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Acoustic Phenomena in Hip Resurfacing
Koen De Smet, MD; Alessandro Calistri, MD
AMC Ghent, Krijgslaan 181, 9000 Ghent, Belgium
Background: While providing superior hardness and improved wear
characteristics, hard bearings such as metal-on-metal, or ceramic-on-ceramics
bearings have different lubrication properties than hard on soft (metal- or
ceramic-on-poly) bearing couples. A failure in this lubrication mechanism in
metal-on-metal resurfacing prostheses can lead to squeaking and has been
reported by different authors. Other more frequently encountered acoustic
phenomena in resurfacing are clicking, popping or grinding noises that patients
may experience in different episodes of their prosthesis life.
Methods: In a series of more then 2700 MOM resurfacings with different
designs, the different acoustic findings, patient sensation and clinical
exams/scores are reported. Patients are asked to report any noise or feeling in
the 6 weeks, 1 year and 2 year follow-up. Impingement with 90 degrees of flexion
and internally rotation is noted on examination, as well as abnormal x-ray
findings, such as high abduction angles of the cup.
Results: Popping noises and clicking noises are reported in 20 to 25% of
the patients with all prosthesis designs. They occur in the immediate
postoperative period were the two parts of the prosthesis, with the increased
fluid and not healed surrounding structures, lead to a looser fit. After a
follow up of 6 months these phenomena disappear unless there is an impingement
problem that results in subluxation of the prosthesis. Impingement or steep cups
with edge loading can lead in time to grinding noises because of increased wear
at the edge of the cup.
Squeaking is reported in 2% of all Birmingham Hip Resurfacings, and was not
stated in other designs at this moment, where of course theirs series where not
as large or with such a long follow up. Although squeaking is mostly experienced
in the first 2 years after surgery, and is most frequently a one-time, one-day
incident.
Conclusions: Today no adverse consequences could be related to squeaking
noises of the hip. Clicking or grinding noises after 6 months of surgery can
possibly be a negative finding, where it is a result of impingement and/or edge
loading.
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