Morphological analysis of the proximal femur using quantitative computed tomography

Structural characteristics, biomechanics and clinical significance of calcar femorale: A review

The calcar femorale, first identified by Merkel in 1874, plays a pivotal role in the weight-bearing capacity of the proximal femur, and its structural integrity is crucial for the efficient distribution of mechanical loads. Originating at the vertical ridge where the pubofemoral ligament anchors, this bony prominence extends laterally behind the neutral axis from the medial to lateral aspects. Its presence is not merely an anatomical curiosity but significantly influences the biomechanics of the hip joint by providing additional strength and support against compressive forces encountered during activities such as walking or jumping. Despite its clear description in orthopedic texts, misconceptions persist about its exact function and importance. This article delves into the nuanced anatomy and biomechanical properties of the calcar femorale, offering a detailed literature-based examination that demonstrates its relevance in clinical practice. The review highlights how the robustness of the calcar femorale contributes to the prevention of femoral neck fractures as well as the stabilization of hip prostheses. Furthermore, the indispensable role of the calcar femorale in surgical outcomes is discussed, especially in the context of fracture repair and joint replacement, thus illustrating its enduring significance in contemporary medical applications.

Mapping the Spatial Evolution of Proximal Femur Osteoporosis: A Retrospective Cross-Sectional Study Based on CT Scans

Purpose

The purpose of this study was to quantify the modifications occurring in osteoporosis at the level of the human proximal femur throughout the trabecular structure, along with the identification of certain anatomic regions preferentially affected by osteoporosis. Another goal was to map the evolution of the radiodensity of the trabecular bone as osteoporosis progresses to an advanced stage.

Methods

The study included CT scans (right femur) from 51 patients, out of which 40 had various degrees of osteoporosis, but no other local pathology. Ten regions of interest in two orthogonal slices have been identified and the differences in radiodensity as well as their evolution have been statistically analyzed in terms of relative and absolute changes.

Results

A detailed spatial map showing the evolution of osteoporosis was obtained. As osteoporosis evolved, the relative decrease in radiodensity was inversely correlated to the radiodensity of the healthy bone. In particular, the region covering the Ward triangle decreased the most, by an average 61-62% in osteopenia and 101-106% in advanced osteoporosis, while the principal compressive group was affected the least, showing a decrease by an average 14-15% in osteopenia and 29-32% in advanced osteoporosis. The absolute decrease in radiodensity was not correlated to the radiodensity of the healthy bone and was shifted to the inferior-posterior edge of the femur. Inside the femoral head, the upper region was affected the most in absolute terms, while the greater trochanter was less affected than the femoral neck. The maximum metaphyseal cortical bone density was unaffected by the progression of osteoporosis.

Conclusion

Significant differences were noticed in terms of the absolute and relative osteoporotic changes in radiodensity related to different anatomical regions of the human femoral bone. These differences become more pronounced as the disease progresses.

Proximal femoral bionic nail-a novel internal fixation system for the treatment of femoral neck fractures: a finite element analysis

Introduction: Currently, cannulated screws (CSs) and dynamic hip screws (DHSs) are widely used for the treatment of femoral neck fractures, but the postoperative complications associated with these internal fixations remain high. In response to this challenge, our team proposes a new approach involving triangular-supported fixation and the development of the proximal femoral bionic nail (PFBN). The primary objective of this study is to investigate the biomechanical differences among CSs, DHSs, and the PFBN in their capacity to stabilize femoral neck fractures. Methods: A normal proximal femur model was constructed according to the CT data of a normal healthy adult. A femoral neck fracture model was constructed and fixed with CSs, DHSs, and the PFBN to simulate the fracture fixation model. Abaqus 6.14 software was used to compare the biomechanical characters of the three fracture fixation models. Results: The maximum stresses and displacements of the normal proximal femur were 45.35 MPa and 2.83 mm, respectively. Under axial loading, the PFBN was more effective than DHSs and CSs in improving the stress concentration of the internal fixation and reducing the peak values of von Mises stress, maximum principal stress, and minimum principal stress. The PFBN fixation model exhibits superior overall and fracture section stability in comparison to both the DHS fixation model and the CS fixation model under axial loading. Notably, the maximum stress and peak displacement of the PFBN and bone were lower than those of the DHS and CS fixation models under bending and torsional loading. Conclusion: The PFBN shows considerable improvement in reducing stress concentration, propagating stress, and enhancing the overall stability in the femoral neck fracture fixation model compared to DHSs and CSs. These enhancements more closely correspond to the tissue structure and biomechanical characteristics of the proximal femur, demonstrating that the PFBN has great potential for therapeutic purposes in treating femoral neck fractures.

Fatty Acid Composition of Proximal Femur Bone Marrow Adipose Tissue in Subjects With Systemic Lupus Erythematous Using 3 T Magnetic Resonance Spectroscopy

BACKGROUND

Systemic lupus erythematosus (SLE) is a chronic, inflammatory disease with common musculoskeletal manifestations, notably reductions in bone quality. Bone marrow adipose tissue composition and quantity has been previously linked to bone quality and may play a role in SLE pathophysiology but has not been thoroughly studied.

PURPOSE

To use magnetic resonance spectroscopy (MRS) to investigate bone marrow adipose tissue quantity and composition in proximal femur subregions of untreated SLE patients compared to controls and treated patients.

STUDY TYPE

Prospective.

SUBJECTS

A total of 64 female subjects: 28 SLE, 15 glucocorticoid (GC)-treated SLE and 21 matched controls.

FIELD STRENGTH/SEQUENCE

Stimulated echo acquisition mode (STEAM) sequence at 3 T.

ASSESSMENT

MRS was performed at multiple echo times in the femoral neck and trochanter regions and fatty acids (FA) composition was computed.

STATISTICAL TESTS

Intergroup comparisons were carried out using ANOVA. A P value < 0.05 was considered statistically significant.

RESULTS

SLE patients had significantly higher saturated FA compared to controls in both the femoral neck (+0.12) and trochanter (+0.11), significantly lower monounsaturated FA in the trochanter compared to controls (-0.05), and significantly lower polyunsaturated FA in the femoral neck compared to both controls (-0.07) and SLE patients on GC therapy (-0.05).

DATA CONCLUSION

SLE patients have altered proximal femur marrow fat metabolism, which may reflect a manifestation of, or play a role in, the altered inflammatory response of these patients.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 2.

Occult fracture propagation in patients with isolated greater trochanteric fractures: patterns and management

OBJECTIVE

To demonstrate the degrees of occult intertrochanteric extension on MRI in patients with a greater trochanteric fracture on radiography or computer tomography (CT) and whether these patients undergo conservative or surgical management with hardware.

MATERIALS AND METHODS

Retrospective review was performed of 146 patients (104 females, 42 males, ages 33-102) who had follow-up MRI after identification of a greater trochanteric fracture without intertrochanteric extension on radiography or CT. Extent of intertrochanteric extension was recorded. Subsequently, EMR review was performed to see if patients underwent surgery. Specific note was made of hardware type. Analysis was performed to determine if there is a correlation with fracture type and surgical management as well as fracture type and age and gender.

RESULTS

Nineteen patients had horizontal greater trochanter fractures without intertrochanteric extension; none underwent surgery. Seventeen patients had a vertical fracture along the lateral femoral cortex; one underwent surgery. Thirty-three patients had a fracture with intertrochanteric extension less than 50% in the mid coronal plane; 21 underwent surgery. Forty patients had intertrochanteric extension greater than 50% in the midcoronal plane not contacting the medial cortex; 28 underwent surgery. Thirty-seven patients had fractures contacting the medial cortex; 28 underwent surgery. There was significant difference with fractures extending 50% or greater of the midline of the intertrochanteric region undergoing surgical management compared with fractures less than 50% (p < 0.0001).

CONCLUSION

MRI identifies the presence and extent of occult intertrochanteric fractures in patients with greater trochanteric fractures. Description of intertrochanteric fractures on MRI helps determine the patient's treatment course and influence surgical decisions.

Triangular support intramedullary nail: A new internal fixation innovation for treating intertrochanteric fracture and its finite element analysis

BACKGROUND

Proximal femoral nail anti-rotation (PFNA) and Gamma nail were recommended for intertrochanteric fracture, however, with high rate of post-operation complications. The triangular support intramedullary nail (TSIN) was designed to reduce the risk of postoperative complications related to Gamma nail and PFNA, and the aim is to compare the biomechanical characters of Gamma nail, PFNA and TSIN for fixation of intertrochanteric fracture and prove the rationality of the concept of triangle fixation in the treatment of intertrochanteric fractures.

METHODS

The finite element model of proximal femur was constructed according to the CT data of femur. Intertrochanteric fracture models with Evans type Ⅰ and Ⅳ were established and fixed with Gamma nail, PFNA and TSIN by UG-NX 12.0. The finite element analysis software was used to compare the stress distribution and displacement of three implants fixation models.

RESULTS

Under axial loading of 600 N, the peak stress and maximum displacement of intact proximal femur was 13.78 MPa and 1.33 mm, respectively. The maximum stress of TSIN for fixation of Evans type Ⅰ and Ⅳ intertrochanteric fractures was 86.23 MPa and 160.63 MPa which was significantly lower than that of Gamma nail and PFNA. The maximum relative displacement of fracture section in Gamma nail and PFNA fixation models was 0.18 mm and 0.19 mm which has 135% and 148% higher than in TSIN fixation models for fixing Evans type Ⅰ intertrochanteric fracture, and 0.47 mm and 0.59 mm which has 91% and 140% higher than in TSIN fixation models for stabilization of Evans type Ⅳ intertrochanteric fracture.

CONCLUSION

Compared with Gamma nail and PFNA fixation, TSIN has superior advantages in stress distribution and construct stability. We believe that triangle fixation concept help to reduce the risk of post-operative complications associated with PFNA and Gamma nail and improve the clinical effect of intertrochanteric fracture.

Computer Navigation-Aided Excision of Proximal Femoral Osteochondroma: Surgical Technique

Purpose

Symptomatic osteochondroma of the proximal femur necessitates a surgical excision. The purpose of this study was to describe a novel technique of computer navigation-aided excision for osteochondromata of the proximal femur. Outcomes of this technique are also presented.

Methods

A total of 13 patients underwent computer navigation-aided excision of osteochondromata of the proximal femur from February 2012 to August 2016 in our institution. They were enrolled in this study. OrthoMap 3D (Stryker Orthopaedics, Mahwah, NJ, USA), a commercially available navigation software system, was used to merge computed tomography images of the proximal femur with an osteochondromata with the image of a normal proximal femur. Using the normal proximal femur as a template, intended resection margins for the proximal femur with osteochondromata were planned and then executed using intraoperative navigation guidance. Patients were followed up clinically and radiographically. The physical and mental health of patients was assessed with the Musculoskeletal Tumor Society (MSTS) score.

Results

Eight patients had isolated exostoses. Five patients had tumors associated with multiple hereditary exostoses. For tumors projecting posteriorly or posteromedially, a posterolateral approach was used. For tumors projecting anteriorly or medially, an anterior approach was used. Prophylactic fixation was performed in four patients who required an anterior approach. The mean duration of the surgery was 189 minutes. There were no intraoperative fractures or postoperative complications. A secondary procedure was not needed for any case. The mean MSTS score at a mean follow-up of 17 months was 28.6 (maximum MSTS score: 30).

Conclusions

This is the first study to report a novel application of computer navigation for aiding the excision of osteochondromata of the proximal femur. It demonstrated favorable postoperative functional scores with a low rate of complications. The applicability, safety, and efficacy of this technique were demonstrated. It is particularly useful for resections involving large tumors that can obscure anatomical landmarks and for patients with associated proximal femoral deformity.

Titanium Alloy Gamma Nail versus Biodegradable Magnesium Alloy Bionic Gamma Nail for Treating Intertrochanteric Fractures: A Finite Element Analysis

OBJECTIVE

To using finite element analysis to investigate the effects of the traditional titanium alloy Gamma nail and a biodegradable magnesium alloy bionic Gamma nail for treating intertrochanteric fractures.

METHODS

Computed tomography images of an adult male volunteer of appropriate age and in good physical condition were used to establish a three-dimensional model of the proximal femur. Then, a model of a type 31A1 intertrochanteric fracture of the proximal femur was established, and the traditional titanium alloy Gamma nails and biodegradable magnesium alloy bionic Gamma nails were used for fixation, respectively. The von Mises stress, the maximum principal stress, and the minimum principal stress were calculated to evaluate the effect of bone ingrowth on stress distribution of the proximal femur after fixation.

RESULTS

In the intact model, the maximum stress was 5.8 MPa, the minimum stress was -11.7 MPa, and the von Mises stress was 11.4 MPa. The maximum principal stress distribution of the cancellous bone in the intact model appears in a position consistent with the growth direction of the principal and secondary tensile zones. After traditional Gamma nail healing, the maximum stress was 32 MPa, the minimum stress was -23.5 MPa, and the von Mises stress was 31.3 MPa. The stress concentration was quite obvious compared with the intact model. It was assumed that the nail would biodegrade completely within 12 months postoperatively. The maximum stress was 18.7 MPa, the minimum stress was -12.6 MPa, and the von Mises stress was 14.0 MPa. For the minimum principal stress, the region of minimum stress value less than -10 MPa was significantly improved compared with the traditional titanium alloy Gamma nail models. Meanwhile, the stress distribution of the bionic Gamma nail model in the proximal femur was closer to that of the intact bone, which significantly reduced the stress concentration of the implant.

CONCLUSION

The biodegradable magnesium alloy bionic Gamma nail implant can improve the stress distribution of fractured bone close to that of intact bone while reducing the risk of postoperative complications associated with traditional internal fixation techniques, and it has promising clinical value in the future.

Morphology of Proximal Femur in South-West Coast of India

Introduction

With a higher proportion of young individuals undergoing uncemented hip arthroplasty, a close match in the dimension of the proximal femur and the implanted prosthesis is paramount. This is a study to gain insight into geographical variation in proximal femur morphology to determine the reference values to design uncemented femoral stems for a south Indian population, and also the effect of ageing and gender on the proximal femur morphology.

Materials and Methods

The study comprised of two groups. For the first group, 50 unpaired dry femur bones were obtained from adult human cadavers; and the second group was a clinical group of 50 adult patients. Standardised radiographic techniques were used to measure the extra-cortical and intra-cortical morphometric parameters. Based on these, dimensionless ratios were calculated to express the shape of the proximal femur. The data were expressed in terms of mean and standard deviation and a comparison made with other studies.

Results

A significant difference was noted across various population subsets within the Indian subcontinent and also in comparison to the Western population, suggestive of regional variation. The measurements made in cadaveric bone differed significantly from those in live patients, especially the femoral head diameter and extra-cortical and intra-cortical width. Femoral offset, head height and diameter were significantly less in females.

Conclusion

The south Indian population needs customised implants with an increase in neck shaft angle and a decrease in intra-cortical and extra-cortical width for press fit in hip arthroplasty. The variation between the two sexes must also be accounted for during prosthesis design.

The calcar femorale: A new perspective

It is the role of the hip joint to support the superincumbent body weight while its complex range of movement, under a variety of stresses, allows the individual to undertake a wide range of physical activities. It is then perhaps not surprising that a recent anatomical study shows that the upper femur has a structure commensurate with the complexity of its movements. Mechanically, the upper femur consists of two separate bones: the combined femoral head and neck and the femoral shaft. Both bones consist of a mixture of two different types: cancellous bone and cortical bone, each with its own characteristics. Both bones are subjected to two different forces: those of weight bearing and movement and those of bone modelling. In the face of these complexities, this article tenders some theoretical considerations as to how this region functions and deals with these particular problems. From an anatomical viewpoint, the calcar femorale plays a central role in the mechanical structure of the femoral neck and is pivotal in the management of the stresses to which the region is subjected.

Traditional and bionic dynamic hip screw fixation for the treatment of intertrochanteric fracture: a finite element analysis

PURPOSE

The dynamic hip screw (DHS) is widely used for fixing intertrochanteric femur fractures. A porous bionic DHS was developed recently to avoid the stress concentration and risk of post-operative complications associated with titanium alloy DHSs. The purpose of this study was to compare the effects of traditional titanium alloy, bionic titanium alloy, and bionic magnesium alloy DHS fixation for treatment of intertrochanteric fractures using finite element analysis.

METHODS

A three-dimensional model of the proximal femur was established by human computed tomography images. An intertrochanteric fracture was created on the model, which was fixed using traditional and porous bionic DHS, respectively. The von Mises stress, maximum principal stress, and minimum principal stress were calculated to evaluate the effect of bone ingrowth on stress distribution of the proximal femur after fixation.

RESULTS

Stress concentration of the bionic DHS model was lower compared with traditional DHS fixation models. The von Mises stress, maximum principal stress, and minimum principal stress distributions of bionic magnesium alloy DHS models improved, along with simulation of the bone healing process and magnesium alloy degeneration, assumed to biodegrade completely 12 months post-operatively. The distribution of maximum principal stress in the secondary tension zone of the bionic DHS model was close to the intact bone. In the minimum principal stress, the region of minimum stress value less than - 10 MPa was significantly improved compared with traditional DHS models.

CONCLUSION

The bionic magnesium alloy DHS implant can improve the stress distribution of fractured bone close to that of intact bone while reducing the risk of post-operative complications associated with traditional internal fixations.

The Effect of Valgus Reduction on the Position of the Blade of the Proximal Femoral Nail Antirotation in Intertrochanteric Hip Fractures

Background

The purpose of this study was to evaluate the quantitative association between the degree of reduction and the position of the blade of the proximal femoral nail antirotation (PFNA) in intertrochanteric hip fractures.

Methods

From March 2009 to April 2015, 530 patients treated with PFNA for intertrochanteric hip fractures were retrospectively reviewed. Patients were divided into a valgus reduced group (group 1) and a non-valgus reduced group (group 2), and the "valgus reduced" was defined as valgus reduction over 5°. We compared the calcar referenced tip-apex distance (calTAD) and the area between the blade of PFNA and the medial cortex of the femoral neck between the two groups.

Results

The calTAD was measured as 22.5 ± 4.1 mm in group 1 and 24.8 ± 3.8 mm in group 2 (p < 0.05). The area between the blade and the medial femoral neck was measured as 135.5 ± 49.8 mm² in group 1 and 145.1 ± 54.8 mm² in group 2 (p = 0.074). The area corrected for the length difference in the femoral neck was 0.55 ± 0.16 in group 1 and 0.79 ± 0.19 in group 2 (p < 0.05).

Conclusions

Valgus reduction resulted in less calTAD and inferior position of the blade at the femoral neck in the treatment of intertrochanteric hip fractures with PFNA.

Fragility fractures of the proximal femur: review and update for radiologists

Proximal femoral fragility fractures are common and result in significant morbidity and mortality along with a considerable socioeconomic burden. The goals of this article are to review relevant proximal femoral anatomy together with imaging, classification, and management of proximal femoral fragility fractures, and their most common complications. Imaging plays an integral role in classification, management and follow-up of proximal femoral fragility fractures. Classification of proximal femoral fragility fractures is primarily based on anteroposterior hip radiographs. Pertinent imaging features for each category of proximal femoral fractures that would guide management are: differentiating nondisplaced from displaced femoral neck fractures, distinguishing stable from unstable intertrochanteric fractures, and determining the morphology and comminution of subtrochanteric fractures. Treatment of proximal femoral fragility fractures is primarily surgical with either arthroplasty or internal fixation. Intramedullary nailing is used in the treatment of some types of proximal femoral fragility fractures and may be associated with unique complications that become evident on postoperative follow-up radiographs.

3T chemical shift-encoded MRI: Detection of altered proximal femur marrow adipose tissue composition in glucocorticoid users and validation with magnetic resonance spectroscopy

BACKGROUND

Osteoporosis (OP) results in weak bone and can ultimately lead to fracture. Drugs such as glucocorticoids can also induce OP (glucocorticoid-induced osteoporosis [GIO]). Bone marrow adipose tissue composition and quantity may play a role in OP pathophysiology, but has not been thoroughly studied in GIO compared to primary OP.

PURPOSE/HYPOTHESIS

Chemical shift-encoded (CSE) MRI allows detection of subregional differences in bone marrow adipose tissue composition and quantity in the proximal femur of GIO compared to OP subjects and has high agreement with the reference standard of magnetic resonance spectroscopy (MRS).

STUDY TYPE

Prospective.

SUBJECTS

In all, 18 OP and 13 GIO subjects.

FIELDS STRENGTH

3T.

SEQUENCE

Multiple gradient-echo, stimulated echo acquisition mode (STEAM).

ASSESSMENT

Subjects underwent CSE-MRI in the proximal femurs, and for each parametric map regions of interest (ROIs) were assessed in the femoral head (fHEAD), femoral neck (fNECK), Ward's triangle (fTRIANGLE), and the greater trochanter (GTROCH). In addition, we compared CSE-MRI against the reference standard of MRS performed in the femoral neck and Ward's triangle.

STATISTICAL TESTS

Differences between OP/GIO were investigated using the Mann-Whitney nonparametric test. Bland-Altman methodology was used to assess measurement agreement between CSE-MRI and MRS.

RESULTS

GIO compared with OP subjects demonstrated: decreased monounsaturated fat fraction (MUFA) (-2.1%, P < 0.05) in fHEAD; decreased MUFA (-3.8%, P < 0.05), increased saturated fat fraction (SFA) (5.5%, P < 0.05), and decreased T 2 * (-3.8 msec, P < 0.05) in fNECK; decreased proton density fat fraction (PDFF) (-15.1%, P < 0.05), MUFA (-9.8%, P < 0.05), polyunsaturated fat fraction (PUFA) (-1.8%, P < 0.01), increased SFA (11.6%, P < 0.05), and decreased T 2 * (-5.4 msec, P < 0.05) in fTRIANGLE; and decreased T 2 * (-1.5 msec, P < 0.05) in GTROCH. There was high measurement agreement between MRI and MRS using the Bland-Altman test.

DATA CONCLUSION

3T CSE-MRI may allow reliable assessment of subregional bone marrow adipose tissue (bMAT) quantity and composition in the proximal femur in a clinically reasonable scan time. Glucocorticoids may alter the lipid profile of bMAT and potentially result in reduced bone quality.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:490-496.

Calcar Femorale in Patients with Osteoarthritis of the Hip Secondary to Developmental Dysplasia

Background

We investigated whether the calcar femorale, a cortical septum in the region of the lesser trochanter of the femur, correlates with results of femoral stem implantation in patients with osteoarthritis of the hip secondary to developmental dysplasia using computed tomography.

Methods

This retrospective study included 277 hips (41 males and 236 females; age, 37 to 92 years) of patients who had presented to Okayama Medical Center with hip pain. Of these, a total of 219 hips (31 males and 188 females) had previously undergone total hip arthroplasty. According to the Crowe classification, 147 hips were classified as Crowe grade I, 72 hips as Crowe grade II–IV, and 58 hips as normal.

Results

The calcar femorale was identified in 267 hips (96.4%). The calcar femorale was significantly shorter and more anteverted in Crowe grade II–IV hips than in Crowe grade I or normal hips. Significant differences in the shape of the calcar femorale were found according to the severity of hip deformity. Three stem designs were analyzed: single-wedge (59 hips), double-wedge metaphyseal filling (147 hips), and modular (13 hips). Single-wedge stems were inserted more parallel to the calcar femorale rather than femoral neck anteversion, while other types of stems scraped the calcar femorale.

Conclusions

The angle of the calcar femorale differs according to the severity of hip deformity, and the calcar femorale might thus serve as a more useful reference for stem insertion than femoral neck anteversion in total hip arthroplasty using a single-wedge stem.

Hip fractures in the elderly-: A Clinical Anatomy Review

As elderly populations rise worldwide, the amount of hip fractures have continued to increase and result in substantial medical burdens in many countries. This increase goes hand-in-hand with an increase in surgical procedures to correct hip fractures. The medical burden imparted by hip fractures and their corrective surgeries necessitate a clinically relevant understanding of the hip joint including the vascular, neural, and musculoskeletal structures directly associated with and neighboring the joint. It is critical to appreciate how the normal hip anatomy is disrupted by a fracture and how this disruption is heavily influenced by the fracture's location. The effects of advancing age on the integrity of the hip joint and the risk of hip fractures further complicate hip anatomy. Consequentially, normal hip anatomy, aging and the pathology introduced by fractures play major roles in how hip fractures are approached surgically. This article aims to review the clinically relevant anatomy of the healthy hip joint, age-related changes that influence the joint, hip fractures, and corrective surgeries for hip fractures. Clin. Anat. 30:89-97, 2017. © 2016 Wiley Periodicals, Inc.

Fracture risk predictions based on statistical shape and density modeling of the proximal femur

Increased risk of skeletal fractures due to bone mass loss is a major public health problem resulting in significant morbidity and mortality, particularly in the case of hip fractures. Current clinical methods based on two-dimensional measures of bone mineral density (areal BMD or aBMD) are often unable to identify individuals at risk of fracture. We investigated predictions of fracture risk based on statistical shape and density modeling (SSDM) methods using a case-cohort sample of individuals from the Osteoporotic Fractures in Men (MrOS) study. Baseline quantitative computed tomography (QCT) data of the right femur were obtained for 513 individuals, including 45 who fractured a hip during follow-up (mean 6.9 year observation, validated by physician review). QCT data were processed for 450 individuals (including 40 fracture cases) to develop individual models describing three-dimensional bone geometry and density distribution. Comparison of mean fracture and non-case models indicated complex structural differences that appear to be responsible for resistance to hip fracture. Logistic regressions were used to model the relation of baseline hip BMD and SSDM weighting factors to the occurrence of hip fracture. Area under the receiver operating characteristic (ROC) curve (AUC) for a prediction model based on weighting factors and adjusted by age was significantly greater than AUC for a prediction model based on aBMD and age (0.94 versus 0.83, respectively). The SSDM-based prediction model adjusted by age correctly identified 55% of the fracture cases (and 94.7% of the non-cases), whereas the clinical standard aBMD correctly identified 10% of the fracture cases (and 91.3% of the non-cases). SSDM identifies subtle changes in combinations of structural bone traits (eg, geometric and BMD distribution traits) that appear to indicate fracture risk. Investigation of important structural differences in the proximal femur between fracture and no-fracture cases may lead to improved prediction of those at risk for future hip fracture.

Inter-individual variability of bone density and morphology distribution in the proximal femur and T12 vertebra

Bone geometry, density and microstructure can vary widely between subjects. Knowledge about this variation in a population is of interest in particular for the design of orthopedic implants and interventions. The goal of this study is to investigate the local variability of bone density and microstructural parameters between subjects using a novel inter-subject image registration approach. Human proximal femora of 29 and T12 vertebrae of 20 individuals were scanned using a HR-pQCT and a micro-CT system, respectively. A pre-defined iso-anatomic mesh template was morphed to each micro-CT scan. For each element bone volume fraction and other morphological parameters (Tb.Th, Tb.N, Tb.Sp, SMI, DA) were determined and assigned to the element. A coefficient of variation (CV) was calculated for each parameter at each element location of the 29 femora and 20 T12 vertebrae. Contour plots of the CV distribution revealed very detailed information about the inter-individual variation in bone density and morphology. It is also shown that analyzing large sub-volumes, as commonly done in previous studies, would miss much of this variation. Detailed quantitative information of bone morphological parameters for each sample in the femur and the T12 database and their inter-individual variability are available from the mesh templates as supplementary data (http://w3.bmt.tue.nl/nl/fe_database/). We expect that these results can help to optimize implants and orthopedic procedures by taking local bone morphological parameter variations into account.

The paradox of Wolff's theories

The upper femur has long held a fascination for both clinicians and bioengineers as it contains two trabecular columns obviously related to its function. In this respect two theories as to the formation of these columns have developed, both associated with Wolff: the Trajectorial Theory, which relates mainly to the passage of forces through the cancellous bone of the upper femur, and Wolff's Law of bone formation, which describes the bone's reaction to these forces and relates to bone in general. The two concepts nevertheless are often used synonymously. The Trajectorial Theory propounds that these cancellous structures in the femoral neck are due to both tension and compression forces, while modern day concepts of Wolff's Law only acknowledge the action of compression forces: and herein lies the paradox. The Trajectorial Theory and Wolff's Law, when applied to the upper femur, are mutually exclusive. The evidence, anatomical and physiological, indicates that bone forms within the femoral neck solely under the influence of compression forces. This would indicate that the Trajectorial Theory is not appropriate for this region. An alternative conceptual way of looking at this region is presented which eliminates this theory and resolves the paradox.

Subchondral bone density distribution in the human femoral head

OBJECTIVE

This study aims to quantitatively characterize the distribution of subchondral bone density across the human femoral head using a computed tomography derived measurement of bone density and a common reference coordinate system.

MATERIALS AND METHODS

Femoral head surfaces were created bilaterally for 30 patients (14 males, 16 females, mean age 67.2 years) through semi-automatic segmentation of reconstructed CT data and used to map bone density, by shrinking them into the subchondral bone and averaging the greyscale values (linearly related to bone density) within 5 mm of the articular surface. Density maps were then oriented with the center of the head at the origin, the femoral mechanical axis (FMA) aligned with the vertical, and the posterior condylar axis (PCA) aligned with the horizontal. Twelve regions were created by dividing the density maps into three concentric rings at increments of 30° from the horizontal, then splitting into four quadrants along the anterior-posterior and medial-lateral axes. Mean values for each region were compared using repeated measures ANOVA and a Bonferroni post hoc test, and side-to-side correlations were analyzed using a Pearson's correlation.

RESULTS

The regions representing the medial side of the femoral head's superior portion were found to have significantly higher densities compared to other regions (p < 0.05). Significant side-to-side correlations were found for all regions (r(2) = 0.81 to r(2) = 0.16), with strong correlations for the highest density regions. Side-to-side differences in measured bone density were seen for two regions in the anterio-lateral portion of the femoral head (p < 0.05).

CONCLUSIONS

The high correlation found between the left and right sides indicates that this tool may be useful for understanding 'normal' density patterns in hips affected by unilateral pathologies such as avascular necrosis, fracture, developmental dysplasia of the hip, Perthes disease, and slipped capital femoral head epiphysis.

The role of the calcar femorale in stress distribution in the proximal femur

OBJECTIVE

To investigate the role of the calcar femorale in stress distribution in the proximal femur.

METHODS

Twenty-five specimens of proximal femurs were fixed to simulate single-limb stance. Strain gauges were applied to record the strain under different loads. Strain values of 27 selected sites in the proximal femur were recorded and analyzed at the level of 100 N, 200 N, 300 N, 400 N, 500 N, 600 N and 700 N, respectively before and after disruption of the calcar femorale.

RESULTS

When a normal load was being borne, strain values measured in the posterior and medial aspects of the proximal femur were greater than those measured in the anterior and lateral aspects, no matter whether the calcar femorale was disrupted or not. However after disruption of the calcar femorale, strain values in the posterior and medial aspects of the proximal femur increased significantly, whereas those of the anterior and lateral aspects decreased significantly.

CONCLUSION

The calcar femorale redistributes stress in the proximal femur by decreasing the load in the posterior and medial aspects and increasing the load in the anterior and lateral aspects.

Brief communication: radiographic study of metatarsal one basal epiphyseal fusion: a note of caution on age determination

This study examines radiographs of first metatarsals of 131 individuals from age 17-88 years to determine whether internal basal epiphyseal lines may be visible past the age of metatarsal fusion, which usually occurs between 14 and 16 years of age (Scheuer and Black: The juvenile skeleton. San Diego: Elsevier Academic Press,2004). In 29% (38 out of 131) of the radiographed first metatarsals (MT1s) the basal epiphyseal scar is visible, including in one individual who was 80 years old. Statistically, there was no relationship between the loss of the epiphyseal scar and age. Thus, the presence of the epiphyseal scar does not necessarily indicate subadult age. These data suggest that OH 8's radiographically visible basal epiphyseal line has no bearing on whether it is a subadult or not.

More than just a bump: cam-type femoroacetabular impingement and the evolution of the femoral neck

Recent orthopaedic literature has implicated femoroacetabular impingement, the pathologic abutment of structural aberrancies in the proximal femur and acetabular rim, as an important cause of groin pain in young individuals and a potential factor in early idiopathic osteoarthritis. The etiology and risk factors for developing cam-type morphology are still unknown. The osseous anatomy of the proximal femur in humans is the culmination of nearly 400 million years of evolution. Coxa recta and coxa rotunda are the two predominant morphologies in modern animals. While the former, characterized by a straight head-neck junction, is often present in cursorial creatures, the latter, [corrected] distinguished by high offset at this junction, is exemplified in most humans. Based on the ontology and phylogeny of the proximal femur, coxa rotunda probably developed from a more primitive coxa recta. We believe that cam-type morphology is neither a redevelopment of coxa recta nor a malformation such as slipped capital epiphysis. The aspherical osteocartilaginous bump is associated with an extended physis and has been noted to appear during mid-adolescence. While this protuberance may contribute to future pathology, the authors feel that increased loading of the hip, not impingement activities, during late childhood and early adolescence predispose patients to develop this morphology.

Changes in proximal femoral mineral geometry precede the onset of radiographic hip osteoarthritis: The study of osteoporotic fractures

OBJECTIVE

Radiographic hip osteoarthritis (RHOA) is associated with increased hip areal bone mineral density (aBMD). This study was undertaken to examine whether femoral geometry is associated with RHOA independent of aBMD.

METHODS

Participants in the Study of Osteoporotic Fractures in whom pelvic radiographs had been obtained at visits 1 and 5 (mean 8.3 years apart) and hip dual x-ray absorptiometry (DXA) had been performed (2 years after baseline) were included. Prevalent and incident RHOA phenotypes were defined as composite (osteophytes and joint space narrowing [JSN]), atrophic (JSN without osteophytes), or osteophytic (femoral osteophytes without JSN). Analogous definitions of progression were based on minimum joint space and total osteophyte score. Hip DXA scans were assessed using the Hip Structural Analysis program to derive geometric measures, including femoral neck length, width, and centroid position. Relative risks and 95% confidence intervals for prevalent, incident, and progressive RHOA per SD increase in geometric measure were estimated in a hip-based analysis using multinomial logistic regression with adjustment for age, body mass index, knee height, and total hip aBMD.

RESULTS

In 5,245 women (mean age 72.6 years), a wider femoral neck with a more medial centroid position was associated with prevalent and incident osteophytic and composite RHOA phenotypes (P < 0.05). Increased neck width and centroid position were associated with osteophyte progression (both P < 0.05). No significant geometric associations with atrophic RHOA were found.

CONCLUSION

Differences in proximal femoral bone geometry and spatial distribution of bone mass occur early in hip OA and predict prevalent, incident, and progressive osteophytic and composite phenotypes, but not the atrophic phenotype. These bone differences may reflect responses to loading occurring early in the natural history of RHOA.