Among K2- and K3-level unilateral transtibial amputees, a combination of standardized gait training and an appropriate prosthetic foot can promote greater external work symmetry, according to a study recently published in Prosthetics and Orthotics International.

“In prosthetics, the current prescription guidelines suggest the K-level of the amputee should match the K-level categorization of the prosthetic foot,” Vibhor Agrawal, PhD, assistant professor of the University of Miami Miller School of Medicine, Department of Physical Therapy, told O&P Business News. “Since many K3 feet have have similar characteristic such as energy return properties as well as a full heel-to-toe plate, we wanted to see if K2 amputees would benefit from using a K3 foot with a ‘J-shaped’ ankle design.”

K2 vs. K3 level feet

Five K2 and five K3 unilateral transtibial amputees (TTAs) underwent six different testing sessions where researchers collected ground reaction forces data with force plates and F-scan sensors. In the first two sessions, participants were tested in their existing prosthesis following 2 weeks of standardized gait training. A study socket and one of four randomized test feet were used in sessions 3 through 6 with an accommodation period of 10 days to 14 days with each foot. To determine symmetry of gait dynamics between limbs at self-selected walking speeds, researchers calculated Symmetry in External Work (SEW) for positive and negative work at each session. SEW is a measure of gait dynamics which assesses the effort provided by each limb in moving the body during ambulation.

The intraclass correlation coefficient for test and retest was high, indicating excellent reliability of F-scan sensors with TTAs and confirmed the stability of participants’ gait. Study results showed that after standardized gait training, positive work symmetry significantly increased over baseline in K3 participants and approached statistical significance in K2 participants. Positive work symmetry was not significantly different between feet among K2 participants. However, researchers found negative work symmetry of the K3 foot was significantly better than K1 and K2 feet. According to study results, although neither positive nor negative work SEW values were significantly different among feet in K3 participants, the difference between K3 and K1 feet approached statistical significance.

“We only had five participants in the K2 group, but our results show significant differences between the K1/K2 and K3 feet,” said Agrawal, who also has a secondary appointment at the Miami Department of Veterans Affairs Medical Center. “The bottom line is if K2 amputees are properly trained to use K3 feet with ‘J-shaped’ ankle design, they can have greater external work symmetry during walking or simply, both limbs are working equally.”

K-level prescription guidelines

According to Agrawal, these study results question the relevance of the current K-level categorization and prescription of prosthetic feet and help support clinicians’ claims that K2 amputees who are properly trained can benefit from K3 prosthetic feet.

The researchers also noted the appropriateness of the K-level categorization of prosthetic foot assignment has not been validated. According to the researchers, if one of the clinical goals for prescription of the prosthetic foot is symmetry of work between lower limbs, study results suggest there is a need for “an objective determinant for prescribing prosthetic feet and categorizing feet with respect to their functional contribution to amputees within each K-level.”

“These results could change the prescription guidelines that are in place, and more importantly these could change the reimbursement for prosthetic feet,” Agrawal said. “Right now our profession is suffering from RAC audits and insurers are asking for the K-levels of patients to see if they are fit with the right prosthetic foot or not. What our results show is both K2 and K3 amputees would benefit from a K3 foot with ‘J-shaped ankle, if they are trained to use the K3 foot.” — by Casey Murphy

For more information:
Agrawal V. Prosthet Orthot Int. 2013;37:396-403.

Disclosure: Agrawal has no relevant financial disclosures.

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