Dynamic in vitro analysis of tractile forces of the anterior cruciate ligament (ACL) transplant using patellar and semitendinosus muscle tendon: a cadaver study.

PURPOSE: The presented biomechanical study focused on the in vitro analysis of tractile forces working on the anterior cruciate ligament (ACL) and the ACL transplants, respectively, using a semitendinosus and/or patellar tendon during a passive flexion-extension movement (150-0°). MATERIAL AND METHODS: Overall, 15 fresh frozen human knee joint pairs were examined. At first during arthroscopy, the tibial insertion of the ACL was drilled using a special hollow drill. Thereby, a bone cylinder was exposed at which a dynamometer was attached to enable for direct registration of tractile forces on the ACL via the connection between ACL-dynamometer and computer. The ACL transplant was fixed at the femur using a so-called endo-button, whereas the dynamometer was attached to the tibial end of the ACL transplant. The dynamic part of the examination was performed using the knee kinemator device developed by Plitz and Wirth et al. using different preload. RESULTS: The curves of the tractile forces of the ACL were qualitatively homogeneous with only low force values in the middle flexion position, whereas during maximum flexion and extension the forces increased reaching a maximum in the 0° position. Also, in testing the ACL transplants a force decrease between 0 and 50° flexion was recognized with even greater forces resulting at the 150° position depending on the anterior position of the femoral drill channel for implanting the ACL transplant. The amount of pre-loading showed no influence on the form of the tractile force curve. However, by enhancing the preload to 70 N, the maximal force in the ACL transplant increased significantly. CONCLUSION: The tractile forces assessed within the ACL during passive flexion movements between 10 and 90° were not greater than the forces measured in the ACL transplants. Thus, the clinical consequence is that in the early postoperative phase passive mobilization might be performed in this motion range without putting the ACL transplant at risk for damage.

[Damage to implants due to high-frequency electrocautery : analysis of four fractured hip endoprostheses shafts]. / Implantatschädigung durch Einsatz eines Hochfrequenzmessers : Analyse von vier Hüftendoprothesenschaftbrüchen.

In revision surgery of joints, high-frequency electrocauterization instruments are used for homeostasis and dissection of soft tissue. If there is contact of these instruments with the metal implants, flashover can occur. This can lead to thermal microstructural changes in the material and as a consequence may reduce the fatigue strength of the implant. Four cases of hip revision surgeries were analysed. In all cases flashovers occurred and secondarily, the titanium hip endoprosthesis stem broke in the neck section of the prosthesis. The conducted investigations showed that contact between the high-frequency instrument and the anterolateral aspect of the endoprosthesis neck had occurred. Electrothermal implant damage was found in the broken area. If in hip revision surgery the stem is not to be replaced, contact between high-frequency instruments and the metal implant should be avoided.

[Material and technical aspects of mega prostheses]. / Materialtechnische Aspekte bei Megaendoprothesen.

So-called mega implants were developed especially for the therapy of tumour diseases, but since these prostheses are considered to be custom-made products, they are excluded from the usual test specifications required by the German Act on Medical Devices. Based on the fact that these mega prostheses are specially manufactured and meant to be implanted in a certain patient, only casting technologies can be used. Forging procedures commonly used for so-called normal prostheses cannot be applied here. Thus only Co-Cr-Mo cast alloys can be used. Additional technologies are used for manufacturing partial pelvic implants. By means of CT plastic models are made so that the corresponding mega implants can be properly customized afterwards. Nowadays numerous bloomed surfaces and surface structures are offered to improve the engraftment behaviour.

Tissue attachment strength and adhesion formation of intraabdominal fixed meshes with cyanoacrylat glues.

OBJECTIVE: The aim of this study was to evaluate the technique of prosthetic mesh fixation in laparoscopic intraperitoneal incisional and ventral hernia repair using cyanoacrylat glue (Glubran GEM, Viareggio, Italy) in comparison with fixation methods using spiral tacks (Protack 5mm, Tyco) or transabdominal Prolene 4/0 sutures respectively. METHOD: Through a midline laparotomy 3 pieces (3 x 3cm) of mesh (n = 60) where fixed onto the intact peritoneum on either side of a midline laparotomy in 10 New Zealand White rabbits. Two types of meshes where compared: ePTFE meshes (Gore-Tex Dual Mesh W.L. Gore and Associates, Inc. Medical Products Division, Flagstaff, Arizona, USA) and polypropylene/ polyvinylfluorid meshes (Dyna Mesh - IPOM P.J. Dahlhausen and Co. GmbH, Germany). All animals were killed after 12 weeks. Upon scoring of the adhesions the prosthetic materials were excised en bloc with the anterior abdominal wall for tensile strength analysis and histologic evaluation. RESULTS: In contrast to ePTFE meshes fixed with cyanoacrylat glue, PP meshes fixed with transabdominal sutures as well as with spiral tacks showed the highest percentage and tenacity of adhesions (p<0.033). Independent of the method of fixation, ePTFE meshes revealed a significantly higher shrinkage than PP prosthesis (41% vs 17% related to original mesh surface; p<0.033). The strength of the mesh incorporation was significantly higher in PP meshes (p<0.033). Fixation of PP meshes with cyanoacrylat glue showed an equivalent tensile strength as ePTFE meshes fixed with spiral tacks (6.6 +/- 2.7 N vs 6.6 +/- 3.1N). CONCLUSION: In this rabbit model, intraabdominal fixation of PP composite meshes with cyanoacrylat glue was equivalent to ePTFE mesh fixation with spiral tacks concerning tensile strength analysis. Adhesions between mesh and abdominal wall were found more frequently after PP fixation. In contrast, mesh shrinkage was more evident after ePTFE mesh implantation.

Operative treatment of greater tuberosity fractures of the humerus--a biomechanical analysis.

BACKGROUND: Fractures of the greater tuberosity of the humerus present with increasing frequency. However, no biomechanical data about the optimal fixation technique of greater tuberosity fractures is available. This biomechanical cadaver study compares the stability of three standard fixation techniques used for the treatment of greater tuberosity fractures of the proximal humerus. METHODS: In 21 fresh frozen proximal humeri, standardized fractures of the greater tuberosity were created. The specimens were randomly assigned to one of three operation techniques: wire tension banding, two cancellous screws and transosseous sutures. These constructs were mechanically tested by applying an increasing force to the supraspinatus tendon. Load to 5mm displacement (load to 5mm yield point) and load to failure (maximum stretch strength) were measured in Newton (N). FINDINGS: Load to 5mm yield point values showed no significant differences between tension banding (498 N, SD 153) and two cancellous screws (400 N, SD 174) (P>0.01). Both techniques showed significantly higher values than transosseous sutures (185 N, SD 132) (P<0.01). Load to failure values were significantly higher for tension banding (1054 N, SD 125) than screws (842 N, SD 140) and sutures (480 N SD 101) (P<0.01). The difference between screws and sutures was also significant (P<0.01). INTERPRETATION: Tension banding and two cancellous screws provided the strongest fixation for isolated fractures of the greater tuberosity.

Development of a new suturing technique for tendon graft preparation: an animal cadaver study.

BACKGROUND: This study should analyze ten different suturing techniques for tendon graft preparation to allow the development of an entirely new suturing technique. METHODS: Extensor tendon grafts of fattening bulls' forelegs were sutured with Ethibond Excel size three (six metric) fibers (Ethicon, Somerville, New York, USA). The tendon/suture complexes were biomechanically tested with a hydraulic testing machine applying traction according to a standardized protocol. The testing was observed to find out why the failure at the maximum traction load occurred. The mean values for the maximum tension and extension stiffness were recorded for each suturing technique. FINDINGS: An entirely new suturing technique was developed based on the observations and biomechanical results. The newly developed suture was also tested and provided a higher traction stability than the other ten techniques that had been evaluated. Compared to the other ten techniques the new technique was ranked 3rd in terms of extension stiffness and reached 10.3 N/mm. INTERPRETATION: The new technique evolved in the course of this study provided promising results. Therefore this study provides initial evidence that this technique could be useful in clinical routine.

Biomechanical investigations on chondromalacia of the knee after meniscal flap lesion and partial meniscal resection: an experimental model.

Meniscal tears and resections may cause chondral lesions of the knee. To eliminate muscular control during investigation of this problem, we designed a biomechanical setup based on a knee-joint simulator, ensuring physiological, free-motion mobility of the joint. Fresh human knee specimens with intact cartilage were exposed to loads to 2,000 N at a frequency of 0.85 Hz during 48 hours of gait. After a preliminary test series, 18 specimens were divided into three groups: group I was tested with unchanged meniscal status, group II with arthroscopically induced mobile flap tears at the posterior horns of the menisci, and group III after partial resection of the posterior horns. Motion patterns between the groups changed after as little as a few hours due to increased translation in group III. Macroscopic and histological examination and scanning electron microscopy revealed severe chondromalacic changes after meniscal resection. We conclude that meniscal resection-however partial-may have considerable joint-damaging potential if muscle control is lacking whereas mobile flap tears maintain stability. Our findings might explain the differences in clinical reports on cartilage status after partial meniscal resection. This study underlines the importance of muscle training when active stabilisation of the knee is reduced after partial meniscal resection.

A theoretical and numerical approach to optimal positioning of the patellar surface replacement in a total knee endoprosthesis.

The clinical results of total knee joint arthroplasty with patellar replacement have shown that postoperative problems arise, especially under unfavourable biomechanical conditions. The findings concerning retropatellar contact forces have been obtained by means of different methods, partly through experimental investigations and partly through theoretical considerations. But so far patellar replacement criteria and the resulting changes of the retropatellar contact force were not taken into consideration in other studies. Our mathematical model is based on a mechanical one and the parameter study considers the influence of the height of the patellar surface replacement upon different biomechanical parameters at varying positions. The results suggest that the patellar replacement should therefore be kept as low as possible, thus reducing the retropatellar contact force to a minimum, especially in the extremely stressed flexion areas of up to about 90 degrees.

A dynamic shoulder model: reliability testing and muscle force study.

This study introduces a dynamic shoulder model, where forces were applied to individual muscles in ten cadaveric specimens. The model provided reproducible glenohumeral joint motion and thereby allowed the investigation of active, glenohumeral joint mechanics. Forces were created by servo-actuated hydrodynamic cylinders and applied to the deltoid muscle and to the rotator cuff through wire cables. Computerized regulation initiated precise, time controlled cycles of glenohumeral joint motion. The position of the glenohumeral joint in all spatial orientations was measured and recorded using an ultrasonic sensor device. Reproducibility of glenohumeral joint motion was demonstrated on the basis of five cycles of glenohumeral joint elevation. Repeatability variance of position measurements for five cycles of elevation averaged 0.80 degrees for abduction, 0.75 degrees for anteflexion and 1.36 degrees for internal rotation. Arm weight and force distribution at the shoulder musculature were estimated according to the literature. In comparison to estimated physiologic conditions, a one third increase of arm weight led to a significant (p < 0.05) decrease of elevation of 20%, a one third decrease of arm weight to an average increase of elevation of 18% (p < 0.05). Exclusion of the supraspinatus muscle caused a significant (p < 0.05) 6% decrease of elevation of the glenohumeral joint. Without force applied to the subscapularis and infraspinatus/teres minor muscles, elevation decreased 16% (p < 0.05). A decrease of glenohumeral joint elevation of 25% resulted when force was applied to the deltoid muscle alone (p < 0.05).

Changes in cadaveric cancellous vertebral bone strength in relation to time. A biomechanical investigation.

STUDY DESIGN: A biomechanical study was conducted during a 3.5-day period to test for changes occurring in pullout strengths of cancellous screws inserted into human cadaveric vertebral bodies. OBJECTIVES: To quantify, within the testing time of 3.5 days, the possible changes to the mechanical properties of cadaveric vertebral bodies, resulting from structural degradation caused by postmortem, time-dependent, autolytic processes during mechanical testing of implant-bone biomechanics. SUMMARY OF BACKGROUND DATA: Biomechanical testing of whole spinal implants and analysis of the screw-bone interface of spinal implants is an area of clinical interest that frequently requires the use of cadaveric spine specimens. Changes in vertebral bone properties during the testing period may invalidate experimental results, but no data are available on degradation of bone during the testing period. METHODS: Anterior oblique cancellous screws were inserted into human vertebral bodies from which the ventral cortex had been removed. The pullout strength was measured at 0, 24, 60, and 84 hours after insertion. The tests were performed on 48 human vertebral bodies, which were stored by freezing to -23 C, thawed for testing, and kept at room temperature during the testing time for as long as 84 hours. RESULTS: The axial pullout strength showed no statistically significant change during 84 hours (P = 0.15). There were no significant differences attributable to vertebral level from T4 to L4, probably because the ventral cortices had been removed (P = 0.7). CONCLUSIONS: During 3.5 days, there were no changes in pullout strength of vertebral cancellous bone. In biomechanical studies during a maximum period of 3 days with a small number of cadaveric spines (e.g., four spine specimen) the time-dependent changes in pullout strength play a less significant role than do the interspine differences. Interspine differences should be regarded as an important factor to be considered in the design of biomechanical tests.

Autologous perichondral tissue for meniscal replacement.

Our aim was to examine the potential of autologous perichondral tissue to form a meniscal replacement. In 18 mature sheep we performed a complete medial meniscectomy. The animals were then divided into two groups: 12 had a meniscal replacement using strips of autologous perichondral tissue explanted from the lower rib (group G) and six (group C) served as a control group without a meniscal replacement. In all animals restriction from weight-bearing was achieved by means of transection and partial resection of tendo Achillis. Six animals (four from group G and two from group C) were each killed at 3, 6 and 12 months. The grafts and the underlying articular cartilage were removed and studied by gross macroscopic examination, light microscopy, SEM, polarised light examination, and by biomechanical tests. In all the transplanted animals a new perichondral meniscus developed. After three months the transplants resembled normal menisci in size and thickness, while in the control animals only small rims of spontaneously grown tissue were seen. Microscopically, the perichondral menisci showed a normal orientation of collagen fibres and normal cellular characteristics, but in the central region, areas of calcification disturbed the regular tissue differentiation. Healing tissue in control animals lacked the normal fibre orientation and cellularity. SEM of perichondral menisci showed surface characteristics similar to those of normal sheep menisci without fissures and lacerations; the control specimens had these defects. The femoral and tibial cartilage in contact with the new menisci had normal surface characteristics apart from one animal with slight surface irregularities. Control animals showed superficial lesions after three months which increased at six to 12 months postoperatively. Microangiography of the newly grown tissue demonstrated a less intense vascularisation after three months when compared with normal menisci. The failure stress and tensile modulus of perichondral menisci were significantly lower than those of normal contralateral menisci, and spontaneously regenerated tissue in meniscectomised animals had even lower values. There were no significant differences in values between newly grown perichondral menisci and spontaneously grown tissue.

Medial meniscus replacement by a tendon autograft. Experiments in sheep.

In 20 skeletally mature female merino sheep, divided into four groups, we performed total medial meniscectomy, removal of the middle third of the patellar tendon, and tenotomy of the calcaneal tendon of the right hind leg. Group I (control) had no additional procedures. In the other three groups the medial meniscus was replaced by the middle third of the patellar tendon from the ipsilateral knee. The animals were killed at three (group II), six (group III), or 12 months (group IV) and the tendon-meniscus examined macroscopically, by light and scanning electron microscopy, and biomechanically. Remodelling of the tissue had taken place by 12 months but the failure stress and tensile modulus for the tendon-meniscus were lower than for the normal meniscus. Our evidence suggests that, in sheep, replacement of a meniscus by a tendon autograft may decrease the severity of the degenerative changes that occur after meniscectomy.

Influence of a mono-centric knee brace on the tension of the collateral ligaments in knee joints after sectioning of the anterior cruciate ligament--an in vitro study.

OBJECTIVE: To analyze the influence of knee bracing on the tension of the medial and lateral collateral ligaments in anterior cruciate ligament deficiency. DESIGN: The tension of the collateral ligaments in anterior cruciate ligament deficient knees was measured with and without knee bracing using an in vitro model. BACKGROUND: Anterior cruciate ligament deficiency increases the tension in both collateral ligaments at the knee joint. Therefore knee braces should reduce that tension increase. However, that effect has never been proven quantitatively. METHODS: After anterior cruciate ligament-transection, the forces of the medial (anterior/posterior part) and lateral collateral ligament were measured in ten fresh human cadaver knees at 0 degrees, 20 degrees, 40 degrees, 60 degrees, 80 degrees and 100 degrees of flexion, with and without application of a mono-centric knee brace. To quantify the ligament forces, strain gauges were fixed at the bony origins of the ligaments. RESULTS: Bracing led to a significant decrease of ligament forces (20-100 degrees: P < 0.0001) in the anterior part of the medial collateral ligament in all joint positions. In the posterior aspect, this effect was observed only at 40 degrees (P < 0.0001) and 80 degrees (P = 0.001) of flexion. In the lateral collateral ligament, bracing caused a strain reduction from 60 degrees to 100 degrees of flexion (P < 0.0001). Therefore a flexion angle dependent effect of knee bracing on the strain was seen in the posterior aspect of the medial and in the lateral collateral ligament in anterior cruciate ligament deficient knee joints. CONCLUSIONS: Application of a mono-centric knee brace leads to a significant position dependent reduction of collateral ligament tension after anterior cruciate ligament-rupture.

Investigations on mechanism of Salter-1-fractures of the greater trochanter.

This study aims at clarifying why the apophysis of the greater trochanter very rarely separates, in contrast to other apophyses of the hip region. The inclination and area measurement of the greater trochanteric growth plate and the mode of insertion of the muscles on the apophysis were analyzed on the basis of 16 anatomic femoral specimens from newborn to children of 14 years of age. The physiological muscle cross section Q of the muscles inserting at the greater trochanter was determined on 6 specimens. In a cross-sectional radiological study, carried out on 1350 hip joints of healthy children, the inclination of the greater trochanter growth plate was measured. The anatomical and radiological findings show that the nearly plane-shaped greater trochanter growth plate remains inclined at a 50 degree angle to the horizontal body line and is loaded from a diagonally craniolateral direction throughout the total growth period. The lateral surface of the apophysis is covered by a fibrous connection which joins the insertion areas of the gluteus medius, minimus and vastus lateralis muscles. The vastus lateralis muscle is intimately bound to the vastus intermedius muscle by fibrous tissue. According to the results of the physiological muscle cross sections these four muscle groups can form a counteracting muscle sling, which transforms the traction forces at the surface of the greater trochanter into pressure forces in line with a tension band effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Strain measurement at the knee ligament insertion sites.

We describe the modification of an existing method of ligament strain measurement at the knee joint in detail. At ten fresh joint specimens we used that technique where strain gauges are attached to the ligamentous insertions and origins. We both improved the preparation of the attachment site and the application of the strain gauges. In a special apparatus the specimens were moved from 0 degree extension to 100 degrees flexion while simulating muscle strength and axial force. Testing was performed at the posterior cruciate ligament with both intact and transsected anterior cruciate ligament. In contrast to other existing techniques it does not affect the motion of the joint or the integrity and the function of the ligaments. Unlike the original description of that method we could register a loading behaviour of the posterior cruciate ligament that is similar to those reported in the literature.

[A dynamic shoulder model for biomechanical measurements of shoulder specimen]. / Ein dynamisches Schultermodell für biomechanische Messungen an Schulterpräparaten.

The article discusses a dynamic shoulder model capable of simulating the forces generated by the rotator cuff and the deltoid muscle, and elevation movements of the glenohumeral joint using, a computer-aided servohydraulic unit. In 10 cadaver shoulder specimen, the effects of the loss of function of the supraspinatus muscle on maximum elevation was determined with an ultrasound system. Changes in the so-called impingement pressure below the coracoacromial arch were determined with the aid of capacitive pressure sensors. With the supraspinatus muscle inactive/ absent, the maximum elevation of the humerus showed a decrease of 6% (p < 0.05), which, however, was overcome by an increase in deltoid power of only one-third of the supraspinatus muscle power loss. For a simulated isolated supraspinatus defect, the subacromial pressure below the coracoacromial arch decreased by 8% (p > 0.05). These results confirm clinical investigations showing that isolated lesions affecting the supraspinatus tendon often fail to produce symptoms and thus require no surgical reconstruction.

[Measuring ligament elasticity of the knee joint--elasticity measuring strip and its alternatives]. / Banddehnungsmessung am Kniegelenk--Der Dehnungsmessstreifen und seine Alternativen.

Those techniques for measuring ligament tension at the knee joint that are most commonly cited and easiest to carry out are discussed. These include four techniques based on the use of strain gauges. Apart from the Omega transducer and the buckle transducer, there is also the tendon force transducer, and the application of strain gauges to the bony ligament insertion sites. Other indirect measuring methods considered are the mercury strain transducer and the Hall effect transducer. The parameter measured with all of these methods is fluctuating current or voltage, which is then correlated with ligament tension. Three direct measurements are also discussed: the separation distances of marked fibres of the ligaments, replacement of fibres by threads, and a load cell/bone plug construction. The measured value is equated with the effective change in ligament length.

[Effect of the manufacturing process on creep and wear properties of UHMWPE (ultra-high molecular weight polyethylene)]. / Der Einfluss des Verarbeitungsverfahrens auf die Kriech- und Abriebeigenschaften von UHMWPE.

The creep and wear behaviour of pressed UHMWPE and extruded UHMWPE was compared, taking Chirulen and extruded UHMWPE of the Lennite type as examples. Using the ring-on-disc test, the wear and deformation volumes per 360,000 cycles were determined. The static tests were performed at surface pressures of 5.62 MPa and 9.37 MPa, while the test duration was 41.86 and 100 hours, respectively. The surface pressures result from the axial forces of 900 N and 1500 N, respectively, and a ring surface analogous to the DIN 58,835 and ISO 6474 standards. Between conventionally pressed and the extruded UHMWPE material differences of up to 350% in the sums of wear and deformation were found. It was noted that already at low surface pressures the extruded UHMWPE is more susceptible to creep deformation than is the conventionally pressed material, and that this effect dramatically increases at high surface pressures.

[Method for in vivo measurement of intraosseous pressure of the patella]. / Methode zur In-vivo-Messung des intraossären Druckes an der Patella.

During the development of degenerative joint disease (osteoarthritis, chondropathy), a diagnostic or even pathogenetic role is attributed to the phenomenon of intraosseous pressure (IOP). Owing to technical problems and a lack of systematic experimental or clinical studies on the control mechanisms of the IOP, the actual importance of this factor is still not known with certainty. Now, a measuring method that enables correct recording of the IOP and standardized on-line processing of the measured signal minimize artefact-related problems. The technique is evaluated for reliability in an in vitro model of the human patella and in a limited clinical study of the IOP in patients undergoing knee surgery for various reasons. Factors such as intra-articular effusion, joint position or changes in intra-articular soft tissue are examined for their influence of the primary signal.

[Effect of surface energy on wear characteristics of material combinations for the artificial hip joint]. / Der Einfluss der Oberflächenenergie auf das Abriebverhalten von Materialpaarungen für das künstliche Hüftgelenk.

One of the factors determining the wear of UHMWPE used as acetabular cup material is the lubricating properties of the head materials. In order to determine the lubricating properties, the wettability of Al2O3, ZrO2, CoCrMo and N-coated TiAl6V4 was established. Wettability is determined by the surface energy of the head material (solid-state material), which was measured via the contact angle of drops of fluid. As head material, appropriate rings from the Ring-on-Disc Test as per International Standard 6474 were used. The poorest wettability was associated with CoCrMo. The wettability of Al2O3 and ZrO2 was comparable. Worthy of note is the tendentially good wettability of N-coated TiAl6V4.