[Clinical manifestation and quantitative analysis on roentgenography of unknownetiology osteoarthritic disease in Chongzhou city of Sichuan province]

OBJECTIVE

To investigate the clinical manifestation and radiological features of unknown-etiology ostearthritic disease in Shigeng village of Chongzhou city in Sichuan province so as to lay a basis for further study.

METHODS

The data were analyzed retrospectively. The epidemiology investigation, physical examination, movement functional assessment, lab test and X-ray examination were performed on 116 villagers of 3 years and more than. Quantitative analysis on roentgenography was conducted.

RESULTS

Sixty-four villagers had unknown ostearthritic disease,the prevalence was 55.2%; 17 patients were limp, the prevalence of limp was 26.6%, onset age mainly focused under 40 years. Main manifestation of osteoarthritic disease was fixed pain of knee joint or hip joint, and bilateral pain was significantly more than single pain, but local fever and swelling were not obvious. Mild or moderate pain account for 73.5% of patients, and pain was aggravated after physical labor or movement and could be relieved after rest. Joint pain had no influence on joint movement function for long time, leading to a limp due to the joint functional disorders at late stage. Physical examination illustrated the flexion contracture of the hip and limitation of internal and external rotation. The Harris scores were 86.5 +/- 17.1(left hip) and 86.3 +/- 17.2. 46 (right hip), and the excellent or good result was achieved in 46 patients, fair and poor results in 18 patients. The average HSS scores were 88.4 +/- 9.3 (left knee) and 88.2 +/- 11.0(right knee). The excellent or good result was achieved in 61 patients, fair and poor results in 3 patients. The X-ray films showed degenerative disorders of hip joint such as narrowing of the joint space (47.6%), articular surface sclerosis and deformation (30.2%), shallow and increased density acetabulum, increased obliquity and insufficient coverage of the femoral head by the acetabulum, and increased femoral neck-shaft angles. Radiological features of knee joint were bony spur or bony bridge,osteoporosis,incomplete and thickening articular surface with sclerosis and deformation, degenerative disorders.

CONCLUSION

Main clinical manifestation of unknown osteoarthritic disease in Chongzhou city was fixed pain of bilateral knee joint or combined with hip joint pain at early stage.and functional limitation in hip joint at late stage. Main radiological feature was hip joint degeneration. To effectively control the osteoarthritic disease of this area, much more etiology researches should be done.

Changes in the bone mineral density in the acetabulum and proximal femur after cementless total hip replacement

Our aim in this prospective study was to compare the bone mineral density (BMD) around cementless acetabular and femoral components which were identical in geometry and had the same alumina modular femoral head, but differed in regard to the material of the acetabular liners (alumina ceramic or polyethylene) in 50 patients (100 hips) who had undergone bilateral simultaneous primary total hip replacement. Dual energy X-ray absorptiometry scans of the pelvis and proximal femur were obtained at one week, at one year, and annually thereafter during the five-year period of the study.

At the final follow-up, the mean BMD had increased significantly in each group in acetabular zone I of DeLee and Charnley (20% (15% to 26%), p = 0.003), but had decreased in acetabular zone II (24% (18% to 36%) in the alumina group and 25% (17% to 31%) in the polyethylene group, p = 0.001). There was an increase in the mean BMD in zone III of 2% (0.8% to 3.2%) in the alumina group and 1% (0.6% to 2.2%) in the polyethylene group (p = 0.315). There was a decrease in the mean BMD in the calcar region (femoral zone 7) of 15% (8% to 24%) in the alumina group and 14% (6% to 23%) in the polyethylene group (p < 0.001). The mean bone loss in femoral zone 1 of Gruen et al was 2% (1.1% to 3.1%) in the alumina group and 3% (1.3% to 4.3%) in the polyethylene group (p = 0.03), and in femoral zone 6, the mean bone loss was 15% (9% to 27%) in the alumina group and 14% (11% to 29%) in the polyethylene group compared with baseline values. There was an increase in the mean BMD on the final scans in femoral zones 2 (p = 0.04), 3 (p = 0.04), 4 (p = 0.12) and 5 (p = 0.049) in both groups.

There was thus no significant difference in the bone remodelling of the acetabulum and femur five years after total hip replacement in those two groups where the only difference was in the acetabular liner.

[Femoro-acetabular impingement: a cause of groin pain and early hip osteoarthritis in younger patients]

In Denmark, approximately 7,000 hip joints are replaced by total hip arthroplasties annually. In 80% of the cases, the diagnosis is idiopathic end-stage osteoarthritis. Scientifically this is hardly acceptable. However, the last decade has witnessed a proliferative research in biomechanically important, often subtle, malformations of the hip joint which are thought to play an important role pathogenetically for the development of hip osteoarthritis and hip pain especially in younger, active patients. The common denominator for these malformations is that they cause femoro-acetabular impingement during hip flexion and internal rotation. Repetitive microtrauma damages the acetabular labrum and cartilage, and the osteoarthritic cascade is initiated in earnest. This review evaluates new research relating to this paradigm.

Effects of pelvic positioning and simulated dorsal acetabular rim remodeling on the radiographic shape of the dorsal acetabular edge

A radiographic study was conducted to evaluate the effect of pelvic rotation and of simulated dorsal acetabular rim (DAR) remodeling on the radiographic appearance of the dorsal acetabular edge (DAE). The DAE is the line connecting the cranial and caudal rims of the acetabulum when viewing a pelvic radiograph made with the dog in the ventrodorsal position with the hind limbs extended. In this study, it was hypothesized that the DAE would change with pelvic rotation and simulated DAR damage. Ventrodorsal radiographs of eight canine pelves were made at 0 degrees, 5 degrees, and 10 degrees of left and right pelvic rotation over its longitudinal axis. These radiographs were repeated following removal of 2, 4, and then 6 mm of bone from the right DAR of each pelvis. The ratio of acetabular width to maximum depth of the DAE was calculated. The area between the DAE and a straight line connecting the cranial and caudal acetabular rims was measured digitally. The DAE depth and area changed with pelvic rotation, and with increasing simulated DAR damage. A linear relationship between the obturator foramina width ratio and pelvic rotation allowed estimation of the degree and direction of pelvic rotation. Equations were developed from the data to assist with the estimation of the amount of DAR remodeling on a clinical radiograph.

Assessment of acetabular version by plain radiograph

Radiographs are routinely used to assess the condition and position of the acetabular component. The condition of the cement mantle, or the ingrowth potential, is usually easily recognized. Component-bone position can be assessed by using the method of Ranawat or by measuring abduction angles. Assessment of the version of an acetabular component is often overlooked. This angle or position is important relative to instability, impingement, and motion abnormality. The opening angle or version can be implied from a true acetabular or cross-table lateral radiograph, but good-quality views are often difficult to obtain on an outpatient basis. Using the simple technique presented here, clinicians can assess the acetabular component for version on the basis of plain anteroposterior pelvis and hip radiographs.

Influence of acetabular rim profile on hip dislocation

Dislocation is the second most common complication in total hip arthroplasty, with reported incidences of up to 8 per cent. The authors' hypothesis is that, by modifying the rim of an acetabular component in order to shift the femoral neck contact position towards the periphery of the acetabulum, the torque required to dislocate the hip joint can be increased without reducing the range of motion. Three liners were designed and their dislocation characteristics mechanically evaluated using a custom experimental test jig designed to simulate the seated leg-cross. On the basis of torque and energy to dislocate and angle at dislocation, the hypothesis was accepted; geometrically varying the contact area between the femoral neck and the acetabular rim appear to be a powerful way to modify hip dislocation characteristics.

The potential for bone loss in acetabular structures following THA

Attempts to preserve periacetabular bone stock following total hip replacement have largely ignored the potential for stress shielding in the acetabulum. We sought to quantify the change in stress distribution in acetabular bone with components of varying material stiffness by developing a high-resolution 3-D finite element model from CT scans of a young female donor. Periprosthetic bone stresses and strains on the left pelvis were compared with hemispherical cups of various material properties and with a horseshoe shaped polymeric design described in the recent literature. We observed unphysiologic periacetabular bone stress and strain fields for all designs tested. For hemispherical components, reduction of the acetabular shell material modulus caused modest changes in bone stress compared to the changes in implant geometry. The horseshoe shaped cup more effectively loaded the acetabular structures than the hemispherical design. Our results suggest stress and strain fields in pelvic structures after introduction of hemispherical acetabular components predict inevitable bone adaptation that can not be resolved by changes in implant material properties alone. Radical changes in implant design may be necessary for long-term maintenance of supporting structures in the reconstructed acetabulum.

Importance of head diameter, clearance, and cup wall thickness in elastohydrodynamic lubrication analysis of metal-on-metal hip resurfacing prostheses

The main design features of metal-on-metal (MOM) hip resurfacing prostheses in promoting elastohydrodynamic lubrication were investigated in the present study, including the femoral head diameter, the clearance, and the cup wall thickness. Simplified conceptual models were developed, based on equivalent uniform wall thicknesses for both the cup and the head as well as the support materials representing bone and cement, and subsequently used for elastohydrodynamic lubrication analysis. Both typical first- and second-generation MOM hip resurfacing prostheses with different clearances and cup wall thicknesses were considered with a fixed large bearing diameter of 50 mm, as well as a 28 mm diameter MOM total hip replacement bearing for the purpose of comparison. The importance of the head diameter and the clearance in promoting elastohydrodynamic lubrication was confirmed. Furthermore, it was also predicted that a relatively thin acetabular cup in the more recently introduced second-generation MOM hip resurfacing prostheses would be capable of improving elastohydrodynamic lubrication even further.

Clinical and radiological outcome of total hip replacement five years after pamidronate therapy

Bisphosphonates reduce peri-prosthetic bone loss in the short term after total hip replacement but the mid- and longer term effects are not known. The aims of this randomised trial were to examine the effect of a single dose of 90 mg of pamidronate on the clinical and radiological outcome and peri-prosthetic bone mineral density in 50 patients (56 hips) over a five-year period, following total hip replacement.

At five years, 37 patients (42 hips) returned for assessment. The Harris hip scores were similar in the pamidronate and placebo groups throughout the study. Also at five years, four patients, two from each group had osteolytic lesions on plain radiography. These were located around the acetabular component in three patients and in the femoral calcar in one. The femoral and acetabular peri-prosthetic bone mineral density in the pamidronate group and the control group was similar at five years.

Pamidronate given as a single post-operative dose does not appear to influence the clinical outcome or prevent the development of osteolytic lesions at five years after total hip replacement.

A Biomechanical Study of Periacetabular Defects and Cement Filling

Periacetabular bone metastases cause severe pain and functional disability in cancer patients. Percutaneous acetabuloplasty (PCA) is a minimally invasive, image-guided procedure whereby cement is injected into lesion sites. Pain relief and functional restoration have been observed clinically; however, neither the biomechanical consequences of the lesions nor the effectiveness of the PCA technique are well understood. The objective of this study was to investigate how periacetabular lesion size, cortex involvement, and cement modulus affect pelvic bone stresses and strains under single-legged stance loading. Experiments were performed on a male cadaver pelvis under conditions of intact, periacetabular defect, and cement-filling with surface strains recorded at three strain gage locations. The experimental data were then employed to validate three-dimensional finite element models of the same pelvis, developed using computed tomography data. The models demonstrated that increases in cortical stresses were highest along the posterior column of the acetabulum, adjacent to the defect. Cortical stresses were more profoundly affected in the presence of transcortical defects, as compared to those involving only trabecular bone. Cement filling with a modulus of 2.2GPa was shown to restore cortical stresses to near intact values, while a decrease in cement modulus due to inclusion of BaSO4 reduced the restorative effect. Peak acetabular contact pressures increased less than 15% for all simulated defect conditions; however, the contact stresses were reduced to levels below intact in the presence of either cement filling. These results suggest that periacetabular defects may increase the vulnerability of the pelvis to fracture depending on size and cortical involvement and that PCA filling may lower the risk of periacetabular fractures.

Design factors influencing performance of constrained acetabular liners: finite element characterization

Constrained acetabular liners are utilized to deal with the infrequent but devastating problem of recurrent dislocation. While an encouraging treatment of last resort, the clinical performance of contemporary constrained liners has been somewhat mixed. There are multiple factors contributing to this variability, one of which is the limited understanding of the intrinsic mechanical characteristics of these specialty devices. To address this issue, a three-dimensional, materially nonlinear, multi-surface contact finite element model of a representative constrained liner was created. The model was physically validated, and then used for parametric testing to explore the effects of individual design features. The model was exercised for both intra-operative assembly and lever-out dislocation. It was found that the coefficient of friction between the femoral head and the liner substantially affected both the force required to seat the femoral head into the liner during assembly, and the peak moment resisting dislocation (226% increase in assembly force for friction coefficients of 0.2 versus 0.0; 49% reduction in dislocation moment for friction coefficients of 0.013 versus 0.135). As expected, the cup opening radius also had a dominant effect on both maneuvers: decreasing the opening radius from 13.9 to 13.6 mm increased assembly force by 506 N and increased the dislocation moment by over 3.5 N-m, whereas the influence of other design parameters was much more modest.

Finite Element Analysis of the Long-Term Fixation Strength of Cemented Ceramic Cups

Clinical studies have shown that adequate fixation of ceramic cups using bone cement is difficult to achieve. As the cement-ceramic bond strength is low, a satisfactory fixation strength requires a cup design that allows mechanical interlocking, although such a design will probably promote cement cracking and therefore cup loosening in the long term. An investigation has been carried out to establish whether a cemented ceramic cup can be designed in such a way that both a satisfactory initial fixation strength is obtained and cement cracking is reduced to levels found around PE cups functioning well in vivo. By means of finite element analysis, the fatigue loading of three geometrically different cemented acetabular cups, with ceramic and PE material properties, has been simulated, and the severity of the crack patterns produced in the cement has been analysed. Furthermore, the fixation strength has been analysed by simulating a pull-out test prior to and after fatigue testing. All ceramic cups produced much larger amounts of cement damage during fatigue testing than any PE cup, caused by stress concentrations in the cement that were attributable to the high stiffness of the ceramic. Even a completely smooth ceramic cup produced more damage than a sharp-grooved PE cup. Owing to the excessive cement cracking, the fixation strength of the ceramic cups dropped after fatigue loading. It is concluded that cemented ceramic cups have an increased risk of long-term mechanical failure by comparison with PE cups, and that a ceramic cup design that combines sufficient fixation strength with low cement failure may be difficult to achieve.

Cemented Cup Stability during Lever-Out Testing after Acetabular Bone Impaction Grafting with Bone Graft Substitutes Mixes Containing Morselized Cancellous Bone and Tricalcium Phosphate-Hydroxyapatite Granules

Bone defects after failed total hip arthroplasty can be reconstructed with impacted morselized bone grafts and a cemented cup. In the near future the amount of bone grafts available for surgical purposes will be insufficient. Ceramic calcium phosphates [tricalcium phosphate (TCP) and hydroxyapatite (HA)] have been widely considered as potential bone graft substitutes or bone graft extenders. In the past, mechanical experiments have been performed to determine implant stability of bone grafts and ceramic TCP-HA granules mixes under a compressive load. However, in-vivo migration studies suggest that shear loading may be equally important. This in-vitro study investigated the initial stability of cups reconstructed with various mixes of bone grafts and ceramic TCP-HA granules in a lever-out situation, where shearing is the predominant loading mode. It was found that the cups reconstructed with mixes of bone graft and TCP-HA granules exhibited greater mechanical stability than the cups reconstructed with bone grafts only. It is concluded that from a mechanical standpoint, when considering shear force resistance, 50–50 per cent volume mix and 25–75 per cent volume mix of morselized cancellous bone graft and TCP-HA granules both provide adequate initial cup stability and can be used for acetabular reconstructions with the bone impaction grafting technique.

3D non-linear analysis of the acetabular construct following impaction grafting

The study investigates the short-term behaviour of the acetabular construct following revision hip arthroplasty, carried out using the Slooff-Ling impaction grafting technique; using 3D finite element analyses. An elasto-plastic material model is used to describe the constitutive behaviour of morsellised cortico-cancellous bone (MCB) graft, since it has been shown that MCB undergoes significant plastic deformation under normal physiological loads. Based on previous experimental studies carried out by the authors and others, MCB is modelled using non-linear elasticity and Drucker Prager Cap (DPC) plasticity. Loading associated with walking, sitting down, and standing up is applied to the acetabular cup through a femoral head using smooth sliding surfaces. The analyses yield distinctive patterns of migration and rotation due to different activities. These are found to be similar to those observed in the clinical setting.

Berneese periacetabular osteotomy for residual hip dysplasia in adults--a case report and review of literature

Pelvic osteotomy for acetabular dysplasia has been introduced to improve acetabular coverage of the femoral head and reduce the risk of secondary osteoarthrosis. Several surgical methods for acetabular reorientation have been proposed for this purpose by reorientation of the acetabulum single, double, triple, spherical and periacetabular osteotomies. We report our first experience with periacetabulur berneese osteotomy described by Prof. R. Ganz and now the procedure of choice in appropriately selected patients. Fifteen years old boy who presented with complaints of fall and pain in the right gluteal region for 5 days duration that increased with walking. Examination revealed an antalgic gait. Rest of his examination was normal except mild tenderness in the right buttock area. His plain X-rays revealed an incidental finding of dysplastic left hip with deficient lateral coverage, deformed femoral head, coxa magna and mild coxa valga. In addition he had focal arthritic changes over the superolateral acetabulam with sclerosis and cyst formation. His anterior center-edge angle was 24 degrees with an acetabular index of 44 degrees. He had grade II arthritic changes according to the Tonnis classification of osteoarthritis. A periacetabulur ganz osteotomy was performed. Correction was confirmed with intraoperative X-rays. His post operative course was smooth and he was allowed full weight bearing at 8 weeks when X-rays showed satisfactory healing of osteotomy.

Bone remodelling around a cemented polyethylene cup

The aims of this study were to examine the repeatability of measurements of bone mineral density (BMD) around a cemented polyethylene Charnley acetabular component using dual-energy x-ray absorptiometry and to determine the longitudinal pattern of change in BMD during the first 24 months after surgery.

The precision of measurements of BMD in 19 subjects ranged from 7.7% to 10.8% between regions, using a four-region-of-interest model. A longitudinal study of 27 patients demonstrated a transient decrease in net pelvic BMD during the first 12 months, which recovered to baseline at 24 months. The BMD in the region medial to the dome of the component reduced by between 7% and 10% during the first three months, but recovered to approximately baseline values by two years.

Changes in BMD in the pelvis around cemented acetabular components may be measured using dual-energy x-ray absorptiometry. Bone loss after insertion of a cemented Charnley acetabular component is small, transient and occurs mainly at the medial wall of the acetabulum. After two years, bone mass returns to baseline values, with a pattern suggesting a uniform transmission of load to the acetabulum.

Deformation of press-fitted metallic resurfacing cups. Part 2: Finite element simulation

The deformation of metallic acetabular cups employed for metal-on-metal hip resurfacing procedures was considered theoretically using the finite element method in the present study, following on the experimental investigation reported in Part 1. Three representative cups, characterized by the cup wall thickness as thin, intermediate, and thick, were considered. For the intermediate cup, the effects of both the size and the diametral interference on the cup deformation were investigated. Both two-dimensional axisymmetric and three-dimensional finite element models were developed to examine the important parameters during and after the press-fit procedure, and in particular the deformation of the metallic cup. The theoretical prediction of the cup deformation was in reasonable agreement with the corresponding experimental measurement reported in Part 1. The most significant factor influencing the cup deformation was the cup wall thickness. Both the size and the diametral interference were also shown to influence the cup deformation. It is important to ensure that the cup deformation does not significantly affect the clearance designed and optimized for tribological performances of metal-on-metal hip resurfacing prostheses. Furthermore the contact parameters at the cup and bone interface associated with the press fit were also discussed.

Problematic sites of third body embedment in polyethylene for total hip wear acceleration

A computational model was developed to identify the sites of third body particle embedment in a total hip acetabular component surface that are most problematic in terms of roughening the overpassing regions of the femoral head counterface, leading in turn to most severely accelerated polyethylene wear. The analytical approach used was to calculate loci of acetabular sites that, during the gait cycle, overpass previously documented regions of kinetically most critical femoral head roughening. Instantaneous local contact stress and sliding distance were postulated as factors contributing to the severity of the femoral head scratching/roughening which would be expected, due to otherwise-similar particles embedded along each such acetabular overpass locus. The computational results showed that the location of debris embedment was a potent determinant of the amount of polyethylene wear acceleration expected. The data also showed that the supero-lateral aspect of the acetabular cup is consistently and by far the most problematic area for third body particle embedment.

The safe-zones for combined cup and neck anteversions that fulfill the essential range of motion and their optimum combination in total hip replacements

Reduction of the range of motion (ROM) until prosthetic impingement of a total hip replacement may lead to frequent impingement, subluxation and dislocation especially for patients with good hip movement. The ROM until prosthetic impingement can be calculated using the technical ROM (theta) and the cup and neck positions by a previously created mathematical formula. A larger (theta) with proper cup and neck positions results in a larger ROM. However there was only one paper written in English, which revealed the optimum theoretical combination of cup and neck anteversions. ROM of more than 110 degrees flexion, 30 degrees internal-rotation at 90 degrees flexion, 30 degrees extension and 40 degrees external-rotation were defined as the criteria for essential ROM for ADL. The safe-zones for combined cup anteversion (betaanat) and neck anteversion (b) were defined as the areas that fulfill all the criteria of ROM without prosthetic impingement. The safe-zones were created for 35 degrees , 45 degrees and 55 degrees cup abductions (alpha) and for 120 degrees and 135 degrees (theta). The safe-zones for combined (betaanat) and (b) were much larger for a 135 degrees (theta) than a 120 degrees (theta). Their safe-zones showed that (b) should be reduced if (betaanat) is increased and choosing a lower (alpha) requires that the sum of (betaanat) and (b) should be higher and vice versa. A (theta) of more than 135 degrees is recommended as it further increases the size of the safe-zone and provides a larger ROM, and the optimum values of combined cup and neck anteversions can be estimated by the formula: (alpha) + (betaanat) + 0.77(b) = 84.3.

A comparison of structural and mechanical properties in cancellous bone from the femoral head and acetabulum

Mechanical interlock obtained by penetration of bone cement into cancellous bone is critical to the success of cemented total hip replacement (THR). Although acetabular component loosening is an important mode of THR failure, the properties of acetabular cancellous bone relevant to cement penetration are not well characterized. Bone biopsies (9mm diameter, 10mm long) were taken from the articular surfaces of the acetabulum and femoral head during total hip replacement. After mechanical and chemical defatting the two groups of bone specimens were characterized using flow measurement, mechanical testing and finally serial sectioning and three-dimensional computer reconstruction. The mean permeabilities of the acetabular group (1.064 × 10−10 m2) and femoral group (1.155x 10−10m2) were calculated from the flow measurements, which used saline solution and a static pressure of 9.8 kPa. The mean Young's modulus, measured non-destructively, was 47.4 MPa for the femoral group and 116.4MPa for the acetabular group. Three-dimensional computer reconstruction of the specimens showed no significant differences in connectivity and porosity between the groups. Results obtained using femoral head cancellous bone to investigate bone cement penetration and fixation are directly relevant to fixation in the acetabulum.

Analysis of elastohydrodynamic lubrication in McKee—Farrar metal-on-metal hip joint replacement

An elastohydrodynamic lubrication (EHL) analysis was carried out in this study for a typical McKee-Farrar metal-on-metal hip prosthesis under a simple steady state rotation. The finite element method was used initially to investigate the effect of the cement and bone on the predicted contact pressure distribution between the two articulating surfaces under dry conditions, and subsequently to determine the elastic deformation of both the femoral and the acetabular components required for the lubrication analysis. Both Reynolds equation and the elasticity equation were coupled and solved numerically using the finite difference method. Important features in reducing contact stresses and promoting fluid-film lubrication associated with the McKee-Farrar metal-on-metal hip implant were identified as the large femoral head and the thin acetabular cup. For the typical McKee-Farrar metal-on-metal hip prosthesis considered under typical walking conditions, an increase in the femoral head radius from 14 to 17.4 mm (for a fixed radial clearance of 79 μn) was shown to result in a 25 per cent decrease in the maximum dry contact pressure and a 60 per cent increase in the predicted minimum film thickness. Furthermore, the predicted maximum contact pressure considering both the cement and the bone was found to be decreased by about 80 per cent, while the minimum film thickness was predicted to be increased by 50 per cent. Despite a significant increase in the predicted minimum lubricating film thickness due to the large femoral head and the thin acetabular cup, a mixed lubrication regime was predicted for the McKee Farrar metal-on-metal hip implant under estimated in vivo steady state walking conditions, depending on the surface roughness of the bearing surfaces. This clearly demonstrated the important influences of the material, design and manufacturing parameters on the tribological performance of these hard-on-hard hip prostheses. Furthermore, in the present contact mechanics analysis, the significant increase in the elasticity due to the relatively thin acetabular cup was not found to cause equatorial contact and gripping of the ball.

The effect of acetabular cup size on the short-term stability of revision hip arthroplasty: A finite element investigation

The study uses idealized two-dimensional finite element models to examine the behaviour of the acetabular construct following revision hip arthroplasty, carried out using the Slooff-Ling impaction grafting technique. The behaviour of bone graft was considered in detail, with non-linear elasticity and non-associated plasticity being adopted. Load was applied to the acetabular construct through a femoral head using smooth sliding surfaces. In particular, four models were subjected to two idealized cyclic load cases to investigate the effect of acetabular cup size on the short-term stability of the acetabular construct. The study suggests that benefits may be gained by using the largest practical size of acetabular cup.

The Bernese periacetabular osteotomy: clinical, radiographic and mechanical 7-15-year follow-up of 26 hips

BACKGROUND

The Bernese periacetabular osteotomy is used in dysplastic hips to increase the load-bearing area of the hip and to prevent osteoarthritis. The aim of our work was to determine the contact hip stress before and after the osteotomy and to compare the relief of stress with the long-term radiographic and clinical outcome.

PATIENTS AND METHODS

We followed 26 dysplastic hips (26 patients) for 7-15 years after the index operation. Clinical evaluation was based on the WOMAC score, osteoarthrosis was evaluated with the Tönnis classification, the angles of lateral (CE) and anterior (VCA) femoral coverage were measured, and biomechanical parameters were studied.

RESULTS

Periacetabular osteotomy increased the mean CE from 15 degrees to 37 degrees , and the mean VCA from 22 degrees to 38 degrees . The mean normalized peak contact stress was reduced from 5.2 to 3.0 kPa/N. Four hips required total hip arthroplasty after an average of 4.5 years, 8 hips showed considerable arthrosis progression, and 14 hips had no or mild arthrosis at follow-up. Preoperative WOMAC score, preoperative Tönnis grade and postoperative normalized peak contact stress were the most important predictors of outcome.

INTERPRETATION

The Bernese periacetabular osteotomy improves the mechanical status of the hip. Long-term success depends on the grade of arthrosis preoperatively and on the magnitude of operative correction of the contact hip stress.

Acetabular Cup Geometry and Bone-Implant Interference have More Influence on Initial Periprosthetic Joint Space than Joint Loading and Surgical Cup Insertion

Environmental variations in patient-dependent and surgical factors were modeled using robust optimization with a finite element acetabular cup-pelvis model. A previously developed statistical optimization scheme was used to: (1) determine the cup geometry and the optimal cup-bone interference that maximized bone-implant contact areas and minimized changes in the gap volume between the implant and bone surface during gait loading and unloading; and (2) determine the relative contributions of design, patient-dependent, and surgical factors to variations in bone-implant contact areas and a change in gap volume. The statistical analyses indicated that the design variables, namely the equatorial diameter and eccentricity, explained most of the variations in the performance measures. Further, the hemispherical designs performed better than the nonhemispherical designs. The 58mm hemispherical cup, with 2mm diametral interferences, minimized the change in gap volume and attained 82% and 81% of the maximum predicted total and rim contact areas, respectively. The equatorial diameter and eccentricity, not the patient-dependent and surgical factors, explained most of the variations in the performance measures. Perfect surface apposition was not attained with any of the cup designs.

Anteversion of the acetabulum and femoral neck in early walking age patients with developmental dysplasia of the hip

Computed tomography measurements were made to quantify the relationship between the anteversion of the acetabulum and femoral neck in 27 early walking age patients (age range; 18-48 months) with developmental dysplasia of the hip. The centre-edge angle and acetabular index were measured in standard pelvis radiographs, and anteversion of acetabulum and femoral neck were measured by use of two-dimensional computed tomography in 25 complete dislocated, 19 subluxated and 10 unaffected hips (a total of 54 hips). The diagnosis of dysplasia, subluxation and complete dislocation of developmental hip dysplasia were determined radiographically using Ishida's criteria. There were statistically significant differences between the three groups for the centre-edge angle, the acetabular index, and acetabulum anteversion. There was no statistically significant difference between the three groups for femoral neck anteversion. The acetabular anteversion was found to be 13.4+/-2.8 degrees (mean+/-SD) in unaffected hips, 16.7+/-1.9 degrees in subluxated hips and 19.8+/-2.5 degrees in complete dislocated hips. There was statistically significant difference between the three groups, with a wide range of acetabular anteversion values noted in all groups (9-26 degrees ). The acetabular anteversion was increased on the dislocated side in each patient and we found no retroverted acetabulum. On the other hand there was no significant difference between the groups with regards to femoral neck anteversion. We conclude that confirming anteversion of the acetabulum and the femoral neck by two-dimensional computed tomography is needed in treatment planning of early walking age patients with developmental hip dysplasia.

Five-year clinical, radiological and postmortem results of the Cambridge Cup in patients with displaced fractures of the neck of the femur

The Cambridge Cup has been designed to replace the horseshoe-shaped articular cartilage of the acetabulum and the underlying subchondral bone. It is intended to provide physiological loading with minimal resection of healthy bone.

The cup has been used in 50 women with displaced, subcapital fractures of the neck of the femur. In 24 cases, the cup was coated with hydroxyapatite. In 26, the coating was removed before implantation in order to simulate the effect of long-term resorption.

The mean Barthel index and the Charnley-modified Merle d’Aubigné scores recovered to their levels before fracture. We reviewed 30 women at two years, 21 were asymptomatic and nine reported minimal pain. The mean scores deteriorated slightly after five years reflecting the comorbidity of advancing age. Patients with the hydroxyapatite-coated components remained asymptomatic, with no wear or loosening. The uncoated components migrated after four years and three required revision. This trial shows good early results using a novel, hydroxyapatite-coated, physiological acetabular component.

Tilt and rotation correction of acetabular version on pelvic radiographs

Anteroposterior pelvic radiographs are the gold standard of imaging for mechanical hip problems. However, correct interpretation is difficult because the projected morphologic features of the acetabulum and nearly all routinely used hip parameters depend on individual pelvic position, which can vary considerably during acquisition. We developed software that recreates the projected acetabular rim and the measured hip parameters as if obtained in a standardized orientation. The vertical and horizontal distances between two easy identifiable points were used as indicators of tilt and rotation. These points were the middle of the sacrococcygeal joint and the middle of the upper border of the symphyseal gap. Calibration of the indicators was achieved by means of serial pelvic radiographs of 20 cadaver pelves. Validation of tilt indicator in 100 patients and a theoretical error analysis revealed that for accurate tilt prediction an additional one-time lateral radiograph of the pelvis is mandatory. The computer-assisted method allows standardized evaluation of anatomic morphologic differences of femoral coverage (dysplasia, retroversion), making their clinical relevance for development of early osteoarthritis more valuable.

Outcome of periacetabular osteotomy: joint contact pressure calculation using standing AP radiographs, 12 patients followed for average 2 years

BACKGROUND

Due to wide variations in acetabular structure of individuals with hip dysplasia, the measurement of the acetabular orientation may not be sufficient to predict the joint loading and pressure distribution across the joint. Addition of mechanical analysis to preoperative planning, therefore, has the potential to improve the clinical outcome. We analyzed the effect of periacetabular osteotomy on hip dysplasia using computer-aided simulation of joint contact pressure on regular AP radiographs. The results were compared with the results of surgery based on realignment of acetabular angles to the normal hip.

PATIENTS AND METHODS

We studied 12 consecutive periacetabular osteotomies with no femoral head deformity. The median age of patients, all females, was 35 (20-50) years. The median follow-up was 2 years (1.3-2.2). Patient outcome was measured with the total score of a self-administered questionnaire (q-score) and with the Harris hip score. The pre- and postoperative orientation of the acetabulum was defined using reconstructed 3D CT-slices to measure angles in the three anatomical planes. Peak contact pressure, weight-bearing area, and the centroid of the contact pressure distribution (CP-ratio) were calculated.

RESULTS

While 9 of 12 cases showed decreased peak pressure after surgery, the mean changes in weight-bearing area and peak contact pressure were not statistically significant. However, CP-ratio changed (p < 0.001, paired t-test) with surgery. For the optimal range of CP-ratio (within its mid-range 40-60%), the mechanical outcome improved significantly.

INTERPRETATION

Verifying the correlation between the optimal CP-ratio and the outcome of the surgery requires additional studies on more patients. Moreover, the anatomically measured angles were not correlated with the ranges of CP-ratio, suggesting that they do not always associate with objective mechanical goals of realignment osteotomy. Mechanical analysis, therefore, can be a valuable tool in assessing two-dimensional radiographs in hip dysplasia.

A new modified technique of triple osteotomy of the innominate bone for acetabular dysplasia

A new modified technique of triple osteotomy of the innominate bone has been devised and implemented for the treatment of residual acetabular dysplasia in children with developmental dysplasia of the hip. The procedure is done through a two-incision approach. The ischium, pubis, and iliac bones are osteotomized, with resection of a triangular wedge of bone from the outer cortex of the proximal part of the ilium. The resection of the triangular wedge of bone from the outer cortex alone creates a slot with the intact inner cortex serving as a stabilizing abutment where the distal posterior aspect of the ilium fits. This osteotomy allows for extensive coverage of the femoral head with greater stability. The stable construct of the osteotomy and pelvic fixation facilitates early weight bearing and obviates the need for hip spica cast immobilization. Since its conception the new triple osteotomy has been done in 11 children (13 hips). The preoperative vertical center edge angle of Weiberg was 8.9 degrees (range, 5 degrees -17 degrees ). The postoperative vertical center edge angle was a mean of 45.6 degrees (range, 31 degrees -58 degrees ). The last followup vertical center edge angle was a mean of 44.9 degrees (range, 29 degrees -58 degrees ). The mean preoperative acetabular angle of Sharp was 53 degrees (range, 48 degrees -61 degrees ). The postoperative acetabular angle was a mean of 25.4 degrees (range, 19 degrees -40 degrees ). The last followup acetabular angle was a mean of 28 degrees (range, 18 degrees -41 degrees ). All patients went on to have bony unions on their innominate bone. We describe the technique for the osteotomy and presents preliminary results of all patients who had the procedure.

Long-term results of the dial osteotomy in the treatment of high-grade acetabular dysplasia

The dial osteotomy, an acetabular reorientation procedure based on radiographs, was developed by R. H. Eppright for treatment of hip dysplasia; however, long-term results are not recorded. The aim of this study was to evaluate retrospectively the results of the dial osteotomy as done in 37 patients (44 hips) at an average followup of 12.6 years. Articular pressures with the application of a time and pressure algorithm were calculated from radiographs to correlate calculated intraarticular pressures with progression of degenerative disease. Clinical results at followup were 32 (73%) satisfactory and 12 (27%) unsatisfactory hips. Six (13%) hips failed between 10-20 years (average 14.7 years). A satisfactory result correlated with the preoperative functional score. Radiographically, the anterior center-edge angle increased from an average of 6.7 degrees to 37.9 degrees. At followup, radiographic indices of degeneration indicated that eight (18%) hips had improved, 18 (41%) had stabilized, and 18 (41%) had deteriorated. Severin indices improved in 21 (48%) hips. Joint space width at followup provided the only correlation between radiographic parameters and clinical result. Contact pressures were reduced from 4.45 MPa to 1.12 MPa. The cumulative exposure to articular pressures averaged 61.6 MPa-years, and did not correlate with radiographic parameters or clinical success.

LEVEL OF EVIDENCE

Therapeutic study, Level IV (case series--no, or historical control group). See the Guidelines for Authors for a complete description of levels of evidence.

Migration of the acetabular component: effect of cement pressurization and significance of early radiolucency: a randomized 5-year study using radiostereometry

BACKGROUND

Cementing technique is a crucial factor in prosthesis fixation. No randomized studies have been published, however, comparing the outcome of conventional fingerpacking with the outcome of pressurization of the cement prior to cup insertion.

PATIENTS AND METHODS

We randomized 50 THAs to either fingerpacking or sequential pressurization (including individual pressurization of each anchorage hole) and followed the patients with RSA for 5 years. The penetration of cement into the anchorage holes was measured on digital radiographs. Postoperative radiolucent lines around the cup were correlated to later RSA results. For clinical evaluation, we used SF-36 and HHS.

RESULTS

The pressurized group of THAs was more stable regarding changes in inclination. We found no other difference in the migratory behavior. The cement penetration into the anchorage holes was deeper with the pressurization technique than with fingerpacking. For the whole group taken together, there was a strong relation between the presence of radiolucent lines as measured on the postoperative radiograph and later migration observed by RSA at 2 and 5 years.

INTERPRETATION

Pressurization of the cement produced better cement penetration and increased the cup stability in terms of changes in inclination. Early findings of radiolucent lines can predict later unfavorable cup migration.

The use of structural distal femoral allografts for acetabular reconstruction. Average ten-year follow-up

BACKGROUND

Acetabular fixation during revision total hip arthroplasty in patients who have a nonsupportive superior dome and proximal migration of the acetabular component (a Paprosky Type-IIIa defect) cannot be achieved reliably with use of a hemispherical porous-coated component alone. The purposes of the present study were to determine the long-term results associated with the use of a porous-coated hemispherical acetabular component, supported with a distal femoral structural allograft, for revision at the site of a Type-IIIa defect and to determine if graft resorption leads to late failure.

METHODS

Thirty-one patients who had an acetabular reconstruction with use of a distal femoral allograft for the treatment of a Type-IIIa defect between January 1985 and December 1990 were followed annually with clinical and radiographic evaluations. At the time of the latest follow-up, eight patients had died and one patient had been lost to follow-up. One of the patients who died had had a clinical failure at 4.5 years postoperatively and was included in the analysis. Therefore, twenty-three patients, who had had an average age of sixty-one years at the time of the index procedure, were evaluated at an average of 10.3 years postoperatively.

RESULTS

Five acetabular components were re-revised because of aseptic loosening at an average of 5.3 years after the index procedure. Radiographically, all but one of the remaining components were stable and showed evidence of bone ingrowth. The average Merle D'Aubigné and Postel hip score improved from 5 points preoperatively to 10 points at the time of the latest follow-up. Allograft bone resorption, although difficult to quantitate, was observed around six of the seventeen stable components and around two of the five components that failed clinically.

CONCLUSIONS

Acetabular revision with use of a porous-coated acetabular component along with a structural distal femoral allograft for the treatment of a Type-IIIa defect demonstrated a high rate of clinical and radiographic success after an average of ten years of follow-up.

Evaluierung des Fügeverhaltens und der Rückhaltekräfte von Schnapp-Pfannen für den künstlichen Hüftgelenkersatz / Evaluation of the assembling and retention forces of constraint liners for total hip replacement

Dislocation is a severe complication after total hip replacement which may cause revision surgery in some cases. The use of constraint inserts that are coupled to the femoral head by a snapping mechanism provides an opportunity for treatment of recurrent dislocations. This study was aimed to investigate the assembling and retention forces of a specific constraint liner. Using a universal testing machine the assembling forces were determined for head sizes of 28 and 32 mm and the clinically mostly used as well as the maximum cup size. Subsequently, under variation of load direction and pull-out velocity the retention forces were investigated. For primary assembly of the head the required compressive forces were in a range from 197 N and 283 N depending on head and cup size (each size n = 3). Repeated assembly led to a decrease of these forces up to 29%. The retention forces always were slightly below the assembling forces, i. e. forces to remove the heads from the inserts were between 183 N and 230 N (each size n = 3). Repeated disconnection caused a decrease of the retention forces up to 16%. An increase of load velocity as well as an oblique load direction resulted in an enhancement of the retention forces. For all investigated implant sizes the retention force for the femoral head was approximately ten-times less than the interface strength between the insert and the metal-back. In case of correct implant handling the risk of disconnection between the tested constraint insert and the corresponding metal-back has not to be considered in clinical practice.

Primärstabilität von Press-fit Hüftpfannen – eine in-vitro Studie – / Initial Stability Of Press-fit Acetabular Cups – An In-Vitro Study –

AIM OF THE STUDY

Mechanical lever-out tests were performed in vitro to investigate the initial stability of press fit acetabular cups.

METHOD

Five different uncemented, hemispherical press-fit cups were implanted in a standardized manner into Sawbones, Polyurethane foam blocks. Each cup was levered-out by using a 250 mm stainless steel rod, which was connected to the acetabular cup. Loads were then applied to the rod causing the cup to be diplaced. Lever-out forces were recorded by a computer.

RESULTS

The results of the lever-out forces ranged between 39,2 and 50,8 Nm. The highest initial stability was achieved by two Titanium cups with a Titanium plasmaspray coating, a flattened pole and a sharp equatorial edge. According to our trials the equatorial rim of the polyurethane cavity is the crucial area for the implant's initial stabilty. There the highest amount of attrition was observed.

CONCLUSION

To guarantee a high reproducibilty of the tests it is essential to pay particular attention to the quality of the polyurethane foam blocks, to the exactness of the reaming procedure and to a defined cup insertion. However as our trials were carried out under optimized labaratory conditions one must be careful not to over-interpret its results. Intraoperatively primary stability is also influenced by the quality of the bone.

Use of custom triflanged acetabular components in revision total hip arthroplasty

Difficulty persists in consistently treating massive acetabular defects in revision total hip arthroplasty. A relatively new treatment option for these complex cases is a custom triflanged acetabular component created from anatomic data derived from a computed tomography scan of the pelvis. The custom triflanged acetabular component achieves fixation on the remaining ilium, ischium, and pubis with multiple fixation screws while the acetabular defect is filled with cancellous allograft bone. A retrospective review was done of 26 hips (26 patients) with massive periacetabular bone loss (Paprosky Type 3B) reconstructed with a custom triflanged acetabular component. Twenty-three of 26 patients (88.5%) were considered clinically successful at short-term followup (average, 54 months; range, 24 to 85 months), with stable fixation and reconstruction of periacetabular bone. Three failures occurred from loss of ischial fixation in two patients with a preoperative pelvic discontinuity and one patient with severe osteopenia. These devices should be used with caution in patients with a preoperative pelvic discontinuity unless additional column plating is done.

Protrusio acetabuli presenting as a complex pelvic mass after total hip arthroplasty

BACKGROUND

The differential diagnosis in an elderly woman with a complex pelvic mass includes benign and malignant diseases.

CASE

A woman in her ninth decade was discovered to have both a breast mass and a pelvic mass at examination. After diagnostic breast biopsy results that confirmed invasive breast carcinoma, pelvic examination and ultrasonography were performed. The ultrasonogram demonstrated a large complex pelvic mass. The patient underwent an exploratory laparotomy at the time of her mastectomy. The pelvic mass was a protrusio acetabuli resulting from a prior right total hip arthroplasty.

CONCLUSION

A complex pelvic mass secondary to protrusio acetabuli is a rare clinical finding.

Femoroacetabular impingement caused by a femoral osseous head-neck bump deformity: clinical, radiological, and experimental results

Femoroacetabular impingement is often associated with reduced femoral anteversion or an osseous bump deformity on the femoral head-neck junction. We report prospectively on 17 patients showing an osseous bump at the anterolateral head-neck junction on radiography (22 hips) and typical signs of femoroacetabular impingement on clinical examination. Following three plans of treatment, nine patients (10 hips) underwent nonoperative treatment, and eight patients (12 hips) had surgery. In eight hips with labral defects but minor cartilage damage, the bump was surgically removed via trochanter flip osteotomy. Two hips were treated surgically through an anterior surgical approach without hip dislocation. Four hips with severe signs of osteoarthritis and significantly reduced range of motion underwent total replacement. To elucidate a local osteogenic differential potential, tissue specimens of the perilesional capsule were investigated immunohistochemically. Various antigens and protein synthesis products served to identify osteoblastic and progenitor cells. There was a significant improvement in internal rotation and pain relief in patients who underwent surgical resection of the osseous bump. No avascular osteonecrosis or other significant severe side effects were observed during follow-up. In contrast, no nonoperatively treated patients improved. Furthermore, immunohistochemical studies showed perilesional recruitment of osteoprogenitor cells.

Geometric measurements of the acetabulum in adult Malawians: radiographic study

OBJECTIVES

To determine the acetabular depth as well as acetabular and centre edge angles; to assess the influence of sex, if any, in these geometric measurements; and to determine the prevalence of hip dysplasia in adult Malawians.

DESIGN

A retrospective study.

SETTING

Queen Elizabeth Central Hospital (QECH) and Blantyre Adventist Hospital (BAH).

MAIN OUTCOME MEASURES

The acetabular and centre edge angles, acetabular depth and the prevalence of hip dysplasia were determined.

MATERIALS AND METHODS

Two hundred and fifty three bilateral radiographs of the hip from adults, 133 men and 129 women, were used to measure the acetabular depth, angle and centre edge angle using a calliper and goniometer. The radiographs were taken from patients with no underlying bone disease between January 1997 and February 2001 at QECH and BAH.

RESULTS

The prevalence of hip dysplasia was 11.54% for men and 13.16% for women with respect to centre edge angles but this difference by sex was not significant (P>0.1). However, the prevalence of hip dysplasia with respect to centre edge angle showed significantly more dysplasia in Malawian men than Nigerian and Chinese men (P<0.001 and P<0.05, respectively). Centre edge angles also showed a wider range in Malawian men (19-51 degrees right, and 15-52 degrees left) than women (18-45 degrees right, 20-46 degrees left). In both hips, the acetabular angles were more obtuse in men (35.52 degrees right, 34.21 degrees left) than women (29.43 degrees right, 29.29 degrees left), and this difference was significant (P<0.001). The ranges of acetabular angles were wider in women (11-38 degrees right, 8-40 degrees left) than men (24-49 degrees right, 20-40 degrees left). Acetabular depth was also greater in men than in women (P<0.01 right hip, P<0.02 left hip).

CONCLUSION

Sex influences geometrical measurements of the acetabulum. The prevalence of hip dysplasia with respect to centre edge angle was significantly higher in women than men and the prevalence for men with respect to centre edge angle was significantly different when compared with Nigerian and Chinese men. This information will assist clinicians in the region and Malawi in particular to interpret hip X-rays of African patients.

[Computer-assisted periacetabular triple osteotomy for treatment of dysplasia of the hip]

AIM

Besides general risks, reorienting periacetabular osteotomies include the risks of over- or under-correction. Therefore, intraoperative computer-assisted control of the pelvic fragment may allow for precise reorientation of the acetabulum in all planes.

METHODS

The advantages and problems of a computer assisted periacetabular osteotomy are demonstrated in a 19 year old female with spastic paresis and severe secondary dysplasia of the hip over a postoperative follow up period of 2 years. Because of progressive subluxation of the left femoral head with initial degenerative changes of the hip joint a pelvic triple osteotomy as described by Tönnis and an intertrochanteric derotation-varus osteotomy were performed. The intraoperative control of the acetabular position was optimized by CT based navigation. To compare and evaluate the pre- and postoperative clinical and functional outcome, X-rays, CT scans and a gait analysis were applied.

RESULTS

The computer assisted orthopedic surgery (CAOS) technique allows for precise intraoperative control following reorientation of the acetabular fragment in all three planes. The pre- and postoperative clinical and radiological findings were compared and the result was classified as good.

CONCLUSION

Although the costs and logistics for pelvic osteotomies are increased by CAOS technology, the authors favor this technique for corrective surgery of complex acetabular deformities, although individual parameters need to be considered in each patient.

Rotational acetabular osteotomy for acetabular dysplasia of the hip with a giant acetabular bone cyst: a case report

In acetabular dysplasia of the hip joint accompanied by a giant acetabular bone cyst, rotational acetabular osteotomy may cause serious complications, such as bone necrosis after surgery or fracture of the fragile acetabulum during the operation. In a patient with this condition, we performed a two-stage operation: first, autogenous bone grafting supplemented with hydroxyapatite filling, then rotational acetabular osteotomy (after new bone formation had been assured). Radiographs and CT scans showed favorable fusion of the grafted bone. Some 18 months after the second operation, arthrograms showed no inflow of contrast medium from the articular cavity into the bone cyst region, although this had been observed before treatment. Thus, an effective remodeling of bony congruency was indicated in the mobile acetabulum 5 years after the second operation. This two-stage operation appears to be useful for correcting acetabular dysplasia accompanied by a giant bone cyst and to carry a reduced risk of serious complications, such as deterioration of the articular surface of the acetabulum or necrosis of the translocated acetabulum.

[Significance of primary stabilization of the acetabular part of hip endoprosthesis in revision arthroplasty with extensive bone defects]

In this article author discuss medium term results of first or next secondary replacement of acetabular part of hip endoprosthesis--after filling up cavernous or segmental bone defects. There were analysed 104 operated hips 70 (67.3%) female and 34 (32.7%) male. Bilateral hip arthroplasty (in two sessions) was performed in 14 women and 5 men. The average age was 69.8 years. The mean time between the primary arthroplasty and the revision was 12.1 years. The follow up was 2-15 years, mean 5.4 years. Cemented acetabulum was used in 71 revisions (68.3%), self-threaded in 19 (18.3%) and pressed in 14 (13.5%). Destabilization and migration of acetabular part of prosthesis appeared in 14 events (13.5%). Radiolucency local zones on X-ray referred to possible pseudomembrane round the acetabular part without clinical manifestations were shown in 19 cases (18.3%). The study demonstrated that migration of acetabular part of hip prosthesis due to secondary stabilisation deficiency took place in hips were proper primary stabilisation was not achieved because of extensive bone defects.

Validation of acetabular cup wear volume based on direct and two-dimensional measurements: hip simulator analysis

The volumetric wear in retrieved cups can be assessed by mathematical conversion based on linear measurements and by a fluid-displacement method. We used a hip simulator model to produce wear in 22-, 28-, and 32-mm hip implants and then assessed the volumetric wear using a gravimetric wear method. We then compared the findings with those obtained with the linear and fluid-displacement methods. For the linear method, we translated the linear wear to the volumetric wear using the equations developed by Charnley et al., Kabo et al., and Hashimoto et al. The fluid-displacement method showed the strongest correlation with the gravimetric wear method, and it was found to overestimate the volume slightly (by 3%-9%). According to the linear wear conversion, however, the equation by Kabo widely underestimated the volume by 33%-40%. The equation used by Charnley tended to overestimate the volume (by 4%-17%), whereas Hashimoto's equation tended to slightly underestimate the volume (by 2%-12%). The fluid-displacement method demonstrated an average error of 0.34% +/- 13.40% when the wear exceeded 400 mm(3). The linear wear was thus converted to the volume wear most accurately using Hashimoto's equation, with the average error being -3.8% +/- 14.0%. Of the four measurement modalities, the fluid-displacement method showed the most accurate results. We therefore confirmed that the fluid-displacement method is the most accurate way to determine volumetric wear in retrieved cups.

A preliminary report on prevalence of acetabular labrum tears in sports patients with groin pain

To the best of our knowledge, this prospective study is the first to investigate the prevalence of acetabular labrum tears in athletes presenting with groin pain. Eighteen athletes who presented to our sports clinic with groin pain, underwent clinical assessment and magnetic resonance arthrography (MRa) to detect presence or absence of acetabular labrum tears. Ethical committee approval and informed consent was obtained from each patient. In four out of these eighteen athletes (22%) the MRa demonstrated the presence of acetabular labrum tear. Three of them underwent arthroscopic debridement of their acetabular labrum tears and returned to their sporting activities within 8 months. Clicking sensation of the hip was a sensitive (100%) and specific (85%) clinical symptom to predict labral tears. The internal rotation-flexion-axial compression manoeuvre was sensitive (75%) but not specific (43%). The Thomas test was neither sensitive nor specific. The conclusion of the study is that acetabular labrum tears can be a common cause of groin pain in athletes. Sports clinicians managing athletes with groin pain have to be well aware of the condition.

Radiological remodelling of the acetabulum in Perthes' disease

Thirty-four patients were studied throughout the evolution of Perthes' disease. The acetabular changes included osteopoenia of the roof, irregularity of its contour, and decrease in its depth. These changes were proportional to the femoral head involvement. The purpose of the study was to assess the effect of the morphological changes of the femoral head on the acetabulum and the outcome, and to determine the extent to which coxa magna and acetabular enlargement induced by Perthes disease in childhood persist into adolescence. Radioisotope scans of the hip were examined in fourteen children with unilateral Perthes' disease and comparison was made with the contralateral hip. These scans showed increased uptake on the lateral part of the acetabulum and no uptake over the avascular part of the femoral head. Average follow-up was ten years and children were followed up on average from six years to fifteen years of age. Six readings of the measurements of various dimensions of the acetabulum and the femoral head were done. CT scan also showed irregularity in the acetabulum. Statistical tests lead to the conclusion that the decrease in the depth of the acetabulum was secondary to the femoral head involvement and the extent of its dimensional changes affected the final congruity between the femoral head and the acetabulum. Also the remodelling potential of the acetabulum decreases as the child grows older. Therefore containment procedures could be done by femoral osteotomy in younger children, whereas acetabular osteotomy may benefit older children.

Functional outcomes of acetabular fractures

BACKGROUND

The Musculoskeletal Function Assessment is a validated, well-designed, self-administered questionnaire that is useful for determining health status. The modified Merle d'Aubigné clinical hip score is the most generally accepted clinical grading system for evaluating the results of acetabular fracture treatment. The purpose of the present study was to evaluate the relationship between the Musculoskeletal Function Assessment and modified Merle d'Aubigné scores in evaluating the results of acetabular fracture treatment.

METHODS

One hundred and fifty patients with an acetabular fracture met the criteria for inclusion in the present study, which included a minimum of two years of postoperative follow-up, a complete physical examination with use of the Merle d'Aubigné score, and successful completion of the Musculoskeletal Function Assessment questionnaire. Patients were stratified according to a number of factors, including the type of fracture and whether the fracture was an isolated injury or was part of a multiple-injury complex. The mean duration of follow-up was five years (range, two to seventeen years).

RESULTS

The mean modified Merle d'Aubigné score was 16.8 (range, 9 to 18), and the mean Musculoskeletal Function Assessment score was 24.9 (range, 0 to 79). The Spearman correlation coefficient between the Merle d'Aubigné score and the Musculoskeletal Function Assessment score was -0.61 (p < 0.0001). Stratification of the patients did not alter these overall results. However, the presence or absence of associated injuries was a significant factor for the Merle d'Aubigné score (p = 0.03). In addition, the Merle d'Aubigné score data were asymmetric, demonstrating a ceiling effect.

CONCLUSIONS

The Musculoskeletal Function Assessment scores for these patients were relatively high compared with those for the normal population, indicating that complete return to a preinjury functional level is uncommon despite a good-to-excellent Merle d'Aubigné clinical score. Furthermore, the ceiling effect demonstrated by the Merle d'Aubigné score (despite its high correlation with the Musculoskeletal Function Assessment score) limits its usefulness as a method for evaluating the outcome of treatment of acetabular fractures. There have been few published clinical studies in which the Musculoskeletal Function Assessment score has been used as an outcome measure, and reference values are lacking. The present study provides initial guideline reference values for use in the evaluation of patients following an acetabular fracture.

Early acetabular protrusio following hemiresurfacing of the hip for osteonecrosis in sickle cell disease

A case report is presented of a patient with acetabular protrusio 2 years following hemiresurfacing of the femoral head for osteonecrosis associated with sickle cell disease. Renewed interest in bone-preserving hip arthroplasty has led to increased use of hemiarthroplasty and femoral resurfacing in young patients with arthritis. In cases of osteonecrosis, especially that associated with sickle cell disease, awareness of this potential complication is important.

Constrained acetabular cups: a cadaveric biomechanical evaluation

Reports indicate that constrained acetabular cups may reduce range of motion and catastrophically fail, although the biomechanics of dislocation have not been reported. We measured the available motion in 6 constrained cups (from 2 manufacturers) when anatomically placed in cadaver pelves. We measured the torque and rotation necessary to dislocate the hip. Range of motion was measured using a custom jig and revealed a functional range of motion with all cup positions. Extension was limited to 0 degrees with anteversion of 11 degrees to 29 degrees. Thus, anteversion of <10 degrees is recommended. Torque and rotation to produce dislocation was 7 ft-pounds and 11 ft-pounds and 82 degrees and 72 degrees, for each manufacturer. Torques were reduced with subsequent dislocations. We recommend consideration of polyethylene replacement if dislocation occurs. Dislocation occurred at the ball-polyethylene interface without catastrophic failure.