Bone motion analysis from dynamic MRI: acquisition and tracking

RATIONALE AND OBJECTIVES

For diagnosis, preoperative planning and postoperative guides, an accurate estimate of joint kinematics is required. It is important to acquire joint motion actively with real-time protocols.

MATERIALS AND METHODS

We bring together MRI developments and new image processing methods in order to automatically extract active bone kinematics from multi-slice real-time dynamic MRI. We introduce a tracking algorithm based on 2D/3D registration and a procedure to validate the technique by using both dynamic and sequential MRI, providing a gold standard bone position measurement.

RESULTS

We present our technique for optimizing jointly the tracking method and the acquisition protocol to overcome the trade-off in acquisition time and tracking accuracy. As a case study, we apply this methodology on a human hip joint.

CONCLUSION

The final protocol (bFFE, TR/TE 3.5/1.1 ms, Flip angle 80 degrees , pixel size 4.7 x 2.6 mm, partial Fourier reduction factor of 0.65 in read direction, SENSE acceleration factor of 2, frame rate = 6.7 frames/s) provides sufficient morphological data for bone tracking to be carried out with an accuracy of 3 degrees in terms of joint angle.

Cup alignment error model for total hip arthroplasty

Almost all computer-assisted orthopaedic surgery systems that rely on the anterior pelvic plane definition, such as in computed tomography and magnetic resonance image-based, fluoroscopy-based, and nonimage total hip replacement approaches, are derived from identifying two pairs of pelvic bony landmarks: anterior superior iliac spines and the pubic tubercles. Although these systems strive to achieve cup alignment accuracy of approximately 1 degree, even a minor failure to correctly identify these anatomic landmarks can lead to higher inaccuracies in the final cup alignment. This study shows how to examine the effects of these inaccuracies on the final acetabular cup implant orientation during total hip replacement by generating a kinematic model, which then is simulated. Simulation results indicate that, for example, a total error of 4 mm in measuring the anterior superior iliac spine and the pubic tubercles would result in a final cup orientation of 47 degrees and 27 degrees in abduction and version respectively, resulting in a 2 degrees abduction error and 7 degrees error in version when targeting 45 degrees abduction and 20 degrees version results. These calculations can be repeated for any error values.

Radiological assessment of femoral neck-shaft and anteversion angles in adult Nigerian HIPS

A trigonometric calculation of projected femoral neck shaft or cetrum-collum-diaphysis angle (CCD angle) and anteversion angle (AT angle) were assessed in normal adult Nigerian hips using the standardised biplane radiography described by Müller and Rippstein. A mean CCD angle and AT angle of 121 degrees+/-6 (SD) and 28 degrees+/-5 (SD) respectively were obtained in the 116 Nigerian adult hips assessed. The values obtained were inconsistent with quoted reference ranges of 130 degrees+/-7 and 10 degrees+/-7 respectively. There was however no significant difference between the female and male CCD and AT angles.

Estimates of prevalence of hip dysplasia in Golden Retrievers and Rottweilers and the influence of bias on published prevalence figures

OBJECTIVE

To estimate prevalence of canine hip dysplasia (CHD) in Golden Retrievers and Rottweilers and identify sources of bias in published reports.

DESIGN

Prospective study.

ANIMALS

200 clinically normal Golden Retrievers and 140 clinically normal Rottweilers between 24 and 60 months of age referred for hip evaluation (group 1) and 93 clinically normal dogs evaluated for Orthopedic Foundation for Animals (OFA) hip certification (group 2).

PROCEDURE

Hip-extended pelvic radiographs from group 1 dogs were screened for CHD. Radiographs were evaluated twice; the first interpretation used an OFA-type subjective 7-point scoring system, and the second included the caudolateral curvilinear osteophyte as an additional sign of degenerative joint disease. The OFA submission rate of group 2 dogs was determined from the number of official reports returned from the OFA.

RESULTS

Prevalence of CHD in Golden Retrievers ranged from 53% to 73% and in Rottweilers ranged from 41% to 69%. Among dogs referred for OFA evaluation, radiographs from 49 (53%) were submitted to OFA. Of submitted radiographs, 45 (92%) were normal; of radiographs not submitted, 22 (50%) were normal. Radiographs with normal-appearing hips were 8.2 times as likely to be submitted to the OFA. Compared with Golden Retrievers, Rottweiler radiographs were significantly more likely to be submitted for OFA certification.

CONCLUSIONS AND CLINICAL RELEVANCE

Prevalence of CHD in these 2 breeds may be much higher than previously reported in the United States. Results suggest substantial bias in the OFA database, which causes lower estimates of prevalence of CHD.

Anatomic considerations for the choice of surgical approach for hip resurfacing arthroplasty

A number of surgical exposures have been advocated over the past 20 years by the pioneers of resurfacing hip arthroplasty and include the anterior, anterolateral, lateral, and posterolateral approaches. Not all of these approaches, however, appear to provide adequate exposure while respecting the local biology that seems to be imperative for the procedure. Based on an anatomic study, the most "bio-logical" surgical approach for hip resurfacing arthroplasty appears to be through a lateral or posterolateral approach using a digastric trochanteric osteotomy combined with an anterior hip dislocation. These exposures avoid injury to the medial femoral circumflex artery supplying the femoral head and allow access and treatment to the commonly observed hip pathologies that are frequently located anteriorly.

Anatomical study of the proximal femur in the fetus

Two angles effectively describe the upper femur geometry: The neck shaft angle (NSA) and anteversion (AV). AV and NSA decrease from birth until they reach their adult values, but little work has focused on in-utero life. Our aim was to determine if and how AV and NSA change through the fetal life. Eighty-seven femurs from 44 formalin preserved fetuses were sampled to achieve a biometry. Correlation tests and linear regression showed that AV was highly correlated with age: AV increases during the second half of gestation. No conclusion can be given concerning NSA. It is speculated that these changes may be caused by mechanical stresses.

Potential of P40 plastination for morphometric hip measurements

Total hip replacement has become one of the most successful surgical operations over the past 25 years. The duration of a total hip prosthesis depends on primary stability, and many studies have tried precisely to evaluate hip joint morphology to obtain excellent contact between bone and prosthetic component. This study performed a morphometric analysis of the human hip joint using, for the first time, the P40 plastination procedure. We cut 42 hip joint compounds into slices 3 mm thick; for exact distance measuring the sections were scanned into the computer. The following mean measurements for hip geometry were obtained: vertical diameter of acetabulum 4.894+/-0.274 cm, depth of acetabulum 1.643+/-0.245 cm, femoral head radius 2.268+/-0.149 cm, femoral neck length 4.3670+/-0.528 cm, acetabular perimeter 6.711+/-0.434 cm, vertical diameter of labrum acetabulare 4.759+/-0.476 cm, depth of labrum acetabulare 2.599+/-0.395 cm, sum of femoral head and neck lengths 6.759+/-0.550 cm, hip axis length 11.859+/-1.007 cm, femoral neck axis length 10.12+/-0.555 cm, and femoral neck diameter 3.349+/-0.276 cm. All of these data reveal a significant gender difference. Our aim was to indicate an unconventional and new method of gaining morphometric hip data by using plastination.

Angular orientation of trabecular bone in the femoral head and its relationship to hip joint loads in leaping primates

The elastic properties and mechanical behavior of trabecular bone are largely determined by its three-dimensional (3D) fabric structure. Recent work demonstrating a correlation between the primary mechanical and material axes in trabecular bone specimens suggests that fabric orientation may be used to infer directional components of the material strength and, by extension, the hypothetical loading regime. Here we quantify the principal orientation of trabecular bone in the femoral head and relate these principal fabric directions to loading patterns during various locomotor behaviors. The proximal femora of a diverse sample of prosimians were scanned using a high-resolution X-ray computed tomography scanner with resolution of better than 50 mum. Spherical volumes of interest were defined within the femoral heads and the 3D fabric anisotropy was calculated using the mean intercept length and star volume distribution methods. In addition to differences in bone volume and anisotropy, significant differences were found in the spatial orientation of the principal trabecular axes depending on locomotor behavior. The principal orientations for leapers (Galago, Tarsius, Avahi) are relatively tightly clustered (alpha(95) confidence limit: 8.2; angular variance s: 18.2 degrees ) and oriented in a superoanterior direction, while those of nonleapers are more variable across a range of directions (alpha(95): 16.8; s: 42.0 degrees ). The mean principal directions are significantly different for leaping vs. nonleaping taxa. These results further suggest a relationship between bone microstructure in the hip joint and locomotor behavior and indicate a similarity of loading across leapers despite differences in kinematics and phylogeny.

The natural history of human gait and posture. Part 2. Hip and thigh

The human fossil record is one of the most complete for any mammal. A basal ancestral species, Australopithecus afarensis, exhibits a well-preserved postcranium that permits reconstruction of important events in the evolution of our locomotor skeleton. When compared to those of living apes and humans, it provides insights into the origin and design of the modern human frame. Evolutionary aspects of the human hip and thigh are reviewed, including the unusual corticotrabecular structure of the human proximal femur, and our markedly elongated lower limb. It is postulated that the latter may be more related to birthing capacity than to locomotion.

A review of hip arthroscopy and its role in the management of adult hip pain

The diagnosis and management of patients presenting with hip pain is often challenging. A thorough history and physical examination, imaging studies and selective injections can help define the source of pain in many of these individuals. As technology and technical skills continue to improve, the role for hip arthroscopy will continue to expand. Further well-designed studies will better refine the indications for hip arthroscopy in managing patients with hip pathology.

[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.

Computed tomographic measurements of the hip morphology of 10 healthy German shepherd dogs

Linear measurements were made by computed tomography of the diameter of the femoral head, the width and depth of the acetabulum and the dorsal and ventral acetabular rim distances in 10 healthy German shepherd dogs, and angular measurements were made of the axial acetabular index, acetabular anteversion, and the dorsal and ventral centre-edge angles. There were no significant differences between the measurements made on the left and right sides. The width of the acetabulum was about twice its depth, and was a little larger than the diameter of the femoral head. The mean values of the axial acetabular index, acetabular anteversion, and ventral and dorsal centre-edge angles were 100.9 degrees, 25.1 degrees, 48.0 degrees and 12.2 degrees, respectively.

The normal hip joint space: variations in width, shape, and architecture on 223 pelvic radiographs

OBJECTIVES

To determine the range of normal radiographic joint space width (JSW) values and the shape of the normal hip, and the influence of age, sex, dysplasia, coxa profunda, and acetabular roof curve abnormalities on these values.

METHODS

On routine conventional pelvic radiographs taken in the supine position in patients with no history of hip or lumbar pain, JSW was measured at three points (superolateral, apical, superomedial), together with the VCE, HTE, and neck shaft angles; acetabular depth; and femoral head diameter.

RESULTS

223 radiographs (446 hips) from 127 women and 96 men (mean age 51.3 years) were examined. Interindividual variations in JSW were large (apical site: 4.19 (0.92) mm; range 2-7). Mean JSW values were higher at the superolateral site than at the apical and superomedial sites in nearly 80% of cases. Women had lower JSW values than men. JSW values did not fall with age. Marked right/left JSW asymmetry was seen in 13/221 (5.9%) subjects. Eight cases of acetabular dysplasia (7 unilateral) and 16 cases of coxa profunda were found, but no cases of acetabular protrusion. The JSW was thicker in dysplastic hips, and thinner in hips with coxa profunda. A roof curve abnormality was found in 96/446 (21.5%) hips.

CONCLUSIONS

Normal JSW values vary widely; the JSW is commonly narrower at the superomedial site than at the apical site, and is sometimes asymmetric. The roof curve is dysmorphic in about 20% of patients. These findings may have important implications for epidemiological studies and early diagnosis of osteoarthritis of the hip.

Factors influencing hip joint space in asymptomatic subjects. A survey of 4151 subjects of the Copenhagen City Heart Study: the Osteoarthritis Substudy

OBJECTIVE

The aims of the study were to investigate the distribution of hip joint space width (JSW) in asymptomatic subjects without radiologic evidence of degeneration, and investigate the influence of age, sex, physical parameters, occupational activity, and smoking on JSW.

MATERIALS AND METHODS

The distribution of minimum JSW was determined in hip joints in standardized, weight-bearing pelvic radiographs of the Copenhagen City Heart Study: The Osteoarthritis Substudy cohort of 4151 subjects. Asymptomatic subjects without radiologic osteoarthritis were included (1018M/1554F). Occupational exposure to repeated daily lifting, smoking, and physical parameters were registered for each individual.

RESULTS

Overall, female minimum JSW was significantly smaller compared with male JSW (P < 0.0001). Female minimum JSW decreased significantly with age (P < 0.0001), while male minimum JSW remained relatively unaltered throughout life (P(right) = 0319, P(left) = 0.18). Minimum JSW correlated positively with height, weight, and BMI, as did femoral head radius. Multiple logistic regression analysis revealed significant influence of sex and age on minimum JSW in females only. Positive or adverse effects of cigarette smoking on hip JSW were not documented. Type and duration of occupational exposure to repeated daily lifting did not affect hip JSW significantly.

CONCLUSION

Minimum JSW decreased progressively with age in women, while it was unaltered in men. A history of smoking or different occupational exposure to repeated daily lifting did not influence minimum hip JSW significantly. Differences in body mass index, height or weight did not significantly influence minimum hip joint JSW.

Variations of caudal, central, and cranial acetabular anteversion according to the tilt of the pelvis

Variations of acetabular anteversion measured at the level of the diameter of the acetabulum according to the tilt of the pelvis are known. But the values of this anteversion at other levels of the acetabulum, near the roof or near the obturator foramen, are unknown. Attracted by the very changeable morphology of the acetabular cover, we studied the caudal, central, and cranial acetabular anteversion of 12 pelvises in four positions of dorsal-ventral inclination. The caudal, central, and cranial acetabular anteversion diminished with the ventral tilt of the pelvis. The anteversions also diminished from the caudal part of the acetabulum to the cranial part, whatever the inclination of the pelvis. These notions represent a reference that, once completed with clinical studies of healthy volunteers and patients presenting an anomaly of the acetabulum cover, will enable researchers to define threshold values of normal and pathological conditions.

False profile radiography for the evaluation of Legg-Calvé-Perthes disease

False profile radiography (FPR), as proposed by Lequesne and de Sèze, depicts the pathology on the anterolateral acetabular wall and femoral head. A study was conducted to find out the differences between normal anteroposterior radiography and FPR. Twenty-seven patients with Legg-Calvé-Perthes disease who had not been operated on previously and 50 recruits without any pathology were studied for the acetabulum-head index of Heyman-Herndon (HHI) and center-edge angles (CEs) in antero-posterior radiographs and VCA angles in FPR. The VCA angle is most useful to detect anterolateral coverage of the femoral head in lateral pillar C hips. FPR is an easy, reliable and cheap technique to evaluate the anterolateral parts of the femoral head, and the acetabulum.

Southwick's head-shaft angles: normal standards and abnormal values observed in obesity and in patients with epiphysiolysis

Southwick's angles measured in the anteroposterior and Lauenstein frog-leg views have been used for planning surgical treatment of deformities caused by slipped capital femoral epiphysis (SCFE). Clinically established epiphysiolysis is associated with a decrease in anteroposterior angles and an increase in Lauenstein angles. Obesity is one of the factors involved in the development of SCFE, but its influence in Southwick's angles has not been previously described. Additionally, few reports describe normal values adjusted for sex and bone age. In this study, we determined Southwick's angles in normal control participants (n=70), in patients with obesity (n=31) and in patients with epiphysiolysis (n=33). The intra-observer variations were 1.7 and 23.3% for the anteroposterior and Lauenstein angles, respectively. No significant differences were detected in the control group when these individuals were compared according to sex or chronological age. Obese patients showed a significant increase in the anterposterior angle when compared with control individuals. The hip with epiphysiolysis presented a significant reduction in the anteroposterior angle and an increase in the Lauenstein angle, when the same was compared with the contralateral hip or with the control values. In patients with unilateral SCFE the Lauenstein angle of the normal hip was detected as increased, which was possibly related to the obesity associated with decreased insulin resistance presented by these patients. We conclude that the detection of risk for developing SCFE should include an expanded clinical and radiological profile characterized by pubertal males who present obesity associated with insulin resistance and an increase in Southwick's anteroposterior angle.

Assessment of the functional method of hip joint center location subject to reduced range of hip motion

Motion analysis of the lower extremities usually requires determination of the location of the hip joint center. The results of several recent studies have suggested that kinematic and kinetic variables calculated from motion analysis data are highly sensitive to errors in hip joint center location. "Functional" methods in which the location of the hip joint center is determined from the relative motion of the thigh and pelvis, rather than from the locations of bony landmarks, are promising but may be ineffective when motion is limited. The aims of the present study were to determine whether the accuracy of the functional method is compromised in young and elderly subjects when limitations on hip motion are imposed and to investigate the possibility of locating the hip joint center using data collected during commonly studied motions (walking, sit-to-stand, stair ascent, stair descent) rather than using data from an ad hoc trial in which varied hip motions are performed. The results of the study suggested that functional methods would result in worst-case hip joint center location errors of 26mm (comparable to the average errors previously reported for joint center location based on bony landmarks) when available hip motion is substantially limited. Much larger errors ( approximately 70mm worst-case), however, resulted when hip joint centers were located from data collected during commonly performed motions, perhaps because these motions are, for the most part, restricted to the sagittal plane. It appears that the functional method can be successfully implemented when range of motion is limited but still requires collection of a special motion trial in which hip motion in both the sagittal and frontal planes is recorded.

A clinical method for locating the femoral head centre during total knee arthroplasty

Localisation of the femoral head centre (FHC) during total knee arthroplasty (TKA) is necessary when assessing the overall alignment of the leg using an extramedullary guide for the femur. On-table radiographs for this purpose are time consuming and inconvenient. We describe a clinical method for estimating the FHC: it is marked 1.5 cm lateral to the point where the femoral artery crosses the line joining the pubic tubercle and the anterior superior iliac spine. Using this method the estimated FHC was within 15 mm of the anatomic centre in 84% of cases, and within 24 mm in 99%. This translates into possible knee alignment errors of 2 degrees and 3 degrees, respectively. As alignment error of up to +/-3 degrees is compatible with satisfactory clinical results of TKA, our method provides useful approximation of the FHC. For greater accuracy however, an on-table radiograph is recommended.

Assessment of cartilage thickness utilising reflectance spectroscopy

A new principle for cartilage layer thickness assessments in joints is presented. It is based on the differences between the absorption spectra of cartilage and subchondral bone (containing blood). High-resolution ultrasound measurements of cartilage thickness were compared with reflection spectroscopy data from the same area of bovine hip joint condyles. A simple mathematical model allowed calculation of thickness and comparison with ultrasound data. The cartilage thickness was changed by being ground in short episodes. For thicker cartilage layers, a high degree of reflection in the 400-600 nm wavelength interval was seen. For thinner cartilage layers, the characteristics of the spectra of blood and bone dominated those of cartilage. The mean (+/- SD) thickness of intact cartilage was 1.21 +/- 0.30 mm (n = 30). In an exponential regression model, spectroscopic estimation of cartilage thickness showed a correlation coefficient of r = 0.69 (n = 182). For thinner cartilage layers (d < 0.5 mm), the mean model error was 0.19 +/- 0.17 mm. Results from a bi-layer Monte Carlo simulation supported the assumption of an exponential relationship between spectroscopy data and reference ultrasound data. The conclusion is that optical reflection spectroscopy can be used for cartilage layer thickness assessment.

Posterolateral minimal incision for total hip replacement: technique and early results

There presently exists in the arthroplasty community a new and heightened level of interest in minimally invasive techniques for total joint replacement. Several investigators have published their personal experience with differing techniques, all concluding that there are multiple advantages to this concept for total hip arthroplasty. The author's perception is that the advantages of minimally invasive posterolateral approach total hip arthroplasty are multiple. They include more rapid rehabilitation and more prompt return to activities of daily living. There has been a clear impression that patients experience less postoperative pain and improved satisfaction. A concomitant decrease in hospital stay has been noted. Patients undergoing the procedure today have an average length of hospital stay of 48 hours, which represents a 30% decrease in hospital stay over the last year. Other advantages include improved cosmesis and potentially reduced blood loss without increasing complication rates. Surgeons performing this procedure require familiarity with the local anatomy, because the technique is certainly more demanding than is traditional arthroplasty. It is perhaps a technique best applied by surgeons performing more than 50 total hip arthroplasties a year. The two keys to successful application of the technique are adequate surgical training and use of specialized instrumentation. It is a difficult procedure to teach, because only one person is able to access a good view of the anatomy at any one time. With respect to component positioning, there may be a tendency to vertical cup placement early in one's experience. This is avoided by proper location of the skin incision and by use of a dog legged acetabular component inserter that facilitates proper positioning of the component despite the prominence of the distal angle of the skin incision. A tendency to eccentric reaming of the acetabulum may be noted if the proximal femur is not adequately retracted anteriorly. One must beware of the potential for inadvertent levering of the acetabular reamers on the posterior aspect of there tracted femur if the operative surgeon is not performing the reaming of the acetabulum. Particularly in patients who are larger there may be a tendency toward an excessively posterior starting point in the femoral canal when broaching the femoral component. This is best avoided by careful attention at this portion of the procedure to any pressure being applied to the broach handle by the proximal corner of the skin incision. The skin incision must be lengthened at this point if the problem presents. Finally, there remains a risk for proximal skin abrasion, particularly when one is beginning to decrease, the incision length in posterolateral approach to total hip arthroplasty. The evolution of proximal femoral elevators and skin protectors has decreased this risk to an extremely low level.

Minimally invasive hip replacement: rationale, applied anatomy, and instrumentation

The term minimally invasive hip replacement encompasses a diverse range of surgical approaches through which hip replacement may be performed. These surgical approaches are technically demanding and are best performed using specially designed instruments that help to compensate for the reduced surgical exposure. The early results using these techniques are encouraging, although the literature is lacking evidence from well designed prospective trials comparing MIS techniques with standard approaches. The studies that exist suggest that patient satisfaction is high, bleeding may be reduced, recovery of function may be faster, and there may be the potential to reduce lengths of hospital stay, and all this may be achieved without increasing complication rates. These results,however, have been achieved by a small number of high-volume surgeons, and the authors feel it is essential that as these techniques are introduced into widespread practice the results be studied carefully.

Hip-spine relationship: a radio-anatomical study for optimization in acetabular cup positioning

The criteria for acetabular cup positioning during total hip replacement are a matter of considerable discussion, particularly with regards to the optimal degree of anteversion. "Anatomical anteversion" is defined in the transverse plane, and "surgical anteversion" in the sagittal plane. Computed tomography measurements of anteversion are characteristic of a given transverse section plane and fail to take into account the position of the pelvis. We suggest a simple method for evaluating acetabular cup position in both the transverse and sagittal planes during standing and sitting. By shedding new light on the relationships between the pelvis and the spine, this method may help to understand some cases of impingement, instability or abnormal wear.

Comparable ultrasound measurements of ten anatomical specimens of infant hip joints by the methods of Graf and Terjesen

PURPOSE

To define which sonographic section planes relative to the acetabular inlet plane will produce analyzable images with the methods of Graf and Terjesen.

MATERIAL AND METHODS

Anatomical specimens of infant hip joints were investigated in a water bath using the methods of Graf and Terjesen. Acetabular position was varied in defined increments with respect to the ultrasound beam. The alpha angles and the femoral head coverage (FHC) were measured.

RESULTS

To obtain images analyzable by the two methods, the ultrasound beam had to intersect with the acetabular inlet plane at defined angles. The acetabular notch had to be anteriorly rotated from the ultrasound beam plane by at least 20 degrees. Beam entry within a 50 degrees sector posterior to the perpendicular on the inlet plane resulted in analyzable images. The stepwise multiple linear regression analysis showed that alpha angles and FHC were much affected by the coronal-plane transducer tilt.

CONCLUSION

The fact that caudal tilts of the transducer are associated with reduced alpha angles and FHC values should be kept in mind in clinical ultrasound investigations. It is recommended that the transducer should be put on the greater trochanter perpendicular to the transverse axis of the body.

[Artificial contrasting of the hip joint in children and adolescents: X-ray anatomic study]

The diagnostic capacities of currently available radiation diagnostic techniques in imaging some anatomic structures of the hip joint (HJ) were determined on the basis of studies of 70 sectional sets of HJs in children and adolescents aged 0 to 13 years through X-ray and anatomic comparisons. Magnetic resonance imaging (MRI) is the method of choice in visualizing the cartilaginous and soft-tissue structures of HJ in children and adolescents. MR-arthrography extends the capacities of the technique in imaging the articular surfaces and intraarticular structures of the joint. Contrast enhancement of the HJ cavity during X-ray study and computed tomography may be an alternative to MRI as it makes it possible to well visualize the cartilaginous head of the femur, the cartilaginous borders of the cotyloid cavity, the limbus, etc. Double contrasting enhances the capacities of detailed imaging of the articular surfaces, intraarticular structures, capsules, and ligamentous apparatus of HJ. The studies performed have specified the time course of anatomic changes during HJ growth and defined the method of choice or an alternative procedure of radiation techniques in the diagnosis of these changes, which is of great importance for early detection of pathological changes and for choice of therapeutic and diagnostic policy.

Effect of slide track shape on the wear of ultra-high molecular weight polyethylene in a pin-on-disk wear simulation of total hip prosthesis

Prosthetic joints appear to show a strong relationship between the type of relative motion and wear, requiring careful consideration in the design of wear simulators. This relationship was studied with a 12-station pin-on-disk device, specifically adapted for the wear simulation of prosthetic hip joints. Each station had a unique motion, characterized by the so-called slide track, the track of the pin on the disk. The slide track shapes included 10 ellipses, their aspect ratio (AR) varying from 1.1 to 11.0, and a circle and a straight line as extreme cases. Hence for the first time in hip wear simulation, the motion was systematically varied over a wide range. Conventional UHMWPE pins were tested against polished CoCr disks in diluted calf serum three times for 3 million cycles. Below the AR value of 5.5, the polyethylene wear factor and wear mechanisms agreed with clinical observations. Above this value, the wear factor decreased to unrealistically low values, and the wear surface topography differed from that of retrieved acetabular cups. The wear particles, however, were similar to those isolated from periprosthetic tissues, irrespective of the AR value. In conclusion, it is recommended that the AR value be kept well below the critical point of 5.5.

Radiographic evaluation of screw position in revision total hip arthroplasty

Injury to intrapelvic structures during removal of screws in revision acetabular arthroplasty is an uncommon, yet potentially serious complication. Bicortical screws are at greatest risk for causing injury during removal, especially if directed toward intrapelvic vessels and nerves. Complications can be minimized with thorough evaluation of screw position before revision surgery. A study of seven cadaveric pelves was done to determine if plain radiographic views provide useful information regarding screw position. In each pelvis, bicortical transacetabular screws were fixed in all acetabular quadrants 15 mm longer than the measured depth. Afterward, anteroposterior, inlet, Judet, and cross-table lateral radiographic views were obtained and intrapelvic dissections were done. Radiographs and intrapelvic dissections were compared to determine screw position. We found that the obturator and iliac oblique (Judet) views were most useful in defining screw position. The iliac oblique view clearly revealed screws that violated the quadrilateral surface and therefore were directed toward the obturator vessels and nerve. The obturator oblique view revealed screws that violated the anterior column and therefore were directed toward the external iliac vessels. The lateral view additionally clarified such screws by determining general anterior or posterior direction.

Reproducibility of fan-beam DXA measurements in adults and phantoms

As part of a multicenter study, we examined the intersite reproducibility of bone mineral content (BMC) and areal density (BMD) among three fan-beam dual-energy X-ray absorptiometry (DXA) instruments from one manufacturer, all using the same software version. Spine, femur, and body-composition phantoms were each scanned nine times at each center. Over a 3-wk period, the same 10 adults were scanned once at each of the three centers. For the spine and femur phantoms, the precision errors were 0.3-0.7%. For the body-composition phantom, the precision errors were 0.8-2.8%. The intersite coefficients of variation for the human measurements varied from 1.1 to 6.8%, depending on the bone site. We conclude that even when using the same fan-beam DXA model and software, an intersite cross-comparison using only phantoms may be inadequate. Comparisons based solely on the use of a spine phantom are insufficient to ensure compatibility of human bone mineral data at other bone sites or for the whole body.

Stripe wear rates in alumina THR?Comparison of microseparation simulator study with retrieved implants

Alumina-on-alumina hip implants with microseparation were run in a hip simulator for comparison of the nonseparation simulator mode and retrievals. The 28-, 32-, and 36-mm Biolox-forte implants were run to 5 million cycles with the use of 50% newborn calf serum. Howmedica Osteonics Trident cups with titanium backing were used in all sets. In standard (STD) and microseparation (MSX) mode, the typical biphasic wear trend was evident, but the MSX test mode had much higher magnitudes. There was a 5-fold increase for run-in wear and up to a 35-fold increase in steady-state wear. The stripe wear on the ball formed early, but did not progress in grade beyond 0.6 Mc. The locations of the stripes were similar in retrieved and simulator balls. However, the stripes from the simulator were narrower than short-term retrievals and much narrower than some long-term retrievals. The long-term retrieved balls had a grade of wear greater than the simulators. In vivo a broader range of motion occurs and this may lead to the wider stripe observed on the retrievals. These observations suggested that simulators could produce the loading and kinematics similar to a patient walking but not necessarily the variety of motions possible in the in vivo situation.

Bone mineral density and hip axis length in Singapore's multiracial population

Ethnic differences in bone density and hip geometry are known to exist, even within the same population. A recent study in Singapore showed that there were significant racial differences in hip fracture rates, with Chinese having the highest incidence of hip fractures. The aim of this study was to compare the bone mineral density (BMD) and hip axis length in Chinese, Malay, and Indian women. A total of 1575 women aged 20-59 yr were recruited, of which 77.6% (1222) were Chinese, 7.7% (122) Malays, and 14.7% (231) Indians. There was no significant difference in peak BMD of both lumbar spine and femoral neck among the three ethnic groups. However, in the older age group (50-59 yr), both Chinese and Malay women had significantly lower femoral neck BMD compared to Indian women. There was no significant loss in BMD of the lumbar spine between the second and fifth decades in all the three races. Between the second and fifth decade, Chinese and Malay women had significant bone loss in the femoral neck of 6.6% and 8.2%, respectively, whereas Indian women did not show any significant bone loss. Chinese women had significantly longer hip axis length compared to either Malay or Indian women (9.87 +/- 0.52 cm vs 9.67 +/- 0.49 cm; p < 0.005; and 9.69 +/- 0.55 cm, p < 0.05, respectively). The initial findings suggest racial differences in bone density and hip geometry exist in the local community. Future research should include prospective, longitudinal studies to determine the age-related bone loss in these three racial groups. It is also important to investigate the differences of spine and hip fracture rates and their relationship with bone density and hip axis length.

Morphological characteristics of the acetabulum

The aim of this research was to accurately measure the surface of the semi lunar articular surface of the pelvis (facies lunata acetabuli) and the variability of the acetabular geometry, as well as to determine the correlation between measured parameters. 30 macerated anatomical specimens of pelvic bones were measured. The radius and depth were measured in the classical way, while cartilaginous surface area was measured using small fragments of measuring paper to avoid errors in measurement due to the curvature of the surface. Computerized calculations provided accurate surface values. In our research, facies lunata acetabuli measured 2294+/-329 mm2. Diameter of the opening of the acetabulum measured 25.8+/-1.9 mm. Acetabular depth was 30+/-3.2 mm. Correlations between the surface area of the facies lunata acetabuli and the radius of the acetabular opening curvature (r=0.71), surface area of the facies lunata acetabuli and the depth of the acetabulum (r=0.80) and the radius of the acetabular opening curvature and the depth of the acetabulum (r=0.80) were confirmed. For precise assessment of the facies lunata acetabuli surface area, the simplest and the cheapest method is the method of measurement using small fragments of measuring paper and software analysis. There is a significant correlation between the depth, opening of the acetabulum and surface area of the facies lunata.

Discriminatory ability of quantitative ultrasound measurements is similar to dual-energy X-ray absorptiometry in a Brazilian women population with osteoporotic fracture

The discriminating ability and relevance of clinical risk factors, quantitative ultrasound (QUS) variables, X-ray-based bone mineral density (BMD) and hip axis length (HAL) measurements to evaluate the risk of osteoporotic fracture in elderly Brazilian women were examined in this study. QUS at the calcaneus (Achilles +, Lunar), HAL and BMD measurements (DPX-L, Lunar) at several anatomical sites were performed in 275 postmenopausal Caucasian women. Patients with suspected secondary osteoporosis were excluded. One hundred twenty-two (44.4%) women had had previous osteoporotic fracture. All of the subjects were over 50 years old (range 53-93) and answered a questionnaire that included details concerning aspects of lifestyle, diet, hormonal factors and drug use. Lateral thoracic and lumbar radiographs were taken and an independent radiologist reviewed the X-rays for the presence of vertebral fractures. After adjustments for age, the most relevant risk factors to discriminate patients with osteoporotic fracture from normal non-fracture controls were Stiffness index (OR 2.8 per standard deviation; 95% confidence interval 2.3, 8.7), familial history of hip fracture (OR 2.6 per standard deviation; 95% confidence interval 2.2, 5.4), femoral neck BMD (OR 2.3 per standard deviation; 95% confidence interval 1.9, 4.2), age (OR 2.1 per standard deviation; 95% confidence interval 1.6, 2.8) and weight (OR 1.9 per standard deviation; 95% confidence interval 1.5, 2.6). HAL measurements did not associate significantly with the risk of hip fracture in this population. The ability of QUS measurements discriminate between patients with fractures from those without was similar to, if not better, than X-ray-based BMD measurements. However, a combination of QUS and BMD measurements did not significantly improve fracture discrimination compared with either technique alone. Association of clinical risk factors with QUS or BMD measurements seems, on the other hand, to increase the sensibility to identify patients at risk of osteoporotic fractures.

Acoustic transmission in normal human hips: structural testing of joint symmetry

An acoustical technique has been developed for the measurement of structural symmetry of the hip joints. A mild vibratory force was applied to the sacrum and sound signals were picked up at both hips by a pair of microphones installed in two stethoscopes. These stethoscope-microphone assembles were calibrated to achieve a difference in relative sensitivity of less than 0.2 dB. The relative transmission of sound signals was analysed and compared between both hips by a dual-channel signal analyser. Twenty-seven healthy adults, 20 healthy pre-school children and 19 normal neonates were tested. Results from these three groups showed high coherence of the sound signals and that the discrepancy between both hips was smallest in the frequency range of 200-315 Hz. For normal neonates, the sound signals maintained a high coherence (gamma2>0.97) and small discrepancy (D<1.25 dB) between both hips. This study has shown that the acoustical technique provides a practical structural testing for bony symmetry of the hips and the results offer a baseline for further investigation into developmental dysplasia of the hip (DDH) in neonates. Clinical screening for DDH is still problematic in developing countries.

An approach for hip joint center calculation for use in seated postures

In seated postures, such as those in office or automotive seats, locating the hip joint center (HJC) using three markers on the pelvis has been difficult if not impossible. A two-target approach by Bell et al. (J. Biomech. 23 (1990) 617) has been used, however, this method was shown to have inaccuracies when compared to the three-target method developed by Seidel et al. (J. Biomech. 28 (1995) 995). A new two-target method that is specific to the seated environment, has better accuracy than the Bell et al. approach, and is based on the Seidel et al. approach was developed and tested on 13 seated subjects. This new method used three targets and an initial reference file to estimate the HJC location. Once the HJC was located, assumptions were made that the magnitudes between the HJC and the respective anterior superior iliac spine, and the HJC and the respective lateral epicondyle remained constant. The primary concern when evaluating this new method was the affect of seated posture movement, in particular leg splay and spinal flexion on the assumptions. The results obtained with the new approach were compared to Seidel et al. and provided HJC locations with average differences of 3.8, 1.2 and 2.8mm for spinal flexion in the anterior/posterior, medial/lateral and superior/inferior directions, respectively, and 2.3, 1.0 and 1.4mm for knee splay. The proposed method provided better HJC estimation than the Bell et al. approach particularly in the superior/inferior dimensions.

A sonographic study of perinatal hip development: from 34 weeks of gestation to 6 weeks of age

A sonographic study of perinatal hip development was performed by consecutive measurement of Graf's alpha and beta angles in fetal and newborn hips. The study group consisted of infants with sonographically normal hip findings at birth. Forty fetuses were examined by fetal hip sonography at 34, 36 and 38 weeks of gestation. Postnatally, hip sonography was performed in the first and sixth week of age. Maturation curves of the bony (alpha-angle) and cartilaginous (beta-angle) acetabular roof from 34 weeks of gestation to 6 weeks of age were established. Prenatally, the mean alpha-angles were above the level that corresponds to a mature hip joint. A significantly higher value of the mean alpha-angles was found after birth. The mean beta-angles of the fetuses did not differ from those of the newborns. Our results revealed that the fetal hip joint is sonographically mature at 34 weeks of gestation. Further progression of hip development occurs around term.

Long-term wear of ceramic matrix composite materials for hip prostheses under severe swing phase microseparation

The purpose of this study was to evaluate the long-term wear performance of alumina matrix composite (AMC) heads against alumina matrix composite inserts and alumina matrix composite heads against alumina (Al) inserts with the use of a hip-joint simulator incorporating severe swing phase joint microseparation. The wear of AMC on Al produced an average wear rate of 0.61 mm3/million cycles over the 5-million-cycle test duration. The wear of AMC on AMC produced an average wear rate of 0.16 mm3/million cycles over the 5-million-cycle test duration. Both the AMC on alumina and AMC on AMC produced significantly lower wear than previously tested HIPed alumina, where an average wear rate of 1.84 mm3/million cycles was reported over 5 million cycles. The wear mechanisms and wear debris of AMC on AMC and AMC on Al were similar to those observed in previous alumina retrieval studies with stripe wear caused by intragranular fracture and wear debris consisting of predominantly uniform 10-20-nm-sized particles and a few irregular particles up to 3 microm in size.

Anterior acetabular head index of the hip on false-profile views. New index of anterior acetabular cover

The vertical-centre-anterior margin (VCA) angle quantifies the anterior cover of the femoral head. However, when the femoral head is deformed it may be difficult to identify its centre. We have therefore created a new index, the anterior acetabular head index (AAHI) which is measured on the false-profile radiograph. We measured the VCA and AAHI angles in 312 hips in which the centre-edge angle was >25 degrees. There were 250 patients, 86 men and 164 women, whose ages ranged from 20 to 65 years. The mean AAHI was 84.1% (81.7% in women and 88.5% in men). There was a correlation between the AAHI and VCA angles. Our data suggest that the AAHI is useful in the evaluation of anterior acetabular cover and that it is higher in men than in women.

The shape of the Neandertal femur is primarily the consequence of a hyperpolar body form

Neandertal femora are distinct from contemporaneous near-modern human femora. Traditionally, these contrasts in femoral shape have been explained as the result of the elevated activity levels and limited cultural abilities of Neandertals. More recently, however, researchers have realized that many of these femoral differences may be explained by the cold-adapted bodies of Neandertals vs. the warm-adapted bodies of near-modern humans. This study explicitly tests this proposed link between climate-induced body proportions and femoral shape by considering the entire hip as a unit by using geometric morphometric methods adapted to deal with articulated structures. Based on recent human patterns of variation, most contrasts in shape between the femora of Neandertals and near-modern humans seem to be secondary consequences of differences in climate-induced body proportions. These results, considered in light of hip mechanics during growth, highlight the importance of developmental and functional integration in determining skeletal form.

Hip geometry and its role in fracture: what do we know so far?

As the number of hip fractures continues to rise, finding better ways to identify people at risk becomes crucial. In the past decade, several measures of hip geometry have been studied as possible risk factors for hip fracture. Among them, hip axis length (HAL) shows the greatest promise for enhancing fracture risk assessment in the clinical setting, followed by neck shaft angle (NSA) and femoral neck width (FNW). Studies have shown that both age and/or a loss of body weight are associated with changes in some of the geometric parameters, which subsequently indicate the decrease in hip strength. The greater hip strength in black women and men resulting in a lower incidence of fractures compared with white women is also attributed to more favorable geometric parameters. Asian women, who have a lower incidence of fractures than white women, have a shorter HAL and a smaller NSA. In general, a longer HAL and a greater NSA and FNW all increase the risk of fracture, though controversies exist due to the use of different subject populations and measurement tools. Overall evidence suggests assessing hip geometry para-meters can significantly improve the ability of identifying people at risk of fracture, but more development in measurement software and more research are necessary to make it applicable in clinical settings.

Tomographic study of the arthroscopic approaches to the hip joint

PURPOSE

The anatomic depth of the hip joint has long been one of the limiting factors in the development of arthroscopy of this particular joint. A major factor would seem to be variation in body size. The main purpose of this study was to quantify the distance between the joint and the skin in usual arthroscopic approaches.

TYPE OF STUDY

In vivo radiologic study using computed tomography.

METHODS

We studied the distance from the center of the acetabulum to the skin. The lines that we studied correspond to the paratrochanteric, the anterolateral, and anterior arthroscopic entry points.

RESULTS

Although notable differences exist from one individual to another, the average values of the aforementioned are 12.4 cm, 11.2 cm, and 9.8 cm, respectively. The distances of these portals are greater in women than in men (P <.05), and there is no statistically significant relationship to age.

CONCLUSIONS

The results of the present work suggest that surgical tools needed for arthroscopy of the hip should be more than 16 cm long to guarantee performing hip arthroscopy comfortably in more that 95% of the population.

Age and sex differences in hip joint space among asymptomatic subjects without structural change: implications for epidemiologic studies

OBJECTIVE

The prevalence of hip osteoarthritis (OA) increases significantly with age. Although it is not clear whether joint space loss at the hip is a feature of normal aging or a reflection of the OA process, epidemiologic criteria for OA are based on narrowing alone. The aim of this study was to determine whether changes in joint space width occur with age, and whether there are sex differences, in asymptomatic subjects without hip OA.

METHODS

We identified a total of 1,806 subjects who had undergone intravenous urography between 1994 and 1996 and sent a questionnaire to the 1,527 of these subjects who were alive in 1998; 1,031 replies (68%) were received. All radiographs were read by an observer blinded to age, sex, and pain status. Individual radiographic features of OA (narrowing, osteophyte, sclerosis, and cysts) were graded, and an overall qualitative grade was allocated, according to a standard atlas. Minimum joint space width (JSW) was measured by metered caliper to within 0.1 mm. A total of 276 women (mean age 63 years) and 257 men (mean age 64 years) were identified who had never had hip pain (defined as having ever had pain on most days for at least 1 month) and who had no evidence of either joint space narrowing or osteophyte (grade 0, no structural changes). The minimum JSW in either hip was tabulated according to age.

RESULTS

JSW measurement was reproducible (95% confidence limits of agreement) to within +/-0.5 mm. At all ages, men had larger JSW than women (3.85 mm in women, 4.19 mm in men, mean difference 0.34 mm; 95% confidence interval [95% CI] 0.24, 0.44). A significant decline in JSW with age was seen in women, with a mean difference between ages 45-54 and 75-84 years of 0.36 mm (95% CI 0.15, 0.58; P = 0.001). No significant change in JSW with age was seen in men (mean difference 0.16 mm; 95% CI -0.11, 0.43). Analysis of an additional 64 women and 61 men who were without hip pain and had overall qualitative grade 1-2 changes gave similar results. Implementing these results to alter the threshold for definition of hip OA in women from < or =2.5 mm to < or =2.2 mm reduced the prevalence of hip OA from 10.6% to 5.6%.

CONCLUSION

These sex differences in joint space have significant implications in terms of the major emphasis on joint space narrowing in definitions of hip OA. Women also have a significant progressive decline in joint space with age that is not seen in men. This suggests that in women, loss of cartilage may be an age-related phenomenon that is independent of other aspects of structural change. Consideration should be given to the development of sex-specific definitions of hip "OA."

[Normal values of several acetabular angles on hip radiographs obtained from individuals living in the Eskişehir region]

OBJECTIVES

To determine the normal values of several radiographic acetabular angles in individuals of Eskişehir region.

METHODS

The acetabular index (AI) angle, acetabular angle (AA) of Sharp and the ACM angle were measured in 1162 normal hips (n=581, 251 males, 330 females; mean age 33 years; range 5 to 75 years). For AI angle, Hilgenreiner's line and the line connecting the lower end points of the sclerotic lines of the acetabular roofs were used for reference in subjects between five to 11 years with an open Y cartilage and in those with closed Y cartilage, respectively. AA and ACM angles were measured by the same method in all subjects.

RESULTS

The mean AI angle between 5-11 years was 12.9+/-4.5 degrees; the upper normal limit for the Hilgenreiner's AI angle was derived as 22 degrees. The mean AI angle above age 11 was 3.3+/-4.7 degrees and the upper normal limit for the AI angle defined by Tönnis after age 11 was found as 13 degrees. Significant linear correlations were found between the AI angle and age for 5-11 years (p=0.002) and above 11 years (p=0.001), respectively. The mean AA angle was 39.2+/-4.6 degrees. There was a significant linear correlation between the AA angle and age (p=0.001). The upper limits for the AA angle in normal juvenile, adolescent, and adult hips were found as 52 degrees, 49 degrees, and 45 degrees, respectively. The mean ACM angle was 41.9+/-3.3 degrees. A significant linear correlation was observed between the ACM angle and age (p=0.001). The upper limit for the ACM angle in normal hips was assessed as 49 degrees in all age groups.

CONCLUSION

The authors of this study propose that the normal limits of acetabular angles obtained from our own population be used as reference values in interpreting standard radiographs of the hip.

Hip biomechanics: importance to functional imaging

Although well recognized the hip joint is not well understood. In many respects knowledge of the hip is similar to that of the knee several decades ago. Increased understanding of the hip's structure and function will improve our ability to diagnose and treat pre-end-stage hip joint disease. This article describes relevant anatomy and mechanics and details the crucial role that imaging plays in current assessments of hip function.

Hip arthroscopy in the pediatric population

Hip arthroscopy has obvious advantages over arthrotomy in the pediatric population. Hip arthroscopy, used as a diagnostic or therapeutic tool, is significantly less invasive than arthrotomy and allows for quicker recovery and return to activities. In addition, arthroscopy avoids dislocation of the femoral head and the corresponding risk of osteonecrosis. Current indications for hip arthroscopy in pediatric patients include septic arthritis, labral disorders, slipped capital femoral epiphysis, and Legg-Calvé-Perthes disease. The role of hip arthroscopy in the pediatric population will continue to expand because of its attractiveness as a less invasive option for evaluating the hip.

[The head-body index used to access femoral head size]

Basing on an analysis of 260 X-rays of healthy hip joints in children and adults the authors present a head-body index (according to Kruczyński), used to assess femoral head size. The index is defined as the ratio of the circumference of circle drawn around the femoral head to the body width of the femur (measured below the minor trochanter). In patients less than 17 years old the index was 170 (SD-14.6).

The femoral collodiaphyseal angle in Malawian adults

We used unilateral anteroposterior radiographs to measure the collodiaphyseal angle of the hip in 368 Malawian adults--222 men and 146 women 18 to 76 years old. The angle ranged from 105 degrees to 144 degrees (mean, 121.09 degrees; SD, 7.17 degrees). Results confirmed that the angle was wider in men than in women-indicating dimorphism based on sex--but no Malawian could be identified by sex using the recommended demarking point method of Jit and Singh (1966). The importance of the angle and its usefulness to practicing orthopedic surgeons in this part of the world are emphasized.

Traumatic hip dislocation in athletes

Sports injuries are increasingly prevalent. Dislocations of the hip are rare; however, they are seen in high-velocity sports such as football and rugby. The injuries may be described as anterior or posterior, and classified according to severity of injury. It is critical to the sports medicine practitioner to promptly recognize and manage this complex injury. This article presents a functional management algorithm including reduction techniques for the simple hip dislocation. Early reduction minimizes complications in all studies. Immediate on-field reduction has been performed successfully and safely in a limited number of cases. An aggressive rehabilitation protocol is proposed to assist the athlete back to sporting activity as soon as possible. The potential benefits of early reduction limit the risk of avascular necrosis of the femoral head and sciatic neuropathy; therefore, further investigation into the standard use of this immediate reduction technique is warranted.