Una-Crutch (Rochester Institute of Technology)


Kyra Wilson-Houck, Ana Allen, Joanna Dzionara-Norsen, Dan Sawicki, Beverly Liriano


The purpose of this project is to redesign the handles of a standard axilla crutch to feature a connection mechanism which is easy for users with lower extremity injuries to control.  The Una-Crutch is a device that is added onto the standard axilla crutches to reduce the inconvenience of handling the crutches when they are held in one hand and to allow versatility when only one crutch is needed for mobility.  The aim of this device is to give crutch users the option to connect two separate crutches into one functional crutch by replacing each handle on a pair of standard crutches with handles that can connect.  As the user heals and begins to feel more comfortable with the support of one crutch, the user can connect the two crutches together by the connection mechanism at the handles while still having the option to revert back to two crutches at any point.

Through the efforts of product design, build, user testing, analysis of feasibility, and analysis of manufacturability, our team has redesigned the handles of the standard crutch to feature a connection mechanism that can be targeted towards the majority of crutch users and be produced in high volumes.


When a lower extremity injury occurs, medical crutches are normally issued to the patient and become a very crucial piece to the injured person’s mobility.  There is little difficulty associated with using standard crutches in open areas but in smaller spaces, it is easier to use a single crutch. In addition, users typically transition from using two crutches to using one crutch for support during the healing process as the injured extremity can bear more load.  With a product that gives users the option of one or two crutches, this healing process can be more consistent with the doctor’s advice.  Therefore, it is important that a person can alternate between using one and two crutches.

By designing the Una-Crutch system with capabilities of combining two individual crutches into one and separating the crutches back into two, a person’s mobility can always be at its full potential. With this system, users can effectively connect the crutches in situations where two crutches are a burden.  These instances include ascending and descending stairs, doing daily tasks around the house (such as cooking) when the use of one’s hand is necessary, bending down to pick up dropped objects or objects off of the floor, etc. By creating this accessory for standard crutches users can add utility to something they already own and add independence to their current situation.

With an intuitive locking mechanism, the Una-Crutch can easily be connected all while ensuring the standard crutch capabilities of user comfort and safety while providing ease of use and connection.  Since the Una-Crutch only replaces the handgrips of the standard crutches, users are assured that the product will still function as intended and will still be considered a safe medical device, regardless of the combined or separated state the Una-Crutch is used in.


The primary motivation for this project is to redesign the handles of the standard two-crutch product to feature a connective mechanism.  The initial prototype of the Una-Crutch designed by our customer in the September 2013 – May 2014 school term was not designed with load-bearing capabilities, an effective connective mechanism, or the potential for cheap mass production. Refinement in the connective mechanism was required in this design, without compromising user comfort and maintaining functionality of crutches in supporting injured users.

In addition to maintaining the functionality of a standard crutch, the goals of this project are to analyze the original Una-Crutch prototype, identify opportunities to improve this design and connective mechanism, create a product that is easy to use base on user testing results, analyze the engineering feasibility of the product, define the production costs of high volume manufacturing, and meet the Customer Requirements and Engineering Requirements that are outlined below.  The final result will be a functional prototype which will be manufactured for market production.

Customer Requirements categorized and ranked on an importance scale of 1-10.


Engineering Requirements to reflect the customer requirements.


Several designs of reconstructed crutches and connective mechanisms were considered. The team selected three designs and numerous foam axilla pads and handles to prototype and introduce to user feedback groups. Three prototypes in total were created in order to gain feedback on eurgonomics and potential connective mechanisms.

Sketch and prototype of sliding button connective mechanism.
Sketch and prototype of cheetah leg crutch and male/female axilla pad and handgrips connections.
Sketch and prototype of a variation of the Lofstrand crutch (a type of crutch that uses arm cuffs instead of axilla pads for support


User feedback results on crutch redesign and connective mechanism prototypes. Seven users participated and gave a (+,-,0) score for their impressions of each prototype. (+ meaning they would use the device, – meaning they would not, 0 meaning indifferent). It can be noted that the sliding button had a +4 rate as a connection mechanism, while the Lofstrand crutch had a -2 rate as being aesthetically pleasing.


From the user feedback groups, it was concluded that most users prefer an axilla pad and handgrip which is very similar in shape and thickness of the standard crutch axilla pads and handgrips. This introduces the concept that each component of standard crutches is already designed with the user in mind.  Crutch pads and handgrips are produced in a certain size to fit a large portion of users’ anthropometric figures.  In addition, user testing concluded that:

·         Simple is better. If the action of connecting the separate crutches is more difficult than just setting the unnecessary crutch down, then the connective mechanism needs to be simplified.

·         Symmetry in our crutch design is important. Asymmetric designs in axilla pads, handgrips, and crutch frames may make the user question its comfort and stability.

·         Users prefer the look of the standard axilla crutch. This is because the standard axilla crutch is familiar and known to be reliable.

After learning that users preferred the look of the standard axilla crutch, our team then began to focus on creating a connective mechanism that would be added on to the standard axilla crutch instead of introducing a completely new crutch design. From a manufacturing standpoint, the curves involved in creating a new crutch would be difficult, and the creation of a new crutch would be expensive to create and therefore expensive for customers. By creating an add-on, we were able to keep our innovation simple and affordable, meet our customer requirements, and set our customer up for the opportunity to redesign the crutch in the future with the connective mechanism being the focal point.

We decided that the contact points and our main focus on the standard axilla crutch are the axilla pads, the handles, and the tips. It is also noted that when the two crutches are put together for use as one, the handles are too bulky to use comfortably. Because the handles are the main interface between the user and the product, our focus when creating a connective mechanism is the redesign of the handles to connect and be more ergonomically friendly for the user.

After our decision to focus on the connective mechanisms, two different prototypes of the connective mechanism were initially made. The first type of prototype replaces the handle of the standard axilla crutch and features a “sliding button” connection that was previously tested. The second type of prototype uses extenders to separate the standard axilla crutch handles when the crutches are side-by-side. In addition to separating the handles, additional hardware connects the crutches with a latch design.

Sliding button connection mechanism introduced to first user feedback group.
Latch connective mechanism with extended handles


User feedback results on connection mechanism add-on prototypes. Six users participated ranked the statement on a scale of 1-5. (1-strongly disagree, 2-disagree, 3-neutral, 4-agree, 5-strongly agree). It can be noted that seven statements favored the sliding button connection mechanism, two statements favored the latch connective mechanism, and two statements favored both mechanisms equally.


The handle with the sliding button connection mechanism was tested previously in our first user testing session. Because of the positive feedback we had received with this connective mechanism in both user feedback sessions in addition to the ease of manufacturing and aesthetic appeal, we decided to continue to refine the sliding button connection because it was an improvement that could be implemented to the original crutch as an add-on.


The goal of the Connective Mechanism Handle is to make the simplest connection in the quickest amount of time and the first iteration of the handle was designed with this characteristic in mind.  With the standard handles and axilla pads removed, each redesigned handle can slide onto the crutch shafts and can be secured with the standard steel pin and wing nuts.  Unfortunately, the rivets securing the axilla pad to the shafts have to be destroyed in order to remove them.

On each redesigned handle are two slots to accommodate steel blocks, each at 1 inch in length and 0.75 inches in width.  A slot feature is machined into two of the four steel blocks and the remaining two blocks have a protruding screw fastened to one face.  Each pair of blocks (one with a slot and one with a screw) are joined together in a downward sliding motion, locking the screw into the slot, and connecting the crutches.

Since the rivets in the axilla pad have to be destroyed in order to secure the handle to the shaft, this design was not feasible for assembly purposes.

First iteration prototype, rapid-prototyped as one piece


The second iteration of the Connective Mechanism Handle is aimed to resolve the assembly issue of the first iteration: the rivets that secure the axilla pad to the shafts cannot be removed without destruction.  Each handle of this second iteration is composed of two pieces which come together around the crutch shafts and are secured with the standard pin.

The sliding button connective mechanism is the same from the first iteration.  User testing with this design confirmed the ease of use and quick, intuitive method of crutch connection.

Each handle assembly also includes hard foam handgrips to illustrate shape and form factor.  The next iteration of these handgrips will be produced using a flexible material to maintain user comfort.

Second iteration handle shown in two pieces
Second iteration handles with prototyped handgrips assembled on the crutches and connected with the sliding button.


After creating several iterations of the sliding button handle design, a final design was determined and includes the following components:

Steel Blocks

3D Printed Handle


Additional Hardware


People who have temporary lower extremity injuries are the target market for the Una-Crutch. In the last few years, there have been between 7 million and 10 million crutch pairs sold annually [1-3]. By subtracting the number of crutches sold to those who have terminal lower extremity injuries (such as osteoarthritis, orthopedic impairments, absence or loss of lower extremity, and late effects of injury), the estimate of crutches sold per year drop to between 6.4 million and 9.4 million [4].Because crutches are typically sold at drug stores and hospitals, our long-term goal is to sell the Una-Crutch at CVS stores, Walgreens, Rite Aids, and hospitals. In the future, we hope the Una-Crutch will be available at these locations in Monroe County, NY, and in subsequent years, in the state of New York, the northeast, and the contiguous U.S.

With our current design, to create a quantity to match the estimated annual demand of crutches in all of the 14 Monroe County hospitals located in the state of New York, an initial investment of $53,568.25 will produce 3,675 parts [5,6]. In order to obtain a return on investment, the Una-Crutch device would have to be sold at the Monroe County hospitals for at least $14.58 each. We hope to sell the Una-Crutch for $20.00 and turn a profit of $19,931.75 by the end of the year (assuming all units are sold) [5].

Cost analysis of rapid tooling and machining costs for the production of 3,675 units(to meet the demand of Monroe County hospitals). Summarizes the initial investment, price per unit, units to be sold each quarter, sales in dollar amount from each quarter, and the anticipated profit for the year (assuming all units are sold).



User feedback results on sliding button connection mechanism as outlined previously.


It is a strong opinion among former and current crutch users that a device needs to be created to make the handling of crutches an easier task throughout the healing process.  We feel that we have delivered a device that makes life easier for the majority of crutch users.  By being able to connect two crutches into one in under 30 seconds, it gives all users a simple and easy system to use.  The Connective Mechanism Handle can be applied to all axilla crutch models.  To prove that this design could be successful, we held a large variety of tests to see what users truly thought of the crutch.  First, users were instructed to assemble the two crutches together without any instruction.  Next, users used the two crutches together to walk a short distance and observations were made on their posture and crutch accessibility.  After both tests were completed, data was collected via a survey which is shown in the chart above.   The average scores accumulated show that the handle is more popular then the latch.  From the data, it is fair to say that there is nothing like this on the market that is easy to use and gives the user confidence.

The role of an assistive medical technology was considered when designing the connective mechanism for this product.  The device must maintain crutch function and ensure a reliable connection between the crutches.  Standard axilla crutch handles present a problem for users when ascending and descending stairs or when users need one crutch temporarily.  In these situations, the possibility of combining both crutches in one hand is inconvenient and uncomfortable, while the possibility of leaving one crutch behind is a burden.  A redesigned handle which utilizes the standard crutch frame creates more versatility in location and functionality.

The sliding button design is very quick and intuitive and provides the user with a product that is reliable.  From user testing and feedback, it was determined that these characteristics, as well as a design which users were familiar with, would increase user acceptance.  The handle and handgrip design provides users with a comfortable shape that can be easily utilized on separate and combined crutches and includes sliding button features which allow for a simple, intuitive connection.  Since user feedback drove much of the handle and handgrip design throughout the design and testing phases, the final product incorporates desired characteristics from user preferences.

Handle manufacturing using lightweight and high strength nylon material also does not add a noticeable amount of weight and does not compromise user acceptance of this design for this reason.


Special thanks to the Simone Center; the participants of our user feedback groups; Nazareth Clinic; the Multidisciplinary Senior Design faculty and staff; Dan Harel and the Industrial Design faculty and staff; Dr. Denis Cormier, Mike Bufflin, Rob Kraynik, Jan Maneti, and Dave Hathaway, and the Brinkman Lab faculty and staff; and our guide, Dr. Beth DeBartolo.


[1] Snowbeck, C., 2012, “Bloomington startup committed to building a better crutch,” Pioneer Press, http://www.twincities.com/ci_21761042/building-better-crutch

[2] Goetz, K., 2010, “Aeron chair apprentice invents a new crutch,” Fast Company, http://www.fastcompany.com/1655544/aeron-chair-apprentice-invents-new-crutch

[3] Gallagher, B., 2014, “A leg up,” Popular Science, http://www.popsci.com/bown/2010/innovator/leg

[4] Kaye, H.S., Ph.D., Kang, T., Ph.D., LaPlante, M.P., Ph.D., 2000, “Mobility device use in the United States,” University of California, San Francisco Disability Statistics Center, http://dsc.ucsf.edu/publication.php?pub_id=2&section_id=1

[5] “Cost Estimator.” Injection Molding. CustomPartNet, n.d. Web. 10 Apr. 2014.http://www.custompartnet.com/estimate/injection-molding/?low=1

[6] 2014, “Monroe County Hospitals,” New York State Department of Health, http://hospitals.nyhealth.gov/browse_search.php?form=REGION&rt=Monroe

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