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.

The results of using the Ring uncemented polyethylene-to-metal (UPM) prosthesis in patients with protrusio acetabuli or dysplasia are reported. Fifty-four cases of protrusio were analysed and a modified method of measuring the deformity is described; after operation, remodelling of the medial wall had improved, on average, by 29.6%. For the dysplastic acetabulum the main difficulty is the lack of lateral support for the cup. In order to test the hypothesis that this support improves with an uncemented prosthesis, 38 hips with an average follow-up of 31 months were studied. Lateral support, measured radiographically, showed an average increase of 21%. The remodelling effect may be attributed to the biomechanical design of the prosthesis.

Between January 1988 and January 1991 we performed 100 consecutive cemented total hip replacements using a zirconia head, a titanium alloy stem and a polyethylene cup. We reviewed 78 of these hips in 61 patients in detail at a mean of 5.8 years (1 to 9). Aseptic loosening was seen in 11 hips (14%). Eight needed revision. In total, 37 cups (47.5%) showed radiolucent lines, all at the cement-bone interface, with 18 (23%) involving all the interface. Of the 78 femoral implants, 17 (21.7%) showed radiolucent lines, and two, which had a complete line of more than 1 mm thick, definite endocortical osteolyses. There was also an abnormally high incidence of osteolysis of more than 2 mm at the calcar. Survivorship analysis showed that only 63% were in situ at eight years. These worrying results led us to abandon the use of zirconia heads, since at the same hospital, using the same femoral stem, cement and polyethylene cup, but with alumina femoral heads, the survival rate was 93% at nine years. We discuss the possible reasons for the poor performance of zirconia ceramic

A reduced femoral offset in total hip replacement has been thought to be disadvantageous. We reviewed the results of 54 consecutive primary total hip replacements in 49 patients (mean age of 68 years) performed between August 1990 and December 1994, with a mean follow-up of 8.8 years (. sd. 2.1). The mean pre-operative femoral offset for these hips was 41 mm (. sd. 7.4). All patients received a low-offset Charnley stem and a polyethylene cup inserted by a single surgeon. At their latest follow-up, surviving patients had a significant improvement in the performance of their hip. Three had undergone revision, one each for deep infection, recurrent dislocation and late pain with subluxation. No hips had been revised, or were at risk of revision, for aseptic loosening. The mean annual linear rate of wear was 0.2 mm (. sd. 0.08) for the whole group. There was no correlation between the pre-operative femoral offset and the post-operative rate of wear. Our survivorship estimate was 91% when revision for any reason was taken as an end-point, but 100% if aseptic loosening was considered as the end-point. Our study demonstrates that a low-offset femoral stem can produce good, medium-term results

Aims

The aim of this study was to report the long-term follow-up of cemented short Exeter femoral components when used in primary total hip arthroplasty (THA).

A reversed Delta III total shoulder prosthesis was retrieved post-mortem, eight months after implantation. A significant notch was evident at the inferior pole of the scapular neck which extended beyond the inferior fixation screw. This bone loss was associated with a corresponding, erosive defect of the polyethylene cup. Histological examination revealed a chronic foreign-body reaction in the joint capsule. There were, however, no histological signs of loosening of the glenoid base plate and the stability of the prosthetic articulation was only slightly reduced by the eroded rim of the cup

We retrieved 159 femoral heads at revision surgery to determine changes in surface configuration. Macroscopic wear of the head was observed in three bipolar hip prostheses as a result of three-body wear. There was a considerable change in surface roughness in the internal articulation of bipolar hip prostheses. Roughness in alumina heads was almost the same as that in new cobalt-chromium heads. The annual linear wear rate of polyethylene cups with alumina heads was less than that of cups with cobalt-chromium alloy heads. Polyethylene wear was increased in the prostheses which had increased roughness of the head

We report a long-term review of 60 acetabular components revised using impacted, morsellised bone allografts and a cemented polyethylene cup. The acetabular defects were cavitary (37) or combined (23). Follow-up was for a mean 11.8 years (10 to 15). Further revision was needed in five hips, two for septic and three for aseptic loosening. The overall survival rate at 11.8 years was 90%; excluding the septic cases it was 94%. Acetabular reconstruction with impacted morsellised cancellous grafts and cement gives satisfactory long-term results

We report the results of our continued review of 14 hip arthroplasties using alumina ceramic femoral heads with cross-linked polyethylene cups. There have been no complications and a very low rate of penetration. This was 0.02 mm per year after an initial ‘bedding-in’ period of two years. There has been no change in the mean rate between our earlier study at six years and the current results at 10 to 11 years. The use of these bearing surfaces appears to reduce the potential amount of polyethylene debris and may provide the next logical stage in the development of the Charnley low-friction arthroplasty

We report the results of 24 acetabular reconstructions in which cemented polyethylene cups and tamped corticocancellous allografts were used for severe acetabular bone deficiency. Eleven hips had type-II (cavitary) bone deficiency and 13 had type-III (combined) defects. At a mean follow-up of 5.8 years, two components had migrated more than 5 mm and had accompanying radiolucent zones of more than 2 mm width. A radiolucency 5 mm wide was also seen in zone III of an acetabular implant which had not migrated. None of the patients had required revision because of loosening or infection

In this prospective, randomised study, we have compared the wear rate of cemented, acetabular polyethylene cups articulating with either a 22 mm or a 32 mm cobalt-chromium head. We evaluated 89 patients who had a total of 484 radiographs. The mean follow-up period was 71.4 months (SD 29.1). All the radiographs were digitised and electronically measured. The linear wear rate was significantly higher during the first two years and decreased after this period to a constant value. We suggest that this is partly due to a ‘run-in’ process caused by irregularities between surfaces of the cup and head and an initial plastic deformation of the polyethylene. The mean volumetric wear was 120.3 mm. 3. /year for the 32 mm head, which was significantly higher than the 41.5 mm. 3. /year for the 22 mm heads. The mean linear wear rate was not significantly different. We were, however, unable to find radiological signs of osteolysis in the patients who had higher wear rates

Since wear and loosening of the ultra-high-molecular-weight polyethylene cup are factors which limit the life of an arthroplasty we have attempted to identify factors associated with either low wear (0.02 mm/year or less) or high wear (0.2 mm/year or more). In a series of 1434 Charnley low-friction arthroplasties (1092 patients) 190 (13.2%) showed low wear while 149 (10.4%) showed high wear. We used chi-squared test to assess the significance of various factors. The significant factors of the low-wear group were female gender (p = 0.042), rheumatoid arthritis (p = 0.014), Charnley grade C (p = 0.03) and varus position of the stem (p = 0.003). The use of acetabular cement pressurisation (p = 0.07) and medialisation of the cup (p = 0.07) approached significance. In the high-wear group there was a predominance of men (p = 0.042) with osteoarthritis (p = 0.006) as the underlying hip pathology, and the stem in a valgus position (p = 0.023). Support of the cup by the rim of the acetabulum approached significance (p = 0.07). There was no statistical significance between the two groups for revision for aseptic loosening of the stem or fracture of the stem (p = 0.49). There was a highly significant difference (p < 0.0001) between the two groups for revision for wear and aseptic loosening of the cup, 5.3% compared with 39%. Changes in the cup geometry are probably sufficient to explain the increasing incidence of loosening and revisions with the increasing depth of penetration of the cup. There is much to be gained from the use of a low-wearing ceramic-ultra-high-molecular-weight combination. Tissue reaction to the polyethylene particles cannot be the cause of aseptic loosening of the stem

Aims

We aimed to evaluate the long-term outcome of highly cross-linked polyethylene (HXLPE) cemented acetabular components and assess whether any radiolucent lines (RLLs) which arose were progressive.

Fracture of the polyethylene acetabular cup is a rare late complication of total hip replacement. Five cases are reported. In each one this followed a fall, and involved a Muller arthroplasty which had previously been symptomless. It is postulated that ridges or other irregularities of bone, produced by keying holes, could lead to areas of thin cement and potential weakness of support for the cup

Polyethylene acetabular cups retrieved at revision surgery were measured by a shadowgraph technique to determine linear wear, and the values were compared with those obtained from radiographs. There was a close correlation between them, although the radiographic measurements slightly underestimated the true wear. Average linear wear rates for surface-replacement components were much greater than those for conventional prostheses with femoral heads up to 32 mm in diameter. Volumetric wear, calculated using a new formula, was found to be less than previously reported in vivo, and similar in magnitude to the results of experimental wear tests in vitro. The volumetric wear rates were greatest for the surface-replacement components and, for conventional components, were found to increase in a linear manner with component diameter

One concern about the fixation of HA-coated implants is the possible disintegration of the surface, with the migration of HA granules into the joint space, producing third-body wear. We report a study of six revisions of HA-coated polyethylene RM cups at 9 to 14 years after successful primary arthroplasty. In all six hips, we found HA granules embedded in the articulating surface of the polyethylene, with abrasive wear of the cup and the metal femoral head. The cup had loosened in four hips and three showed severe osteolysis of the proximal femur. Third-body wear due to HA particles from implant coating may produce severe clinical problems with few early warning signs. Further clinical, radiological and histological observations are needed to determine the possible incidence of this late complication in the various types of coating of a variety of substrates

We report a high rate of failure of the Ring polyethylene cementless cup caused largely by granulomatous osteolysis. We have reviewed 126 prostheses inserted from 1986 to 1992 at from 11 to 90 months after surgery. There was radiological evidence of osteolytic granulomas adjacent to the external surface of the cup in 32%, appearing on average at three years from operation. In a subgroup of 59 prostheses followed for at least four years the incidence of such changes was 54%. A total of 27 cups (22%) have required revision, 21 for granulomatous loosening at an average follow-up of five years. In the retrieved prostheses there was obvious polyethylene abrasion and histological examination confirmed the presence of polyethylene wear debris. We found no significant correlation of osteolysis with cup size, although smaller cups were predominant among those having revision

We made a clinical study of polyethylene wear in 240 hips of 187 patients having primary total hip arthroplasties from 1989 to 1990, using uncemented Osteonics components, with a head size of 26 mm. We excluded cups with anteversion of over 20° and measured linear wear by a new method using a digitiser and special software of our design. Follow-up was from two to five years (mean 4.3). The mean age at operation was 50.3 years, with more men than women (1.4:1). The mean linear wear per year was 0.15 mm; this did not increase with the longevity of the prosthesis (p = 0.54). In 59 hips showing evidence of osteolysis, the mean linear wear rate was significantly higher at 0.23 mm/year (p < 0.001). The mean linear wear rate also correlated significantly with age at the time of operation (p = 0.008), but we found no significant correlations with body-weight, gender, aetiology of the disease, thickness of polyethylene, or cup position. Our new method of measurement is time-saving and reproducible. The results confirm the greater rate of linear wear of polyethylene in patients showing osteolysis and in those who are younger

We analysed revised Mathys isoelastic polyacetal femoral stems with stainless-steel heads and polyethylene acetabular cups from eight patients in order to differentiate various types of particle of wear debris. Loosening of isoelastic femoral stems is associated with the formation of polyacetal wear particles as well as those of polyethylene and metal. All three types of particle were isolated simultaneously by tissue digestion followed by sucrose gradient centrifugation. Polyacetal particles were either elongated, ranging from 10 to 150 μm in size, or shred-like and up to 100 μm in size. Polyethylene particles were elongated or granules, and were typically submicron or micronsized. Polyacetal and polyethylene polymer particles were differentiated by the presence of BaSO. 4. , which is added as a radiopaque agent to polyacetal but not to polyethylene. This was easily detectable by back-scattered SEM analysis and verified by energy dispersive x-ray analysis. Two types of foreign-body giant cell (FBGC) were recognised in the histological specimens. Extremely large FBGCs with irregular polygonal particles showing an uneven, spotty birefringence in polarised light were ascribed to polyacetal debris. Smaller FBGCs with slender elongated particles shining uniformly brightly in polarisation were related to polyethylene. Mononucleated histiocytes containing both types of particle were also present. Our findings offer a better understanding of the processes involved in the loosening of polyacetal stems and indicate why the idea of ‘isoelasticity’ proved to be unsuccessful in clinical practice

Many different designs of total hip arthroplasty (THA) with varying performance and cost are available. The identification of those which are the most cost-effective could allow significant cost-savings. We used an established Markov model to examine the cost effectiveness of five frequently used categories of THA which differed according to bearing surface and mode of fixation, using data from the National Joint Registry for England and Wales. Kaplan–Meier analyses of rates of revision for men and women were modelled with parametric distributions. Costs of devices were provided by the NHS Supply Chain and associated costs were taken from existing studies. Lifetime costs, lifetime quality-adjusted-life-years (QALYs) and the probability of a device being cost effective at a willingness to pay £20 000/QALY were included in the models.

The differences in QALYs between different categories of implant were extremely small (<  0.0039 QALYs for men or women over the patient’s lifetime) and differences in cost were also marginal (£2500 to £3000 in the same time period). As a result, the probability of any particular device being the most cost effective was very sensitive to small, plausible changes in quality of life estimates and cost.

Our results suggest that available evidence does not support recommending a particular device on cost effectiveness grounds alone. We would recommend that the choice of prosthesis should be determined by the rate of revision, local costs and the preferences of the surgeon and patient.

Cite this article: Bone Joint J 2015;97-B:449–57.