Femoral Resurfacing Component Research Articles

Femoral Fixation Methods in Hip Resurfacing Arthroplasty: An 11-Year Retrospective Comparison of 4013 Cases

BackgroundThe optimal femoral fixation method remains unclear. To evaluate the role of femoral fixation techniques in hip resurfacing, we present a comparison of 2 consecutive groups: group 1 (739 hips) with cemented femoral components; group 2 (3274 hips) with uncemented femoral components. MethodsWe retrospectively analyzed our clinical database to compare failures, reoperations, complications, clinical results, and radiographic measurements. Groups were consecutive, so cemented cases had longer follow-up. However, all patients from both groups were at least 2 years out from surgery. Two-year clinical and radiographic data were compared. Longer-term comparison data as well as Kaplan-Meier implant survivorship curves specifically focusing on femoral failure modes were analyzed. ResultsKaplan-Meier 10-year implant survivorship using nontraumatic femoral failure as an end point was 98.9% for the cemented and 100% for the uncemented femoral component. The uncemented, group 2 cases showed a significantly lower raw failure rate (1.1% vs 4.6%), 2-year failure rate (0.8% vs 2.8%), 2-year femoral failure rate (0.4% vs 0.9%), and a lower combined rate of femoral complications and failures (0.6% vs 1.8%). In cases that did not fail, patient mean clinical scores, pain scores, and combined range of motion were all significantly better for group 2. ConclusionWe have demonstrated that in the fully porous-coated ReCap device, uncemented femoral fixation is superior to cemented fixation at 11 years follow-up (0.0% vs 1.1% late femoral loosening) in this single-surgeon cohort. Early femoral fractures also reduced from 0.8% to 0.3%, but this may be partially or completely due to a new bone density management program. This study demonstrates better femoral implant survivorship for the uncemented device compared to the cemented femoral resurfacing component for this implant design.

Conversion of Hip Resurfacing With Retention of Monoblock Acetabular Shell Using Dual-Mobility Components

BackgroundRetention of the acetabular component is an option during conversion from hip resurfacing arthroplasty (HRA) to total hip arthroplasty (THA). The purpose of this study was to compare clinical outcomes of conversion of the femoral resurfacing component with retained acetabular components (RAC) and use of dual-mobility femoral heads to outcomes of patients treated with both component (BC) revisions. MethodsA retrospective review was performed of the clinical outcomes of HRA to THA conversions performed at a single institution between 2008 and 2017. ResultsSeventy-one conversions were included (27 RAC and 44 BC). Average age at time of conversion was 54.4 years (range, 30-68 years). Median time to conversion was 5.14 (2.77-7.41) years and median follow-up post-conversion was 1.7 (0.33-4.0) years. There were no significant differences in indications for conversion between the 2 groups with the majority performed for complications related to elevated metal ions and aseptic loosening. Harris Hip Scores improved from pre-conversion to post-conversion in both cohorts (P < .01). There were no significant differences in pre-conversion and post-conversion metal ion levels between the RAC and BC groups. Serum metal ion levels decreased significantly in both cohorts (P < .01). There were 6 additional revisions in the cohort (4 in BC, 2 in RAC) at a median 2.94 (1.99-3.85) years post-conversion. Two RAC patients had intraprosthetic dislocations with extensive polyethylene wear requiring acetabular revision at median 3.92 (3.85-3.98) years post-conversion. Overall, there were a higher number of complications in the BC group related to acetabular fracture, failure of osseointegration, and periprosthetic joint infection; however, this did not reach statistical significance (P = .27). ConclusionSalvage of an appropriately positioned, well-fixed HRA acetabular component is a reasonable option in the setting of conversion to THA using dual-mobility components. This technique avoids the morbidity of acetabular revision and was associated with a decrease in metal ion levels and improvements in short-term functional outcomes comparable to a BC revision.

Influence of femur size and morphology on load transfer in the resurfaced femoral head: A large scale, multi-subject finite element study

Femoral resurfacing has become an increasingly popular procedure, especially for young, active patients. The procedure is known to alter load transfer through the proximal femur and this has been linked with the most commonly observed complication, neck fracture. An intriguing observation noted by registry data and clinical studies is an inverse relationship between implant size and revision rate. While computational analysis has become an established part of biomedical engineering, the majority of work uses a single or small set of bone models, with a single implant size, due to the constraints of time and data availability. Therefore, it has been infeasible to run a study incorporating natural inter-patient variability or the performance of smaller implants could not be meaningfully studied. In previous work a statistical model of the whole femur was used to generate large numbers of unique, realistic, FE-ready femur models describing both geometry and material properties. The current study demonstrates a methodology for virtually implanting and performing stress analysis of cemented femoral resurfacing components, with model specific sizing and orientation. Automated analysis of 400 generated femurs, in both implanted and intact configurations showed the strain changes induced by resurfacing. This produced a statistically meaningful number of results and allowed the examination of outliers. Results showed increased femoral neck strain changes potentially increasing the risk of neck fracture, associated with smaller, less dense femurs and smaller implant sizes; agreeing with clinical observations. The study demonstrates a methodology for more comprehensive analyses, based on populations rather than individuals.

A custom-made guide for femoral component positioning in hip resurfacing arthroplasty: development and validation study

In the field of hip resurfacing arthroplasty, accurate femoral component placement is important to achieving a positive outcome and implant survival in both the short and long term. In this study, femoral component placement was defined preoperatively using virtual computed tomography-based surgical simulation of a classical posterior surgical approach. Custom-made surgical drill guides were produced to reproduce the surgical plan in the operating room. We first developed a custom-made guide for guide-wire placement to position the femoral resurfacing component. Then, to assess the accuracy in vivo, the custom-made guide was evaluated in five patients with normal anatomy. The first hypothesis of this patient study was that the use of custom-made neck guides would allow for an average accuracy within the range of ±4° for the drill path and ±4 mm for the entry point of the guide-wire. A second hypothesis was that three-dimensional preoperative planning would enable the prediction of an implant size differing by a maximum of one size from the size eventually implanted.The presented hip resurfacing guide performed well in terms of fit, stability and accuracy. The in vivo accuracy study revealed an accuracy of 4.05 ± 1.84° for the drill path and 2.73 ± 1.97 mm for the entry point of the guide-wire. The predicted component sizes and the implanted component sizes differed maximally by one size, confirming our hypothesis. We conclude that these preliminary data are promising, but require further validation in a full clinical setting in larger patient groups.

Femoral Revision in Hip Resurfacing Compared With Large-Bearing Metal-on-Metal Hip Arthroplasty

It has been suggested that revision of the femoral component of hip resurfacing after femoral failure would be straightforward and have an outcome comparable to primary total hip arthroplasty (THA). We have compared the outcome of femoral side–only revision resurfacings to the results of primary modular large-bearing metal-on-metal THA. Fourteen consecutive patients underwent revision surgery of the failed femoral component, to a cemented tapered stem (CPT, Zimmer, Warsaw, Indiana) with a large modular metal head (Smith and Nephew Orthopaedics Ltd, Memphis, Tennessee, or Adept, Finsbury Orthopaedics, Surrey, England). The acetabular component was found to be well fixed, well orientated, and was left in situ. The 14 matched patients in the primary THA group received the same components. At a mean follow-up of 49 months (range, 30-60 months), clinical outcome measured using the Oxford and Harris Hip Scores showed no significant difference ( P = .11, P = .45, respectively). Operative time and blood loss were comparable for both groups. We conclude that revision of the failed femoral resurfacing component gives excellent results.

The impact of seating forces from a cementless femoral component in hip resurfacing arthroplasty on the femoral head – A cadaver study using μ-CT analysis

Recent studies have assumed micro-fractures of the femoral head during hip resurfacing arthroplasty as a possible reason for fractures at the implant/neck junction. The purpose of this study was to analyze whether implantation of a cementless femoral hip resurfacing component which requires high seating forces, causes micro-fractures of the femoral head. A cementless hip resurfacing femoral component was installed on 20 human, cadaveric femoral heads with an impaction device that generated 4.5 kilonewton force in one group and by hand in the other. Before and after impaction, the specimens were scanned with a μ-CT-System. The CT datasets were segmented and registered for detection of small trabecular fractures. The average percentage of shared voxels was 80.29% (standard deviation 3.24%). Change in bone structure after impaction (19.71%) was found on the surfaces of all samples. No formation that was ascribed to fracture was found. No difference between the specimens that were impacted by hand or by impaction device was noted. No fractures of the cancellous femoral head during installation of a cementless femoral THR component occurred. Cementless hip resurfacing might not increase the risk of fracturing the cancellous femoral head during implantation in a cadaveric μ-CT study.

Influence of the change in stem length on the load transfer and bone remodelling for a cemented resurfaced femur

The effect of a short-stem femoral resurfacing component on load transfer and potential failure mechanisms has rarely been studied. The stem length has been reduced by approximately 50% as compared to the current long-stem design. Using 3-D FE models of natural and resurfaced femurs, the study is aimed at investigating the influence of a short-stem resurfacing component on load transfer and bone remodelling. Applied loading conditions include normal walking and stair climbing. The mechanical role of the stem along with implant–cement and stem–bone contact conditions was observed to be crucial. Shortening the stem length to half of the current length (long-stem) led to several favourable effects, even though the stress distributions in the implant and the cement were similar in both the cases. The short-stem implant led not only to a more physiological stress distribution but also to bone apposition (increase of 20–70% bone density) in the superior resurfaced head, when the stem–bone contact prevailed. This also led to a reduction in strain concentration in the cancellous bone around the femoral neck–component junction. The normalised peak strain in this region was lower for the short-stem design as compared to that of the long-stem one, thereby reducing the initial risk of neck fracture. The effect of strain shielding (50–75% reduction) was restricted to a small bone volume underlying the cement, which was approximately half of that of the long-stem design. Consequently, bone resorption was considerably less for the short-stem design. The short-stem design offers better prospects than the long-stem resurfacing component.

Functional Results of Isolated Femoral Revision of Hip Resurfacing Arthroplasty

Conversion of a failed femoral resurfacing component is reportedly a straightforward procedure; however, little has been published regarding the functional results following revision. Our primary aim was to compare the functional results for a group of patients who had had isolated femoral component revision after a failed hip resurfacing with those for a group of patients with a surviving hip resurfacing. Our secondary aim was to identify whether the mode of failure affects functional outcome. Between 1997 and 2002, data were prospectively collected on 5000 Birmingham Hip Resurfacing procedures. One hundred and seventy-seven hips were revised, and, of those, seventy-six had an isolated femoral component revision. We reviewed the modes of failure and the post-revision clinical outcomes for this subgroup (the revised implant group) and compared the results with those for the patients who had a surviving hip resurfacing implant (the surviving implant group). The median Harris and Merle d'Aubigné hip scores were significantly better in the surviving implant group than in the revised implant group (median Harris score, 96 compared with 82 [p < 0.001]; median Merle d'Aubigné score, 17 compared with 14 [p < 0.001]). When we analyzed outcomes following revision, we found that the mode of failure affected outcome. Patient satisfaction and clinical outcomes were worse following revision because of femoral component loosening in comparison with revision because of femoral neck fracture or revision because of femoral head collapse or osteonecrosis. In these three subgroups, the median Harris hip scores were 66, 87, and 92, respectively, and the median Merle d'Aubigné scores were 10, 14, and 15, respectively. Six of fifteen patients in the femoral loosening group believed that they were worse or much worse after the revision than they had been before the primary procedure, compared with four of twenty-five patients in the femoral neck fracture group and two of twenty-two patients in the femoral head collapse or osteonecrosis group. Four patients (four hips) experienced complications as a consequence of revision surgery (three deep infections and one case of loosening of an uncemented femoral stem). The functional results for patients who had revision of the femoral component of a current-generation metal-on-metal resurfacing arthroplasty were worse than those for patients with a surviving hip resurfacing. Patients who had revision because of femoral component loosening had worse outcomes than those who had revision because of femoral neck fracture or femoral head collapse or osteonecrosis.

Influence of bone density on the cement fixation of femoral hip resurfacing components

In clinical outcome studies, small component sizes, female gender, femoral shape, focal bone defects, bad bone quality, and biomechanics have been associated with failures of resurfacing arthroplasties. We used a well-established experimental setup and human bone specimens to analyze the effects of bone density on cement fixation of femoral hip resurfacing components. Thirty-one fresh frozen femora were prepared for resurfacing using the original instruments. ASR resurfacing prostheses were implanted after dual-energy X-ray densitometer scans. Real-time measurements of pressure and temperature during implantation, analyses of cement penetration, and measurements of micro motions under torque application were performed. The associations of bone density and measurement data were examined calculating regression lines and multiple correlation coefficients; acceptability was tested with ANOVA. We found significant relations between bone density and micro motion, cement penetration, cement mantle thickness, cement pressure, and interface temperature. Mean bone density of the femora was 0.82 +/- 0.13 g/cm(2), t-score was -0.7 +/- 1.0, and mean micro motion between bone and femoral resurfacing component was 17.5 +/- 9.1 microm/Nm. The regression line between bone density and micro motion was equal to -56.7 x bone density + 63.8, R = 0.815 (p < 0.001). Bone density scans are most helpful for patient selection in hip resurfacing, and a better bone quality leads to higher initial component stability. A sophisticated cementing technique is recommended to avoid vigorous impaction and incomplete seating, since increasing bone density also results in higher cement pressures, lower cement penetration, lower interface temperatures, and thicker cement mantles.

Letter to the Editor: Femoral Component Positioning in Hip Resurfacing with and Without Navigation

To the Editor: I read with interest the article entitled “Femoral Component Positioning in Hip Resurfacing With and Without Navigation” by Ganapathi et al. [4]. I agree with the authors that intraoperative technical errors during femoral preparation in resurfacing hip prostheses are important reasons for short-term and midterm failures of this procedure, which technically is more challenging than conventional THA [4]. In my opinion, it is possible to single out at least four procedural traps worthy of note. First, as the femoral component is provided with a central stem to aid in alignment and initial stability, it is mandatory to perform a perfect central matching drilling of the femoral head to avoid the central stem becoming load-bearing. Although these prostheses are sold together with increasingly better head-centering devices, a minimal intraoperative mistake is always possible. Error at this point concerns inclination of the bony channel, the first trap of the surgical procedure; therefore, an accurate preoperative plan is required to select the proper stem and cup sizing, while shortening surgical times. Nevertheless, a preoperative plan cannot eliminate all errors. Relatively small deviations from anatomic alignment of a resurfacing hip component, should the central stem be inserted slightly inclined, result in marked localized increases in loading of the femoral neck under conditions approximating single-limb stance [8] because the stem is not designed to be load-bearing [3]. This aspect relates to the second trap, namely, possible notching of the flanged profile of the femoral component owing to its consequent inclination. According to Anglin et al. [1], a femoral resurfacing component placement greater than 10° can lead to greater probability of notching. Shimmin and Back [7] reported fracture of the femoral neck after substantial varus placement of the femoral component and intraoperative notching of the femoral neck. In my opinion, the possible mechanism of fracture could be that the prosthetic cup flange involved in notching during weightbearing may start to angulate and eventually loosen from repeated loadings during gait or other activities. Consequent fractures of the neck are well described [2]. Even if performed perfectly, reaming of the neck and additional drilling of the channel for the central stem subtract a certain quantity of bone leading to its weakening. This aspect concerns the third trap, the bony reaming, hazardous but required by the manufacturer and completely surgeon-independent. A possible demonstration of the damaging action of bony reaming is given by the narrowing of femoral necks after resurfacing arthroplasty of the hip as described by Hing et al. [6], which may be attributable to excessive surgical dissection around the femoral neck that damages extraosseous vessels [2]. Once in place, the metal of the central stem may cause bone resorption [5] that becomes apparent only when a fracture of the bony neck occurs. This is the fourth and last trap. Therefore, the central stem, provided to improve insertion of the femoral resurfacing component, may be associated with unforeseen complications in time.

Role of Surgical Position on Interface Stress and Initial Bone Remodeling Stimulus around Hip Resurfacing Arthroplasty

Valgus alignment of femoral resurfacing components has been advocated to reduce proximal femur loading and thus minimize the risk for femoral neck fractures. However, such reduction in loading may exacerbate undesirable stress shielding. This study examined the effect of extreme implant orientations (±15°) and stem canal overreaming on initial bone remodeling stimulus using finite element models. The changes in implant-cement interface stresses due to implant alignment were also evaluated. The valgus model showed increased initial bone resorption stimulus, which extended distally and peripherally around the femoral neck. The peak implant-cement interface shear stress for the varus model was 10.9 MPa, exceeding the interface shear strength. Overreaming of the stem canal eliminated distal tip loading, but proximal stress shielding was still unavoidable. These data show bone loading and interface fixation trends emanating from valgus and varus implant positions that will be of interest to practicing physicians.

Position of Hip Resurfacing Component Affects Strain and Resistance to Fracture in the Femoral Neck

Retrieval studies have suggested that the cause of femoral implant failure after metal-on-metal hip resurfacing is multifactorial. Both varus positioning of the femoral component and notching of the superior part of the femoral neck have been associated with femoral component failure. The hypotheses of this study were that placement of a femoral resurfacing component alters femoral neck loading and that the cortical strain pattern reflecting this loading is directly related to the spatial orientation of the resurfacing component. An additional hypothesis was that notching of the superior part of the neck during implantation results in a decreased resistance to neck fracture under axial loading. Varus, anteverted, retroverted, and anatomic positions of the femoral component were tested in sixty-four cadaveric femora. Simulated stance-phase loading was applied, and the shear strain on the femoral neck cortex was quantified with use of a photoelastic method. Preimplantation and postimplantation strain levels were compared over the entire neck region with use of generalized estimating equations. The influence of anteversion and retroversion of the component and notching of the superior part of the neck on the neck strength were evaluated. Placement of the implant in 10 degrees of varus alignment relative to anatomic positioning increased strain on the superior aspect of the neck by 19% to 23% compared with intact femora. Anteverted and retroverted placement of the implant produced elevated strain in the anterior-inferior and posterior-inferior aspects of the neck, respectively. Placement of the component stem in alignment with the anatomic neck axis decreased neck cortical strain 6% to 19% compared with intact femora. Notching of the superior aspect of the neck decreased neck strength by 21%. Relatively small deviations from anatomic alignment of a resurfacing hip component result in marked localized increases in loading of the femoral neck under conditions approximating single-limb stance. Neutral positioning of the femoral component results in localized strain reduction. Notching of the superior aspect of the femoral neck significantly reduces the resistance to fracture (p = 0.008).

Influence of bone density on total hip resurfacing arthroplasty in patients with osteonecrosis of the femoral head – A radiological analysis

Osteonecrosis of the femoral head is a more progressive disease for which many patients will eventually require total hip arthroplasty. With the advent of improved metal-on-metal prostheses, total hip resurfacing arthroplasty has emerged as a viable treatment option. However, it remains controversial whether this procedure should be used in patients with osteonecrosis when the femoral resurfacing component is implanted onto non-vital bone. In this study the bone mineral density (BMD) of osteonecrotic femoral heads were compared with the BMD of osteoarthrotic femoral heads. The purpose of this study was to analyse the differences between these two groups to gather information that may be useful in predicting the outcome of total hip resurfacing arthroplasty in cases of severe osteonecrosis of the femoral head. The femoral heads were classified according to the ARCO classification using MRI. For DEXA analysis the femoral heads were subdivided into three regions: the cranial femoral head (R1), the caudal femoral head (R2), and the proximal femoral neck (R3). In R3, BMD in osteonecrotic femoral heads was significantly lower than in those with osteoarthrosis and in R2 it was significantly higher. It can be assumed that a higher BMD in the caudal femoral head (R2) is caused by a "reactive interface" that occurred in this region especially in ARCO IV femoral heads. This fact, the lower BMD in the proximal femoral neck (R3) and the individual expansion of the osteonecrotic region should be considered when planning resurfacing arthroplasty for femoral head necrosis.

Use of Metal-on-Metal Total Hip Resurfacing for the Treatment of Osteonecrosis of the Femoral Head

Recently, with the advent of improved metal-on-metal prostheses, total hip resurfacing has emerged as a viable arthroplasty option. However, it remains controversial whether this procedure should be used in patients with osteonecrosis when the femoral resurfacing component is cemented onto dead bone. The purpose of this study was to analyze the clinical and radiographic outcomes of metal-on-metal total hip resurfacing arthroplasty in patients with osteonecrosis of the femoral head. In addition, this group was compared with a matched group of patients who were diagnosed as having osteoarthritis. Forty-two osteonecrotic hips that were treated with a metal-on-metal total hip resurfacing arthroplasty were studied. They were matched by gender, age, prosthesis, surgeon, and surgical approach to forty-two osteoarthritic hips that were treated with the same metal-on-metal prosthesis. In the osteonecrosis group, there were twenty-five men and eleven women, and in the osteoarthritis group, there were twenty-eight men and thirteen women. The mean age at the time of surgery was forty-two years. Patients were followed both clinically and radiographically for a mean of forty-one months. The clinical outcomes were similar for both groups, with a good or excellent outcome in thirty-nine hips (93%) with osteonecrosis and a good or excellent outcome in forty-one hips (98%) with osteoarthritis. In each of the two groups, there were two failures that required conversion to a standard total hip arthroplasty. Survivorship curves were similar for the two patient groups. The short-term results for metal-on-metal total hip resurfacing for this challenging patient population with osteonecrosis were excellent and comparable with those seen in patients with osteoarthritis. We await long-term results to see if these early results are maintained. Prognostic Level II. See Instructions to Authors on jbjs.org for a complete description of levels of evidence.

USE OF METAL-ON-METAL TOTAL HIP RESURFACING FOR THE TREATMENT OF OSTEONECROSIS OF THE FEMORAL HEAD

Background: Recently, with the advent of improved metal-on-metal prostheses, total hip resurfacing has emerged as a viable arthroplasty option. However, it remains controversial whether this procedure should be used in patients with osteonecrosis when the femoral resurfacing component is cemented onto dead bone. The purpose of this study was to analyze the clinical and radiographic outcomes of metal-on-metal total hip resurfacing arthroplasty in patients with osteonecrosis of the femoral head. In addition, this group was compared with a matched group of patients who were diagnosed as having osteoarthritis. Methods: Forty-two osteonecrotic hips that were treated with a metal-on-metal total hip resurfacing arthroplasty were studied. They were matched by gender, age, prosthesis, surgeon, and surgical approach to forty-two osteoarthritic hips that were treated with the same metal-on-metal prosthesis. In the osteonecrosis group, there were twenty-five men and eleven women, and in the osteoarthritis group, there were twenty-eight men and thirteen women. The mean age at the time of surgery was forty-two years. Patients were followed both clinically and radiographically for a mean of forty-one months. Results: The clinical outcomes were similar for both groups, with a good or excellent outcome in thirty-nine hips (93%) with osteonecrosis and a good or excellent outcome in forty-one hips (98%) with osteoarthritis. In each of the two groups, there were two failures that required conversion to a standard total hip arthroplasty. Survivorship curves were similar for the two patient groups. Conclusions: The short-term results for metal-on-metal total hip resurfacing for this challenging patient population with osteonecrosis were excellent and comparable with those seen in patients with osteoarthritis. We await long-term results to see if these early results are maintained. Level of Evidence: Prognostic Level II. See Instructions to Authors on jbjs.org for a complete description of levels of evidence.

The relationship between the design, position, and articular wear of acetabular components inserted without cement and the development of pelvic osteolysis.

Between 1983 and 1987, an acetabular component with a unique chamfered-cylinder design was inserted without cement in 134 hips. With use of this design, initial stability is achieved through a cylindrical interference fit with the peripheral rim of the acetabulum, without the need for pegs, spikes, or screws. At an average of sixty-four months (range, forty to ninety-six months) after implantation, follow-up data were available for 113 hips (ninety-three patients). No component had been revised for loosening or was radiographically loose. However, the prevalence of balloon-like osteolysis of the pelvis was 17 per cent (nineteen hips). This bone loss was generally not associated with pain or other symptoms. Ten of the nineteen hips that were associated with pelvic osteolysis (including six of the nine that were associated with osteolysis of the ilium) had been reconstructed with use of an acetabular component that had no holes in the shell (that is, the shell was completely solid). This finding indicates that, while elimination of holes through the acetabular shell may have advantages, it will not prevent pelvic osteolysis. The osteolysis of the ilium was associated with a lateral opening of the acetabular component of more than 50 degrees (p < 0.0001). All of the hips in this series had insertion of a porous-ingrowth femoral resurfacing component made of titanium alloy. These components are no longer used. Revision of the femoral side due to osteolysis provided a unique opportunity to inspect directly forty-two clinically well functioning acetabular components. All of the polyethylene liners and acetabular shells were found to be rigidly fixed. Inflammatory tissue at the periphery of the implant-bone interface resulted in circumferential resorption of periacetabular bone despite rigid fixation of the component. This is direct evidence that a process of bone resorption similar to that reported at the cement-bone interface of cemented acetabular components can occur at the implant-bone interface of components inserted without cement. At the reoperation, a communication that had led to the pelvic osteolysis was found through areas of bone resorption at the periphery of the implant-bone interface. These areas were essentially cystic and were filled with a mixture of fluid and friable, yellow-tan tissue. It appeared that the osteolytic process had expanded into the soft cancellous bone and marrow while being contained by the denser cortical shell of the pelvic bones.(ABSTRACT TRUNCATED AT 250 WORDS)

Resurfacing Arthroplasty

Although obvious theoretic advantages accrue from resurfacing arthroplasty of the hip, the indications for the procedure are controversial because the failure rate is high and loosening is unacceptably frequent. To determine the role of osteonecrosis in these failures, the viability of bone within the femoral head was determined by histologic examination of bone inside 25 failed femoral resurfacing components. The bone was substantially alive throughout the femoral head in 23 of 25 cases (92%). In two cases, the bone of the femoral head was dead. Both of these hips had clinically failed because of femoral neck fracture. This histologic evaluation indicates that bone death is not an inevitable consequence of femoral head resurfacing and the use of polymethylmethacrylate fixation.

Hemiresurfacing for femoral head osteonecrosis

A modified THARIES femoral resurfacing component was used as a hemiarthroplasty in 11 young adult patients (12 hips) with osteonecrosis. The mean follow-up period was 39 months (range, 24–62 months). In all of the hips, the necrosis had advanced to the stage of subchondral femoral head fracture and segmental depression but there was a relatively normal acetabulum. Ten hips have maintained satisfactory improvement of UCLA pain, walking, and function hip scores. One hip was revised to an uncemented total replacement, and one has some residual pain. No case failed because of component loosening. The modified femoral THARIES component was used as a preferable alternative to unipolar or bipolar hemiarthroplasty, and the results appear to be comparable in this difficult group of patients. Hemiresurfacing was conceived not as a definitive procedure but rather as a time-buying measure to improve symptoms and function and to allow the performance of a technically uncompromised total hip arthroplasty at a future date.