A patient who loses a limb due to a rare condition presents a challenge to prosthetists because current technologies and methods may not apply to his or her specific disorder. One way to address the challenge is to incorporate research and development engineers into the clinical problem-solving process.
Though multidisciplinary approaches have been successful in addressing complex health issues in other fields,1–4 few O&P facilities engage engineers in the patient care process, and where cooperation between clinicians and engineers has occurred, inadequate documentation of the design process renders the results unusable for the rest of the industry. This report documents the process and results of collaboration between a clinical practice and a research and development facility to manage a patient with proximal femoral focal deficiency (PFFD).
PFFD is a malformation characterized by a deficient acetabulum and a short femoral shaft that is flexed, abducted, and externally rotated.5 The malformation is rare, occurring once in 52,000 live births.5 Amputation is often required to treat severe cases of PFFD. After amputation, a transfemoral prosthesis is usually prescribed.5 Even with proven surgical treatments, PFFD patients commonly exhibit significant gait abnormalities on the affected and sound sides. On the affected side, there is usually a pause in hip extension during mid-stance, an absence of toe-off power generation, and a constantly abducted femur. The sound side usually displays increased hip power generation during stance phase, mid-stance ankle vaulting to assist with ground clearance of the prosthetic limb, and lateral trunk bending toward the sound side during toe off.5 Further complicating a PFFD patient's gait are malformations of the femur and acetabulum joint, which cause increased vertical movement in the prosthetic socket compared to other transfemoral amputees.5 Left untreated, the resulting increased forces on the intact limb and altered body mechanics can cause osteoarthritis, back pain, and other musculoskeletal problems.
The elevated vacuum (EV) prosthesis is a promising technology for the management of PFFD, but no record of its implementation with patients affected by PFFD has been found. EV systems maximize surface contact between the socket wall and the liner, enabling high frictional forces that improve fit and suspension.6 Decreased vertical movement inside the socket can contribute to a more efficient gait, which could lessen the negative secondary effects of a PFFD patient's use of the prosthesis. Furthermore, EV has the potential to normalize patient gait. A recent study showed that EV prostheses enabled better stance phase and step-length symmetry when compared with patellar-tendon-bearing (PTB) designs in transtibial amputees.7 However, recent research shows that morphological changes in the hip anatomy during gait hinder the achievement of a proper proximal seal,8,9 which is crucial for the maintenance of the vacuum environment in the socket. Therefore, the primary challenge to success with EV transfemoral prostheses—and PFFD patients in particular—is developing alternative methods for sealing.
The patient is a 51-year-old male with PFFD of his left limb. His malformation is considered a Class D on the Aitken scale, the most severe malformation, characterized by the absence of both the acetabulum and femoral head. The patient's femoral shaft is extremely short, and the proximal end is pointed. He is a patient at Dayton Artificial Limb, Ohio. Until age five, the patient's condition was treated non-surgically with an orthosis/prosthesis that lengthened his limb. At age five, he underwent a Boyd amputation, and he has since been treated clinically as a transfemoral amputee. His amputation did not include knee arthrodesis. The patient has used a number of non-vacuum prostheses for 44 years, with the most recent being an ischial-bearing ramus containment socket with Silesian belt suspension (IBRCSB) (Figure 1). The patient required no assistive devices to ambulate with his prosthesis and was classified as a K3 ambulator. The patient does not drink alcohol or smoke, but he is being treated for high blood pressure. He works as a clerk in the county auditor's office and lives with his family in a single-story home. The patient has been bowling three games a week for the past 25 years.
At age 48, the patient complained of muscle fatigue to his treating physiatrist. He presented with an inefficient gait, and after examination, weak hip flexors were identified as the cause. At the time, he was fit with a partial suction socket with a single-ply sock. Because the knee was not surgically fused, the patient was experiencing hip instability; this, along with the general instability in the socket, contributed to the fatigue. The physiatrist recommended that he reduce his activity and prescribed treatment by a physical therapist for strengthening exercises. The patient's prosthetist suspected that the patient's gait would continue to worsen as a result of the PFFD and socket instability issues, and eventually these issues would lead to further complications. While EV could possibly improve the patient's gait via improved socket fit and stability, there was not a suitable EV prosthetic solution for PFFD patients at the time, so the prosthetist contacted a local prosthetic development facility for help in creating a custom EV prosthesis for the patient.
Throughout the treatment process, four unique socket designs and various sealing methods were designed and tested on the patient (Figure 2): a double-wall socket; a laminated ramus containment socket with sealing sleeve; proximal and internal seals; and a sealing sheath.
In June 2008, clinicians began fitting the patient with an EV socket system. The preferred method of fitting at the time was a double-wall system design in which the inner socket was sealed and interfaced with the patient's residuum. The design was originally developed for transfemoral amputees, and it allowed the seal to be moved farther down the residuum where fewer morphological changes occur during gait. The inner socket was then anchored to an outer portion, which served as a frame for support and to attach the knee frame, foot, and other distal components of the prosthesis. A thermoplastic, double-wall test socket with a lanyard anchoring system was fabricated and fit to the patient (Figure 3). Sub-atmospheric pressure was created between an Ottobock custom polyurethane liner and inner socket, while the outer socket provided stability. The seal would be maintained with an Ottobock sealing sleeve, which is commonly used by transtibial amputees. The sealing sleeve creates a seal against the liner proximal to the inner socket brim. An Ottobock mechanical pump was the vacuum source for this prosthesis.
The patient was pleased with the resulting small improvements in his gait, and he was able to perform activities of daily living (ADL), like mowing the lawn and washing his car, with less fatigue than with the IBRCSB prosthesis. Although the patient theoretically benefitted from even force distribution in the socket, the rigid inner socket was insecurely attached to the outer socket by a Velcro lanyard. This issue, along with small, incremental contact discrepancies between the inner socket and outer frame, prevented adequate proprioception of the prosthesis. The patient described the sensation as a loose, heavy feeling in his limb. The vacuum pressure fluctuated as the patient ambulated, which also could have contributed to the heavy feeling.
Ideally, a single-wall socket would improve the patient's proprioception and control of the prosthesis by eliminating the movement between the inner and outer sockets, so clinicians at Prosthetic Design Inc. (PDI), Dayton, Ohio, designed and fabricated a single-wall, laminated, ramus containment socket featuring an EV attachment plate and air transfer manifold. Along with the attachment plate and manifold, the prosthesis included an Evolution custom silicone cushion liner fabricated to match the attachment plate, theoretically preventing a void in the distal region of the socket. The system was sealed above the socket at the interface between the silicone cushion liner and sealing sleeve, which was also attached to the socket where it formed the distal seal. The socket brim was lowered to allow sufficient sealing surface area (two to three inches of liner to sealing sleeve contact) above the socket.
Throughout his initial fitting, the patient experienced fluctuating vacuum pressure during ambulation due to voids created by the physical changes of the proximal residuum. When the patient sat on a hard surface, a hole developed in the soft thermoplastic elastomer (TPE) sealing sleeve, rendering it ineffective. Because the single-wall socket had a higher proximal brim than the inner socket used in the double-wall design, there was limited space for the sealing sleeve proximal to the socket brim, especially on the medial side. The limited sealing surface available above the medial socket brim caused a majority of the vacuum seal issues.
Additionally, the patient reported a general instability in the prosthetic socket, which translated into an inconsistent gait and increased use of his intact musculature in an attempt to normalize his gait pattern. This was a direct result of lowering the anterolateral socket wall in an attempt to gain more surface area to seal the socket system. Anatomically, the natural knee joint on the affected side was destabilized by lowering the socket wall in this area. At this point, PDI clinicians determined that one of the engineering criteria for the socket was a high anterolateral wall as well as a high posterior wall to provide a counter force. This force coupling would serve to stabilize the natural, unfused knee joint, which was responsible for destabilization in the socket design.
Since the transtibial-style sealing method was ineffective for this patient, the search continued for a method to seal the socket system. The next method the engineering team tried involved reflecting the top of the silicone cushion liner over the brim of the socket and then using a TPE sealing sleeve attached to the socket to interface with the reflected liner, as recommended by one liner manufacturer10 (Figure 4).
Unfortunately, a reliable seal was not achieved with this design because upon sitting, air entered the space between the limb and the liner. Although vacuum was maintained, the patient was able to slide the socket and liner off his limb. Once again, sitting on a hard surface presented the opportunity for a hole to develop in the soft, silicone cushion liner at the point of the posterior socket brim. This disturbed the vacuum seal and negatively affected socket fit. Clearly, neither a sealing sleeve nor liner reflection method would work with this patient.
In September 2008, the engineering team proposed a third design that incorporated a silicone bladder/seal filled with air that was attached to the proximal brim of the patient's socket. The team theorized that the seal would adapt to the intermittent changes in the proximal tissue during ambulation and when the patient was sitting. When it proved to be an inadequate seal, once again due to the extreme morphological changes in the patient's upper-thigh tissue, the engineers created a second internal seal using a D-shaped ring adapted from a window seal, which was adhered to the inner wall inside the socket (Figure 5).
However, the thick, D-shaped seal caused the patient discomfort because it contacted a high-pressure area on his residual limb. The seal also continually failed during ambulation. As the patient shifted his weight onto his sound side, the proximal tissue on the prosthetic side deformed and broke the seal. Finally, the engineers abandoned the design because of concerns with the durability of the adhesion between the socket and seal material as well as the unreliability of its sealing capability. The information gained through this "failure" made it clear to the engineering team that a thinner, flange-shaped seal attached to a sheath or the liner itself was needed. The thinner, flange design would decrease the bulk of the seal and allow for increased seal quality as vacuum was applied below the seal.
The fourth and final design was implemented in January 2010. The proximal bladder and D-ring internal seals on the socket were replaced by an Evolution Industries independent sealing sheath (Figure 6). This component provided the same type of internal seal as the D-ring, but by attaching the seal to the flexible sheath, its durability and reliability were greatly improved. A seal and sheath combination was chosen as opposed to a seal and liner solution due to the flexibility of allowing the prosthetist to choose the location of the seal to maximize limb surface area under vacuum.
To solve some of the D-ring's issues, the patient was casted for the socket while wearing the sheath, and the lower durometer silicone of the sheath allowed it to deform easily against the socket wall. Both of these changes reduced the pressure on the sensitive areas of the patient's residual limb. By moving the internal seal two inches distal to the medial socket wall, the changes in the proximal tissue did not affect the quality of seal and vacuum level obtained. He was able to maintain consistent vacuum levels throughout the gait cycle and during various activities including sitting.
Innovations in the patient's socket and components followed those in the sealing technology. To increase the patient's anterior-posterior stability, the final laminated socket included higher-than-normal anterolateral and posterior socket walls (Figure 7). In particular, these modifications stabilized the patient's proximal tissue and knee joint by countering the patient's naturally abducted femur. An Össur release valve was laminated into the socket to assist donning and doffing by allowing air transfer through the socket wall. The attachment plate and air manifold were excluded from this design in order to level the prosthetic knee center with that of the patient's sound side. Removal of these components allowed the engineers to bring the knee center up an additional 18mm to help closer match the level of the sound side knee. The patient's mechanical vacuum pump was therefore connected to the socket directly through an Ottobock slight socket connector.
During ambulation in the clinic in January 2010, the patient described a "pins and needles" sensation, which was identified by the prosthetist as paresthesia. Upon further investigation, the prosthetist noted that the paresthesia was felt when vacuum pressure reached 10 in-Hg and higher. Following several attempts to remedy the issue via socket volume changes, the prosthetist contacted the engineers and asked about a possible means of controlling vacuum pressure in a system using a mechanical pump. In response, the engineering team developed a vacuum pressure regulation valve (Figure 8).
With the regulation valve, the prosthetist controlled the vacuum pressure within the patient's socket by adjusting the compression of an internal spring. The pressure was regulated to 8 in-Hg, which prevented the onset of the patient's paresthesia.
For the first six months with the final design, the patient elected not to wear the EV prosthesis to work because it lacked a cosmetic cover. After receiving a cosmesis, the patient was able to incorporate it into his ADL, as well as his favorite pastime, bowling. Following incorporation into his daily routine, the patient reports that the muscle pain and fatigue he had experienced with his old prosthesis has been significantly reduced. The patient says that he particularly enjoys that he no longer has to use the Selisian belt for suspension and rotation control.
The patient has been able to increase his activity after receiving the final EV prosthesis. At the time of reporting, the patient had been wearing the final prosthesis that included the interior sealing sheath and regulation valve for six months. He wears it during evenings and on weekends, especially during strenuous activities such as mowing the lawn, household cleaning tasks, running errands, and bowling. These activities combine for approximately 54 hours of EV prosthesis use per week. The patient reports minimal fatigue, and his gait symmetry is much improved. The patient says that he is walking better and likes the way his shoulders stay level as he walks. This is directly related to the lateral trunk bending toward the sound side to compensate for lack of power generation in the affected side. Because the link between the patient and the socket has been improved, he is able to use more of his existing residual limb muscle power to advance or swing the prosthesis through during swing phase. This, combined with the suspension quality afforded by the EV socket system, has effectively decreased the gait inefficiencies inherent with the old prosthesis.
Discussion And Conclusions
This case is representative of the challenges that rare conditions present to practitioners. The initial problems facing this patient—fatigue and muscle strain—are common to patients with PFFD, but the prosthetic industry's standards were insufficient to manage them.2 Instead of reducing activity level, this patient was able to improve his functional capability thanks to the unconventional inclusion of development engineers in his prosthetic solution.
Time and resources available to the clinician and the engineering team constrained the scope of their collaboration. Additionally, no formal functional measures were implemented to quantify the patient's progress with each successive version of the EV prosthesis, so self-reports and qualitative judgments were used to assess the quality of the design developed by the team. More reports should be written to document the value of collaboration between product developers and clinicians.
For this patient, common treatment methods most likely failed because of his age, unique malformation, and unusual surgical management. Incorporating research and development engineering into this patient's treatment had several advantages. The treating prosthetist worked with the engineers to apply the design process to patient care. The team dealt with a challenge in the patient's treatment, moved through alternative designs until a solution was found, and eventually developed a way for the patient to benefit from advanced technology. Furthermore, the engineering firm was able to develop several new products, which include a silicone liner with distal connector geometry, sealing sheath (Aura), and the vacuum-pressure regulation valve, which they continue to test and will eventually make commercially available. A team approach that involves both prosthetists and engineers can bring significant benefits to a patient's quality of life.
Erin Sutton is a clinical researcher at Dayton Artificial Limb, a research and development co-op at Prosthetic Design Inc. (PDI), and student at University of Dayton, Ohio. Rob Hoskins, BS, BME, is a research and development engineer at PDI and a clinical consultant for Dayton Artificial Limb. Tyler Fosnight works for Dayton Artificial Limb, PDI, and the University of Cincinnati Department of Biomedical Engineering, Ohio. For more information, contact Hoskins at
Author's note: Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the editor of this magazine.
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