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components (78 %) that remained rigidly fixed were supported by graft over 50% coverage. 1,7,8Therefore, many authors recommend that the extent of coverage of the acetabular component bythe graft should be < 50 % of the contact area. Kobayashi et al. 7 recommended more proximalplacement of the socket, resulting in a high hip center, to obtain adequate coverage in THA foracetabular bone deficiency due to DDH when it is not possible to achieve >50% coverage of thesocket by the ilium at the level of the true acetabulum.In the current study, the sockets were inserted and fixed within anatomic position as much aspossible to re-establish to the true (original) acetabulum. Installation of the socket within thetrue or original acetabulum in THA has beneficial for reducing loosening and revision rate 9 ;restoring acetabular bone stock; and avoiding bony impingement of the hip joint. However, therisk of collapse of the graft becomes high, because the lower the position of the socket, themore the covering ratio of the graft increases. On the other hand, whether the bone graft for theroof of the acetabulum collapses or not is somewhat dependent on mechanical strength of thegraft. Use of a high strength biomaterial, such as solid HA, as a graft seems to reduce the riskof collapse of the graft in cases when the covering ratio exceeds 50%.In revision THAs with lateral acetabular bone deficiency, such as D’Antonio (AAOS) type III,the use of oblong cup is one option. Landor et al. 10 provided evidence in favor of the use ofoblong implants indicating that the major advantage was the anchoring of an oblong cup in thepatient’s own load-bearing bone. However, the success of these cementless techniquesdepended on the degree and location of bone loss. 11 In case of loosening of the oblong cup,bone deficiency might be extremely large. In addition, there are no reports on the use of theoblong cup for acetabular reconstruction in primary THA in patients with DDH.Dr. Terayama, one of the authors of this study, introduced the Charnley technique andprosthesis of low friction arthroplasty for the hip to Japan in 1970. Long term results of hisoperated series reported excellent radiological and clinical outcomes, including cases withcoverage of the socket by the graft ranging from 5% to 49%. 7 However, similar to the report byShinar and Harris 1 , revision rates increased in cases of coverage of 50 % or more. Because ofthose increased failure rates, he developed the technique to utilize a solid biomaterial to preventcollapse of the graft in 1993. A solid hydroxyapatite (HA) block was chosen due to itsbiological characteristics and was designed specifically for clinical use in cases of severe DDHor acetabular bone defect due to socket loosening cases in revision THA.We carefully observed the initial case clinically and radiographically for 10 years beforeconfirming that this technique could provide long-term implant stability. Encouraged by theresults in this one test case, we used the HA block in an additional 13 cases in which thecoverage of the socket by the graft was 50 % or more. Clinical and radiographical follow-up ofthe latter cases have also shown no evidence of loosening and need for revision, althoughduration of follow-up is relatively short, average of 4.7 +/- 0.6 years (range, 4.0 to 5.5).In Japan, solid or porous HA as granules or plastic materials have been commonly usedclinically 12,13 , and their excellent osteoconductivity has also been recognized in animalstudy. 14 Mechanical properties of the solid HA, with porosity of 2% or less and size 6mm indiameter x 10mm height, were 600 +/- 264 MPa (megapascal) for compressive strength and 81+/- 17 MPa for flexural one in vitro. 15 The properties of the porous HA, whose porosity was42% and size was 10mm in diameter x 20mm height, were 35 +/- 3.9 MPa for compressivestrength and 16 +/- 3.2 MPa for flexural one in vitro. 15 These strengths are extremely high incomparison with polymethylmethacrylate bone cement as well as human bone. 16 Based onthese data, we developed the HA composite consisting of solid material for most part and asmall porous portion to interface with bone. In the initial test case, the rigidly fixed HA blockresulted in stable socket fixation. If bulk bone graft alone had been used for this acetabularreconstruction, it might have resulted in implant failure because there is radiographic evidencethat the autograft was partially resorbed.file:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]