The Next Revolution: MPKs for K2 Ambulators

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By Gary Wall, MSPO, CPO

When treating the K2 transfemoral population, we are often left yearning for the safety and control we have with microprocessor-controlled knee (MPK) technology for our K3 population. A recent Clinical Practice Guideline recommends MPKs for K2 ambulators are "indicated to enable increases in level ground walking speed and walking speed on uneven terrain while substantially reducing uncontrolled falls and increasing measured and perceived balance."1 Kahle et al. state, "MPK use may reduce uncontrolled falls by up to 80 percent as well as significantly improve indicators of fall risk" in K2 above-knee amputees.2 Two studies also showed that reevaluation of K2 patients' Medicare functional level after accommodation to the C-Leg improved to K3 status in 44 to 50 percent of subjects respectively.2-3

With this knowledge, clinicians should review medical coverage articles to determine coverage options for their patients. Some insurers have policies in place granting coverage for K2 MPKs and others are actively considering coverage on a national level (i.e., Medicare). You can capitalize on this technology with three words: awareness, familiarity, and advocacy.

Awareness begins by reading patients' medical policy articles so you know what they cover; keep in mind this may change frequently. Some policy articles may have clauses allowing for the provision of devices not normally allowed if certain criteria are met. Following the insurer's guidelines, using words found in the medical policy in your clinical documentation, and painting a specific narrative of your patient by not relying on templates will increase your chances of success.

Familiarity starts with becoming knowledgeable about MPKs. A lack of familiarity is demonstrated in the number of MPKs returned for servicing with the default programming unchanged, indicating the practitioner never programmed the knee for the patient. Every practitioner should familiarize himself or herself with at least one MPK, preferably two (one swing default knee and one stance default knee) and know how to program them for optimum patient outcomes.

Advocacy begins with informing our representative bodies that K2 MPKs is a priority topic because acceptance at the federal and state levels is crucial for provision of this technology to our patients.

How do we determine appropriate candidates? One recommendation, while not perfect, uses speed as a determinant for use and provides a helpful guideline for deciding whether to trial a patient on an MPK.

1. Patients who walk less than 60m in the 2MWT on their non-MPK have not been studied with MPK interventions. This does not mean they disqualify for an MPK trial fitting, but no research-based suggestions or recommendations can be given. 

2. Patients who walk 60-95m in the 2MWT on their non-MPK may benefit from using an MPK for safety and to improve the abilities required for community ambulation. Their walking speed suggests microprocessor swing control may not be necessarily.

3. Patients who walk more than 95m in the 2MWT on their non-MPK may benefit from using a MPK for safety, community ambulation, and indoor ADLs. Their walking speed justifies microprocessor swing and stance control.

Adapted from Kanneberg et al.4

Becoming familiar with MPK technology, acquainting yourself with medical policy articles, and advocating for your patients on all levels will ensure that your patients acquire the best clinical care, and you and your practice are not passed over by O&P's next revolution.

Gary Wall, MSPO, CPO, is a practitioner at Del Bianco Prosthetics and Orthotics, Raleigh, North Carolina. He can be contacted at


1.  Stevens, P. M., and S. R. Wurdeman. 2019. Prosthetic Knee Selection for Individuals with Unilateral Transfemoral Amputation." Journal of Prosthetics and Orthotics, vol. 31, no. 1, pp. 2–8, doi:10.1097/jpo.0000000000000214.

2.  Kahle, J. T., M. J. Highsmith, S. L. Hubbard. 2008. Comparison of nonmicroprocessor knee mechanism versus C-Leg on Prosthesis Evaluation Questionnaire, stumbles, falls, walking tests, stair descent, and knee preference. Journal of Rehabilitation Research and Development, 45(1):1–14.

3.  Hafner, B. J., D. G. Smith. 2009. Differences in function and safety between Medicare Functional Classification Level-2 and -3 transfemoral amputees and influence of prosthetic knee joint control. Journal of Rehabilitation Research and Development46(3):417–33.

4.  Kannenberg, Andreas, et al. 2014. Benefits of Microprocessor-Controlled Prosthetic Knees to Limited Community Ambulators: Systematic Review. Journal of Rehabilitation Research and Development, vol. 51, no. 10, pp. 1469–1496, doi:10.1682/jrrd.2014.05.0118.