[Impingement Free Motion in Total Hip Arthroplasty - How Can We Implement It?]. / Impingementfreie Bewegung nach Hüft-TEP - wie realisieren?

INTRODUCTION: Prosthetic impingement and insufficient soft tissue tension are still the most important factors responsible for early dislocation after total hip arthroplasty. Optimal positioning of both prosthetic components, the stem and the socket, optimising their design and restoring individual hip biomechanics, are of the upmost importance in reducing the risk of impingement. This study describes the concept of the combined safe zone (cSafe-Zone) that provides guidelines for the optimal positioning of both components. MATERIAL AND METHODS: A computerised CAD model of a total hip prosthesis was used to systematically investigate the effect of design parameters, such as head-to-neck ratio, CCD shaft angle, as well as positioning parameters, such as cup inclination and cup anteversion and stem antetorsion, on the range of motion. We looked for all positioning combinations that allow the predefined range of movement (= iROM, intended range of movement) and thus define the combined safe zone. The analysis was carried out with straight stems, anatomical and short stems. The size of the cSafe-Zone was chosen as the optimising criterion and the largest cSafe-Zone was considered to define the optimal component positions. These optimal relative orientations of cup and stem were engraved onto the surface of the navigation trial head and used to position the cup during surgery. RESULTS: This new combined safe zone is not static but dynamic; it varies in size and position and is specific for each prosthesis system. High stem antetorsion should be combined with lower cup anteversion and vice versa. Thus, cup anteversion and stem antetorsion are complementary. CCD shaft angles above 135° reduce the size of the cSafe-Zone and are therefore not recommended. Larger head sizes allow lower cup inclinations, i.e. the recommended cup inclination for a 28 mm head is 40 to 45°, for 32 mm 38 to 42° and for 36 mm 35 to 40°. This also increases the so-called jumping distance. Anatomical stems require less cup anteversion than straight stems. CONCLUSION: The concept of combined safe-zone delivers clear guidelines how to position both components of a total hip prosthesis in order to maximise range of movement and to reduce the risk of prosthetic impingement. It is the basis of the stem-first surgical technique. Computer-based navigation or mechanical instruments can be used to implement this new concept in surgical practice.

[Ligament-controlled positioning of the knee prosthesis components]. / Ligamentkontrollierte Positionierung der Knieprothesenkomponenten.

BACKGROUND: There are at least two predominant goals in total knee replacement: first, the surgeon aims to achieve an optimal postoperative kinematic motion close to the patient's physiological range, and second, he aims for concurrent high ligament stability to establish pain-free movement for the entire range of motion. A number of prosthetic designs and surgical techniques have been developed in recent years to achieve both of these targets. OBJECTIVES: This study presents another modified surgical procedure for total knee implantation. As in common practice the osteotomies are planned preoperatively, referencing well-defined bony landmarks, but their placement and orientation are also controlled intraoperatively in a stepwise sequence via ligamentous linkages. METHOD: This method is open to all surgical approaches and can be applied for PCL-conserving or -sacrificing techniques. The anterior femoral osteotomy is carried out first, followed by the distal femoral osteotomy. Then, the extension gap is finalized by tensioning the ligaments and "top-down" referencing at the level of the tibial osteotomy, followed by finishing the flexion gap in the same way, except that the osteotomy of the posterior condyles is referenced in a "bottom-up" fashion. DISCUSSION: Hence, this technique relies on both bony and ligament-controlled procedures. Thus, it respects the modified ligamentous framework and drives the prosthetic components into the new ligamentous envelope. Further improvement may be achieved by additional control of the kinematics during surgery by applying modern computer navigation technology.

Containment versus impingement: finding a compromise for cup placement in total hip arthroplasty.

Recommendations for cup containment and impingement may provide conflicting directions for component orientation in total hip arthroplasty. For optimal containment, the cup is positioned with respect to the acetabular bone, resulting in coincidence of the rim of the cup and the acetabulum. This results in good coverage and symmetric load transfer, leading to good long-term stability, but occasionally necessitates more abduction of the cup than that recommended by the safe zone. On the other hand, placement of the cup for an optimal range of motion would lead to only partial containment, with a higher risk of component loosening and revision. The most effective compromise is to use a prosthesis that has a large safe zone, realised by a high head-to-neck ratio, and orienting the cup such that a good containment is achieved and the safe zone is respected. Computer navigation or smart aiming devices may help to find the best relative orientation.

The impact of the CCD-angle on range of motion and cup positioning in total hip arthroplasty.

BACKGROUND: Biomechanical analysis and clinical experience reveal that offset total hip stems increase soft tissue tension and reduce the risk for dislocation in total hip arthroplasty. Most of these stems have a smaller neck-shaft-angle to increase the offset. This study investigates if changing the neck-shaft-angle has an impact on how cup and stem should be positioned with regard to range of motion. METHODS: A mathematical model of a total hip arthroplasty was developed to analyze range of motion until impingement between cup and neck. Range of motion was determined for each combination of neck-shaft-angles and additional parameters like cup inclination, cup anteversion, stem antetorsion, head/neck ratio and design of the cup opening. RESULTS: A maximized range of motion is achieved for neck-shaft-angles between 125 degrees and 131 degrees . Reducing the neck-shaft-angle by one degree requires reducing the cup anteversion by about 2 degrees and increasing the cup inclination by 0.45 degrees . Stems with neck-shaft-angles more than 135 degrees are not recommended when the head/neck ratio is 2.3 or less. INTERPRETATION: Stems with a reduced neck-shaft-angle for an increased offset should be coupled with cups that are inclined slightly higher and less anteverted as compared to a standard stem. Precise recommendations for optimal component positioning can only be given for a specific prosthesis system regarding all parameters.

[Secondary stability of cemented and non-cemented acetabular implants ex-vivo under dynamic load].

OBJECTIVE: To measure the bone-prosthetic implant interface micromovement during the application of physiological load by using a material testing system (MTS). METHODS: The cadaveric hip specimens were used to simulate a single leg stance and the joint in the neutral position. Micromovement was recorded via a 3-dimensional transducer in the acetabula of postmortem specimens, which had been preserved in formalin. The study data of the cemented and uncemented prosthsis refereed to the lone-term clinical process and the radiological status and experimental results. RESULTS: Cemented cups showed higher transverse relative motion up to 90 microm, whereas the maximum transverse movement of the non-cemented cup was 60 microm. Orthogonal motion perpendicular to the implant surface showed compression for all cups at all sites. CONCLUSION: The results indicate that there are large differences in survival time between 2 groups. That could not be compared statistically in secondary stability. Nevertheless, according to the results, the amount of micromotion of press-fit cup is relatively less than that of cemented polyethylene cup, which is instrumental in bone ingrowth and secondary stability.

Compliant positioning of total hip components for optimal range of motion.

Impingement between femoral neck and endoprosthetic cup is one of the causes for dislocation in total hip arthroplasty (THA). Choosing a correct combined orientation of both components, the acetabular cup and femoral stem, in manual or computer-assisted implantation will yield a maximized, stable range of motion (ROM) and will reduce the risk for dislocation. A mathematical model of a THA was developed to determine the optimal combination of cup inclination, cup anteversion, and stem antetorsion for maximizing ROM and minimizing the risk for cup-neck impingement. Single and combined hip joint motions were tested. A radiographic definition was used for component orientation. Additional parameters, such as stem-neck (CCD) angle, head-neck ratio, and the design of the acetabular opening, were also considered. The model showed that a maximized and safe ROM requires compliant, well-defined combinations of cup inclination, cup anteversion, and stem antetorsion depending on the intended ROM. Radiographic cup anteversion and stem antetorsion were linearly correlated. Additional internal rotation reduced flexion, and additional external rotation reduced extension, abduction and adduction. The articulating hemispheric surface of acetabular cups should be oriented between 40 degrees and 45 degrees of radiographic inclination, between 20 degrees and 28 degrees of radiographic cup anteversion, and should be combined with stem antetorsion so that the sum of cup anteversion plus 0.7 times the stem antetorsion equals 37 degrees. Final component orientation must also consider cup containment, implant impingement with bone and soft tissue, and preoperative skeletal contractures or deformities to achieve the optimal compromise for each patient.

[Preliminary results after multiple knee injuries with operative reconstruction of chronic posterior-lateral instabilities]. / Erste Ergebnisse einer neuen Technik zur Rekonstruktion des hinteren Kreuzbandes bei komplexen chronischen Knieverletzungen.

AIM: The operative treatment of posterior knee instability is a difficult problem and the literature does not offer methods as good as ACL reconstruction. METHODS: With a new operative approach the authors have attempted to improve the surgical procedure and the final outcome in terms of stability and function. To illustrate our clinical findings, 20 cases of chronic posterior-lateral knee instability were retrospectively reviewed following PCL reconstruction. We examined 5 women and 15 men. The average follow-up period was 14 months (6 - 24 months) and the average age was 30 (17 - 59) years. RESULTS: Subjectively all patients were satisfied with the surgical outcome and there were no intraoperative technical difficulties and no patient had a postoperative problem. The p.-a. instability measured at 20 degrees of knee flexion was preoperatively 11.7 mm, postoperatively 7.2 mm and 6.7 mm on the uninjured side. The Lysholm score was preoperatively 59 (35 - 71) points and postoperatively 85 (65 - 100) points. 19 patients returned to work and 14 patients were able to participate in sports. CONCLUSION: The results demonstrate that the knee still does not have a normal stability postoperatively, but the results were reproducible and the method appears to be reliable.

Load transfer and fixation mode of press-fit acetabular sockets.

Adequate initial fixation is a prerequisite for osseointegration and secondary stability of noncemented cups. Physiologic force transmission between the cup and acetabulum guarantees the best long-term fixation. To study load transfer within the natural hip joint and in the bone-implant interface of 2 different hemispherical noncemented press-fit cups, 10 hips were investigated in an experimental setup simulating single-leg stance. Load distribution and contact area were measured using prescale pressure-sensitive films and digital image analysis. Three dominant locations near the periphery of the acetabulum could be identified. Main load transfer occurs in the cranial region of the acetabulum, where it is buttressed by the iliac bone; the second location is at the posterior-inferior region at the ischial facet, and the third location is at the anterior region, where support is provided by the pubic bone. Peripheral rim contact was present in both cups but not completely circumferential. It showed marked loading at the same 3 locations similar to the natural hip joint. The ilioischial diagonal axis produced the highest press-fit. Peak local forces were found at the ischial and iliac facets. Local forces can be grouped into an iliac, an ischial, and a pubic group contributing 55%, 25%, and 20% to the total hip joint force. Pole contact was not present in the natural hip and with the biradial press-fit cup with flattened pole area but was observed with the pure hemispherical cup. Hence, stable fixation of an acetabular cup is achieved best by a 3-point-like bony support at the iliac, ischial, and pubic bone. The acetabular fovea does not provide functional support of the femoral head or endoprosthetic socket. In revision surgery, remaining peripheral bone stock at the iliac, ischial, and pubic locations allows stable implantation of primary cups.

[Cementless socket fixation based on the "press-fit" concept in total hip joint arthroplasty]. / Zementfrei pfannenverankerung nach dem "Press-Fit-Konzept" bei der Totalprothesen-Arthroplastik der Hüfte.

PURPOSE OF THE STUDY: The key problem of implant fixation in THR is stress distribution, i.e. load transmission between bone and implant. The closer the load transfer is to the original physiological situation, the easier the adaptation of the periprosthetic bone to the new biomechanical conditions after implantation of the cup and the safer is its longlasting fixation. The aims of the studies were 1) to get information about the physiological load transfer in the normal hip joint, 2) to get information about the load transfer between acetabulum and acetabular sockets and vice versa, 3) to measure the periacetabular pelvic bone deformation as the stimulator of the remodelling process (third stage of osseointegration) in the normal hip joint and in hip joints fitted with different acetabular cups, 4) to study the morphological stages of osseointegration of a non-cemented press-fit cup and to compare the morphological structure of the periacetabular bone with the biomechanical data obtained by the in vitro studies and finally, 5) to compare the clinical and radiological outcome of follow-up studies of the senior author's "Press-Fit cup" with the theoretical hypotheses according to the experimental observations. MATERIAL AND METHODS: Load transfer between the acetabular bone and the femoral head on one side and press-fit cups has been determined by strain gauge measurements, finite element studies, pressure sensitive Fuji prescale films, CT-osteoabsorptiometry and telemetric measurements. Periacetabular deformation has been measured by Imetric Markers. Osseointegration of the senior author's press-fit cup and, thus, the remodelling process of the bony structures adjacent to the cup have been studied in autopsy specimens of THRs which have been in situ for several years. RESULTS: Load transfer measurements have shown that the main load in the original acetabulum as well as in the acetabulum fitted with a press-fit cup is transmitted to the periphery, especially to the acetabular cortical rim whereas the subchondral bone is exposed to lower, predominantly meridional (tension) stresses. Direct measurements of the periacetabular deformation under load revealed an increase of the peripheral press-fit with increasing stability of a (oversized) press-fit cup. Both the normal as well as the acetabulum fitted with a non-cemented cup deforms in a postero-medial direction. The histo-morphology of the periacetabular bone of autopsy specimens showed excellent bony in- and ongrowth of a porous titanium coating (SULMESH) and bone formation, especially at the periphery in zone 1 and 3 according to DeLee and Charnley. CONCLUSION: The studies have shown that the subchondral bone plate of the acetabulum has very little supportive function for non-cemented press-fit cups. For the preparation of the acetabulum it is, therefore, more important to ream the sclerotic subchondral bone until there is a well vascularized, well bleeding bone bed to facilitate osseointegration of a non-cemented acetabular socket than to preserve the subchondral bone plate as is the case in cement fixation. A non-cemented press-fit socket must transmit load predominantly to the cortical bone of the acetabular rim. Therefore, a too far medial positioning of the cup, and therefore loosing contact to the cortical rim, must be avoided under all circumstances. The clinical experience with acetabular revisions and with conversions of hip arthrodeses into a THR (where there is no subchondral bone at all) have shown the superiority of a well vascularized over a sclerotic (even mechanically stronger) bone bed. Furthermore, it has been shown that the additional use of screws for fixation of an acetabular cup is not only unnecessary but can be deleterious and causes complications including osteolysis and aseptic loosening.

[Achilles tendon ruptures: 25 year's experience in sport-orthopedic treatment]. / Die Achillessehnenruptur -- Erfahrungen aus 25 Jahren sportorthopädischer Behandlung.

From 1972 - 1996 570 Achilles tendon ruptures in 565 patients were treated in the Sportklinik Stuttgart. The 499 men and 66 women had an average age of 38 years. For the diagnosis of a Achilles tendon rupture Ultrasound and MRI are important procedures, but clinical history and examination are still the best methods to find an Achilles tendon rupture (100%). However,the Actiology of the Achilles tendon rupture is still controversial and cannot be answered by these methods. Opposed to the degenerative theory, biomechanical experiments show that any Achilles tendon can tear when the calf muscle is tensed before the tendon is quickly stretched. We found that 69.8% of the patients with Achilles tendon rupture had a real trauma. Regardless of that, the treatment of the ruptured Achilles tendon has considerably changed over the last ten years. Responsible for this development are the positive experiences at the field of sports medicine with minimally invasive methods and the early functional treatment after knee surgery. Since we use an early functional rehabilitation concept instead of plaster immobilisation, all methods to treat a ruptured Achilles tendon have been improved. 43.5% of the patients after plaster immobilisation and 28.8% of the patients after early functional rehabilitation had a subjectively felt force reduction. Other important selecting criteria are the risk factors related to treatment method. Minimal invasive percutaneous Achilles tendon repair is considerably better than conservative therapy with a high rate of re-rupture (9.8%) and better than the open surgical repair, which carries a higher risk of infection (2.2%)

[Contact surface and pressure load at implant-bone interface in press-fit cups compared to natural hip joints]. / Kontaktfläche und Druckbelastung im Implantat-Knochen-Interface bei Press-Fit-Hüftpfannen im Vergleich zum natürlichen Hüftgelenk.

The implantation of an endoprosthetic socket into the acetabulum alters the mechanical stresses in the periacetabular region in a significant manner compared with the natural hip joint. In this way, a remodelling process is initiated. Primary stability to achieve osseointegration and a loading of the acetabulum owing to the biomechanical interaction between cup and bone that is similar to the natural joint, are important prerequisites for a long-term bony integration of the implant. Therefore, the intra-articular pressure distribution in eight hip joints of fresh-frozen human pelvic cadavers and in the bone/implant interface of two press-fit cups was investigated using pressure-sensitive Prescale films. A modular cup with a pure hemispherical shape (PCA cup) and a monoblock cup with a biradial surface and flattening of the pole (press-fit cup) were tested. Loads of up to twice body weight were introduced into the sacrum, simulating a single-leg stance with the hip in neutral flexion. The results were extracted from the pressure prints applying digital image processing methods. It was demonstrated that intra-articular contact occurs over the whole articular surface of the joint, with contact areas between 39.0% and 56.9% of the hemisphere, showing zones of higher pressures where the acetabulum is supported by the iliac, ischial and pubic bone. The biradial press-fit cup showed mean contact areas of 44.7% of its surface when inserted under press-fit only. This area was enlarged to 53.0% and to 64.2% with increasing load. The corresponding figures for the PCA cup are 45.1%, 48.9% and 57.1%. The low-profile PCA cup produces a small band of high pressure near the periphery, and with increasing load its pole area comes into contact with the acetabular fossa. Occasionally, irregular gaps do occur. The press-fit cup enlarges the contact area from the periphery to the pole within its optimised biradial contact zone until the lunar surface is loaded. The acetabular fossa remains unloaded owing to the flattening of the pole. This load distribution is close to that of the natural hip joint. The pressure distribution of both cups is also characterised by three zones at the iliac, ischial and pubic bones showing a higher load transmission.

CGP 6809--a new nitrosoureido-sugar derivative with activity in human tumor xenografts.

CGP 6809 [ethyl-6-deoxy-3,5-di-O-methyl-6-(3-methyl-3-nitrosoureido)-alpha-D- glucofuranoside] is a new methylnitrosoureido-sugar derivative that has been shown to be active against a broad spectrum of transplantable tumours in mice and rats. We investigated the anti-tumour effect of CGP 6809 in ten selected, human tumour xenograft lines growing s.c. in nude mice. The p.o. administration of 125 mg/kg per day for 10-15 days was less toxic (lethality 12% in tumour-bearing nude mice) than the i.p. injection of 62.5 mg/kg per day (lethality 22%). The anti-tumour effect was similar for both application routes; two large bowel cancers responded to treatment with CGP 6809, rectal cancer CXF 158 showed a remission, and the rapidly growing, undifferentiated colonic cancer CXF 280 exhibited a transient no-change. Furthermore, remissions were observed in the epidermoid lung cancer LXF 322 and in thyroid cancer 117. Tumour progression was found in another epidermoid lung cancer and in three stomach cancers, one melanoma, and one soft tissue sarcoma. CGP 6809 is a promising new agent for clinical trials, especially for large bowel and epidermoid lung cancer.

[Calibration of pressure-measuring foil in biomechanics]. / Untersuchungen zur Eichung der Druckmessfolie in der Biomechanik.

Concerning the calibration of the Prescale foil - a pressure sensitive foil, which shows a monochromatic, pressure depending coloration when loaded - some interesting new facts were ascertained. The coloration of the foil does not depend on the pressure load only, but also on the material of the pressing bodies. Calibration using hard material (high Elastic-Module, e.g. steel) results in a lower maximal optical density compared to soft material (low Elastic-Module, e.g. a hydraulic system) at the same pressure level. Due to wellknown facts of the pressure conditioned in a joint, a hydraulic system is more equivalent to joint conditions. Therefore, a calibration method based on a hydraulic system should be preferred if the Prescale foil is used in biomechanics. Furthermore, the density of coloration depends on the speed of pressure increase, too. A faster load of a particular pressure results in a denser coloration. Pressure increase during calibration shall be the same as during investigation. Both effects are statistically significant.