P. Griss

Implant fixation by bone ingrowth

The term osseointegration referred originally to an intimate contact of bone tissue with the surface of a titanium implant; the term bone ingrowth refers to bone formation within an irregular (beads, wire mesh, casting voids, cut grooves) surface of an implant. The section dealing with the historical background describes the development of macroporous, microporous, and textured surfaces with an emphasis on the evolution of porous and textured metal surfaces. The principal requirements for osseointegration and bone ingrowth are systematically reviewed as follows: i) the physiology of osseointegration and bone ingrowth, including biomaterial biocompatibility with respect to cellular and matrix response at the interface; ii) the implant surface geometry characteristics; iii) implant micromotion and fixation modes; and iv) the implant-bone interface distances. Based on current methods of bone ingrowth assessment, this article comparatively reviews and discusses the results of experimental studies with the objective of determining local and systemic factors that enhance bone ingrowth fixation.

Lumbar spine curvature during office chair sitting

Prolonged sitting is generally accepted as a high risk factor in low back pain and it is frequently suggested that a lordotic posture of the lumbar spine should be maintained during sitting. We asked whether the sagittal curvature of the lumbar spine during sitting is affected by the seat tilt, backrest and the direction of the synchronised mechanism of the back and seat tilt (synchro tilt). Two office chairs were tested by multibody analysis interfacing a human model with a chair model. Results indicate that a synchronised mechanism of an office chair representing a posterior tilt of the seat while the backrest is reclined maintains an evenly distributed lumbar lordosis. The segmental angles are between 3.1 and 3.6 degrees at the lumbar vertebrae 1/2-4/5 (L1/2-L4/5). These lumbar spine segmental angles are not sensitive to the backrest height. In contrast, a synchro tilt concept with a reduction of the seats posterior tilt while the backrest is reclined causes a strong reduction of the lumbar lordosis in backrest recline with a maximum reduction from 11.7 to 2.8 degrees in L4/5. As a consequence of these results, a synchro tilt concept with a posterior tilt of the seat while the backrest is reclined is preferable from the lumbar spine kinematics point of view.

Prevention of heterotopic bone formation after total hip arthroplasty: a prospective randomised study comparing postoperative radiation therapy with indomethacin medication.

Abstract Heterotopic ossification (HO) after total hip arthroplasty is known to be a major complication with an impact on the functional outcome. Efforts have been made to prevent the occurrence of HO by means of either radiation therapy or pharmacotherapy. To date, there are no data available regarding the relative benefit of radiation versus medication with non-steroidal anti-inflammatory drugs. The objective of this study was to compare single-dose 600-cGy radiation therapy with indomethacin medication for their effect on the prevention of heterotopic bone formation after total hip arthroplasty. In all, 154 patients were included in the study. All patients underwent primary total hip arthroplasty due to osteoarthritis. Patients were randomly assigned to three different therapeutic groups. (a) The radiation group received a single radiation dose of 600 cGy between the 2nd and 4th postoperative day. (b) The indomethacin group received an oral application of indomethacin 2 × 50 mg per day from the 1st to 42nd postoperative day. (c) The control group received neither radiation nor indomethacin medication. There were significant group differences (P < 0.001). A least significant difference test (LSD) revealed that the mean of the control group was significantly different from that of the radiation and indomethacin groups. The 13 patients (8.4%) classified Brooker 3 or 4 were all in the control group. Again, this effect was statistically significant (chi-square, P < 0.001). In conclusion, this study demonstrated that both radiation and indomethacin therapy are effective in the prevention of postoperative HO. The choice for either one of the treatments has to be based on availability, contraindications, side-effects, practicability, standardisation and cost. Based on these considerations together with the results of this study, we currently use postoperative radiation with 600 cGy for all patients undergoing primary total hip arthroplasty.

Standardized evaluation of long-term results after anterior lumbar interbody fusion

A total of 113 patients, excluding those with tumor, spondylitis, and idiopathic scoliosis, underwent anterior lumbar interbody fusion (ALIF) with autologous iliac crest graft between 1984 and 1991 at our department. The proportion of these who were failed back patients was higher than that reported in the literature. Evaluation of functional outcome was feasible in 80 patients, utilizing Oswestry and Marburg scores, which were closely intercorrelated. The overall results yielded an improvement in the Oswestry score of 35.7 percentage points. A subset of 52 patients who were evaluated twice, showed the same results at an average of 6.6 years as they did at 2.3 years following surgery. Functional results showed a weak correlation with postoperative height loss of the intervertebral space. Influencing factors for the functional result were: postoperative compensation claim, age, and obesity. Of the professional people involved, 19.4% did not return to any occupation. Patients satisfied with the result had significantly greater functional improvement. Younger patients with additional dorsal distraction prior to ALIF for reduction of severe spondylolisthesis fared better than patients with ALIF alone. The rate of complications was low and did not contribute to the postoperative functional result. On the basis of these results further prospective studies have been designed and are currently underway.

Der Einfluss der Femur- und Tibiakomponentenrotation auf das patellofemorale Versagen beim künstlichen Kniegelenkersatz

ZusammenfassungPatellofemorale Komplikationen stellen eine der häufigsten Ursachen für das Versagen in der Knieendoprothetik dar. Es bestehen allerdings nur wenige klinische Studien, die das patellofemorale Versagen mit der Patellapositionierung bzw. der Femur- und Tibiakomponentenrotation korrelieren. Insbesondere fehlten bisher Studien, die die oben genannten Parameter bei Patienten mit bzw. ohne femoropatellarem Versagen bei ansonsten gleichen Bedingungen hinsichtlich Implantatwerkstoff, Implantatdesign und Verankerungstechnik miteinander vergleichen.Zwischen 1985 und 1992 wurden 171 Miller-Galante-I-(MG-I-)Knieprothesen implantiert.Seit 1999 mussten 20% aller implantierten MG-I-Prothesen, die eine “Metal-backed-Patellakomponente” aufwiesen, revidiert werden; 18 von diesen 34 Patienten wurden mit 18 Patienten als sog. “gematchte” Kontrollgruppe verglichen. Die Zuordnung der Kontrollgruppe erfolgte nach den Kriterien Geschlecht,Body-mass-Index (BMI) und Alter.Der einzige Unterschied in der Kontrollgruppe war, dass sie keine Probleme mit dem Streckapparat aufwiesen.Zur Bestimmung der Komponentenlokalisation wurden konventionelle Röntgenaufnahmen im a.-p.-Strahlengang,Patellatangentialaufnahmen in 30° und Computertomographien (CTs) durchgeführt.Die hier durchgeführte Studie zeigte einen signifikanten Gruppenunterschied in Hinblick auf die Höhe der Patellaersatzkomponente sowie einen Trend in Hinblick auf die Rotationsfehlstellung der Tibiakomponente. Mögliche Gründe für die Rotationsfehlstellung der femoralentibialen Prothesenkomponente wie auch Richtlinien zur Vermeidung der Rotationsfehlstellung werden diskutiert.AbstractPatellofemoral complications are among the most common causes for revision surgery in total knee arthroplasty. So far no quantitative assessment has been made of the femoral and tibial malalignment or the positioning of the patellar component and the type of patellofemoral complication or failure. In particular, no comparative studies are available that include patients with and without patellofemoral failure in respect to the above-mentioned parameters when implant material, implant design, and fixation technique were identical.Between 1985 and 1992, 171 MG I total knee arthroplasties were performed.Since 1999, 20% of all the implanted MG I knee arthroplasties (all with metal-backed patellar component) had to be revised.Of those 34 patients, 18 were pair matched with 18 control patients based on the criteria of sex, body mass index, and age.The only difference in the control group was that they did not suffer any malfunction of the patellofemoral mechanism.To assess the patella component localization, conventional AP radiographs, patellar merchant view radiographs in 30°, and CT scans were performed.This study has demonstrated a significant difference for the thickness of the patellar component and a trend regarding the rotational malalignment of the tibial component. Potential causes for the malrotation and guidelines to prevent rotational malalignment are discussed.

Degeneration model of the porcine lumbar motion segment: effects of various intradiscal procedures

SummaryIn an experimental study with 18 minipigs, we have tried to establish a model for the standardized evaluation of mechanical, histological and radiological phenomena of degenerative and reparative processes within the lumbar motion segment. Comparing different operative techniques revealed that the intradiscal application of hyaluronic acid into the nuclear defect is likely to enhance the regeneration process. Using the measurement of disc compliance, a semiautomatic picture analyzer and a new semiquantitative disc score could make future studies more comparable. From this basis, the intradiscal application of hyaluronic acid deserves further evaluation.

Validation data for periprosthetic bone remodelling theories

Periprosthetic adaptive bone remodelling after total hip arthroplasty (THA) has been frequently simulated in computer models, combining bone remodelling theory with finite element analysis. Unfortunately, there still subsist a lack of clinical data, which are necessary for validation of these simulation results. Therefore, the objective of the current project is to collect prospective volumetric bone density data with a clinical computerized tomography study in seven patients after THA. A retrospective study 12 years after implantation in 11 patients was added. A data set of about 100000 bone voxels for each femur was collected. In all prospective cases, the predominant change is seen during the first year. The average density reduction in the horizontal slices was between 50 and 150 Hounsfield units (HU) (approx. 10%; p<0.001) after 2 years. Loss of density is particularly strong distal of the minor trochanter and decreases from proximal to distal. For the 12 years retrospective study, the contralateral femur provided the control. Similar trends comparable to the prospective 2-year follow-up CT density values were seen in most cases with density reductions of up to 400 HU (30%). However, in one of these cases there was no difference between the operated and the control density. As far as we are aware, this is the first collection of fully prospective 3D validation data in vivo for periprosthetic adaptive bone remodelling theories. The data are also unique as they are suitable for direct patient-specific 3D finite element meshing and individual weight-related loading.

A comparative clinical outcome evaluation of smooth (10–13 year results) versus rough surface finish (5–8 year results) in an otherwise identically designed cemented titanium alloy stem

BackgroundWe retrospectively compared the influence of surface finish with respect to the long-term durability of a cemented titanium alloy stem of the same design but different surface finish.MethodsFrom 1984 to 1994, the stem was made of a titanium-aluminum-vanadium alloy. A total of 201 patients with 220 smooth stems (mean follow-up 11xa0years and 4xa0months) out of 612 implanted between 1984 and 1987 and 319 patients with 343 rough stems (mean follow-up 5xa0years and 10xa0months) out of 812 implanted between 1991 and 1993 could be reviewed clinically and radiologically for comparison. The average age of the patients with the smooth stem was 58.1xa0years and of the patients with the rough stem, 62.2xa0years. In both groups, 35% of patients were male and 65% female.ResultsThe mean Merle dAubigné hip score increased from 10.5 to 16.0 points in the smooth stem group and from 11.0 to 16.9 points in the rough stem group. The distribution of radiolucent lines, according to the zones of Gruen, was similar in both groups. The smooth stem required revision in 18 cases after a mean follow-up of 11xa0years and 4xa0months and the rough stem in 30 cases after a mean follow-up of 5xa0years and 10xa0months. The survival analysis (Kaplan-Meier) revealed 95.4% survival after 13xa0years for the smooth femoral component and 76.7% survival after 8xa0years for the rough femoral component.ConclusionsThe implantation of titanium alloy stems with a rough surface finish cannot be recommended because of its high aseptic loosening rate.

Size and direction of hip joint forces associated with various positions of the acetabulum.

When total hip replacement is performed, the position of the acetabular component may affect wear and component survival time. We considered the questions: In what way does displacement of the hip joint center alter (1) the magnitude and (2) the direction of the resultant force? Biomechanical tests were carried out on a human multibody model. After displacement of the hip joint center, the resultant forces were calculated for the single leg stance. With the flexed single leg stance, maximum hip joint forces were observed with lateral, cranial, posterior displacement. The peak forces were affected by the modeling of a gluteus maximus wrapping point at the ischial tuberosity and were overestimated when this was removed. With the straight single leg stance, posterior displacement decreases the total load on the hip joint because of the increased leverage of the rectus femoris. With regard to the direction of the resultant force, medial displacement increases the angles in both planes, cranial displacement increases it in the sagittal plane (cranial, posterior-caudal, anterior), and anterior displacement decreases the angle in the sagittal plane and increases it in the frontal plane (medial, cranial-lateral, caudal). The direction of the force is relatively insensitive to displacement of the hip joint center. The results presented here indicate a marked increase in the force after lateral, cranial, posterior displacement of the center in the flexed single leg stance. To avoid extreme joint loading and to reduce the wear after total hip arthroplasty, the cranial and posterior regions of the acetabulum should be fully reconstructed. A high hip joint center has an adverse effect on the magnitude of the force, although the directions are hardly affected by it.

The Blood Supply of the Growth Plate and the Epiphysis: A Comparative Scanning Electron Microscopy and Histological Experimental Study in Growing Sheep

The blood supply of the growth plate has been described in the late 50s and early 60s, and there was controversial discussion about the existence of transphyseal vessels. The vascular supply of growth plate and epiphysis of the proximal tibia was reinvestigated using a modern technique, the Mercox-perfusion method, in six sheep aged 6-24 weeks. A comparison was made among pure perfusion specimens, the corrosion casts, and histological sections. The metaphyseal, epiphyseal, and perichondral blood supply systems were confirmed. However, there was evidence of regular transphyseal anastomoses between the metaphyseal and epiphyseal system. Based on the histological arrangement of the blood vessels, the arterial blood flow would appear to be from the metaphysis to the epiphysis. The existence of transphyseal arterial vessels originating metaphyseally and seen both in cast preparations and histological sections was added to the present description of the blood supply of the growth plate. Age-related differences in the vascularization of the growth plate were not found in this study.