Abstracts Posters SICOT-SOF meeting Gothenburg 2010 _2_

Poster
Topic: Arthroplasty - Hip
Abstract number: 23225
ROLE OF LARGE FEMORAL HEADS (≥36 MM) ON DISLOCATION RATES
Chitranjan RANAWAT
Hospital for Special Surgery, New York (UNITED STATES)
Background: Hip dislocation still remains a common complication after Total Hip
Replacement (THR) and a cause for a revision surgery. The outcomes for dislocated
hips are substantially worse compared to non-dislocating hips. Advances in surgical
techniques and implant designs have lowered the dislocation rates to 1-3%. Various
implants such as constrained prosthesis, Tripolar Bearing Surfaces, and using large
heads are available options to treat this condition. The purpose of this study was to
assess incidence of dislocation in patients receiving a 36 mm head with a minimum
of 1 yr follow-up. Methods: Two groups of patients (from 2004 to 2008) that
underwent THR were enrolled in this study. First group included 188 patients with
ceramic head component and high cross linked poly (HXLP) and second group was
188 cases with metal head implant and HXLP. Both patients were followed for at
least one year after surgical procedure. All patients had a posterior approach with
repair of posterior capsule and proper myofascial tension. Rate of dislocation was
noted at the time of follow-up.Results: First group (188 patients with ceramic on
HXLP) included 139 males and 49 females. Mean age was 60.8 years old (range 34
to 82). In all cases a ceramic head size of 36 mm was used. At the time of 1 year
follow-up, we did not have any cases of dislocations.In second group (108 patients
with metal on HXLP) that included 51 males and 57 females, mean age was 75.3
years old (range 50 to 92). In all patients a metal head size of 36 mm of greater was
used. At the 1 year follow-up, we had only one case of hip dislocation which was in
an elderly patient and associated with dementia. Conclusion: Several studies have
shown that large head size implants reduces the dislocation rate regardless of
bearing type surfaces. This is due to the fact that a with large head size, a greater
range of motion is needed before the femoral neck impinges on the acetabular
component and start to sublux or dislocate. Although rate of hip dislocation with
posterior approach is twice as anterior, our data on using a large head size of 36 mm
or larger showed no dislocation with ceramic on HXLP and only 0.9% rate with metal
on HXLP.Several key factors to reduce the dislocation rate include restoration of
anatomic geometry and center of rotation, maintaining or increasing the offset,
preventing leg length discrepancy and proper repair of posterior capsule. Large head
sizes can not eliminate dislocations. Other issues such as dementia, non-compliancy
and hypermotility should be considered as well.
9