Prosthetic Suspension in a Case of "Tibial Kyphosis" JAMES F. RICHARDS, JR., M.D.

LEWIS N. MELTZER, C.P.O.


Summary

This case report describes an interesting bilateral congenital lower-limb amputee with a tibial deformity we have called "tibial kyphosis." The deformity itself has furnished considerable prosthesis suspension and permitted modification of the prostheses. The unusual aspects of the prostheses are the suspension, the areas of weight-bearing, the inserts, and the inclusion of diagonal posterior brims.

Case Report

M.W., a 14-year-old boy, presented himself to the Orlando Juvenile Amputee Clinic in September 1972. This patient had a congenital deficiency of both legs as well as a bilateral foot deficiency which had been converted at age two and one-half to very long below-knee amputations by Dr. Charles Franz in Grand Rapids, Michigan. The child had worn approximately one new pair of prostheses a year, including many different kinds which ran the gamut from limbs with strap suspension to those without. He arrived in atypical PTB prostheses with no patellar- tendon-bearing shelf and no supracondylar strap. A previously existing posterior window had been sealed over, and a Kemblo pad appeared to be the source of suspension. The child, living in a small Florida town many miles from Orlando, had difficulty attending clinic sessions.

Clinically the long below-knee stumps can be described as having an anterior bow of the tibia, the convexity forward, with a dimple in the skin over the midtibia or slightly lower than midtibia bilaterally ( Figure 1-A and Figure 1-B ). The limbs measure 24.5 cm in length, and we referred to the tibias as having "kyphotic curves." The fibulas are absent.

At the time of our first examination the patient's existing prostheses had a distal Silastic fill, and the patient was wearing several light stockings on each stump. Our initial approach was similar, using acrylic inserts with Kemblo pads laminated between two layers of Perlon tricot. The patient had skin breakdown from the usual wool stump socks, and we switched to cotton stump socks.

The present prostheses are functionally similar to our first version. We changed to soft inserts with posterior pads made of the same material as the inserts (Silastic impregnated into stump socks). In making inserts of this type, several advantages were found:

  1. Distal pads made from a combination of Silastic 385 and 386 bond well with the insert.
  2. Additional buildups can easily be made of Silastic with any desirable range of durometer or firmness.
  3. Impregnating a sock increases longevity of the insert.
  4. If considerable stump shrinkage occurs, extra thickness can be achieved by laminating additional socks with Silastic. The patient thus can continue wearing one stump sock if this procedure is used. For extremely sensitive stumps and extensive scarring this type insert has been used with good results.

The insert is fabricated over the usual modified and lacquered cast covered with a polyvinyl alcohol (PVA) sheet, followed by a five-ply stump sock and a PVA bag. A 50-50 mixture of Silastic RTV 385 and Medical Fluid 360 is used along with sufficient Silastic Catalyst #706, without the use of vacuum. Extra thickness can be achieved or prevented as needed. After the Silastic sets, the PVA bag is sealed, and the normal rigid socket is fabricated over the insert and the PVA bag. A thin cast sock, sewed-end stockinette, or nylon hose is worn outside the insert to aid donning, thereby allowing the insert to slide into the socket. A diagonal posterior brim was incorporated in the fabrication as is the case with most of the below-knee prostheses made by Hanger, Inc., in Orlando, Florida 3 .

For M.W., suspension is primarily from the anteriorly directed forces of the posterior pads along with circumferential pressure and the lifting effect of the slight angle of the proximal tibias. Weight-bearing is accomplished by combinations of total contact, angle of the distal tibias, medial-tibial flares, and end-bearing, and inclusion of the patellar-tendon shelves ( Figure 2 ).

The only problem has been the great distance of the patient from the clinic and prosthetic service. The patient walks reasonably well for a bilateral below-knee amputee. He has auxiliary pelvic suspension which he uses for safety purposes only while he is participating in school athletics. Other than that he does not use any auxiliary suspension.

X-rays ( Figure 3-A and Figure 3-B ) show the left leg with weight-bearing and dependent, demonstrating the excursion of the limb in the prosthesis without any other suspension than that described in the text. The right leg is essentially the same.

Conclusion

We have presented an interesting bilateral congenital lower-limb deformity, converted surgically to long below-knee amputations early in the patient's life. The anterior bowing has been referred to as "tibial kyphosis," a term previously used in the literature 2,3 . The interesting thing to us was the manner in which the anterior bowing could be utilized to furnish suspension in this case.

References:
1. Badgley, C. E., S. J. O'Connor, and D. F. Kudner, Congenital kyphoscoliotic tibia. J. Bone Joint Surg., 34-A:349, 1952.

2. Pellicore, Raymond J., Jean Sciora, C. N. Lambert, and Robert Hamilton, Incidence of bone overgrowth in the juvenile amputee population. Inter-Clin. Inform. Bull., 13:15:1 8, December 1974.

3. Thranhardt, H. E., Diagonal-posterior-brim below-knee prosthesis. Presented at American Orthotic and Prosthetic Association National Assembly, Atlanta, Georgia, October 25, 1974.