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Fitting a Knee Disarticulation as a BK Utilizing the ALPS Locking Pin as a Pseudo-Tibial Lever: A Single Case Review

Jason M. Jennings, CPO
Leslie D. Wontorcik, CP

ABSTRACT

The result of a knee disarticulation amputation allows the distal redundant tissues, which were left mobile, to be actively ranged from full extension to approximately 45 degrees of simulated knee flexion. It could not be determined from the intraoperative notes whether a myoplasty or myodesis was performed, however, the patella was left intact.

Several previous attempts at prosthetic fitting were tried. Both transtibial and knee disarticulation designs were used, with less than desirable outcomes.

The current approach focuses on the ability of the patient to actively range the distal tissues of his residual limb. Using the elasticity of the ALPS Clear Pro liner for mobility and suspension we were able to use the locking pin as a pseudotibial lever. The prosthetic design incorporated a supracondylar/suprapatellar type of socket with joints and corset, ALPS Clear Pro liner with clutch lock, Otto Bock endoskeletal components, and an Otto Bock single axis foot.

Key Words: Prosthetic Knee Device.

Introduction

Various techniques on knee disarticulation surgical procedures have been described (1-5). A variation of the traditional procedures was also described (6). This specific surgical procedure reduced the length of the femur, leaving the condyles intact for suspension, providing better options for prosthetic knee joints.

Prosthetic management of these amputations has also been described with slight variations for suspension and choice of prosthetic knee joints. The basic designs that have been described are the leather socket with outside joints, or a laminated socket with outside joints, tibial shank, and prosthetic foot. More recently the design of the four-bar knee has led to more functional, cosmetic knee disarticulation prostheses (7,8). The differences in these designs are the methods used for suspension, most of which are supracondylar (9).

Roll-on silicone liners are one of the most recent developments in the suspension of both transtibial and transfemoral prostheses (10-12). These liners provide good positive suspension and a shock absorbing shear resistant interface between the prosthetic socket and residual limb. A new variation using one of these commercially available liners will be presented in the following discussion.

History

This case involves a 70-year-old Caucasian male whose medical history was normal until 1985. He was diagnosed as having a malignant schwannoma in his right calf. The tumor was excised in February 1985, followed by irradiation therapy. The wound was closed with a split thickness skin graft which failed; a second attempt at closure was tried with a myocutaneous flap that also failed. Several episodes of cellulitis followed, which were unresponsive to antibiotic therapy. Eventually he was diagnosed with osteomyelitis of the proximal tibia and underwent a knee disarticulation in May 1989. At the time of his first fitting, he presented clinically as a five- to seven-centimeter transtibial amputee with fairly normal range at the knee, but the distal mass was soft tissue only (see Figure 1) . Over a fairly short time, his residual limb went through significant changes in shape and volume, requiring several prosthetic fittings. Initially, with the redundant distal tissues, two transtibial fittings took place. As a result of continual soft tissue shrinkage, two successive knee disarticulation prostheses were designed. With the continually rapid changes in limb volume and limb shape, these first four fittings were minimally successful for short periods of time.

With the stabilization of limb volume we were able to take a long term approach to the case. The stabilized residual limb presents as a one centimeter firm mass distal to the condyles. The mass is mobile and selectively controlled through a flexion/extension range of 45 degrees (see Figure 2) .

Current Prosthetic Approach

With increasing use of the ALPS^a Clear Pro silicone liner at the University of Michigan, we considered using this type of liner for suspension. Once the liner was donned on the patient's residual limb, it became apparent that he could flex and extend the locking from full extension to 45 degrees of knee flexion. This provided a pseudotibial lever, which could be used to flex and extend the prosthesis with his own muscle control similar to a transtibial design. With this approach in mind we decided to fabricate a temporary fiberglass socket directly over the patient's residual limb to test our idea. We felt this would be possible since the patient could tolerate end bearing.

To insure maximum range of motion with the liner we re-donned it with the patient's limb fully extended. We then placed one Poly Sof Sock^b over the liner and placed a new clutch lock^c on the locking pin. We proceeded to fabricate a fiberglass socket fixing the clutch lock directly into the distal end. Next, we removed the fiberglass wrap and trimmed it to what could be described as a supracondylar/suprapatellar socket. The socket was attached to an Otto Bock 5R1^d attachment block with Seigelharz^e. This was then attached to a Durr Fillauer alignment unit^f and Otto Bock Pylong with an Otto Bock single axis foot^h for the dynamic alignment. Good sagittal plane stability was achieved with normal linear and angular adjustments and the resultant ground reaction forces from the single axis foot. Coronal plane stability, however, was still lacking. We took the thigh lacer portion from his first transtibial prosthesis and attached it to the exterior surface of the fiberglass socket with Siegelharz, directly over the apex of the femoral condyles, trying to reduce mechanically induced inner socket motion. This greatly improved coronal plane stability allowing the patient to ambulate with the use of his cane. Although successful ambulation was possible, sitting was somewhat difficult because he could only flex the socket to 45 degrees. This resulted from the combination of the limited range of his soft tissues, the elasticity of the ALPS and the position of the posterior socket brim relative to the soft tissues in the posterior thigh. Even with these limitations, the patient was allowed to take the prosthesis home for a trial.

With the completion of one successful week of homewear, the patient was optimistic about this prosthetic approach despite its design limitations. The prosthesis was transferred to a Durr-plexi check socket (see Figure 3) , and the patient continued to wear the prosthesis in a check socket stage for six weeks. During that time, the patient experienced minor irritations over the posterior lateral femoral condyle and an irritation of his residual limb that he described as a "brush burn." We felt this was due to motion within the socket caused by flexion and extension of the socket over the bony prominences of the patient's residual limb. No observable irritation was present on the surface of his skin. The patient also experienced a skin rash at the proximal edge of the ALPS Clear Pro and we recommended the patient change body soaps from Dial to Ivory and begin applying ALPS A&D Ointment^j on the rash before donning the liner.

After completion of the check socket stage, the patient chose to continue with this approach to his prosthetic management. We transferred the check socket to a laminated socket, utilizing his old thigh corset to minimize cost. A MIND prefabricated cosmetic cover^k was placed on the prosthesis (see Figure 4) . After completion of the first two weeks of wear, the patient was still experiencing a skin rash at the proximal edge of the ALPS liner. The patient was issued a container of ALPS detergent^l to cleanse his residual limb and was seen at a later date for follow-up. During that time, the skin rash had completely disappeared, but the patient was experiencing a slight skin breakdown over the posterolateral femoral condyle. This area was ground out for relief within the socket and a slight angular change was made to the adduction angle of the socket and to the angle of the uprights on the thigh lacer. After these modifications, the patient stated the pain in this area was reduced and he wished to try the prosthesis for two weeks. During the last visit, the breakdown was completely healed and the sensation of a "brush burn" had been eliminated. The patient stated he was very pleased with his new prosthesis. The one thing the patient said he would change would be the ability to flex the prosthesis a few more degrees to ease getting in and out of a car.

Discussion

The patient states he is more comfortable and confident because he knows the foot will be there for him. He doesn't worry about falling like he did when using the previous knee disarticulation designs. The patient states he has not fallen while utilizing this prosthesis and that he has mowed his lawn and walked in the mall for Christmas shopping this past year.

From a clinical point of view, some of the advantages of this design are: 1) partial end bearing, 2) partial vertical loading through the joints and corset, 3) good positive suspension, 4) a shear resistant shock absorbing interface between the patient's residual limb and the prosthetic socket, 5) use of the locking pin as a pseudotibial lever for the advancement and placement of the prosthesis, 6) use of ground reaction forces from a very stable socket to foot relationship to achieve good sagittal plane stability, 7) use of ground reaction in combination with the joints and corset to obtain good coronal plane stability.

Some of the disadvantages of the prosthesis are: 1) limited range of active knee flexion due to unusual design of the socket, the elasticity of the ALPS clear pro liner, and the limited range of motion of the distal tissues of the patients residual limb; and 2) total reliance on ground reaction forces from the single-axis foot to maintain sagittal plane knee stability. Even though the patient can advance and place the tibial shank with the locking pin, once initial loading has occurred no active weight-bearing control is present with the pseudotibial lever.

Conclusion

Despite the limitations of the current design, the functional qualities of the prosthesis have resulted in a better outcome than the initial transtibial or transfemoral designs. When addressing the problem of limited flexion of the prosthesis, an idea to incorporate a step-up type of hinge has been suggested but not yet machined.

We feel this approach has become the best design for the patient. We hope with the continuing experience of the patient and his feedback, we will be able to improve upon this design in the future.

References:

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