Contact pressures in the flexed hip joint during lateral trochanteric loading

Anteroinferior Hip Instability in Flexion During Dynamic Arthroscopic Examination Is Associated With Abnormal Anterior Acetabular Horn

Background:

The stabilization of the femoral head is provided by the distal acetabulum when the hip is in a flexed position. However, the osseous parameters for the diagnosis of hip instability in flexion are not defined.

Purpose/Hypothesis:

To determine whether the osseous parameters of the distal acetabulum are different in hips demonstrating anteroinferior subluxation in flexion under dynamic arthroscopic examination, compared with individuals without hip symptoms. The hypothesis was that the morphometric parameters of the anterior acetabular horn are distinct in hips with anteroinferior instability compared with asymptomatic hips.

Study Design:

Case-control study; Level of evidence, 3.

Methods:

A total of 30 hips with anteroinferior instability in flexion under dynamic arthroscopic examination were identified. A control group of 60 hips (30 patients), matched by age and sex, was formed from individuals who had undergone pelvis magnetic resonance imaging (MRI) for nonorthopaedic reasons. Unstable and control hips were compared according to the following parameters assessed on axial MRI scans of the pelvis: anterior sector angle (ASA), anterior horn angle (AHA), posterior sector angle (PSA), posterior horn angle (PHA), acetabular version, lateral center-edge angle, acetabular inclination (Tönnis angle), and femoral head diameter.

Results:

The coverage of the femoral head by the anterior acetabular horn was decreased in unstable hips compared with the control group (mean ASA, 54.8° vs 61°, respectively; P < .001). Unstable hips also had a steeper anterior acetabular horn, with an increased mean AHA compared with controls (52.5° vs 46.8°, respectively; P < .001). An ASA <58° had a sensitivity of 0.8, a specificity of 0.68, a negative predictive value of 0.87, and a positive predictive value of 0.56 for anteroinferior hip instability. An AHA >50° had a sensitivity of 0.77, a specificity of 0.72, a negative predictive value of 0.86, and a positive predictive value of 0.57 for anteroinferior hip instability. There was no statistically significant difference in the mean PSA, PHA, acetabular version, lateral center-edge angle, acetabular inclination, or femoral head diameter between unstable hips and controls.

Conclusion:

Abnormal morphology of the anterior acetabular horn is associated with anteroinferior instability in hip flexion. The ASA and AHA can aid in the diagnosis of hip instability.

Abnormal Joint Loading During Gait in Persons With Hip Osteoarthritis Is Associated With Symptoms and Cartilage Lesions

BACKGROUND

Hip joint loading in persons with hip osteoarthritis (OA) is not well studied, and its associations with symptoms and lesions are unknown.

OBJECTIVES

To determine whether hip joint loading differs between people with and without radiographic hip OA, and to identify its associations with patients' symptoms and cartilage morphology.

METHODS

Forty-eight patients (28 male; mean ± SD age, 56.0 ± 12.2 years) with hip OA and 95 controls (40 male; age, 43.2 ± 13.6 years) participated in this cross-sectional analysis. Pelvic radiographs, questionnaires, magnetic resonance imaging (MRI), and gait analysis were conducted. The Hip disability and Osteoarthritis Outcome Score (HOOS) was used to assess symptoms. Cartilage morphology was graded on MRI scans using the Scoring Hip Osteoarthritis with Magnetic Resonance Imaging (SHOMRI) system. Biomechanical variables included peak external hip joint moment (Newton meters per kilogram) and moment impulses (Newton meters times milliseconds per kilogram) in all planes. Generalized estimating equations were used to compare the biomechanical characteristics between groups. In the patients with OA, associations of moment impulses with HOOS and SHOMRI scores were assessed with partial correlations.

RESULTS

The OA group exhibited higher peak external hip flexion and adduction moments (P<.001) and higher hip flexion, adduction, and external rotation moment impulses (P = .001-.039). Increased hip flexion moment impulses were correlated with worse HOOS subscale scores (r = -0.361 to -0.424, P<.05) and worse femoral SHOMRI grades (ρ = 0.256-0.315, P<.05). Increased hip external rotation moment impulses were correlated with worse femoral SHOMRI grades (ρ = 0.283-0.372, P<.05).

CONCLUSION

Persons with hip OA exhibited abnormally high hip joint loads during walking, and high loads were associated with worse self-reported symptoms and cartilage morphology. J Orthop Sports Phys Ther 2019;49(12):917-924. Epub 14 Oct 2019. doi:10.2519/jospt.2019.8945.

Strength and range of movement deficits are associated with symptom severity in people scheduled for hip arthroscopy

BACKGROUND

Identifying the physical impairments associated with worse symptoms and greater functional limitations in people with hip pain could enable targeted rehabilitation programmes designed to improve quality of life. The objective of this study was to compare physical characteristics between subgroups of symptoms and functional limitation severity in individuals with hip pain scheduled for arthroscopic surgery.

METHODS

Hip range of motion (ROM) and muscle strength were measured in 114 individuals (48 women; aged 32 ± 8 years) with hip pain scheduled for hip arthroscopy. Pain and disability were measured with the International Hip Outcome Tool (iHOT33) subscale of Symptoms and Functional Limitation, and a cluster analysis was used to identify mild, moderate and severe subgroups. Between-group differences were then evaluated using multivariate analysis of covariance, including sex as a covariate, followed by post hoc testing. Significance was set at 0.05.

RESULTS

Lesser hip muscle strength in all directions was reported in the severe symptoms and functional limitation group compared to the mild group. Hip flexion ROM differed when comparing the moderate to both the mild and severe subgroups. Hip internal rotation did not differ between subgroups of severity.

CONCLUSIONS

Individuals with hip pain and severe scores in the iHOT33 subscale of symptoms and functional limitations present with significantly lesser hip muscle strength and hip flexion ROM than individuals with moderate or mild scores. Targeted programmes to improve hip strength and flexion ROM in more severe patients may help reduce symptoms and improve function.

SIGNIFICANCE

Individuals with severe hip pain and functional limitation possess significantly lesser muscle strength and flexion ROM than individuals with moderate or mild scores.

Is quality of life following hip arthroscopy in patients with chondrolabral pathology associated with impairments in hip strength or range of motion?

INTRODUCTION

If physical impairments that are associated with poorer outcomes can be identified in people with chondrolabral hip pathology, then rehabilitation programmes that target such modifiable impairments could potentially be established to improve quality of life. The aim of this study was to examine the relationship between quality-of-life PROs and physical impairment measurements in people with chondrolabral pathology post-hip arthroscopic surgery.

METHODS

This was a cross-sectional study where multiple stepwise linear regression analyses were conducted to determine which physical impairment measurements were most associated with poorer quality-of-life patient-reported outcomes (PROs). Eighty-four patients (42 women; all aged 36 ± 10 years) with hip chondrolabral pathology 12- to 24-month post-hip arthroscopy were included. The Hip disability and Osteoarthritis Outcome Score Quality-of-life (HOOS-Q) subscale and International Hip Outcome Tool (IHOT-33) PROs were collected. Measurements of active hip ROM and strength were assessed.

RESULTS

Modifiable post-surgical physical impairments were associated with PRO in patients with chondrolabral pathology. Greater hip flexion ROM was independently associated with better scores in both HOOS-Q and IHOT-33 (adjusted r ² values ranged from 0.249 to 0.341). Greater hip adduction strength was independently associated with better HOOS-Q and IHOT-33 (adjusted r ² 0.227-0.317). Receiver Operator Curve analyses determined that the limit value for hip flexion ROM was 100° (sensitivity 92 %, specificity 75 %), and hip adduction strength was 0.86 Nm/kg (sensitivity 96 %, specificity 70 %).

CONCLUSIONS

Hip flexion ROM and adduction strength were associated with better quality-of-life PRO scores in patients with chondrolabral pathology 12- to 24-month post-hip arthroscopy. These impairments could be targeted by clinicians designing rehabilitation programmes to this patient group.

LEVEL OF EVIDENCE

Cross-sectional study, Level IV.

Subregional Anatomical Distribution of T2 Values of Articular Cartilage in Asymptomatic Hips

OBJECTIVE

A standardized definition of normative T2 values across the articular surface of the hip must be defined in order to fully understand T2 values for detecting early degeneration. Therefore, in this article, we seek to lay foundational methodology for reproducible quantitative evaluation of hip cartilage damage using T2 mapping to determine the normative T2 values in asymptomatic individuals.

DESIGN

Nineteen prospectively enrolled asymptomatic volunteers (age 18-35 years, males 10, females 9, alpha angle 49.3º ± 7.2º) were evaluated with a sagittal T2 mapping sequence at 3.0 T magnetic resonance imaging. Acetabular and femoral cartilage was manually segmented directly on the second echo of the T2 mapping sequence by 3 raters, twice. Segmentations were divided into 12 subregions modified from the geographic zone method. Median T2 values within each subregion were compiled for further analysis and interrater and intrarater reliability was assessed.

RESULTS

In the femur, the posterior-superior subregion was significantly higher (P ≤ 0.05) than those in the posterior-inferior and anterior-inferior subregions. In the acetabulum, the anterior-inferior subregion was significantly higher (P ≤ 0.001) than in the anterior-superior, middle, and posterior-inferior subregions. T2 values of the posterior-superior subregion were significantly higher (P ≤ 0.05) than the anterior-superior, middle, and posterior-inferior subregions. Interrater agreement was generally fair to good.

Strength of the porcine proximal femoral epiphyseal plate: the effect of different loading directions and the role of the perichondrial fibrocartilaginous complex and epiphyseal tubercle - an experimental biomechanical study

BACKGROUND

The high loads on adolescent athletes' musculoskeletal system are known to cause morphological and degenerative changes in bone, intervertebral discs and joints. It has been suggested that the cam deformity of the proximal femoral head originates from a subclinical slipped capital femoral epiphysis (SCFE) as a result of non-physiological loading. The perichondrial fibrocartilaginous complex (PFC) and the epiphyseal tubercle are believed to stabilise the proximal femoral epiphysis, but their role is still unclear. The aim of the present study was to develop an experimental, biomechanical model to evaluate the strength of the porcine proximal femoral epiphysis in different loading directions and, furthermore, to investigate the stabilising role of the PFC and the epiphyseal tubercle.

METHODS

A descriptive laboratory study. An in-vitro model was developed and nine young (5 months) porcine proximal femoral epiphyses were loaded to failure; three in the anterior-posterior direction, three in the lateral-medial direction and three in the vertical direction. The injured proximal femoral epiphyses were then examined both macroscopically and histologically.

RESULTS

Anterior and lateral loading of the proximal femoral epiphysis resulted in failure of the epiphyseal plate, while vertical loading resulted in a fracture epiphyseolysis. The epiphysis was weakest when exposed to a lateral load and strongest when exposed to a vertical load. Despite histological epiphyseolysis, the PFC was intact in 15 of 27 (56%) slices. In histological examinations, the epiphyseal tubercle appears to halt the slide of the epiphysis.

CONCLUSIONS

We have developed an experimental, biomechanical model to measure the strength of the proximal femoral epiphyseal plate in different loading directions. The strength of the proximal femur was weakest through the epiphyseal plate. The epiphysis was weakest when exposed to a lateral load and strongest when exposed to a vertical load. The epiphyseal tubercle and the PFC stabilise the epiphysis when the epiphyseal plate is damaged. The findings in the present study indicate that overloading the hips in growing individuals can disrupt the epiphyseal plate. These findings may have implications when it comes to understanding the pathogenesis of cam deformity of the hip.

Biomechanical factors in planning of periacetabular osteotomy

OBJECTIVE

This study addresses the effects of cartilage thickness distribution and compressive properties in the context of optimal alignment planning for periacetabular osteotomy (PAO).

BACKGROUND

The Biomechanical Guidance System (BGS) is a computer-assisted surgical suite assisting surgeon's in determining the most beneficial new alignment of a patient's acetabulum. The BGS uses biomechanical analysis of the hip to find this optimal alignment. Articular cartilage is an essential component of this analysis and its physical properties can affect contact pressure outcomes.

METHODS

Patient-specific hip joint models created from CT scans of a cohort of 29 dysplastic subjects were tested with four different cartilage thickness profiles (one uniform and three non-uniform) and two sets of compressive characteristics. For each combination of thickness distribution and compressive properties, the optimal alignment of the acetabulum was found; the resultant geometric and biomechanical characterization of the hip were compared among the optimal alignments.

RESULTS

There was an average decrease of 49.2 ± 22.27% in peak contact pressure from the preoperative to the optimal alignment over all patients. We observed an average increase of 19 ± 7.7° in center-edge angle and an average decrease of 19.5 ± 8.4° in acetabular index angle from the preoperative case to the optimized plan. The optimal alignment increased the lateral coverage of the femoral head and decreased the obliqueness of the acetabular roof in all patients. These anatomical observations were independent of the choice for either cartilage thickness profile, or compressive properties.

CONCLUSION

While patient-specific acetabular morphology is essential for surgeons in planning PAO, the predicted optimal alignment of the acetabulum was not significantly sensitive to the choice of cartilage thickness distribution over the acetabulum. However, in all groups the biomechanically predicted optimal alignment resulted in decreased joint contact pressure and improved acetabular coverage.

Relationship between femoroacetabular contact areas and hip position in the normal joint: an in vitro evaluation

PURPOSE

Different approaches have been proposed to diagnose femoroacetabular impingement (FAI) condition and hip instability. It is still debatable which test is the most effective to make a correct diagnosis. The true mechanics of the hip during particular physical examination manoeuvres is unknown.

METHODS

Eight fresh frozen hips were passively taken through 3 different commonly used positions for FAI diagnosis and hip instability: 90° Flexion-Adduction-Internal Rotation, Hyperextension-Adduction-External Rotation and Hyperextension-Neutral-External Rotation. Kinematics and anatomical data were acquired by an optoelectronic system. The contact areas between acetabulum and femoral head were analysed to determine whether these tests are able to localize regions of the hip that may give patients pain.

RESULTS

In the hip positions where the femur was in Hyperextension-External Rotation, the contact area was mainly concentrated in the posterosuperior area of the acetabulum, while during 90° Flexion-Adduction-Internal Rotation position, there was a wider distribution of contact, not specific to the anterolateral acetabulum.

CONCLUSIONS

The results confirm the ability of the Hyperextension-External Rotation tests to particularly analyse the posterior region of the acetabulum. Placing the hip in 90° of Flexion-Adduction-Internal Rotation allows for testing a wider zone of the acetabulum and is not specific to abutment of the femoral head-neck region against the anterolateral acetabulum.

Finite element prediction of cartilage contact stresses in normal human hips

Our objectives were to determine cartilage contact stress during walking, stair climbing, and descending stairs in a well-defined group of normal volunteers and to assess variations in contact stress and area among subjects and across loading scenarios. Ten volunteers without history of hip pain or disease with normal lateral center-edge angle and acetabular index were selected. Computed tomography imaging with contrast was performed on one hip. Bone and cartilage surfaces were segmented from volumetric image data, and subject-specific finite element models were constructed and analyzed using a validated protocol. Acetabular contact stress and area were determined for seven activities. Peak stress ranged from 7.52±2.11 MPa for heel-strike during walking (233% BW) to 8.66 ± 3.01 MPa for heel-strike during descending stairs (261% BW). Average contact area across all activities was 34% of the surface area of the acetabular cartilage. The distribution of contact stress was highly non-uniform, and more variability occurred among subjects for a given activity than among activities for a single subject. The magnitude and area of contact stress were consistent between activities, although inter-activity shifts in contact pattern were found as the direction of loading changed. Relatively small incongruencies between the femoral and acetabular cartilage had a large effect on the contact stresses. These effects tended to persist across all simulated activities. These results demonstrate the diversity and trends in cartilage contact stress in healthy hips during activities of daily living and provide a basis for future comparisons between normal and pathologic hips.

Prevalence of facet joint degeneration in association with intervertebral joint degeneration in a sample of organ donors

Among the most common causes of low back pain are strain on the muscles and ligaments associated with the spine, degeneration of the intervertebral discs (IVDs), and osteoarthritis of the facet joints. It is not clear, however, how these latter two conditions are related to each other in terms of their development during a patient's lifetime. The facet joint is the sole synovial joint of the spine but because it is difficult to image its degenerative history as well as its relationship to other degenerative factors within the spine remain elusive. We compared the gross and histologic characteristics of the lumbar spine from a sample of organ donors to the integrity of their associated IVDs as assessed through magnetic resonance imaging. In our study sample, we found that facet joint degeneration was common, occurring as early as 15 years of age, while the IVD could still remain intact. Facet degeneration was more severe at the L4/5 level and progressed along with IVD degeneration with age. Because such early degenerative changes in the facet joint are somewhat surprising, degeneration of this joint should not be overlooked when assessing OA of the spine and causes of lower back pain.

Fiber optic pressure sensing with conforming elastomers

A novel pressure sensing scheme based on the effect of a conforming elastomer material on the transmission spectrum of tilted fiber Bragg gratings is presented. Lateral pressure on the elastomer increases its contact angle around the circumference of the fiber and strongly perturbs the optical transmission of the grating. Using an elastomer with a Young's modulus of 20 MPa, a Poisson ratio of 0.48, and a refractive index of 1.42, the sensor reacts monotonically to pressures from 0 to 50 kPa (and linearly from 0 to 15 kPa), with a standard deviation of 0.25 kPa and maximum error of 0.5 kPa. The data are extracted from the optical transmission spectrum using Fourier analysis and we show that this technique makes the response of the sensor independent of temperature, with a maximum error of 2% between 25°C and 75°C. Finally, other pressure ranges can be reached by using conforming materials with different modulii or applying the pressure at different orientations.

Validation of finite element predictions of cartilage contact pressure in the human hip joint

Methods to predict contact stresses in the hip can provide an improved understanding of load distribution in the normal and pathologic joint. The objectives of this study were to develop and validate a three-dimensional finite element (FE) model for predicting cartilage contact stresses in the human hip using subject-specific geometry from computed tomography image data, and to assess the sensitivity of model predictions to boundary conditions, cartilage geometry, and cartilage material properties. Loads based on in vivo data were applied to a cadaveric hip joint to simulate walking, descending stairs, and stair-climbing. Contact pressures and areas were measured using pressure sensitive film. CT image data were segmented and discretized into FE meshes of bone and cartilage. FE boundary and loading conditions mimicked the experimental testing. Fair to good qualitative correspondence was obtained between FE predictions and experimental measurements for simulated walking and descending stairs, while excellent agreement was obtained for stair-climbing. Experimental peak pressures, average pressures, and contact areas were 10.0 MPa (limit of film detection), 4.4-5.0 MPa, and 321.9-425.1 mm(2), respectively, while FE-predicted peak pressures, average pressures, and contact areas were 10.8-12.7 MPa, 5.1-6.2 MPa, and 304.2-366.1 mm(2), respectively. Misalignment errors, determined as the difference in root mean squared error before and after alignment of FE results, were less than 10%. Magnitude errors, determined as the residual error following alignment, were approximately 30% but decreased to 10-15% when the regions of highest pressure were compared. Alterations to the cartilage shear modulus, bulk modulus, or thickness resulted in +/-25% change in peak pressures, while changes in average pressures and contact areas were minor (+/-10%). When the pelvis and proximal femur were represented as rigid, there were large changes, but the effect depended on the particular loading scenario. Overall, the subject-specific FE predictions compared favorably with pressure film measurements and were in good agreement with published experimental data. The validated modeling framework provides a foundation for development of patient-specific FE models to investigate the mechanics of normal and pathological hips.

Development and Validation of Patient-Specific Finite Element Models of the Hemipelvis Generated From a Sparse CT Data Set

To produce a patient-specific finite element (FE) model of a bone such as the pelvis, a complete computer tomographic (CT) or magnetic resonance imaging (MRI) geometric data set is desirable. However, most patient data are limited to a specific region of interest such as the acetabulum. We have overcome this problem by providing a hybrid method that is capable of generating accurate FE models from sparse patient data sets. In this paper, we have validated our technique with mechanical experiments. Three cadaveric embalmed pelves were strain gauged and used in mechanical experiments. FE models were generated from the CT scans of the pelves. Material properties for cancellous bone were obtained from the CT scans and assigned to the FE mesh using a spatially varying field embedded inside the mesh while other materials used in the model were obtained from the literature. Although our FE meshes have large elements, the spatially varying field allowed them to have location dependent inhomogeneous material properties. For each pelvis, five different FE meshes with a varying number of patient CT slices (8–12) were generated to determine how many patient CT slices are needed for good accuracy. All five mesh types showed good agreement between the model and experimental strains. Meshes generated with incomplete data sets showed very similar stress distributions to those obtained from the FE mesh generated with complete data sets. Our modeling approach provides an important step in advancing the application of FE models from the research environment to the clinical setting.