At first, I was skeptical. Maybe resistant is a better word. It took years to get really good at making good fitting sockets, and I’m proud of the fact that I can take a cast and often get a good fit with little or no adjustments needed.
I just got back from Oslo, Norway from a meeting with people from around the world who are also now believers. The “grand master” of Össur Direct Socket (DS), Anton Johannesson, CP hosted us and listened to our case studies. He shared some of his own cases, wisdom, and ideas for the future. We toured two of his beautiful facilities and our enthusiastic group nerded out on all facets of DS.
So, what is Össur DS and how’s it different than a traditional socket? I’ll start by explaining two theories of socket design: 1) Pressure distribution theory; 2) Hydrostatic weight bearing theory.
Traditional transtibial designs which use a pressure distribution theory include: Patella tendon bearing (PTB) and total surface bearing (TSB). Both designs are made from a cast or scan and are modified by loading and unloading certain anatomical zones (PTB) or by reducing size globally (TSB). Modification is needed because the cast or scan represents the surface of the residual limb and liner but does not account for compression of tissue under loading.
Össur DS uses hydrostatic weight bearing theory. The residual bone and soft tissue is compressed into a solid mass during the formation of definitive socket.
And yes, I did say formation of definitive socket on the residual limb! That’s the second big difference- the process. With traditional sockets, the cast or scan needs to be modified by the prosthetist to get a good fit. A check socket is used to verify fit and sometimes more than one check socket is needed. When proper fit is ensured, the socket is usually poured up with plaster and a definite socket is then fabricated. This process can take up to a month to complete.
With Össur DS, the process is completed in the same day. Anton has spent years perfecting this method and it works so long as the steps are carefully followed. Multiple layers of composite fabric are placed over residual limb and casting liner and are covered inside and out by thin silicone sheathing. A two part resin is injected into the material and while the resin is curing, a casting bladder is used to create equalized pressure on the residual limb. The resin sets off in ten minutes, making a lightweight socket weight rated and ISO tested up to 365#. After trim lines are established and components bolted onto the plate, we work on static and dynamic alignment. Very rarely, have I had to adjust anything inside of the socket.
As limb volume changes, as with other sockets, it may be necessary to make adjustments later. Also, I’ve had to remake some sockets if the pressure wasn’t optimal or if pad placement wasn’t right. We’ve occasionally converted a a DS into a traditional carbon fiber design if a flexible inner socket is necessary. Also, really cool is that several different lock options and suction/vacuum units can fit into the same socket if a change is determined to be necessary.
For transfemoral Össur DS design, a similar method is used, although the bladder is not usually necessary considering the desired compression is achieved with the tight silicone sleeves. A silicone brim is laminated into the upper part of socket which fits snugly around the top of hip and gets flipped over the socket for ease of donning. A pin lock or seal in suction suspension can be used. Patients are finding this to be more comfortable as it reduces groin pressure and increases hip range of motion.
We have had a large acceptance rate of Össur DS and the prosthetists I got to meet with in Oslo are seeing the same results. Patients report increased satisfaction with socket fit and the overall experience of getting a socket made.
Very few transtibial and transfemoral residual limbs fall outside the parameters of Össur DS, but like anything in prosthetics, there’s always exceptions. Extreme shapes and sizes of residual limbs may not work well. Upper extremity and young pediatric options are not currently available.
So, how is Össur DS making me a better prosthetist? 1) it allows me to use a repeatable, reliable method to make a socket rather than trusting my artistic skills which introduce human error; 2) I can record such things as pad placement, pressure settings, and brim size in my notes in case a remake is needed or for future socket replacements; 3) I’m saving my patients time off work and number of trips and I’m able to re-invest this time into outcome testing and quality of appointment time. 4) The skill in fitting a socket does not go away. I am able to compound my experience fitting more and more limb shapes and through collaboration, I am getting better and better results with fewer remakes.
In summary, I’m really excited about how Össur DS is improving quality of amputee care. The clinics that Anton oversees in Scandinavia have almost fully adopted this approach over the past five or so years now. I look forward to talking with prosthetists new to the technology and celebrating awesome patient outcomes!
Check out these time lapse videos to see the process: