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New Possibilities with The Sfx Stance Phase Flexion Adapter  

Jennifer Latham Robinson

New Possibilities:  The Sfx Stance Phase Flexion Adapter

Leafing through the pages of orthotic and prosthetic magazines, it would be easy to miss the brief introductions to the new Hosmer Sfx adapter for above knee prosthetic designs.  Like many developments in the prosthetic industry, this device is small, yet significant.  The Hosmer Sfx is an adjustable stance flexion adapter that can be added to most endoskeletal knee shin systems.   According to Hosmer mechanical engineer, Erik Stefansson, this specialized product can “add another level of comfort” for many above the knee amputees. 

Stefansson explains to, “The idea for this product was originated by the Chairman and CEO of Fillauer, Inc. Karl Fillauer. Based on his vast experience and knowledge of the industry, we determined there was an opportunity to market this product.”

Most stance flexion knees are targeted for moderate to advanced level ambulators.  Stance phase flexion could be described to the layperson as the shock absorption, or flexion, which occurs during the stance phase.  The stance phase occurs when the amputee is putting full weight on the prosthesis during the gait cycle.  Most low level prosthetic knee units are weight activated and fully locked during the stance phase.  So, at heel strike, the standard low level geriatric prosthetic knee unit generally does not absorb shock. 

The Hosmer Sfx unit is an adapter than can be fitted to a lower level prosthetic knee unit, allowing this knee unit to now add the feature of flexion shock absorption during the stance phase.  Stefansson has heard this described by users as “walking on air”.  Shock absorption can also provide greater stability when walking over uneven terrain.  Stefansson adds, “Because the unit only activates during early stance, it does not steal any energy from push off because it becomes rigid like a normal tube clamp adapter during mid-stance.”  The stance flexion feature, or flexion shock absorption, can also reduce hip hiking and allow for a smoother, softer gait.  Some geriatric users may perceive stance flexion as unstable, particularly if it is coupled with a multiaxial prosthetic foot; however, Stefansson notes that “improved stability is the main benefit over comfort.”  With this unit, since the flexion can be gradually introduced and adjusted, users can better acclimate to the increased movement.  Stance flexion of up to 10° is possible with this knee adapter, with the normal range usually between 5-7°.  At just 8 ½ ounces, this adapter is a pragmatic, light weight option for those who want to increase a low level ambulator’s comfort, and possibly explore the possibility of a higher functioning knee unit. 

The Sfx is billable under the HCPCS procedure code for stance phase flexion, L5850.  Every prosthetic component assigned a HCPCS procedure code is assigned an appropriate functional activity level.  Functional activity levels range from 0 (no potential or motivation to ambulate) to 4 (the typical athlete).  The typical prosthetic knee with stance phase flexion directly incorporated into it is targeted for a level 3 or 4 ambulator.  This means that lower level ambulators would not normally quality for this feature.  This Sfx adapter now opens the window of possibilities for lower level ambulators to quality for the stance phase flexion feature.  It adds passive function to simple, geriatric prosthetic locking knees.  Among the many knees appropriate for this adapter, Stefansson recommends the Hosmer S.A.L.K. and W.A.L.K. as well as the S.A.F.K and S.P.K.  The clearance required from the knee center is 3” for the soft and medium versions, and 1” for the firm version.  This measurement is from the knee center to the top of the Sfx.  This unit is not recommended for users with long residual limbs, due to the clearance required.

This stance phase flexion adapter provides prosthetists with a unique opportunity to gradually transition a low level ambulator into a knee unit with a greater level of function, without the need for a total knee unit upgrade.  For the users, it’s a chance to improve activity level, stability, and comfort.  For the insurance companies, it’s a low cost alternative to an otherwise high cost prosthetic feature.  The prosthetic industry is all about options right now.  The Sfx is a new one.

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mark b : re: New Possibilities with The Sfx Stance Phase Flexion Adapter commented on Tuesday, June 02, 2009 8:46:26 AM

In general I find stance flexion disconcerting for pt's even though it is theoretically a good idea. Even some people with C-legs sometimes have a hard time with stance flexion.

When I saw this item, I saw it as a possible device to give more plantarfelxion in an other wise stiffer dynamic response foot. Is this at all reasonable?

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