The custom triflange cup: build it and they will come.

The custom triflange is a patient-specific implant for the treatment of severe bone loss in revision total hip arthroplasty (THA). Through a process of three-dimensional modelling and prototyping, a hydroxyapatite-coated component is created for acetabular reconstruction. There are seven level IV studies describing the clinical results of triflange components. The most common complications include dislocation and infection, although the rates of implant removal are low. Clinical results are promising given the challenging problem. We describe the design, manufacture and implantation process and review the clinical results, contrasting them to other methods of acetabular reconstruction in revision THA.

Metal ion levels after metal-on-metal total hip arthroplasty: a five-year, prospective randomized trial.

BACKGROUND: The U.S. Food and Drug Administration has requested post-market surveillance data, including data on metal ion levels, regarding metal-on-metal total hip arthroplasty. We performed a prospective, randomized study of metal ion levels in erythrocytes, serum, and whole blood at five years after 28 and 36-mm metal-on-metal and 28-mm metal-on-polyethylene total hip arthroplasty. METHODS: One hundred and five enrolled patients were randomized equally to the three bearing surface options and were blinded with regard to their treatment group. Metal ion measurements and clinical evaluations were performed at regular intervals. RESULTS: Cobalt and chromium ion levels in all blood sample types at the five-year time point were significantly lower in the metal-on-polyethylene group than in each of the two metal-on-metal groups (p < 0.001) with the exception of chromium in erythrocytes (p = 0.194). Cobalt in serum (p = 0.029) and erythrocytes (p = 0.002) showed significant increases from two to five years in the 36-mm metal-on-metal group; similar increases were not seen in the 28-mm metal-on-metal group. At five years, five patients in the 36-mm metal-on-metal group and none in the 28-mm metal-on-metal group had cobalt or chromium levels of >7 ppb. Correlations among levels in serum, erythrocyte, and whole blood were stronger for cobalt than for chromium. One patient in the 36-mm metal-on-metal group underwent revision because of an adverse local tissue reaction. CONCLUSIONS: The 36-mm metal-on-metal bearing underperformed the 28-mm metal-on-metal bearing with respect to metal ion levels. The authors are closely following all patients treated with metal-on-metal total hip arthroplasty.

Long-term results using the anatomic medullary locking hip prosthesis.

None.

Pattern of osteolysis around two different cementless metal-backed cups: retrospective, radiographic analysis at minimum 10-year follow-up.

In this retrospective study, we analyzed the formation of osteolysis with 2 cementless cups to evaluate if surface holes in metal shells influence the radiographic pattern of osteolysis. At a minimum of 10 years' follow-up, serial radiographs of 112 hips with Arthropor cups (having multiple shell holes) and 126 hips with Anatomic Medullary Locking (AML) cups (with no holes) were reviewed. Despite differences in variables other than cup design that can affect polyethylene wear and osteolysis rates, the incidence of osteolysis between the groups was coincidentally similar (47.3%, Arthropor; 47.6%, AML). The time of onset of osteolysis (mean, 7.5 and 7.4 years) also was similar. The radiographic pattern of the osteolytic lesions, which is largely a factor of cup design, differed. The Arthropor group had significantly larger lesions in Charnley zone I and significantly more hips with retroacetabular lesions (Charnley zones I and II); however, these lesions did not compromise cup stability. Patients with AML cups had more and larger lesions in the greater trochanter.

A clinically practical method of manually assessing polyethylene liner thickness.

BACKGROUND: Most orthopaedists do not have access to contemporary computer-assisted radiographic techniques and therefore must use manual radiographic methods to assess polyethylene wear. The accuracy of most manual methods, however, has not been verified on clinical radiographs. In this study, we used manufacturer-developed wear templates to measure polyethylene wear and compared that technique with two other commonly used manual radiographic methods. Our purpose was to compare the accuracy of these techniques and thus determine their usefulness in assessing polyethylene wear in individual patients. METHODS: We analyzed seventeen polyethylene liners that were retrieved during revision operations after a mean of 12.0 years in situ. With use of digital calipers, we directly measured the true minimum polyethylene thickness of the explanted liner. We then measured the polyethylene thickness on anteroposterior pelvic radiographs that had been made before the revision. Three different manual techniques were used to evaluate the radiographs: the Dorr method, the Livermore method, and the newly described wear-template method. The minimum polyethylene thickness that was calculated with use of each of these methods was compared with the thickness as determined by direct measurement of the explanted liner. RESULTS: The mean error for the Dorr method (1.54 +/- 1.21 mm) was significantly greater than that for both the Livermore method (0.07 +/- 0.62 mm) and the wear-template method (-0.04 +/- 0.28 mm) (p < 0.01). The mean error for the Dorr method was significantly greater than zero (p < 0.01), indicating that this method consistently overestimated the true measurement. In contrast, the mean errors for the Livermore and wear-template methods were not significantly different from zero (p = 0.64 and 0.58, respectively), indicating that these methods did not consistently underestimate or overestimate the true measurement. However, the large standard deviations for all three methods suggest that the ranges in error are wide. The limits of agreement for the Livermore technique ranged from a 1.17-mm underestimation to a 1.31-mm overestimation of the true thickness of the polyethylene; those of the wear-template technique were smaller, ranging from a 0.60-mm underestimation to a 0.52-mm overestimation. CONCLUSION: The practicing orthopaedist needs an accurate and efficient method for determining the polyethylene thickness of modular acetabular components. We found that the template method best met this requirement because it involved a simple procedure: placing the template over the radiograph and measuring the distance between the femoral head and the inner surface of the metal shell. The other methods were less accurate, required additional information from the manufacturer, were more time-consuming, and were not as easy to demonstrate to the patient.

Modular component exchange for treatment of recurrent dislocation of a total hip replacement in selected patients.

BACKGROUND: Exchange of modular components is a treatment option for the correction of recurrent dislocation of a total hip replacement. In this study, we reviewed our experience with this technique in order to define patient selection criteria and to report the outcome of treatment. METHODS: Of 2935 hips treated with primary porous-coated total hip arthroplasty, fourteen (in fourteen patients) that met certain preoperative and intraoperative criteria were treated with modular component exchange because of recurrent hip instability. The primary arthroplasties in these fourteen patients had been performed through a posterior approach. At the revisions, we removed any sources of osseous or soft-tissue impingement that contributed to dislocation. Acceptable stability at the completion of component exchange was defined as stability in maximum flexion, in full extension with external rotation, and in at least 45 degrees of internal rotation with the hip in 90 degrees of flexion and maximum adduction. RESULTS: One patient was lost to follow-up. At a mean of 5.8 years (range, 2.8 to 11.8 years) after the revision, ten of the remaining thirteen patients had not had a dislocation. Of the three patients in whom the hip dislocated after the modular component exchange, only one had recurrent dislocation; thus, recurrent dislocation was eliminated in twelve of thirteen patients. CONCLUSIONS: In selected cases, modular component exchange for the treatment of recurrent hip dislocation has a success rate comparable with that of more extensive operations. This method should be considered because it avoids the morbidity associated with revision of well-fixed components. However, to ensure the appropriateness of this surgical option, each patient must be thoroughly evaluated to identify all factors that contribute to instability and adequate intraoperative stability must be achieved.

The relationship between lysis and loosening in failed anatomic medullary locking components.

Lysis does not cause loosening of extensively porous-coated, apparently well-fixed femoral components. We attribute this in large part to the fact that the area of strongest bone ingrowth is in the femoral diaphysis remote from the joint space. In contrast, for the acetabular component, osteolysis can be the sole or a contributing factor to loosening. We attribute this difference to the fact that the bone-implant interface of the acetabular component is much closer to the joint space and more readily accessible to osteolytic damage. In the future, with improved bearing surfaces, lysis may occur less frequently. Whether lysis is diminished as a result of these new designs, the authors contend that without adequate initial fixation, loosening will still occur. Because of our observations concerning osteolysis and loosening, we are more cautious in revising patients for osteolyis and do not revise when osteolysis first becomes apparent. Rather, we closely monitor osteolysis in these patients. For us, the question of when to operate for osteolysis remains unanswered.

Effect of femoral stiffness on bone remodeling after uncemented arthroplasty.

The current study examined the relationships among femoral stiffness, implant stiffness, and bone remodeling in 40 femurs retrieved at autopsy from 20 patients with unilateral uncemented hip replacements. The purpose of the study was to determine if the magnitude of periprosthetic bone loss after arthroplasty was correlated with, and could be predicted from, stem and femoral stiffness terms. For analysis, the contralateral normal femur was used as a control to represent the unremodeled condition of the in vivo implanted femur. Bone loss attributable to remodeling was quantified by video-densitometric analysis. Stiffness terms were calculated as the product of the elastic modulus and geometric properties digitized from cross-sectional slab radiographs. Femoral stiffness calculations accounted for variations in modulus attributable to patient differences in bone mineral density and geometric properties attributable to differences in the shape of individual femurs. Similarly, calculations of implant stiffness accounted for variations in implant shape. Results showed axial bone stiffness was the variable most strongly correlated with bone loss. Individual stem stiffness terms were not significantly correlated with bone loss. Multiple linear regression analysis, using stem-to-bone stiffness ratios as independent variables, accounted for 46% of the variance in bone loss data. In the regression analysis, the axial stem-to-bone stiffness ratio was the strongest correlate with bone loss. Although these results show the influence of mechanical stiffness factors on bone remodeling, other factors (hormonal status, drugs, disease, activity level) could represent the variance in bone loss data not accounted for in the study.

Total hip arthroplasty using porous-coated femoral components in patients with rheumatoid arthritis.

We studied the results of total hip arthroplasty (THA) using AML porous-coated femoral components at a mean follow-up of 11 years in a non-selected, consecutive series of patients with rheumatoid arthritis. We reviewed 64 patients with 82 primary THAs using these components. There were seven men (8 hips) and 57 women (74 hips) with a mean age of 55.1 years (24 to 80) at the time of surgery. Nine patients (11 hips) died before the two-year follow-up. Of the remaining 71 hips, only one stem was revised for aseptic loosening. Survivorship for the stems was 98.1% (95% confidence interval (CI) 94.5 to 100.0) at ten years, using a life-table analysis, with revision for any reason as an endpoint. Of the 70 unrevised stems, 66 (94%) had bony ingrowth, while four (6%) were radiologically loose at the most recent follow-up (mean 11.4 years). Our study shows the excellent long-term results which can be achieved with porous-coated femoral components in patients with rheumatoid arthritis.

Effect of radiographic quality on computer-assisted head penetration measurements.

Even the most sophisticated computer-assisted radiographic techniques of measuring femoral head penetration into the polyethylene liner depend on the quality of the radiograph being evaluated, which varies greatly in clinical settings. The authors of this study sought to determine how the accuracy and reproducibility of three commercially available computer-assisted measurement systems differed when measuring optimal radiographs (with sharply defined component edges) and suboptimal radiographs (with less well defined edges). Using three computer-assisted measurement systems, the authors measured head penetration on simulated and clinical hip radiographs. All systems calculated head penetration as the movement of the head center relative to the cup center. To define the periphery of the prosthetic head and cup, one method (System One) used the human eye and a digitizing tablet, whereas the other two methods (System Two and System Three) used digital edge detection algorithms. For simulated hip radiographs, error was calculated as the absolute value of the difference between the known amount of head penetration, determined by a coordinate measuring machine, and the amount of penetration determined by the software. Three way analysis of variance showed a significant difference in absolute error among the three measurement techniques. System One had a significantly smaller absolute error (0.11 +/- 0.06 mm) than did System Two (0.25 +/- 0.25 mm) and System Three (0.19 +/- 0.13 mm). In addition, three-way analysis of variance showed that optimal radiographs were associated with a significantly lower absolute error (0.14 +/- 0.09 mm) than were suboptimal radiographs (0.23 +/- 0.22 mm). For optimal radiographs, there was no significant difference in error among the three measurement methods; all systems were accurate and reproducible. However, for suboptimal radiographs absolute error increased and varied widely, and a significant difference among the methods existed. These data show the susceptibility of head penetration measurements to radiographic technique and underscore the importance of good quality radiographs for all analyses of head penetration.

Wear-through of a modular polyethylene liner: four case reports.

Four patients in whom the S-ROM Total Hip System Polydial polyethylene liner was used illustrate the importance of, and difficulties in, detecting polyethylene wear-through before a complete acetabular revision is necessary. The patients in these cases had full thickness polyethylene wear-through 11 or more years after total hip arthroplasties. Dorr and Livermore wear measurements from radiographs of the patients underestimated the actual wear and did not indicate wear-through. Because excessive head penetration was not evident radiographically with the S-ROM components, the cases showed the necessity of using additional measures to diagnose wear-through, particularly with these components. Repeat radiographs at a higher kilovoltage were used to better visualize the outline of the femoral head, and hip aspiration was used to diagnose metallosis. These cases also showed the importance of yearly followup evaluations, especially 10 or more years after surgery for patients with the S-ROM Polydial locking mechanism.

Long-term results using the anatomic medullary locking hip prosthesis.

Since the introduction of cementless total hip arthroplasty in the early 1980s, concern has shifted from component loosening toward polyethylene wear and osteolysis. The current review of 223 consecutive unselected Anatomic Medullary Locking femoral and acetabular components extends the followup on a series of patients previously reported on at 5 and 10 years. The purposes are to describe the reasons for revisions and to assess the onset and size of osteolytic lesions, with the hypothesis that osteolysis represents an important cause of loosening. The population included 204 patients (211 hips) with mean followup of 13.9 years (range, 2-18 years). Among them, 122 patients (129 hips) had a minimum 15-year followup. Minimum 2-year radiographs with a mean radiographic followup of 12.2 years (range, 2-18 years) were available for 204 hips (197 patients). Of the entire study group, 39 hips (38 patients) had 44 component revisions, increasing the number of revisions by 24 since this series was reported previously. Twenty-six patients (27 hips) had their first revision surgery more than 10 years after the primary surgery. The most common reason for revision of original components was wear or osteolysis occurring in 22 of the 39 hips (21 of 38 patients). The overall loosening rate was 3.4% (seven of 204) for femoral components and 5.4% (11 of 204) for acetabular components. Twenty-four percent of hips (48 of 204) had evidence of femoral or pelvic osteolytic lesions larger than 1.5 cm2. Femoral osteolysis was not associated with any case of femoral loosening, whereas seven of the 11 loose acetabular components were associated with pelvic lesions larger than 1.5 cm2.

Surgical treatment of pelvic osteolysis.

Sixty-eight well-fixed acetabular cups with osteolysis in the pelvis and polyethylene wear were identified from a series of 124 reoperations for failed cementless sockets. The well-fixed sockets requiring reoperation were subdivided based on whether the liner was exchanged and lytic lesion grafted (Type I case) or the socket was removed and a complete revision was done (Type II case). In 40 patients (Type I cases), the polyethylene liner was exchanged and the osteolytic lesions were debrided. Allograft bone chips were packed into the lytic defect in 29 patients. In the remaining 11 patients, the lesions were debrided but not grafted. At final followup, all of the acetabular components were radiographically stable. No new osteolytic lesions were identified. Approximately 1/3 of the lesions had resolved completely regardless of whether they were grafted. The remaining 2/3 had decreased in size. In 28 patients (Type II cases), the socket was revised. Both strategies were successful in arresting the process of osteolysis during the course of this study (mean, 3.5 years). However, removal of well-fixed sockets was associated with significantly more bone loss.

Patient self-testing of prothrombin time after hip arthroplasty.

We determined whether total hip arthroplasty (THA) patients could test their own prothrombin time reliably over 6 weeks of anticoagulation prophylaxis with a portable device that measures prothrombin time and whether self-testing would improve or maintain the quality of care at a lower cost than our standard procedure. Forty-six THA patients participated in the study and were compared with a matched group managed with our standard protocol using a home health-care nurse. Seven patients (15%) could not be trained to obtain the blood sample, and others required multiple finger sticks to obtain valid results. However, the results from the 29 patients completing the study showed high reliability when compared with results obtained through standard protocol. Self-testing saved about $260 per patient over the cost of venipuncture. Patient self-testing of prothrombin time using the device in this study is reliable and cost-effective for monitoring the anticoagulation status after THA in a select group of elderly patients.

The accuracy and reproducibility of radiographic assessment of stress-shielding. A postmortem analysis.

BACKGROUND: Although periprosthetic bone loss remains a major concern in total hip arthroplasty, radiographic assessment of such loss is both difficult and subjective. In the present study, we assessed the ability of orthopaedic surgeons to reproducibly recognize changes in periprosthetic bone density on radiographs. We hypothesized that assessment of periprosthetic bone loss on plain radiographs is not reliable enough to justify its use in outcomes research. METHODS: Twenty-nine unilateral total hip replacements and the surrounding bone were retrieved at autopsy, and radiographs were made; radiographs of the contralateral, normal femur were also made after implantation of an identical prosthesis and used as a control. Three orthopaedic surgeons independently examined the specimen radiographs and classified bone loss in each of sixteen femoral zones. Bone loss was recorded as present if the bone of the femur that had had in vivo implantation showed evidence of cortical thinning, increased porosity, or decreased density (either cortical or trabecular) when compared with the control femur. The kappa coefficient was used to quantify interobserver and intraobserver reproducibility in determining bone loss for the 464 zones examined and in determining the Engh and Bobyn stress-shielding classification of each femur. In fourteen femoral pairs, bone loss was also quantified with dual-energy x-ray absorptiometry, and the resulting value was then compared with the bone-loss classification that had been determined radiographically. RESULTS: First, the surgeons agreed on the presence or absence of bone loss in 73 percent (337) of the 464 zones. The interobserver kappa value of 0.58 denoted only good reproducibility. The intraobserver reproducibility was better; the surgeon's initial evaluation of bone loss agreed with his second evaluation for 90 percent of the zones (kappa = 0.74). Second, the three surgeons agreed on the degree of stress-shielding, according to the Engh and Bobyn classification, in 66 percent (nineteen) of the twenty-nine femora. The kappa value for this comparison was only 0.27, indicating marginal reproducibility. Third, although there was some agreement among reviewers when there was 20 to 60 percent reduction in bone-mineral content as determined with dual-energy x-ray absorptiometry, excellent agreement among the examiners (kappa = 0.85) was not achieved until bone loss averaged 70 percent. CONCLUSIONS: On the basis of these results, we suggest caution in interpreting results from studies of femoral bone loss that have used plain radiographic analysis if the authors have not provided interobserver reliability data. We question the utility of evaluating periprosthetic bone loss on radiographs, since the loss is not reproducibly recognized until 70 percent of the bone is gone.

Osteonecrosis of the femoral head treated with cementless total hip arthroplasty.

BACKGROUND: The treatment of young patients who have osteonecrosis of the femoral head associated with collapse or substantial secondary degeneration remains a therapeutic challenge, with total hip arthroplasty being a treatment of choice. However, concerns about the durability of the results of hip arthroplasty in this population necessitate long-term evaluation of this treatment option. To determine its advantages and limitations, we evaluated the results of cementless total hip arthroplasty in a consecutive series of young patients with advanced osteonecrosis. METHODS: We reviewed the results of fifty-five consecutive primary total hip arthroplasties, after an average of 117 months of follow-up, in forty-five patients with a preoperative diagnosis of advanced osteonecrosis of the femoral head (Ficat and Arlet stage III or IV). The average age was thirty-one years (range, twenty-one to forty years) at the time of the operation. We collected data prospectively with the use of patient questionnaires and radiographs. RESULTS: Five patients died and one patient was lost to follow-up before the time of the minimum five-year follow-up; this left forty-eight hips in thirty-nine patients for inclusion in the study. Ten (21 percent) of the forty-eight hips required revision. No revisions were due to aseptic failure of the femoral component. Of the remaining twenty-nine patients (thirty-eight hips), twenty-seven (93 percent) reported few or no functional limitations and twenty-three (79 percent) could walk an unlimited distance at the time of the latest follow-up. Pain was absent or mild in twenty-five patients (86 percent). Twenty-three patients (79 percent) were employed full-time. Radiographically, thirty-seven femoral components (97 percent) were bone-ingrown and the remaining component was judged to be fibrous stable. All thirty-eight acetabular components were bone-ingrown. CONCLUSIONS: Cementless total hip arthroplasty remains a reasonable treatment option for advanced osteonecrosis of the femoral head. Wear of the bearing surface continues to limit the long-term success rate, but we are encouraged by the predictable long-term stability of the bone-implant interface achieved with cementless fixation. These results compare favorably with those of published reports of total hip arthroplasty with cement in younger patients with osteonecrosis.

Comparison of in vivo wear between polyethylene liners articulating with ceramic and cobalt-chrome femoral heads.

At yearly intervals we compared the radiological wear characteristics of 81 alumina ceramic femoral heads with a well-matched group of 43 cobalt-chrome femoral heads. Using a computer-assisted measurement system we assessed two-dimensional penetration of the head into the polyethylene liner. We used linear regression analysis of temporal data of the penetration of the head to calculate the true rates of polyethylene wear for both groups. At a mean of seven years the true rate of wear of the ceramic group was slightly greater (0.09 mm/year, SD 0.07) than that of the cobalt-chrome group (0.07 mm/year, SD 0.04). Despite the numerous theoretical advantages of ceramic over cobalt-chrome femoral heads, the wear performance in vivo of these components was similar.

Extended slide trochanteric osteotomy for revision total hip arthroplasty.

BACKGROUND: The purpose of this study was to assess the rate of union, time to union, and complications associated with the extended slide trochanteric osteotomy. We also evaluated how outcomes were influenced by the preoperative cortical-bone thickness, the preoperative cancellous-bone quality of the greater trochanter, the number of cables used to reattach the trochanteric osteotomy fragment, and the use of cortical strut augmentation. METHODS: We reviewed the results for forty-six hips in forty-five patients who underwent a revision total hip arthroplasty with an extended slide trochanteric osteotomy between December 1991 and December 1996. Twenty-three patients were men, and twenty-two were women; the mean age at the time of the operation was 66.3 years. Two hips had an isolated acetabular revision, fifteen had an isolated femoral revision, and twenty-nine had acetabular and femoral revisions. One patient (one hip) was lost to follow-up. RESULTS: At a mean of forty-four months after the operation, the rate of union of the distal osteotomy site was 98 percent (forty-four of forty-five hips), with no change in the femoral component position. The time to union was not significantly correlated with the number of cables, the preoperative cortical-bone thickness, or the preoperative cancellous-bone quality of the greater trochanter. Interestingly, the time to bridging-callus union was significantly longer in the hips with a strut allograft than in the hips without a strut allograft (p = 0.04, t test for independent samples). Two fractures of the osteotomy fragment occurred, but neither necessitated another revision. CONCLUSIONS: The extended slide trochanteric osteotomy allows extensive acetabular and femoral exposure, facilitates removal of distal cement or a well fixed porous-coated stem, and allows reliable reattachment and healing of the trochanteric fragment.