Sonographic appearance of the iliocapsularis muscle of the hip

Effect of Changes in Iliocapsularis Cross-sectional Area on Hip Arthroscopy Outcomes: Clinical and Magnetic Resonance Imaging Follow-up

Background

The function of the iliocapsularis (IC) muscle is still unclear. Previous studies have reported that the cross-sectional area of the IC may be useful in identifying borderline developmental dysplasia of the hip (BDDH).

Purpose

To evaluate the pre- to postoperative changes in IC cross-sectional area in patients with femoroacetabular impingement (FAI) and to determine if there are any associations with clinical outcomes after hip arthroscopy.

Study Design

Cohort study; Level of evidence, 3.

Methods

The authors retrospectively evaluated patients who underwent arthroscopic surgery for FAI at a single institution between January 2019 and December 2020. Patients were divided into 3 groups according to lateral center-edge angle: BDDH group (20°-25°), control group (25°-40°), and pincer group (>40°). Supine anteroposterior hip radiographs, 45° Dunn view radiographs, computed tomography scans, and magnetic resonance imaging (MRI) scans were obtained for all patients preoperatively and postoperatively. The cross-sectional areas of the IC and the rectus femoris (RF) were measured on an axial MRI slice at the level of the femoral head center. Preoperative and final follow-up scores on the visual analog scale for pain and the modified Harris Hip Score (mHHS) were compared between groups with the independent-samples t test.

Results

A total of 141 patients (mean age, 38.5 years; 64 male, 77 female) were included. The preoperative IC-to-RF ratio of the BDDH group was significantly higher than that of the pincer group (P < .05). In the BDDH group, there was significant pre- to postoperative decrease in IC cross-sectional area and the IC-to-RF ratio (P < .05 for both) as well as a significant correlation between the preoperative IC cross-sectional area and the postoperative mHHS (r = 0.434; P = .027).

Conclusion

Patients with BDDH had a significantly higher preoperative IC-to-RF ratio than patients with pincer morphology. A higher preoperative IC cross-sectional area was associated with better postoperative patient-reported outcomes after arthroscopy for the treatment of FAI combined with BDDH.

Ultrasound and shear-wave elastography characteristics of the iliocapsularis muscle in pincer-type femoroacetabular impingement

BACKGROUND

The iliocapsularis muscle is a structure of the anterior hip, which may play a key role in stabilizing the hip joint, but to our knowledge no studies exist describing ultrasound (US) and shear-wave characteristics of this muscle.

OBJECTIVES

To investigate the anatomic dimensions and elasticity of the iliocapsularis muscle in patients with pincer-type femoroacetabular impingement (FAI) and normal hips using gray-scale US and shear-wave elastography (SWE).

DESIGN

Case-control study.

SETTING

Sports medicine and ultrasound department within a tertiary hospital.

PARTICIPANTS

Thirty-three patients (33 hips) with pincer-type FAI and 37 healthy volunteers (37 hips).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

US parameters (anteroposterior diameter, transverse diameter and circumference) of the iliocapsularis muscle in patients with pincer-type FAI and volunteers. Shear-wave velocity and Young's modulus of the iliocapsularis muscle in patients with pincer-type FAI and volunteers in both neutral and external rotation positions.

RESULTS

Significant differences were not observed in the anatomic dimensions of the iliocapsularis muscle between patients with pincer-type FAI and volunteers. The iliocapsularis muscle in patients with pincer-type FAI had significantly lower shear-wave velocity and Young's modulus than the volunteers (p < .05). The cutoff value of the maximum velocity in the external rotation position was 3.35 m/s, which separated pincer-type FAI patients from volunteers and revealed the highest accuracy with sensitivity, specificity, and accuracy of 78.8%, 48.6%, and 64.3%, respectively.

CONCLUSION

The anatomic dimensions of the iliocapsularis muscle in pincer-type FAI patients and volunteers were similar; however, iliocapsularis stiffness in patients with pincer-type FAI was significantly lower than that of the volunteers. SWE can demonstrate altered muscle stiffness of the iliocapsularis muscle in pincer-type FAI patients, which might be used to help make clinical decisions.

Age- and sex-related differences of muscle cross-sectional area in iliocapsularis: a cross-sectional study

Background

This study aimed to determine in how many individuals the iliocapsularis muscle (IC) could be identified on magnetic resonance imaging (MRI) and whether age and sex are associated with the cross-sectional area (CSA) of the IC.

Methods

Thirty-seven healthy younger adults and 40 healthy older adults were assigned to four groups: 1) 20 younger men; 2) 17 younger women; 3) 20 older men; and 4) 20 older women. The CSAs of the IC, IP, the rectus femoris (RF) and the quadriceps (QUAD) were quantified on an axial MRI.

Results

The number of individuals with the identified IC was n = 17 (85.0%) of 20 younger men, n = 15 (88.2%) of 17 younger women, n = 18 (90.0%) of 20 older men, and 19 (95.0%) of 20 older women. Our results showed the main effect of sex, but not age, in the CSA of the IC. The men-groups had larger CSA of the IC than the women-groups; however, no difference in CSA of the IC was found between the younger and older groups. Meanwhile, the main effects of age and sex were found for the IP, RF, and QUAD; thus, younger or men groups have larger CSAs of the three muscles than the older or women groups. The IC muscle can be discriminated in 85% – 95% of healthy individuals.

Conclusion

Although sex and age are associated with the CSA of lower-limb muscles other than the IC, only sex is associated with the CSA of the IC.

Anatomical features of the iliocapsularis muscle: a dissection study

Purpose

Iliocapsularis (IC) overlies the anteromedial hip capsule and is an important landmark in anterior approaches to hip arthroplasty. Previously believed to be part of iliacus, few publications describe the prevalence, attachments, fibre direction, blood supply, innervation, and size of IC. This study was aimed to determine these anatomical features using embalmed bodies and whether they vary between sides, sex, and age.

Methods

Thirty-eight formalin-fixed adult bodies were dissected and the prevalence, presence of a connective tissue raphe, attachments, fibre direction, blood supply, and innervation, were documented. Length and width were measured, and significant differences were investigated with t tests.

Results

Iliocapsularis was present in all bodies examined, originating from the inferior border of the anterior inferior iliac spine, and inserting 20 mm distal to the lesser trochanter in 54 muscles (71%). Iliocapsularis was supplied by a thin branch from the femoral nerve and by branches of the lateral circumflex femoral and deep femoral arteries and veins. Muscle fibre direction was from superolateral to inferomedial. Mean length was 116.8 ± 11.2 mm and width was 12.8 ± 3.1 mm, with no significant differences between sides, sex, and age.

Conclusion

This was the first study to document the venous drainage and compare the dimensions with sides, sex, and age, using adult bodies. However, the true function of IC is still unknown. Iliocapsularis is a constant muscle, distinct from iliacus, which is relevant to orthopaedic surgeons and physical rehabilitation specialists, particularly for postoperative patient care.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00276-022-02905-y.

Assessment of the iliocapsularis muscle on magnetic resonance imaging

INTRODUCTION

Morphologic features of Iliocapsularis (IC) may aid clinical decision-making in the symptomatic hip. The relationship between IC muscle size and underlying hip pathology is emerging; however, research is limited in the imaging literature. The purpose of this study was to determine the reliability and reproducibility of measurements of the IC muscle and its MRI appearances. It also looked for any association between IC dimension and axial levels, side, gender and bony features of hip instability.

METHODS

Retrospective study of 37 MRI scans were assessed by four observers. MRI axial T1 images were used to define the IC anatomy, measure the IC and rectus femoris at the femoral head centre (FHC) and adjacent levels and calculate the iliocapsularis-to-rectus femoris (IR) ratio. Measurements were repeated at least 2 weeks later. Radiographic assessment of the lateral centre edge angle, acetabular index and femoral neck-shaft angle were also conducted.

RESULTS

The IC was always present, but was well-defined in only 4% of cases with fair agreement. The intraclass correlation coefficient for reliability and reproducibility was the highest for IC width 0.94 (0.91-0.96). No significant correlation was identified between the IR ratio and radiographic parameters.

CONCLUSION

Iliocapsularis is visible and reliably measured on MRI despite observers considering the muscle to be not well-defined. Despite gender differences in muscle size, the IR ratio was unchanged. There is a significant difference in the IR ratio above and below the FHC; therefore, clinicians need to be aware of how this may impact the clinical use when utilising the IR ratio.

A systematic review and meta-analysis of iliocapsularis muscle: an important landmark in orthopedic surgery

PURPOSE

Iliocapsularis (IC) is a small muscle overlying the capsule of the hip joint. Although recent attention is being given to this muscle by orthopedic surgeons who encounter it during the anterior approach to total hip arthroplasty, little is known about its anatomical features. The aim of this study was to review the anatomy of IC, and describe its' origin, insertion, blood supply, innervation, muscle fiber characteristics and size. The function, clinical relevance and comparative anatomy of IC were also appraised.

METHODS

Using Evidence-Based Anatomy methodology, electronic databases were searched with the terms "iliocapsularis", "iliacus minor", "iliotrochantericus", and "ilioinfratrochantericus" to identify eligible studies.

RESULTS

Six studies (n = 287 lower limbs) examining the anatomy of IC were included. The pooled prevalence (PP) of the IC was 98.7% (95% CI 96.5-100.0). It arises from the inferior facet of the anterior inferior iliac spine (AIIS) and attaches inferior to the lesser trochanter. Attached to the anteromedial capsule along its entire length, IC has the largest capsular contribution of any of the hip muscles (73.8 ± 27.3 × 16.1 ± 4.4 mm). Thus, it is an important landmark in anterior surgical approaches to the hip joint.

CONCLUSION

The anatomy of IC is becoming more relevant with the increasing use of anterior approaches to hip surgery. With attachments to the AIIS, the lesser trochanter as well as the length of the capsule, this muscle is an important landmark in total hip arthroplasty.

LEVEL OF EVIDENCE

Level V.

Pericapsular hip muscle activity in people with and without femoroacetabular impingement. A comparison in dynamic tasks

OBJECTIVES

Compare anterior pericapsular muscle activity between individuals with and without femoroacetabular impingement syndrome (FAIS) during dynamic tasks, to investigate whether muscle activity is consistent with a role in retracting the capsule to prevent impingement and active restraint of the femoral head in walking.

DESIGN

Cross-sectional.

SETTING

University-laboratory.

PARTICIPANTS

Thirteen athletes with FAIS and 13 pain-free controls.

MAIN OUTCOME MEASURES

Muscle activity was recorded using fine-wire (Iliocapsularis, iliacus and anterior gluteus minimus) and surface (rectus femoris) electromyography (EMG), during three hip flexion tasks (active and assisted hip flexion; squatting) and four walking trials.

RESULTS

Iliocapsularis EMG amplitude was no different between active and assisted hip flexion tasks around 90° of hip flexion in FAIS. There was no difference in EMG between groups in squatting. The pattern of burst activity preceding peak hip extension in iliacus, iliocapsularis, and anterior gluteus minimus was similar in both groups during walking.

CONCLUSION

In FAIS, similar activation of iliocapsularis during active and assisted hip flexion, despite reduced flexion torque demand in the latter, suggests a role in capsular retraction or enhanced hip joint protection. Pericapsular muscle activity in advance of peak hip extension during walking is consistent with a proposed contribution to femoral head control.

Iliocapsularis muscle in human fetuses

PURPOSE

To determine the incidence of the iliocapsularis muscle in fetal period and its relationship with the hip joint capsule.

METHODS

Twenty-one formalin-fixed fetuses (12 female and 9 male) with a mean gestational age of 29 ± 3.89 weeks (range 25-36) were dissected to reveal morphological properties of iliocapsularis muscle.

RESULTS

Iliocapsularis muscle was observed in 39 out of 42 sides (92%). Its proximal attachment was detected either below the proximal attachment of rectus femoris muscle in 21 out of 39 sides (54%), or it was forming a common tendon with rectus femoris on the anterior inferior iliac spine in 10 out of 39 sides (26%), or it was forming an arch along the superior-medial-inferior sides of the proximal attachment of rectus femoris muscle in 8 out of 39 sides (20%). Muscle fibers originating from the anteromedial part of hip joint capsule were also constant in all sides. Distal attachment of iliocapsularis muscle was distal to the lesser trochanter in all specimens. Its form was as a broad muscle in 32 out of 39 sides (82%) and as a thin rectangular muscular slip in 7 out of 39 sides (18%). Iliopsoas and iliocapsularis muscles had their particular fascia in 34 out of 39 sides (87%), and in the other 5 sides, there was no fascia which prominently separated the two muscles. Its length was longer in females than males (p = 0.031) and it was wider on the right side (p = 0.029). Linear functions were y = 0.49 + 0.17 × weeks and y = 6.94 + 0.89 × weeks for width and length, respectively.

CONCLUSION

Data obtained with the present study about iliocapsularis muscle in fetal period revealed that it is an individual and constant muscle. Its dimension, location, and course over the hip joint capsule support the idea that it tightens the hip capsule and stabilizes the femoral head.

The hominid ilium is shaped by a synapomorphic growth mechanism that is unique within primates

The human ilium is significantly shorter and broader than those of all other primates. In addition, it exhibits an anterior inferior iliac spine (AIIS) that emerges via a secondary center of ossification, which is unique to hominids (i.e., all taxa related to the human clade following their phyletic separation from the African apes). Here, we track the ontogeny of human and other primate ossa coxae. The human pattern is unique, from anlage to adulthood, and fusion of its AIIS is the capstone event in a repositioning of the anterior gluteals that maximizes control of pelvic drop during upright walking. It is therefore a hominid synapomorphy that can be used to assess the presence and age of bipedal locomotion in extinct taxa.

Iliocapsularis: Technical application of fine-wire electromyography, and direction specific action during maximum voluntary isometric contractions

The iliocapsularis muscle of the anterior hip may play an important role in hip function, but no electromyographic (EMG) recordings have been made. This muscle provides the most substantial muscular attachment to the anterior hip capsule and is hypothesised to have a dynamic role to limit capsular impingement and to augment joint stability. Current understanding of the function of iliocapsularis is based on limited cadaveric and radiographic studies. Located deep over the hip joint it would require intramuscular fine-wire EMG to evaluate its activity directly with limited cross-talk from overlying muscles. The primary aim of this study was to describe a new technique for insertion of intramuscular EMG electrodes into iliocapsularis and to report its activation during different directions of hip maximum voluntary isometric contraction (MVIC). Fifteen healthy volunteers (10M, mean age (SD) 22 (2) years) who were free from hip pain were recruited for electrode insertion and to perform MVIC's in six directions at 0° and three directions at 90° of hip flexion. Intramuscular electrodes were successfully inserted into the iliocapsularis muscle with guidance from real-time ultrasound imaging. The greatest muscle activity occurred during resisted hip flexion at 90° (Median (IQR); 100.0 (1.2) % MVIC) and lowest activity during hip extension, 0° (0.5 (0.3) % MVIC). These findings have implications for our understanding of iliocapsularis' functional role. This paper provides the first report of intramuscular electrode insertion into iliocapsularis with guided technical instructions for future EMG investigations in other populations and tasks.