Host response - Orthopaedic Biomaterials in Research and Practice - page 357

Pre-implantation
(32)

At removal
(32)

Not
sensitive
(19)

Not
sensitive
(16)

50%

59%

Sensitive
(7)

22%

50%

Sensitive
(13)

Sensitive
non-
migrators
(9)

41%

28%

FIGUre 14.5 development of hypersensitivity during fracture treat-
ment by internal fixation (from K. merritt, personal communication.)

preoperative metal sensitivity run the risk of activation by implantation,
whereas those who are insensitive preoperatively have a real probability
(in this case 3 of 19 or 16%) of becoming sensitized.
Delayed hypersensitivity (and rare anaphylactic responses) to methyl
methacrylate monomer has been reported, but seems to be an important
problem only for persons with repetitive exposure to uncured PMMA,
such as dentists and orthopaedic surgeons (Figure 14.5). One study
(Clementi et al. 1980; see Table 14.5) suggests a relationship between
sensitivity to PMMA and TJR device loosening. Immune responses
to other polymers in orthopaedic clinical use have not been reliably
reported, although there is growing evidence for such a response to sili-
cones. Immune responses to ceramics are highly unlikely owing to the
extremely low solubility of these materials; they have not been reported
in an orthopaedic context.

aseptic
lymphocyte-
dominated
vascular-associated
lesion

ALVAL is an inflammatory reaction caused by a delayed hypersensitiv-
ity response to metallic wear debris and corrosion products. Metal debris
degradation products complex with local proteins and begin an allergic
response through the formation of haptens, which initiate an antibody
reaction. The reaction is similar to delayed type (Type IV) hypersensi-
tivity response to repeated exposure to, in this case, metallic debris.
Histopathologic descriptions of ALVAL are somewhat nondescript
and similar to failed arthroplasty soft tissues generally. ALVAL is char-
acterized by areas of coagulated necrosis, subsurface band-like infiltrate
of macrophages and giant cell granulomas, and perivascular aggregates
of lymphocytes (predominantly B cell). There will also potentially be
synovial inflammation and hyperplasia. Unique and distinguishing fea-
tures of ALVAL are the presence of dense perivascular inflammatory
infiltrate, along with the overall magnitude of chronic inflammation.
Although there is little consensus on the differences between ALVAL
and metallosis, and patients often show a mixture of different reactions,
there is some distinguishing the responses. Metallosis is thought to be a