James W. Pritchett MD, 901 Boren Ave. #900, Seattle, WA 98104
Cross-linked polyethylene has much less wear than conventional polyethylene and
can used in a more bone conserving thickness of 4 mm. We have used it for hip
resurfacing since 2001.
This study evaluated the effectiveness of a highly cross-linked polyethylene
acetabular component for hip resurfacing in patients under age 50. I posed 5
questions: (1) What are the functional results, (2) What are the complications,
(3) What is the 10-year implant survivorship, (4) What is the femoral head
penetration into the polyethylene, and (5) What is the bone conservation?
Participants and Methods:
There were 160 resurfacing procedures (144 participants) using a 2 piece acetabular shell and a
cementless femoral component (fig. 1). Participants averaged 43 years of age at
the time of surgery (range, 23 – 49.5 years) and 70% were women. Inclusion
criteria were patients with adequate acetabular bone and a high enough head-neck
ratio so that the reconstruction would not violate the femoral neck cortices or
medial acetabular wall. The largest cross-linked polyethylene available was 49
mm so only patients with smaller femoral geometries were included. The Harris,
WOMAC, and UCLA hip scores were used to assess pain, activity, and function and
participants were asked about their satisfaction with the procedure. Digital
radiography and computed tomographic scans were used to evaluate femoral head
penetration and osteolysis. Removed polyethylene liners were analyzed.
The median follow-up was 11.5 years (range, 10 – 14 years). One participant was
lost to follow-up and 1 died. The mean Harris Hip Score was 95 and 95% of the
participants rated the results of their procedure as excellent. The average UCLA
activity score was 8. One patient underwent successful revision surgery for
acetabular loosening. Four participants underwent successful revision to a total
hip replacement because of femoral neck fracture (2), femoral loosening, or
infection. The Kaplan-Meier survivorship was 96%. There were no revisions for
polyethylene wear and there were no instances of osteolysis. The medial
acetabular wall thickness averaged 7.3 mm (range, 1.5 mm – 14.9 mm). The mean
inclination angle was 39 degrees. The mean femoral head penetration was 0.05 mm/year
(range, .028 – .09 mm/year).
Hip resurfacing with a highly cross-linked polyethylene acetabular component is
a reliable procedure at mid-term follow-up. The rate of polyethylene wear is
below the osteolytic threshold of .1 mm/yr. The preservation of both acetabular
and femoral bone is reasonable even in comparison to thin metal shells available
for metal-on-metal resurfacing and total hip replacement. The functional results
are comparable to those of metal-on-metal resurfacing without the concerns of a
metal bearing couple. The procedures are demanding and patient selection is
critical to the success of the procedure. Although long-term follow-up is needed
to determine if implant survivorship with highly cross-linked polyethylene
acetabular components will equal that of metal-on-metal prostheses, the low rate
of femoral head penetration suggests that many years of use in young highly
active participants are possible.
As of June 11, 2015 we have now done more than 700 polyethylene resurfacing cases. We still have not experienced a
bearing surface related failure. We typically do patients up to age 65 and treat both male and female patients. Cemented but more often cementless femoral components are used. We strongly prefer polyethylene for all femoral head sizes less than 48 mm. We have not released our implants for use beyond our own center. We agree with the withdrawal of smaller BHR’s.