Cementless Vektor-titan stem in total hip arthroplasty

INTRODUCTION

Cementless THR is a well established, and a widely accepted optimal procedure for younger patients. The cementless Vektor-Titan stem is made of Ti6AI7Nb, has got the shape of a three-dimensional cone, and an optimal proximal anchoring property.

MATERIALS AND METHODS

The aim of this prospective study was to scrutinise the outcome of 250 Vektor-Titan stems in cementless THRs with an average follow-up time of 3.0 years (Min: 1, Max: 6). The average age of the patients including 148 women and 102 men was calculated with 54.6 years (Min: 22.5, Max: 77.7).

RESULTS

The score according to Merle d'Aubigné improved from preoperative 9.3 (Min: 7, Max: 13) to postoperative 17.0 (Min: 14, Max: 18). Distal cortical hypertrophy and proximal atrophy was detected in 4 cases. Single atrophy of the proximal femur was found in additional 3 cases. Progressive radiolucent lines in zone 1 and 7 according to Gruen were observed in one case. Postoperative local and general complications were seen as two subfascial hematomas, two single dislocations, two recurrent dislocations of the hip prosthesis, 6 lesions of the sciatic nerve (one persisting), two deep venous thrombosis, two pneumonias, and one lethal pulmonary embolism. A stable proximal fixation was achieved in 242 of 250 cases (96.8%).

CONCLUSION

The results of this study using the Vektor-Titan stem in cementless total hip arthroplasty showed that the principle of proximal fixation was optimized. Long term follow-up studies are needed to confirm these good results.

Dependency issues in survival analyses of 55,782 primary hip replacements from 47,355 patients

Artificial hip joints are used in only one hip for about 85 per cent of the patients and in both hips (bilateral) for about 15 per cent of the patients. The occurrence of bilateral prostheses and the influence they have in survival analyses of joint arthroplasties are seldom considered. In this study we therefore focus on issues related to bilateral primary hip prostheses, time to revision surgery, and some commonly used statistical methods. We used information from 47,355 patients with 55,782 primary hip prostheses reported to the Norwegian Arthroplasty Register between 1987 and 2000. Due to the large number of diagnoses, fixation techniques for the prostheses, and combination of prostheses brands, we furthermore considered a 'homogeneous' subset of 8703 prostheses from 7930 patients with primary osteoarthritis, and Charnley prosthesis fixed with antibiotic-containing Palacos cement. Kaplan-Meier curves for all prostheses, ignoring that some patients have bilateral prostheses, were compared with Kaplan-Meier curves using only the first inserted prostheses, and with survival curves modified for patients with bilateral prostheses. Cox regression analyses were used to assess explanatory variables and to adjust for confounding factors. The results from the ordinary Cox regression analyses were compared with results from a marginal model, a shared gamma frailty model, and a model using a time dependent covariate to condition on failures in the opposite hip. We found no practical difference between the three calculated survival curves for the hip replacement data. The ordinary Cox-model and the marginal model gave equivalent results. In the shared gamma frailty model estimates for the risk factors were comparable with the former two approaches. The estimated frailty variance was higher when all data were used, even after adjustment for confounding factors. For the 'homogeneous' data the estimated frailty variance was negligible. Using a time dependent covariate to condition on previous revisions in the opposite hip, we found a higher risk of revision for the remaining primary hip prosthesis if the opposite hip had been revised (RR = 3.49, p < 0.0001). There was no difference in risk for revision between right and left hip prostheses. If the time interval between the two primary operations was more than two years, for the full data, the first hip prosthesis had an increased risk of revision compared to prostheses in patients with only one prosthesis (RR = 1.25, p = 0.01). For the 'homogeneous' data no statistically significant difference was found between unilateral and bilateral prostheses. A revision in one hip, for patients with bilateral prostheses, is a risk factor for revision of the other hip. Thus, in analyses of prostheses survival, dependencies between two hip prostheses from one patient should be considered. However, ignoring possible dependencies does not necessarily have an impact on the results on standard risk factors.

[Change of offset after implantation of hip alloarthroplasties]

The purpose of the present study was to evaluate the change of the offset after implantation of hip alloarthroplasties. In an experimental study the X-ray templates of 90 different implants (594 different sizes) were digitized (cup and stem) and virtually implanted in the hip joint of 50 consecutive patients who were on the waiting list for hip replacement. Implantation was performed on AP X-rays paying heed to the fit of the shaft and adequate leg length. In total 4500 implantations were performed. After virtual implantation the change of the offset was calculated. There was a wide variance in the ability to fit the implants to the individual patient. For some patients it seems to be extremely difficult to adapt the implant without changing the offset. Some implant designs were only suitable for 2 patients while other designs were suitable for 40 patients (mean: 17). The average change of the offset was 0.27 cm. Considering only the cases in which a change occurs this value increases up to 0.56 cm.For the individual patient the average number of implants that were suitable was 30 (range: 1-67) of a total of 90 designs. Here the average change of the offset was 0.4 cm (-1.04 -- +1.54 cm). Considering only the cases in which a change occurs this value increases up to 0.64 cm. In the majority of the cases the presently available implants do not allow anatomic reconstruction of the individual offset.

A kinematic model for calculating cup alignment error during total hip arthroplasty

Reduced range of motion, prosthetic impingement, and joint dislocation can all result from misalignment of the acetabular component (i.e. cup alignment) in patients undergoing total hip arthroplasty. Most methods for acetabular component alignment are designed to provide 45-50 degrees abduction and 15-25 degrees of operative anteversion (also known as flexion) with respect to the anterior pelvic plane coordinate system. Yet in most cases, this coordinate system is not assigned properly, due to differences in patient anatomy and improper positioning in the operating room. This misalignment can result in an error in the cup alignment, which can cause the above-mentioned consequences. This work presents a complete mathematical formulation for the analysis of the inaccuracies related to the anterior pelvic plane axes (APPA) definition and their effect on final cup orientation. We do this by introducing a method taken from Kinematics of Mechanisms, and by representing the errors in the APPA as three concurrent axes of rotation, followed by the version and abduction rotations which are defined relative to the previous rotations. We also present a sensitivity analysis of the results by introducing differential changes between sequential coordinate frames, which simulates the errors in the APPA and their effect on cup orientation. Finally, we demonstrate a computational method which provides corrected version and abduction angles to achieve the desired cup orientation, given that the actual measurement errors are known.

Risikofaktoren für heterotope Ossifikationen in der primären Hüftgelenkstotalendoprothetik

AIM

The purpose of this study was to determine the important predisposing factors associated with heterotopic ossifications (HO) after total hip arthroplasty.

METHOD

589 patients were examined 6 months after primary total hip arthroplasty with regard to periarticular ossifications. Several predetermining factors were evaluated using the hospitalization records and preoperative X-ray examination.

RESULTS

A significantly increased frequency of heterotopic ossifications was found for male gender, patients with very high body mass index (BMI), low preoperative range of motion (ROM), long duration of operation and large preexistent osteophytes (p < 0.05). Only one out of the one hundred patients with an BMI < 22.6 developed severe HO (Brooker III). Out of the one hundred patients with the best preoperative ROM (> or = 140 degrees ) only one case developed severe ossifications (Brooker III). There was no correlation with the use of acrylic bone cement or the patient's age. The frequency of HO was significantly reduced both as well by nonsteroidal antiinflammatory drugs as from postoperative radiation prophylaxis.

CONCLUSION

In patients undergoing total hip arthroplasty with low preoperative ROM in the hip joint, large osteophytes and a very high BMI an efficient prophylaxis against HO is of great importance.

[Factors influencing perioperative morbidity and mortality in primary hip arthroplasty]

INTRODUCTION

In the present study we examined preoperative parameters that may identify patients at high risk for postoperative complications after endoprosthetic joint replacement.

MATERIALS AND METHODS

The incidence of risk factors and perioperative complications in 628 primary hip arthroplasties (THA) (549 patients) was investigated in an unselected, retrospective study. Concomitant illnesses were found in 426 cases. Intra- and postoperative complications (93 specifically orthopedic and 42 common ones) were observed in 104 cases.

RESULTS

High risk scores based on Lutz and Klose criteria, a prolonged operation time, and the number of previous operations were significantly correlated to the incidence of postoperative complications. In contrast, obese patients had a significantly lower rate of intra- and postoperative complications and a diminished perioperative blood loss. THAs performed under intubation anesthesia led to a higher blood transfusion volume. The patient's age and the kind and quantity of concomitant illnesses did not influence the perioperative complication rate.

CONCLUSION

The complication rate of elective primary THAs is not dependent on risk factors suspected up to now such as advanced patient age or the kind and quantity of concomitant illnesses. High-risk patients can only be determined by complex scores, not by single parameters. Adiposity becomes a relevant economic factor only by dint of the prolonged operation time.

[Total hip replacement in childhood, adolescence and young patients: a review of the literature]

AIM

Which implants and fixation techniques should be recommended in total hip replacements in children, adolescents and young adults?

METHODS

A literature survey served to elucidate the results of recent papers in total hip arthroplasty (THA) over the last three decades. For this literature review the following items were used for a MedLine inquiry: "young patient", "children", "adolescents", "hip arthroplasty", "total hip replacement" and "hip endoprosthesis". Different disorders, implant types and surgical techniques were compared and discussed.

RESULTS

Although some authors still favor a cementing fixation technique forA'acetabular shell and stem components in total hip replacements for young patients, most results of the present studies show the effectiveness of cementless fixation techniques. The indication for or against an implant should be include the preexisting diseases, daily activity, abnormal anatomic findings and consider the patient's expectations. Most studies investigated inhomogeneous probands treated with different implant types and are therefore of only limited appropriateness for reliable conclusions.

CONCLUSIONS

Cementless fixation in THA is a sufficient technique in total hip replacement in young patients. There are only few data available in the literature dealing with the outcome of one implant type within a defined clinical picture.

[Total hip arthroplasty in Austria. Results of a nationwide survey based on a questionnaire]

Besides the number of annual total hip arthroplasty (THA) surgeries (11,978 primary THA, 148 implantations per 10(5) inhabitants), little is known about the state of total hip replacement in Austria. We collected information about different aspects of THA treatment regimens. A questionnaire was developed and sent to all chairmen of orthopedic and traumatology departments posing 22 questions regarding type of THA, surgical technique, number of surgeries, data collection, physical therapy and mobilization, length of hospital stay, and recommendations on sport activities as well as activities of daily life. In Austria cementless THA predominates (according to the questionnaire survey 85%). Postoperative mobilization with cementless implants is prescribed as full weight bearing in 52%, partial weight bearing in 42%, and no weight bearing in 6%. The length of hospital stay with cementless insertion is 14.2 days and with cemented implantation 14.9 days; the use of crutches is recommended for 6.0 and 5.4 weeks, respectively. Hip scores for documentation are used before surgery in 65% of orthopedic departments and 13% of traumatology departments and in the postoperative follow-up in 62% and 13%, respectively. In-patient rehabilitation is prescribed by 74% of orthopedic and 26% of traumatology departments. Austria ranks among the top nations in Europe regarding the number of total hip arthroplasty implantations. Documentation is insufficient and needs to be improved. In some aspects of managing patients with total hip arthroplasties there are remarkable differences between orthopedic and traumatology departments.

[Dislocation after total hip arthroplasty]

From 1997 to 2002 in the Department of Traumatology there had been performed 488 total hip replacements: 334 in men and 454 in women at the age between 20 and 84 (average 63.6). The procedures were performed by 12 surgeons and postero-lateral approach was used. Dislocation was found in 22 patients (4.51%): 14 women and 8 men. Majority of dislocation occurred during first 8 weeks after an operation and 68% of them happened during first 6 weeks. The surgical treatment was necessary in 10 cases (45% of all dislocation): 3 patients had only a surgical reposition and 7 patients had a revision arthroplasty. There was found that most cases of dislocation took place at the age above 81 years. Dislocation occurred 5 times more frequently in patients operated on for a femoral neck fractures then for coxarthrosis. The prosthesis TT1 most often dislocated possibly due to its shape (low Head Neck Ratio). Based on our own experience we find dislocation is a multifactorial complication and precise description of causes is usually very difficult.

Polyethylene wear in total hip prostheses: the influence of direction of linear wear on volumetric wear determined from radiographic data

PURPOSE

To develop a new mathematical model for calculating the volumetric wear of polyethylene cups from known values of the radius of the prosthesis head, the extent of linear wear and the direction of linear wear determined from standard antero-posterior radiographs.

METHOD

A new mathematical model was developed. The results of this new mathematical model were compared with the results obtained using the standard, frequently used mathematical model, which takes into consideration only the radius of the prosthesis head and the extent of linear wear of the polyethylene cups. The results of both mathematical models were further compared with the results obtained by direct measurement of volumetric wear using the fluid displacement method.

RESULTS

Comparison of the mathematical models shows that the average volumetric wear calculated using the new mathematical model is 8.5% smaller than the average volumetric wear determined by the fluid displacement method, while the average volumetric wear calculated by standard mathematical model is 17.5% higher. The results of the new mathematical model are, thus, notably less biased than those of the standard one.

CONCLUSION

In calculating the volumetric wear from antero-posterior radiographs, not only the radius of the prosthesis head and the extent of the linear wear but also the direction of the latter has to be considered.

[Cases of complex endoprosthetic surgery of the hip joint]

140 complex endoprosthetics of the hip joint were performed in 124 patients treated in the traumatology and arthrology Center of the Buyrdenko Main Military Clinical Hospital during the period from 1988 to 2001. It constituted 14.3% of all patients with diseases and trauma sequelae of such localization treated in the Hospital. There were 6 main patient groups in whom the pathological changes were considerably expressed and required the special approaches to the operation, i.e. the primary simultaneous bilateral hip joint endoprosthetics. The patients' age was 17-65 (the mean age 48.7), while during the conventional primary endoprosthetics the mean age was 68. We have developed the method of hip joint endoprosthetics performed in two stages. (Patent No 2173108 RF). This method was applied in 16 patients (group 1-11 and group 2-5 patients). The post-operative follow-up period lasted 1-6 years. Excellent and good results were obtained in 14 (87.5%) patients that were evaluated according to Harris's method. We think that it is reasonable to consider the primary complex endoprosthetics as the independent type of surgical intervention as it requires the special approaches to planning and performance of the operation, high skill and special up-to-date equipment.

Current attitudes to total hip replacement in younger patients: a comparison of two nations

INTRODUCTION

Orthopaedic surgeons performing total hip replacements (THR) today are faced with a vast array of options. Inspired by a recent UK study, we wanted to determine the current trend in prosthesis choice, fixation and bearing surfaces used in 'young' Australian patients, and to compare this trend to the UK.

METHODS

A questionnaire identical to that used in the UK study was posted to all current members of the Australian Orthopaedic Association and returned questionnaires were directly compared to the UK results on a percentage-of-responses basis.

RESULTS

Two hundred and forty-six valid responses were received. The number of THR reported to be performed by these respondents (15 789) was equivalent to the estimated number of prostheses sold here during the same period (15 624). The UK results showed a predominant use of Charnley and Exeter femoral prostheses, an all-polyethylene acetabular component, and cement fixation of both the acetabular and femoral components for both their older and younger patients. In younger patients, Australian surgeons favoured uncemented fixation techniques for the femur (57%vs 23%), and especially the acetabulum (85%vs 32%). There was a higher percentage use of modular design (95%vs 67%) and a very high use of ceramic as a bearing surface, 49% (vs 25%) using it for the femoral head, and 21% (vs 2%) employing a ceramic-on-ceramic bearing combination.

DISCUSSION

Despite being privy to the same published papers, the THR prosthesis and fixation preferences of UK and Australian orthopaedic surgeons are markedly different. This may be because of interpretation of papers, peers, personal experience, patient assessment, budgets, institutions, theories, fashions, differences in autonomy and advertising.

A nationwide followup study of autoimmune and connective tissue disease among hip and knee implant patients

Because implants can provoke varied immune system responses, we assessed whether hip and knee implant recipients had an increased risk of autoimmune/connective tissue diseases (AI/CTDs). Using national registry data from Sweden, we compared hospitalization rates for AI/CTD in 101,771 hip and 23,891 knee implant recipients to rates in the general population. Hip patients were followed up to 22 years and knee patients up to 14 years postimplantation. Our findings indicate that it is unlikely that hip or knee implantation results in any increased risk for most AI/CTDs. After long-term followup, the associations we observed with polyarteritis nodosa and fibrositis could be the basis for future investigations.

Revision and complication rates in 654 Exeter total hip replacements, with a maximum follow-up of 20 years

BACKGROUND

Iceland's geographical isolation with a stable and small population gives a rare opportunity for follow-up studies of medical interventions. Total hip replacements (THR) have been done at FSA Central Hospital in Akureyri, Iceland since 1982 with the Exeter hip implant being in use from the beginning.

METHODS

Hospital records for all patients operated on with THR between 1982 and the end of 1999 were reviewed and the patients were followed until the end of 2001. Information was gathered regarding the indication for primary surgery, the reason for revision if needed, as well as that of any complications. Survival statistics were used to calculate the cumulative revision rate.

RESULTS

The mean age at primary THR was 68.4 years for males and 68.8 years for females. 654 primary THRs were done; of which 571 (87 %) were due to osteoarthritis. 37 of the primary arthroplasties had been revised before the end of year 2001.

CONCLUSION

We have in this unique 2-20 year study of 654 THRs with no loss to follow-up for the patients, found revision rates that conform with the large Swedish THR registry. Complication rates in general are in agreement with that reported for other comparable patient groups, while infection rates appear lower.

An automated method to position prosthetic components within multiple anatomical spaces

The level of fit and fill of a stem in the host femur is the most critical factor for the mechanical stability and success of the prosthesis. It would be useful to have a simulation tool able to investigate the anatomical compatibility of a new implant in a large library of femoral anatomies in the early phases of the design process. In order to realise this tool, it is necessary to develop an automatic method for the positioning of the stem in a database of anatomies. The aim of this study was to develop and evaluate a method for the automatic positioning of the stem geometry in the anatomical CT dataset. Two different strategies were considered: a completely automatic registration technique and a semi-automatic method based on an anatomical referencing. The two procedures were compared to the manual positioning obtained by an expert surgeon in a set of nine CT datasets. For both methods in each femur the positioning and the orientation of the stem were good. The results showed a better level of fitting for the automatic method, while the shift of the hip joint centre was lower for the anatomical referencing technique. However, the anatomical referencing method requires a higher computational effort without being significantly better than the automatic method. For this reason, the automatic method should be chosen to develop the automatic positioning of a stem in a database of anatomies.

Total hip arthroplasty with use of the cementless Zweymüller Alloclassic system. A ten to thirteen-year follow-up study

BACKGROUND

The Zweymüller Alloclassic total hip arthroplasty system is widely used, although few intermediate-term studies have been published. The purpose of the present study was to evaluate the clinical and radiographic results of this system after ten years.

METHODS

One hundred and twenty-four consecutive primary total hip arthroplasties were performed with the Zweymüller Alloclassic cementless system at our institution between February 1988 and March 1991, and 104 hips (ninety-four patients) were retrospectively reviewed after a minimum duration of follow-up of ten years. The mean age of the patients at the time of the arthroplasty was 62.3 years (range, twenty-five to seventy-seven years). The mean duration of follow-up was 11.3 years. Standard radiographs were made for all patients immediately after the operation, at six and twelve months, and annually thereafter for at least ten years. Cox multivariate regression analysis was performed to assess the influence of various factors on survival of the implant.

RESULTS

The cumulative probability of not having a revision of any prosthetic component for any reason was 94.1% (95% confidence interval, 91.9% to 96.3%) at twelve years in the best-case scenario and 85.3% (95% confidence interval, 82.1% to 88.5%) at twelve years in the worst-case scenario for the entire series of 124 hips. Among the 104 hips in the follow-up study, three acetabular components and no stems were revised. Two hips had level-4 pain according to the system of Merle D'Aubigné and Postel. Seven acetabular components (7%) were loose at twelve years, and all stems had radiographic evidence of stable fixation. Acetabular cup loosening was related to a vertical cup angle (p = 0.0008, Student t test), acetabular wear of > or =1 mm (p = 0.001, Fisher exact test), and a 32-mm femoral head (p = 0.001, Fisher exact test). Although femoral osteolysis was seen in eighteen hips (17%) at twelve years, all osteolytic cavities were proximal and focal.

CONCLUSIONS

The Zweymüller Alloclassic prosthesis, particularly its femoral stem, demonstrated good results and durable fixation at a minimum of ten years of follow-up.