Kazuhiko Sonoda

The role of sclerotic changes in the starting mechanisms of collapse: A histomorphometric and FEM study on the femoral head of osteonecrosis

PURPOSE To assess the distributions of stress, strain, and fractured areas using a finite element model (FEM), and examine the osteoclastic activity histopathologically in osteonecrosis of the femoral head. METHODS Three femoral heads were obtained during hip arthroplasty for femoral head osteonecrosis. One sample with a normal area, two samples with a non-sclerotic boundary without collapse (Type 1), two samples with a non-collapsed sclerotic boundary (Type 2), and two samples with a collapsed sclerotic boundary (Type 3) were collected from each femoral head for the FEM and histopathological analyses. FEM was performed using CT data, and the distributions of von Mises equivalent stress, octahedral shear stress, octahedral shear strain, and simulated fractured area were evaluated. Furthermore, the osteoclast count at the boundary was compared for each type. RESULTS In normal and Type 1 samples, the distributions of von Mises equivalent stress, octahedral shear stress, octahedral shear strain, and the fractured area were equally concentrated along the whole analytical range; however, in the Type 2 and 3 samples, they were concentrated along the thickened bone trabeculae at the boundary, which corresponded to the fractured area. Histopathologically, a significantly increased osteoclast number was observed only at the collapsed sclerotic boundary. CONCLUSION These results demonstrated that both shear stress and shear strain tend to be concentrated on thickened bone trabeculae at the boundary. Fracture analyses revealed that the boundary of sclerotic changes, which results from the repair process, may be the starting point of the fracture. Additionally, the osteoclastic activity increases after collapse.

Contralateral osteonecrosis of the femoral head newly developed after increasing the dose of corticosteroids

Nontraumatic osteonecrosis of the femoral head (ONFH) is a debilitating disorder that commonly affects 30to 50-year-old individuals, with corticosteroid use being one of the major causative factors [1]. Although the precise pathogenesis of corticosteroid-induced ONFH remains unclear, both high-dose oral corticosteroid therapy and corticosteroid pulse treatment have been reported to be risk factors, highlighting the importance of the dose of corticosteroids in the development of corticosteroid-induced osteonecrosis [2–7]. Corticosteroid-induced osteonecrosis often affects both femoral heads (50–70 %), and bilateral ONFH is considered to develop concurrently [1, 2]. In contrast, in patients with unilateral ONFH, it is rare that new osteonecrotic lesions subsequently develop in the contralateral femoral head. To our knowledge, there are no reports in the literature regarding the development of new corticosteroidinduced ONFH lesions on the contralateral side. Here we report the case of a patient who developed new ONFH in the contralateral hip after increasing the dose of corticosteroids for a different underlying disease. We clearly indicate that written informed consent for publication was obtained from the patient. Case report

Degeneration of articular cartilage in osteonecrosis of the femoral head begins at the necrotic region after collapse: a preliminary study using T1 rho MRI

ObjectiveThe purpose of this study is to evaluate the role of collapse on the degeneration of articular cartilage in patients with osteonecrosis of the femoral head (ONFH).Materials and methodsSixteen hips in 12 patients (four men, eight women; mean age, 34.8 years) with a history of systemic corticosteroid treatment were studied using T1 rho magnetic resonance imaging (MRI). Six hips had collapsed ONFH, five had non-collapsed ONFH, and five had no osteonecrosis (controls). Using oblique coronal images, we divided the articular surface of necrotic femoral heads into a region just above the necrotic bone (necrotic zone) and another above the living bone (living zone). T1 rho value was evaluated for each zone.ResultsThe mean T1 rho value in the necrotic zone was significantly higher in the collapsed ONFH group (48.4 ± 2.7 ms) than in the non-collapsed ONFH group (41.0 ± 0.9 ms). In the collapsed ONFH group, the mean T1 rho value was significantly higher in the necrotic zone (48.4 ± 2.7 ms) than in the living zone (43.5 ± 2.5 ms). In the non-collapsed ONFH group, there was no significant difference between the mean T1 rho values of the necrotic and living zones. In the collapsed ONFH group, the mean T1 rho value of the necrotic zone and the interval from pain onset to the MRI examination were positively correlated.ConclusionsThe current T1 rho MRI study suggested that the degeneration of articular cartilage in ONFH begins at the necrotic region after collapse.

Common site of subchondral insufficiency fractures of the femoral head based on three-dimensional magnetic resonance imaging

ObjectivesThe objective of this study was to investigate the common sites of subchondral insufficiency fractures of the femoral head (SIF) based on three-dimensional (3-D) reconstruction of MR images.Materials and methodsIn 33 hips of 31 consecutive patients diagnosed with SIF, 3-D reconstruction of the bone, fracture, and acetabular edge was performed using MR images. These 3-D images were used to measure the fractured areas and clarify the positional relationship between the fracture and degree of acetabular coverage.ResultsThe fractured area in the anterior portion was significantly larger than in the posterior area. In 11 cases, the fractures contacted the acetabular edge and were distributed on the lateral portion. The indices of acetabular coverage (center-edge angle and acetabular head index) in these cases were less than the normal range. In the remaining 22 cases, the fractures were apart from the acetabular edge and distributed on the mediolateral centerline of the femoral head. The majority of these cases had normal acetabular coverage.ConclusionsThe common site of SIF is the anterior portion. In addition, two types of SIF are proposed: (1) Lateral type: the contact stress between the acetabular edge and lateral portion of the femoral head causes SIF based on the insufficient acetabular coverage, and (2) Central type: the contact stress between the acetabular surface and the mediolateral center of the femoral head causes SIF independent from the insufficiency of acetabular coverage. These findings may be useful for considering the treatment and prevention of SIF.

Genome-wide Association Study of Idiopathic Osteonecrosis of the Femoral Head

Idiopathic osteonecrosis of the femoral head (IONFH) is an ischemic disorder that causes bone necrosis of the femoral head, resulting in hip joint dysfunction. IONFH is a polygenic disease and steroid and alcohol have already known to increase its risk; however, the mechanism of IONFH remains to be elucidated. We performed a genome-wide association study using ~60,000 subjects and found two novel loci on chromosome 20q12 and 12q24. Big data analyses identified LINC01370 as a candidate susceptibility gene in the 20q12 locus. Stratified analysis by IONFH risk factors suggested that the 12q24 locus was associated with IONFH through drinking capacity. Our findings would shed new light on pathophysiology of IONFH.

Histopathologic findings of spontaneous osteonecrosis of the knee at an early stage: a case report

We histopathologically examined a surgically resected full specimen obtained from an early-stage spontaneous osteonecrosis of the knee (SPONK). On a mid-coronal cut section of the resected medial femoral condyle, a linear fracture line paralleling the subchondral bone endplate was found. Histopathologically, prominent callus formation was seen comprising of reactive woven bone and granulation tissue on both sides of the fracture. Fracture-related bone debris was focally observed at the osteochondral side of the fracture. Definitive features of antecedent bone infarction such as creeping substitution and bone marrow necrosis were not detected. These findings suggested that SPONK was the result of a subchondral fracture rather than primary osteonecrosis.

Computed tomography findings of subchondral insufficiency fractures of the femoral head

Objectives The objective of this study was to describe the appearance of Subchondral insufficiency fracture (SIF) by computed tomography (CT). Methods Images of 52 consecutive patients diagnosed with SIF were retrospectively reviewed. CT was available for five patients (7 cases). Results Corresponding to a low-intensity band on MR images, a radiolucent or sclerotic band was observed on CT images. Conclusion The present study is the first to report CT findings of SIF. A radiolucent or sclerotic band was observed on CT images. The results of the present study provide useful information for diagnosis of SIF.

Effects of sclerotic changes on stress concentration in early-stage osteonecrosis: A patient-specific, 3D finite element analysis: FINITE ELEMENT ANALYSIS IN OSTEONECROSIS

Stress distribution remains unclear in early‐stage osteonecrosis of the femoral head (ONFH). To clarify this issue, we generated patient‐specific finite element models (FEMs) from 51 patients with ONFH. Patients’ hips were classified into three groups: ONFH without a sclerotic boundary (Stage 1, n = 6), ONFH with a sclerotic boundary (Stage 2, n = 10), and ONFH with both a sclerotic boundary and <2 mm collapse (Stage 3, n = 35). Four hips without ONFH were used as controls. Stress distribution in each FEM was compared with magnetic resonance imaging (MRI) and computed tomography (CT) results. Fifteen wholly resected femoral heads in Stage 3 hips were assessed by micro‐CT. Furthermore, we histologically examined three Stage 2 femoral heads that subsequently developed subchondral fractures after FEM analyses. In all FEMs of both control and Stage 1 hip, stress was equally distributed on the femoral head surface. However, in all FEMs of both Stages 2 and 3 hips, stress was concentrated at the lateral boundary of the femoral head surface, corresponding to both a low‐intensity band on T1‐weighted MRI images and sclerotic changes on CT. On micro‐CT, subchondral fractures consistently began at the lateral boundary with sclerotic changes, in which bone volume fraction was increased. Histology showed breakage of subchondral plates at the junction between necrotic and reparative zones. In early‐stage ONFH, sclerotic changes caused stress concentration, which can trigger subchondral fractures at the lateral boundary. Clinical Significance: Our results will clarify the pathogenic mechanism of collapse in ONFH.

Effects of intertrochanteric osteotomy plane and preoperative femoral anteversion on the postoperative morphology of the proximal femur in transtrochanteric anterior rotational osteotomy: 3D CT-based simulation study

BACKGROUND Transtrochanteric anterior rotational osteotomy (ARO) is joint-preserving surgery for patients with osteonecrosis of the femoral head (ONFH). During ARO, femoral neck-shaft varus angulation by changing intertrochanteric osteotomy plane is often designed to obtain a sufficient postoperative intact ratio. However, the effect of intertrochanteric osteotomy plane on postoperative femoral anteversion has not been well examined. Therefore, we performed a simulation study of ARO to determine how intertrochanteric osteotomy plane and preoperative femoral anteversion affect both femoral neck-shaft varus angle and postoperative femoral anteversion. HYPOTHESIS Both femoral neck-shaft varus angle and postoperative femoral anteversion are predicted by intertrochanteric osteotomy plane and preoperative femoral anteversion in ARO. MATERIALS AND METHODS Using CT-data obtained from 10 hips in 10 patients with ONFH, ARO was simulated. On anteroposterior view, basic intertrochanteric osteotomy line (AP-view line) was defined as the perpendicular line to the femoral neck axis. On lateral view, basic intertrochanteric osteotomy line (lateral-view line) made through the cut surface of greater trochanter was defined as the perpendicular line to the lateral axis of the femur. By changing either AP-view or lateral-view line, 49 ARO models/hip were produced, in which femoral neck-shaft varus angle and postoperative femoral anteversion were assessed. RESULTS With increase in the vertically-inclined degree of AP-view line, both neck-shaft varus angle and postoperative femoral anteversion increased. With increase in the posteriorly-tilted degree of lateral-view line, neck-shaft varus angle increased, whereas postoperative femoral anteversion decreased. The approximation equations based on the multiple regression analyses were as follows: neck-shaft varus angle≈vertically-inclined degree of AP-view line×0.9+posteriorly-tilted degree of lateral-view line×0.8+preoperative femoral anteversion×0.7; postoperative femoral anteversion≈vertically-inclined degree of AP-view line×1.1-posteriorly-tilted degree of lateral-view line×0.8. DISCUSSION The postoperative morphology of proximal femur was nearly defined by intertrochanteric osteotomy plane with preoperative femoral anteversion, which is useful for preoperative planning in terms of both achieving a sufficient postoperative intact ratio and maintaining femoral anteversion. LEVEL OF EVIDENCE Level IV case series without control group.

Use of a long distally fixed intramedullary stem to treat a periprosthetic femoral fracture following total hip arthroplasty using a thrust plate hip prosthesis: A case report

Highlights • We report a periprosthetic fracture following the use of a discontinued prosthesis.• Marked bone ongrowth on the thrust plate made it difficult to remove.• A long distally fixed intramedullary stem was selected for revision.• Sufficient implant preparation based on precise preoperative planning is necessary.