Simulating osteoarthritis: the effect of the changing thickness of articular cartilage on the kinematics and pathological bone-to-bone contact in a hip joint with femoroacetabular impingement

Femoroacetabular impingement (FAI) is a pathomechanical process by which the human hip can fail. The effect of attenuated cartilage on the kinematics and the pathological bone-to-bone contact of an osteoarthritic hip joint with FAI are still unknown. The current study is aiming to simulate osteoarthritis of a cam-type femoral head with cartilage thinning of varying severity. A three-dimensional model of the left hip joint of a male patient diagnosed with FAI was obtained from preoperative computerised tomography data using density segmentation techniques. The kinematics of FAI was simulated using a finite element method. As the acetabulum and femur came into contact, the penetrations were detected, and the contact constraints were applied according to the penalty constraint enforcement method. The translation and rotation parameters were defined in a single step for each one of three cases: healthy cartilage and 2 mm (one-sided thinning) and 4 mm (two-sided thinning) worn out articular cartilages. The results of the analysis show that thinning of the cartilage at the hip joint adversely affects impingement, as a range of motion decreased with progressive thinning of the articular cartilage. In the presence of attenuated cartilage, equating osteoarthritis, the pathomorphology of the cam lesion, likely determines the extent of damage on the rim of the acetabulum, as well.     

Radiographic Predictors of Hip Pain in Femoroacetabular Impingement

The primary diagnosis of femoroacetabular impingement is based on clinical symptoms, physical exam findings, and radiographic abnormalities. The study objective was to determine the radiographic findings that correlate with and are predictive of hip pain in femoroacetabular impingement (FAI). One hundred prospective patients with unilateral FAI symptoms based on clinical and radiographic findings were included in this study. All patients filled out a WOMAC pain questionnaire. Two independent-blinded surgeons assessed antero-posterior and lateral radiographs for 33 radiographic parameters of FAI. Correlations between pain scores and radiographic findings were calculated. A matched radiographic analysis was performed comparing symptomatic versus asymptomatic hips. Radiograph findings were also compared between males and females. Weak positive correlations were identified between increasing pain scores with radiographic findings of posterior wall dysplasia, presence of a shallow socket, and a more lateral acetabular fossa relative to the Ilioischial line. A symptomatic hip had a lower neck shaft angle, greater distance from Ilioischial line to acetabular fossa and larger distance from cross-over sign to superolateral point of the acetabulum when compared to the asymptomatic hip in the same patient. Symptomatic hips in males had more joint space narrowing, femoral osteophytes, higher alpha angles and larger, more incongruent femoral heads compared to females. Females had more medial acetabular fossa relative to the Ilioischial line and smaller femoral head extrusion index. Similar to other musculoskeletal conditions, radiographic findings of FAI are poor predictors of hip pain.     

Current concepts in management of femoroacetabular impingement

Femoroacetabular impingement (FAI) is an increasingly recognized condition, which is believed to contribute to degenerative changes of the hip. This correlation has led to a great deal of interested in diagnosis and treatment of FAI. FAI can be divided into two groups: cam and pincer type impingement. FAI can lead to chondral and labral pathologies, that if left untreated, can progress rapidly to osteoarthritis. The diagnosis of FAI involves a detailed history, physical exam, and radiographs of the pelvis. Surgical treatment is indicated in anatomic variants known to cause FAI. The primary goal of surgical treatment is to increase joint clearance and decrease destructive forces being transmitted through the joint. Treatment has been evolving rapidly over the past decade and includes three primary techniques: open surgical dislocation, mini-open, and arthroscopic surgery. Open surgical dislocation is a technique for dislocating the femoral head from the acetabulum with a low risk of avascular necrosis in order to reshape the neck or acetabular rim to improve joint clearance. Mini-open treatment is performed using the distal portion of an anterior approach to the hip to visualize and to correct acetabular and femoral head and neck junction deformities. This does not involve frank dislocation. Recently, arthroscopic treatment has gained popularity. This however does have a steep learning curve and is best done by an experienced surgeon. Short- to mid-term results have shown relatively equal success with all techniques in patients with no or only mild evidence of degenerative changes. Additionally, all techniques have demonstrated low rates of complications.     

Open‐MRI measures of cam intrusion for hips in an anterior impingement position relate to acetabular contact force

Open MRI in functional positions has potential to directly and non‐invasively assess cam femoroacetabular impingement (FAI). Our objective was to investigate whether open MRI can depict intrusion of the cam deformity into the intra‐articular joint space, and whether intrusion is associated with elevated acetabular contact force. Cadaver hips (9 cam; 3 controls) were positioned in an anterior impingement posture and imaged using open MRI with multi‐planar reformatting. The β‐angle (describing clearance between the femoral neck and acetabulum) was measured around the entire circumference of the femoral neck. We defined a binary “MRI cam‐intrusion sign” (positive if β < 0°). We then instrumented each hip with a piezoresistive sensor and conducted six repeated positioning trials, measuring acetabular contact force (F). We defined a binary “contact‐force sign” (positive if F > 20N). Cam hips were more likely than controls to have both a positive MRI cam‐intrusion sign (p = 0.0182, Fisher's exact test) and positive contact‐force sign (p = 0.0083), which represents direct experimental evidence for cam intrusion. There was also a relationship between the MRI cam‐intrusion sign and contact‐force sign (p = 0.033), representing a link between imaging and mechanics. Our findings indicate that open MRI has significant potential for in vivo investigation of the cam FAI mechanism. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:205–216, 2016.     

Femoroacetabular impingement. A common cause of hip complaints leading to arthrosis

The exact cause of the idiopathic osteoarthritis of the hip has not been identified, although the cause of hip degeneration in developmental dysplasia can clearly be attributed to an excessive axial loading. Based on the development of a surgical technique for the safe surgical dislocation of the hip and the associated possibility of intraoperative joint evaluation, we have found motion-induced joint damage in many of these hips. This begins peripherally at the acetabular rim, progressing centrally. This so-called "femoroacetabular impingement" (FAI), leads, by an increased acetabular coverage and/or a missing sphericity of the femoral head, to an abutment of the femoral head/neck junction against the acetabular rim, or even entering of the non-spherical femoral head into the hip. It initiates damage to the labrum and/or acetabular cartilage. Frequently, this becomes symptomatic in the second or third decade of life in patients with increased sport activity. Based on the predominance of the acetabular or femoral pathology, two different types of FAI, the pincer and the cam can be differentiated. Apart from these morphological alterations, supraphysiological mobility and overuse can contribute to FAI. The impingement concept has led to a new type of mainly intracapsular hip surgery.     

Editorial Commentary: Cam Femoroacetabular Impingement Requires Dynamic Assessment of Beta-Angle (Femoroacetabular Excursion Angle) and Consideration of Femoral and Acetabular Version: Cam Impingement in Patients With Acetabular or Femoral Retroversion May Warrant Greater Osteoplasty

Radiographs, magnetic resonance imaging, and computed tomography scans have been commonly used to evaluate femoroacetabular impingement (FAI) and are well accepted forms of surgical planning. Assessing and addressing both the femoral and acetabular sides result in a combination of “one-sided” treatments that, in sum, net a successful treatment of FAI. However, combining one-sided approaches may not consider the dynamic interaction of the femoral head with the acetabulum. Elevated alpha angles alone can be indicative of a cam-type lesion without necessitating the presence of functional FAI. The presence of a cam-type lesion on lateral radiographs, as suggested by a positive alpha angle, does not necessitate a decrease in clearance between the femoral head and acetabular rim as measured by the beta angle. Assessment of the beta angle, or femoroacetabular excursion angle, has the potential to address dynamic nature of FAI more accurately by directly measuring the degree of clearance between the femoral head and acetabulum. In addition, a comprehensive assessment of physical examination findings, particularly range of motion, as well as a summation of acetabular and femoral version (as measured by the McKibbin Index), are required. Cam-type of FAI poses a larger challenge in the patient with acetabular or femoral retroversion, which may warrant greater and more localized osteoplasty, distally, during hip arthroscopy.     

Eccentric Rotational Acetabular Osteotomy Using Computed Navigation Guidance for Developmental Dysplasia of the Hip,Sacroiliac Fusion,and Femoroacetabular Impingement Owing to Acetabular Retroversion: A Case Report

BackgroundDevelopmental dysplasia of the hip (DDH) is the main factor that causes secondary osteoarthritis of the hip (hip OA). Acetabular retroversion results in pincer‐type femoroacetabular impingement (FAI), and this is also known to cause secondary hip OA. However, few cases of DDH with acetabular retroversion have been reported, and there is no definite opinion on the optimal treatment. We report a rare case of DDH and FAI owing to acetabular retroversion and dysostosis of the sacroiliac joint that was treated with eccentric acetabular rotational osteotomy (ERAO) using navigation guidance.Case PresentationA 27‐year‐old woman presented with DDH and acetabular retroversion with FAI and dysostosis of the sacroiliac joint on the contralateral side. We performed ERAO using computed navigation guidance and improved the coverage and retroversion of the acetabulum. The acetabular anteversion angle improved from 1° retroversion to 9° anteversion after surgery, the center edge angle improved from 18° to 43°, and the acetabular head index improved from 69% to 93%. The cam lesion of the femur was resected. The Harris Hip Score improved from 55.7 to 100 points at the final examination 2 years after surgery.ConclusionsIn this rare case of DDH and FAI, ERAO using computed navigation guidance accurately improved the coverage and retroversion of the acetabulum.     

Comparative study of the intrinsic mechanical properties of the human acetabular and femoral head cartilage

Biphasic creep indentation methodology and an automated indentation apparatus were used to measure the aggregate modulus, Poisson's ratio, permeability, thickness, creep and recovery equilibrium times, and percentage of recovery of normal articular cartilage in 10 human hip joints. These properties were mapped regionally to examine the mechanical factors involved in the development of site-specific degenerative lesions in the acetabulum and femoral head. The results indicate that there are significant differences between these properties regionally in the acetabulum and femoral head and between the two anatomical structures. Specifically, it was found that cartilage in the superomedial aspect of the femoral head has a 41% larger aggregate modulus than its anatomically corresponding articulating surface in the acetabulum. In addition, the supermedial aspect of the femoral head has the greates aggregate modulus (1.816 MPa) within the hip joint. During sitting, the inferior portion of the femoral head is in contact with the anterior acetabulum, and the anterior acetabulum has a 53% greater aggregate modulus than the inferior femoral head. This area below the fovea on the femoral head has the least aggregate modulus (0.814 MPa) within the hip joint. These mismatches in the compressive modulus of opposing articulating surfaces may contribute to degeneration of cartilage in the superomedial acetabulum and the inferior femoral head. Our findings support the clinical observation that these areas are frequent sites of early degeneration.     

人工股骨头置换术中置入不同直径假体球头的有限元分析

目的 :针对老年股骨颈骨折行人工股骨头置换术中,借助三维有限元分析的方法 ,探讨置入不同直径的假体球头后的髋关节生物力学变化,观察对髋关节应力分布变化,以便选择出合适的假体球头尺寸。方法:利用薄层CT资料及人工股骨头假体相关参数建立装配有不同假体球头直径的人工股骨头置换术后髋关节有限元模型(M0:术前模型;M1:球头直径=原股骨头直径;M2:球头直径=原股骨头直径+1 mm;M3:球头直径=原股骨头直径-1 mm;M4:球头直径=原股骨头直径-2 mm),并加载关节合力及相关肌肉的负荷,模拟人缓慢行走时单足站立状态,分析不同直径假体植入后髋臼周围骨质及软骨的应力分布及变化。结果:(1)M1～M4中骨盆均出现了不同程度的应力集中,M3的骨盆Von Mises应力峰值为44.8 MPa,与术前最为接近,增量约13.4%,且M3的骨盆位移在术后4组模型中最小,为1.40 mm;其次是M1,应力峰值为47.3 MPa,增量约19.7%,骨盆位移为1.59 mm。(2)在髋臼区域,M3的Von Mises应力峰值为23.3 MPa,与术前最为接近,增量约6.3%,其次是M1,应力峰值为24.0 ...     

碳—钛组合式人工股骨头临床应用15年随访

自1980年4月至1995年4月,应用碳—钛组合式人工股骨头治疗髋关节疾患319例。随访最短1年,最长15年。随访结果:股骨颈骨折组优良率93％,股骨头无菌性坏死组优良率89.8％。余者2例失败,4例髋关节周围钙化,2例碳质头略大,3例假体下沉,1例类风湿性髋关节强直,术后关节再强直。1例髋臼硬化,4例6髋关节明显疼痛。4例死于心血管疾病。我们体会到碳质材料具有良好的物理、化学性能和生物相容性,是一种优良的人工关节材料。碳—钛组合式人工股骨头是目前优良的人工假体之一。     

Roles of radiograph, magnetic resonance imaging, threedimensional computed tomography in early diagnosis of femoro-acetabular impingement in 17 cases

Objective: To evaluate the roles of radiograph, magnetic resonance imaging (MRI), three-dimensional computed tomography (3-D CT) in early diagnosis of femoro-acetabular impingement (FAI) in 17 cases. Methods: Plain radiographs of the pelvis, 3-D CT, and MRI of the hip were made on 17 patients with groin pain, which was worse with prolonged sitting (i.e. hip flexion). There was no history of trauma or childhood hip disorders in the patients who did not complain of any other joint problems or neurologic symptoms. All patients had positive anterior or posterior impingement test. Plain radiographs included an antero-posterior (AP) view of the hip and a cross table lateral view with slight internal rotation of the hip. CT scan was performed with the Lightspeed 16 row spiral (General Electric Company, USA) at 1.25 mm slice reconstruction. MRI scan was performed on the Siemens Avanto (Siemens Company, Germany)1.5T supraconducfion magnetic resonance meter. The CT and MRI scans were taken from 1 cm above the acetabulum to the lesser trochanter in 5 series. Results: The plain radiographs of the pelvis showed that among the 17 patients, 12 (70.59%) had "Cam" change of the femoral head, 6 (35.29%) had positive "cross-over" sign, and 17 (100%) had positive "Pincer" change of the acetabulum. The 16 row spiral CT noncontrast enhanced scan and 3-D reconstruction could discover minus femoral offset and ossification and osteophyte of the acetabulum labrum in all the 17 cases (100%). The MRI noncontrast enhanced scan could discover more fluid in the hip joint in 15 cases (88.33%), subchondral ossification in 3 cases (17.6%), and labium tears in 3 cases (17.6%). Conclusions: Plain radiographs can provide the initial mainstay for the diagnosis of FAI, 3-D CT can tell us the femoral offset, while MRI can show labrum tears in the very early stage of FAI. Basically, X-ray examination is enough for the early diagnosis of FAI, but 3-D CT and MRI may be useful for the treatment.     

Editorial Commentary: Not Yet Convinced That the Femoroacetabular Impingement Resection (Fair) Arc Measurement Provides a “Fair” Assessment of Cam Resection Principles

Hip arthroscopy has proven to be an effective surgical approach for the treatment of femoroacetabular impingement (FAI) syndrome. Studies have shown that patients typically have improved functional outcomes and high rates of return to activity following cam lesion resection and reshaping of the femoral head-neck junction. However, despite these favorable outcomes, there is still a steep and well-recognized learning curve in FAI hip arthroscopy. Although it is common dogma to consider an ideal reshaping of the femoral head-neck junction as being perfectly spherical, the ability to achieve this intraoperatively can be quite challenging. A new tool is the “femoroacetabular impingement resection (FAIR) arc,” measured on a 45° Dunn lateral radiograph where a best-fit circle incorporates the region immediately inferior to the anteroinferior iliac spine, the subspine region, and lateral femoral neck base. The maximal radial distance height is then measured from the circumference of this circle to the apex of the cam lesion. This radiographic aid may assist with intraoperative estimate of appropriate cam lesion resection depth. While I tend to utilize preoperative radiographs and intra-operative neck sclerosis to determine cam resection depth, I continue to seek out other ways to effectively perform a femoral osteoplasty. While my initial attempt to utilize the FAIR index in my practice did not seem effective, I will continue to test this measurement in my patients.     

The Concept of Femoroacetabular Impingement: Current Status and Future Perspectives

Femoroacetabular impingement (FAI) is a recently proposed mechanism causing abnormal contact stresses and potential joint damage around the hip. In the majority of cases, a bony deformity or spatial malorientation of the femoral head or head/neck junction, acetabulum, or both cause FAI. Supraphysiologic motion or high impact might cause FAI even with very mild bony alterations. FAI became of interest to the medical field when (1) evidence began to emerge suggesting that FAI may initiate osteoarthritis of the hip and when (2) adolescents and active adults with groin pain and imaging evidence of FAI were successfully treated addressing the causes of FAI. With an increased recognition and acceptance of FAI as a damage mechanism of the hip, defined standards of assessment and treatment need to be developed and established to provide high accuracy and precision in diagnosis. Early recognition of FAI followed by subsequent behavioral modification (profession, sports, etc) or even surgery may reduce the rate of OA due to FAI. Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article.     

Subject-specific Patterns of Femur-labrum Contact are Complex and Vary in Asymptomatic Hips and Hips With Femoroacetabular Impingement

Background

Femoroacetabular impingement (FAI) may constrain hip articulation and cause chondrolabral damage, but to our knowledge, in vivo articulation and femur-labrum contact patterns have not been quantified.

Purpose

In this exploratory study, we describe the use of high-speed dual-fluoroscopy and model-based tracking to dynamically measure in vivo hip articulation and estimate the location of femur-labrum contact in six asymptomatic hips and three hips with FAI during the impingement examination. We asked: (1) Does femur-labrum contact occur at the terminal position of impingement? (2) Could range of motion (ROM) during the impingement examination appear decreased in hips with FAI? (3) Does the location of femur-labrum contact coincide with that of minimum bone-to-bone distance? (4) In the patients with FAI, does the location of femur-labrum contact qualitatively correspond to the location of damage observed intraoperatively?

Methods

High-speed dual-fluoroscopy images were acquired continuously as the impingement examination was performed. CT arthrogram images of all subjects were segmented to generate three-dimensional (3-D) surfaces for the pelvis, femur, and labrum. Model-based tracking of the fluoroscopy images enabled dynamic kinematic observation of the 3-D surfaces. At the terminal position of the examination, the region of minimal bone-to-bone distance was compared with the estimated location of femur-labrum contact. Each patient with FAI underwent hip arthroscopy; the location of femur-labrum contact was compared qualitatively with damage found during surgery. As an exploratory study, statistics were not performed.

Results

Femur-labrum contact was observed in both groups, but patterns of contact were subject-specific. At the terminal position of the impingement examination, internal rotation and adduction angles for each of the patients with FAI were less than the 95% confidence intervals (CIs) for the asymptomatic control subjects. The location of minimum bone-to-bone distance agreed with the region of femur-labrum contact in two of nine hips. The locations of chondrolabral damage identified during surgery qualitatively coincided with the region of femur-labrum contact.

Conclusions

Dual-fluoroscopy and model-based tracking provided the ability to assess hip kinematics in vivo during the entire impingement examination. The high variability in observed labrum-femur contact patterns at the terminal position of the examination provides evidence that subtle anatomic features could dictate underlying hip biomechanics. Although femur-labrum contact occurs in asymptomatic and symptomatic hips at the terminal position of the impingement examination, contact may occur at reduced adduction and internal rotation in patients with FAI. Use of minimum bone-to-bone distance may not appropriately identify the region of femur-labrum contact. Additional research, using a larger cohort and appropriate statistical tests, is required to confirm the findings of this exploratory study.

Electronic supplementary material

The online version of this article (doi:10.1007/s11999-014-3919-9) contains supplementary material, which is available to authorized users.     

Changes in the stress in the femoral head neck junction after osteochondroplasty for hip impingement: A finite element study

The surgical treatment of femoroacetabular impingement (FAI) often involves femoral osteochondroplasty. One risk of this procedure is fracture of the femoral neck. We developed a finite element (FE) model to investigate the relationship between depth of resection and femoral neck stress. CT data were used to obtain the geometry of a typical cam‐type hip, and a 3D FE model was constructed to predict stress in the head–neck after resection surgery. The model accounted for the forces acting on the head and abductor muscular forces. Bone resection was performed virtually to incremental resection depths. The stresses were calculated for five resection depths and for five different activities (i) standing on one leg (static case); (ii) two‐to‐one‐to‐two leg standing; (iii) normal walking; (iv) walking down stairs; and (v) a knee bend. In general, both the average Von Mises stresses and the area of bone that yielded significantly increased at a resection depth of ≥10 mm. The knee bend and walking down stairs demonstrated the highest stresses. The FE model predicts that fracture is likely to occur in the resection area first following removal of a third (10 mm) or more of the diameter of the femoral neck. We suggest that when surgeons perform osteochondroplasty for hip impingement, the depth of resection should be limited to 10 mm. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1999–2006, 2012     

The mechanical cause of congenital dislocation of the hip joint: Dynamic ultrasound study of 5 cases

5 hip joints with untreated congenital dislocation of the hip were examined for hip movement by ultrasound. With the hip joint flexed, the direction of the dislocated femoral head was posterior to the acetabulum. The dislocated femoral head displaced more posteriorly when the knee joint was extended, with the hip joint held in flexed position. As the dislocated hip was extended, on the other hand, the direction of the dislocated femoral head was anterior to the acetabulum. The dislocated femoral head displaced more anteriorly when the baby tried to bend the hip with the joint held in extended position.

These findings indicate that a fetal posture with the hip flexed and the knee extended predisposes to the development of CDH by the action of hamstrings, and that an infant posture with the hip extended is likely to provoke femoral head dislocation by the action of the iliopsoas.     

Experimentally induced cam impingement in the sheep hip

Sheep hips have a natural non‐spherical femoral head similar to a cam‐type deformity in human beings. By performing an intertrochanteric varus osteotomy, cam‐type femoro‐acetabular impingement (FAI) during flexion can be created. We tested the hypotheses that macroscopic lesions of the articular cartilage and an increased Mankin score (MS) can be reproduced by an experimentally induced cam‐type FAI in this ovine in vivo model. Furthermore, we hypothesized that the MS increases with longer ambulatory periods. Sixteen sheep underwent unilateral intertrochanteric varus osteotomy of the hip with the non‐operated hip as a control. Four sheep were sacrificed after 14, 22, 30, and 38‐weeks postoperatively. We evaluated macroscopic chondrolabral alterations, and recorded the MS, based on histochemical staining, for each ambulatory period. A significantly higher prevalence of macroscopic chondrolabral lesions was found in the impingement zone of the operated hips. The MS was significantly higher in the acetabular/femoral cartilage of the operated hips. Furthermore, these scores increased as the length of the ambulatory period increased. Cam‐type FAI can be induced in an ovine in vivo model. Localized chondrolabral degeneration of the hip, similar to that seen in humans (Tannast et al., Clin Orthop Relat Res 2008; 466: 273–280; Beck et al., J Bone Joint Surg Br 2005; 87: 1012–1018), can be reproduced. This experimental sheep model can be used to study cam‐type FAI. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 580–587, 2013     

Treatment of congenital dislocation of the hip in older children

The aims of treatment of a child with congenital dislocation of the hip (CDH) untreated until walking age should be to reestablish the mechanics of the hip joint and avoid complications, especially avascular necrosis, thus delaying the development of osteoarthritis. The pathology in the older child shows that both soft tissues and bony parts are distorted to some degree. The acetabular index and center-edge (CE) angle evaluations are helpful in the initial evaluation and in the follow-up examinations. A computed tomography (CT) scan may be helpful in determining a reduction and distinguishing between dysplasia and subluxation. A controversy still exists as to the relative value of closed and open reduction in the treatment of a child who has reached walking age. For most surgeons, in a child up to three years of age, a careful closed reduction following a period of traction is the most useful form of treatment. The home traction program has been successful in this age group. For gentle closed reduction all maneuvers must be done as gently as possible and carried out as "positioning" the leg rather than forcing a reduction. The indications for open reduction are (1) if the femoral head persistently lies above the triradiate cartilage on roentgenographic examination, (2) if the arc of reduction and redislocation is less than 25 degrees after an adductor tenotomy, (3) if the femoral head will not enter the acetabulum, (4) if the femoral head is still laterally placed in the acetabulum after four weeks of partial reduction, and (5) if a previous reduction has failed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Range of motion and stability in total hip arthroplasty with 28-, 32-, 38-, and 44-mm femoral head sizes

The purpose of this study was to evaluate, via experimental models, the effect of larger head sizes for total hip arthroplasty on the type of impingement, range of motion (ROM), and joint stability. Testing was conducted using an anatomic full-size hip model (anatomic goniometer) and a novel anatomic dislocation simulator with 28-, 32-, 38-, and 44-mm diameter femoral heads within a 61-mm acetabular shell. Femoral heads >32-mm provided greater ROM and virtually complete elimination of component-to-component impingement. A significant increase in both flexion before dislocation and displacement between the femoral head and acetabulum to produce dislocation occurred with femoral heads >32-mm in diameter. These data indicate that larger femoral heads offer potential in providing greater hip ROM and joint stability.     

Finite Element Analysis Examining the Effects of Cam FAI on Hip Joint Mechanical Loading Using Subject-Specific Geometries During Standing and Maximum Squat

Background:

Cam femoroacetabular impingement (FAI) can impose elevated mechanical loading in the hip, potentially leading to an eventual mechanical failure of the joint. Since in vivo data on the pathomechanisms of FAI are limited, it is still unclear how this deformity leads to osteoarthritis.

Purpose:

The purpose of this study was to examine the effects of cam FAI on hip joint mechanical loading using finite element analysis, by incorporating subject-specific geometries, kinematics, and kinetics.

Questions:

The research objectives were to address and determine: (1) if hips with cam FAI demonstrate higher maximum shear stresses, in comparison with control hips; (2) the magnitude of the peak maximum shear stresses; and (3) the locations of the peak maximum shear stresses.

Methods:

Using finite element analysis, two patient models were control-matched and simulated during quasi-static positions from standing to squatting. Intersegmental hip forces, from a previous study, were applied to the subject-specific hip geometries, segmented from CT data, to evaluate the maximum shear stresses on the acetabular cartilage and underlying bone.

Results:

Peak maximum shear stresses were found at the anterosuperior region of the underlying bone during squatting. The peaks at the anterosuperior acetabulum were substantially higher for the patients (15.2 ± 1.8 MPa) in comparison with the controls (4.5 ± 0.1 MPa).

Conclusions:

Peaks were not situated on the cartilage, but instead located on the underlying bone. The results correspond with the locations of initial cartilage degradation observed during surgical treatment and from MRI.

Clinical Relevance:

These findings support the pathomechanism of cam FAI. Changes may originate from the underlying subchondral bone properties rather than direct shear stresses to the articular cartilage.