or ambulation in level surfaces at a ﬁxed cadence. Typical of the limited and unlimited household ambulator|
|K-Level 2||Has the ability or potential for ambulation with the ability to transverse low-level environmental barriers such as curbs, stairs, or uneven surfaces. Typical of the limited community ambulator.|
|K-Level 3||Has the ability or potential for ambulation with variable cadence. Typical of the community ambulator who has the ability to transverse most environmental barriers and may have vocational, therapeutic, or exercise activity that demands prosthetic use beyond simple locomotion.|
|K-Level 4||Has the ability or potential for prosthetic ambulation that exceeds basic ambulation skills, exhibiting high impact, stress, or energy levels. Typical of the prosthetic demands of the child, active adult, or athlete.|
Unilateral or Bilateral Lower limb amputees. However, bilateral amputee subjects with amputation levels higher than trans-tarsal foot amputations may be tested only with the AMPPRO because it is not physically possible for them to perform the AMPnoPRO.
However, an AMP-Bilat was developed that adapted the scoring for people with bilateral limb loss. These changes included not deducting points for using hands to rise from a chair or immediate balance in standing. In the AMPPRO people with bilateral limb loss will score lower and thus show a lower potential for ambulation, these factors are taken into consideration in the AMP-Bilat.  Example of the AMP-Bilat Form.
Methods of Use
The total score range for the AMP is 0 to 42 points. In its AMPnoPRO conﬁguration, the highest possible score is 38 points because item 8, single-limb standing, is eliminated (standing on the prosthetic side is impossible). By using an assistive device, the subjects’ potential total score possibilities increase by 5 points (to 43 and 47 points for the AMPnoPRO and AMPRO, respectively), depending on the type of assistive device used during testing.
Most AMP items offer 3 scoring choices: 0 indicates inability to perform the task, 1 implies minimal level of achievement or that some assistance was required in completing the task, and 2 denotes complete independence or mastery of the task
The items are organized with an increasing level of difficulty to allow for the progressive assessment of the amputee.
Items 1 and 2 test the ability to maintain sitting balance. The sitting reach test assesses the ability to displace one’s center of mass (COM) and to return to balanced sitting without falling. If the amputee subject does not have the ability to sit and reach in sitting independently, then the possibility for even limited prosthetic use is remote and the amputee subject therefore would be classed as a level K0.
Items 3 through 7 are designed to examine the amputee subject’s ability to maintain balance while performing the relatively simple task of transferring from chair to chair and standing unchallenged. These skills are necessary for a level 1 amputee subject who would receive a prosthesis for transfers and simple standing activities. The ability to perform these test items safely would probably suggest that the patient could manage a prosthesis in limited situations, especially in a supervised environment.
Items 8 through 13 are more challenging activities related to standing balance. Subject performs several tests including; single-limb balance, modiﬁed standing reach test, nudge test, and check reactive balance. In order to maintain balance during these tests subject requires adequate somatosensory and vestibular systems. Succeeding these tests means that the amputee subject has the potential to be a safe household ambulator; that is, he/she can function at level K2
AMP items 14 through 20 evaluate the quality of gait and the ability to negotiate speciﬁc obstacles. These qualities are defined as k3 ambulator or level 4 suggesting, the amputee subject can perform all skills with greater ease.
Item 21 accounts for the use of particular assistive devices.
The concurrent validity of the AMP was tested against 2 known tests, the 6-minute walk, which is a rehabilitation standard, and the Amputee Activity Survey (AAS), which has been shown to be a valid subjective instrument for amputee subjects. The 6-minute walk distance showed a moderate to high positive relationship with both the AMPnoPRO and AMPPRO (r =.69, P<.0001; r=.82, P<.0001, respectively). The AAS had a high to moderate positive correlation to the AMPnoPRO and AMPPRO (r=.67, P<.0001; r=.77,P<.0001, respectively).
Predictive validity of the AMP was also examined by ﬁrst determining the relationship between the 6-minute walk distance and the AMPnoPRO test, age, time after amputation, and comorbidity. The overall model was statistically signiﬁcant (P<.0001) indicating that together these variables do a fairly good job of explaining the variance in the 6-minute walk distance.
Another study with 82 patients with lower limb loss compared the predictive ability of the AMPnoPRO to a single limb balance test, and the Lower-Extremity Motor Coordination Test. They measured outcome with the TUG, the 2-min Walking Test, and K levels. The AMPnoPRO was found to be the best statistical predictor for mobility outcome with a prosthesis. Further research is needed as this was a small sample size. 
Gailey et al tested the intra and inter-rater reliability of the AMP with and without a prosthesis using Intra-class correlation coefﬁcients (ICCs). The inter-rater score demonstrated excellent reliability (.99) for the AMPPRO and the AMPnoPRO. Test-retest intra-rater reliability also had excellent reliability, with rater 1 and rater 2 ICC scores of .96 and .98, respectively, for the AMPPRO. ICC scores for the AMPnoPRO were .97 and .86, respectively, for rater 1 and rater 2.
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