The anterior pelvic plane (APP) angle is often used as a reference to decide pelvic alignment for hip surgeons. However, Rousseau criticised the validness of the APP angles because the APP angles in standing position measured on conventional standing X-ray films never showed correlation with the other pelvic alignment parameters, such as sacral slope (SS). We measured the APP angles, SS and pelvic tilt (PT) on the non-distorted anteroposterior (AP) and lateral digitally reconstructed radiography (DRR) images in supine position (with CT scans) and AP and lateral X-ray images in standing position (with EOS X-ray machine [EOS imaging, Paris, France]) by using of the same EOS software. Our data showed that the pre- and post-operative APP angles correlated with SS and PT in both supine and standing positions. Our non-distorted high quality images and the EOS software revealed these correlations. Therefore, we can still use the APP angles to decide pelvic alignment for patients who undergo total hip arthroplasty (THA). Recent papers demonstrated positional or chronological dramatic changes of the APP angles between pre- and post-operative states in patients who underwent THA. The EOS system will be a powerful tool to investigate these changes of the pelvic alignments.

Introduction

The safe zone of the acetabular cup for THA was discussed based on the AP X-ray films of hip joints. A supine position is still used to determine the cup position for CAOS such as navigation systems. There were few data about the implant positions after THA in standing positions. The EOS X-Ray Imaging Acquisition System (EOS system) (EOS imaging Inc, Paris, France) allows image acquisition with the patients in a standing or sitting position. We can obtain AP and lateral X-ray images with high-quality resolution and low dose radiation exposure. Recently, we have obtained the EOS system for the first time in Japan. We investigated 3D accuracy of the EOS system for implant measurements after THA.

An ultra-high molecular weight polyethylene (UHMWPE) is widely used as bearing material in artificial joints, however, UHMWPE wear particles are considered to be a major factor in long-term osteolysis and loosening of implants. The wear particles activate macrophages, which release cytokines, stimulating osteoclasts, which results in bone resorption. The biological activity of the wear debris is dependent on the volume and size of the particles produced. Many researchers reported that the volume and size of particles were critical factors in macrophage activation, which particles in the size range of 0.1–1 mm being the most biological active.

To minimize the amount of wear of UHMWPE and to enlarge the size of UHMWPE wear particle, a nano-level surface texturing on Co-Cr-Mo alloy as a counterface material was invented. Although the generally-used surface for a conventional artificial joint has 10 nm roughness (Surface A), the nano-level textured surface invented has a superfine surface of 1 nm with 3% of groove and dimples against the bearing area. The depths of groove and dimples are less than 50 nm (Surface F).

Pin-on-disc wear tester capable of multidirectional motions was used to verify that the nano-textured surface is the most appropriate for artificial joint. UHMWPE pin with an average molecular weight of 6.0 million was placed in contact with the disc and the contact pressure was 6.0 MPa. The disc and pin were lubricated by a water-based liquid containing the principal constituents of natural synovial fluid. Sliding speed of 12.12 mm/s had been applied for total sliding distance of 15 km.

The superfine surface with nano-level grooves and dimples (Surface F) reduced the amount of UHMWPE wear, this would ensure the long-term durability of artificial joint. The wear particles isolated from lubricating liquid were divided broadly into two categories; one is “simple type” and the other is “complicated type”. The lengths in a longitudinal direction (L_l) and its orthogonal direction (L_s) for each particles (>150) were measured, and the each aspect ratio (= L_l/L_s) was calculated. No significant difference was found in the ratio between simple type and complicated type, and in the distributions of aspect ratios. However, the distributions of L_l, which means the size of UHMWPE wear particle, were dramatically changed by using the nano-textured surface (Figure 2). These results suggest that the nano-textured surface does not change the morphological aspect of UHMWPE particle but enlarges the size of UHMWPE particle.

Cells (RAW264.7, blood, Mouse) were cultured with the particles in supplemented Dulbecco's modified Eagle's medium for 24 h in an atmosphere of 5% CO₂ in air at 37 degrees C, and the quantitative PCR was performed for genetic expression of IL-6 (Figure 3). The wear debris generated on the nano-textured surface inhibited the genetic expression of IL-6, which does not induce the tissue reaction and joint loosening.

Total hip arthroplasty (THA) using minimally invasive surgeries (MIS) now become popular operative procedures. It is not easy to understand geometric information of pelvis and femur in the restricted operative fields during MIS-THA. Recently, THA in supine position comes into the limelight again to place acetabular cups in an optimum position because we can minimise the intra-operative pelvic motion during THA in supine position. To verify the usefulness of supine position, we measured the angels of acetabular trial cups intra-operatively using the CT-based navigation system. The trial cup positions were placed according to a conventional acetabular cup alignment guide. We compared the angles of acetabular trial cups between supine and lateral positions through the same MIS antero-lateral (AL) surgical approach.

Thirty eight hips underwent THA in lateral position (the AL group; average age: 63.9 years old, female: 29 cases, 33 hips, male: 5 cases, 5 hips) and 40 hips underwent THA in supine position (the AL Supine group; average age: 62.2 years old, female 40 cases, 40 hips) were subjected in this study. The single surgeon (the first author) performed all surgeries. We used the Roettinger's modified Watson-Jones approach in both groups. The pelvic registration for navigation was carried out using the CT-fluoro matching procedure with VectorVision Hip (BrainLAB, Germany). After acetabular reaming, the acetabular trial cups were placed into the reamed acetabulum to be at 45 degrees of operative inclination (OI) and at 20 degrees of operative anteversion (OA) using a conventional acetabular cup alignment guide. These angles of the trial cups were measured intra-operatively using the CT-based navigation system, VectorVision Hip. After removing the acetabular trial cup, the acetabular cups were placed using the navigation system. Trilogy cups (Zimmer, USA) and AMS HA shells (JMM, Japan) were used in this study.

The average angles of OI were 45.7 degrees (SD 5.5 degrees) in the AL group and 46.3 degrees (SD 4.6 degrees) in the AL Supine group. The average angles of OA were 30.0 degrees (SD 13.5 degrees) in the AL group and 23.5 degrees (SD 8.2 degrees) in the AL Supine group. The hip numbers whose errors were less than 10 degrees were 13 hips in the AL group and 26 hips in the AL Supine group, respectively. There was significant difference in hip numbers whose errors of angles were less than 10 degrees between the AL and Supine groups. The hip numbers whose errors were less than 5 degrees were 7 hips in the AL group and only 6 hips in the AL Supine group, respectively. There was no significant difference in hip numbers whose errors of angles were less than 5 degrees between the AL and Supine groups. The error values of OI were less than 10 degrees except one hip in both groups. However, the error values of 25 hips in the AL group were more than 10 degrees.

In lateral position, the pelvis easily rotated when the affected lower extremity was extended, externally rotated, and adducted during the femoral preparation in the AL group, which resulted in malalignment of acetabular OA. In contrast, most hips could be set with the error values less than 10 degrees in the AL Supine position because the pelvis could be stabilised on the operative table. In addition, landmarks, such as bilateral antero-superior iliac spines and the symphysis pubis, were palpable in supine position. However, the hips with error values less than 5 degrees were only 6 out of 40 hips even though in supine position. Using MIS techniques, we can provide more stable hip joint just after surgery since the muscles surrounding hip joints can be preserved. We have to place acetabular cups in an optimum position to achieve wide range of hip motion to prevent dislocation and to provide limitation-free daily activities for patients. These data suggests that we should use more accurate guide systems for acetabular cup replacement such as navigation systems, patient specific templates, and patient specific mechanical instruments to place acetabular cups in an optimum position.

The purpose of this study was to evaluate the effect of previous femoral osteotomy on the outcome of total hip replacement performed for degenerative arthritis secondary to developmental dysplasia of the hip.

Eighty three primary total hip arthroplasties were performed in sixty-nine patients with osteoarthritis secondary to developmental hip dysplasia (DDH) with a minimum three year follow up. Twenty six hips had undergone previous femoral osteotomy (eleven hips, femoral osteotomy alone (FO); fifteen hips, combined femoral and pelvic osteotomy and fifty-seven hips, no previous surgery. The non operative patients with DDH served as an age and sex matched control group (control). Cementless arthroplasty was performed in seventy-eight hips. The mean duration from femoral osteotomy to primary THA was 22.9 years. The mean follow up was 7.6 years (FO) and 7.2 years (control).

The overall revision rate was 15.4 % (FO) and 21.1 % in the Control group (p> 0.05). Twenty-one hips had one or more complications during or after surgery. The FO group had a higher femoral fracture rate (23.1%) compared to controls (10.5%) (p< 0.05). At latest mean follow-up (7.4 yrs (range, two to sixteen)), the mean Harris hip score was eighty-five (FO) and eighty-five (control group) (p> 0.05). The function and pain scores in the femoral osteotomy group were similar to the controls (p> 0.05). The requirement for bone grafting was similar and operative time significantly greater (FO) compared to controls. The frequency of radiolucent lines around the femoral component in the FO group (36%) was significantly higher than the control group (12.2%) (p< 0.05). Survival analysis was performed with the Kaplan-Meier method. At ten years, the survival of the acetabular component was 84.6%/73.6% and for the femoral component 92.2%/96% in the FO/control group.

Patients with a prior femoral osteotomy have no significant difference in functional outcome, overall complication rate or revision rate compared to controls. However, there is a significant increase in femoral fracture and operative time. Previous femoral osteotomy does not compromise the functional outcome of subsequent total hip arthroplasty.

Purpose: To determine the differences in bone remodelling between a metaphyseal and a diaphyseal fixed stem in uncemented total hip arthroplasty.

Methods: Twenty-three patients undergoing uncemented total hip arthroplasty (28 hips) utilizing a metaphyseal fit stem were matched to 27 patients (32 hips) undergoing uncemented total hip arthroplasty utilizing a diaphyseal fit stem. Patients were matched for age, gender and follow-up. All patients were assessed by clinical and radiographic examination at 6 weeks, 3 months, 6 months and yearly thereafter. Radiographs were assessed for periprosthetic bone remodelling, canal fill, canal shape and bone quality using the cortical index and the Singh index. At latest follow-up all radiographs were assessed for frequency and time of appearance of spot welds, cortical hypertrophy and development of pedestal formation. All patients were assessed clinically utilizing the modified Harris hip score.

Results: At one year there was no difference in the clinical results between the two groups of patients utilizing the modified Harris hip score 90.6 + 1.5 in metaphyseal fit stems versus 91.7 + 1.7 for diaphyseal fit stems (p> 0.05). There was no statistical difference between the two groups in either femoral canal shape or bone quality–canal-to-calcar ratio 0.49 versus 0.45 (p> 0.05); cortical index 0.45 versus 0.44 (p> 0.05); Singh index 3.44 versus 3.70 (p> 0.05). In assessing canal fill proximal canal fill was statistically greater in metaphyseal fit stems and distal canal fill was significantly greater in diaphyseal fit stems (p< 0.01). There was a statistically significant increase in the frequency and timing of spot welds in metaphyseal stems at 3 months and 6 months (p< 0.05) but no difference in the frequency of spot welds at 1 year and 2 years. Cortical hypertrophy was significantly increased at 6 months, 1 year and 2 years in metaphyseal fit stems as compared to diaphyseal fit stems (p< 0.05). There was no difference in pedestal formation at 1 year or 2 years between the two stem groups (p> 0.05).

Conclusions: After one year the only significant difference between these two groups of patients is increased cortical hypertrophy in those patients undergoing metaphyseal versus diaphyseal stem insertion. Both stem designs demonstrated bone remodelling with no differences in spot welds or pedestal formation. At two years there was no functional difference between these two patient groups.

Purpose: In uncemented total hip arthroplasty, stem design is one of the important factors influencing bone remodeling. The purpose of this study was to determine the differences in bone remodeling between metaphyseal and diaphyseal fit stems.

Methods: Twenty-three patients undergoing total hip arthroplasty (28 hips) with metaphyseal fit stems were matched to 27 patients (32 hips) undergoing uncemented total hip arthroplasty with diaphyseal fit stems. Preoperative radiographs were assessed for canal fill, canal shape, and bone quality. Postoperative radiographs were assessed for frequency and time of appearance of peri-prosthetic bone remodeling including spot welds, cortical hypertrophy and pedestal formation. All patients were examined by a modified Harris Hip Score.

Results: The proximal canal shape and bone quality were similar in both groups. There was no difference in the frequency of spot welds at 1 year and 2 years. Spot welds were mainly located in Gruen zone 1. Cortical hypertrophy was greater (p < 0.05) at 6 months, 1 year and 2 years with the metaphyseal fit stem. Cortical hypertrophy was found only in Gruen zones 3 and 5. Halo pedestal formation was greater (p < 0.05) at 6 months with the metaphyseal fit stem but not at 1 year and 2 years. Calcar rounding was observed in 25 hips (90.0%) with metaphyseal fit stems and twenty hips (62.5%) with diaphyseal fit stems. At the last follow-up, average HHS was similar (90.6 +/− 1.5 / 91.7 +/− 1.7; metaphyseal / diaphyseal fit stems). No patient developed aseptic loosening.

Conclusions: This is the first study to determine differences in bone remodeling between a metaphyseal and a diaphyseal fixed stem in uncemented THA. After one year, the only significant difference between these two groups was cortical hypertrophy, which was greater in patients undergoing metaphyseal fit stem insertion. Both stem designs demonstrated bone remodeling with no differences in spot welds or pedestal formation. At two years, there was no functional difference between these two patient groups. To further elucidate the relation between radiographic and clinical results, longer term follow-up is required.