Direct Skeletal Prosthetic Attachment

Direct Skeletal Prosthetic Attachment
by Zach Harvey CPO

            As a prosthetist, I strive for the perfect socket fit and design.  However, even when I’m at my best and my patients keep coming back in for adjustments, as I want them to, the comfort level and wear time is merely a product of residual limb presentation, patient motivation, my skills, and the technology that’s available.  Our combined effort leads to an optimal outcome, as good as we can get.  Adjustable sockets and interfaces are continuing to develop (see my April, 2016 blog ), but what if “as good as it gets” could become “much better?”  What if we could bypass the socket altogether?

Transcutaneous (through the skin) Osseointegration (OI) refers to the firm anchoring of a surgical implant (as in dentistry or in bone surgery) by the growth of bone around it.  Archeological evidence of OI dates back as far as 4000 years ago from China.  Human remains were found with carved bamboo teeth pounded through the gums into bone.   In the early 1950’s, Swedish professor Per Ingvar Branemark began conducting experiments on the legs of rabbits using titanium implants and discovered that bone grew directly into the implant, making it difficult to remove.  This unintended discovery later led to stronger implant designs.  In 1965, the first humans received dental implants directly attached to bone.  Osseointegration is now commonplace in dental/craniofacial reconstruction, bone anchored hearing implants, and joint replacements. 

In a two stage OI procedure, the fixture is allowed to heal.  Later, the abutment is surgically inserted.  In a one stage procedure, the fixture and abutment are implanted at the same time.

In a two stage OI procedure, the fixture is allowed to heal.  Later, the abutment is surgically inserted.  In a one stage procedure, the fixture and abutment are implanted at the same time.

            So, why not try OI with an amputated limb?  After all, prosthetic sockets are hot, sweaty, and range from uncomfortable to painful.  Plus, the residual limb moves around inside the socket.  Sockets can be difficult to don and sometimes don’t stay on very well.  Volume fluctuations can easily change the fit of the socket, causing a risk of skin breakdown.  High socket trim lines are sometimes necessary, but may restrict joint range of motion.  Wouldn’t it make sense to directly connect the prosthesis to the skeleton?  The short answer is yes, and yes it’s being done.  That said, there are risks associated with the procedure.  However, before we go into the risks, it’s beneficial to have a basic understanding of the history of this procedure as it relates to amputated limbs. 

            In 1990, Per Ingvar Branemark’s son, Rickard Branemark, MD, PhD, performed the first transcutaneous OI on a person with transfemoral amputation. Starting in 1995, this procedure started to be used clinically in Sweden, Germany, and the United Kingdom.  Each country’s implant design was slightly different, but they incorporated a similar two stage procedure in which a fixture was surgically placed inside the intramedullary rod of the femur and then the skin closed to allow healing.  An abutment for use with a prosthesis is later attached through the skin to the fixture.  A fail-safe mechanism is used in between the abutment and the prosthetic knee in order to protect the fixture from the risk of failure.  This mechanism would break away before the implant in the case of a fall.  Fast forward to today, and OI is being performed in a few more countries throughout the world for various amputation levels, including arms, thumbs, and fingers.  The procedure has been somewhat slow to adopt in the United States due to long rehabilitation times and studies reporting high infection rates, some requiring implant removal.  However, newer implant designs could address this problem and there are a few centers within the United States that are starting to perform OI surgeries.  The Veterans Administration in Salt Lake City is currently conducting a study with 10 veteran amputees and carefully measuring outcome data1.  This will lead to 300 additional surgeries to include other surgical centers across the nation within the next 3-4 years. 

            One benefit of OI is osseoperception, which is the feeling and proprioception (spatial awareness) gained through OI. This feeling is helpful, taking away cognitive demand and reliance on eyesight when walking, in the case of a lower limb amputee.  This is also thought to attribute to reduction of phantom limb pain.  Osseoperception is not present with a prostheses that incorporates a socket and it’s obvious why this is the case when we look at how much movement occurs with the bone and soft tissue in relation to the socket.  This movement also translates into increased energy expenditure and an increased need in compensatory gait mechanics.  In other words, it’s harder to walk symmetrically and it takes more effort.  For both lower and upper extremity prosthesis wearers, there is decreased range of motion and more effort required due to movement of the residual limb inside the socket.  Pistoning (up and down movement) causes wasted energy as well as friction against the skin.  With OI, wherever the bone moves, the prosthesis follows.   Research has shown an increase in walking speed, quality of life, function (K-level), prosthetic wear time, and mobility following OI. 

Retired Army Lieutenant, Ed Salau decending stairs after receiving percutaneous osseointegration surgery as part of the Salt Lake City VA research study

Retired Army Lieutenant, Ed Salau decending stairs after receiving percutaneous osseointegration surgery as part of the Salt Lake City VA research study

As mentioned above, however, there are some risks associated with OI.  In a study out of Sweden2 published in 2009, 100 patients with transfemoral OI surgery had about a 30% infection rate with 68 patients still using the implant.  Similar infection rates were reported out of Germany.  A standardized 18-month rehabilitation protocol, called OPRA, was developed in 1999.  This prolonged timeframe is certainly a drawback to the procedure, although the timeframe has now become more customized.  An Australian group3 has published results of an accelerated rehabilitation protocol of 4+ month following surgery with good overall results, but with 27/50 patients experiencing adverse effects such as infections and fractures due to falls.  Some of the goals of the Salt Lake City VA study are to assess bone remodeling over time, and to reduce the number of surgeries and amount of rehabilitation time.  Traditionally, patients who are too active may not be good candidates for OI because high impact activities, such as running, are not permitted.  With better implant designs and better understanding of the strength at the implant at the molecular level, we will be able to predict how much impact a device is capable of withstanding.   Hopefully, this new understanding will lead to the abiity for individuals with OI to engage in high impact activities. 

At Presbyterian St Luke hospital, where I work, Dr. Ronald Hugate, MD will be performing the first percutaneous OI one-stage procedure on two patients with his unique design.  As an engineer and orthopedic oncologist, Dr. Hugate has spent a number of years designing and testing this method in partnership with universities, veterinarians, and a company called Zimmer Biomet.  The design incorporates trabecular metal with porosity designed for bone, muscle, and skin to integrate with, thus sealing off the abutment.  This could be a very big advancement with regard to infection risk.  One patient who will be having this one-stage OI done has bilateral transfemoral/knee disarticulation amputations, and will be receiving the implant on his shorter side.  The other patient, Jace, has a unilateral transfemoral amputation.  I’ve known Jace for almost 10 years and worked with him periodically at Walter Reed trying every kind of socket design to keep up with his active lifestyle.  He deployed back to combat in intelligence after amputation and has since then retired from the military.  It’s exciting to know that this procedure may help both patients become more mobile. 

 retired Staff Sgt. Jace Badia will likely not miss “socket slop” after experiencing the direct skeletal attachment with percutaneous osseointegration. 

 retired Staff Sgt. Jace Badia will likely not miss “socket slop” after experiencing the direct skeletal attachment with percutaneous osseointegration. 

            Osseointegration is not likely to replace prosthetic sockets overnight. Even as methods and technology advance, not everyone will be a candidate.  For example, someone with past infection risk, poor vascularity, or poor bone density would likely not be a candidate for OI.  I see OI as a tool to advance mobility and quality of life, especially beneficial for those people with amputations who are suffering from few prosthetic options or struggle with getting a comfortable fit.  Examples are very short residual limbs, large amounts of soft tissue mass, fingers and thumbs.  With stronger implant designs and techniques to reduce the risk of infection, I see this as a viable option for a select patient population.  I’m excited to see how this progresses and am optimistic about the future!

 

References:

1.  https://www.ncbi.nlm.nih.gov/pubmed/19675986

2. http://medicine.utah.edu/pmr/conference/files/2012/L.Myers-Osseointegration-Sat-Track2.pdf

3.  http://www.humanimaltrust.org.uk/wp-content/uploads/2016/09/APPENDIX-FIVE-Australian-OI-prosthesis-paper-BJJ-2016.full_.pdf

 

Prosthetics and Water Sports By Zach Harvey, C.P.O.

 

            A common question I get as a Prosthetist is whether or not a prosthesis can be worn in the water.  Many prosthetic components, such as feet and knees, are water-resistant, meaning that it’s okay to be caught in a rain storm or splash water on them without causing damage.  Some components are entirely waterproof, meaning it’s okay to completely submerge them in water.  A prosthetist can help in selecting appropriate components for a person whose lifestyle is such that he or she is going to be exposed to water.  If a certain component is not water-resistant or waterproof, a protective cover and skin could be another option to assure the components will not be damaged.  Protective covers and skins can not only help to extend the overall life of components, they also help to restore the shape and skin tone of the prosthesis so it’s visible appearance is more similar to a person’s biological limb. 

 

Showering with a prosthesis is a possibility, although most people do not choose to do this because it’s necessary to clean the residual limb anyway.  Equipping the shower with grab bars and a shower chair is important to reduce the chance of falls.  Alternatively, a shower leg can be made from an older foot and socket, and may make sense in situations such as showering in an unfamiliar environment where an accessible bathroom is not available.  

Swimming with a prosthesis is a possibility, although most people take it off because it is easier to swim without a prosthesis.  The prosthesis can be taken off at the edge of the pool and covered up with a towel to prevent it from getting wet. For those swimming for the first time after losing a limb, balance in the water is going to be different and it may take some time to adapt.  Persons with upper extremity limb loss may benefit from a specialized prosthesis or paddle-type device with straps around the residual limb, such as in the picture below.  As a general rule, the prosthesis should be rinsed with fresh water anytime it's exposed to chlorine or salt water.

Swimming in the ocean adds the challenges of sand getting in and on the prosthesis, and also getting from the shore into deep enough water to start swimming.  Sand is the enemy when it comes to prosthetic feet.  Sand inside the footshell will act just like sandpaper and rub holes through the spectra sock.  This eventually exposes the carbon fiber (or similar) foot to rubbing on the rubber footshell, and causes the carbon to wear prematurely.  The solutions to this are to prevent as much sand from getting into the footshell as possible by using a high sock or grocery bag, and then to remove the footshell shortly after exposure to sand and to rinse off the foot, sock, and footshell.  It's important to ask your prosthetist how to remove and put the footshell back on properly.  In addition to the sand issue, getting into the water can be challenging.  It would certainly be disappointing, to say the least, if an incoming tide were to sweep away a leg at water's edge.  A waterproof prosthesis is ideal for walking into deep enough water to start swimming.  In order to ensure it doesn't end up on the end of a fisherman's line someday, a secondary form of suspension, such as a sleeve or belt, is highly advised.  Rinsing off the prosthesis with fresh water will reduce rust and corrosion of any metal parts from the salt water.  For avid beach-goers, a prosthesis that is completely corrosive-resistant and that has a solid footshell or a footshell filled with expandable foam will make life easier.

Triathlon is a race involving swimming, cycling, and running (in that order).  Most races will allow a "handler" to provide assistance for getting out of the water and in transitions.  Talking to the race director ahead of time can help ensure that the handler can set up the participant's towel, leg, etc., ideally at water's edge.  Since wearing a prosthesis during the swim is not allowed ( at least in ITU or USAT races), getting to and from the water's edge can be a challenge.  Many race directors will allow an in-water start for amputees.  Alternatively, crutches may be an option for some to get from the start line to the  water.  Crutches would then be left with the handler.  Upon finishing the swim, a handler can help when getting out of the water, stripping the wetsuit, and donning prosthesis.  Crutches are generally not helpful when exiting the water because wet skin slides around easily on the armpit pads of the crutches and can be dangerous.

Snorkeling and scuba diving are possible without the use of a prosthesis.  However, it may be easier to climb the ladder on the boat while wearing a prosthesis.  Specialized feet that lock out in 90* or in full extended position are also available and may be beneficial.  This is conductive for the use of fins, which help give better propulsion and symmetry in the water.  Neutral buoyancy is a necessary concept in scuba diving and since the prosthesis tends to want to float to the surface, that will need to be taken into account.  Ankle weights are a good option for novice divers and a prosthesis with a hollow shell that fills with water is a good option for avid divers.

Wakeboarding and waterskiing can be done with or without the use of a prosthesis.  One option for waterskiing is to use only one ski and no prosthesis.  If a prosthesis is worn, wetting the prosthetic foot makes it easier to get into the binding.  The tow rope can be held onto with the elbow for a person with a below elbow amputation or with only the sound arm.  A number of adaptive devices are available for non-upright waterskiing.  At a novice level, specialized knees are available with shock units to offer a more athletic stance.  Certain waterproof microprocessor knees can be programmed by a prosthetist to lock in a certain amount of flexion as well.

Kayaking and stand up paddle boarding are possible for those with arm and/or leg amputations and can be done with or without a prosthesis.  Adaptive equipment may be necessary, especially for those with arm amputations.  Specialized prosthetic devices are available to help a person hold onto a paddle.  Safety is paramount and one consideration is to ensure that the terminal device can release from the paddle with a strong force.  For kayaking, another safety consideration is ensuring that the prosthetic leg does not become entrapped in the event that the kayak is overturned.  For this reason, it is advised that a full prosthesis not be worn inside a kayak.  The use of a gel liner and old socket without a foot attached can prevent injury to the residual limb and can facilitate balance by pushing against the side of the kayak without risking entrapment.  Stand up paddle boarding is easier to learn while kneeling than standing, so that might be a good place to start.  Non-slip shoes, such as aqua socks, may help prevent the footshell from sliding on the paddle board when an individual does stand up.

In conclusion, water sports are possible for people who have sustained almost any level(s) of amputation with the right equipment and instruction.  Preventing damage to components is simple and requires only rinsing the prosthesis with fresh water following exposure to chlorine, salt water, and sand.  Safety in the water is of utmost importance and participation in skilled adaptive programs is strongly advised.