A femoral model with all relevant muscles and hip capsule ligaments

Specimen-specific finite element representations of implanted hip capsules

The hip capsule is a ligamentous structure that contributes to hip stability. This article developed specimen-specific finite element models that replicated internal-external (I-E) laxity for ten implanted hip capsules. Capsule properties were calibrated to minimize root mean square error (RMSE) between model and experimental torques. RMSE across specimens was 1.02 ± 0.21 Nm for I-E laxity and 0.78 ± 0.33 Nm and 1.10 ± 0.48 Nm during anterior and posterior dislocation, respectively. RMSE for the same models with average capsule properties was 2.39 ± 0.68 Nm. Specimen-specific models demonstrated the importance of capsule tensioning in hip stability and have relevance for surgical planning and evaluation of implant designs.

Anterior Inferior Iliac Spine (AIIS) and Subspine Hip Impingement

BACKGROUND

Abnormal morphology of the anterior inferior iliac spine (AIIS) and the subspine region of the acetabular rim are increasingly being recognised as a source of symptomatic extra-articular hip impingement. This review article aims to highlight important differences in the pathogenesis, clinical presentation and management of extra-articular hip impingement from both the AIIS and subspine bony regions, and the outcome following surgical intervention.

METHODS

A literature review was undertaken to examine the supporting evidence for AIIS and subspine hip impingement. A narrative account of the Author's professional experience in this area, including operative technique for arthroscopic correction, is also presented.

RESULTS

Abnormal morphology of the AIIS and subspine region has been classified using cadaveric, radiological and arthroscopic means; the clinical presentation and operative treatment has been documented in several case series studies. Dual pathology is often present - recognition and treatment of both intra- and extra-articular components are necessary for good postoperative outcome.

CONCLUSIONS

AIIS and sub-spine hip impingement should be considered as distinct pathological entities, which may also co-exist. Symptom relief can be expected following arthroscopic deformity correction with the treatment of concomitant intra-articular pathology. Failure to recognise and treat the extra-articular component may affect postoperative outcome.

LEVEL OF EVIDENCE

V.

The Stress-Strain Data of the Hip Capsule Ligaments Are Gender and Side Independent Suggesting a Smaller Contribution to Passive Stiffness

Background

The ligaments in coherence with the capsule of the hip joint are known to contribute to hip stability. Nevertheless, the contribution of the mechanical properties of the ligaments and gender- or side-specific differences are still not completely clear. To date, comparisons of the hip capsule ligaments to other tissues stabilizing the pelvis and hip joint, e.g. the iliotibial tract, were not performed.

Materials & Methods

Hip capsule ligaments were obtained from 17 human cadavers (9 females, 7 males, 13 left and 8 right sides, mean age 83.65 ± 10.54 years). 18 iliofemoral, 9 ischiofemoral and 17 pubofemoral ligaments were prepared. Uniaxial stress-strain properties were obtained from the load-deformation curves before the secant elastic modulus was computed. Strain, elastic modulus and cross sections were compared.

Results

Strain and elastic modulus revealed no significant differences between the iliofemoral (strain 129.8 ± 11.1%, elastic modulus 48.8 ± 21.4 N/mm²), ischiofemoral (strain 128.7 ± 13.7%, elastic modulus 37.5 ± 20.4 N/mm²) and pubofemoral (strain 133.2 ± 23.7%, elastic modulus 49.0 ± 32.1 N/mm²) ligaments. The iliofemoral ligament (53.5 ± 15.1 mm²) yielded a significantly higher cross section compared to the ischiofemoral (19.2 ± 13.2 mm²) and pubofemoral (15.2 ± 7.2 mm²) ligament. No significant gender- or side-specific differences were determined. A comparison to the published data on the iliotibial tract revealed lower elasticity and less variation in the ligaments of the hip joint.

Conclusion

Comparison of the mechanical data of the hip joint ligaments indicates that their role may likely exceed a function as a mechanical stabilizer. Uniaxial testing of interwoven collagen fibers might lead to a misinterpretation of the mechanical properties of the hip capsule ligaments in the given setup, concealing its uniaxial properties. This underlines the need for a polyaxial test setup using fresh and non-embalmed tissues.

Tensile properties of the hip joint ligaments are largely variable and age-dependent - An in-vitro analysis in an age range of 14-93 years

INTRODUCTION

Hip joint stability is maintained by the surrounding ligaments, muscles, and the atmospheric pressure exerted via these structures. It is unclear whether the ligaments are capable of preventing dislocation solely due to their tensile properties, and to what extent they undergo age-related changes. This study aimed to obtain stress-strain data of the hip ligaments over a large age range.

METHODS

Stress-strain data of the iliofemoral (IL), ischiofemoral (IS) and pubofemoral ligament (PF) were obtained from cadavers ranging between 14 and 93 years using a highly standardized setting. Maximum strains were compared to the distances required for dislocation.

RESULTS

Elastic modulus was 24.4 (IL), 22.4 (IS) and 24.9N/mm² (PF) respectively. Maximum strain was 84.5%, 86.1%, 72.4% and ultimate stress 10.0, 7.7 and 6.5N/mm² for the IL, IS and PF respectively. None of these values varied significantly between ligaments or sides. The IS' elastic modulus was higher and maximum strain lower in males. Lower elastic moduli of the PF and higher maximum strains for the IS and PF were revealed in the ≥55 compared to the <55 population. Maximum strain exceeded the dislocation distance of the IS without external hip joint rotation in females, and of the IS and cranial IL under external rotation in both genders.

DISCUSSION

Tensile and failure load properties of the hip joint ligaments are largely variable. The IS and PF change age-dependently. Though the hip ligaments contribute to hip stability, the IS and cranial IL may not prevent dislocation due to their elasticity.

Strains caused by daily loading might be responsible for delayed healing of an incomplete atypical femoral fracture

Atypical femoral fractures are insufficiency fractures in the lateral femoral diaphysis or subtrochanteric region that mainly affect older patients on bisphosphonate therapy. Delayed healing is often seen in patients with incomplete fractures (cracks), and histology of bone biopsies shows mainly necrotic material inside the crack. We hypothesized that the magnitude of the strains produced in the soft tissue inside the crack during normal walk exceeds the limit for new bone formation, and thereby inhibit healing. A patient specific finite element model was developed, based on clinical CT images and high resolution μCT images of a biopsy from the crack site. Strain distributions in the femur and inside the crack were calculated for load cases representing normal walk. The models predicted large strains inside the crack, with strain levels above 10% in more than three quarters of the crack volume. According to two different tissue differentiation theories, bone would only form in less than 1-5% of the crack volume. This can explain the impaired healing generally seen in incomplete atypical fractures. Furthermore, the microgeometry of the crack highly influenced the strain distributions. Hence, a realistic microgeometry needs to be considered when modeling the crack. Histology of the biopsy showed signs of remodeling in the bone tissue adjacent to the fracture line, while the crack itself contained mainly necrotic material and signs of healing only in portions that seemed to have been widened by resorption. In conclusion, the poor healing capacity of incomplete atypical femoral fractures can be explained by biomechanical factors, and daily low impact activities are enough to cause strain magnitudes that prohibit bone formation.

The Le Fort system revisited: Trauma velocity predicts the path of Le Fort I fractures through the lateral buttress

OBJECTIVE

To examine the effect of trauma velocity on the pattern of Le Fort I facial fractures.

METHOD

A retrospective medical record review was conducted on a consecutive cohort of craniofacial traumas surgically treated by a single surgeon between 2007 and 2011 (n=150). Of these cases, 39 Le Fort fractures were identified. Patient demographic information, method of trauma and velocity of impact were reviewed for these cases. Velocity of impact was expressed categorically as either 'high' or 'low': high-velocity fractures were those caused by a fall from >1 story or a motor vehicle collision; low-velocity fractures were the result of assaults with a blunt weapon, closed fist or falls from standing height. The vertical position of each fracture was measured at its point of entry on the lateral buttress and its point of exit on the piriform aperture. To allow for comparison across individuals, values were expressed as ratios based on their location on the face relative to these landmarks. A Wilcoxon rank-sum test was used to compare the fracture heights caused by high- and low-velocity trauma.

RESULTS

The results revealed that high-velocity traumas to the face create Le Fort I fractures at a higher point in the lateral buttress compared with low-velocity traumas. There was no difference between heights at the piriform aperture.

CONCLUSION

High-velocity trauma resulted in higher Le Fort I fracture patterns compared with low-velocity trauma.

The Le Fort system revisited: Trauma velocity predicts the path of Le Fort I fractures through the lateral buttress

Objective

To examine the effect of trauma velocity on the pattern of Le Fort I facial fractures.

Method

A retrospective medical record review was conducted on a consecutive cohort of craniofacial traumas surgically treated by a single surgeon between 2007 and 2011 (n=150). Of these cases, 39 Le Fort fractures were identified. Patient demographic information, method of trauma and velocity of impact were reviewed for these cases. Velocity of impact was expressed categorically as either ‘high’ or ‘low’: high-velocity fractures were those caused by a fall from >1 story or a motor vehicle collision; low-velocity fractures were the result of assaults with a blunt weapon, closed fist or falls from standing height. The vertical position of each fracture was measured at its point of entry on the lateral buttress and its point of exit on the piriform aperture. To allow for comparison across individuals, values were expressed as ratios based on their location on the face relative to these landmarks. A Wilcoxon rank-sum test was used to compare the fracture heights caused by high- and low-velocity trauma.

Results

The results revealed that high-velocity traumas to the face create Le Fort I fractures at a higher point in the lateral buttress compared with low-velocity traumas. There was no difference between heights at the piriform aperture.

Conclusion

High-velocity trauma resulted in higher Le Fort I fracture patterns compared with low-velocity trauma.