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PubMed1996

[Wear behavior of coupled aluminum oxide ceramics-carbon fiber bond as hip acetabulum inlay in a simulated trial].

Hip-simulator studies were carried out to investigate the initial wear between a femoral head made of aluminium oxide ceramic and a CFRP-(carbon fibre-reinforced plastic) inlay in a titanium cup. A load of 2500 N and a frequency of 0.857 Hz were applied. After 200,000 cycles, the centre of the head had moved 9 microns into the liner. After 500,000 cycles, the cup centre had moved inwards by a further micron, and the near radius had increased by 2 microns. After 750,000 cycles the position of the centre of the head remained unchanged, while the mean radius had increased a further 2 microns. After one million cycles any further changes remained below the measuring capability (1 micron) of the system.

Aluminum Oxide↗
PubMed1996

The effect of variable size posterior wall acetabular fractures on contact characteristics of the hip joint.

The indications for open reduction and internal fixation of posterior wall acetabular fractures associated with a clinically stable hip joint are unclear. In previous work a large posterior wall defect (27% articular surface area) resulted in significant alteration of load transmission across the hip; specifically, there was a transition from evenly distributed loading along the acetabular articular surface to loading concentrated mainly in the superior portion of the articular surface during simulated single leg stance. However, the majority of posterior wall fractures involve a smaller amount of the articular surface. Posterior wall acetabular fractures not associated with instability of the hip are commonly treated nonoperatively. This practice does not account for the size of the posterior wall fracture. To study the biomechanical consequences of variably sized articular defects, a laboratory experiment was conducted evaluating three progressively larger posterior wall defects of the acetabulum during simulated single leg stance using superlow Fuji prescale film (Itochu International, New York): (a) 1/3 articular surface width through a 50 degrees arc along the posterior wall of the acetabulum, (b) 2/3, and (c) 3/3 articular width defects through the same 50 degrees arc along the posterior wall of the acetabulum. In the intact acetabulum, 48% of the total articular contact was located in the superior acetabulum. Twenty-eight percent of articular contact was in the anterior wall region of the acetabulum and 24% in the posterior wall region. After the 1/3 width posterior wall defect, 64% of the articular contact was located in the superior acetabulum (p = 0.0011). The 2/3 width posterior wall defect resulted in 71% of articular contact area being located in the superior acetabulum (p = 0.0006). After the 3/3 width posterior wall defect, 77% of articular contact was located in the superior acetabulum, significantly greater than the intact condition (p < 0.0001) and 1/3 width defect (p = 0.0222). The total absolute contact areas for all defect conditions were significantly less than the intact conditions. The results of this study reconfirm the observation that posterior wall fractures of the acetabulum significantly alter the articular contact characteristics in the hip during single leg stance. The relationship between defect size and changes in joint contact showed that the smallest defect resulted in the greatest alteration in joint contact areas, whereas larger defects resulted in minor increments of change in contact area. This finding is of concern because the clinical practice of managing acetabular fractures nonoperatively if the hip joint is stable is based on the supposition that the joint retains enough integrity to function without undue risk of late posttraumatic osteoarthritis. A better understanding of the natural history of stable posterior wall acetabular fractures is needed to ascertain whether some of these fractures merit operative repair.

Acetabulum↗
PubMed1999

Types of persistent dysplasia in congenital dislocation of the hip.

This article reports five types of persistent bony dysplasia in patients with congenital dislocation of the hip (CDH), suggests the pathogeneses, and discusses the treatment options. We consider the five types to be (1) maldirected acetabulum, (2) capacious acetabulum, (3) false acetabulum, (4) lateralized acetabulum, and (5) femoral deformity. The maldirected acetabulum persists when the acetabulum continues to face forward and laterally. The capacious acetabulum arises from joint instability; capsular laxity permits the proximal femur to slide within the acetabulum. The false acetabulum results from an ectopic fibrocartilaginous cavity in the pelvis created by the subluxated or dislocated femoral head.44 The lateralized acetabulum occurs with ossification of the cotyloid cavity from longstanding lateral subluxation or dislocation or premature closure of the triradiate cartilage. Femoral deformities include valgus and anteversion of the femoral neck, capital femoral physeal growth arrest, discrepancy between the greater trochanter and the femoral head, and femoral head asphericity. After clinical and radiographic evaluation, we believe that an understanding of the pathogeneses and types of dysplasia will facilitate appropriate treatment programs. Treatments consist of acetabular redirection, acetabular reconstruction, femoral osteotomies, and salvage procedures.

Acetabulum↗
PubMed1981

[A study on the stress analysis of the pelvis by means of the three-dimensional photoelastic experiments (author's transl)].

The processes are as follows: 1) Life-sized photoelastic models molded from a cadaver pelvis are made of Epoxy resin. 2) In order to practice the stress freezing process, the models are set to our original loading apparatus in the electric heater. The forces exerted on the hip models are both body weight and four kinds of muscular forces, those of the abductor, adductor, rectus femoris and gluteus maximus. 3) After the stresses are frozen in the models, they are cut off into slices to observe isochromatic and isoclinic lines. 4) In the stress analysis both the shear difference method and the double slice method are utilized to obtain more accurate stress distributions. And the results have been summarized as follows: 1) In the ring-shaped slices large stresses are observed especially at four areas; namely the central area of the iliac bone, the acetabulum proximal to the ilium, the pubic ramus and the area adjacent to the sacroiliac joint. The specific areas where hydrostatic pressure works are seen at two points in the deep acetabular cavity. 2) The principal stress lines of almost all slices tend to flow smoothly and monotonously along the ilium, the sacrum and the pubic bone, but as they approach the acetabulum they run in complex patterns and make some singular points. 3) Around the acetabulum the principal stress lines of one group run in concentric circles and those of the other group radiate in all directions from the center of the acetabulum at the upper half of the dome which supports the load. The stress here was 5 to 6 times greater than in the lower half of the dome. 4) The acetabulum is stretched vertically and deformed into an oval shape. The horse shoe-shaped articular facet is deformed as both beaks approach each other. 5) As for the slices of the pelvic ring the normal acetabulum tends to be obviously deformed as it holds or embraces the femoral head. As a result of this deformity the stability between the acetabulum and the head increases. On the other hand the dysplastic acetabulum shows none of those phenomena. 6) The iliac bone of the pelvic ring is deformed into the "S" shape and the pubic ramus the "C" shape, the "S" shape, or the "Z" shape depending on the limb position. The pelvic ring tends to be deformed into a heart shape during abduction.

Acetabulum↗
PubMedDate not supplied

Biomechanical evaluation of a low anterior wall fracture: correlation with the CT subchondral arc.

OBJECTIVE: To measure the effect of a simulated low anterior wall fracture of the acetabulum on load transmission in the hip joint. DESIGN: We measured the contact areas and pressure between the acetabulum and the femoral head of cadaveric pelves in three different conditions: intact, with an operatively created fracture of the anterior wall, and after anatomic reduction and internal fixation of the fracture. SETTING: Hips were loaded in simulated single-limb stance. Pressure and area measurements were made with Fuji pressure-sensitive film. SPECIMENS: Seven hip joints in seven whole pelves were tested. INTERVENTION: Anterior wall fractures were anatomically reduced and fixed. MAIN OUTCOME MEASUREMENTS: Contact area, load, and mean and maximum pressures were measured. RESULTS: Anterior wall fractures in our specimens entered the hip joint an average of 9.7 millimeters from the vertex of the acetabulum, corresponding to a 45-degree roof arc measurement. Peripheral loading seen in the intact acetabulum was disrupted after fracture. The loading pattern was not restored to preinjury levels with anatomic reduction and fixation. There was no significant change in the contact area (p = 0.43), force (p = 0.06), or mean (p = 0.57) or maximum (p = 0.20) pressures in the superior aspect of the acetabulum after creation of the anterior wall fracture. CONCLUSIONS: These results differ from those of previous studies with posterior wall acetabulum fractures, where significant increases in force and mean and maximum pressures were noted in the superior acetabulum after fracture. The lack of significant increases in superior acetabular pressures is discussed in relation to the mean computed tomographic subchondral arc of approximately ten millimeters in our specimens.

Acetabulum↗
PubMed2006

[Early primary total hip arthroplasty for acetabular fractures in elderly patients].

PURPOSE OF THE STUDY: The aim of this pilot study was to evaluate the clinical and functional outcomes of total hip arthroplasty (THA) in patients with acetabular fractures due to a low-energy injury. Acute primary THA included an antiprotrusion cage and autologous bone grafting of the acetabulum. This prospective study was carried out between 1998 and 2004. MATERIAL: Ten patients, of whom six were men, (average age, 71 years; range, 60 to 83 years) with acetabular fractures were treated by THA. Two patients had type A2, two had type B1, three had type B2 and three had type B3 fractures, as assessed by the AO classification. X-ray showed osteoporosis due to decreased bone mass in all patients, and dislocations of the fragments in the weight-bearing area of the joint exceeded 1 cm. The average follow-up was 36 months. METHODS: Indications for primary THA included, in addition to higher age, displacement in the fracture line exceeding 1 cm, a fracture line extending to the weight-bearing part of the acetabulum, presence of hip arthritis, cartilage injury, defects of the weight-bearing area of either the femoral head or acetabulum, and Pipkin type IV injury. The interval between accident and surgery ranged from 6 to 12 days (average, 9.5). Three surgical techniques were used, namely, cemented THA with a polyethylene cup cemented into an acetabulum-stabilizing cage; reconstruction with a cementless RSC acetabular component; internal fixation using screws and a cemented cup. Bone grafting of the acetabulum was used in all patients. Evaluated were basic operative parameters, complications, X-ray findings, ability to walk and Merle d'Aubigne scores. RESULTS: The average operative time was 100 min, the average blood loss was 1000 ml. Hip motion showed the following average values: flexion, 110 degrees ; extension, 10 degrees ; rotation, 30 degrees -0 degrees -30 degrees ; adduction, 25 degrees ; abduction, 35 degrees . All patients returned to their preoperative range of motion. X-ray examination showed good reduction, bone graft was completely incorporated in the acetabulum, and no displacement or signs of loosening or graft migration were recorded. Two patients had Brooker type I heterotropic ossification. The final evaluation of function at 36 months on the basis of the Merle d'Aubigne classification showed excellent and good results in four (57 %) and three (43 %) patients, respectively. The remaining three patients had a shorter follow-up, but were fully mobile with no complications observed. DISCUSSION: It has been reported that bony union of acetabular fracture after open reduction and internal fixation (ORIF) was achieved in 74 % patients younger than 60 years, but in only 44 % of the patients older than 60 years. Secondary THA following ORIF is a demanding technique. Due to adhesions and a frequent malposition of the acetabulum, THA is associated with and increased risk of infection, tendency to develop para-articular ossifications, and a higher risk of early component loosening than in the standard procedure. One of the options is to perform acetabular stabilization and primary THA at one stage. The results of our study are fully in agreement with those reported for THA in hip arthritis or dislocated fracture of the femoral neck. CONCLUSIONS: Acute primary THA with the use of a antiprotrusion cage and bone grafting for acetabular fractures in elderly patients allows us to employ only one surgical technique for definitive repair. It provides primary stability and immediate pain relief, permits graded weight-bearing and early pain-free mobilization, and may also treat hip arthritis, if it exists. This technique has also good prospects for a selected group of younger patients in whom the treatment of acetabular fractures has a poor prognosis. Key words: acetabular fracture, elderly patient, primary total hip arthroplasty.

Acetabulum↗
PubMed1989

[Classification of deformities of the glenoid labrum in congenital hip dislocation].

The authors have developed their own classification of the deformities of labrum glenoidale in congenital hip dislocation. Open reposition was performed by the Ludloff procedure. The basic material for their work was the group of patients operated on at I. Orthopaedic Clinic of the Faculty of General Medicine of Charles University in Prague in the years 1970-1985. In the course of this period they operated on 78 hip joints in 70 children, out of which 8 operations were bilateral, the group comprised 17 boys and 53 girls, operation was performed on 30 right hip joints and 48 left ones. The age of children ranged from 5 to 23 months. The average age of children in time of operation was 9.3 months. On the basis of the cadaver material the authors have found out that glenoidale represents an extensive part of acetabulum. Labrum glenoidale is considerably more sizable in the dorsal parts of acetabulum so that the head seems to be completely enveloped by ligamentary limbus and the acetabulum seems to form at least half of the ball-shaped surface. In the dorsal and upper parts the acetabulum is from great part formed by a fibrous structure which is easily deformed. The pressure applied to the head dorsally can result in its dislocation just because the cartilaginous model of acetabulum is flat in its dorsal and proximal parts. This easily deformable structure is under certain conditions deformed by pressure of the head in such a way that in the first phase in the course of the onset of the dislocation it is always everted and in the second phase the evertion lither persists or the head shifts over the margin of the limbus and the limbus is then inverted by reposition force. The authors present in their work the classification of the limbus. Proceeding from operation findings they divide limbi into four groups according to differences in their shape: Type I: regularly annular (everted) limbus--it corresponds to a normal anatomic shape, it is not pronouncedly deformed and does not present an impediment to reduction. Type II: inverted gracilis limbus--it is exaggerated in comparison to the normal one, usually it is inverted in the acetabulum, it is never rigid but elastic. Together with the structure of capsule it can be an impediment to reduction. It can be relatively easily everted. Type III: inverted callous limbus--it is sizable, rigid, reducing by its position the capacity of the acetabulum. The reduction is usually difficult.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetabulum↗
PubMed1997

[Correlation between ultrasonography and roentgen imaging].

For examination of the infant hip we cannot do without the use of an imaging method. The interpretation of ultrasound and X-ray studies does not always lead to uniform results. To clear up the so far unknown relationship between ultrasound and X-ray studies, sonomorphologic and radiomorphologic examinations were performed on 14 hip joints of children between 36 weeks and 12 1/2 months of age. A discrepancy between the X-ray and ultrasound image is always found when the contour line of the acetabulum does not correspond to the mid-portion but rather to the ventral or dorsal section of the acetabulum in correct projection of the X-ray image. The evaluation of the ultrasound image is then based on a bony shape differing from the one on the X-ray image. If the radiologic contour line of the acetabulum is determined by the mid-portion of the acetabulum, the angle of the acetabulum in the X-ray image and the alpha angle in the ultrasound image always add up to 90 degrees. This leads to the conclusion that a correspondence between ultrasound and X-ray findings only exists when the mid-portion of the acetabulum defines the acetabular contour line in the X-ray image. Generally, however, there is no constant relation between the X-ray summation image and the ultrasound image. The maximum error found by experiment is 8 degrees in the X-ray determination of the acetabular angle, 11 degrees in the ultrasound determination of the alpha angle and 28 degrees in the ultrasound determination of the beta angle. The ultrasound examination has a higher value regardless of its margin of error, which is inherent in any metric method, because the critical mid-portion of the acetabulum can be judged with this procedure. We are of the opinion that the X-ray image is not decisive for therapy and prognostic assessment in these cases.

Aging↗
PubMedDate not supplied

[Periprosthetic mineral density in cement-free hip replacement arthroplasty].

SUBJECT: We analysed the periprosthetic bone mineral density (BMD) in a prospective longitudinal study over two years after operation and in a separate cross-sectional study more than five years after implantation of cementless total hip arthroplasty (CLS-stem, Mecron threaded acetabular cup) by using dual-energy X-ray absorptiometry (DEXA). MATERIALS AND METHODS: In n = 53 patients (29 women, 24 men) we analysed the periprosthetic BMD prospectively in certain periods. All patients had an uncomplicated postoperative course and good clinical outcome (Merle d'Aubigne score > 12). In the cross-sectional study we analysed 23 patients (13 women, 10 men). Regions of Interest (ROI) were defined according to Gruen et al. for the periprosthetic femur and to De Lee and Charnley for the periprosthetic acetabulum. RESULTS: BMD significantly decreases in the periprosthetic femur as well as in the periprosthetic acetabulum during the first three months. In men BMD reaches its lowest values between six months (femur) and one year (acetabulum) after operation and then increases to 96.2% at the femur and 93.8% at the acetabulum. In women BMD decreases during the entire follow-up to 89.4% at the periprosthetic femur and 80.0% at the periprosthetic acetabulum. In the proximal zones 1 and 7 of the femur and the cranial-medial zone II of the acetabulum we observed the highest decrease of mineralisation. More than five years after implantation of the prosthesis BMD in the femur showed only little changes. On the other side BMD around the threaded acetabular cup significantly decreased to 67.4% in women and 79.1% in men. CONCLUSION: The results reflect the different stress on the periprosthetic bone after implantation of the prosthesis and fit to earlier reported good clinical results of the CLS-stem and to increased loosening rate of threaded acetabular cups after five years. Analysing changes of mineralisation in cementless total hip arthroplasty DEXA together with the analization scheme according to Gruen at the femur and to De Lee and Charnley at the acetabulum is a useful method and has been reliable in clinical practise.

Absorptiometry, Photon↗
PubMed1994

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 superomedial aspect of the femoral head has the greatest 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.

Acetabulum↗
PubMed2002

[Cementless socket fixation based on the "press-fit" concept in total hip joint arthroplasty].

PURPOSE OF THE STUDY: The key problem of implant fixation in THR is stress distribution, i.e. load transmission between bone and implant. The closer the load transfer is to the original physiological situation, the easier the adaptation of the periprosthetic bone to the new biomechanical conditions after implantation of the cup and the safer is its longlasting fixation. The aims of the studies were 1) to get information about the physiological load transfer in the normal hip joint, 2) to get information about the load transfer between acetabulum and acetabular sockets and vice versa, 3) to measure the periacetabular pelvic bone deformation as the stimulator of the remodelling process (third stage of osseointegration) in the normal hip joint and in hip joints fitted with different acetabular cups, 4) to study the morphological stages of osseointegration of a non-cemented press-fit cup and to compare the morphological structure of the periacetabular bone with the biomechanical data obtained by the in vitro studies and finally, 5) to compare the clinical and radiological outcome of follow-up studies of the senior author's "Press-Fit cup" with the theoretical hypotheses according to the experimental observations. MATERIAL AND METHODS: Load transfer between the acetabular bone and the femoral head on one side and press-fit cups has been determined by strain gauge measurements, finite element studies, pressure sensitive Fuji prescale films, CT-osteoabsorptiometry and telemetric measurements. Periacetabular deformation has been measured by Imetric Markers. Osseointegration of the senior author's press-fit cup and, thus, the remodelling process of the bony structures adjacent to the cup have been studied in autopsy specimens of THRs which have been in situ for several years. RESULTS: Load transfer measurements have shown that the main load in the original acetabulum as well as in the acetabulum fitted with a press-fit cup is transmitted to the periphery, especially to the acetabular cortical rim whereas the subchondral bone is exposed to lower, predominantly meridional (tension) stresses. Direct measurements of the periacetabular deformation under load revealed an increase of the peripheral press-fit with increasing stability of a (oversized) press-fit cup. Both the normal as well as the acetabulum fitted with a non-cemented cup deforms in a postero-medial direction. The histo-morphology of the periacetabular bone of autopsy specimens showed excellent bony in- and ongrowth of a porous titanium coating (SULMESH) and bone formation, especially at the periphery in zone 1 and 3 according to DeLee and Charnley. CONCLUSION: The studies have shown that the subchondral bone plate of the acetabulum has very little supportive function for non-cemented press-fit cups. For the preparation of the acetabulum it is, therefore, more important to ream the sclerotic subchondral bone until there is a well vascularized, well bleeding bone bed to facilitate osseointegration of a non-cemented acetabular socket than to preserve the subchondral bone plate as is the case in cement fixation. A non-cemented press-fit socket must transmit load predominantly to the cortical bone of the acetabular rim. Therefore, a too far medial positioning of the cup, and therefore loosing contact to the cortical rim, must be avoided under all circumstances. The clinical experience with acetabular revisions and with conversions of hip arthrodeses into a THR (where there is no subchondral bone at all) have shown the superiority of a well vascularized over a sclerotic (even mechanically stronger) bone bed. Furthermore, it has been shown that the additional use of screws for fixation of an acetabular cup is not only unnecessary but can be deleterious and causes complications including osteolysis and aseptic loosening.

Acetabulum↗
PubMed2004

[A study on new computer-aided modeling method of hip joint].

The main reason of invalidation of prosthetic hip joint is the prostheses flexibility and shift, dislocation and disjunction. Promoting the long time stability of the prostheses is the key of improving the long term hip joint replacement effect. Former research work was focused on the upper segment of femur, and assumed the acetabulum cup to be a spheric concave, and the external form of acetabulum prostheses was basically semi spheric. This paper presents a method of acquiring the point data on the surface of the hip bone using the reverse engineering technology. By analyzing the acetabulum surface fitting error we use rotating elliptical surface to fit the acetabulum surface, together with the optimal technique to build up the CAD model of acetabulum surface. We compare the fitting error between the sphere fitting and rotating elliptical surface fitting and get the result that the rotating elliptical surface fitting error is smaller than the sphere fitting error, and the rotating elliptical surface can describe the shape of the acetabulum better.

Acetabulum↗