Metal-on-metal articulation in total hip arthroplasty: preliminary results in 57 cases.

BACKGROUND: Aseptic loosening of hip prostheses may lead to implant failure and necessitate revision surgery. Metal-on-metal hip articulation has characteristics that may minimize prosthesis loosening when compared with other forms of hip articulation. The purpose of the present prospective study was to identify early problems that may contraindicate the use of the 'prosthesis femorale modulaire' (PFM) metal-on-metal prosthesis. METHODS: The preliminary results of 57 metal-on-metal total hip arthroplasties performed by one surgeon (RR) from 1994 to 1996 in Lismore, New South Wales, are presented here. Data were obtained using patient questionnaires, physical examination and by examination of radiographs. RESULTS: A total of 87.6% of patients had an excellent or good outcome, according to the Harris rating system, at the latest review. The two patients with poor results had obvious alternative causes for their continuing symptoms. There was no radiological evidence of bone or prosthesis failure during the period of follow-up. CONCLUSIONS: The preliminary results are comparable with those of other authors who have examined the early results of metal-on-metal total hip arthroplasty.

Acetabular screw rings and surface treatment.

The Zweymüller truncated self tapered threaded ring is forged in pure titanium with a 3- to 5-mu grit blasted surface roughness. Among 167 consecutive primary total hip arthroplasties prospectively studied, two threaded components failed to achieve initial stability, with one requiring almost immediate revision. One hundred twenty-six hips have been fully documented with a 5-year minimum followup. The mean modified Harris hip score improved from 44.4 points preoperatively to 91 points at 7 years average followup (range, 60-121 months). Bone to implant gap rate decreased from 54.7% after surgery to 2.4% at last review, with only one detectable early migration that had secondary stable osseointegration. Annual linear wear of more than 0.2 mm per year could be detected in only one ceramic on polyethylene bearing surface with one corresponding femoral osteolysis granuloma. At the 9- to 10-year interval, the survivorship with definite loosening as a failure was 98.7%. Delayed loosening by failure of an initially stable reconstruction, progressive lucencies, liner disassociation, or worrisome osteolysis have not been observed. These midterm results are much better than those of former screw rings with smooth surface finishes. The main reason for the general failure and justified abandonment of threaded polished components may not be the screw in mechanism of their primary fixation, but the lack of an appropriate surface for bone ingrowth and osseointegration.

Design of the femoral component for cementless hip replacement: the surgeon's perspective.

Few guidelines are currently available to the surgeon when choosing a specific femoral component for cementless total hip replacement (THR). A survey of the members of the American Association for Hip and Knee Surgeons (AAHKS) was conducted to gain insight into the importance of implant material, stress shielding, and micromotion in the selection of cementless femoral components. A comprehensive survey was distributed to 300 orthopedic surgeons selected from the members of the AAHKS; 169 of the 300 surgeons completed the detailed questionnaire. The results of the survey were analyzed using the SPSS software package to obtain general trends in opinion, and a stepwise regression analysis was used to correlate responses with training and clinical experience. Interestingly, there was little consensus among surgeons with respect to the relative importance of implant material, stress shielding, and micromotion in the selection of prostheses for cementless THR. In general, bone loss secondary to stress shielding was the least important issue, and axial and rotational micromotion were considered progressively more significant problems. Cementless titanium alloy stems were perceived as offering no significant advantage over cobalt chrome alloy stems. Moreover, there was no consensus as to whether a collar was advantageous. Prosthesis stability, restoration of motion, and a proven clinical record were more important to surgeons than were ease of implantation and removal, cost, and availability.

Effect of a centralizing device on cement mantle deficiencies and initial prosthetic alignment in total hip arthroplasty.

Sixty consecutive patients undergoing a primary hybrid total hip arthroplasty were randomized to receive a femoral component either with or without a distal centralizing device. The group with a centralizer had significantly fewer patients with cement mantle deficiencies (excessively thin areas of cement) than the group without a centralizer (P < .001). Furthermore, the centralizer group was, on average, in a neutral alignment, whereas the group without a centralizer was in a varus alignment (P < .001). It was concluded that the distal centralizing device significantly decreases the incidence of cement mantle deficiences and reproducibly aids in achieving a more neutral prosthetic alignment.

Increased awareness of glove perforation in major joint replacement. A prospective, randomised study of Regent Biogel Reveal gloves.

An intact barrier between the hands of the surgeon and the patient remains the single most important factor in protection against infection for both. Increasing the awareness of possible glove perforation without skin penetration will decrease the risk of contamination. We performed a prospective, randomised trial comparing the incidence of glove perforation using a new type of glove (Regent Biogel Reveal) and standard double-gloves in total hip and knee replacement. One or more perforations was detected in 14.6% of all gloves. The new gloves increased significantly the awareness of perforation. Multiple perforations at the base of the ring finger were found in surgeons who wore wedding rings during the operation and we recommend that rings be removed before undertaking surgery.

Cement pressurisation during hip replacement.

The newer techniques of cementing aim to improve interlock between cement and bone around a femoral stem by combining high pressure and reduced viscosity. This may produce increased embolisation of fat and marrow leading to hypotension, impaired pulmonary gas exchange and death. For this reason the use of high pressures has been questioned. We compared finger-packing with the use of a cement gun by measuring intramedullary pressures during the cementing of 31 total hip replacements and measuring physiological changes in 19 patients. We also measured pressure in more detail in a laboratory model. In the clinical series the higher pressures were produced by using a gun, but this caused less physiological disturbance than finger-packing. The laboratory studies showed more consistent results with the gun technique, but for both methods of cementing the highest pressures were generated during the insertion of the stem of the prosthesis.

[Ceramic-to-ceramic combination. Relic or renaissance?]. / Die Keramik-Keramik-Paarung. Schattendasein oder Renaissance?

More than 20 years after the introduction of the alumina-alumina bearing system for total hip replacements (THRs) in Germany, this combination still only accounts for a small percentage of the conventional combinations with polyethylene cups. Follow-up examinations of ceramic-ceramic THRs with early alumina quality result in an extreme range of linear wear rates from 30 nm to 3.7 mm per year. Simulator tests confirm the potential for minimal debris generation but also show the sensitivity of the system to malpositioning and un-smooth repositioning.

[Comparative tribological studies of Chirulen, Hylamer and Enduron combined with A1203]. / Vergleichende tribologische Untersuchungen von Chirulen, Hylamer und Enduron gepaart mit Al2O3.

The creep and wear behaviour of Chirulen, Hylamer and Enduron, materials which differ only in their manufacturing procedures, was examined and compared. Chirulen is manufactured by being pressed into form by plates, whereas Hylamer and Enduron are shaped by tubes. Hylamer differs from Enduron in that intermediate material processing is undertaken with the goal of improving the initial material. The wear and deformation rate was determined by means of the ring-on-disc testing device after 360,000 cycles and after 1.0 x 10(6) cycles, respectively. The static tests for the determination of wear were carried out at a contact stress of 5.62 MPa and a testing time of 100 h in analogy to the ring-on-disc tests. Chirulen and Hylamer demonstrated comparable wear with a tendency toward a lower wear rate in Hylamer, while Enduron presented a clearly higher wear rate.

[Cementless fixation of the endoprosthesis using trabecular, 3-dimensional interconnected surface structures]. / Zementlose Endoprothesenverankerung mittels trabekulären, dreidimensional interkonnektierenden Oberflächenstrukturen.

While the principle of enlarging the surface area has been recognized and used in different ways for some time, there is often no schematic, detailed description or fundamental research. Taking a surface structure consisting of trabecular three-dimensional connecting elements, essential parameters are shown, making it clear that the flexible dynamic reaction of the effective "anchoring space" with a suitable specified shape (construction height, alignment, network) can be reproducibly shaped and used. This has led to a hip endoprosthesis with a graduated surface structure. The construction height of the trabecular structure varies, decreasing from proximal to distal.

[In-vivo wear of the slide combinations ceramics-polyethylene as opposed to metal-polyethylene]. / In-vivo-Verschleiss der Gleitpaarungen Keramik-Polyethylen gegen Metall-Polyethylen.

The present study deals with long-term dimensional changes in cemented Müller-type total hip endoprostheses. Creep and wear contribute to different extents to the dimensional changes in polyethylene. The total amount of polyethylene wear is represented by the displacement of the femoral head into the socket. Within the first postoperative years, the head shifts up to a relatively high rate of about 0.5 mm per year. This rate diminishes after 5 years to an average of about 0.1 mm (ceramics) and 0.2 mm (metal) per year. Values exceeding 0.2 mm per year for the shift of the femoral head are considered to be unfavourable with regard to a probable loosening of the prosthesis. In this study we determined the orientation of the centre of the prosthetic head in relation to the wire marker of the polyethylene cup, comprising in all 369 total hip prostheses. After an average of 77 months, 96% of the prostheses with ceramic heads (n = 109) had a wear rate of less than 0.2 mm per year. Using metal heads (Protasul-2 and Protasul-10) this rate could only be measured in 71% (n = 109) of the prostheses (61.5 months). The combination ceramics-polyethylene produces half of the total amount of wear produced by metal-polyethylene. Younger patients should preferably be treated with a ceramic ballhead.

[Low loosening rate of a cemented titanium straight shaft prosthesis in long-term follow-up]. / Niedrige Lockerungsrate einer zementierten Titan-Geradschaftprothese im längerfristigen Verlauf.

Aseptic loosening is still a major problem in total hip replacement. We studied the mid-term results of a straight stem femoral prosthesis made from titanium alloy (BiContact) and implanted with the use of bone cement. 250 hips in 238 patients have been implanted between 8/87 and 12/88 and followed up. 172 patients were alive and could be reached after 7 years. Two patients had to undergo revision surgery within the follow up period, and in two other patients radiolucencies could be found. A loosening rate of 1.2% and a rate of radiolucencies of another 1.2% indicate that the combination of a titanium alloy stem prosthesis with bone cement not necessarily leads to early loosening or a high loosening rate, which has been supposed by several authors. The design of the individual prosthesis seems to be of greater importance than the materials used.

The influence of the stem-cement interface in total hip replacement--a comparison of experimental and finite element approaches.

Experimental and finite element investigations were carried out on axisymmetric models of the femoral component of a total hip replacement. In one instance, the interface between the stem and the surrounding bone cement was assumed to be rigidly bonded; in a second, it was allowed to slip. For the latter case, a friction coefficient of 0.2 was determined experimentally. The predictions of the finite element models demonstrated excellent agreement with the results from the experimental tests at all sites where comparisons were made, thus validating these models. The effect of stem-cement slip was shown to reduce the maximum shear stress in the cement mantle by approximately 30 per cent.

Long-term results and survivorship of Protasul 10 straight stem Müller femoral hip prosthesis.

In a retrospective study 88 consecutively cemented Protasul 10 straight stem total hip prostheses, implanted during a two year period, were investigated. After a nine to ten year period 8 hips had been revised. In the clinically and radiologically checked group, the patients' opinion was in 82% very good or good, in 9% moderate and in 9% bad. The X-Ray findings showed in 20% an initial or advanced loosening of the stem and/or the cup. The survivorship after a nine to ten year period is 89%.

Charnley wear model for validation of hip simulators--ball diameter versus polytetrafluoroethylene and polyethylene wear.

Wear rates of polytetrafluoroethylene (PTFE) and polyethylene cups were compared in 9-channel and 12-channel simulators, using serum lubrication and gravimetric techniques for wear assessment. Cobalt-chromium (CoCr) and alumina ceramic femoral heads in 22-42 mm diameter range were used to validate simulator wear rates against clinical data. This was also the first study of three femoral head sizes evaluated concurrently in a simulator (with three replicate specimens) and also the first report in which any wear experiments were repeated. Fluid absorption artefacts were within +/-1 per cent of wear magnitude for PTFE and +/-8 per cent for polyethylene and were corrected for. Wear rates were linear as a function of test duration. Precision within each set of three cups was within +/-6 per cent. The wear rates from experiments repeated over 15 months were reproducible to within +/-24 per cent. However, the magnitudes of the simulator wear rates were not clinically accurate, the PTFE wear rates (2843 mm3/10(6) cycles; 22 mm diameter) were over three times higher than in vivo, the polyethylene 30 to 50 per cent on the low side (23 mm3/10(6) cycles; 22 mm diameter). Volumetric wear rate increased with respect to size of femoral head and a linearly increasing relationship of 7 8 per cent/mm was evident with respect to femoral head diameter for both PTFE and polyethylene. These data compared well with the clinical data.

Factors contributing to the wear of polyethylene in clinical practice.

Wear of polyethylene is a major contributor in the failure of total joint replacement. A number of different factors may predispose to increased wear of polyethylene. These can be broadly categorized as (i) material polymorphism, (ii) poor design features and (iii) three-body wear. Many of these factors contribute to the wear encountered in clinical practice. These mechanisms are reviewed and examples identified in which they have resulted in increased wear.

Fixation of ultrahigh-molecular-weight polyethylene liners to metal-backed acetabular cups.

Locking mechanisms and metal-liner interface surfaces of six modular acetabular systems were evaluated to determine their effect on micromotion and backside wear of the polyethylene liner. Rotational and axial motion between the metal shell and polyethylene liner was measured in the Duraloc (DePuy, Warsaw, IN), Harris-Galante (Zimmer, Warsaw, IN), Impact (Biomet, Warsaw, IN), Lip Loc (Biomet), Precision Osteoloc (Howmedica, Rutherford, NJ), and Reflection (Smith & Nephew Orthopaedics, Memphis, TN) designs at the start of each test, and at 1 million, 5 million, and 10 million cycles. At 10 million cycles, the Lip Loc and Reflection cups had significantly lower rim micromotion than the Duraloc and Harris-Galante cups (F < .0010). The Impact, Precision Osteoloc, and Reflection cups had significantly lower rim subsidence than the Harris-Galante cup (F < .0025). The Harris-Galante cup had significantly greater rotational micromotion than the Lip Loc cup (F < .0074), and had significantly greater interface slippage than the Impact and Reflection cups (F < .0070). The Lip Loc produced significantly lower dome micromotion than the Harris-Galante (F < .0300). The Lip Loc and Reflection cups had significantly less backside wear than the Duraloc and Harris-Galante cups (P < .0001), the Impact cup (P < .0243), and the Precision Osteoloc (P < .0027) cup.

Uncemented total hip arthroplasty in osteonecrosis: a 2- to 10-year evaluation.

All patients undergoing uncemented total hip arthroplasty for end stage hip disease related to osteonecrosis of the femoral head were assessed prospectively between November 1983 and October 1992. The results of clinical evaluation using the Harris Hip score and radiographic assessment of fixation were analyzed to identify features of success or failure that may be unique to this population. Four different stem types and 4 different acetabular components were used. Sixty-four patients had 98 hips implanted during the time of the study. The 42 male and 22 female patients averaged 41 years of age (range, 21-69 years). Average followup was 87.3 months (7.3 years; range, 31-134 months). The cause of osteonecrosis was corticosteroids (42 hips), alcohol (27 hips), trauma (5 hips), and other (24 hips). Three patients (5 hips) have died and 4 patients (6 hips) are lost to followup. At last followup 65 of 87 hips (75%) remained radiographically stable and clinically functional, 18 of 87 (21%) have been revised, and 4 were failing (osteolysis). Of the 22 hips with revision or impending failure, 4 were for technical reasons on the femoral side and 18 were for acetabular wear. Patient factors such as weight or underlying disease state did not seem to influence the ability to achieve stable fixation or contribute to accelerated failure. Failures related primarily to problems of first generation devices including accelerated wear of acetabular components, technical issues of femoral component placement (undersizing of components or femoral fracture), and the use of noncircumferentially coated femoral components. Age may be a factor in early failure. This 10-year experience with total hip arthroplasty for the patient with end stage hip disease due to osteonecrosis suggests that uncemented total hip arthroplasty can be applied predictably to this younger, potentially more active patient population.

[Modularity of prostheses]. / La modularité des prothèses.

Modularity allows a large choice of implants, like the use of cementless acetabular cups inducing bone ingrowth. The length and direction of the neck may also be adapted to be new joint. Risks of modularity are: implant dissociation, restriction of joint mobility, and especially augmentation of metal debris as a potential source of polyethylene wear. It is then critical to play attention to implant design, material choice and planning of the arthroplasty.

Acetabular supporting ring in total hip replacement.

A series of 14 total hip arthroplasties with a Müller acetabular supporting ring including 3 primary and 11 revision arthroplasties is reviewed. This device was used in cases of acetabular bone deficiency, and bone graft was added in 11 cases. The mean length of follow-up was 39.9 months. Twelve patients had good or satisfactory results, while two operations failed. These results indicate that the acetabular supporting ring is a useful implant in cases with acetabular bone stock deficiency.