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The article describes the features of the most commonly-used acetabular components in first implants in light of development in construction as regards intrinsic features, materials used, biological behavior, and design. The following versions are examined: screwable cone-shaped trunk, cemented polyethylene, cemented metal-back, HA-coated press-fit, expansion, dysplastic hip, and anti-dislocating components. The screwable cone-shaped trunk acetabular component takes hold in the acetabular bone through torsion and compression, and threading provides greater stability as compared to equivalent models that have wings or screws. Cemented polyethylene acetabular components are characterized by low costs and good results, on the condition that some specific parameters are respected (the presence of a dry bone bed, pressurization of the cement, use in elderly patients who do very little physical activity). Cemented metal-back acetabular components have features similar to polyethylene components, from which they differ because of the possibility of being able to substitute the internal polyethylene component without having to revision the entire acetabulum. HA-coated press-fit components have solved the problems encountered in cemented versions, such as loosening and the generation of polyethylene particulate, at the same time obtaining excellent osteo-integration. The expansion cup self-stabilizes thanks to a memory effect due to the contraction-relaxation mechanism with which it is lodged, adapting to the micro-movements of the acetabulum. Components used in the dysplastic hip are particular versions with a reduced diameter that have specific hooks that provide stabilization, capable of settling in the pathologic bone with minimum reaming of the same. Anti-dislocation cups are special models that have bipolar inserts or a ring (plastic or metal) that blocks the head in the prosthetic acetabulum, obstructing its dislocation.

The authors propose a preoperative evaluation protocol for cases of dislocation of the prosthetic cup complicated by intrapelvic migration, obtained by studying 20 cases of prosthetic loosening with protrusion of the acetabular component in the pelvis, treated by reimplantation or explantation. In all of the patients, accurate preoperative planning was carried out, because of the considerable frequency of dislocation, compression or damage to the vascular and nervous structures deriving from migration inside the pelvis of the acetabular component. The authors suggest that in all cases of acetabular loosening evaluation involve standard X-rays, bone scan with technethium99 and with marked granulocytes, CT scan. When the cup protrudes in the pelvis, prior to surgery, CT scan with contrast medium will be required, and if the risk of vascular involvement exists, angiography should also be carried out.

Medium-term results in the treatment of acetabular bone loss using bulk and/or morselized bone allografts supported by acetabular reinforcement rings are reported. A total of 164 hips in 157 patients were treated by means of this reconstruction technique. The devices employed were Müller ARRR in 24 cases and Burch-Schneider APC in 140. Mean follow-up was 67 months (minimum 12, maximum 123). A total of 4 patients developed deep infection that was treated by resection-arthroplasty. Aseptic loosening of acetabular implant following extensive resorption of bone graft was observed in 5 cases: 3 of the cases underwent acetabular revision. Clinical results were evaluated based on the Harris Hip Score: mean values of 35 and 78 were assessed preoperatively and at follow-up, respectively. X-ray signs of incorporation of bone graft were observed in all cases that progressed successfully.

Testing conducted on a hip joint simulator verified the Charnley hypothesis that the diameter of the prosthetic head is proportional to wear. The study was conducted by pairing heads in Ortinox TM with acetabular cups in polyethylene at high molecular weight (UHMWPE). A comparison between the different sizes of the heads (26 and 30 mm in diameter) showed a different trend in the wear rate; in particular, the head with a smaller diameter behaves better tribologically than the head with a larger diameter.

Problems related to the use of total hip arthroplasty and the properties of the materials used to make prostheses have encouraged wear phenomena of the epiphysis-acetabulum combination of international importance and acknowledgement. Based on a review of the literature, the authors analyze the most recent years of study of wear phenomena and discuss the choice of materials to be used in total hip arthroplasty implant, with particular interest in any potential defects.

It was the purpose of the study to investigate the initial stability, with or without screws, of 3 acetabular components with press-fit anchoring, by measuring bone-prosthesis micromovements during the application of physiological loading on the hip simulated in the laboratory. The prostheses, already used clinically, were characterized by different shapes and coatings. For the purposes of the study a total of 30 acetabula were used in 10 human pelves in polyurethane and 5 human pelves preserved at -20 degrees. The pelves were assembled on a hydraulic bench test with a steel jig that could be oriented, and they were cemented with polymethylmethacrylate. Three electromagnetic transducers with sensitivity of up to 1 micron (+ 500 microns) were used to measure the micromovements between the prosthesis and the acetabular rim in its three anatomical quadrants. Bone-prosthesis micromovements were recorded during 5 consecutive load tests, from 0 to 2.39 kN (244 kg). Experimental studies have shown that bone-prosthesis micromovement that exceeds 150 microns obstructs bone integration. The most significant micromovement was observed for all of the prostheses, without accessory screws, in the iliac quadrant, but only the hemispherical one with a semi-smooth surface in zirconium oxide surpassed the threshold of 150 microns. Prostheses with a porous surface demonstrated good stability (102 +/- 33 microns and 94 +/- 36 microns, respectively). None of the prostheses demonstrated micromovement exceeding 90 microns in the area corresponding to the pubis and the ischium. The use of 2 accessory screws sensitively increased the stability of all of the prostheses on the ilium, reducing the average micromovement by 40 microns. Reduction of micromovement was less on the pubis and on the ischium.

The authors report the indications and short-term results obtained in a series of 99 total hip prostheses with a screwed acetabulum and cemented stem. The principles which inspired their choice and the criteria used to select patients are discussed. The results obtained, evaluated both clinically and radiographically, are satisfactory, particularly with regards to percentage of pain symptoms in the femur.

A total of 187 alumina screwed porous-ceramic coated sockets (An.C.A.), 48 screwed smooth-surfaced Lord sockets, and 251 cemented polyethylene sockets were radiographically evaluated at an average follow-up of 30, 51 and 96 months respectively. After 6 years the Lord prostheses revealed a 38% incidence of loosening, similar to that observed for cemented sockets 10-12 years after surgery. The An.C.A. prostheses revealed radiographic loosening equal to 12% (6 cases) in the first 50 implants, and only 0.7% in the remaining 137 cases: overall, the An.C.A. acetabular prosthesis revealed an index of radiographic loosening equal to 3.3% (7/187). To guarantee "osteointegration" of the porous coating of An.C.A. sockets optimal stability must be obtained when the prosthesis is screwed in. Because the mid-term follow-up for this clinical experience is relatively short (30 months), an opinion on the reliability of the screwed "porous" sockets must await confirmation.

Between 1976 and 1982, 126 low friction arthroplasties were implanted in primary arthrosis of the hip. The displacement rate or acetabular loosening related to the type osteoblastic response to the disease were studied. The hips were subdivided into three groups based on the radiographical aspect observed prior to implant. The atrophic type revealed a greater incidence for this type of complication (27.3%) whereas cases classified as normotrophic revealed a 5.6% incidence and hypertrophic a 6.1% incidence. The authors conclude that the type of bone response in primary arthrosis plays an important role in the occurrence of acetabular mobilization, and that osteoblastic response may be considered to be of prognostic value together with other well-known factors in the evolution of this type arthroplasty.

Since 1987 the authors have used sonography (US) as the means to detect dysplasia and congenital dislocation of infant hips, to define severity of the disease, and to monitor the results during treatment. In this paper the authors report their experience in 2000 examined babies. In 20 young patients, mainly females, 25 pathologic joints were detected and classified as 2c-4 hips. Orthopedic treatment employed Pavlick harness and, in case of partial success, Milgram abduction pillow too. This treatment has always been successful, except for a case with severe dislocation with echostructural changes in the acetabular cartilage. In this case, surgery was necessary. "Delayed ossification" (type 2b hips) and physiological immatury (type 2a hips) with alpha angle greater than or equal to 55 degrees were not splinted in abduction: normal maturity has always been attained without dysplastic involutions. Our experience confirmed US value in the early diagnosis of congenital acetabular dysplasia, when clinics exhibited evident limitations. Nonetheless, management and economical problems are still to be solved, due to the relationship of the widespread use of US in infant population and to its successful results, also considering the low incidence of the examined pathologic condition.

The authors describe a clinic case regarding a 23 year-old man affected by an osteoid osteoma of the hip's posterior edge of the cotyloid cavity. The illness had been treated for two years as a lumbar disc syndrome. As any objective clinic sign missed at the hip's level and given the rarity of the location, only surgical removal was able to cure the patient.