Reconstruction of massive acetabular bone defects in primary and revision THA is challenging for reconstructive joint surgeons. The use of porous metal augments is one of the options. The advantages of porous metal augments are easy to use, modularity and lack of resorption. We investigated the radiological results of porous metal augments used for massive acetabular bone defects in primary and revision THA.

Forty-one hips in forty patients had porous metal augments between 2011 and 2016. Thirty of the procedures were revision arthroplasties and 11 were primary procedures (Crowe type III in 5 hips, Crowe type IV in 3, septic hip sequalae in 2 and RA in one). Four of the revisions were second-stage reimplantation after infection. The Paprosky classification for revision was 2B in 4 hips, 2C in one, 3A in 3 and 3B in 22. Regenerex augments were used in 39 hips and trabecular metal augments were used in 2. Thirty-six cups were cemented and 5 cups were uncemented.

Mean follow-up was 37.6 months (range, 1–82). Radiographic findings of osteointegration between host bone and the porous metal augments were assessed. The presence or absence of radiolucent lines between cement or cup/host bone and augment/host bone interface was noted.

Two revisions were performed due to infection, one month and 66 months after operation. The other implants were stable without any complications. Osteointegration between host bone and the porous metal augments were recognized in 36 hips. Radiolucent lines between cement/host bone interface, less than 1 mm in width, were visualized in 2 hips.

Porous metal augments are convenient and our short-term results showed excellent radiological results for massive acetabular bone defects in primary and revision THA.

Introduction

The KneeAlign2 (OrthAlign, Inc., Aliso Viejo, CA) is a portable accelerometer-based navigation device for use in performing the distal femoral resection in total knee arthroplasty (TKA). This device works as a computer-assisted surgical system. It does not require the use of a large console for registration and alignment feedback.(image1,2)

Introduction

There have been many attempts to reduce the risk of femoral component loosening.

Using a tapered stem having a highly polished stem surface results in stem stabilization subsequent to debonding and stem-cement taper-lock and is consistent with force-closed fixation design.

In previous congress of ISTA in Hawaii, we reported the results about accuracy of the cup center position in our image-free navigation system. In the new version of our navigation system, leg elongation and offset change as well as cup center position can be navigated. In this study, we therefore investigated the accuracy of cup center position, leg elongation and offset change.

Twenty four THA operations were performed with using the image-free OrthoPilot THA3.1 dysplasia navigation system (B. Braun Aesculap, Tuttlingen, Germany) between August 2009 and December 2009 by three experienced surgeons. In this system, cup center height was shown as the distance from tear drop, and cup medialization was shown as horizontal distance from inner wall of acetabulum. Leg elongation and offset change were navigated by comparing the two reference points in femur between registration before neck resection and that after inserting the trial implant. After operation, the cup angles were measured on CT image, and cup center position, leg elongation and offset change were measured on plain radiography. We compared these values that indicated by the navigation system to those measured on the CT image and the plain radiography.

The average cup inclination was 37.5 ± 7.0 degree and anteversion was 22.2 ± 4.7 degree. The average absolute difference between navigation and measured angles were 5.2 ± 4.0 degree in inclination, 5.9 ± 4.0 degree in anteversion. The difference of cup height was 5.8 ± 3.9 mm, cup medialization was 3.8 ± 2.7 mm, leg elongation was 4.3±3.3mm, and offset was 5.4±4.1mm, respectively.

By using this new version navigation system, we can plan the cup center position and navigate it within smaller error of vertical and horizontal direction than the previous system. Moreover, leg elongation and offset change can be satisfactory navigated during operation. However surgeon's skill and learning curve might have influence the accuracy. We have to continue to evaluate this system and make effort to further improvement.

Nowadays navigation system for THA is widespread and contributes to accurate cup installation as for cup abduction and anteversion angles. On the other hand, cup center position is very important to prevent leg length discrepancy and to acquire appropriate muscle tension especially for DDH cases. However planning and accuracy of cup center position was rarely mentioned when the efficacy of navigation systems were discussed. We therefore examined not only accuracy of cup angles, but also of cup center position in our image-free navigation system for DDH.

One hundred three THA operations were performed with using the image-free OrthoPilot hip navigation system (B. Braun Aesculap, Tuttlingen, Germany) between May 2006 and July 2008 by three experienced surgeons. In this system, we can measure the length between two different points marked by special pointer during surgery. Thus we pointed the upper rim of obturator foramen (this mark was estimated the lower tip of tear drop, and the bottom of reaming hole (this mark was estimated same height from cup center position) before cup installation and measured the vertical length between them(op length). After operation, we measured the vertical length from tear drop to cup center on the x-ray film (xp length), and compared these two values.

The average difference of two values were 6.41±4.17 mm ((op length)-(xp length)). Secondly we divided them into two groups, large error group (> 0.7mm) and small error group (< 0.6mm) and investigated the cause of large error. As result, large error was influenced by difference of surgeons, whereas not influenced by patient’s etiology and BMI.

By using image-free navigation system for DDH, we can plan the cup center position and install it within the error of 6.4mm. This will contribute to avoid a lot of hesitations during surgery. However surgeon’s skill and habitants have influence on this technique. We have to investigate this system and make effort to further improvement continuously.

Direct anterior approach (DAA) is an inter-muscular approach that needs no muscle detached. In THA through DAA approach, exposure of the acetabulum is facilitated, while the key points of this approach are femoral lift-up and hip extension to get sufficient access to the femoral canal. To investigate the strategy for femoral lift-up, we released the capsule step by step and measured the distance of femoral lift-up at each step in cadavers and clinical cases. The effects of hip extension on femoral lift-up were also evaluated.

Three fresh frozen cadavers were used. In supine position, the hip joint was exposed through DAA by two experienced surgeons. After anterior capsulotomy and femoral head resection, posterior capsule release was performed followed by superior capsule release in one side, and superior release was followed by posterior release in the other side. Finally, internal obturator muscle was released in both side. At each step, the distance of femoral lift-up was measured under the traction force of 70N. The effects of hip extension were investigated in 0, 15 and 25 degrees hyper-extension. Thirty-six THA were performed through DAA. Posterior capsule release was performed followed by superior capsule release in 13 hips, and superior release was followed by posterior release in 23 hips. At each step, the distance of femoral lift-up was measured under the traction force of 70N at each step same as the cadaver study.

In cadaver study, anterior capsulotomy and posterior capsule release affected little the femoral lift-up. The distance increased after superior capsular release. The distance decreased as hip hyperextension unless the superior capsule was released. The effect of internal obturator muscle release was not observed. In clinical studies, the same tendency was observed in clinical cases. Superior capsule release was the most effective for the femoral lift-up.

The results of this study indicate that superior capsule release is the first step for the femoral liftup. The second step is hip extension to get access to the femoral canal. By performing these procedures step by step, rasping and stem insertion can be achieved with minimal soft tissue release.

In image-free navigation system, three bony landmarks (typically both anterior superior iliac spines (ASIS) and pubic symphysis) are registered intraoperatively by manual palpation. If the registration of bony landmarks is inaccurate, the final orientation of the cup determined by the navigation system will also be inaccurate. We therefore examined intra-and intersurgeon variability in registration and the distance between registration points in each bony landmark with two surgical positions.

Thirty-seven THAs were performed in the lateral position and 15 THAs were performed in the supine position. The cup was fixed using the image-free Ortho-Pilot hip navigation system (B. Braun Aesculap, Tuttlingen, Germany). The registration was repeated two more times by operator and assistant, and the intra-and intersurgeon variability of cup abduction angle and anteversion was analyzed by ICC (intraclass correlation coefficients). In 25 hips, the distance between intrasurgeon registration points and that between intersurgeon registration points in each landmark were calculated.

The ICC in the lateral position ranged between 0.59 and 0.81, and between 0.85 and 0.95 in the supine position. The ICCs of cup abduction angle for the intra-and intersurgeon variability were 0.92 and 0.95 for the supine position and 0.65 and 0.59 for the lateral position. Those of anteversion were 0.93, 0.85, and 0.81, 0.72, respectively.

The variability of registration of collateral and contralateral ASIS in the lateral position was greater than that in the supine position.

In image-free navigation system, the variability of registration points depended on bony landmarks and patient position. The registrations of pubic symphysis in the supine position and all bony landmarks in the lateral decubitus position are standing further improvement.

Introduction: In total hip arthroplasty, the angle of acetabular component is a critical factor for the postoperative dislocation and the longevity of prostheses. The angle is principally determined in relation to anterior pelvic plane. It is reported that the pelvis tends to tilt posteriorly along with aging. Furthermore, the pelvic tilt might change after THA. The changes might be infiuenced by the hip condition and lumbar lordosis. We measured the pelvic tilt and the lumbar lordosis, and evaluated the effects of contralateral hip and lumbar lordosis on pelvic tilt after THA.

Materials and Methods: Fifty-one unilateral patients and 30 bilateral patients were enrolled in this study. The diagnosis was dysplastic osteoarthritis in all patients. In unilateral patients, the hip was affected in one side and the other hip was normal or acetabular dysplasia without symptoms. In bilateral patients, THAs in both hips were done within two months.

Pelvic inclination angle (PIA) and lumbar lordotic angle (LLA) were measured on the standing lateral X-rays before operation and 1-month, 6-month and 1-year post-operation. The effects of patient age, BMI, ROM of the hip, preoperative PIA and LLA on the changes of PIA were statistically investigated using multiple linear regression analysis. We divided the patients into three groups with regard to pre-operative PIA (anterior group: PIA < 0, intermediate group: 0 < PIA < 10, posterior group: PIA > 10) and with regard to pre-operative LLA (insufficient group: LLA < 20, moderate group: 20 < LLA < 40, severe group: LLA > 40).

Results: Overall, significant factor was only preoperative PIA. In bilateral cases, preoperative PIA and patient age affected the changes of PIA after THA. In patients with severe lordosis, preoperative PIA and LLA were significant factors. PIA increased in anterior tilt group and PIA did not change in intermediate group, while PIA gradually decreased in posterior group. In insufficient lordosis group, PIA remarkably increased after THA compared with that in severe group.

Discussion: Pelvic tilt after THA has been reported without considering the conditions of contralateral hip and lumbar spine. By categorizing patients with regard to the conditions of hips and lumbar spine, we can prospect the tendency of the direction of PIA changes. These results indicated that pre-operative PIA was related the changes of PIA in bilateral group. PIA slightly increased in all bilateral patients, PIA tended to close each other in unilateral patients. Further investigation is necessary to prospect the estimated PIA value after THA.

In revision total hip arthroplasty (THA), it is essential to cope with the bone stock loss. The acetabular bone loss is reconstructed by bulk bone grafts, bone chips, bone cement or jumbo cup. The impaction bone-grafting (IBG) technique is a technique that can restore acetabular bone loss, while enough bone allografts are not easy to obtain and the quality is not always sufficient. Thus we mixed hydroxyapatite (HA) granules into bone chips to supplement the volume and the mechanical strength of allografts. To investigate the dynamic migration of cemented cup fixed with IBG, we made acetabular bone defect models and the migration of the cup was traced by a high-speed photography camera.

Composite test blocks were used as synthetic acetabulum models. A hemisphere defect of 60mm in diameter was made. We tested 4 different bone/HA ratio; 100%/0%, 75%/25%, 50%/50% and 0%/100%. Each group consisted of 6 specimens. The grafted materials were impacted using impactors. Then, a 46 mm polyethylene cup was fixed with bone cement. The specimens were clamped to the MTS mechanical tester at an angle of 20 degrees. A dynamic load of 150 N to 1500 N with a frequency of 1 Hz was applied for 15 minutes, followed by a dynamic load of 300 N to 3000 N for the same time period. Then the load was released for 15 minutes. The cup migration was traced by the camera during loading and releasing. This camera captures 15 images per second thus it enables us to trace the migration of the cup during cyclic loading. The cup migration at the end of 3000N loading was measured. Elastic recoil was defined as the difference between the migration at the end of 3000N loading and that when the load reached to 0N. Visco-elastic recoil was defined as the difference between the migration at the release of loading and that after 15 minutes. Data were investigated by Pearson’s correlation coefficient test.

A strong negative correlation (r = −0.71) was observed significantly between the amount of the migration and bone/HA ratio. In elastic recoil, statistically significant correlation was (r = −0.55) observed. In visco-elastic recoil, there is no correlation between the amounts of the visco-elastic recoil and bone/HA ratio.

In the reconstruction of bone defects, initial stability of the cup is a first step to expect the long term survival. The initial stability depends on the mechanical properties of the grafted materials. To supplement the volume and mechanical strength of bone allografts, we added HA granules to the bone chips. In the current study, the cup migration was smaller by adding HA granules. Elastic recoil was affected, while visco-elastic recoil was not affected. These results indicated that the mixture of HA granules to bone chips stabilized the cup during loading period and load releasing period.

The introduction of porous tantalum metal (Trabecular Metal; Zimmer, Warsaw, IN) for acetabular component fixation in total hip arthroplasty has shown optimum fixation qualities and “gap filling” effect. Recently, trabecular metal was introduced in tibial component for total knee prosthesis, however its effect on the bone mineral density (BMD) was not reported. The purpose of this study was to compare the BMD of proximal part of the tibia between trabecular metal and another cemented tibial component.

31 knees receiving trabecular metal tibial component and 33 knees receiving cemented tibial component (PFC Sigma RP, Depuy, Warsaw, IN) had dual energy x-ray absorptiometry (DEXA) scans at preoperatively and 3 weeks, 3, 6, 12, 18, 24 months post-operatively. To assess peri-prosthetic BMD, three regions of interest (ROI) were measured for each case. They were medial aspect (ROI 1), center aspect (ROI 2) and lateral aspect (ROI 3) of tibia. Average follow up period was 1.8 (range: 1.5 to 2) years. In both groups, BMD in tibia decrease postoperatively. Comparing postoperative decrease of BMD in lateral aspect of tibia (ROI 3) between both groups, it was significantly less in trabecular metal component (−0.09 g/cm2 +/−0.27) than cemented tibial component (−0.31 g/cm2 +/− 0.21) (p=0.0007).

We conclude that trabecular metal tibial component showed a favorable effect on BMD of proximal part of the tibia after total knee arthroplsaty.

Highly closslinked polyethylene has been developed to reduce polyethylene wear and to expect the longevity of THA. In daily activity of patients, total hip prostheses repeatedly suffer impact loading. However, the mechanical properties, especially impact load transmission, are not well investigated and the viscoelasticity might influence the loosening of cemented all-polyethylene cup. In this study, the impact load transmission through the complex of polyethylene cup, ceramic ball and metallic femoral stem was investigated.

Impact compressive tests on the complex were performed using Hopkinson pressure bar apparatus. Conventional and highly crosslinked polyethylene cups of three different sizes (40mm, 50mm, 56mm)were compared. The impact load was applied either from the cup or from the stem. The impact load transmission ratio (ILTR) i.e. the ratio of the magnitude of transmitted load to that of incident one was investigated. The loading pulse profiles were theoretically calculated based on the one dimensional elastic wave propagation theory and were compared with experimental results.

The ILTR was independent of the cup size in all experimental conditions. When the impact load was applied from the cup, the ILTR was not different between two types of polyethylene. On the other hand, when the impact load was applied from the stem, the ratio was greater than the previous loading condition, while the ratio of crosslinked polyethylene was significantly lower than that of conventional one (p < 0.05). The theoretically predicted stress pulse profiles were well correlated to the experimental ones.

The lower ILTR in highly crosslinked polyethylene is considered to be due to lower stiffness. These mechanical properties increase the deformity of the cup and may cause the loosening of the cup. These results indicated that the ILTR was not different among cup sizes, while the ratio was significantly affected by the loading conditions and the type of polyethylene.

Highly crosslinked polyethylene has been developed to reduce polyethylene wear and to expect the longevity of THA. In daily activity of patients, total hip prostheses repeatedly suffer impact loading. However, the mechanical properties, especially impact load transmission, are not well investigated and the viscoelasticity might influence the loosening of cemented all-polyethylene cup. In this study, the impact load transmission through the complex of polyethylene cup, ceramic ball and metallic femoral stem was investigated.

Impact compressive tests on the complex were performed using Hopkinson pressure bar apparatus. Conventional and highly crosslinked polyethylene cups of three different sizes (40mm, 50mm, 56mm) were compared. The impact load was applied either from the cup or from the stem. The impact load transmission ratio (ILTR) i.e. the ratio of the magnitude of transmitted load to that of incident one was investigated. The loading pulse profiles were theoretically calculated based on the one dimensional elastic wave propagation theory and were compared with experimental results.

The ILTR was independent of the cup size in all experimental conditions. When the impact load was applied from the cup, the ILTR was not different between two types of polyethylene. On the other hand, when the impact load was applied from the stem, the ratio was greater than the previous loading condition, while the ratio of crosslinked polyethylene was significantly lower than that of conventional one (p < 0.05). The theoretically predicted stress pulse profiles were well correlated to the experimental ones.

The lower ILTR in highly cross linked polyethylene is considered to be due to lower stiffness. These mechanical properties increase the deformity of the cup and may cause the loosening of the cup. These results indicated that the ILTR was not different among cup sizes, while the ratio was significantly affected by the loading conditions and the type of polyethylene.

Introduction: Recently, highly cross-linked polyethylene has been highlighted in THAs, which is thought to reduce wear. However, little is known about an accurate nature of cross-linked polyethylene particles and long term wear in vivo. One of the authors implanted all polyethylene cups irradiated by 100 Mrad in 1970’s. Recently, we performed two revisions with this cup. In the present study, we extracted polyethylene particles and analyzed them.

Methods: Case1 was revised for a stem fracture and ace-tabular loosening at 25 years postoperatively and case2 for acetabular loosening at 27 years postoperatively. There was no osteolysis on X rays. We extracted polyethylene particles using a tiussue digestion and iamge analysis using computed iamge analyzer developed by Cambell.

Results: Equivalent circle diameter (ECD) was 0.73mm, roundness was 0.69, aspect ratio (AR) was 1.4 and number of particles was 6.0x108/g wet tissue in case1. ECD was 0.57mm, roundness was 0.62, AR was 1.54 and number of particles was 5.8x108/g in case2. SEM showed that granule or globular shapes were abundant and fibril shapes were rare.

Discussion and conclusion: Cross-linked polyethylene particles were less, a little smaller and much rounder in compared with our previous result of conventional polyethylene particles in peri-implant tissue after more than 25 years postoperatively in vivo.

Impaction allografting is one of the techniques for reconstruction of femur during revision total hip arthroplasties. The initial stability of the stem fixed with impacted morsellized allogtafts and cement depends on multiple factors. The aim of this study was to investigate the stability of stem in reference to the size of bone chips, femoral bone defect and implant design.

Morsellized grafts of human femoral heads were prepared using a reciprocating type bone mill or a rotating type bone mill. Femoral bone defect was created at proximal medial cortex. Two types of polished stem were tested; CPT stem and VerSys CT stem (Zimmer Inc.). The cross section of the stem was relatively rectangular in CPT stem, while round in VerSys CT stem. Morsellized grafts were impacted into an over-reamed plastic bone and the stem was fixed with PMMA bone cement. Cyclic compression test and torsional test were performed using an Instron type machanical tester. Bone chips prepared by a reciprocating type bone mill contained large chips with broad size distribution, which represented high stiffness in compression test and high maximum torque in torsional test. Femoral bone defect and implant geometry did not affect the axial stability of stem, while large bone defect and round shape stem showed significantly lower maximum torque.

These results indicated that the size of bone chips, femoral bone defect and implant geometry affected the initial stability of the stem. Impaction grafting seems to be a technically demanding procedure, however several factors can be controlled to obtain secure implant stability.

As for the number of patients who requires total knee arthroplasty (TKA), Asian-Pacific countries will be the most important market. However, due to the paucity of anthropometric data on the proximal tibia in this population, many prostheses designed for Caucasian knees have been introduced without specific modification.The aim of the current study was to analyze the geometry of the proximal tibia to design the optimum component for the Japanese population.

Anthropometric data on the proximal tibia of 100 knees in 80 patients undergoing TKA was obtained. Briefly, anterior-posterior (AP) and medial-lateral (ML) lengths were measured with a combination of two different methods, namely on the computed tomography (CT) images obtained preoperatively and intraoperative direct measurement on tibial resection surface. Reproducible measurement was possible only when the intraoperative measurement was combined with the corresponding CT images while the direction of measurements being aligned to the epicondylar axis of the femur.

It was shown that smaller components with an ML of around 60 mm were rarely required. Tibial component size variation should focus on an ML length of 65 to 75 mm because 76 of 100 knees (76 %) fell into this size range. When the subjects were confined to women, 70 of 77 knees (91%) were included in this size range. The intraoperative AP to ML ratio had a negative correlation with the ML length (r = −0.412, P < 0.0001) indicating that bigger knees were shallower in the AP direction. The size variation of currently popular pros-theses were not in accordance with the geometry of the tibial resection surface shown in this study.

The results of this study applied to a cross-section of the Japanese population can be used by manufacturers to create a prosthesis suitable for most of the Asian-Pacific population.

Aim: In alumina-on-alumina (Al/Al) THA, microsepa-ration is reported to accelerate wear and to be a risk factor of alumina cup fracture. While microseparation after THA is detected during walking, microseparation also occurs in relation to the hip position. Using Al/Al THA with cemented polyethylene-back alumina cup, the microseparation is clearly visible on plain roentgen-ograms. The aim of this study is to investigate the factors that affect hip position related microseparation. Materials and Methods: We performed 65 primary Al/Al THA. An average age at operation was 61.1 years and an average follow-up period was 29.5 months. Roentgenograms were taken in hip neutral position, abduction, adduction, external rotation and internal rotation. Results: Microseparation was observed in 15 hips (23.1%); 10 hips with hip external rotation and 5 hips with hip abduction. An average abduction angle of the cup was 33.5±9.8 degrees with microseparation and 36.6±7.3 degrees without microseparation. An average anteversion of the cup was 9.7±6.7 degrees and 7.8±5.8 degrees, respectively. The factors that brought about microseparation were postoperative muscle weakness in 3 hips, impingement in 9, cup malposition (abduction angle: 19, 23 degrees) in 2, and short off-set stem in one. Discussion and Conclusions: It should be noted that microseparation is not a rare phenomenon and it occurs in hip particular position even if it can not be detected on routine roentgenograms.

Introduction: Based on epidemiological results, steroid (glucocorticoid) hormone is accepted as a major causative agent of osteonecrosis, though its pathomechanism is not elucidated. However, not all patients who receive high doses of steroid develop osteonecrosis. This fact suggests risk factor(s) for steroid-induced osteonecrosis. In order to identify such risk factors, the association of CYP3A6 (a major enzyme metabolizing glucocorticoid in rabbit) level with the incidence and extent of osteonecrosis in a rabbit model was determined.

Materials and Methods: In this rabbit model, the CYP3A6 level was modulated by an inhibitory (Itraconazole, 150mg p.o. twice a day for 3 weeks) or inducing agent (rifampicin, 100mg/kg i.p. in first 3 days). Three weeks after modulation of CYP3A6, steroid-induced osteonecrosis was generated by i.m. injection of methyl-prednisolone (20mg/kg BW). Three weeks later, the animals were sacrificed and bilateral femurs were excised and examined histologically for bone and marrow necrosis.

Results: In control animals without modulation of CYP3A6, focal and/or extensive necrosis was noted in 5 of 7 animals. In Itraconazole-treated animals, all of 5 animals revealed extensive necrosis in femoral bone marrow. In rifampicin- treated animals, incidence of necrosis was similar to that of controls but necrotic foci were significantly smaller than those in controls.

Discussion: These experimental results indicated that low level of steroid-metabolizing enzyme CYP3A6 (CYP3A4 in humans) at the time of steroid treatment might be a risk factor for extension of steroid-induced bone necrosis, and that induction of CYP3A6 might prevent steroid-induced bone necrosis.

The purpose of this study was to investigate the bone anatomy in determining the rotational alignment in total knee arthroplasty (TKA) using CT scan. Axial CT images of eighty-four varus osteoarthritic knees undergoing TKA were analysed. On the images of the distal femur and the proximal tibia, base line for anterior-posterior axis of each component was drawn based on the epicondylar axis for the femur and medial one-third of the tibial tuberosity for the tibia. Angle between these two lines was analysed as the rotational mismatch between the components when they were determined based on the anatomical landmark of each bone. Thirty-eight knees (45%) showed more than 5-degree mismatch and seven knees (8.3%) showed the mismatch more than 10-degree. There was a tendency to put the tibial component in external rotation relative to the femoral component when they were aligned to medial one-third of the tibial tuberosity. The results have indicated that the landmark of each bone was the intrinsic cause of the rotational mismatch between the components. The surgeons performing TKA surgery should aware of this fact and should align the tibial component in a compromised position, if necessary, to have overall satisfactory clinical outcome.