Tuesday, December 21, 2010

Part Three: Early Failure of MoM bearings in Hip Resurfacing and large-diameter hip replacement/Jrnl of Bone and Joint Surgery, Jan 2010.

My key take-a-ways (reminder/I am not a physician so this is a consumer perspective of what I believe to be the highlights of this study):

(1)   Although debris from MoM replacements may cause local tissue reaction, systemic effects (materials that affect more than one area of the body) have yet to be demonstrated. I think this is important because the litigators certainly have been claiming that the high levels of Cr and Co levels can cause other things such as cancer, kidney problems that would affect other body areas.

(2)    There  is currently no clear consensus in the literature defining the boundaries of the following terms (interesting given the clear delineation in these terms by the litigators;
a.       Metallosis
b.      ALVAL (aseptic lymphocyte-dominated vasculitis-associated lesion)
c.       Pseudotumor
(3)   Generally, tissues examined following revision surgery often exhibit a combination of the above pathologies. They used the term ARMD as an umbrella term to describe joint failures associated with all of these pathologies.
                                                    i.      Without exception, the literature reports an increased incidence of these problems in women.

(4)   87 patients received full hip implants vs a resurfacing procedure not approved for the Depuy hip in the US.  Of these 87 patients, 6% thus far have required replacement after an average of 41 months.
a.       The authors stated that the figures “likely represent the best case scenario.

(5)   There were statistically significant differences in 7 areas between the symptomatic and asymptomatic groups:  Whole blood levels and serum levels of Cr and Co, the angle of the component that fits into the concave surface of the pelvis and the size of the femur.

(6)   Patients experiencing joint failure as a consequence of ARMD:
a.       Have significantly smaller, suboptimally oriented components
b.      Greater wear
c.       Increase in the production of metal debris increases the risk of adverse local tissue reactions
                                                    i.      Levels of blood ion levels correlate well with wear
d.      The location of the articular contact in the standing position of the patient is crucial in the development of high ware states.
                                                    i.      The closer the contact lies to rim of the concave component the greater the chance of increased level of blood/metal ion levels.
                                                  ii.      The smaller the contact patch to the rim distance, the greater the incidence of the symptoms (ARMD.)
                                                iii.      Women are more likely to experience greater ion concentrations due among other things to the smaller joint size.
e.       High metal ion concentrations are associated with a disturbing amount of tissue necrosis even when the patient remains asymptomatic.
f.       Other studies have concluded that massive concentrations of CR and CO ions in the joint fluid alone could alone explain the tissue necrosis.
g.      Chromium is likely sequestered in the joint space while Cobalt is more easily released into the circulation.
h.      Greater failure is experienced when the femoral head is less than 49mm-Ask your surgeon what the size of the femoral joint head was.

(7)   Surgeons must consider the following in placing MoM implants in order to reduce failures when performing the MoM hip implants:
a.       Implant design
b.      Expected component size
c.       Positioning of  the acetabular implant


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