Synovial joints, total replacement

The major factors limiting the effective life of a total replacement synovial joint are loosening of one or more of the prosthetic components, a variety of medical problems (e g. infection) and wear. Most internal prostheses now consist of metallic and polymeric components and it is the penetration of the former into the latter which is the subject of this paper. 

The development of satisfactory total replacement synovial joints is sometimes described as the major advance in orthopaedic surgery in recent times. The hip joint was the first major load bearing joint to respond to the efforts of surgeons, engineers and materials scientists in the past two decades to develop satisfactory replacements, but attention is now focussed upon the more complex knee joint. 

Goldring, S.R., SchiUer, A.L., Roelbe, M. et al., 1983. The synovial-like membrane at the bone-cement interface in loose total hip replacements and its proposed role in bone lysis. J. Bone Joint Surg. 65A 575. 

Lamovec, J., Zidar, A., Cucek-Plenicar, M. et al. (1988) Synovial sarcoma associated with total hip replacement. A case report. Addendum Osteosarcoma associated with a Charnley-Muller hip arthroplasty. J. Bone Joint Surg. 70A, 1558-1560. 

The use of crosslinked polyethylene in knee replacements is still relatively new and there are few studies into the wear occnrring in vivo. Iwakiri et al. (2009) measured the number of wear particles contained in synovial fluid removed from the knee joint of patients with a total knee replacement the implants in each patient were the same design, bnt the bearing surface in four knees had a crosslinked polyethylene insert, whereas three knees had an insert made from conventional UHMWPE. The number of wear particles was less for the crosslinked polyethylene insert (0.28 x 10 ) compared with the conventional UHMWPE insert (6.87 x 10 ). Rohrl et al. (2007) measured the penetration of the femoral head into acetabular sockets manufactured... 

The rheology of synovial fluid after total joint replacements, has not been fiilly charactadzed, particular under high ear rates (10 - 10 s ) likely to be expa iaiced in hip implants unda physiological walking conditions. 

The viscosity of fluids like water and synovial fluid is known to be little affected by pressure [14]. The same observation is likely to apply to the serum solutions used in many joint simulators in laboratory testing. The lubricant in total hip replacements, in vivo and in simulators, can thus be treated as an iso-viscous fluid. 

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