Journal of NeuroEngineering and Rehabilitation

evidence suggesting that compared to NMPK, MPK is associated with improvements in walking speed [ 24 – 26 ] , gait symmetry [ 13 , 27 ] , the ability to negotiate obstacles in the environment [ 11 , 15 , 26 , 28 ] , and safety in terms of reduced stumbles and falls. However, while there is some evidence suggesting improvement in other dimen- sions such as energy efficiency [ 11 , 24 , 29 – 32 ] and phys- ical activity [ 28 , 30 , 33 ] , the results are inconclusive. Falls and fall-related mortality Based on the simulation results, the risk of major in- jurious falls is reduced by 79% in MPK users com- pared to NMPK users, as the incidence rate decreases from 104 to 22 per 1000 person-years, and the inci- dence rate of minor injurious falls decreases from 78 to 16 per 1000 person-years (Fig. 1 ) . Meanwhile, the incidence rate of fall-related deaths is 3 and 14 per 1000 person-years in MPK and NMPK users, respect- ively. That is, 11 lives would be saved by MPK if we observed 1000 amputees for 1 year. Incidence of osteoarthritis Kaufman and colleagues [ 34 ] observed that, compared to NMPK, MPK reduces the moment about the knee – an indirect measure of the force absorbed by the knee – of the prosthetic limb by 30%. Thus, based on expert opin- ion, it was assumed that MPK would reduce the onset of osteoarthritis from 20 to 14 per 100 persons in a 10-year period. Incorporating these estimates into the simulation model resulted in 16 fewer incidences of osteoarthritis per 100 persons attributable to MPK over the ten-year model period. Quality of life On average, subjects experienced a 10% improvement in quality of life when using MPK compared to NMPK, measured by the Prosthesis Evaluation Questionnaire (PEQ) summary score [ 15 , 28 , 30 , 35 , 36 ] . Seelen [ 37 ] re- ports a 37% higher score in the 36-Item Short Form Health Survey (SF-36) in all amputees as well as recent amputees when they wore MPK compared to NMPK (Fig. 2 ) . The EuroQol five dimensions questionnaire (EQ-5D) scores converted from SF-36 were 0.92 and 0.71 for MPK and NMPK users, respectively, which is consistent with the literature where the MPK group scored 21% higher in EQ-5D than the NMPK group [ 38 – 40 ] . According to the simulation results, the total number of life years in MPK users is 8.8 years greater than in NMPK users (554.4 vs. 545.7) if we observed 100 MPK users and 100 NMPK users over 10 years. Adjusting for Table 1 Model parameters, assumptions and data sources (Continued) Model parameter Base case Range Data sources Physical therapy cost in year 2 MPK $1621.68 $1459.51 - $1783.85 a NMPK $1347.47 $1212.72 - $1482.21 a Health utilities [ 37 – 40 ] MPK 0.82 0.75 – 0.83 NMPK 0.66 0.60 – 0.92 Discount rate 3.00% 2.00 – 5.00% [ 76 ] MPK microprocessor-controlled knees, NMPK non-microprocessor controlled knees. K1-K4: Medicare Functional Classification Level 1 to 4, respectively a There are no range values directly from the literature; in the sensitivity analyses, they were derived through varying the base case value up and down by 10%. The design of the studies comparing the effectiveness of MPK to NMPK: Prospective cohort study [ 26 , 39 , 59 , 60 ] ; Retrospective cohort study [ 37 , 40 ] ; Cross-sectional study [ 38 ] ) Fig. 1 Injurious Falls and Fall-related Deaths Among MPK and NMPK Users, Note: MPK: microprocessor-controlled knees; NMPK: non-microprocessor controlled knees Chen et al. Journal of NeuroEngineering and Rehabilitation 2018, 15 (Suppl 1):62 Page 53 of 72