Serum aluminium and cobalt levels after ceramic-on-ceramic and metal-on-metal total hip replacement.

In a randomised study, 28 patients with a mean age of 62.2 years (32 to 81) with osteoarthritis or avascular necrosis of the hip received either a ceramic-on-ceramic or a metal-on-metal total hip replacement. Apart from the liners the acetabular and femoral components were made of Ti-Al-Nb alloy. The serum aluminium and cobalt levels were measured before, and at one year after surgery. The 15 patients in the ceramic-on-ceramic group had a median pre-operative aluminium level of 1.3 microg/l (0.25 to 8.4) and a cobalt level below the detection limit. At one year the aluminium level was 1.1 microg/l (0.25 to 2.3) and the cobalt level was 0.4 microg/l (0.15 to 0.7). The 13 patients in the metal-on-metal group had a median pre-operative aluminium level of 1.9 microg/l (0.25 to 4.4) and a cobalt level below the detection limit. At one year the median aluminium level was 0.9 microg/l (0.25 to 3.9) whereas the cobalt level was 1.4 microg/l (0.5 to 10.5). This increase in the cobalt level at one year was significant (p < 0.001). Our findings indicate that ceramic-on-ceramic bearings do not cause elevated levels of serum aluminium in the first post-operative year.

Changes in bone mineral density in the proximal femur after cementless total hip arthroplasty. A five-year longitudinal study.

We investigated prospectively the bone mineral density (BMD) of the proximal femur after implantation of a tapered rectangular cementless stem in 100 patients with a mean age of 60 years (16 to 87). It was determined using dual energy x-ray absorptiometry, performed one week after surgery and then every six months until the end-point of five years. The BMD increased significantly in Gruen zones 2, 4 and 5 by 11%, 3% and 11% respectively, and decreased significantly in Gruen zones 1, 6 and 7 by 3%, 6% and 14% respectively, over the five-year period. The net mean BMD did not change over this time period. The changes in the BMD were not confined to the first 12 months after surgery. This investigation revealed no change in the overall periprosthetic BMD, but demonstrated a regional redistribution of bone mass from the proximal to distal zones.

[Six to ten year results of use of the alloclassic hip prosthesis--a multicentre survival analysis]. / 6 - 10-Jahres-Ergebnisse des zementfreien Alloclassic-Hüftsystems--Eine multizentrische Survival-Studie.

AIM: This prospective study describes This retrospective multicenter study was undertaken to calculate mid- and long-term survival rates of the cementless Zweymüller/Alloclassic total hip prosthesis. MATERIAL AND METHODS: The rectangular titanium stem and threaded cup have been in use since 1986. The ball head is made of alumina ceramic, the inlay of UHMW polyethylene. Five hospitals in Austria, France and Germany cooperated in the follow-up of 848 patients operated between October 1986 and September 1990 (mean age 62.2 years, 62% women, 38% men, mean patient weight 73.8 kg, body mass index 26.8). 468 patients were followed clinically, 320 patients interviewed on the phone, 29 sent a letter. No information was available concerning the remaining 31 patients. Probabilities of implant survival were estimated with the Kaplan-Meier method. RESULTS: 98 patients (11.5%) had died at a median follow-up time of 81.1 months. The probability of survival at 81.1 months was 98.6% looking at stem and cup. There was no significant association of survival of the prosthesis and patient weight, gender or body mass index. CONCLUSION: Our results are in accordance with previously published data of smaller series using the Zweymüller/Alloclassic( total hip. The survival rate of this cementless rectangular titanium prosthesis for the reported follow-up time compares favorably with contemporary cemented hip prostheses.

[Diagnostic imaging in hip prostheses]. / Bildgebung bei Hüftprothesen.

Hip arthroplasty has become a common and still increasing procedure for the treatment of osteoarthritis, advanced head necrosis, post-inflammatory arthritis or rheumatoid arthritis. Radiography is the most important imaging modality for monitoring the normal, asymptomatic hip arthroplasty. Radiographs are obtained at the end of a surgical treatment, to exclude complications like fracture or component misplacement. In the follow-up radiographs are used for the diagnosis of loosening and infection of the hip arthroplasty as well as soft tissue ossification. Together with the history and clinical information, the analysis of morphological findings allows to find the grade of loosening. MRI has been advocated in the diagnosis of infection, in particular in the localisation of soft tissue involvement. Imaging, especially by radiographs, is used for the evaluation of the normal and complicated follow-up of hip arthroplasty.

[Risk factors for dislocation of a cementless total hip endoprosthesis--a statistical analysis]. / Risikofaktoren für die Luxation einer zementfreien Hüfttotalendoprothese--Eine statistische Analyse.

AIM: This retrospective study aimed at the statistical identification of risk factors for dislocation for a certain cementless hip endoprothesis. MATERIAL AND METHOD: At our department 2605 primary total hip arthroplasties were performed between 1987 and 1997. In 40 patients (1.5%) a dislocation occurred. These patients were compared with a control group matched in number. RESULTS: No difference was found in both groups with respect to age, height, weight, body-mass index, and diagnosis. A tendency was found that more males were involved in the dislocation group. There were more previous operations found in this group (p = 0.005). Also significant was the fact, that patients in the dislocation group more often had epidural anaesthesia (p = 0.02), more often the implantation of the smaller 28-mm head (vs. 32 mm) (p = 0.02), and a higher inclination angle of the acetabular component (p = 0.02). No difference was found in terms of the surgeons experience, the postoperative leg length, femoral offset, medialisation, cranialisation and antetorsion of the acetabular component. CONCLUSION: Dislocation after total hip arthroplasty is a multifactorial complication. With the use of the Alloclassic/Zweymüller total hip endoprothesis, a higher risk for dislocation was found for patients with previous hip surgery, the use of the smaller endoprosthesis head, a high acetabular inclination angle, and in the use of epidural anaesthesia.

Aggressive warming reduces blood loss during hip arthroplasty.

UNLABELLED: We evaluated the effects of aggressive warming and maintenance of normothermia on surgical blood loss and allogeneic transfusion requirement. We randomly assigned 150 patients undergoing total hip arthroplasty with spinal anesthesia to aggressive warming (to maintain a tympanic membrane temperature of 36.5 degrees C) or conventional warming (36 degrees C). Autologous and allogeneic blood were given to maintain a priori designated hematocrits. Blood loss was determined by a blinded investigator based on sponge weight and scavenged cells; postoperative loss was determined from drain output. Results were analyzed on an intention-to-treat basis. Average intraoperative core temperatures were warmer in the patients assigned to aggressive warming (36.5 degrees +/- 0.3 degrees vs 36.1 degrees +/- 0.3 degrees C, P< 0.001). Mean arterial pressure was similar in each group preoperatively, but was greater intraoperatively in the conventionally warmed patients: 86+/-12 vs 80+/-9 mm Hg, P<0.001. Intraoperative blood loss was significantly greater in the conventional warming (618 mL; interquartile range, 480-864 mL) than the aggressive warming group (488 mL; interquartile range, 368-721 mL; P: = 0.002), whereas postoperative blood loss did not differ in the two groups. Total blood loss during surgery and over the first two postoperative days was also significantly greater in the conventional warming group (1678 mL; interquartile range, 1366-1965 mL) than in the aggressively warmed group (1,531 mL; interquartile range, 1055-1746 mL, P = 0.031). A total of 40 conventionally warmed patients required 86 units of allogeneic red blood cells, whereas 29 aggressively warmed patients required 62 units (P = 0.051 and 0.061, respectively). We conclude that aggressive intraoperative warming reduces blood loss during hip arthroplasty. IMPLICATIONS: Aggressive warming better maintained core temperature (36.5 degrees vs 36.1 degrees C) and slightly decreased intraoperative blood pressure. Aggressive warming also decreased blood loss by approximately 200 mL. Aggressive warming may thus, be beneficial in patients undergoing hip arthroplasty.

Biologic attachment of an allograft bone and tendon transplant to a titanium prosthesis.

An Achilles tendon allograft with its bony insertion was used to bridge a Titanium implant, containing an endoprosthetic tendon anchor, and the sheep biceps muscle. Twelve sheep were operated on unilaterally and followed up clinically and histologically for 2, 4 (n = 2), 8, and 12 months (n = 4). Full function of the front limb was regained after 8 to 12 weeks. There were no signs of mechanical loosening at all times. The morphologic changes at the bone block and implant fixation site were an initial revascularization of the allograft bone, which was observed at 2 months and enhanced at 4 months but occurred without any evidence of bone remodeling. This was changed in all specimens taken at 8 and 12 months where intensive new bone development, remodeling, and bone ingrowth in the titanium implant was found. Bone mass was shifted significantly to the tendon insertion half of the bone block because of a creeping substitution of the cancellous allograft bone and bone ingrowth to the implant. Overall bone mass slightly decreased with time but resorption of allograft bone outweighed new bone development only at lesser loaded areas. Transplantation of a bone and tendon allograft to an implant resulted in a revitalized, mechanically stable, and biologically anchored compound.

Function of reinserted abductor muscles after femoral replacement.

We compared two methods of reconstruction of the abductor mechanism in 15 patients after prosthetic replacement of the upper femur, to assess abductor strength and function. Six patients in group I had direct fixation of the gluteus medius tendon and a segment of the original bone to the prosthesis. Nine patients in group 2 had the abductor tendon fixed to the iliotibial band. We assessed clinical function, isometric muscle strength and muscle cross-sectional area for each patient. The patients in group 1 had better clinical and functional results (p = 0.059), with average peak torques for hip abduction of 92% of that in the non-operated leg in group 1, and of 57% in group 2. Group 1 had a mean muscle cross-sectional area of 69% and a mean value of strength per cross-sectional area of 134% when compared with the control side. The respective values for group 2 were 52% and 91%. Direct fixation of the abductor muscles to the prostheses gave improved function and higher isometric abductor muscle force.

Detection of orthopaedic prostheses at airport security checks.

We studied the detection of joint replacements at airport security checks in relation to their weight, using two types of detector arch. A single-source, unilateral detector showed different sensitivities for implants on different sides of a test subject. All implants weighing more than 145 g were detected by one of the arches. The degree of detection was directly related to the logarithm of the weight of the prosthesis in patients, with a linear correlation (r2 = 0.61). A bilateral arch detected all prostheses weighing over 195 g. With their usual sensitivity settings many joint replacements were detectable; an identification pass containing the site and weight of such prostheses would help to avoid the need for body-search procedures.

Elevated serum cobalt with metal-on-metal articulating surfaces.

We determined serum cobalt levels in 55 patients by atomic absorption spectrophotometry before and after implantation of uncemented total hip arthroplasties. In a randomised, prospective trial 27 wrought Co-28Cr-6Mo-0.2C metal-on-metal articulations were compared with 28 ceramic-on-polyethylene hips which did not contain cobalt. Other sources of iatrogenic cobalt loading were excluded. The metal-on-metal group produced detectable serum cobalt levels (median 1.1 microg/l after one year) which were significantly different (p < 0.0001) from those of the ceramic-on-polyethylene control group (median below detection limit of 0.3 microg/l after one year). Our findings indicate that metal-on-metal bearings generate some systemic release of cobalt.

Mechanical characteristics of four allograft tendon-to-muscle anastomotic techniques.

Four methods of allograft tendon-to-muscle anastomosis were tested in single cycle distraction to failure using 10 anastomosed ovine calcaneal tendon-biceps brachii units. The tendon-muscle units were compared to intact ovine biceps brachii muscle units. Methods of tendon-to-muscle anastomosis were derived from modifications of existing muscle tendon repair and tenorrhaphy techniques. Load to failure (N), stiffness (N/cm), distraction (cm), and modes of failure were recorded. Of the four methods tested, the side-to-side technique demonstrated the highest load to failure (152.1 N), the greatest stiffness (17.6 N/cm), the least distraction (2.99 cm) before failure, and the least amount of muscle tissue trauma at failure. Results indicate that, of the methods tested, the side-to-side technique offers the greatest initial stability and should therefore allow adequate revascularization and healing of the anastomosis site.

[Hallux rigidus operated on by Keller and Brandes method: radiological parameters of success and prognosis]. / Hallux rigidus operiert nach Keller und Brandes: Radiologische Erfolgs- und Prognoseparameter.

PURPOSE: The aim of this study was to evaluate the pre- and postoperative radiographic findings of hallux rigidus treated with Keller and Brandes arthroplasty to determine the radiographic outcome and to identify a prognostic marker. METHODS: 83 patients with a total of 121 cases of hallux rigidus operated using Keller and Brandes arthroplasty were followed up (mean 9.7 y). A comparison of the pre- and postoperative radiographs, the clinical and subjective findings was predicated on a five point scale: 1. percentage of proximal phalanx resected ( < 33%, 33-50%, > 50%), 2. joint space, 3. ratio of the length of the first and second metatarsals, 4. first intermetatarsal angle, and 5. hallux valgus angle. RESULTS: In the patient group which had 33-50% of the proximal phalanx excised (n = 67. 55%) the highest patient satisfaction was observed (96%). If resection of the proximal phalanx exceeded 50% (n = 13. 11%), non physiologic dorsiflexion of the toe occurred and patients were dissatisfied (62%). Excision of less than 33% of the hallux (n = 41. 34%) was associated with a recurrent hallux rigidus. No other evaluated radiological parameter proved to be of significance. CONCLUSION: The most important radiological parameter in the evaluation of the outcome of Keller and Brandes arthroplasty as a surgical treatment method for hallux rigidus was the percentage of the proximal phalanx which had ben excised.

Effects of freeze/thaw conditioning on the tensile properties and failure mode of bone-muscle-bone units: a biomechanical and histological study in dogs.

Eight pairs of canine supraspinatus bone-muscle-bone units were mechanically tested to failure in tension. One side was tested immediately post mortem, and the other side was tested after exposure to a standard freeze/thaw process (-60 degrees C). The failure site was analyzed histologically. Fresh specimens had greater values for ultimate strength (p < 0.001), stiffness (p < 0.001), and energy to failure (p < 0.001). All specimens failed in the muscle close to the musculotendinous junction. The length of muscles subjected to the freezing process was reduced (9.3%). In addition, the load-displacement curves for the fresh and frozen specimens showed marked differences in shape. The loss of tensile strength in muscle tissue is due to damage of the intracellular contractile elements caused by postmortem autolysis; this type of damage is increased as a result of the freeze/thaw process. The freeze/thaw process significantly altered the tensile properties of normal muscle tissue, no matter how carefully it was done. One cannot expect to receive representative data if muscle is frozen and thawed.

Tendons attached to prostheses by tendon-bone block fixation: an experimental study in dogs.

To develop a method of tendon attachment to a metallic endoprosthesis, we evaluated fixation strength, clinical function of the tendon, and morphological changes in an experimental model. The canine supraspinatus tendon was removed from the greater tubercle of the humerus and attached to a titanium prosthesis. In 12 animals, the bone block underlying the tendon insertion was preserved and attached in one limb; the soft part of the tendon was attached directly to the prosthesis in the contralateral limb. Fixation strength was evaluated after 16 weeks of in vivo implantation (12 specimens) and compared with the in vitro fixation strength (12 specimens) and with intact normal controls (six specimens from cadavera). Function of the tendon in vivo was evaluated by force-plate analysis (at 3-week intervals). All specimens were evaluated histologically. Sixteen weeks after surgery, the tendon-bone block attachment was significantly stronger (mean, 16%) than the direct tendon attachment and not significantly different from the normal control, and the direct tendon attachment was significantly weaker (mean, 68%) than the normal control. There was significantly more weight-bearing on the limbs with a tendon-bone block attachment than on the limbs with a direct tendon attachment at both 3 and 6 weeks postoperatively. Both front legs showed increased weight-bearing with time, but the differences were not statistically significant. Anchorage by tissue ingrowth to the titanium prosthesis was found consistently--there was bone ingrowth in the tendon-bone block attachments and fibrous tissue ingrowth in the direct tendon attachments. When a bone block was preserved, the strength and stiffness were comparable with those of a normal tendon insertion.(ABSTRACT TRUNCATED AT 250 WORDS)

Fixation of canine tendons to metal.

For the purpose of developing a method to attach tendons directly to the prosthesis, canine supraspinatus tendons were attached in vitro to a metallic surface, using 3 different fixation devices: a spiked polyacetal washer (Synthes), a spiked soft tissue fixation plate (Synthes), and a newly designed Enhanced Tendon Anchor (ETA), which straddled the tendon with interlocking spikes oriented at a 20-degree angle. 2 methods were used: 1) the tendon was fixed directly to the metallic surface, or 2) a bone block containing the tendon insertion was fixed to the metallic surface. The specimens were tested for initial fixation strength in tension to failure; intact bone-muscle-tendon-bone units were used as controls. Bone block fixations were stronger than direct tendon fixations when the spiked washer or the ETA was used; this was not true of the fixation plate. The ETA was stronger than the other techniques in ultimate strength in both direct tendon fixation and bone block fixation. The soft tissue fixation plate was found to be weaker than the other techniques in bone block fixation.

Effect of homologous fibrin adhesive on callus formation and extracortical bone bridging around a porous-coated segmental endoprosthesis in dogs.

Modular, porous-coated, titanium segmental endoprostheses were implanted bilaterally in the femoral diaphysis of 7 adult mixed-breed dogs. Autogenous bone graft in particle form was placed around the implant and bone. In 1 limb, homologous fibrin adhesive was mixed with the graft in situ before soft tissue closure. The contralateral limb was grafted in identical manner, but without fibrin adhesive, and served as a control. Radiography was performed immediately after surgery and 1, 2, 3, 4, 6, 8, 10, and 12 weeks later to assess callus area and bone remodeling. At 12 weeks, dogs were euthanatized and bone/implant fixation strength was tested under torsion and compared with values for 6 in vitro controls. Histomorphometric and microradiographic analyses of transverse sections of the distal portion of the implanted femurs were performed. Radiographic callus area was significantly (P < 0.05) smaller in the femurs grafted with fibrin adhesive, compared with the contralateral control. New bone formation (21.4 +/- 1.8% vs 19.2 +/- 2.4%), unlabeled bone (64.8 +/- 3.0% vs 67.9 +/- 4.2%), porosity (13.9 +/- 0.7% vs 12.9 +/- 0.8%), and bone ingrowth into the porous coating (10.3 +/- 0.9% vs 10.0 +/- 1.2%) were not significantly different between fibrin- and nonfibrin-grafted implants, respectively. There were no significant differences in torsional strength of implant fixation between the fibrin- and nonfibrin-grafted femurs or between the in vivo implanted femurs and the in vitro controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanical characteristics of proximal femoral reconstruction after 50% resection.

Six techniques of proximal femoral replacement were compared in vitro with the use of compression, bending, and torsional testing in a canine model. One femur of each pair was osteotomized in the midshaft region, and the proximal portion was replaced with one of six techniques. These techniques included (a) a segmental proximal femoral endoprosthesis cemented into the distal femur with no allograft (technique ES); (b) a long-stem endoprosthesis press-fit into an allograft and cemented into the distal femur with a transverse osteotomy (technique AT); (c) the same construct as technique AT, but with a step-cut at the osteotomy (technique AS); (d) a long-stem endoprosthesis interlocked into an allograft and cemented into the distal femur with a transverse osteotomy (technique AI); (e) a short-stem endoprosthesis cemented into an allograft combined with one plate laterally stabilizing the allograft to the distal femur with a transverse osteotomy (technique AP1); and (f) the same construct as technique AP1, but with an additional plate cranially (technique AP2). A long-stem endoprosthesis cemented into the contralateral intact femur served as the control. Techniques that involved a long-stem endoprosthesis and cementing distally (AT, AS, and AI) were more resistant in torsion than the plated replacement techniques (AP1 and AP2). The segmental replacement construct (ES) was equal to or stronger than all other techniques under each testing condition. In torsion, the addition of a step-cut (AS) significantly lowered angular displacement of the reconstruction when compared with the reconstruction with a transverse osteotomy (AT) (p < 0.05). Bones with one-plate fixation (AP1) were significantly weaker in torsional stiffness and maximum torque and in mediolateral bending (p < 0.05) than all other techniques. The addition of a second plate (AP2) increased the mechanical properties of the construct so that it was greater than the one-plate method and was equal to (bending and compression) or still weaker (torsion) than the other techniques. The results indicate that segmental replacement methods and allograft/endoprosthetic composites that involve long-stem endoprostheses fixed with cement are mechanically superior to methods that involve short-stem endoprostheses with single or double plating at the osteotomy sites.

Dual energy x-ray absorptiometry of implanted femora after cemented and press-fit total hip arthroplasty in a canine model.

The effect of a press-fit and cemented titanium alloy endoprosthesis on the measurement of bone mineral density (BMD) of the proximal femur in a canine model with dual energy x-ray absorptiometry (DXA) was determined. Seven regions of interest, corresponding to zones 1-7 according to Gruen et al., were measured. Eight unpaired femora were scanned with DXA before implantation (five separate scans per femur), after press-fitting with a titanium alloy femoral component (five separate scans per femur); and after cementing with the same component (five separate scans per femur). When the titanium alloy endoprosthesis was press-fit, the BMD of five of seven regions of the proximal femur increased significantly (range, 2.7-23.1%; mean, 11.2%), although the mean precision error of this measurement was not altered (before implantation, 1.1%; after press-fit 1.8%). Cementing of the implant caused a variable effect on BMD, resulting in a decrease in distal regions where cortical bone was relatively thin compared with the cement mantle (regions 3, 4, and 5) and in an increase in the other regions. Cementing of the implant significantly increased the mean precision error of measurement to 7.2% (range, 1.1-12.6%).

Effects of axial dynamization on bone healing.

The effects of early dynamization (physiologic axial compression) on canine fracture healing at six weeks were studied. Bilateral transverse mid-tibial osteotomies were created and initially stabilized with a 2-mm gap using relatively rigid external fixators. Seven days after osteotomy, the telescoping mechanism of one of the fixators on each dog was released (dynamized), resulting in physiologic loading of the osteotomy, while the contralateral fixator remained locked as a rigid control. The dynamized osteotomy closed, and increased functional weight bearing resulted from 3 weeks on. Radiographically the amount of periosteal callus increased over time, but no difference in callus size was seen between the dynamized fractures and the controls. Torsional mechanical testing found the dynamized osteotomies to be significantly stiffer, and they tended to tolerate more maximum torque than the controls. Microscopic evaluation found no difference in the volume of the periosteal and endosteal calluses or in the tissues constituting them. However, a significantly greater proportion of the dynamized osteotomy gap was filled with new bone. These results suggest that dynamization in this delayed union model improved fracture healing by reducing fracture gap size and increasing weight bearing, not by altering the pathway of fracture healing.

Effect of titanium endoprostheses on bone mineral density measurements, using quantitative computed tomography.

Quantitative computed tomography has been used extensively to measure bone mineral density; particularly in the vertebral column and in the proximal portion of the femur in human beings with osteoporosis. Other potential applications of this technique include evaluation of bone adjacent to metallic endoprostheses and evaluation of fractures as they heal. Unfortunately, metal causes severe image degradation, principally seen as starburst streaking. One method used to decrease these artifacts is by imaging less-attenuating materials, such as titanium alloy. Titanium decreases image degradation sufficiently to allow accurate determination of the geometric properties of cadaveric bone. In our study, the effect of a titanium segmental endoprosthesis on bone mineral density measurement was determined by use of bone specimens from dogs and calibration standards. Titanium decreased the bone mineral density of calibration solutions from 6.8 (500 mg/cm3) to 17.7% (250 mg/cm3), and increased bone mineral density of cortical bone by 5.3%. Titanium did not affect the repeatability of these scans, indicating that the error caused by titanium was systematic and can be corrected. Our data were suggestive that quantitative computed tomography can be used to measure bone mineral density of cortical bone adjacent to titanium endoprostheses, with a predictable increase in density measurement.