The relationship of head size versus metaphyseal fit with the Austin Moore hemiarthroplasty

Abstract

Purpose It has previously been suggested that failure to achieve 70% metaphyseal fit with the Austin Moore prosthesis predisposes to subsidence and failure of the prosthesis secondary to stem loosening. We performed a radiological review to test this hypothesis, and determine whether a correlation existed between head size and metaphyseal fit of the uncemented Austin Moore hip prosthesis. Methods Post-operative radiographs of 102 uncemented Austin Moore hemiarthroplasty patients were retrospectively reviewed. Three observers blinded to the head size of the prosthesis, measured the percentage metaphyseal fit of each stem, using a previously published technique. Results Eighty-six females and 16 males were included in this study. Eighteen of the radiographs were excluded for incorrect implantation, narrow stem insertion, and un-interpretable post-operative radiographs. Implants with a head size of 42 mm had an average metaphyseal fit of 84.5%. Those with head size 54 mm had only a 56% metaphyseal fit. The result was strongly associated with an R value of −0.93. Conclusion We have shown an inverse correlation exists between prosthesis head size and metaphyseal fit. Austin Moore prostheses with head sizes greater than 49 mm are likely to be loose from the moment of insertion. This poses a particular risk in men. In our study, only one male required prosthesis with a head less than 49 mm. In these patients, use of an alternative prosthesis such as a bipolar uncemented or cemented hemiarthroplasty is recommended.

Evaluation of functional outcome of intracapsular fracture neck of femur with Austin Moore prosthesis at a tertiary care hospital in Srikakulam

“…In 2010, Nader N.T. Rehmatullah et al [25] showed an inverse correlation between prosthesis head size and metaphyseal fit in their study. They stated that AMP with head sizes greater than 49mm are likely to be loose, and in such cases, the use of an uncemented bipolar or cemented Hemiarthroplasty is recommended.…”

Two years outcome of cemented Austin Moore hemiarthroplasty for fracture neck femur

“…At least 70% canal fill by the stem of the prosthesis at the level of lesser trochanter is necessary to avoid excessive subsidence of the prosthesis and pain according to Yau et al [10]. Rehmatullah et al [46] found an inverse relationship between prosthesis head size and metaphyseal fit. Austin Moore prosthesis with head size 42 mm had an average 84.5% fit whereas a 54 mm head had only 56% fit in their study.…”