Anatomical Study of the Interosseous Ligament of the Tibiofibular Syndesmosis: An Analysis of Osseous Morphology and Attaching Interposing Structures.

BACKGROUND: The morphological features of the interosseous tibiofibular area in relation to the tensile stress of the interosseous ligament (IOL) have rarely been discussed. The purpose of the present study was to investigate the IOL on the basis of osseous surface morphology and macroscopic and histological anatomy. We hypothesized that the osseous surface of the interosseous tibiofibular area has a specific feature corresponding to the fibrous structure in the IOL. METHODS: Eighteen ankles from 15 cadavers were analyzed. Micro-computed tomography (micro-CT) images were obtained for all specimens to observe the osseous surface in the syndesmosis and to visualize the distribution of cortical bone thickness. Fifteen ankles were macroscopically analyzed, and the other 3 ankles were histologically analyzed. RESULTS: Micro-CT imaging revealed the osseous prominence on the medial side of the fibula. Cortical thickness mapping showed that the thickness of the cortical bone on the medial side of the fibula proximal to the prominence (mean and standard deviation, 1.4 ± 0.5 mm; p < 0.001) was greater in comparison with the other quadrants, namely, the proximal part of the tibia (0.8 ± 0.2), distal part of the fibula (0.7 ± 0.2), and distal part of the tibia (0.5 ± 0.1). Macroscopic analysis indicated that the perforating branch of the fibular artery ran through the proximal top of the IOL, which formed a thickened fiber and was attached to the fibular prominence. Histological analysis revealed that the thickened fibrous part of the IOL attached to the fibula via the fibrocartilaginous insertion. At the middle of the IOL, thin and fatty-like tissue was interposed between the tibia and the fibula. CONCLUSIONS: We observed that the osseous prominence of the fibula corresponded to the proximal thickened part of the IOL via the fibrocartilaginous attachment. The thickened proximal part of the IOL was consistently found in this location; we believe that this finding was related to the fact that the fibular artery perforated the adjacent distal part of the interosseous membrane (IOM). CLINICAL RELEVANCE: The location of the prominence on the medial aspect of the fibula could be a helpful clue as to the ideal location of syndesmotic fixation.

Potential bone fragility of mid-shaft atypical femoral fracture: Biomechanical analysis by a CT-based nonlinear finite element method.

INTRODUCTION: The authors previously reported a CT-based nonlinear finite element analysis (nonlinear CT/FEA) model to investigate loading stress distribution in the femoral shaft of patients with atypical femoral fractures (AFFs). This showed that stress distribution, influenced primarily by femoral bowing, may determine the location of AFF. Here, we demonstrate the locational characteristics associated with AFFs in an Asian, specifically Japanese, population regarding bone strength. This is the second report from our multicentre research project suggesting a possible new concept of diagnostic criteria or treatment according to AFF subtype. PATIENTS AND METHODS: A multicentre prospective study was conducted at 12 hospitals in Japan from August 2015 through June 2018. We recruited three study groups composed of elderly females over the age of 60 years-the mid-shaft AFF group (n = 14; 80.0 ±â€¯6.5 years), the subtrochanteric AFF group (n = 15; 73.9 ±â€¯6.8 years), and the control group who had sustained unilateral hip fracture (n = 21; 82.1 ±â€¯7.1 years)-and analysed femoral neck bone density and strength. Bone strength of the femoral neck was predicted with an evaluation method using nonlinear CT/FEA in both standing and falling configuration. RESULTS: Femoral neck bone density and strength were significantly higher in the subtrochanteric AFF group compared with the mid-shaft AFF and control groups (p <  0.0001). No significant difference was seen in bone strength between the mid-shaft AFF and control groups (standing, p =  0.7616; falling, p =  0.3803). CONCLUSIONS: AFF has different features, in terms of bone strength, depending on fracture location. At the very least, Japanese patients with mid-shaft AFF could be at high risk of hip fracture because of bone fragility, in contrast to the firm bone of subtrochanteric AFF. For internal fixation of mid-shaft AFF using an IM nail, cervical screw insertion toward the femoral head might be recommended to prevent possible hip fracture.