A calculation of the forces acting on the human acetabulum during walking. Based On in vivo force measurements, kinematic analysis and morphometry

Outcomes for the Arthroscopic Treatment of Femoroacetabular Impingement Syndrome With Acetabular Retroversion: A 3D Computed Tomography Analysis

BACKGROUND

Increased attention has been directed toward the acetabular morphology in the management of patients with femoroacetabular impingement syndrome (FAIS). Whether acetabular version influences patient-reported outcomes remains poorly understood.

PURPOSE

To use computed tomography (CT)-based 3-dimensional (3D) bone models to (1) quantify acetabular version in patients with FAIS, (2) compare acetabular version on 3D bone models with current plain radiographic parameters, and (3) explore the relationship between the magnitude of acetabular version and minimum 2-year clinical outcomes after hip arthroscopy.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

Three-dimensional models of the pelvis and femur were generated by semiautomated segmentation and aligned to a standard coordinate system. Acetabular version was quantified at the 3-o'clock position, and 3 groups were identified: acetabular retroversion (AR; <15°), normal acetabular version (NV; 15°-25°), and acetabular anteversion (AA; >25°). Patient demographic characteristics, plain radiographic parameters, and clinical outcomes were analyzed, including the Hip Outcome Score-Activities of Daily Living, Hip Outcome Score-Sports Subscale, modified Harris Hip Score (mHHS), International Hip Outcome Tool (iHOT-12), and visual analog scale (VAS) for pain and satisfaction.

RESULTS

Preoperative CT scans were acquired in 105 consecutive patients before hip arthroscopy for FAIS, of which 84 (80.0%) completed minimum 2-year patient-reported outcomes. The mean ± SD age and body mass index of patients were 33.9 ± 12.6 years and 26.0 ± 5.4, respectively; 70.2% were female. The number of patients and the mean central acetabular version within each group were as follows: AR (n = 12; 11.3°± 2.7°), NV (n = 56; 20.7°± 2.9°), and AA (n = 16; 28.5°± 2.7°). Posterior wall sign was the only plain radiographic parameter that was significantly more observed in the AR group than in the other 2 groups. At minimum 2-year follow-up, significant between-group differences in the mHHS, iHOT-12, and VAS for pain and satisfaction (P < .05) were appreciated, while post hoc analysis with Bonferroni correction (P < .0167) found lower scores on the mHHS, iHOT-12, and VAS for pain and satisfaction in patients with AR as compared with NV. Lower scores on the VAS for satisfaction were reported in patients with AR when compared with AA (P = .006) but not on the mHHS (P = .023), iHOT-12 (P = .032), or VAS for pain (P = .072).

CONCLUSION

Traditional plain radiographic indices to describe AR, including crossover sign and ischial spine sign, were not reliable in defining AR according to 3D models derived from CT scans. Only the posterior wall sign was observed in a higher proportion in the AR group. Patients with AR demonstrated inferior outcomes when compared with patients with NV and AA after hip arthroscopy for FAIS.

Biomechanical analysis of fixation methods in acetabular fractures: a systematic review of test setups

Purpose

Optimal anatomical reduction and stable fixation of acetabular fractures are important in avoiding secondary dislocation and osteoarthritis. Biomechanical studies of treatment options of acetabular fractures aim to evaluate the biomechanical properties of different fixation methods. As the setup of the biomechanical test can influence the experimental results, this review aimed to analyze the characteristics, comparability and clinical implications of studies on biomechanical test setups and finite element analyses in the fixation of acetabular fractures.

Methods

A systematic literature research was conducted according to the PRISMA guidelines, using the PubMed/MEDLINE and Web of Science databases. 44 studies conducting biomechanical analyses of fixation of acetabular fractures were identified, which met the predefined inclusion and exclusion criteria and which were published in English between 2000 and April 16, 2021. The studies were analyzed with respect to distinct parameters, including fracture type, material of pelvis model, investigated fixation construct, loading direction, loading protocol, maximum loading force, outcome parameter and measurement method.

Results

In summary, there was no standardized test setup within the studies on fixation constructs for acetabular fractures. It is therefore difficult to compare the studies directly, as they employ a variety of different test parameters. Furthermore, the clinical implications of the biomechanical studies should be scrutinized, since several test parameters were not based on observations of the human physiology.

Conclusion

The limited comparability and restricted clinical implications should be kept in mind when interpreting the results of biomechanical studies and when designing test setups to evaluate fixation methods for acetabular fractures.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00068-022-01936-9.

Biomechanical analysis of transverse acetabular fracture fixation in the elderly via the posterior versus the anterior approach with and without a total hip arthroplasty

This study provides the first biomechanical comparison of the fixation constructs that can be created to treat transverse acetabular fractures when using the “gold-standard” posterior versus the anterior approach with and without a total hip arthroplasty in the elderly. Synthetic hemipelvises partially simulating osteoporosis (n = 24) were osteotomized to create a transverse acetabular fracture and then repaired using plates/screws, lag screws, and total hip arthroplasty acetabular components in one of four ways: posterior approach (n = 6), posterior approach plus a total hip arthroplasty acetabular component (n = 6), anterior approach (n = 6), and anterior approach plus a total hip arthroplasty acetabular component (n = 6). All specimens were biomechanically tested. No differences existed between groups for stiffness (range, 324.6–387.3 N/mm, p = 0.629), clinical failure load at 5 mm of femoral head displacement (range, 1630.1–2203.9 N, p = 0.072), or interfragmentary gapping (range, 0.67–1.33 mm, p = 0.359). Adding a total hip arthroplasty acetabular component increased ultimate mechanical failure load for posterior (2904.4 vs. 3652.3 N, p = 0.005) and anterior (3204.9 vs. 4396.0 N, p = 0.000) approaches. Adding a total hip arthroplasty acetabular component also substantially reduced interfragmentary sliding for posterior (3.08 vs. 0.50 mm, p = 0.002) and anterior (2.17 vs. 0.29 mm, p = 0.024) approaches. Consequently, the anterior approach with a total hip arthroplasty may provide the best biomechanical stability for elderly patients, since this fixation group had the highest mechanical failure load and least interfragmentary sliding, while providing equivalent stiffness, clinical failure load, and gapping compared to other surgical options.

Labral tears with axial plane disorders

OBJECTIVES

This study aims to determine if there is an axial plane coverage insufficiency in patients with symptomatic labral tears compared to the contralateral asymptomatic side and healthy control subjects.

PATIENTS AND METHODS

This retrospective study was conducted between December 2017 and January 2019. Thirty patients (21 males, 9 females; mean age 28 years; range, 20 to 36 years) operated due to unilateral symptomatic acetabular labral tears secondary to femoroacetabular impingement were evaluated. Twenty asymptomatic patients (13 males, 7 females; mean age 27±9 years; range, 19 to 36 years) were included in the control group. The relationship between acetabular morphology and labral tear was investigated with the comparison of unilateral symptomatic hips with contralateral asymptomatic hips and the control group by using radiological parameters on plain radiographs and computed tomography.

RESULTS

When the patient group symptomatic side was compared to the control group, acetabular anteversion angle (A A A) and alpha (α) angle were higher, while posterior acetabular sector angle and horizontal acetabular sector angle were lower. When the asymptomatic side was compared to the control group, AAA was higher in the patient group. There was no difference between the symptomatic and asymptomatic sides in the patient group; the symptomatic side yielded a higher α; angle.

CONCLUSION

Posterior axial plane coverage deficiency in combination with cam deformity (increased α angle) seems to play a role in the pathogenesis of symptomatic acetabular labral tears, even creating a side-to-side difference in some individuals.

Acetabular retroversion: Diagnosis and treatment

Acetabular retroversion (AR) consists of a malorientation of the acetabulum in the sagittal plane. AR is associated with changes in load transmission across the hip, being a risk factor for early osteoarthrosis. The pathophysiological basis of AR is an anterior acetabular hyper-coverage and an overall pelvic rotation.

The delay or the non-diagnosis of AR could have an impact in the overall management of femoroacetabular impingement (FAI). AR is a subtype of (focal) pincer deformity.

The objective of this review was to clarify the pathophysiological, diagnosis and treatment fundaments inherent to AR, using a current literature review.

Radiographic evaluation is paramount in AR: the cross-over, the posterior wall and ischial spine signs are classic radiographic signs of AR. However, computed tomography (CT) evaluation permits a three-dimensional characterization of the deformity, being more reliable in its recognition.

Acetabular rim trimming (ART) and periacetabular osteotomy (PAO) are the best described surgical options for the treatment of AR.

The clinical outcomes of both techniques are dependent on the correct characterization of existing lesions and adequate selection of patients.

Cite this article: EFORT Open Rev 2018;3:595-603. DOI: 10.1302/2058-5241.3.180015

Calculation of muscle forces during normal gait under consideration of femoral bending moments

This paper introduces a new approach for computing lower extremity muscle forces by incorporating equations that consider "bone structure" and "prevention of bending by load reduction" into existing optimization algorithms. Lower extremity muscle and joint forces, during normal gait, were calculated and compared using two different optimization approaches. We added constraint equations that prevent femoral bending loads to an existing approach that considers "minimal total muscular force". Gait parameters such as kinematics, ground reaction forces, and surface electromyographic activation patterns were examined using standardized gait analysis. A subject-specific anatomic model of the lower extremities, obtained from magnetic resonance images of a healthy male, was used for the simulations. Finite element analysis was used to calculate femoral loads. The conventional method of calculating muscle forces leads to higher rates of femoral bending and structural stress than the new approach. Adding equations with structural subject-specific parameters in our new approach resulted in reduced femoral stress patterns. These findings show that our new approach improves the accuracy of femoral stress and strain simulations. Structural overloads caused by bending can be avoided during inverse calculation of muscle forces.

OARSI Clinical Trials Recommendations: Hip imaging in clinical trials in osteoarthritis

Imaging of hip in osteoarthritis (OA) has seen considerable progress in the past decade, with the introduction of new techniques that may be more sensitive to structural disease changes. The purpose of this expert opinion, consensus driven recommendation is to provide detail on how to apply hip imaging in disease modifying clinical trials. It includes information on acquisition methods/techniques (including guidance on positioning for radiography, sequence/protocol recommendations/hardware for magnetic resonance imaging (MRI)); commonly encountered problems (including positioning, hardware and coil failures, artifacts associated with various MRI sequences); quality assurance/control procedures; measurement methods; measurement performance (reliability, responsiveness, and validity); recommendations for trials; and research recommendations.

Axial plane coverage and torsion measurements in primary osteoarthritis of the hip with good frontal plane coverage and spherical femoral head

INTRODUCTION

Mechanical factors play a role in pathogenesis of primary osteoarthritis of the hip. Torsion measures were made to detect whether there is a causal relationship between increase or decrease of femoral anteversion, acetabular anteversion, and osteoarthritis. There are no studies in the literature indicating a relationship between axial plane coverage and osteoarthritis of the hip. Deficient axial plane coverage of femoral head may also play a role in pathogenesis of osteoarthritis.

MATERIALS AND METHODS

Thirty patients with primary osteoarthritis of the hip and 29 control cases were included in the study. We used the method of Anda et al. (Acta Radiol Diagn 27:443-447, 1986; Comput Assist Tomogr 15:115-120, 1991) to measure axial plane anterior, posterior coverages in patients with primary osteoarthritis of the hip. The computerized tomography sections and pelvic radiographs indicated good frontal plane coverage and spherical femoral head. In addition to anterior acetabular sector angle, posterior acetabular sector angle, horizontal acetabular sector angles for axial plane coverage detection, femoral anteversion, acetabular anteversion, and McKibbin instability index were also measured.

RESULTS

Posterior coverage was lower at osteoarthritic hips than the control group's hips (96.0 ± 16.7, 104.2 ± 10.6) (p < 0.05).

CONCLUSION

The results may indicate that in addition to other mechanical factors, axial plane coverage, especially the posterior coverage deficiency, may play a role in the pathogenesis of hip osteoarthritis.

Three-dimensional CT analysis to determine acetabular retroversion and the implications for the management of femoro-acetabular impingement

This study examined the relationship between the cross-over sign and the true three-dimensional anatomical version of the acetabulum. We also investigated whether in true retroversion there is excessive femoral head cover anteriorly. Radiographs of 64 hips in patients being investigated for symptoms of femoro-acetabular impingement were analysed and the presence of a cross-over sign was documented. CT scans of the same hips were analysed to determine anatomical version and femoral head cover in relation to the anterior pelvic plane after correcting for pelvic tilt. The sensitivity and specificity of the cross-over sign were 92% and 55%, respectively for identifying true acetabular retroversion. There was no significant difference in total cover between normal and retroverted cases. Anterior and posterior cover were, however, significantly different (p < 0.001 and 0.002). The cross-over sign was found to be sensitive but not specific. The results for femoral head cover suggest that retroversion is characterised by posterior deficiency but increased cover anteriorly.

Hip disease in the young, active patient: evaluation and nonarthroplasty surgical options

As a distinct entity, femoroacetabular impingement has been suggested to be a preosteoarthritic mechanism. The condition occurs when the proximal femur repeatedly comes into contact with the native acetabular rim during normal hip range of motion. Early diagnosis and surgical management are imperative to delay degenerative changes associated with these conditions. Femoroacetabular impingement is most prevalent in young, active patients. Physical examination should include evaluation of gait and foot progression angle, as well as leg length measurement, hip range of motion, and abductor strength. Imaging studies, including plain radiographs and magnetic resonance arthrography, aid in accurate diagnosis. Surgical treatment options include surgical hip dislocation, periacetabular osteotomy, and hip arthroscopy.

Legs evolved only at the end!

Talking about legged locomotion often evokes the idea that animals using such devices are perfectly adapted to this kind of motion and should be copied by robotics. The aim of this contribution is to show that the evolution of legs comes late in phylogeny, be it in arthropods or vertebrates. Neural control of legs in vertebrates has to deal with conservative arrangements 'invented' for axial locomotion of metameric organisms. The structure of this paper is to show the importance of axial driven propulsion in vertebrates without legs, with legs and only at the end how limbs move the body in eutherian mammals.

The relationship between acetabular retroversion and osteoarthritis of the hip

Excessive acetabular cover secondary to a retroverted acetabulum causes pincer impingement, which may cause early osteoarthritis of the hip. Our aim was to determine if there was a relationship between acetabular version and osteoarthritis of the hip. Using image processing and analysis software we studied 117 CT images of the hip in patients aged less than 65 years who had undergone a CT virtual colonoscopy. The mean CT joint space of the 18 hips with acetabular retroversion was narrower compared with the 99 hips with normal acetabular alignment (p < 0.0001). A correlation of r = 0.46 (p < 0.01) was found between right hip acetabular version and the mean right hip joint space and of r = 0.31 (p = 0.02) between left hip acetabular version and the mean left hip joint space. Acetabular retroversion is associated with radiological evidence of osteoarthritis of the hip. An understanding of the mechanical basis of osteoarthritis of the hip allows early treatment of the underlying structural abnormality and prevents progression of the degenerative condition.

The prevalence of acetabular retroversion among various disorders of the hip

BACKGROUND

Acetabular retroversion can result from posterior wall deficiency in an otherwise normally oriented acetabulum or from excessive anterior coverage secondary to a malpositioned acetabulum, or both. Theoretically, a retroverted acetabulum, which adversely affects load transmission across the hip, may occur more frequently in hips with degenerative arthritis. The aim of this study was to assess the prevalence of acetabular retroversion in normal hips and in hips with osteoarthritis, developmental dysplasia, osteonecrosis, and Legg-Calvé-Perthes disease.

METHODS

We retrospectively examined anteroposterior radiographs of the pelvis of 250 patients (342 hips). Fifty-six patients (112 hips) had normal findings; sixty-six patients (seventy hips) had osteoarthritis; sixty-four (seventy-four hips), developmental dysplasia; thirty (thirty-six hips), osteonecrosis of the femoral head; and thirty-four (fifty hips), Legg-Calvé-Perthes disease. The sole criterion for a diagnosis of acetabular retroversion was the presence of a so-called cross-over sign on the anteroposterior radiograph of the pelvis.

RESULTS

The prevalence of acetabular retroversion was 6% (seven of 112 hips) in the normal group, 20% (fourteen of seventy hips) in the osteoarthritis group, 18% (thirteen of seventy-four hips) in the developmental dysplasia group, 6% (two of thirty-six hips) in the group with osteonecrosis of the femoral head, and 42% (twenty-one of fifty hips) in the group with Legg-Calvé-Perthes disease. In patients with Legg-Calvé-Perthes disease, the prevalence of acetabular retroversion was 68% in twenty-five hips with Stulberg class-III, IV, or V involvement. In contrast, only four (16%) of twenty-five hips with Stulberg class-I or II involvement had acetabular retroversion. The difference was significant (p = 0.0002). Patients with osteoarthritis, developmental dysplasia, or Legg-Calvé-Perthes disease are significantly more likely to have acetabular retroversion than are normal subjects (p < 0.05).

CONCLUSIONS

Acetabular retroversion occurs more commonly in association with a variety of hip diseases, in which the prevalence of subsequent degenerative arthritis is increased, than has been previously noted.

Anatomical and biomechanical investigations of the iliotibial tract

Divergent descriptions of the anatomic location and biomechanical function of the iliotibial tract (IT) can be found in the literature. This study attempted to obtain exact data regarding the anatomic course and material characteristics including the biomechanical properties of this structure. The following were its aims: (1) anatomical investigations of the IT; (2) mechanical properties of the IT; (3) femoral head centralizing force of the IT and subligamentous forces in the height of the greater trochanter in different joint positions by using a custom-made measuring prosthesis and a subligamentous positioned sensor; (4) construction of a finite element model of the proximal femur including the IT and measuring the femoral neck angle under variation. The hip joints and IT in a total of 18 unfixed corpses were evaluated. We studied the anatomic relationship to surrounding structures, as well as the material properties with the help of tensile strength testing utilizing an uniaxial apparatus. During the test, a load-displacement curve was registered, documenting the maximum load and deformation of the IT. To measure the subligamentous pressure at the height of the greater trochanter, a custom-made sensor with a power-recording instrument was constructed. Furthermore, an altered hip prosthesis with a pressure gauge at the height of the femoral neck was used to measure the forces which are directed at the acetabulum. The investigations were done in neutral-0 position and ab/adduction of the hip joint of the unfixed corpse. In addition, we varied the femoral neck angle between 115 degrees and 155 degrees in 5 degrees steps. To confirm the subligamentous forces, we did the same measurements intraoperatively at the height of the greater trochanter before and after hip joint replacement in 12 patients. We constructed a finite element model of the proximal femur and considering the IT. The acquisition of the data was done at physiological (128 degrees), varus (115 degrees), and valgus (155 degrees) femoral neck angles. The influencing forces of the IT at the height of the greater trochanter and the forces at the femoral head or the acetabulum could be measured. Our anatomical investigations revealed a splitting of the IT into a superficial and a deep portion, which covers the tensor fasciae latae. The tensor fasciae latae has an insertion on the IT. The IT continues down the femur, passing over the greater trochanter without developing an actual fixation to the bone. Part of the insertion of the gluteus maximus radiates into the IT. The IT passes over the vastus lateralis and inserts at the infracondylar tubercle of the tibia or Gerdy's tubercle, at the head of the fibula, as well as at the lateral intermuscular septum. Portions also insert on the transverse and longitudinal retinaculum of the patella. Concerning the material properties of the IT, we found a structural stiffness of 17 N/mm extension on average (D = 17 N/mm). The subligamentous measurements at the height of the greater trochanter in the unfixed corpse and intraoperatively during hip joint replacement showed an increase of the forces during adduction and a decrease during abduction of the hip joint. We found thereby a maximum increase up to 106 N with 40 degrees adduction. Concerning the femoral neck angle, we can state that valgus leads to lower subligamentous forces and varus to higher subligamentous forces. The forces directed at the acetabulum, which were measured by the prosthesis with a sensor along the femoral neck, showed a decrease with varus angles and an increase with valgus angles. The highest force of 624 N was measured with 40 degrees adduction and an angle of 155 degrees. The finite element model of the proximal femur showed a sole hip joint-centralizing force of the IT of 655 N with a femoral neck angle of 128 degrees after subtraction of the gluteal muscle force and the body weight. At 115 degrees, we found an increase up to 997 N and a decrease to 438 N at 155 degrees. Concerning the resulting forces in the acetabulum, we found opposite forces in comparison with the force of the IT at the height of the greater trochanter: at 115 degrees, a femoral head-centralizing force of 1601 N; at 128 degrees, 2360 N; and at 155 degrees, 2422 N. By our investigations, we can approximately prove the hip joint-centralizing force of the IT. By variation of the femoral neck angle and the position of the hip joint, we can predict the subligamentous force of the IT and the resulting force at the femoral head or at the acetabulum. The intraoperative measurement of the subligamentous forces of the IT is a good monitoring mechanism for the persistent hip-centralizing function of the IT in the course of hip joint replacement. The surgeon has the opportunity to check the stability of the hip joint after replacement. The finite element model gives the opportunity to check the divergent relative strength by variation of the femoral neck angle and the tension of the IT. In this way, the changes in the forces induced by a displacement osteotomy could be estimated preoperatively.

Acetabular retroversion is associated with osteoarthritis of the hip

Primary osteoarthritis of the hip may have a structural basis. It was hypothesized that the radiographic appearance of acetabular retroversion could be created by altering the morphologic features of the acetabular walls, and that acetabular retroversion, as defined on an anteroposterior radiograph of the pelvis, is associated with osteoarthritis of the hip. A model pelvis was used to simulate normal, augmented, deficient, and rotated walls of the acetabulum, and radiographs were taken to compare the projections of the modified acetabular walls with the known plain radiographic appearance of a retroverted acetabulum. One hundred thirty-one good quality anteroposterior radiographs of the pelvis taken before total hip arthroplasty for idiopathic hip osteoarthritis were compared with 99 good quality radiographs taken for nonorthopaedic reasons. The prevalence of radiographic acetabular retroversion is 20% among patients with idiopathic hip osteoarthritis and 5% among the general population. The appearance of acetabular retroversion on an anteoroposterior radiograph of the pelvis is created by deficiency of the posterior wall of the acetabulum. There is a statistically significant association between radiographic acetabular retroversion and hip osteoarthritis. These findings have applicability to understanding the mechanical etiology of hip osteoarthritis, and to surgical technique during periacetabular osteotomy and total hip arthroplasty.

Contact Stresses in the Human Hip: Implications for Disease and Treatment

Contact stresses in the hip articular surfaces relate in some way to normal maintenance as well as destruction of joints. In vivo determinations of cartilage-on-cartilage contact pressure histories have never been reported, and current technology does not allow such measurements without the potential for artifact: all experimental methods require introducing some material between the surfaces, and all numerical methods have yet to be fully validated. Nonetheless, a variety of distinct experimental and numerical approaches lead to estimates of contact stresses and surprisingly, despite the choice of technique, values for peak contact stresses lie within a range of one order of magnitude (i.e. 0.5–5.0 MPa) and usually closer. Pathological conditions increase this to the range of over 5.0 MPa, while surgical procedures designed to reduce peak pressures theoretically can achieve reductions. Two critical unresolved issues are 1.) What aspect of the contact stress history (e.g. contact stress gradients over time) in fact cause the biological responses? 2.) What level of contact stress history is tolerated by the cartilage? Future research will need to address these critical issues.

Quantitative determination of joint incongruity and pressure distribution during simulated gait and cartilage thickness in the human hip joint

The objective of this study was to provide quantitative data on hip-joint incongruity and pressure during a simulated walking cycle and on articular-cartilage thickness in the same set of specimens. Using a casting technique in eight specimens of the human hip (age: 18-75 years), we determined the width of the joint space (incongruity) required at minimal load for contact at four phases of the gait cycle. The pressure distribution, measured with pressure-sensitive film, was determined at physiologic load magnitudes on the basis of in vivo measurements of hip-joint forces. Cartilage thickness was assessed with A-mode ultrasound. At minimal loading, the average maximum width of the joint space ranged from 1.1 to 1.5 mm in the acetabular roof, with the contact areas located ventro-superiorly and dorso-inferiorly throughout the gait cycle. At physiological loading, the width decreased and the contact areas covered the complete articular surface during midstance and heel-off but not during heel-strike or toe-off. The pressure distribution was inhomogeneous during all phases, with average maximum pressures of 7.7 +/- 1.95 MPa at midstance. The cartilage thickness varied considerably throughout the joint surfaces; maxima greater than 3 mm were found ventro-superiorly. These data can be used to generate and validate computer models to determine the load-sharing between the interstitial fluid and the solid proteoglycan-collagen matrix of articular cartilage, the latter being relevant for the initiation of mechanically induced cartilage degeneration.