How are Wheelchair cushions tested for Medicare code compliance?

The current Medicare policy on wheelchair cushion testing outlines two methods for cushion testing, simulation testing and human subject testing (PDAC-Local Medical Review Policy – Final – Wheelchair Seating). The simulation methodology will be outlined in this paper.

The simulation method uses standardized models of the human buttocks known as Cushion Loading Indenters (CLIs) to measure loaded contour depth and bottoming out. Human subject tests are used to measure peak interface pressure.

There are three sections of the simulation test. The sample cushion is tested in section one using the Loaded Contour Jig (LCJ) indenter. A Description of the LCJ can be found in the ISO Wheelchair Seating Standard16840-2.

Loaded Contour Depth.                                                                    

The first test uses the LCJ to measure the amount of immersion into the cushion at a load of 140 Newtons (31 pounds) with the cushion resting on a flat horizontal surface. The published cushion test methodology specifies that cushions must allow either 25mm or 40mm of immersion, depending on the cushion code description. The LCJ indenter can be configured in two ways, one with long "trochanter" buttons, and one with short buttons. The distance between the bottom of the "IT" cylinders and the bottom of the "trochanter" buttons is 25mm with the long buttons in place, and 40mm with the short buttons in place. A cushion will pass the test if the trochanter buttons are in contact with the cushion support surface at the prescribed test load of 140 Newtons. The height of the IT section of the indenter above the horizontal surface is recorded during this test.

Loaded Contour Depth and Overload Deflection.

The purpose of this test is to determine if the cushion was “bottoming out” during the loaded contour depth test. Using the LCJ, a load of 187 Newtons (41 pounds) is applied to the cushion for one minute immediately after the five-minute test at 140 Newtons. The height of the IT above the horizontal surface is then recorded. The cushion will have passed the oveload portion of the test if the LJC was able to move downward equal to or greater than 5mm from the height recorded during the previous test; this indicates that the cushion was not bottomed out at the 140N load.

Loaded Contour Depth and Overload Deflection After Simulated Use

The third section of the test protocol is a repeat of the loaded contour depth and overload deflection test after the cushion has been subjected to simulated use equal to 12 or18 months (depending on the cushion code that is being applied for).

To simulate cushion use, the test cushion is subjected to cyclic loading in a heated chamber. The test cushion is preconditioned for 30 minutes in a test chamber maintained at 70 ±2 degrees C. The test cushion was then loaded to 500 ±10 Newtons (112 ±2 pounds) for 15,000 or 22,000 cycles (depending upon the type of cushion) at a rate of 30 times per minute using the ISO 16840-2 Rigid Cushion Loading Indenter (RCLI).

The number of cycles was determined as follows:

For testing simulating 12 months of use:
40 pressure reliefs per day x 30 days per month x 12 months x RF ≈   7,500 cycles

For testing simulating 18 months of use:
40 pressure reliefs per day x 30 days per month x 18 months x RF ≈ 11,000 cycles where RF = 0.5, the reduction factor for testing at an elevated temperature. Accelerated aging of 18 months is achieved by cyclic loading 30 times every minute using the RCLI loading indenter (ISO 16840-2) at a 500 Newton (112 pound) load in combination with an elevated temperature of 70C (+/- 2C).  Combining cyclic loading and elevated temperature will provide accelerated aging equal to 12 or 18 months. A safety factor of 2X is then applied to the equation resulting in 12-month aging at 15,000 cycles and 18-month aging at 22,000 cycles.

The Loaded Contour Depth and Overload Deflection test that follows the accelerated aging is conducted after allowing the cushion to rest at room temperature (20C +/- 2C) for a minimum time period of 12 hours. The pass/fail test in this section repeats the Loaded Contour depth and Overload depth tests in parts one and two. To pass the third section of the test, the LCJ indenter must achieve 25mm or 40mm of immersion at standard load (140N), and increase immersion by 5mm or greater at overload (187N). Failure of the indenter to increase immersion by at least this much would indicate that the cushion is beginning to bottom out after 18 months of simulated use.

What Are the Current Seat Cushion Codes and Reimbursement Rates? 

CMS Codes for Wheelchair Seating - This chart shows the reimbursement rates for wheelchair cushions an2 back supports as of March of 2009. The reimbursement rates are subject to re-calculation as cushions are submitted and the mean price calculations change. There may also be regional differences in the reimbursement rates. These rates can be researched at the PDAC link https://www.noridianmedicare.com/dmefee/search.html