Failure analysis of fractured dental zirconia implants.

OBJECTIVES: The purpose of the present study was the macroscopic and microscopic failure analysis of fractured zirconia dental implants. METHODS: Thirteen fractured one-piece zirconia implants (Z-Look3) out of 170 inserted implants with an average in situ period of 36.75±5.34 months (range from 20 to 56 months, median 38 months) were prepared for macroscopic and microscopic (scanning electron microscopy [SEM]) failure analysis. These 170 implants were inserted in 79 patients. The patient histories were compared with fracture incidences to identify the reasons for the failure of the implants. RESULTS: Twelve of these fractured implants had a diameter of 3.25 mm and one implant had a diameter of 4 mm. All fractured implants were located in the anterior side of the maxilla and mandibula. The patient with the fracture of the 4 mm diameter implant was adversely affected by strong bruxism. By failure analysis (SEM), it could be demonstrated that in all cases, mechanical overloading caused the fracture of the implants. Inhomogeneities and internal defects of the ceramic material could be excluded, but notches and scratches due to sandblasting of the surface led to local stress concentrations that led to the mentioned mechanical overloading by bending loads. CONCLUSIONS: The present study identified a fracture rate of nearly 10% within a follow-up period of 36.75 months after prosthetic loading. Ninety-two per cent of the fractured implants were so-called diameter reduced implants (diameter 3.25 mm). These diameter reduced implants cannot be recommended for further clinical use. Improvement of the ceramic material and modification of the implant geometry has to be carried out to reduce the failure rate of small-sized ceramic implants. Nevertheless, due to the lack of appropriate laboratory testing, only clinical studies will demonstrate clearly whether and how far the failure rate can be reduced.

[Biomechanical aspects of the implant fixation and kinematics of hip resurfacing systems]. / Biomechanische Aspekte zur Implantatverankerung und Kinematik von Oberflächenersatzhüftendoprothesen.

Hip resurfacing is undergoing a resurgence in orthopaedic surgery with an increasing number of implantations. The objective of this article is to present the biomechanical basics of implant anchorage as well as the kinematics of hip resurfacing implants.Today, fixation of the femoral component onto the prepared femoral head is mainly done using bone cement. Depending on the implant design, the bone structures beneath the femoral component can be exposed to stress shielding, followed by degradation of the bone density and subsequent initiation of implant loosening. However, the trabecular bone has the ability to adapt itself to the fixation peg, to additional cement pegs, and to the elastic properties of the femoral component as well. The acetabular component is mainly inserted into the bone stock without using cement. Provided that large prosthetic heads will be applied, thin-walled acetabular cups are crucial for bone-saving preparation of the acetabular bone stock. Nearly all hip resurfacing systems are currently based on metal-on-metal wear-bearing couples. The acetabular components are mainly designed as monoblock implants, which can make subsequent revision difficult. Kinematic analyses show a significantly lower range of motion of hip resurfacing implants compared with modern standard (stemmed) total hip replacement systems. This difference originates from the small ratio of the resurfaced femoral head diameter and the relatively thick neck of the femur. Impingement of the femur neck onto the rim of the acetabular component can result in subluxation, deformation of the bearing surfaces, femoral neck fracture, and impairment of the bony anchorage of the hip resurfacing implants.

Biomechanical and histomorphometric comparison between zirconia implants with varying surface textures and a titanium implant in the maxilla of miniature pigs.

BACKGROUND: Mechanical properties and biocompatibility make zirconia ceramics suitable implant material. The characteristics of tooth-color like, the ability to be machined and the low plaque affinity make zirconia especially suitable as a dental implant material. The influence of surface modification on the osseointegration of this material has not been extensively investigated. PURPOSE: Long-term investigations with titanium implants have shown superior biomechanical results with the sandblasted acid-etched (SLA) surface, demonstrating a high bone-implant interaction. The objective of this study was to compare two different zirconia surface topographies biomechanically and histologically with the well-documented titanium SLA surface. MATERIAL AND METHODS: Zirconia implants with either a machined (ZrO2m) or a sandblasted (rough, ZrO2r) surface were manufactured with the exact same cylindrical shape with a standard ITI thread configuration as the SLA titanium implants. The incisors 2 and 3 were removed from both sides of the maxillae of 13 adult miniature pigs and the tissues left to heal for 6 months. After this time period the animals received a total of 78 implants using a randomized scheme, with the titanium SLA implant used as an only individual reference. After healing periods of 4, 8, and 12 weeks 20, 24, and 25 implants, respectively, were subjected to removal torque tests (RTQ) as the main biomechanical analysis of the of the study. A fewer number was resected on bloc, embedded in methylmethacrylat and analyzed for their direct bone apposition under a light microscope. RESULTS: Surface analysis revealed the highest surface roughness for the SLA-implant, followed by ZrO2r and ZrO2m. The turned ZrO2m implants showed statistically significant lower RTQ values than the other two implants types after 8 and 12 weeks, while the SLA implant showed significantly higher RTQs values than ZrO2r surface after 8 weeks. Differences in the bone apposition were observed in the histomorphometric analysis using light microscopy for all surfaces at any time point. CONCLUSION: The findings suggest that ZrO2r implants can achieve a higher stability in bone than ZrO2m implants. Roughening the turned zirconia implants enhances bone apposition and has a beneficial effect on the interfacial shear strength.

Assessment of cup position from plain radiographs: impact of pelvic tilting.

The acetabular cup position after total hip arthroplasty (THA) regarding its inclination and version angles are influential parameters concerning the postoperative range of motion and dislocation stability. Standard anterior-posterior X-rays remain an important diagnostic instrument to observe the postoperative outcome and to secure quality control after THA, where an optimal positioning of the patient is recommended when taking these X-rays. The purpose of this preliminary study was to determine the effect of pelvic tilting regarding the positioning calculation of the acetabular cup from standard radiographs using a modified method according to Pettersson et al. (Acta Radiol Diagn, 23:259-263, 1982). In our model experiment, we were able to show that pelvic tilting to either side causes a considerable difference between the radiographic and calculated version angles following approximately linear functions. However, pelvic tilting to either side, leads, regarding the calculation of the inclination, to an average deviation between radiographic and calculated inclination angles less than 2 degrees .

[Primary stability of the capsule-labrum complex after reconstruction with the Mitek Bioknotless anchor system in human cadaver models]. / Primärstabilität des Kapsel-Labrum-Komplexes nach Rekonstruktion mit Mitek-Bioknotless-Fadenankern am humanen Schulterkadavermodell.

BACKGROUND: This study examines the postoperative stability of the Mitek Bioknotless anchor system with biomechanical draw-out pulling in human cadaver shoulders. METHOD: With simulation of anterior shoulder dislocation a test group (n=10, Ø 45 years) was tested against a native group (n=8, Ø 47 years). All shoulders were dissected up to the passive stabilizers. In the test group an artificial Bankart lesion was created and repaired with three Mitek Bioknotless anchors. The humeri of both groups were fixed in 60 degrees glenohumeral abduction and 90 degrees external rotation and then dislocated in a ventral direction. For evaluation purposes the ultimate draw-out strength, mode of failure, translation of humeral head, capsular slope, and bone density in the test group were measured. RESULTS: In the test group the ultimate strength was a median of 937 N (min. 554 N, max. 1,294 N) with 28 bony anchor dislocations, 1 suture rupture, and 1 capsular rupture, and in the native group with 6 Bankart and 2 HAGL lesions it was 1,214 N (708 N, 1,471 N). The bone density showed a positive correlation to the draw-out strength regarding cortical density and total density. CONCLUSION: Regarding the high draw-out strength the Mitek Bioknotless anchor system provides enough stability for early functional treatment.

[Influence on load transfer of different femoral neck endoprostheses]. / Die Lastübertragung verschiedener Schenkelhalsendoprothesen auf das Femur.

AIM: Aiming to reduce known complications of stemmed implants, such as resorptive bone remodeling or bone damage in revision, implants with only epi-metaphyseal anchorage have been developed. In the following study the influence of three different femoral neck endoprostheses, CUT, CIGAR (ESKA Implants Lübeck) and TPP (SulzerMedica) on the postoperative load transfer to the femur was investigated in comparison to a cementless hip stem. METHODS: Using a composite femur model and photoelastic coating technique, the pre- and postoperative osseous strain was measured under static loading. The load corresponded to the absolute maximum of the hip joint load during walking. Statistical analysis was based on the interval of 99 % confidence which was generated by the preoperative measurements. RESULTS: The different anchorage concepts of the femoral neck endoprostheses exhibited a significant influence on the load transfer, especially along the medial and lateral cortical bone. But, in comparison, the cementless hip stem caused more pronounced stress-shielding which can induce resorptive bone remodelling. CONCLUSION: One specific femoral neck anchorage concept led to a change from preoperative tension to postoperative compression at the lateral cortical bone. This regionally limited effect may influence in the mid- or long-term the local bone remodeling in a negative manner.

[Failure analysis of total knee replacement. Basics and methodological aspects of the damage analysis]. / Versagensanalyse von Knieendoprothesen. Grundlagen und methodische Ansätze zur Schadensanalyse.

Possible causes for failure of total knee endoprostheses represent wear, malpositioning, maldimensioning and inadequate design of the implant components, manufacturing defects, material fatigue, corrosion, overloading, infection, and allergy against implant materials. There is a broad spectrum of methodical approaches for the analysis of failure cases. Substantial information for the damage analysis is provided by clinical and intraoperative findings, photo documentation, radiographic course as well as all-solid, physical and histological investigations. Principal purposes of damage analysis are the avoidance of further damage events and the gain of information for improvement of implant design and material as well as the optimisation of the biocompatibility of implants and wear products. Both a detection system of incidents and implant failures as well as a complete data collection enables early identification of system-specific, accumulated cases of implant failure.

[Biomechanical aspects of revision components for knee arthroplasty]. / Biomechanische Aspekte von Wechselkomponenten für den Kniegelenkersatz.

Total knee arthroplasty (TKA) is one of the most frequent orthopaedic surgical procedures. Despite continuous improvements in the endoprostheses, instruments, and operative techniques, revision TKA has a rate of about 10% of overall TKA. In addition to the restoration of the periprosthetic bone stock and a precise alignment, the choice of an adequate implant, which meets the patient's specific requirements, has high impact on the outcome. The most significant differences between implants involve the degree of reconstructed joint area (uni-, bi-, tri-compartimental) and the order of the constraining forces between the femoral and tibial component. Implants for revision TKA commonly range from un- or semiconstrained resurfacing implants to fully constrained hinged endoprostheses. In case of severe osseous, ligamentous, and/or muscular defects, special tumor endoprostheses or implants for arthrodesis might be an alternative option.

[Reconstruction of the extensor tendons in revision total knee arthroplasty and tumor surgery]. / Rekonstruktion der Strecksehneninsertion im Rahmen des Knieprothesenwechsels und der Tumorendoprothetik.

Reconstruction of the extensor mechanism in extended revision after total knee replacement and tumor surgery remains a clinically relevant problem. Due to large tibial bone defects with resection of the extensor insertion area, the specific problem of patella ligament refixation frequently arises. Several biological approaches and augmentation techniques have been published. Most of these are associated with a high rate of revision surgery because of failed replacement of the extensor mechanism and unsatisfactory functional outcome. Surgical reconstruction of these tendon defects is complicated by the difficulty of completely neutralizing tensional force across the repair. To overcome this problem, methods have been developed to reinforce the reconstruction with overlapping flaps; in addition, artificial materials are being increasingly used for tension neutralization. These artificial strips need special fixation mechanisms on the tibial component and specific technical modifications of the prosthesis. The present study gives an overview of reconstruction modalities of the extensor mechanism and provides an improved technology for better reconstruction by using artificial strips combined with specific modifications of the tibial component.

[Evaluation of the assembling and retention forces of constraint liners for total hip replacement]. / Evaluierung des Fügeverhaltens und der Rückhaltekräfte von Schnapp-Pfannen für den künstlichen Hüftgelenkersatz.

Dislocation is a severe complication after total hip replacement which may cause revision surgery in some cases. The use of constraint inserts that are coupled to the femoral head by a snapping mechanism provides an opportunity for treatment of recurrent dislocations. This study was aimed to investigate the assembling and retention forces of a specific constraint liner. Using a universal testing machine the assembling forces were determined for head sizes of 28 and 32 mm and the clinically mostly used as well as the maximum cup size. Subsequently, under variation of load direction and pull-out velocity the retention forces were investigated. For primary assembly of the head the required compressive forces were in a range from 197 N and 283 N depending on head and cup size (each size n = 3). Repeated assembly led to a decrease of these forces up to 29%. The retention forces always were slightly below the assembling forces, i. e. forces to remove the heads from the inserts were between 183 N and 230 N (each size n = 3). Repeated disconnection caused a decrease of the retention forces up to 16%. An increase of load velocity as well as an oblique load direction resulted in an enhancement of the retention forces. For all investigated implant sizes the retention force for the femoral head was approximately ten-times less than the interface strength between the insert and the metal-back. In case of correct implant handling the risk of disconnection between the tested constraint insert and the corresponding metal-back has not to be considered in clinical practice.

Comparing biomechanical investigations about different wiring techniques of finger joint arthrodesis.

INTRODUCTION: Multiple operative techniques are currently used for finger arthrodesis in clinical practice. The present study was designed to compare the biomechanical characteristics of typical arthrodesis techniques used in daily practice. MATERIAL AND METHODS: Osteosynthesis techniques comprising wire cerclage, thread cerclage (PDS) or intraosseous wire suture were compared in a biomechanical experiment for resistance against bending loads. The mentioned techniques were applied to artificial specimens with resected articular surfaces or by using the cup-and-cone procedure. In this process, the specimens were tested using various Kirschner-wire insertion angles as well as different arthrodesis angles (20 degrees vs 40 degrees) in a 4-point bending test with each group consisting of 6 specimens of acrylic glass. The forces prevalent in the joint space were determined by prescale pressure measurement foils. RESULTS: Wire tension banding resisted significantly higher bending moments than arthrodeses with thread tension bands (p < 0.05). All set-ups with tension banding techniques tolerated significantly higher loads than the intraosseous wire sutures without additional K-wires (p < 0.05), which showed unfavorable dislocation of contact areas resulting in instability even under relatively minor bending loads. Using the cup-and-cone technique, a geometrically larger contact area could be achieved between two unloaded fragments, but this technique showed no advantages in the opposing bending moments compared with the conventional resection method. In both techniques, a dislocation of contact surfaces towards the palmar direction could be observed with increasing bending moment. While the use of thread tension band fixation reduces the risk of plastic deformation of both osteosynthetic material and bone stock, the problem of resorption rate has to be taken into account when choosing the material for the thread. CONCLUSIONS: Considering pressure distribution and stability with and without bending loads, it is not the most rigid osteosynthesis technique which should be viewed as the ideal treatment. In contrast, it is more important to consider the various and most likely conditions to be expected in daily life after arthrodesis and therefore to chose the type of technique distributing pressure as regularly as possible.

[Experimental analysis of neutral, asymmetric and constraint liners for total hip replacement: investigation of range of motion and protection against joint instability]. / Experimentelle Analyse von neutralen, asymmetrischen und Schnapp-Pfannen für die Hüftendoprothetik. Untersuchungen zur Range of Motion und Luxationssicherheit.

AIM: Recurrent dislocation after total hip replacement is a severe complication, which requires specific treatment and implants. The purpose of the present study was to compare a constraint liner with an elevated rim and standard liner regarding their range of motion and dislocation stability. METHOD: With a test device, range of motion until impingement (ROM (Imp)) and dislocation (ROM (Lux)) were experimentally analyzed using the above-mentioned insert types of a commercial total hip system. On the basis of movement combinations associated with dislocation, the ROM was determined. Further measuring parameter was the resisting moment against subluxation of the femoral head. RESULTS: The constraint liners showed clear restriction of the movements "internal rotation combined with 90 degrees flexion and 0 degrees adduction" and "external rotation with 10 degrees extension and 15 degrees adduction" of up to 20 degrees compared to the neutral liner. ROM (Imp) was only decreased by about 8 degrees with the elevated-rim liner. The constraint liners revealed the highest resisting moments in subluxation, however, at adequate orientation in the acetabular cup the elevated-rim liners provided a higher ROM (Lux) of up to 12 degrees. Both designs were superior to the neutral liner at retroversion and steep cup position regarding resisting moment and ROM (Lux). CONCLUSION: In case of insufficient soft tissue tension the use of constraint liners may increase the dislocation stability, however, in contrast to elevated-rim liners the impingement-free movement interval is clearly reduced. Thus, material damage and high shear stress in the bone interface can result. Therefore, constraint liners should only be used in exceptional cases.

A novel test method for evaluation of the abrasive wear behaviour of total hip stems at the interface between implant surface and bone cement.

After total hip replacement, some cemented titanium stems show above-average early loosening rates. Increased release of wear particles and resulting reaction of the peri-prosthetic tissue were considered responsible. The objective was to develop a test method for analysing the abrasive wear behaviour of cemented stems and for generating wear particles at the interface with the bone cement. By means of the novel test device, cemented hip stems with different designs, surface topographies and material compositions using various bone cements could be investigated. Before testing, the cemented stems were disconnected from the cement mantle to simulate the situation of stem loosening (debonding). Subsequently, constant radial contact pressures were applied on to the stem surface by a force-controlled hydraulic cylinder. Oscillating micromotions of the stem (+/- 250 microm; 3 x 10(6)cycles; 5 Hz) were carried out at the cement interface initiating the wear process. The usability of the method was demonstrated by testing geometrically identical Ti-6A1-7Nb and Co-28Cr-6Mo hip stems (n= 12) with definite rough and smooth surfaces, combined with commercially available bone cement containing zirconium oxide particles. Under identical frictional conditions with the rough shot-blasted stems, clearly more wear particles were generated than with the smooth stems, whereas the material composition of the hip stems had less impact on the wear behaviour.

[Method for the evaluation of factors influencing the dislocation stability of total hip endoprotheses]. / Methode zur Evaluierung von Einflussfaktoren auf die Luxationsstabilität von künstlichen Hüftgelenken.

Dislocation of the artificial joint is a serious complication of total hip replacement. Various factors with an influence on dislocation stability were determined clinically. Our goal was to develop a method for evaluating experimentally the parameters implant design, position and the load situation for their influence on joint stability. With the newly developed testing device the range of motion to impingement and to dislocation can be determined at different implant positions. In addition, the rotational moments on subluxation, i.e. the "levering out" of the femoral head, can be determined. By way of example several hip implants were examined during movements associated with dislocation, e.g. (internal-)rotation in 90 degrees flexion and 0 degrees adduction as well as with (external-)rotation in combination with 10 degrees extension and 15 degrees adduction. Irrespective of implant design and position, the following movement phases can be differentiated: undisturbed motion, impingement, subluxation and, finally, complete dislocation of the head. On the basis of the range of motion of the specific phases, the moments occurring and the direction of dislocation, different implant systems can be compared. In this study the influence of the head diameter on the dislocation stability of the hip endoprosthesis is shown. With the aid of the model presented herein, a data set showing the most favourable and/or most dislocation stable implant position can be acquired for different combinations of the implant components. Additionally, useful information for implant design can be deduced and applied to new developments and/or modifications of existing implant components.

[Damage analysis illustrated by two cases of broken ceramic inserts. Recommendations for avoiding breakages caused by handling]. / Schadensanalyse anhand zweier Fälle von Keramikbrüchen von Pfanneninserts. Empfehlungen zur Vermeidung handhabungsbedingter Brüche.

Due to modular design today's total hip endoprostheses provide the choice of different bearing surfaces. Particle-induced osteolysis is the major reason for implant failure. Therefore, minimization of wear rates is the essential factor for the improvement of long-term function of the implants. The bearing couple ceramic-on-ceramic offers a linear wear rate of about 0.005 mm/year. That is an essential prerequisite for successful treatment of young and active patients. Ceramic femoral heads and taper fixation became standard. After some problems in the 1970s, manufacturers achieved all kinds of improvements. Surgeons learned how to handle ceramic femoral heads correctly. Nowadays ceramic heads are reliable implants. Ceramic inserts have been used since the mid-1990s. Some acetabular systems with ceramic inserts are used in clinical studies, some are approved. Complications with ceramic inserts are rare, e.g., fracturing or chipping off. Mostly those problems are due to mishandling. In this study some clinical failures are analyzed. Recommendations how to improve the handling of ceramic inserts are proposed and discussed.

BISS: concept and biomechanical investigations of a new screw system for electromagnetically induced internal osteostimulation.

INTRODUCTION: The aim of an intraosseous application of electromagnetic alternating fields is to speed up both the regeneration of osteonecroses and bone regeneration. In clinical studies, the efficiency of the technique could be successfully proven by using a transducer coil. The advantage of the traditional technique was the variety of its applications in connection with various osteosynthesis systems; the disadvantage was a possible failure of the contacting leads and the resulting functional breakdown. MATERIALS AND METHODS: A newly developed BISS screw (bipolar induction screw system) with integrated coil and electrodes was compared to a standard cannulated screw used in the traditional technique. The strength of BISS screws ( n=6) and of cannulated screws ( n=6) was evaluated in comparative biomechanical tests. Examinations consisted of torsional and static and dynamic cantilever tests. All screws were made of the same material (TiAl(6)V(4)) and had identical outer dimensions. RESULTS: No significantly lower strengths could be observed when we compared BISS screws with cannulated screws. The BISS screws even showed significantly higher mechanical values due to a reinforcing effect by the attached electrode. CONCLUSION: In the modified concept of the new BISS screw, both coil and electrodes are housed in only one cannulated screw. No negative effects concerning mechanical strength and durability were associated with the new screw concept. This provides for a simpler implantation and makes removal easier, while the risk of a cable tear is avoided.

[Retrospective view of the development of malocclusion surgery and prospects]. / Rückblick auf die Entwicklung der Dysgnathiechirurgie und Ausblick.

DEVELOPMENT: The history of the correction of the jaw deformities began in the US more than 100 years ago with a bilateral osteotomy in a case of mandibular prognathism performed by Vilray Blair. This operation was the starting point for Blair's interest in jaw surgery. In 1907 he already described three different operative techniques for the correction of malpositions of the lower jaw. Between the First and the Second World War no major progress in corrective jaw surgery occurred, until in the fifties of the 20th century a rapid development started off. Mainly in Germany and in Austria new operative techniques not only for the mandible, but also for maxilla and midface were established. Finally, this development reached its height in the simultaneous total osteotomy of upper and lower jaw that was published by Obwegeser in 1970. OUTLOOK: Innovations first of all in regard to technical improvements especially in four fields could be realized within the past 20 years. For planning of a procedure mostly computer-assisted systems combined with video- or laser technique were utilized. The improvement of resorbable materials such as plates and screws can be considered as a major progress. With regard to new operative techniques not only first results with navigation systems but also the introduction of endoscopic osteotomies were reported. Distraction osteogenesis was successfully performed on developmental deformities of the mandible, the maxilla, and the midface, while technical devices are being improved continuously. As in all fields mentioned above development is not yet completed further improvements can be expected.

[Calculation of hallux bending moments from plantar pressure distribution measurement]. / Ermittlung von Hallux-Biegemomenten aus der plantaren Druckverteilungsmessung.

PURPOSE: The following study aims to demonstrate the bending stress on a hallux valgus during normal gait. The bending axis was related to the position of an open wedge osteotomy. The moments were calculated from plantar pressure measurements. METHOD: In the gait analysis laboratory plantar pressure distribution measurement was done with healthy adult volunteers during barefoot gait. From the plantar pressure distribution the vertical forces were derived just for the region hallux metatarsal I. The following calculation of the bending stress regarding to the hypothetic region of the osteotomy was done by integrating the pressure distribution multiplicated with the distance to the osteotomy. The measurements are compared with theoretical values derived from the anatomy of the foot under some plausible assumptions. RESULTS: The results of the mean values of the bending stress were 15.8 +/- 4.8 Nm for the female subjects and 21.6 +/- 5.6 Nm for the male subjects. The amount of the bending moments depended with low significance on the weight. More important is the individual type of gait. CONCLUSION: The measurements show the size of bending stress the plate stabilizing the osteosynthesis has to resist under unfavorable circumstances (for example if the plantar foot muscles are not adequately activated) and if no external stabilization (for example, cast) is used.

[Biomechanical investigations for the development of a SLAP-II-lesion]. / Pathogenese der SLAP-II-Läsion am Schultergelenk. Biomechanische Untersuchungen.

The superior labral-biceps-tendon-complex forms an anatomical and functional unit and combines static and dynamic elements of shoulder stability. At present, only theoretical hypotheses exist on the etiology of the microtraumatic SLAP-II-lesion. To gain further insight into this, an instrument was developed to simulate throwing motions such as the late-cocking/early acceleration phase as well as deceleration/follow-through. Sixteen freshly frozen shoulder specimens were tested, varying the loads on the biceps tendon (25 N, 50 N, 100 N) and the compression of the humeral head against the glenoid (25 N, 50 N, 80 N). Each shoulder had to run through a certain number of cycles during the particular phase of throwing. The tests were stopped after a SLAP-II-lesion was observed, or after a limit of 15,000 cycles. Every 1,000 cycles the results of the tests were checked arthroscopically. A SLAP-II-lesion developed in only 10% of the specimens during the acceleration/ late cocking phase whereas in the deceleration/ follow-through phase 83% developed such a lesion. According to our results, the deceleration/follow-through of the throwing motion seems to be responsible for creating microtraumatic SLAP-II-lesions. One reason is the loss of the centering function of the long head of the biceps tendon during total internal rotation, another is the increased posterosuperior translation of the humeral head in this position, which leads to a non-physiological contact, creating lesions in this area due to the large sheering forces.

[Refixation of the meniscus with the SD meniscal staple: a comparative biomechanical study on cadaver knees]. / Die Meniskusrefixation mit dem SD-Meniskusstaple--eine vergleichende biomechanische Studie am Leichenknie.

GOAL: The failure load of the SD meniscal staple was compared with the 2-0 Etibond meniscus suture in a dynamic test without isolating the meniscus. METHODS: In eight knee joint pairs, a standardized lesion of the posterior part of the medial meniscus was repaired by either three staples (7 mm) or three 2-0 Etibond sutures. After resection of the cruciate ligaments and 15 degrees external rotation, 45 degrees flexion, and 70 kg of axial loading, a tibial translation was exerted on the knee joint. The test was documented on a way force diagram, demonstrating the failure of the device at a sudden load of force. RESULTS: The average load before failure of the meniscus staple was 591.2 N (540-690 N), that of the sutures 850 N (600-1350 N). We did not find any statistical correlation to age,weight, or height of the specimens. The suture migrated, but never ruptured. In two cases the suture caused a radial meniscus lesion. Failure of the staple was detachment of the inferior part in all cases, but no migration. CONCLUSION: This test is based on the dynamic forces of the knee joint on the meniscus. Our measurements show lower failure loads of the staple compared to those of the sutures, but compared to other tests a stable method of meniscus repair.