Features important for long term survival

It can be seen from Table 3.6 that those systems in which the strain gauges were welded inside metal cavities (Mann, Bergmann and Taylor) had a far greater long term success rate than those in which either an epoxy or silicone sealant were used as the primary gauge encapsulant. In these systems the implant circuitry was also housed inside the prosthesis, and an inductively coupled power supply was used. The above accumulated evidence would strongly suggest that these combined features are the main determinants of successful long term operation. With the exception of Rydell, whose measurements were deliberately terminated early for the safety o f the subject, the groups which employed batteries and soft encapsulants (Davy and English) attributed their premature failures in vivo to the use o f these materials.

The method o f telemetry (VHP radio, passive signalling or inductive coupling using separate coils) and site of the implant coil (inside the prosthesis or outside but integral with the prosthesis) have not been found to be critical factors in long term survivability. This is because the former is largely independent o f the environment and a careful coil encapsulation strategy was devised for the case where the implant coil is housed outside the prosthesis [#4.2.4]. The advantages of the system reported in this thesis (Taylor et al. 1997) are that:

i) only one implant and one external coil is needed for both power supply and telemetry,

ii) no implanted radiotransmitter is needed,

iii) the implant coil location (outside the prosthesis) allows for good power transfer efficiency (enabling the system to be powered from batteries rather than a cable).

References

3.0 Rydell NW. Forces acting on the femoral head prosthesis. Acta Orthop Scand Suppl., 1966, 88.

Berilla J, Davy DT, Oyen OJ, Heiple KG. Design and fabrication of a multi-channel strain gage telemetry system. In ‘Implantable Telemetry in Orthopaedics’, April 26-28, 1990. Eds Bergmann, Graichen, Rohlmann. Publ. Freie Universitat Berlin. ISBN 3- 927433-45-4, pp25-33.

Bergmann G, Graichen F, Siraky J, Jendrzynski H, Rohlmann A. Multichannel strain gauge telemetry for orthopaedic implants. J Biomech. 21,1988, p p l69-176.

Bumy F, Donkerwolcke M, Moulart F. Monitoring o f Orthopaedic

Implants. In ‘Implantable Telemetry in Orthopaedics’, April 26-28, 1990. Eds Bergmarm, Graichen, Rohlmann. Publ. Freie Universitat Berlin. ISBN 3-927433-45-4, ppl 1-22.

Brown RH, Burstein AH, Frankel VH. Telemetering In-vivo loads from nail plate implants. J Biomech. 17,1982, pp8I5-823.

Schneider E, Michel MC, Genge M, Perren SM. Loads acting on an Intramedullary Femoral Nail. In ‘Implantable Telemetry in Orthopaedics’, April 26-28, 1990. Eds Bergmarm, Graichen, Rohlmarm. Publ. Freie Universitat Berlin. ISBN 3-927433-45-4, pp22I-227.

Nachemson A, Elfstrom G. Intra-vital wireless telemetry o f axial forces in Harrington rods in patients with idiopathic scoliosis. JBJS, 53A,

I97I,pp445-465.

Rohlmarm A, Bergmarm G, Graichen F. An Instrumented Spinal Internal Fixation Device for In Vivo load measurements. In ‘Implantable Telemetry in Orthopaedics’, April 26-28, 1990. Eds Bergmarm, Graichen, Rohlmarm. Publ. Freie Universitat Berlin. ISBN 3- 927433-45-4, ppI63-I72.

3.1 Rydell NW. Forces acting on the femoral head prosthesis. Acta Orthop Scand Suppl., 1966, 88.

3.2 English TA, Kilvington M. In vivo records of hip loads using a femoral implant with telemetric output (a prelimmaiy report). J Biomed. Eng. Vol 1, No2, April 1979.

English TA. The trochanteric approach to the hip for prosthetic replacement. JBJS 57A, No8, Dec 1975.

Williams JF, Svensson NL. (1968) A force analysis o f the hip joint. Biomed Eng., 3, 365-70.

Kilvington M, Goodman RMF. In vivo hip joint forces recorded on a strain gauged ‘English’ prosthesis using an implanted transmitter.

Engineering in Medicine, MEP Ltd, Vol 10, No4, 1981.

3.3 Mann RW, Hodge WA. In vivo pressures on acetabular cartilage following endoprosthesis surgery, during recovery and rehabilitation, and in the activities o f daily living. In ‘Implantable Telemetry in

Orthopaedics’, April 26-28, 1990. Eds Bergmann, Graichen, Rohlmann. Publ. Freie Universitat Berlin. ISBN 3-927433-45-4, ppl81-204.

Carlson CE, Maim RW, Harris WH. A radio telemetry device for monitoring cartilage surface pressures in the human hip. IEEE Trans, on Biomed. Eng., BME-2, No4, July 1974.

Hodge WA, Carlson KL, Fijan RS, Burgess RG, Riley PC, Harris WH, Maim RW. Contact pressures from an instrumented hip

endoprosthesis. JBJS 71A, No9, ppl378-1386, 1989. 3.4 Bergmann G, Rohlmann A, Graichen F. In vivo hip joint force

measurements in one patient. 1990. Clinical Implant Materials, pp639-644. Advances in Biomaterials, Vol 9, Elsevier Science Publishers BV, Amsterdam. (1990a)

Bergmann G, Kolbel R, Siraky J, Rohlmann A. Direct measurements of hip joint forces in sheep. 2nd meeting o f European Society o f Biomechanics, 13-15 Sept, 1979, Strasbourg.

Bergmann G, Siraky J, Rohlmann A, Kolbel R. Measurement o f spatial forces by the 'matrix' method. Proc. 9th world congress IMEKO, Berlin, 1982, pp395-404.

Bergmann G, Graichen F, Rohlmann A. Instrumentation o f a hip joint prosthesis. In ‘Implantable Telemetry in Orthopaedics’, April 26- 28, 1990. Eds Bergmann, Graichen, Rohlmann. Publ. Freie Universitat Berlin. ISBN 3-927433-45-4, pp35-63. (1990b)

Bergmann G, Graichen F, Rohlmann A. Hip joint loading during walking and running, measured in two patients. J Biomech. 26, 1993 pp969-990.

Bergmann G, Kniggendorf H, Graichen F, Rohlmann A. Influence of shoes and heel strike on the loading o f the hip joint. J Biomech. 28, 1995 pp817-827.

3.5 Davy DT, Kotzar GM, Brown RH, Heiple KG, Goldberg VM, Heiple KG Jr, Berilla J, Burstein AH. Telemetric force measurements across the hip after total arthroplasty. JBJS 70A N o l, 1988 pp45-50. Davy DT, Kotzar GM, Berilla J, Brown RH. Telemeterized orthopaedic

implant work at Case Western reserve University. In ‘Implantable Telemetry in Orthopaedics’, April 26-28, 1990. Eds Bergmann, Graichen, Rohlmann. Publ. Freie Universitat Berlin. ISBN 3- 927433-45-4, pp205-219. (1990)

Brown RH, Burstein AH, Frankel VH. Telemetering in vivo loads from nail plate implants. J Biomech. 15, N o ll, 1982 pp815-823. 3.6 Barlow JW, Goldie IF, Horwood JMK, Lee AJC, Ranson RP. In-vivo

telemetry of strain in a total hip joint. In ‘Proceedings o f a conference on engineering and clinical aspects o f endoprosthetic fixation’, IMechE, London 1984 pp55-62.

Lee AJC, Barlow JW. The Exeter Telemetry System. In ‘Implantable Telemetry in Orthopaedics’, April 26-28, 1990. Eds Bergmann, Graichen, Rohlmann. Publ. Freie Universitat Berlin. ISBN 3- 927433-45-4, pp77-85.

3.8 Taylor SJG, Peny JS, Meswania JM, Donaldson N, Walker PS, Cannon SR. (1997) Telemetry o f forces from proximal femoral replacements and relevance to fixation. J. Biomechanics 30, No. 3, pp225-234.