Acetabular Contact Pressures Research Articles

Femoral and acetabular features explain acetabular contact pressure sensitivity to hip internal rotation in persons with cam morphology: A finite element analysis

BackgroundFemoroacetabular impingement is characterized by premature contact between the proximal femur and acetabulum. The loss of femoral head-neck concavity associated with cam morphology leads to mechanical impingement during hip flexion and internal rotation. Other femoral and acetabular features have been linked with mechanical impingement but have not been comprehensively investigated. This study sought to determine which bony features are most influential in contributing to mechanical impingement in persons with a cam morphology. MethodsTwenty individuals (10 female, 10 male) with a cam morphology participated. Finite element analyses incorporating subject-specific bony geometry derived from computed tomography scans were used to determine which femoral (alpha angle and femoral neck-shaft angle) and acetabular (anteversion angle, inclination angle, depth, and lateral center-edge angle) features accentuate acetabular contact pressure with increasing degrees of hip internal rotation with the hip flexed to 90°. To determine the best predictors of acetabular contact pressure sensitivity to internal rotation, all morphological variables were included in a stepwise regression with the final model subjected to a bootstrapping procedure. FindingsThe stepwise regression revealed that femoral neck-shaft angle, acetabular anteversion angle, acetabular inclination angle, and acetabular depth were the best combination of variables to predict contact pressure sensitivity to internal rotation, explaining 55% of the variance. Results of the bootstrap analysis revealed that a median value of 65% [37%, 89%] variance in sensitivity could be explained by these morphological variables. InterpretationMechanical impingement and the concomitant acetabular contact pressure are modulated by multiple femoral and acetabular features in persons with a cam morphology.

Gluteal activation during squatting reduces acetabular contact pressure in persons with femoroacetabular impingement syndrome: A patient-specific finite element analysis

BackgroundFemoroacetabular impingement syndrome is a motion-related clinical disorder resulting from abnormal hip joint morphology. Mechanical impingement, in which the aspherical femoral head (cam morphology) abuts with the acetabular rim, is created with simultaneous hip flexion, internal rotation, and adduction. Impaired function of the gluteal muscles may be contributory to femoroacetabular impingement syndrome progression. The purpose of this study was to assess the influence of gluteal muscle recruitment on acetabular contact pressure during squatting in persons with cam femoroacetabular impingement syndrome. MethodsEight individuals (4 males, 4 females) with a diagnosis of cam femoroacetabular impingement syndrome underwent CT imaging of the pelvis and proximal femora, and a biomechanical assessment of squatting (kinematics, kinetics, and electromyography). Two maximal depth bodyweight squat conditions were evaluated: 1) non-cued squatting; and 2) cued gluteal activation squatting. Utilizing subject-specific electromyography-driven hip and finite element modeling approaches, hip muscle activation, kinematics, bone-on-bone contact forces, and peak acetabular contact pressure were compared between squat conditions. FindingsModest increases in gluteus maximus (7% MVIC, P < 0.0001) and medius (6% MVIC, P = 0.009) activation were able to reduce hip internal rotation on average 5° (P = 0.024), and in doing so reduced acetabular contact pressure by 32% (P = 0.023). Reductions in acetabular contact pressure occurred despite no change in hip abduction and increased bone-on-bone contact forces occurring in the cued gluteal activation condition. InterpretationOur findings highlight the importance of gluteal activation in minimizing mechanical impingement and provide a foundation for interventions aimed at preventing the development and progression of femoroacetabular impingement syndrome.

Subject-specific geometry affects acetabular contact pressure during gait more than subject-specific loading patterns

Finite element modeling (FEM) can predict hip cartilage contact mechanics. This study investigated how subject-specific boundary conditions and joint geometry affect acetabular cartilage contact mechanics using a multi-scale workflow. For two healthy subjects, musculoskeletal models calculated subject-specific hip kinematics and loading, which were used as boundary conditions for FEM. Cartilage contact mechanics were predicted using either generic or subject-specific FEM and boundary conditions. A subject-specific mesh resulted in a more lateral contact. Effects of subject-specific boundary conditions varied between both subjects. Results highlight the complex interplay between loading and kinematics and their effect on cartilage contact mechanics.

Three-dimensional finite analysis of acetabular contact pressure and contact area during normal walking

This study aims to analyze the contact areas and pressure distributions between the femoral head and mortar during normal walking using a three-dimensional finite element model (3D-FEM). Computed tomography (CT) scanning technology and a computer image processing system were used to establish the 3D-FEM. The acetabular mortar model was used to simulate the pressures during 32 consecutive normal walking phases and the contact areas at different phases were calculated. The distribution of the pressure peak values during the 32 consecutive normal walking phases was bimodal, which reached the peak (4.2 Mpa) at the initial phase where the contact area was significantly higher than that at the stepping phase. The sites that always kept contact were concentrated on the acetabular top and leaned inwards, while the anterior and posterior acetabular horns had no pressure concentration. The pressure distributions of acetabular cartilage at different phases were significantly different, the zone of increased pressure at the support phase distributed at the acetabular top area, while that at the stepping phase distributed in the inside of acetabular cartilage. The zones of increased contact pressure and the distributions of acetabular contact areas had important significance towards clinical researches, and could indicate the inductive factors of acetabular osteoarthritis.

Labral Reconstruction with Iliotibial Band Autograft and Semitendinosus Allograft Improves Hip Joint Contact Area and Contact Pressure: An In-Vitro Analysis

Objectives:Labral reconstruction using iliotibial band (ITB) autograft and semitendinosus (Semi-T) allograft have recently been described in cases of labral deficiency. The current study seeks to understand the biomechanical effects of an intact labrum, segmental labral resection, and labral reconstruction on joint contact area, contact pressure, and peak force.Methods:Ten fresh-frozen human cadaver hips were analyzed utilizing thin-film piezoresistive load sensors to measure contact area, contact pressure, and peak force 1) with the native intact labrum, 2) after segmental labral resection and 3) after graft labral reconstruction with either ITB autograft or Semi-T allograft. Each specimen was examined at 20° extension and 60° flexion. Statistical analysis was conducted through one-way ANOVA with post-hoc Games-Howell tests.Results:For the ITB group, labral resection significantly decreased contact area (20°: 73.2%±5.38, P=0.0010; 60°: 78.5%±6.93, P=0.0063) and increased contact pressures (20°: 106.7%±4.15, P=0.0387; 60°: 103.9%±1.15, P=0.0428). ITB reconstruction improved contact area (20°: 87.2%±12.3, P=0.0130; 60°: 90.5%±8.81, P=0.0079) and contact pressures (20°: 98.5%±5.71, P=0.0476; 60°: 96.6%±1.13, P=0.0056) from the resected state. Contact pressure at 60° flexion was significantly lower compared to the native labrum (P = 0.0420). For the Semi-T group, labral resection significantly decreased contact area (20°: 68.1±12.57, P=0.0002; 60°: 67.5%±6.70, P=0.0002) and increased contact pressures (20°: 105.3%±3.73, P=0.0304; 60°: 106.8%±4.04, P=0.0231). Semi-T reconstruction improved contact area (20°: 87.9%±7.95, P=0.0087; 60°: 92.9%±13.2, P=0.0014) and contact pressures (20°: 97.1%±3.18, P=0.0017; 60°: 97.4%±4.39, P=0.0027) from the resected state. Comparative analysis demonstrated no statistically significant differences between either graft reconstruction in relation to contact area, contact pressure, or peak forces. (Figure 1).Conclusion:Segmental anterosuperior labral resection results in significantly decreased contact area and increased contact pressures, while labral reconstruction partially restores time-zero acetabular contact areas and pressures as compared to the resected state. Although labral reconstruction improved the measured biomechanical properties as compared to the resected state, some of these properties remained significantly different compared to the native intact labrum.

Labral Reconstruction with Iliotibial Band Autograft and Semitendinosus Allograft Improves Hip Joint Contact Area and Contact Pressure: An In-Vitro Analysis

Labral reconstruction using iliotibial band (ITB) autograft and semitendinosus (Semi-T) allograft have been described in cases of labral deficiency. This study explores the biomechanical effects of the intact labrum, segmental labral resection, and labral reconstruction on joint contact area, contact pressure, and peak force. Ten fresh-frozen human cadaver hips were analyzed utilizing thin-film piezoresistive load sensors to measure contact area, contact pressure, and peak force 1) with the native intact labrum, 2) after segmental labral resection and 3) after graft labral reconstruction with either ITB autograft or Semi-T allograft. Each specimen was examined at 20° extension and 60° flexion. Statistical analysis was conducted through one-way ANOVA with post-hoc Games-Howell tests. For the ITB group, labral resection decreased contact area (20°: 73.2%±5.38, P=0.0010; 60°: 78.5%±6.93, P=0.0063) and increased contact pressures (20°: 106.7%±4.15, P=0.0387; 60°: 103.9%±1.15, P=0.0428). ITB reconstruction improved contact area (20°: 87.2%±12.3, P=0.0130; 60°: 90.5%±8.81, P=0.0079) and contact pressures (20°: 98.5%±5.71, P=0.0476; 60°: 96.6%±1.13, P=0.0056) from the resected state. Contact pressure at 60° flexion was lower compared to the native labrum (P = 0.0420). For the Semi-T group, labral resection decreased contact area (20°: 68.1±12.57, P=0.0002; 60°: 67.5%±6.70, P=0.0002) and increased contact pressures (20°: 105.3%±3.73, P=0.0304; 60°: 106.8%±4.04, P=0.0231). Semi-T reconstruction improved contact area (20°: 87.9%±7.95, P=0.0087; 60°: 92.9%±13.2, P=0.0014) and contact pressures (20°: 97.1%±3.18, P=0.0017; 60°: 97.4%±4.39, P=0.0027) from the resected state. Comparative analysis demonstrated no statistically significant differences between either graft reconstruction in relation to contact area, contact pressure, or peak forces Segmental labral resection results in significantly decreased contact area and increased contact pressures, while labral reconstruction partially restores time-zero acetabular contact areas and pressures as compared to the resected state. Although labral reconstruction improved the measured biomechanical properties, some properties remained significantly different compared to the native intact labrum.

Labral Reconstruction With Iliotibial Band Autografts and Semitendinosus Allografts Improves Hip Joint Contact Area and Contact Pressure

Background: Labral reconstruction using iliotibial band (ITB) autografts and semitendinosus (Semi-T) allografts has recently been described in cases of labral deficiency. Purpose/Hypothesis: To characterize the joint biomechanics with a labrum-intact, labrum-deficient, and labrum-reconstructed acetabulum in a hip cadaveric model. The hypothesis was that labral resection would decrease contact area, increase contact pressure, and increase peak force, while subsequent labral reconstruction with ITB autografts or Semi-T allografts would restore these values toward the native intact labral state. Study Design: Controlled laboratory study. Methods: Ten fresh-frozen human cadaveric hips were analyzed utilizing thin-film piezoresistive load sensors to measure contact area, contact pressure, and peak force (1) with the native intact labrum, (2) after segmental labral resection, and (3) after graft labral reconstruction with either ITB autografts or Semi-T allografts. Each specimen was examined at 20° of extension and 60° of flexion. Statistical analysis was conducted through 1-way analysis of variance with post hoc Games-Howell tests. Results: For the ITB group, labral resection significantly decreased contact area (at 20°: 73.2% ± 5.38%, P = .0010; at 60°: 78.5% ± 6.93%, P = .0063) and increased contact pressure (at 20°: 106.7% ± 4.15%, P = .0387; at 60°: 103.9% ± 1.15%, P = .0428). In addition, ITB reconstruction improved contact area (at 20°: 87.2% ± 12.3%, P = .0130; at 60°: 90.5% ± 8.81%, P = .0079) and contact pressure (at 20°: 98.5% ± 5.71%, P = .0476; at 60°: 96.6% ± 1.13%, P = .0056) from the resected state. Contact pressure at 60° of flexion was significantly lower compared with the native labrum (P = .0420). For the Semi-T group, labral resection significantly decreased contact area (at 20°: 68.1% ± 12.57%, P = .0002; at 60°: 67.5% ± 6.70%, P = .0002) and increased contact pressure (at 20°: 105.3% ± 3.73%, P = .0304; at 60°: 106.8% ± 4.04%, P = .0231). Semi-T reconstruction improved contact area (at 20°: 87.9% ± 7.95%, P = .0087; at 60°: 92.9% ± 13.2%, P = .0014) and contact pressure (at 20°: 97.1% ± 3.18%, P = .0017; at 60°: 97.4% ± 4.39%, P = .0027) from the resected state. Comparative analysis demonstrated no statistically significant differences between either graft reconstruction in relation to contact area, contact pressure, or peak force. Conclusion: Segmental anterosuperior labral resection results in significantly decreased contact areas and increased contact pressures, while labral reconstruction partially restores time-zero acetabular contact areas and pressures as compared with the resected state. Although labral reconstruction improved the measured biomechanical properties as compared with the resected state, some of these properties remained significantly different compared with the native intact labrum. Clinical Relevance: Labral reconstruction appears to improve femoroacetabular joint biomechanics as compared with the labrum-resected state; these improved biomechanics may translate into increased joint function clinically.

Influence of Acetabular Liner Design on Periprosthetic Pressures during Daily Activities

In this study, periacetabular pressures produced by different acetabular liner geometries were analyzed using Finite Element Method. The cup models consist of hemispherical metal shells fitted with normal and different chamfered polyethylene liner geometries, with the same degree of femoral head coverage. The aim of this study was to understand the influence of the design parameters of the chamfered liners, which are primarily designed to increase the range of motion (ROM) of the hip joint and reduce the risk of impingement, on the acetabular contact pressures. The cup models were loaded to simulate periacetabular pressures during routine activities. The proposed models have been analyzed considering a cup position of 40olateral abduction and 15oanteversion. The results show that the difference in contact pressure between the normal and chamfer models was not substantial in the given orientation of the cup. Also, the increase of the chamfer angle has a small influence on the maximum contact pressures, although that could be also dependent on the reduction of the polyethylene thickness. Pre-clinical testing of total hip prostheses using Finite Element Method enables the evaluation of contact pressures and stress distribution, and proves to be a valuable tool to analyze the parameters reducing the contact pressure.

A Biomechanical Study of Periacetabular Defects and Cement Filling

Periacetabular bone metastases cause severe pain and functional disability in cancer patients. Percutaneous acetabuloplasty (PCA) is a minimally invasive, image-guided procedure whereby cement is injected into lesion sites. Pain relief and functional restoration have been observed clinically; however, neither the biomechanical consequences of the lesions nor the effectiveness of the PCA technique are well understood. The objective of this study was to investigate how periacetabular lesion size, cortex involvement, and cement modulus affect pelvic bone stresses and strains under single-legged stance loading. Experiments were performed on a male cadaver pelvis under conditions of intact, periacetabular defect, and cement-filling with surface strains recorded at three strain gage locations. The experimental data were then employed to validate three-dimensional finite element models of the same pelvis, developed using computed tomography data. The models demonstrated that increases in cortical stresses were highest along the posterior column of the acetabulum, adjacent to the defect. Cortical stresses were more profoundly affected in the presence of transcortical defects, as compared to those involving only trabecular bone. Cement filling with a modulus of 2.2 GPa was shown to restore cortical stresses to near intact values, while a decrease in cement modulus due to inclusion of BaSO(4) reduced the restorative effect. Peak acetabular contact pressures increased less than 15% for all simulated defect conditions; however, the contact stresses were reduced to levels below intact in the presence of either cement filling. These results suggest that periacetabular defects may increase the vulnerability of the pelvis to fracture depending on size and cortical involvement and that PCA filling may lower the risk of periacetabular fractures.

Cartilage degeneration in relation to repetitive pressure: Case study of a unilateral hip hemiarthroplasty patient

In vivo acetabular contact pressures were measured over 32 months in an elderly man with a pressure instrumented hemiarthroplasty. After death, left (hemiarthroplasty) and right (control) acetabula were explanted. Cartilage thickness and degeneration were quantified from magnetic resonance imaging and histological analysis. Highest repetitive in vivo contact pressures during gait (4.5 to 6.5 MPa) were measured in the superior dome of the acetabulum and decreased at a rate of approximately 1 MPa per year after implant (R2 = 0.48, P < .001). Contact pressure magnitudes measured during gait correlated positively with regional histology score (R2 = 0.34, P < .0001) and negatively with cartilage thickness (R2 = 0.35, P < .0001). Although histology scores were typical of early osteoarthritis (histological grade of 4–6), there were no significant differences in overall histology score for the left and right acetabula (P = .23). We conclude that acetabular cartilage degeneration was explained, in part, by repetitive stress, but the degeneration did not appear to be mediated solely by articulation with the metallic endoprosthesis.

Hip biomechanics during gait.

The literature is devoid of complete descriptions of hip biomechanics during gait. We present for the first time simultaneously acquired in vivo acetabular contact pressures, ground reaction forces, kinematics, hip torques, and electromyographic (EMG) activity during gait with and without a cane from an 85-year-old male with a left instrumented femoral head prosthesis. Highest acetabular contact pressures occurred in all gait trials at the posterosuperior acetabulum, just prior to peak EMG, adductor torque, and ground reaction force during late stance phase. Contralateral cane use reduced both peak acetabular contact pressure and gluteus medius EMG but not adductor torque or ground reaction force. These data identify a small area of high acetabular and femoral head stress that could occur during each of a human's millions of gait cycles annually and indicate that muscle activity, rather than solely body weight, drives hip loading, Clinicians who desire to limit hip loads should reduce both hip muscle contraction and weight bearing in late stance.

Hip stress during lifting with bent and straight knees

"Correct" body mechanics during lifting are believed to protect the back by employing knee and hip flexion while keeping the back straight. Lower limb joint stress, however, has been largely ignored. We compared hip cartilage contact stress during "leg lifting" with "back lifting" (lifting with bent or straight knees, respectively) in a subject fitted with a pressure instrumented hip endoprosthesis. Synchronized pressure data and whole-body kinematics and kinetics were collected simultaneously while the subject lifted an 11.8 kg mass from the floor to waist level. The highest pressure, 13.7 MPa, occurred during leg lifting at the antero-lateral femoral head transducers opposed at maximum hip flexion by the postero-superior quadrant of acetabular cartilage. In back lifting, the highest pressure, 11.5 MPa occurred in the supero-lateral aspect of the head, which during hip extension was opposed by the posterior quadrant of the acetabulum. Maximum pressures and hip torques occurred simultaneously with peak hip flexion, during the initial lifting of the burden from the floor. Acetabular contact pressures during leg lifting were on average twice as great as during back lifting, and both techniques generate much greater hip stress than gait (typically 4-6 MPa). Degenerative changes in the articular surface of the acetabulum occur primarily on the postero-superior aspect, corresponding to the locations of peak contact pressures in the present in vivo data. Thus leg lifting puts more stress on the postero-superior region, and probably contributes to more hip cartilage degeneration, than does back lifting. We conclude that although leg lifting may mechanically protect the back, it substantially increases hip cartilage stress.

Examining Shibboleths of Hip Rehabilitation Protocols Using in vivo Contact Pressures from an Instrumented Hemiarthroplasty

Summary This study uses acetabular contact pressure data from the immediate post-operative period to examine some of the commonly held beliefs about early phase hemiarthroplasty rehabilitation. Data were obtained from an instrumented femoral head prosthesis implanted in an 82-year-old man (height 1.6 m; weight 54.5 kg) with a displaced left hip fracture. Data were collected daily during the two weeks of immediate post-operative hospitalisation. The shibboleths being examined are related to the functional activities: sit-to-stand, ambulation, and stair-climbing. Results support beliefs about rising from a chair: lower pressures were created when rising from a 62 cm hip chair (1.4 MPa) than from a 48 cm standard chair (7.09 MPa): and less pressure was created when rising from a 62 cm hip chair with operated leg out in front (1.21 MPa) than when rising from the same chair with feet together (2.96 MPa). Gait training beliefs are challenged by the study findings: there was no significant difference between touch weight bearing, partial weight bearing, and weight bearing as tolerated; and use of a very commonly used post-operative gait sequence (walker, then operated leg, then non-operated leg) generated a greater peak pressure than an ‘incorrect’ sequence (walker, then non-operated leg, then operated leg). Limited early post-operative stairs data prevented definitive conclusions from being reached about stair-climbing in the early post-operative period. However, examination of data from one year post-operatively demonstrates that unassisted reciprocal gait on stairs creates large (15.52 MPa) acetabular contact pressures. This study uses acetabular contact pressure data from the immediate post-operative period to examine some of the commonly held beliefs about early phase hemiarthroplasty rehabilitation. Data were obtained from an instrumented femoral head prosthesis implanted in an 82-year-old man (height 1.6 m; weight 54.5 kg) with a displaced left hip fracture. Data were collected daily during the two weeks of immediate post-operative hospitalisation. The shibboleths being examined are related to the functional activities: sit-to-stand, ambulation, and stair-climbing. Results support beliefs about rising from a chair: lower pressures were created when rising from a 62 cm hip chair (1.4 MPa) than from a 48 cm standard chair (7.09 MPa): and less pressure was created when rising from a 62 cm hip chair with operated leg out in front (1.21 MPa) than when rising from the same chair with feet together (2.96 MPa). Gait training beliefs are challenged by the study findings: there was no significant difference between touch weight bearing, partial weight bearing, and weight bearing as tolerated; and use of a very commonly used post-operative gait sequence (walker, then operated leg, then non-operated leg) generated a greater peak pressure than an ‘incorrect’ sequence (walker, then non-operated leg, then operated leg). Limited early post-operative stairs data prevented definitive conclusions from being reached about stair-climbing in the early post-operative period. However, examination of data from one year post-operatively demonstrates that unassisted reciprocal gait on stairs creates large (15.52 MPa) acetabular contact pressures.