Introduction. Bulk bone grafting is commonly used in total hip arthroplasty (THA) for developmental dysplasia. However, it is a technically demanding surgery with several critical issues, including graft resorption, graft collapse, and cup loosening. The purpose of this study is to describe our new bone grafting technique and review the radiographic and clinical results. Patients and Methods. We retrospectively reviewed 105 hips in 89 patients who had undergone covered bone grafting (CBG) in total hip arthroplasty for developmental dysplasia. We excluded patients who had any previous surgeries or underwent THA with a femoral shortening osteotomy. According to the Crowe classification, 6 hips were classified as group I, 39 as group II, 40 as group III, and 20 as group IV. Follow-up was at a mean of 4.1 (1 ∼ 6.9) years. The surgery was performed using the direct anterior approach. The acetabulum was reamed as close to the original acetabulum as possible. The pressfit cementless cup was impacted into the original acetabulum. After pressfit fixation of the cup was achieved, several screws were used to reinforce the fixation. Indicating factor for using CBG was a large defect where the acetabular roof angle was more than 45 degrees and the uncovered cup was more than 2 cm (Fig.1). The superior defect of the acetabulum was packed with a sufficient amount of morselized bone using bone dust from the acetabular reamers. Then, the grafted morselized bone was covered with a bone plate from the femoral head. The bone plate was fixed with one screw to compact the morselized bone graft. The patient was allowed to walk bearing full weight immediately after surgery. We measured the height of the hip center from the teardrop line and the pelvic height on anteroposterior roentgenograms of the pelvis and calculated the ratio of the hip center to the pelvic height. We defined the anatomical hip center as the height of the center less than 15 % of the pelvic height, which was nearly equal to 30 mm, because the mean pelvic height was 210 mm. Results. The mean height of the hip center was 9.8 (4.1∼18.0) % of the pelvic height and the 101 (96.2%) cups were placed within the anatomical hip center. Radiographically, in all patients, the host-graft interface became distinct and the new cortical bone in the lateral part of the plate bone appeared within 1 year after surgery (Fig.2, 3). We observed no absorption of the plate bone graft and no migration of the cup at the last follow-up. Conclusion. CBG technique is simple, because the bone graft is always performed after the pressfit of the cup is achieved. Moreover, patients require no partial weight bearing postoperatively, because the cup is supported by the host bone with the pressfit and additional screws. The CBG technique would be an excellent option for the reconstruction of the acetabulum in patients with severe dysplasia to avoid a high hip center and bulky bone grafting

Introduction. Bulk bone grafting of the cup is commonly used in total hip arthroplasty (THA) for developmental dysplasia. However, it carries a risk of the graft collapse in the mid-term or long-term results. The purpose of this study is to describe our new bulk bone grafting technique and review the radiographic and clinical results. Patients and Methods. We retrospectively reviewed 85 hips in 74 patients who had undergone bulk bone grafting in total hip arthroplasty for developmental dysplasia between 2008 and 2013. We excluded patients who had any previous surgeries or performed THA with the femoral shortening osteotomy. According to the Crowe classification, 4 hips were classified as Type 1, 28 as Type 2, 35 as Type 3, and 18 as Type 4. Follow-up was at a mean of 4.0 years (1 to 6.1). The surgery was performed using the direct anterior approach on a standard surgical table. The acetabulum was reamed for as close to the original acetabulum as possible. The pressfit cementless cup was impacted into the original acetabulum. After the pressfit fixation of the cup was achieved, two or three screws were used to reinforce the fixation. The superior defect of the acetabulum was packed with sufficient amount of morselized bone graft. Then, the bulk bone was placed on the morselized bone graft and fixed with one screw. Post-operatively, there were no restrictions to movement or position. On the first day after surgery, the patient was allowed to walk with full weight-bearing. We measured the height of the hip center from the interteardrop line and the pelvic height on anteroposterior roentgenograms of the pelvis and calculated the ratio of the hip center to the pelvic height. We defined the anatomical hip center as the height of the center less than 15% of the pelvic height. Results. The mean height of the hip center was 10.2 (4.1∼18.0)% of the pelvic height and the 81 (95.2%) cups were placed within the anatomical hip center. We observed no collapsed grafts, no severe absorption of the grafts, and no migration of the cup at the last follow-up. Conclusion. In our technique, there is no concern of the bulk bone graft collapse even in the long-term results, because the cup is not supported by the bulk bone graft but by the host bone with the pressfit and additional screws. Moreover, 95.2% of all cups were placed within the anatomical hip center. In conclusion, our new bulk bone graft technique would be simple to perform and an excellent option for the reconstruction of the acetabulum in patients with severe dysplasia

There is increasing interest in the use of image free computer assisted surgery (CAS) in total hip arthroplasty (THA). Many of these systems require the registration of the Anterior Pelvic Plane (APP) via the bony landmarks of the anterior superior iliac spines (ASIS) and pubic tubercles (PT) in order to accurately orient the acetabular cup in terms of anteversion and inclination. Given system accuracies are within 1mm and 1° and clinical validation studies have given accuracy by cup position. However, clinical outcomes contain not only system inaccuracies but also variations due to clinical practice. To understand the effects of variation in landmark acquisition on the identification of the acetabular cup orientation, independent bench testing is required. This requires a phantom model that can represent the range of pelvises, male and female, encountered during THA and introduce deliberate known errors to the acquisition to see the effect on anteversion and inclination angles. However, there is a paucity of information in the literature with regards to these specific pelvic dimensions (pelvic width and height). Therefore the aims of this work were to generate the normal expected range of sizes of the APP for both males and females and to use these to manufacture a phantom model that could be used to assess CT free navigation systems. In the first part of the study 35 human cadavers and 100 pelvic computed tomography (CT) scans were examined. All cadavers had no gross pelvic abnormalities or previous surgeries. Measurements were carried out with cadavers placed in a supine position. The first author made three sets of measurements using a millimeter ruler. Solid steel pins were used to identify the palpated ASISs and PTs. String was tied between the two ASIS pins and the pelvic width measured. The midpoint of the pubic tubercles was taken to be the midpoint of the pubic symphysis. Pelvic height was measured from the midpoint of the ASIS distance (marked on the string) to the midpoint of the PTs. One hundred pelvic CT scans with no bony abnormalities, previous surgery or metal prosthesis (due to artefacts) were obtained retrospectively from the hospital radiological online system (PACS, Kodak). Mimics software (Mimics12 Materialise, Leuven, Belgium) was used to automatically reconstruct three-dimensional (3D) models using the ‘Bone’ thresholding function. This eliminated any soft tissue from the 3D models. The most anterior ASIS and PT points were then identified on the 3D model surface and measurements of distances made. As the software did not allow identification of points not on the model surface it was not possible to directly obtain the midpoint of the ASIS distance. Therefore to obtain the pelvic height measurements the distance between each ASIS and the ipsilateral and contralateral PTs was also measured. The pelvic height was then calculated using trigonometric functions. The ratio of width to height was calculated (ratio > 1 indicating pelvis width greater than pelvis height). Student's t test was used analyse any differences between male and female pelvic measurements with a p<0.05 being statistically significant. Using the results from above an aluminium pelvic phantom model was designed and manufactured. It was machined from a billet of marine grade aluminium alloy using a vertical computer numerical controlled (CNC) milling machine. The top surface represented the APP and sides (which represented the acetabuli) were angled to give anteversion and inclination angles of 20° and 45° respectively. Co-ordinates for ASIS and PT points were given based on the 99% prediction intervals from the pelvic data and additional points were milled to give up to a 20 mm error mediolaterally and also in height. Each co-ordinate point was drilled with a 2.0mm diameter ball-nose cutter to a depth of 1.0mm, these holes designed to accommodate the ball-nosed pointer tip to ensure it remained at the same position in space at all orientations of the pointer. Further to this, known errors in height were introduced using accurately manufactured blocks with similar points milled on the surface to fit a ball-nosed pointer. These blocks could be secured to the top surface of the model using screws. A Perspex base unit with tracker attachments was made to hold the phantom and provide the reference frame. A further support that enables the phantom to also be used in the “lateral” position was manufactured. For the assessment of pelvic size there were 66 females and 69 males, mean age 62.3 years (range from 20 to 99 years). The mean width was 238 mm (SD 20 mm) and mean height was 93 mm (SD 11 mm) with a mean ratio of 2.6 (SD 0.3). There were no statistically significant differences in mean between males and females (p>0.4 in all cases). From this data set the range of APP sizes required to cover 99% of population (width 186 to 290 mm and height 66 to 120 mm) and therefore the measurements for the model were generated. The manufactured model can be used to give the range of pelvis sizes from 170mm to 290mm in width and 60mm to 120mm in height and also to add up to 20 mm of error in palpation of each of the ASISs and PT. This study generated APP sizes to cover 99% of the general population over a wide age range. It illustrated that a single pelvic model would fit both sexes. The model allows the determination of the effects of changes of the pelvic dimensions may have on the acetabular orientation measured on an image free CAS system including the assessment of point acquisition and deliberate errors. The model has been successfully used in preliminary testing and can be used to assess any CT free system