Precise Acetabular Reconstruction For High Developmental Dislocated Hips

Results of Total Hip Arthroplasty (THA) improved with timeattributed to advancement of surgical techniques and implants. Prosthetic acetabular reconstruction for HDDH is still technically challenging. While constructed the cup at the level of the original acetabulum of a HDDH was well accepted, how to prepare the acetabulum to get better coverage and stability remained controversial. The acetabulum in HDDH was shallow,hypoplastic and triangular. The media wall of it was thin and anterior post was deficiency. How to precisely reconstruct the acetabulum to get better coverage and stability?We therefore conducted a computed tomography (CT) study to three-dimensionally simulate reconstructive surgery. We put the acetabular cup at different positions and orientations to investigated (1) how to reconstruct the acetabular cup in HDDH, (2) whether every cup can get enough coverage without bone graft and (3) how the position of the cup influence bony coverage of it.Between June 2007 and July 2009, twenty-seven women and one man with unilateral or bilateral high developmental dislocated hipswere admitted into our hospital for THA. The mean age of the patients was 40.2 years (range, nineteen to fifty-five years), and their average body mass index was 22.6±3.0 kg/m2 (range,18.75 to 30.04 kg/m2). Four patients had bilateral dislocated hips. Therefore, there were 32 highdevelopmental dislocated hips in our study.We used the Mimics medical-imaging program (Materialise, Leuven, Belgium) for 3-D reconstruction and simulated surgery, and we used SOLIDWORKS, a computer-aided design program (DassaultSystemesSolidWorks Corp, Concord, MA,USA) for 3-D bone-implant contact area calculation.Simulated surgical procedures were done using Mimics medical-imaging software. Method of simulated surgery was the same as our previous study on transacetabular screw fixation safe-zone. We put a hemispheric e-cup in the true acetabulum to simulate the surgery. We adjusted the position of the e-cup in three orthographic dimensions to meet the following criteria: (1) maintaining the integrity of the anterior and posterior columns with good bone stock, (2) keeping the e-cup encircled by host bone, and (3) improving coverage of the e-cup by host bone as much as possible. Once the above requirements were met, the cup was regarded as being at surgical position. The center of the e-cup was defined as surgical center of rotation (SCR). The coordinates of the SCR were recorded. We placed another e-cup with the same size at the true acetabulum to find the three dimensional geography center of the acetabular cavity. When the e-cup was at best fit with the inner contour of the acetabulum, the center of the cup was labeled the anatomical center of rotation (ACR).All cups were 180° hemispheric cups and oriented in 45° of abduction. The cups were the same size as that used in actual THAs in the very patient. Its mean size was 40.88 ± 2.92 mm.To measure 3-D bony coverage of the cup, the Mimics files were imported into SOLIDWORKS.The 3-D bony coverage equaled the contact surface area divided by the total outer surface area of the cup. The cup was separated into anterior and posterior portions by the coronal plane that passed through the center of the cup. Bony coverage for each portion and the whole cup was calculated separatelyTo get surgical cup position, medially, posteriorly, and slightly superiorly reaming was needed. The SCR was located 4.18 ± 2.59 mm (-0.99 to 8.96 mm) medially, 4.61± 2.59 mm (0.3 to10.32 mm) posteriorly, and 2.58 ± 2.08 mm (-1.12 to 6.07 mm) superiorly to the ACR(Fig.1A, and Fig. 1B).Every cup could get enough coverage (more than 70%) at SCR. Only 4 cup got less than 80%, and it was when at 5°anteversion. Posterior coverage was fairly good in every hip; however, anterior coverage depended on anteversion. To achieve enough total coverage as well as anterior coverage,25° anteversion or more was needed.Bonycoverage of the cup increased with anteversion. With increased anteversion, especially beyond 25°, anterior bony coverage of the cup increased dramatically and posterior bony coverage decreased slightly.Precise acetabular reconstruction is important for HDDH. Every high dislocated hip can get enough coverage by putting the cup medially, posteriorly and a bit superiorly. Larger anteversion of the cup is suggested for HDDH.