Humeral head necrosis rate at mid-term follow-up after open reduction and angular stable plate fixation for proximal humeral fractures.

INTRODUCTION: Short-term follow-up of angular stable fixation for proximal humeral fractures has been well documented in the literature. Longer follow-up series are difficult to find. However, especially regarding the risk of avascular humeral head necrosis longer follow-up series are high of clinical relevance. METHODS: Forty-eight patients with a mean age of 66 years and treated with open reduction and angular stable internal fixation for proximal humeral fractures were followed up for a mean of 45 months. The clinical and radiographic follow-up (Constant Score (CS), age and gender related Constant Score (agCS), Constant Score in comparison to the contralateral side (%CS) and shoulder anterior-posterior and lateral view and axial view X-rays) was performed postoperatively. RESULTS: Clinical results after 45 months showed a mean CS of 66.2+/-15.4 points with a mean agCS of 90.0+/-23.1%. Evaluation of the %CS showed 77.7+/-17.8%. %CS results showed no significant differences after 45 months in comparison to those obtained after 12 months. However, incidence of avascular necrosis of the humeral head doubled over the follow-up period from 4 cases at 12 months follow-up to 9 cases at final follow-up. CONCLUSION: Results of open reduction and internal fixation with angular stable implants for proximal humeral fractures are reliable, however long-term complications such as avascular necrosis of the humeral head need to be evaluated further on since its incidence increases over the time.

Stabilisation of periprosthetic fractures with angular stable internal fixation: a report of 13 cases.

INTRODUCTION: Periprosthetic fractures of the femur present a challenging surgical problem. The aim of this study was to retrospectively evaluate the outcome of periprosthetic fractures stabilised with an angular stable, less invasive stabilisation system (LISS). PATIENTS AND METHODS: Thirteen patients (ten total hip-, two total knee-, one total hip- and knee-arthroplasty) with periprosthetic fractures were treated with the LISS internal fixator (in ten cases minimal invasive). Six patients had previous operations due to periprosthetic fractures. The average follow-up period was 20 months, follow-up rate 85%. RESULTS: All fractures showed radiographic fracture healing without implant loosening. Except one patient, all patients had returned to their pre-operative activity level. No early post-operative complications were seen. There was one implant failure after 4 months and two cases of malunion. CONCLUSION: The cases showed the internal fixator to be effective for the stabilisation of periprosthetic fractures, even in cases of poor bone quality with good functional outcomes. The internal fixator, with the option of minimal invasive application, is the preferred method of osteosynthesis in periprosthetic fractures.

Locked internal fixator: sensitivity of screw/plate stability to the correct insertion angle of the screw.

OBJECTIVE: Internal fixators with angular stability have been developed to provide high stability without compression of the plate on to the bone. Angular and axial stability of a plate-screw construct can be achieved using a conically threaded screw head undersurface and a corresponding conically threaded plate hole. Furthermore, the insertion angle of the screw must correspond precisely to the axis of the screw hole. This is not always achieved in clinical practice and may result in screw loosening. The objective of this study was to examine the relationship between the stability of the locked screw-plate on the insertion angle of the screw. METHODS: Locking screws were inserted in an isolated (Point Contact Fixator, PC-Fix) or combined (Locking Compression Plate, LCP 4.5) locking hole with the use of an aiming device. The optimal insertion angle for these plates is perpendicular to the plate surface. The screws were inserted with an axis deviation of 0 degrees (optimal condition), 5 degrees , and 10 degrees respective to the optimal angle (variance +/- 1 degrees ). The samples were tested under shear or axial (push out) loading conditions until failure occurred. An Instron materials testing machine was used. RESULTS: Locking screws inserted in the isolated locking hole (PC-Fix) showed a significant decrease of failure load if inserted at 5 degrees and 10 degrees angle. Using an optimal insertion angle (0 degrees ), failure load was 1480 +/- 390 N, with 5 degrees axis deviation 780 +/- 160 N, P = 0.0001, and with 10 degrees axis deviation 550 +/- 110 N, P = 0.0001. Screws inserted in the combined locking hole (LCP) also showed a significant decrease of push-out force of 77% (4960 +/- 1000 N versus 1120 +/- 400 N) with 10 degrees axis deviation. Compared to optimal insertion angle (0 degrees ), bending load to failure did decrease up to 69% (1240 +/- 210 N vs. 390 +/- 100 N) with 10 degrees axis deviation. CONCLUSION: A locking head screw exhibits high stability with a moderate axis deviation in the angle of insertion of up to 5 degrees . However, there is a significant decrease in stability with increasing axis deviation (>5 degrees ). An aiming device is recommended to provide optimal fixation with angular stability.

Deformation of chondrocytes in articular cartilage under compressive load: a morphological study.

The main function of articular cartilage is to transmit load. The objective of this study was to describe the deformation of chondrocytes under static loading and its relation to collagen matrix deformation. Whole intact rabbit knee joints were loaded statically with either high or low magnitude and long or short duration. Specimens were cryopreserved while under load and prepared for morphological evaluation by field emission scanning electron microscopy. With this method an immediate preservation of the chondrocyte in its loaded state was possible. Static compression of articular cartilage produced a zone-specific deformation of chondrocyte shape, depending on the magnitude and duration of load. Under high-force and long-duration loading, the chondrocytes showed considerable deformation concomitant with the highly deformed collagen fibres. Chondrocyte deformation occurred mostly in the transitional and upper radial zones and less in the lower layers. There was no significant change of the chondrocyte shape in the tangential zone under high- or low-force short-duration loading. These results show that the chondrocytes undergo significant changes in shape ex vivo and that they are sensitive to differences in the magnitude and duration of loads being applied. Chondrocyte deformation is strongly linked to the deformation of the surrounding cartilage collagen matrix.

Stabilization of proximal tibial fractures with the LIS-System: early clinical experience in Berlin.

The Proximal Tibia Less Invasive Stabilization System (LISS PLT) is an internal fixator for the treatment of proximal tibial fractures according to the principles of "Minimally invasive surgery". From July 1998 to August 2000 22 fractures were treated in our clinic with the new Proximal Tibia LISS and the prospective course of healing was documented. The period of follow-up was 12 months. The inclusion criteria were defined as proximal tibial shaft fractures and intraarticular proximal tibial fractures of all degrees of severity. A total of 15 proximal medial and lateral tibial plateau fractures (AO 41) and 7 metaphyseal fractures were treated (AO 42), seven of these fractures presented with open soft tissue damage. The average age of the patients treated was 42 years. With a follow-up rate of 91% (2 patients lost to follow-up), definite consolidation of the fracture was seen in 19/20 cases. In one patient, the fracture had only been partially bridged and secondary bone grafting was performed. Radiologically, there was one case of a varus malalignment of 6 degrees, in two further cases there were valgus malalignments of 5 degrees and 7 degrees at the time of surgery. The other cases all healed in correct alignment. In one case, the implant became loose on the distal shaft and was stabilized again using bicortical screws. In a case with type IIIB soft tissue damage, a soft tissue infection became manifest, but healed uneventfully after a revision operation with the implant in situ.

The acute structural changes of loaded articular cartilage following meniscectomy or ACL-transection.

OBJECTIVE: Meniscectomy and anterior cruciate ligament (ACL) rupture have been identified as precursors of osteoarthrosis (OA) in clinical reviews and animal experiments. In this study, the acute effects of these injuries on articular cartilage matrix deformation, preserved in a loaded state using a cryopreservation technique, were studied by scanning electron microscopy (SEM). METHOD: Whole knee joints from adult White New Zealand rabbits (N=87) were loaded ex vivo, using a simulated quadriceps pull under static and cyclic loading conditions, following medial meniscectomy or transection of the ACL. Specimens were plunge-frozen while under load, or following a recovery period, and prepared for SEM by cryofixation. Using SEM and photographic images, the medial tibial plateau cartilage was assessed both qualitatively and quantitatively. RESULTS: After meniscectomy, significantly increased bending and crimping of radial collagen fibers occurred with static loading. Compared to intact knees, the area of tibial cartilage showing an indentation was increased by 80% (P< 0.05), the articular cartilage thickness was significantly more reduced when under load (for high force long duration static loading, intact joints had 53%+/-3 reduction in cartilage thickness compared to 39%+/-4 after meniscectomy, P< 0.05), and it took nearly twice as long for the cartilage thickness to recover following loading. These post-meniscectomy differences were either not present or were minimal when the joint was allowed to extend when loaded. ACL-transection slightly increased collagen deformation in the deeper zones, but only with cyclic loading. CONCLUSION: The findings indicate that, with static loading, significantly increased deformation of articular cartilage collagen structure can occur following meniscectomy, but is minimized by joint motion. This increased deformation may be relevant to the etiology and progression of joint degeneration.

Effect of mechanical load on articular cartilage collagen structure: a scanning electron-microscopic study.

Little is known about the morphological effect of a mechanical load upon articular cartilage. The objective of this study was to describe and quantify the deformation of the articular cartilage collagen structure of the tibial plateau under static loading. Whole intact rabbit knee joints were loaded in vitro by simulating a quadriceps force of 3x, 1x or 0.5x body weight (high, medium, low) over durations of 30 or 5 min (long, short). Specimens were cryopreserved while under load and prepared for morphological evaluation by field emission scanning electron microscopy. Under high force and long duration loading the collagen fibers exhibited high deformation with an increased thickness of the layer of collagen fibers oriented almost parallel to the surface and a cartilage thickness reduced to 54%. Collagen fiber deformation occurred mostly in the transitional and upper radial zone. The area of tibial indentation and the cartilage thickness reduction increased with magnitude and duration of load. The collagen matrix did show a bulging edge at the border of the meniscus and exhibited remarkable deformation under the meniscus.

Freeze-substitution of rabbit tibial articular cartilage reveals that radial zone collagen fibres are tubules.

Investigations of the micromorphology of rabbit tibial articular cartilage using scanning and transmission electron microscopy revealed that the collagenous elements in the tissue form fluid-containing tubular structures. The commonly described radial or deep zone longitudinal fibres were found to be tubular structures with internal diameters of 1-2 microm. The walls of the tubules were composed of tightly packed fibrils of collagen. The tangential zone, close to the tibial plateau, was composed mainly of a spongy arrangement of collagen fibrils, containing bunches of tangentially lying small (< 1 microm) diameter tubules. The application of conventional chemical fixation techniques resulted in the fine detail of this tissue being obscured. When the tissue was frozen, followed by cryo-scanning electron microscopy or freeze-drying, prior to observation in the scanning electron microscope the tubule structures were not obviously present. It was only by applying freeze-substitution techniques, followed by critical point drying or resin embedding, that the structure was revealed clearly. Segregation of water into ice crystals did occur during the freezing process, but the formation of those crystals played no part in creating the tubular morphology observed. A similar structure was still revealed following pre-treatment with glycerol, methanol or Triton X-100, provided that concentration of these additives was not too high. The walls of the tubules in the radial region were composed of straight, longitudinally arranged as well as helically arranged, 30 nm diameter fibrils. The lumen of the tubules appears to be lined by a circumferentially arranged array of approximately 10 nm diameter fibres, spaced at regular intervals of 50-70 nm.

The surface contour of articular cartilage in an intact, loaded joint.

The friction coefficients measured in diarthrodial joints are small. Theories of joint lubrication attribute this efficiency to entrapment or movement of synovial fluid, yet anatomical models of the surface are based on studies of isolated fragments of cartilage, not functional joints. To investigate the functional interrelationship of joint surfaces and synovial fluid, the ultrastructure of loaded joints was examined. Twenty-four New Zealand white rabbit knee joints were loaded either statically or moved ex vivo using simulated muscle forces and then plunge-frozen under load. After fixation in the frozen/loaded state by freeze-substitution fixation, the medial joint compartments were embedded in epoxy resin while still articulated. Bone was trimmed away from the articular surfaces, permitting the cartilage to be sectioned for light and electron microscopy. These joint surfaces were then compared with controls which were not loaded, not moved or had been disarticulated prior to embedding. Articular surfaces of loaded joints were smooth at magnifications from x 35 to x 7500, whereas the tibial surfaces of nonloaded joints were irregular. Small pools of joint fluid were observed at the meniscal edge and beneath the anterior horn of the meniscus. At magnifications of x 40000, the joint surfaces were separated by a uniform 100 nm space containing fluid. An amorphous, electron dense articular surface lamina was present but, when loaded, was thicker and flatter than previously reported. No surface pits or bumps were visible in embedded, loaded joints. This is the first ultrastructural study of intact loaded joints. The findings suggest that fluid film lubrication is present in diarthrodial joints, but the fluid sequestration postulated in several models is not apparent.

Collagen fibre arrangement in the tibial plateau articular cartilage of man and other mammalian species.

Experimental animal models are frequently used to study articular cartilage, but the relevance to man remains problematic. In this study animal models were compared by examination of the collagen fibre arrangement in the medial tibial plateau of human, cow, pig, dog, sheep, rabbit and rat specimens. 24 cartilage samples from each species were prepared and maximum cartilage thickness in the central tibial plateau measured. Samples were fixed, dehydrated, freeze-fractured and imaged by scanning electron microscopy (SEM). At low magnification, 2 different arrangements of collagen fibres were observed: leaf-like (human, pig, dog) and columnar (cow, sheep, rabbit, rat). The porcine collagen structure was the most similar to that of man. This arrangement was consistent from the radial to the upper zones. Under higher magnification at the surface of the leaves, the collagen was more randomly oriented, whereas the columns consisted of parallel collagen fibrils. The maximum thickness of cartilage did not correlate with the type of collagen arrangement but was correlated with the body weight of the species (r = 0.785). When using animal models for investigating human articular cartilage function or pathology, the differences in arrangement of collagen fibres in tibial plateau cartilage between laboratory animals should be considered especially if morphological evaluation is planned.

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.

Deformation of articular cartilage collagen structure under static and cyclic loading.

Relatively little is known about the morphology of articular cartilage under conditions of normal use, yet a more profound knowledge is both critical to the understanding of cartilage function and helpful for the validation of tissue-engineered cartilage. In this study, the deformation of the articular cartilage of the tibial plateau under compressive static and cyclic loading is characterized. Whole knee joints of rabbits were loaded ex vivo while the knee was held statically or allowed to move against resistance. Load magnitudes of quadriceps were maintained at either three (high) or one (low) times body weight for 30 minutes. For cyclic loading, the tibia was flexed between 70 and 150 degrees relative to the femur at 1 Hz with either a cyclic or constant force. The recovery of cartilage after unloading was examined for each loading condition. At the end of the loading, specimens were cryofixed while under load, freeze-substituted, and prepared for scanning electron microscopy. Morphological examination demonstrated significantly higher deformation of the collagen structure throughout all cartilage zones under static loading conditions compared with cyclic loading conditions in which deformation was limited to the superficial regions. The minimum thickness of the cartilage that remained after loading was dependent on the magnitude of load and was significantly smaller with static loads (54% of the thickness of the unloaded controls) than after cyclic loading or constant-force cyclic loading (78 or 66% of the thickness of the unloaded controls, p < 0.05). Acute bending of the collagen fibers was observed under both loading conditions: in the superficial half of the articular cartilage after static loading and in the superficial quarter after cyclic loading. Complete recovery of all deformation occurred within 30 minutes but was significantly faster after cyclic loading. These data suggest that the structure of the collagen of articular cartilage exhibits a zone-specific deformation that is dependent on the magnitude and type of load.

Microwave-enhanced fixation of rabbit articular cartilage.

Cartilage, being highly aqueous, is difficult to preserve for electron microscopy without artefacts. Microwave-enhanced fixation is suggested as a standard method for block samples of this material, with dimensions of up to 12 x 7 x 3 mm. Cartilage samples from the tibial plateau of adult rabbits were fixed by conventional, cryo- or microwave-enhanced fixation. Constant or cyclical microwave irradiation of samples, immersed in fixatives, was carried out to varying final solution temperatures. Microwave-enhanced fixation and staining is shown to be both rapid and reproducible, giving fine structural preservation. Below 323 K microwave fixation always gave excellent preservation of the fine structure within seconds. At higher temperatures thermal artefacts were introduced. In this study the microwave-enhanced fixation is equal in quality to the test conventional immersion fixation and is nearly as fast as cryo-preservation. It provides a standardized, reproducible fixation for morphological studies on cartilage with good process control.