Muscle forces acting on the greater trochanter lead to a dorsal warping of the apophyseal growth plate.

The apophyseal growth plate of the greater trochanter, unlike most other growth plates of the human body, exhibits a curved morphology that results in a divergent pattern resembling an open crocodile mouth on plain antero-posterior radiographs. To quantify the angular alignment of the growth plate and to draw conclusions about the function of the muscles surrounding it, we analyzed 57 MRI images of 51 children and adolescents aged 3-17 years and of six adults aged 18-52 years. We measured the angulation of the plate relative to the horizontal plane (AY angle) and the trajectories of the muscles attaching to the greater trochanter of the proximal femur. From anterior to posterior, the AY angle shows a decrease of 33.44°. In the anterior third, the cartilage is angled at a mean of 51.64°, and in the posterior third, the mean angulation is 18.6°. This indicates that the cartilage in the anterior region of the greater trochanteric apophysis is subject to more vertically oriented force vectors compared to the posterior region, as the growth plates align perpendicular to the force vectors acting on them. Combining the measured muscle trajectories with the physiological cross-sectional areas (PCSA) available from the literature revealed that, in addition to the known internal and external lateral traction ligament systems, a third, dorsally located traction ligament system exists that may be responsible for the dorsal deformation of the AY angle.

Does the Canal Fill Ratio and Femoral Morphology of Asian Females Influence Early Radiographic Outcomes of Total Hip Arthroplasty With an Uncemented Proximally Coated, Tapered-Wedge Stem?

BACKGROUND: Noncement femoral fixation in total hip arthroplasty (THA) has been gaining popularity. However, owing to the numerous varieties of uncemented stems and differing types of femoral stem morphology, it is unclear whether the clinical outcomes of all uncemented stems are equal. The aim of this study was to investigate the relationships between canal fill ratio and femoral morphology and early radiologic outcomes in Japanese patients who underwent THA with an uncemented proximally hydroxyapatite-coated, tapered-wedge stem. METHODS: We retrospectively reviewed 103 patients who had undergone THA using a single proximally coated tapered-wedge stem. The relationships between canal fill ratio and femoral morphology and early radiologic outcomes after THA with those stem were investigated. RESULTS: Eighty-one hips were analyzed after inclusion and exclusion criteria were applied. Failed osteointegration proximally was observed in 4 hips (4.9%). Canal flare index was significantly greater in hips with failed osteointegration than in those with successful osteointegration (P = .009). Distal hypertrophy was observed in 14 hips (17.3%). Proximal-distal matching ratio was significantly lower in hips with distal hypertrophy than in those without (P = .01). Canal fill ratio at 2 cm above the lesser trochanter was smaller in hips with failed osteointegration and distal hypertrophy than in those without (P = .02). CONCLUSION: Suboptimal radiologic changes were seen with greater distal fill with smaller proximal fill and with a narrow femoral canal. It is important to select the stem that can achieve the original concept of intended primary and secondary fixation areas.

Ultrasound-guided injection of the hip: Cadaveric description for the lateral approach.

BACKGROUND: Ultrasound (US)-guided intraarticular hip joint injections are commonly performed using an in-plane anterior approach, which has several limitations. OBJECTIVE: To describe and report a "lateral" (lateral to medial) approach for US-guided intraarticular hip injection. DESIGN: Cadaveric investigation. SETTING: Academic institution, department of anatomy. PARTICIPANTS: One cadaveric specimen. METHODS: Both hips of a single cadaver were injected using the US-guided lateral approach. In the left hip, the needle was inserted and kept in situ. The right hip was injected with white-colored water-diluted latex dye. Subsequently, a layer-by-layer anatomical dissection was performed. MAIN OUTCOME MEASURES: Presence and distribution of latex dye and location of needle tip within the joint capsule of the hip. RESULTS: Anatomical dissection of the left and right hips confirmed the correct intraarticular position of the needle tip and the placement of the latex dye, respectively. During layer-by-layer dissection of the left hip, positions of the lateral cutaneous nerve and the lateral circumflex femoral artery were observed anterior to the needle, 30 mm for the nerve and 8 mm for the artery. CONCLUSIONS: This preliminary study demonstrated that the US-guided lateral approach is a convenient technique to access the hip joint in a cadaveric specimen. Compared with the "classical" anterior technique, the lateral approach may provide several advantages, including improved needle visibility, theoretically decreased risk of vascular injury, and less risk of needle contamination. Because injury to the lateral epiphyseal arteries is possible when lateral approach is used, caution is required, especially in children. These preliminary conclusions will need to be validated in future/larger clinical studies.

Results of revision total hip arthroplasty with Anatomic BR stem: 10-year minimum follow-up.

Twenty cementless total hip revision arthroplasties using Anatomic BR stems were performed in 20 patients. Fourteen patients, with a mean age of 62.6 years (range 41-74 years) at time of revision surgery, were followed retrospectively for a minimum of 10 years (range 11-15 years). Clinical function and radiographic evidence of implant stability were evaluated. Preoperative femoral deficiencies were evaluated radiographically and classified according to Paprosky type as follows: four Type-II, four Type-IIIA, four Type-IIIB, and two Type-IV femurs. Mean preoperative Harris hip score was 46.3 points (range 29-58 points) and improved to 68.8 points (range 45-90 points) at the most recent follow-up examination. Of the 14 patients followed, six had radiographic evidence of subsidence (axial shift of more than 2 mm after revision with long-stem components). Component fixation showed bone ingrowth in three (21%) patients, inconclusive evidence of ingrowth in six (43%) patients, suboptimal but stable fixation in three (21%) patients, and unstable fixation in two (14%) patients. Based on these we results, we conclude that even with circumferential proximal porous coating and improved proximal geometry, nonmodular femoral implant stability remains unpredictable following total hip arthroplasty revision.

The effect of the Rim Cutter on cement pressurization and penetration on cemented acetabular fixation in total hip arthroplasty: an in vitro study.

The Rim Cutter (Stryker Orthopedics, Mahwah, New Jersey) is a tool designed to cut a ledge inside the rim of the acetabulum, onto which a precisely trimmed, cemented, flanged cup can be fitted. The aim was to investigate the effect of the Rim Cutter on the intra-acetabular cement mantle pressure and the depth of cement penetration during cup insertion. The study had two parts. In the first part, hemi-pelvis models were fitted with pressure sensors. Pressure in the acetabulum was measured on insertion of a conventional cemented flanged cup with and without the use of a Rim Cutter to prepare the rim of the acetabulum. The second part assessed cement penetration when the same cups were inserted into a foam shell model. The shell was mounted in a jig and had holes drilled in it; the distance that cement penetrated into the holes was measured. A significant increase in cement pressure at the apex (p = 0.04) and the rim (p = 0.004) is seen when the Rim Cutter is used. Cement penetration in the Rim Cutter group was significantly increased at the rim of the acetabulum (p = 0.003). Insertion of a flanged cup after the acetabulum is prepared with the Rim Cutter leads to a significant increase in cement pressure and penetration during cup insertion in vitro when compared with conventional flanged cups.

A new digital preoperative planning method for total hip arthroplasties.

Preoperative templating is an important part of a THA. The ability to accurately determine magnification of the hip on the radiograph and apply identical magnification to the radiograph and template will improve accuracy of preoperative templating of THA. We designed a templating method using a new way of determining the hip magnification with a linear relationship between magnification of the hip and the reference object on top of the pubis symphysis; the relationship was determined on 50 radiographs. We then compared our method with two other templating methods: an analog method assuming an average hip magnification of 15% and a digital method determining the hip magnification with a one-to-one relationship between the reference object and the hip. All methods were reproducible. Uniform undersizing occurred when templating with the digital method based on the one-to-one relationship; the analog method best predicted the implanted prosthesis size, closely followed by our new digital templating method; the new method will be particularly applicable for preoperative THA when analog methods are replaced by digital methods.

Structural response and relative strength of a laminated composite hip prosthesis: effects of functional activity.

To obtain a better appreciation for the structural performance of a laminated composite hip prosthesis (CP), we examined in situ prosthesis structural response and relative strengths as a function of walking and stair climbing using our previously developed analysis guidelines. Accordingly, we examined overall prosthesis structural response utilizing a global continuum level modeling approach and prosthesis relative strengths using a local microstructural (or ply-level) modeling approach. As a reference and control, we examined the structural performance of the intact natural femur (NAT) and a titanium alloy (Ti) based hip prosthesis. In terms of the overall structural response, i.e., the femur/prosthesis deformational response, stem/bone interfacial stress transfer, and calcar strain energy density restored, the performance of the CP prosthesis was moderately improved over that of the control Ti prosthesis and better approximates the NAT response. In terms of relative strength, we found that the neck of the CP prosthesis failed for all activities with the exception of the mid-stance phase of level walking. However, the prosthesis appears to have sufficient relative strength for function at positions distal to the neck of the prosthesis. While these results dampen enthusiasm for consideration of laminated composite hip prostheses designed with a shape based on a metal alloy implant, they indirectly support consideration of alternate hip prosthesis structural designs such as using a better supported prosthesis neck or utilizing metal/composite hybrid constructions. Importantly, our simulation and analysis approach could be utilized in the design of other laminated composite biomedical structural components.

The relationship between the density of the alveolar processes and that of post-cranial bone.

Skeletal mass declines in all populations with age, and the literature suggests that changes in oral bone may be linked to the status of the post-cranial (systemic) skeleton. However, there is a lack of information defining the relationship between alveolar process bone and the post-cranial skeleton in healthy individuals. The purpose of this study was to determine: (1) if the bone densities of the maxillary and mandibular alveolar processes are related to the bone density of the spine, hip, or radius in healthy women; and (2) if the alveolar process densities decline with age. Forty-one dentate Caucasian women aged 20 to 78 years underwent assessment of post-cranial (systemic) and alveolar process bone. D-speed vertical bitewing and periapical radiographs incorporating aluminum stepwedges, controlled exposure and processing conditions, and a density correction algorithm were used to make alveolar process density assessments with regions of interest (ROIs) apical to crestal bone and intrabony defects. Anteroposterior lumbar (L1 to L4) and lateral lumbar (L2 to L4) spine, total hip (and subregions), and radius bone densities were determined by dual-energy x-ray absorptiometry (DEXA). Correlation analysis revealed significant relationships between maxillary alveolar process bone density and the density of the mandibular alveolar process (r = 0.57, p < or = 0.001), anteroposterior lumbar spine (r = 0.53, p < or = 0.001), lateral lumbar spine (r = 0.52, p < or = 0.001), total hip (r = 0.39, p = 0.01), total radius (r = 0.39, p = 0.01), and age (r = -0.38, p = 0.01). A two-tailed t test comparison revealed significantly greater maxillary alveolar process bone density in women younger than 50 years of age than in those 50 and older (p < or = 0.01). We conclude that the density of maxillary alveolar process bone is significantly related to the density of the mandibular alveolar process, lumbar spine, hip, and radius in healthy women and that maxillary alveolar process bone density declines with age.

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.

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.

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.

Symposium on Surface Replacement Arthroplasty of the Hip. Biomechanics: mutifactorial design choices--an essential compromise?

The main flaws to be overcome in realizing the potential success of the double-cup arthroplasty procedure are failures due to femoral cup loosening, acetabular cup loosening, and femoral-neck fractures. The clinical uncertainties include the selection of a suitable patient with adequate bone stock and the technical difficulties associated with (I) reaming the acetabulum adequately, (2) reaming down onto the neck without violating it, and (3) anchoring the components securely by interdigitation of acrylic cement. The higher frictional torques of the double-cup arthroplasty designs are not a clinical loosening issue--the resulting acetabular cement-bone shear stresses are very low. Computer models of both the femoral and acetabular components predict significant stress shielding of the cancellous bone under metal femoral shells. At the rim of the femoral cup, the stresses are increased by a factor of 3 owing to the stress concentration effect and can rise to a factor of 10 if cystic or osteoporotic changes are present. This finding if confirmed in the three-dimensional models may explain some of the femoral neck fractures. The thin polyethylene acetabular cups may also cause a stress concentration effect on the underlying cement and bone. This may explain the higher incidence of radiographic loosening around the acetabulum in double-cup arthroplasty designs compared with total hip replacements. Metal-backed sockets may reduce cancellous bone stresses and appear advantageous. There is no clinical evidence of unusual wear or wear-related problems. However, new material formulations are now either in use or being planned for the double-cup arthroplasty designs. As yet, there have been no published data on hip simulator wear for the efficacy of any of the current or proposed changes. Biologic fixation appears to be the theme for the 1980s. However, the combination of technology, design instrumentation, and patient selection will be critical in achieving success with this technically difficult procedure.

Alveolar process fractal dimension and postcranial bone density.

OBJECTIVES: Our goal was to determine whether the radiographic fractal dimension of the maxillary and mandibular alveolar processes is related to bone density of the alveolar processes, spine, hip, and radius in healthy women. STUDY DESIGN: Thirty-seven dentate healthy white women aged 20 to 78 years underwent assessment of systemic and alveolar process bone. After a periodontal examination, D-speed vertical bite-wing and periapical radiographs with aluminum step wedges and a density correction algorithm were used to make alveolar process fractal dimension and density calculations within regions of interest that avoided crestal bone and intrabony defects. Anteroposterior (L1-L4) and lateral (L2-L4) lumbar spine, total hip, and total wrist densities were determined by means of dual energy x-ray absorptiometry. RESULTS: Correlation analysis revealed significant relationships between maxillary alveolar process fractal dimension and maxillary alveolar process density (r = 0.47, P < or =.01), mandibular alveolar process density (r = 0.48, P < or =.01), and mandibular alveolar process fractal dimension (r = 0.44, P < or =.05); and between mandibular alveolar process fractal dimension and maxillary alveolar process density (r = 0.54, P < or =.01) and mandibular alveolar process density (r = 0.58, P < or =.001). No significant relationships were found between the maxillary alveolar process or the mandibular alveolar process fractal dimension and the density of any postcranial regions. CONCLUSIONS: In healthy women, the alveolar process radiographic fractal dimension is significantly related to the alveolar process density but is not related to the density of the spine, hip, or radius.

The course of blood vessels in the hip joint capsule of the dog.

The course and the arrangement of capsular blood vessels in the joint capsule's wall, together with their extracapsular origins, were investigated using cleared specimens that had been injected with Latex, or Technovit, or India-ink in serum. Arteries enter areas of the joint capsule's wall near its femoral as well as coxal attachment. The intramural vascular network is arranged in layers which are assigned to the stratum fibrosum and stratum synoviale, with one or two intermediate, less distinct layers in between. The ramification in the network of the stratum fibrosum is mainly stellate. Circular anastomoses connecting the supplied areas are located in the capsule's periphery. In the stratum synoviale, the vascular network is made of close, elongated meshes in a circular extension.

A radiographic and histological analysis of 17 retrieved ultrahigh-molecular-weight polyethylene porous-coated femoral stems.

Radiographic and histological and evaluation for failure of 17 retrieved implants was performed. The implants consisted of a titanium stem with a 3-mm ultrahigh-molecular-weight polyethylene coating and an outer 1.5-mm ultrahigh-molecular-weight polyethylene fiber layer. Particular attention was paid to osteolysis, subsidence, debris, and foreign body reaction. Radiographic analysis showed subsidence (14 of 17), osteolytic lesions (9 of 14), and unique posterior medial exostoses (8 of 14). Histological analysis showed no significant evidence of acrylic bone cement either as debris or reactive tissue. There was an intense foreign body reaction directly related to the amount and size of polyethylene debris.

Total hip replacement using a highly crosslinked polyethylene liner in Asians with small acetabulum.

PURPOSE: To evaluate the medium-term outcomes of total hip replacement (THR) using a thin highly cross-linked polyethylene (HXLPE) liner in an Asian population. METHODS: Medical records of 20 men and 44 women aged 26 to 80 (mean, 59) years who underwent 80 THRs using a thin HXLPE liner by a single surgeon were reviewed. Indications for THR included dysplasia (n = 26), avascular necrosis (n=26), osteoarthritis (n = 22), rheumatoid arthritis (n = 4), and ankylosing spondylitis (n = 2). The surgical technique, implant used, and rehabilitation protocol were standardised. Radiographs were evaluated for cup migration and peri-implant radiolucency. Femoral head penetration was assessed at day 1 and last follow-up using the Kang modification of the Dorr and Wan method and the PowerPoint method. RESULTS: After a mean follow-up of 7.5 (range, 5.0-11.9) years, no patient had undergone acetabular revision. Two hips were revised for the femoral stem. Femoral head penetration did not correlate with sex, age at surgery, hip pathology, acetabular inclination angle, cup size, or liner thickness. The maximum femoral head penetration was 0.09 mm/year, which was below the osteolysis threshold of 0.1 mm/year. The mean ± standard deviation femoral head penetration was 0.29 ± 0.12 mm (or 0.04 ± 0.02 mm/year) by the PowerPoint method and 0.17 ± 0.22 mm (or 0.02 ± 0.03 mm/year) by the Kang modification of the Dorr and Wan method. Femoral head penetration correlated with the number of years of follow-up (p = 0.012). CONCLUSION: The use of a thin HXLPE liner in primary THR for patients with small acetabulum achieved good outcomes after a mean of 7.5 years.

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.

Development of a carbon-carbon hip prosthesis.

This article deals with the use of carbon-fiber-reinforced-carbon materials for the manufacture of hip prosthesis stems. It considers the manufacturing process of carbon-carbon (C-C) composites made of carbon fibers infiltrated either with dense pyrolytic carbon or silicon carbide (SiC) through chemical vapor infiltration. The chemicophysical properties of these composites are examined according to their structures. The long-term response (2 years) of cortical bone to various types of carbon-carbon was evaluated mainly for bone contact and ingrowth. Carbon-carbon coated with calcium phosphate was found to speed up the bone formation as compared to pyrolytic carbon or SiC coatings. The low modulus of elasticity of the C-C materials could be responsible for quicker bone contact as compared to a much stiffer material like sintered aluminum oxide. The biomechanical performance of C-C hip stems was assessed through (a) implantations into cadaver femurs, (b) fatigue testing, and (c) finite element analysis. These tests showed: (a) a better stress transfer as compared to a metal prosthesis having the same design, (b) no fatigue damage, (c) a computerized stem stress distribution in accordance with the fractures obtained during static mechanical testing.

Direct anchorage of Al2O3-ceramic hip components: three years of clinical experience and results of further animal studies.

The biocompatibility of high-purity dense Al2O3-ceramics had been shown to open the possibility of direct cement-free anchorage of joint endoprostheses. Three years of clinical experience with ceramic-metal composite total hip prostheses confirm the biomechanical design criteria used for the acetabular components. They also allow for additional conclusions regarding the reaction of bone tissue towards a bioinert implant. Further research activities are directed towards a solution for biomechanically stable anchorage of the femoral component of hip prostheses.