A new minimal-invasive approach for total hip replacement in sheep.

BACKGROUND: Over the last 50 years arthroplasty became the gold-standard treatment for disabling conditions of the coxofemoral joint. Variations of anterior, lateral, and dorsal incision have been applied, but as each approach requires the incision and reflection of various muscles to gain adequate exposure of the joint results are still controversial. OBJECTIVE: The purpose of this study was to develop a minimal-invasive, tissue-sparing approach in sheep with reduced risks in animal testing. METHODS: 12 mature sheep underwent hip surgery as part of a study to evaluate a hip resurfacing system. In line with the preliminary cadaveric tests a modified, minimal-invasive, musclepreserving surgical approach was sought after. RESULTS: We developed a surgical approach to the coxofemoral joint in sheep using only blunt tissue dissection after skin incision without any limitations in joint exposure or increased blood loss/duration of surgery. CONCLUSION: Even though limitations occur and femoral orientation in sheep differs from man, joint forces have similar relative directions to the bone with similar bony and vascular anatomy. Therefore, this minimal-invasive muscle preserving approach might be a safe and comparable alternative in still inevitable animal testing.

Patients with intolerance reactions to total knee replacement: combined assessment of allergy diagnostics, periprosthetic histology, and peri-implant cytokine expression pattern.

We performed a combined approach to identify suspected allergy to knee arthroplasty (TKR): patch test (PT), lymphocyte transformation test (LTT), histopathology (overall grading; T- and B-lymphocytes, macrophages, and neutrophils), and semiquantitative Real-time-PCR-based periprosthetic inflammatory mediator analysis (IFNγ, TNFα, IL1-ß, IL-2, IL-6, IL-8, IL-10, IL17, and TGFß). We analyzed 25 TKR patients with yet unexplained complications like pain, effusion, and reduced range of motion. They consisted of 20 patients with proven metal sensitization (11 with PT reactions; 9 with only LTT reactivity). Control specimens were from 5 complicated TKR patients without metal sensitization, 12 OA patients before arthroplasty, and 8 PT patients without arthroplasty. Lymphocytic infiltrates were seen and fibrotic (Type IV membrane) tissue response was most frequent in the metal sensitive patients, for example, in 81% of the PT positive patients. The latter also had marked periprosthetic IFNγ expression. 8/9 patients with revision surgery using Ti-coated/oxinium based implants reported symptom relief. Our findings demonstrate that combining allergy diagnostics with histopathology and periprosthetic cytokine assessment could allow us to design better diagnostic strategies.

One step closer to sparing total blood loss and transfusion rate in total knee arthroplasty: a meta-analysis of different methods of tranexamic acid administration.

BACKGROUND: Tranexamic acid (TXA) in orthopedics has recently been gaining favor due to its efficacy and ease of use, both in intravenous (IV) and intraarticular (IA) usage. However, because of safety concerns with IV administration, there has been a growing interest in the IA use of TXA to prevent bleeding. MATERIALS AND METHODS: This study conducted a systematic review and meta-analysis that included 31 randomized, controlled trials in which the effect of systemic and topical TXA on total blood loss (TBL), rates of transfusion, and thromboembolic events was investigated. RESULTS: Compared to the control, the IA administration of TXA led to the significant reduction of mean TBL (p < 0.001), rate of transfusion (p < 0.001), and reduction of rate of thromboembolic events (p = 0.29). Compared to the control group, the IV administration of TXA resulted in significant reduction of mean TBL (p < 0.001), rate of transfusion (p < 0.001), and rate of thromboembolic events (p = 0.66). Although no significant differences in efficacy and safety between the IA and IV administration of TXA were found, the IA method was safer than the IV method in that it reduced rate of transfusion and thromboembolic events. CONCLUSION: This study showed that TXA leads to significant reductions in TBL and the rate of allogeneic transfusions. Generally, no significant difference was detected between IA and IV administration of TXA; however, more studies with focus on safety and efficacy are warranted.

Translation and cultural adaptation of the oxford hip score for Iranian population.

INTRODUCTION: In recent years, outcome assessment related to orthopedic surgeries has increasingly focused on patient-reported questionnaires. The Oxford Hip Score (OHS), self-administered questionnaire, is a reliable, valid, and responsive instrument for assessing hip in patients undergoing Arthroplasty. METHODS: The study involved 105 adult Persian-speaking patients admitted for primary Total Hip Arthroplasty in two hospitals in Isfahan in Iran from September 2009 until April 2011. All of them filled out their scales (Persian OHS, WOMAC, and SF12) in preoperative examination. RESULTS: Mean scores of OHS in first administrations was 42.7 ± 12.7. The Persian OHS overall score demonstrated high reproducibility (ICC,0.93, P < 0.001) and internal consistency (CA, 0.94). PersianOHS had high correlations with WOMAC total score (r = 0.86), function score (r = 0.86), and pain score (r = 0.79), the relationship between the Persian OHS and the WOMAC stiffness subscale was somewhat lower (r = 0.69). The correlation coefficient between the Persian OHS and the PCS of the SF-12 in our study was moderate (r = 0.58). Persian OHS had low correlation with MCS of the SF-12 (r = 0.40). DISCUSSION: Persian OHS had high correlations with WOMAC total score, function score, and pain score. It had moderate correlation with PCS of the SF-12 and low correlation with MCS of the SF-12. CONCLUSIONS: Our study demonstrated the trans-cultural adaptation and validation of the Persian OHS is a reliable and practicable instrument for assessment of function and pain in Iranian patients with hip osteoarthritis.

Recurrent Hydatosis at the Site of Non-union Humerus Fracture.

Hydatid disease is still endemic in several regions of the world and is caused by two species of tapeworms, Echinococcus granulosus and Echinococcus alveolaris. It primary involves liver and lung, and bone involvement is relatively rare (0.2-4%), where it is most commonly seen in the spine. The skeletal involvement is usually due to secondary extension such as hematogenous spread. The disease has usually a silent manifestation until a complication exists; so, many cases are diagnosed intraoperatively. Treatment of hydatid disease because of its bone involvement and spillage of fluid with subsequent contamination seeding is difficult, so it has a high mortality rate and many cases will recur. Therefore, we can prevent these occurrences if we treat hydatid disease completely and in the primary stage. Adjuvant medical treatment, if the diagnosis is known, prevents systemic spread and recurrence. Here, we present a primary recurrent hydatosis at the site of non-union humerus fracture. We have pointed out osseous hydatosis as one of the important differential diagnoses in destructive bone lesions and the necessity of its radical resection.

Intraosseous ganglion cyst of olecranon.

Intraosseous ganglia are benign cysts that usually can be seen in lower extremity; especially around ankle. These cysts have fewer incidences in upper extremity, mainly around the wrist. They are extremely rare in olecranon. These lesions are often asymptomatic. Patient was a 75-year-old man who had trauma many years ago. When he came to our clinic, he complained of severe pain around his elbow that he could not do ordinary activity. He had local tenderness in elbow and 30 degree limitation in extension. In radiography, lytic, multiloculated lesion existed in region of olecranon. After excisional biopsy was done, cavity was cleaned completely with curette and was filled with autogenous bone. At 10-year follow-up, the patient was completely asymptomatic. Control radiograph showed cavity filled completely by bone; there was no evidence of relapse.

Migration analysis of a metaphyseal anchored short-stem hip prosthesis.

BACKGROUND AND PURPOSE: Metaphyseal anchored short-stem hip implants were designed to improve load transmission and preserve femoral bone stock. Until now, only few outcome data have been available and migration studies are one of the few ways of obtaining data that are predictive of implant survival. We therefore evaluated a metaphyseal anchored short-stem hip implant by Ein Bild Roentgen Analyse femoral component analysis (EBRA-FCA). PATIENTS AND METHODS: First, the EBRA-FCA method was validated for the short-stem hip implant. Then 80 of the first 100 consecutive implants were evaluated after at least 2 years. Clinical assessment was performed using the WOMAC and the UCLA score. RESULTS: After 2.7 (2.0-4.2), years none of the implants had been revised and by that time the stems had subsided by a mean of 0.7 mm (SD 1.8) (95% CI: 0.3-1.1). Of the 80 implants, 78 were stable after 2 years, with 74 being primary stable and 4 showing secondary stabilization after initial subsidence. Continuous migration was seen in only 2 patients. The clinical outcome showed good results with a mean WOMAC of 11 (SD 13) and a mean UCLA score of 7.3 (SD 2.0). INTERPRETATION: The metaphyseal anchored short-stem hip implant showed good functional results and a high degree of stability after 2 years. The outcome is comparable to that of clinically proven conventional hip implants and if the results are confirmed by long-term studies, short-stem hip arthroplasty might be an alternative for young patients requiring hip replacement.

Revision of hip resurfacing arthroplasty with a bone-conserving short-stem implant: a case report and review of the literature.

INTRODUCTION: Suitable treatment of early failure of total hip replacement is critical in younger patients, as bone stock is lost and the functional outcome is impaired. CASE PRESENTATION: We report the case of a 56-year-old Caucasian woman with early failure of hip resurfacing arthroplasty. While revision is usually performed with a conventional hip implant, this case report describes for the first time a revision procedure with a bone-conserving short-stem hip implant. CONCLUSIONS: Our approach allows further conservation of femoral bone stock and provides a long-term solution to the patient, which maintains the possibility of using a conventional hip implant should a second revision become necessary.

Efficacy of tibial proximal osteotomy in correction of lower limb alignment indexes in patients with osteoarthritis in medial compartment of knee.

NTRODUCTION: Tibial proximal osteotomy is one of the treatments for patients with knee compartment osteoarthritis. Studies showed 80% good prognosis in five years follow up after osteotomy. Almost always this method is used for pure medial knee compartment osteoarthritis that has a varus deformity. THE AIM of all methods is reforming varus deformity and lower limb alignment to gain 3 to 5 degree extra reformation and take knee in 10 degree valgus. One of the main etiologies for patients inconvenience and no decreasing in their pain is overcorrection or undercorrection, but unfortunately these can't be noticed. Therefore we must make sure that additional stress on the medial joint line was eliminated and regeneration of cartilage was facilitated or at least occurrence of osteochondritis was decreased. So we aimed to determine the efficacy of tibial proximal osteotomy in lower limb alignment indexes in patients with osteoarthritis in medial compartment of knee. MATERIAL AND METHODS: This study is a clinical trial study that has done in Alzahra University Hospital of Isfahan Medical Science University in Iran since June 2010 till February in 2011. Patients had pain, pure medial knee compartment osteoarthritis and varus deformities were determined for study. Patients who wouldn't come for control, those who had no convenience for giving their data or osteoarthritis of all three compartments were excluded from study. Number of patients has determined 40 persons according to previous studies. Sampling occurred convenient. Before any surgical processes, the AP x-ray radiography was applied for alignment view. The demographic and radiographic data was registered. Six months later we applied AP x-ray radiography again and obtained data and analysis them with SPSS software and T-Paired statistical method. RESULTS: The mean of anatomical limb angle before and after surgical process were 5.1 +/- 3.4 varus and 11.9 +/- 3.4 degree valgus, respectively,so with T-test there was a significant difference between them (P < 0.001). The mean of mechanical limb angle before and after surgical process were 12.6 +/- 3.4 varus and 4.75 +/- 3.5 degree valgus, respectively. Therefor with T-test, there was significant difference between them (P < 0.001). CONCLUSION: Results were achieved from this study showed that Tibial proximal osteotomy is appropriate treatment for young and middle age patients with progressive deformity, symptomatic varus knee. Key words: Tibial proximal osteotomy, Knee, Osteoarthritis, Varus deformity.

Biomechanical reconstruction of the hip: comparison between modular short-stem hip arthroplasty and conventional total hip arthroplasty.

PURPOSE: Short-stem hip arthroplasty preserves femoral bone stock which includes the femoral neck. This implies that the stem has to follow the anatomy of the femoral neck. Therefore, it has been questioned whether biomechanical reconstruction of the hip can be safely achieved with SHA. METHODS: Biomechanical reconstruction of the hip was analysed for 50 modular short-stem hip arthroplasties (SHA) and compared to 50 conventional total hip arthroplasties (THA). Biomechanical parameters were analysed on pre- and postoperative pelvic overviews and compared to those of the contralateral side. RESULTS: The position of the acetabular cup (vertical and horizontal hip centre of rotation) changed slightly and was comparable for both groups. Horizontal femoral offset increased more in SHA (6.2 mm) than in THA (2.0 mm). Compared to the contralateral side it was significantly greater after SHA (+3.6 mm) but almost balanced after THA (-0.2 mm). Limb length increased with both procedures (8.0 mm SHA, 9.1 mm THA), but showed a significantly greater discrepancy after SHA (3.3 mm) as compared to THA (1.3 mm). According to the different implant designs, the stem-shaft axis showed a wider varus-valgus range for SHA (6.2° varus to 8.8° valgus) than for THA (2.6° varus to 3.3° valgus). CONCLUSION: Horizontal femoral offset increased more with modular SHA than with conventional THA, but was within a beneficial range. Restoration of limb length appears more difficult in SHA and has a tendency to prolong limb length, which is probably related to the higher femoral resection level. This should be taken into consideration when considering SHA for a patient as well as during implantation.

Sports activity after short-stem hip arthroplasty.

BACKGROUND: No data are available about the sports activity of patients with bone-conserving short-stem hip implants. HYPOTHESIS: Patients can return to a good level of sports activity after implantation of a short-stem hip implant. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: The sports activity level of 68 patients (76 hips) after short-stem hip arthroplasty was assessed for a minimum of 2 years after implantation. In addition to the clinical examination, a detailed evaluation of the patients' sports pattern was obtained. Furthermore, the results were analyzed with regard to gender (female and male) and age (≤55 and >55 years). RESULTS: After a mean of 2.7 years, patients showed a Harris Hip Score (HHS) of 93.6, a Western Ontario and McMaster Universities Arthritis Index (WOMAC) score of 9.5, and a University of California, Los Angeles (UCLA) activity score of 7.6, with each individual participating on average in 3.5 different disciplines after surgery compared with 3.9 before surgery. High-impact activities decreased significantly postoperatively, whereas low-impact activities increased significantly. The duration of the sports activities remained stable, while the frequency actually increased. In contrast, men participated preoperatively in more sports than women (4.3 men vs 3.3 women). However, because of a pronounced decrease in high-impact activities by men, both genders participated in an equal number of sports postoperatively (3.5 men vs 3.5 women). Finally, 45% (n = 31) reported at least one activity that they missed. Most of them were disciplines with an intermediate- or high-impact level. CONCLUSION: Patients with a short-stem hip implant can return to a good level of activity postoperatively. Participation in sports almost reached similar levels as preoperatively but with a shift from high- to low-impact activities. This seems desirable from a surgeon's point of view but should also be communicated to the patient before hip replacement.

Comparison of anterior subcutaneous and submuscular transposition of ulnar nerve in treatment of cubital tunnel syndrome: A prospective randomized trial.

BACKGROUND: This study was designed to compare two methods of surgery, anterior subcutaneous transposition (ASCT) and anterior submuscular transposition (ASMT) of the ulnar nerve in treatment of cubital tunnel syndrome. MATERIALS AND METHODS: This randomized trial study was conducted from October 2008 to March 2009 in the Department of Orthopedic Surgery at University Hospital. Forty-eight patients with confirmed cubital tunnel syndrome were randomized in two groups, and each patient received one of two different surgical treatment methods, either ASCT (n = 24) or ASMT (n = 24). In the ASCT technique, the ulnar nerve was transposed and retained in the subcutaneous bed, whereas in the ASMT, the nerve was retained deep in the transected muscular complex, near the median nerve. Patient outcomes, including pain, sensation, muscle strength, and muscle atrophy were compared between groups. RESULTS: The two groups were similar in baseline characteristics. However, those treated with ASMT had a statistically significant reduction in their pain levels compared with ASCT (21 (87.5%) vs 8 (33.3%), P < 0.05). There were no statistically significant differences between the two groups relative to sensation (11 (45.8%) vs 12 (50%)), muscle strength (17 (70.8%) vs 15 (62.5%)), or muscle atrophy (15 (62.5%) vs 17 (70.8%)) (P > 0.05). CONCLUSIONS: Our results indicate that ASMT are more efficient than ASCT for managing cubital tunnel syndrome. In patients who had ASMT, there were significant reductions of pain compared with ASCT.

Biomechanical evaluation of different offset versions of a cementless hip prosthesis by 3-dimensional measurement of micromotions.

BACKGROUND: Cementless hip prostheses with different offsets are frequently used to restore the rotation center of the hip. However, a rising offset is theoretically associated with a potential risk for increased interface stresses and early loosening. METHODS: To assess this potential risk for cementless stems, the primary stability of the CLS Spotorno stem was examined with respect to three different femoral neck versions (125°, 135° and 145°) measuring 3-dimensional micromotions. For this purpose 18 stems were implanted in composite femurs and tested dynamically using physiological loading conditions considering the necessary adaptation according to the different offsets. Additionally the deformations at the surface of the composite femur were recorded to draw conclusions about the tendency for stress shielding. FINDINGS: The micromotions of the different offset versions were not significantly different. The highest values were obtained at the tip of the stems, even exceeding the critical limit for osseous integration of 150µm. Compared to untreated composite femurs the alteration of the deformations at the surface remained relatively low. A significant difference was only observed in the ventral measurement points. INTERPRETATION: According to the measured micromotions no offset version of the CLS Spotorno can be declared as superior. The assumption that the varus version is characterized by extended interface stresses could not be confirmed. Furthermore, it could be demonstrated that according to the principle of proximal load transfer of the CLS Spotorno stem an osseous integration of the distal part cannot be expected and that the risk for stress shielding appears to be relatively low.

Digital comparison of planned and implanted stem position in total hip replacement using a program form migration analysis.

AIM: One main goal in primary total hip replacement is the reconstruction of preoperative biomechanical conditions by adequate implant positioning. Our aim was to compare the planned and effectively implanted stem position in using a program for digital migration measurement. PATIENTS: We examined 120 cases with this new method based on a modification of the EBRA-FCA program and compared these results to direct plain radiographic methods. In addition, the intra- and inter-observer reliability was determined in 50 cases. RESULTS: We observed a rate of correct prediction of 80% for the size of the stem. The new method revealed a good correlation (0.95 and 0.64 for the position along the stem axis and 0.84 for the stem angle) to direct plain radiographic methods. Regarding the intraclass correlation coefficient for intra- and inter-observer reliability, the results were superior (0.97 vs. 0.81-0.84 and 0.90 vs. 0.74-0.88) compared with direct plain radiographic methods. CONCLUSION: We concluded that the comparison of the planned and implanted stem position using a modified EBRA-FCA method is more reproducible than direct radiographic measurements.

Nickel (Ni) allergic patients with complications to Ni containing joint replacement show preferential IL-17 type reactivity to Ni.

BACKGROUND: Some nickel (Ni) allergic patients develop complications following Ni-containing arthroplasty. In the peri-implant tissue of such patients, we had observed lymphocyte dominated inflammation together with IFN-gamma and IL-17 expression. OBJECTIVES: To determine whether Ni stimulation of peripheral blood mononuclear cells (PBMCs) of such patients would lead to a different cytokine pattern as compared to Ni-allergic patients with symptom-free arthroplasty. PATIENTS AND METHODS: Based on history and patch testing in 15 Ni-allergic patients (five without implant, five with symptom-free arthroplasty, five with complicated arthroplasty) and five non-allergic individuals, lymphocyte transformation test (LTT) was performed using PBMC. In parallel in vitro cytokine response to Ni was assessed by real-time reverse transcriptase-polymerase chain reaction (RT-PCR). RESULTS: All 15 Ni-allergic individuals showed enhanced LTT reactivity to Ni (mean SI = 8.42 +/- 1.8) compared to the non-allergic control group. Predominant IFN-gamma expression to Ni was found both in the five allergic patients without arthroplasty and also in the five allergic, symptom-free arthroplasty patients. In contrast, in the five Ni-allergic patients with arthroplasty-linked complications a predominant, significant IL-17 expression to Ni was seen but not in patients with symptom-free arthroplasty. CONCLUSIONS: The predominant IL-17 type response to Ni may characterize a subgroup of Ni-allergic patients prone to develop lymphocytic peri-implant hyper-reactivity.

Minimally invasive total hip arthroplasty: a randomized controlled prospective trial.

INTRODUCTION: Advantages of minimally invasive total hip arthroplasty (THA) are controversially discussed. METHOD: In this prospective study 51 patients (52 hips) were randomly allocated to a classical lateral or a minimally invasive approach (modification of the Hardinge-approach). Operating time, intraoperative blood loss, postoperative hemoglobin, muscle enzymes CK and myoglobin were recorded. Radiologically the positioning of the prosthesis was analyzed. WOMAC- and Harris Hip Score (HHS) were assessed preoperatively, at discharge, at 6 weeks and 3 months. RESULTS: In the minimally invasive group there was a shorter length of surgery, the scores in the WOMAC and HHS were slightly better at discharge and at the 3 months- examination, myoglobin-rise was slightly less. The positioning of the prosthesis was good in both groups. Minimally invasive THA led to a quicker recovery, at 3 months postoperative there was still a slight difference to the standard group. CONCLUSION: If these slight differences subside has to be examined in studies with a longer follow-up.

Wear of contemporary total knee replacements--a knee simulator study of six current designs.

BACKGROUND: Compared to conventional ultra-high molecular weight polyethylene (UHMWPE), crosslinked polyethylene showed significantly reduced wear rate in hip simulation and early prospective-randomized clinical studies. The crosslinking process can reduce the mechanical properties of UHMWPE, particularly the fatigue strength. UHMWPE fatigue occurs more frequently in the knee joint than in the hip joint due to its higher contact stresses and there is therefore an increased concern of mechanical failure. Therefore, the purpose of this study was to determine the wear behaviour and the wear rates of different current knee designs and bearing materials. METHODS: In a knee-joint-simulator four kinds of crosslinked polyethylene (one produced by sequential irradiation and annealing process, three by different remelting processes, including fixed- and mobile-bearing-types) and two UHMWPE- (fixed- and mobile-bearing) inserts were tested with the appropriate femoral and tibial component recommended from the manufacturer. FINDINGS: All types of crosslinked polyethylene produced statistically significant (P<0.05) lower wear rates than the conventional UHMWPEs without any traces of fatigue. There were no differences in the wear rates between fixed-and mobile-bearings (crosslinked polyethylenes and UHMWPEs; P>0.05). The crosslinked polyethylene tibial inserts manufactured by sequential irradiation and annealing (X3) combined with the Scorpio-knee-design had the lowest wear rates (P<0.05) overall. INTERPRETATION: Fixed- as well as mobile-bearing crosslinked polyethylene tibial inserts are suitable for total knee arthroplasty and showed reduced wear rates compared with conventional UHMWPE. The combination of the fixed-bearing Scorpio-knee-design with a sequential irradiated and annealed crosslinked polyethylene tibial insert (X3) seems to have an advantage in wear generation compared with other fixed- and mobile-bearing knee designs.

Biomechanical evaluation of two types of short-stemmed hip prostheses compared to the trust plate prosthesis by three-dimensional measurement of micromotions.

BACKGROUND: Stemless and short-stemmed hip prostheses have been developed to preserve femoral bone stock. While all these prostheses claim a more or less physiological load transfer, clinical long-term results are only available for the stemless thrust plate prosthesis. In this study, the in vitro primary stability of the thrust plate prosthesis was compared to two types of short-stemmed prostheses. In addition to the well-established Mayo prosthesis, the modular Metha prosthesis was tested using cone adapters with 130 degrees and 140 degrees neck-shaft-angles. METHODS: The prostheses were implanted in composite femurs and loaded dynamically (300-1700 N). Three-dimensional micromotions at the bone-prosthesis interface were measured. In addition, the three-dimensional deformations at the surface of the composite femur were measured to gain data on the strain distribution. FINDINGS: For all tested prostheses, the micromotions did not exceed 150 microm, the critical value for osteointegration. The thrust plate prosthesis revealed similar motions as the short-stemmed prostheses. The short-stemmed prosthesis with the 130 degrees cone tended to have the highest micromotions of all tested short-stemmed prostheses. The thrust plate prosthesis revealed the lowest alteration of bone surface deformation after implantation. INTERPRETATION: The comparably low micromotions of the thrust plate prosthesis and the short-stemmed prostheses should be conducive to osseous integration. The higher alteration of load transmission after implantation reveals a higher risk of stress shielding for the short-stemmed prostheses.

Intolerance reactions to knee arthroplasty in patients with nickel/cobalt allergy and disappearance of symptoms after revision surgery with titanium-based endoprostheses.

Intolerance reactions to metal implants may present as dermatitis, impaired wound healing, effusions, pain or loosening. The clinical relevance of metal allergy in the differential diagnosis is often unclear and patients may even tolerate implants containing metals to which they are allergic. We present four patients with knee arthroplasty in whom after exclusion of infection or mechanical causes, a nickel/cobalt allergy led to replacement surgery with titanium-based prostheses. The subsequent alleviation of symptoms underlined the relevance and usefulness of allergological diagnostics in selected cases of complicated arthroplasty.

[The bending rod prosthesis: an experimental approach to metaphyseal hip arthroplasty]. / Die Biegestabprothese: ein experimenteller Ansatz zur metaphysären Hüftendoprothetik.

The aim of our study was to develop a femoral component for total hip arthroplasty that would exclusively anchor in the metaphysis of the femoral neck. To forego trochanteric fixation, the load needs to be transferred to the metaphysis at as many points as possible. A computer simulation model suggested that an implant with a central cylinder and 16 rods aligned along a thread would be the preferable solution. To evaluate primary implantation stability, 14 fresh frozen cadaver femora were used. A special instrument set was developed to allow for centered implantation of the prosthesis without the need to dissect the greater trochanter. For our tests, we used two prototype implants: one made from titanium and the other from a CoCrMo alloy. For the measurement of micromotions at the medial proximal femur, sinusoid dynamic loading with a force between 300 N and 1700 N and a frequency of 1 Hz was employed. In a neutral position of 16 degrees adduction and 9 degrees antetorsion, the average micromotions measured were 119 microm. Despite these convincing in vitro results with regards to primary stability, circular cut-out of the implant, followed by aseptic osteonecrosis, loosening might still occur in a clinical situation. Animal experiments are therefore required to further evaluate this new implant design.