Host response - Orthopaedic Biomaterials in Research and Practice - page 358

toxic reaction to excessive amount of metal particulate, while ALVAL is
a hypersensitive reaction to a normal amount of metal particulate.
The most common radiographic finding associated with ALVAL and
one of its flagship symptoms is a cystic mass, located either posterolat-
eral to the joint or anterior to the joint. This mass, termed pseudo tumor ,
is an enlarged, fluid-filled soft tissue mass that is neither malignant
nor infective. Some common features of pseudotumors include exten-
sive necrosis of the dense connective tissue, sometimes associated with
cystic degeneration, macrophage, and lympocytic infiltrate. In some
cases, necrosis is so rampant as to prevent histological characterization.
Ultrasonography can be utilized to differentiate solid from cystic lesions.
Most pseudotumors will contain metal ion particles. Pseudotumors, like
other signs of ALVAL and metallosis, are most commonly reported in
association with malpositioning of MOM hips, though these reactions
have also occurred in patients with no evidence of excessive wear or
hypersensitivity and have further occurred in non-MOM hips as well.
Consequently, some of these could be possibly related to patient factors.
It is expected that there are an appreciable number of unrecognized and
asymptomatic pseudotumors.
Campbell et al. (2010) created a 10-point histological scoring system
to distinguish ALVAL in patients with pseudotumor-like tissue responses
in MOM hip arthroplasty and ranked cases with signs of higher wear as
having a lower ALVAL score, as they were also associated with fewer
lymphocytes, more macrophages, and more metal particles. While mac-
rophages and lymphocytes present in all cases, there were two distinct
groups. Those scoring lower on the ALVAL scale had more infiltrates of
macrophages and were associated with smaller lymphocyte aggregates.
They also displayed less disruption of the synovial surface and greater
preservation of normal tissue architecture. Those with a higher ALVAL
score exhibited large, dense lymphocyte aggregates, usually distal to the
surface, will fewer macrophages. These patients, with suspected metal
sensitivity, also described more pain. While there was focal to moderate
necrosis in all tissues, including few intact synovial linings, the most
extensive damage to tissues was in the high-score ALVAL group.
ALVAL should be considered in cases of chronic aching pain with
evidence of synovitis and in the absence of infection or implant fixa-
tion issues. Because of a similarity in histology between ALVAL and
that of, for example, rheumatoid arthritis, diagnosis can be difficult.
Postoperatively, there is often radiographic evidence showing solid and
cystic peri-implant masses. Serology testing may indicate elevated quan-
tities of Co and Cr, though this is not definitive. Ultimately, intraopera-
tive histologic assessment of frozen section of tissue for infection and
acute inflammation is necessary. Unfortunately, this is also not defini-
tive. Mechanical causes of failure can cause similar histology, including
inflammation, fibrosis, and repair, though loosening will likely have a
greater amount of foreign metal and cement debris. Because implant
loosening can accelerate the generation of wear particles, it is difficult
to know whether hypersensitivity to particles is the cause or the result of
the implant loosening.