Function-Orientated Structural Analysis of the Proximal Human Femur

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.

Muscle forces acting on the greater trochanter lead to a dorsal warping of the apophyseal growth plate

The apophyseal growth plate of the greater trochanter, unlike most other growth plates of the human body, exhibits a curved morphology that results in a divergent pattern resembling an open crocodile mouth on plain antero-posterior radiographs. To quantify the angular alignment of the growth plate and to draw conclusions about the function of the muscles surrounding it, we analyzed 57 MRI images of 51 children and adolescents aged 3-17 years and of six adults aged 18-52 years. We measured the angulation of the plate relative to the horizontal plane (AY angle) and the trajectories of the muscles attaching to the greater trochanter of the proximal femur. From anterior to posterior, the AY angle shows a decrease of 33.44°. In the anterior third, the cartilage is angled at a mean of 51.64°, and in the posterior third, the mean angulation is 18.6°. This indicates that the cartilage in the anterior region of the greater trochanteric apophysis is subject to more vertically oriented force vectors compared to the posterior region, as the growth plates align perpendicular to the force vectors acting on them. Combining the measured muscle trajectories with the physiological cross-sectional areas (PCSA) available from the literature revealed that, in addition to the known internal and external lateral traction ligament systems, a third, dorsally located traction ligament system exists that may be responsible for the dorsal deformation of the AY angle.

Fracture morphology and biomechanical characteristics of Pauwels III femoral neck fractures in young adults

BACKGROUND

Pauwels classification, which categorizes types of femoral neck fractures, cannot fully reflect the three-dimensional characteristics of this injury. The purpose of our study was to determine the morphological characteristics of Pauwels III fractures through computed tomography image analysis and summarize the relevant biomechanical characteristics of different morphological fractures.

METHODS

We retrospectively reviewed a total of 209 patients diagnosed with Pauwels type III femoral neck fractures. Fracture reduction was simulated based on mirror symmetry of the bilateral femur by Mimics. The fracture angle was measured and subtypes were defined. Biomechanical characteristics were compared by finite element analysis and validated using a biomechanical experiment, which was performed on a cadaveric sample.

RESULTS

Pauwels III femoral neck fractures can be divided into three subtypes: anterior, posterior, and classical. The proportion of three subtypes was 28.71%, 67.46%, and 3.82%, respectively. The anterior subtype showed the lowest axial stiffness but highest implant and bone stress. High stress distributions was concentrated on the screw-bone interface and screw-plate connections.

CONCLUSIONS

Biomechanical differences across the three subtypes of Pauwels III femoral neck fractures could increase our understanding of the biomechanical characteristics that underlie the Pauwels type III femoral neck fractures (such as, three-dimensional morphology and the stress distribution of bone and implant) that have been associated with high failure rates.

Position of the greater trochanter and functional femoral antetorsion: Which factors matter in the management of femoral antetorsion disorders?

Aims

The primary aim of this study was to define and quantify three new measurements to indicate the position of the greater trochanter. Secondary aims were to define 'functional antetorsion' as it relates to abductor function in populations both with and without torsional abnormality.

Patients and Methods

Three new measurements, functional antetorsion, posterior tilt, and posterior translation of the greater trochanter, were assessed from 61 CT scans of cadaveric femurs, and their reliability determined. These measurements and their relationships were also evaluated in three groups of patients: a control group (n = 22), a 'high-antetorsion' group (n = 22) and a 'low-antetorsion' group (n = 10).

Results

In the cadaver group, the mean anatomical antetorsion was 14.7° (sd 8.5; 0 to 36.5) and the functional antetorsion 21.5° (sd 8.1; 3.6 to 44.3): the posterior tilt was 73.3° (sd 10.8; 46.9 to 88.7) and the posterior translation 0.59 (sd 0.2; 0.2 to 0.9). These measurements had excellent intra and interobserver agreement with a range from 0.93 to 0.99. When the anatomical antetorsion decreased, the greater trochanter was more tilted and translated posteriorly in relation to the axis of the femoral neck, and the difference between functional and anatomical antetorsion increased. The results the three patient groups were similar to those of the cadaver group.

Conclusion

The position of the greater trochanter and functional antetorsion varied with anatomical antetorsion. In the surgical management of femoral retrotorsion, subtrochanteric osteotomy can result in an excessively posterior position of the greater trochanter and an increase in functional antetorsion. Cite this article: Bone Joint J 2018;100-B:712-19.

Apophyseal Avulsion of the Greater Trochanter in an Adolescent: Treatment with Abduction Bracing: A Case Report

CASE

We describe a case of an adolescent athlete who sustained a greater trochanteric avulsion fracture. After conservative management with abduction bracing, the patient made a full recovery, with no signs of osteonecrosis at 12 months. We describe the presentation, the course of recovery, and the literature regarding treatment and outcomes.

CONCLUSION

Isolated fracture of the greater trochanteric apophysis is a rare but possibly devastating injury to the adolescent hip when complicated by osteonecrosis. We describe the successful conservative treatment of this injury in what we believe to be the second such report in the English-language literature.

[Macroscopic and functional anatomy of the apophyseal plate]

Apophyses are growth zones attached to the shaft (corpus) of larger bones. They vary in size and develop their own ossification centres or form as part of an usually fibrocartilaginous tendon or ligament insertion. The structure of the cartilaginous apophyseal plate is very similar to that of an epiphyseal growth plate and like these they are adapted to withstand perpendicular compressive forces without becoming harmed. This is best highlighted by the fact that their mineralized borders always orient themselves perpendicular to the overall resulting force vector. The edges of the apophyseal plates are characteristically bent which allows them to resist moderate shear forces. Like the epiphyseal plates the apophyseal plates exhibit a zonal organization which is not very well adapted to permanently withstand shear forces, especially if they occur under dynamic conditions. In these situations the tendinous insertions with their collagen fibre anchoring system have to provide compensation when balancing the load transmitted across the system.

[The great apophyses: Functional strain and relevance]

BACKGROUND

The structure of apophyses and apophyseal growth plates is not substantially different from those of epiphyses and epiphyseal growth plates. In contrast to epiphyseal growth plates, apophyses and apophyseal growth plates do not contribute to the longitudinal growth of the extremity. They are associated with their adjacent joints, triggering the lengths of their lever arms and influencing their external shape and internal architecture. The formative stimulus on apophyses is given by muscles and tendons inserting at the apophysis or canopying the apophsis.

APOPHYSIS OF THE GREATER TROCHANTER

The apophysis of the greater trochanter significantly contributes to the lever arm length of the hip joint. Its growth activity triggers the neck-shaft angle and finally the centration of the hip joint.

TIBIAL APOPHYSIS

The tibial apophysis interacts with the slope of the proximal tibia and hereby influences the sagittal stability of the knee joint. A damage to the growth plate of the tibial tubercle leads to an anteverted tibial slope and a genu recurvatum difficult to treat.

CALCANEAL APOPHYSIS

The calcaneal apophysis determines the length and position of the calcaneus and herewith influences the torque of the ankle joint. In a nutshell you may regard the apophyses as adjusting screws acting on their adjacent joints and influencing their growth, form and structure.

The underused hip in ipsilaterally orthotics-dependent children

BACKGROUND

The aim of this investigation is the development of primarily healthy hips in children who have required orthoses/protheses over the long term due to ipsilateral distally located deformities of the leg. These children show ipsilateral in-toeing gait and Duchenne's limping followed by a coxa valga antetorta and facultative hip decentration. A practical question is whether these hips are in danger of decompensation. An additional theoretical question is how the external shape and internal architecture changes if a primarily healthy hip is underused.

METHODS

Ten children with healthy hips who are unilaterally long-term orthotics/prosthetics-dependent agreed to undergo an instrumental gait analysis. The results were analyzed and correlated with clinical findings, a common activity score and planimetric radiographic data.

RESULTS

The intra-individual comparison revealed a number of significant changes in the hip of the deformed leg (p < 0.05). Clinically, the internal rotation was increased (15° ± 4.2°), while the external rotation was diminished (13° ± 1.3°). Radiologically, the projected caput-collum-diaphyseal angle, the lesser trochanter to articular surface distance and the head-shaft angle were increased by 11.1° ± 15.4°, 5.8 ± 4.2 mm and 11.9° ± 0.6°, respectively. Both the Sharp and acetabular angles were increased, the former by 3.6° ± 0.6° and the latter by 3.2° ± 0.6°. Kinetic gait analysis showed increased stride length (6.8 ± 3.7 cm), shortened stance phase (6.6 ± 1.6 %) and reduced forces transmitted to the ground (92.2 ± 34.3 N). The kinematic analysis showed increased hip abduction (14.0° ± 8.2°), while the pelvic obliquity was not significantly changed (0.01° ± 0.01°).

CONCLUSIONS

Duchenne's limp and lack of weight-bearing stress are the decisive pathogenic factors of the underused coxa valga and acetabular dysplasia. These changes follow the mechanobiological concept of "function modifies design", which means function influences external shape and internal architecture of bones and joints. As a practical consequence we recommend that one pelvic radiograph be performed as a precaution at the end of puberty of children with these conditions.

LEVEL OF EVIDENCE

Level II retrospective study.

Outcomes after primary open or endoscopic abductor tendon repair in the hip: a systematic review of the literature

PURPOSE

The purpose of this study was to systematically appraise the evidence on primary open and endoscopic abductor tendon repair.

METHODS

A systematic review of the literature was performed to (1) identify the demographic undergoing abductor tendon repair, (2) summarize the overall outcomes after primary surgical abductor tendon repair, (3) identify the type of tear most commonly encountered intraoperatively, (4) summarize the repair methods used, and (5) identify the published complication and tendon retear rates.

RESULTS

A total of 8 articles were identified as eligible for inclusion. All studies were Level IV Evidence. Of the patients undergoing surgical repair, 90% were women. As assessed by a variety of outcome measures, most patients reported good to excellent functional outcomes and pain reduction after open or endoscopic repair. Intraoperatively, tears of the gluteus medius and partial-thickness tears were encountered most often. Tears involving both the gluteus medius and minimus occurred 29% of the time. Complication rates were low for both the open and endoscopic approaches. No tendon retears were documented after endoscopic repair, whereas the retear rate after open repair was 9%.

CONCLUSIONS

Patients undergoing surgical repair for partial- and full-thickness tears are mostly women. Intraoperatively, tears almost always include the gluteus medius, with concomitant tearing of the gluteus minimus in approximately one-third of cases. Both open and endoscopic techniques are viable surgical approaches to repairing abductor tendon tears in the hip that produce good to excellent functional results and reduce pain; however, endoscopic repair appears to result in fewer postoperative complications including tendon retear.

LEVEL OF EVIDENCE

Level IV, systematic review of Level IV studies.

Biomechanical rationale for implant choices in femoral neck fracture fixation in the non-elderly

Femoral neck fractures represent a relatively uncommon injury in the non-elderly population often resulting from high-energy trauma. The cornerstone of their management is anatomic reduction and stable internal fixation of the femoral neck in an attempt to salvage the femoral head. Complications including avascular necrosis of the femoral head, non-union and post-traumatic osteoarthritis are not uncommon. The clinical outcomes of these patients can be improved with good pre-operative planning, optimization of surgical procedures and introduction of new improved implants and techniques. In the herein study, we attempt to describe the biomechanical properties of the hip and compare the performance of the most commonly used devices. Experimental evidence suggests that in Pauwels type III fracture patterns a cephalomedullary nail was significantly stronger in axial loading. Moreover, in unstable basicervical patterns cannulated screws (triangular configuration) demonstrated a lower ultimate load to failure, whereas in subcapital or transervical patterns both the cannulated screws (triangular configuration) and the sliding hip screw demonstrated no compromise in fixation strength. The fracture pattern appears to be the major determinant of the ideal type of implant to be selected. For a successful outcome each patient needs to be considered on an individual basis taking into account all patient and implant related factors.

Functional integrative analysis of the human hip joint: the three-dimensional orientation of the acetabulum and its relation with the orientation of the femoral neck

In humans, the hip joint occupies a central place in the locomotor system, as it plays an important role in body support and the transmission of the forces between the trunk and lower limbs. The study of the three-dimensional biomechanics of this joint has important implications for documenting the morphological changes associated with the acquisition of a habitual bipedal gait in humans. Functional integration at any joint has important implications in joint stability and performance. The aim of the study was to evaluate the functional integration at the human hip joint. Both the level of concordance between the three-dimensional axes of the acetabulum and the femoral neck in a bipedal posture, and patterns of covariation between these two axes were analysed. First, inter-individual variations were quantified and significant differences in the three-dimensional orientations of both the acetabulum and the femoral neck were detected. On a sample of 57 individuals, significant patterns of covariation were identified, however, the level of concordance between the axes of both the acetabulum and the femoral neck in a bipedal posture was lower than could be expected for a key joint such as the hip. Patterns of covariation were explored regarding the complex three-dimensional biomechanics of the full pelvic-femoral complex. Finally, we suggest that the lower degree of concordance observed at the human hip joint in a bipedal posture might be partly due to the phylogenetic history of the human species.

Midterm results after subtrochanteric end-to-side valgization osteotomy in severe infantile coxa vara

BACKGROUND

For the treatment of the severe infantile coxa vara it is mandatory for the orthopaedic surgeon to observe the mechanobiology of the growing hip before and after the surgical intervention. We hereby would like to present our experiences with the subtrochanteric end-to-side valgization osteotomy and to compare the procedure with the alternatively used Y-shaped osteotomy as described by Pauwels.

METHODS

Thirteen patients (20 hips) who had undergone subtrochanteric end-to-side valgization were followed for a mean 6.2 years (range, 0.8 to 12.8 y). At the time of surgery the mean age was 7.1 years (range, 2.0 to 13.3 y), last follow-up examination was performed at a mean of 13.4 years of age (range, 5.1 to 18.3 y). The deformities were etiologically based on 5 entities: congenital coxa vara (n=1), osteochondrodysplasias (n=12), postosteomyelitic coxa vara (n=5), and avascular femoral head necrosis in the course of congenital dysplasia of the hip (n=2). The follow-up rate was 100%.In addition, we analyzed a total of 93 pelvic radiographies with a total of 139 hip joints. Thirty angles and distances were assessed according to parameters described in the literature.

RESULTS

Although preoperatively 12 patients presented with a positive Trendelenburg's sign, it was only present postoperatively in 2 patients. Duchenne's limp reduced from 10 to 1. All of the 15 preoperatively apparent nonunions could be healed by means of surgery. Two hips redeveloped pathologically lowered collodiaphyseal angles postoperatively, one of which had to undergo revision surgery. Preoperatively 15 out of 20 patients (75%) showed nonunions all of which healed after surgery. No recurrence could be seen at the time of the last follow-up.The following angles were assessed on plain radiographies of the pelvis preoperatively and directly postoperatively as well as on the last follow-up at a mean of 85 months: CCD-angle 98 degrees/156 degrees/144 degrees, EY-angle 55 degrees/5 degrees/15.7 degrees, AY-angle 32 degrees/75 degrees/66 degrees, CE-angle 20 degrees/25 degrees/18 degrees, AC-angle 20 degrees/18 degrees/20 degrees. The articulotrochanteric distance was 5 mm/26 mm/14 mm.

CONCLUSIONS

The subtrochanteric end-to-side valgization osteotomy showed to be highly effective in the management of the infantile coxa vara, improving the clinical impairment of the patients postoperatively. All of the preoperatively present nonunions showed osseous consolidation at follow-up examination. Only minor revarization tendencies could be found. The procedure is technically less demanding, safer and more efficient regarding the lengthening of the affected limb in comparison to the Y-shaped intertrochanteric osteotomy as described by Pauwels.

LEVEL OF EVIDENCE

Case-control study (EBM-level III).

A three-dimensional axis for the study of femoral neck orientation

A common problem in the quantification of the orientation of the femoral neck is the difficulty to determine its true axis; however, this axis is typically estimated visually only. Moreover, the orientation of the femoral neck is commonly analysed using angles that are dependent on anatomical planes of reference and only quantify the orientation in two dimensions. The purpose of this study is to establish a method to determine the three-dimensional orientation of the femoral neck using a three-dimensional model. An accurate determination of the femoral neck axis requires a reconsideration of the complex architecture of the proximal femur. The morphology of the femoral neck results from both the medial and arcuate trabecular systems, and the asymmetry of the cortical bone. Given these considerations, two alternative models, in addition to the cylindrical one frequently assumed, were tested. The surface geometry of the femoral neck was subsequently used to fit one cylinder, two cylinders and successive cross-sectional ellipses. The model based on successive ellipses provided a significantly smaller average deviation than the two other models (P < 0.001) and reduced the observer-induced measurement error. Comparisons with traditional measurements and analyses on a sample of 91 femora were also performed to assess the validity of the model based on successive ellipses. This study provides a semi-automatic and accurate method for the determination of the functional three-dimensional femoral neck orientation avoiding the use of a reference plane. This innovative method has important implications for future studies that aim to document and understand the change in the orientation of the femoral neck associated with the acquisition of a bipedal gait in humans. Moreover, the precise determination of the three-dimensional orientation has implications in current research involved in developing clinical applications in diagnosis, hip surgery and rehabilitation.

Long-term result after femoral head substitution in postinfectious aplasia of the femoral head

PURPOSE

This case report presents a new and unique surgical greater trochanter split procedure for reconstructing a hip joint after an infantile hip sepsis with consequent aplasia of the femoral head.

METHODS

One patient underwent the new trochanter split osteotomy for postinfectious aplasia of the femoral head at the age of 4 years. A follow-up of 17 years is presented.

SURGICAL TECHNIQUE

The remaining proximal femur is sagittally split and the medial part is shifted into the acetabulum, preserving the lateral part of the greater trochanter. The osteotomy is fixed by an osseous wedge and K-wires. In contrast to the techniques known so far, it does not harm the vastogluteal muscle sling, thus, significantly reducing abductor lurch. Furthermore, through placing juvenile growth cartilage from the greater trochanter area into the acetabulum, there is, by far, more potential for the regeneration of a femoral head than by the procedures known so far.

CONCLUSION

The presented surgical technique is able to improve the biomechanics of a hip joint with postinfectious aplasia of the femoral head. The growth of a new femoral head and the development of a well-shaped acetabulum is enabled. A clinical outcome with a stable joint and very good clinical function can be achieved.

Study of femoral torsion during prenatal growth: interpretations associated with the effects of intrauterine pressure

The developing fetus is protected from external environmental influences by maternal tissues. However, these structures have a limited elasticity, such that the fetus must grow in a confined space, constraining its size at the end of pregnancy. Can these constraints modify the morphology of the fetal skeleton? The intensity of these constraints increases between 5 months and birth, making it the most appropriate period to address this question. A sample of 89 fetal femora was analyzed, and results provide evidence that during this period, the torsion of the femoral shaft (quantified by means of a new three-dimensional method) increases gradually. Two explanations were considered: this increase could signal effects of constraints induced by the intrauterine cavity, developmental patterning, or some combination of these two. Different arguments tend to support the biomechanical explanation, rather than a programming pattern formation. Indeed, the identification of the femur as a first degree lever, created by the hyperflexion of the fetal lower limbs on the pelvis, could explain the increase in femoral shaft torsion during prenatal life. A comparison with femora of infants is in accordance with this mechanical interpretation, which is possible through bone modeling/remodeling. Although genetic and epigenetic mechanisms may regulate timing of fetal development, our data suggest that at birth, the fetal skeleton also has an intrauterine mechanical history through adaptive bone plasticity.