Morphology of the bovine chondrocyte and of its cytoskeleton in isolation and in situ: are chondrocytes ubiquitously paired through the entire layer of articular cartilage?

OBJECTIVES: We compared the morphology and cytoskeleton of chondrocytes seeded in monolayer or in agarose gels with those retained in situ i.e. within their extracellular matrix-the chondrocyte's natural habitat. METHODS: Cartilage specimens were harvested from adult bovine femora. Chondrocytes were either enzymatically isolated to seed in both monolayer and agarose gel culture conditions or retained in situ. Full thickness cartilage on bone was sliced both parallel and perpendicular to the articular surface. After immunostaining, the morphology of chondrocytes and of their cytoskeletal organization, i.e. distribution of actin and vimentin, in chondrocytes seeded both in monolayer and 3D agarose and those retained in situ, were assessed using confocal laser scanning microscopy. RESULTS: The general cytoskeletal disposition of chondrocytes in situ was similar to that in agarose gel. Actin was seen to form stress fibres only in 2D culture, but not in 3D culture and in situ. In these latter conditions, actin showed a punctate staining pattern. The vimentin meshwork spanned the cytoplasm from the plasma membrane to the nuclear membrane in all culture conditions. However, the organization of the vimentin had a radiate organization in chondrocytes in monolayer and a more circumferential arrangement both in agarose gel and in situ. We further observed: (i) the prevalence of a bichondral configuration of chondrocytes in situ and (ii) the existence of a vimentin link joining some of the sister cells in situ. CONCLUSIONS: Bichondral configuration linked with cytoskeletal elements may potentially be significant for the normal function of the chondrocytes, and therefore have implications for approaches to tissue engineering of cartilage.

Accuracy of MRI vs CT imaging with particular reference to patient specific templates for total knee replacement surgery.

BACKGROUND: The present study compares the accuracy of MRI and CT imaging for the manufacture of patient-specific templates for total knee replacement surgery. METHODS: A total of 10 ovine knees were imaged using MRI and CT scanners. Each set of images was reconstructed in 3D and then used to manufacture physical models of each bone, using rapid prototyping technology. After imaging the soft tissues were removed and specific measurements of the bony anatomy compared with measurements from the MRI and CT models. RESULTS: Bone models generated from MRI scans were dimensionally less accurate than those generated from CT scans. Furthermore, the bone models generated from MRI scans were visibly inferior to those generated from the CT scans. CONCLUSIONS: Current MRI scans do not offer a viable alternative to CT. Although adaptation of the template system to accommodate MRI imaging is possible, the changes required are neither practical nor desirable.

In-situ engineering of cartilage repair: a pre-clinical in-vivo exploration of a novel system.

This investigation explores a new cartilage repair technique that uses a novel method to secure a non-woven multifilamentous scaffold in the defect site after microfracture. The hypothesis is that a scaffold provides a larger surface area for attachment and proliferation of the mesenchymal stem cells that migrate from the bone marrow. Two in-vivo studies were undertaken in an ovine model. The first study, which lasted for 8 weeks, aimed to compare the new technique with microfracture. Chondral defects, 7 mm in diameter, were created in both femoral medial condyles of five ewes. One defect was treated with the new technique while the contralateral knee was treated with microfracture alone. The results revealed that the quantity of repair tissue was significantly greater in the defects treated with the new system. The second study had two time points, 3 and 6 months, and used 13 ewes. In this study, both defects were treated with the new technique but one received additional subchondral drilling in order to stimulate extra tissue growth. The majority of the implants had good tissue induction, filling 50-100 per cent of the defect volume, while the compressive modulus of the repairs was in the range of 40-70 per cent of that for the surrounding cartilage. In addition, hyaline-like cartilage was seen in all the repairs which had the additional drilling of the subchondral bone.

Light and low-frequency pulsatile hydrostatic pressure enhances extracellular matrix formation by bone marrow mesenchymal cells: an in-vitro study with special reference to cartilage repair.

Ovine bone marrow mesenchymal cells (BMMCs) were seeded on to non-woven filamentous plasma-treated polyester scaffolds and cultured in a chondrogenic medium for 4 weeks. Thereafter a pulsatile hydrostatic pressure (PHP) was applied to these cell-scaffolds constructs at an amplitude of 0.1 MPa and frequency of 0.25 Hz, for 30 min a day, over a period of 10 days. Samples (n = 6) were removed 24 h after PHP stimulation at days 1, 4, 7, and 10 for biochemical analysis. Similar analyses were conducted, at the same time points, on control samples that were not subjected to a PHP. The results showed that the glycosaminoglycan (GAG) content did not significantly increase until after the application of a PHP for 7 days. The GAG content was 1.5 and 2.7 times higher in the PHP group than in the control group at days 7 and 10 respectively (p<0.01). The deoxyribonucleic acid (DNA) content was 1.5 times greater in the PHP group than in the control group at day 10 (p<0.01). GAG synthesis amounts, expressed as the total GAG contents per microgram of DNA, were 1.6 and 1.8 times higher in the PHP group than in the control group at days 7 and 10 respectively (p<0.01). The total collagen content in the medium did not change until after PHP application for 10 days, when it was 1.9 times higher than the control (p < 0.05). The results suggest that a light PHP applied at a low frequency has a cumulative stimulatory effect on the BMMCs' metabolic activities including cell proliferation and synthesis of the extracellular matrix.

Effect of a single impact loading on the structure and mechanical properties of articular cartilage.

AIM: To study the effect of a single impact on the structure and mechanical properties of cartilage. MATERIALS AND METHOD: Osteochondral plugs harvested from bovine femora were subjected each to a single impact using an in-house designed drop-tower. Impact masses of different values were released from different drop heights in selected combinations to apply stresses at strain rates and impact energies within specific ranges. Changes in the storage and loss moduli were estimated from cyclic compressive loading test undertaken before and after impact. The conditions of these tests were set to those occurring during walking and running. The extent of the damage on cartilage surface and depth was assessed using optical and confocal microscopy. RESULTS: The storage modulus varied slightly at level walking and running after performing impact tests up to the impact energy of 0.736 J. However, the decrease in the storage modulus was considerable at the impact energy of 1.962 J for test conditions representing both walking and running. This impact energy resulted in strain rate of 1500 s(-1), stress of 25 MPa and energy absorbed per unit volume of 12.79 mJ/mm(3). After impact the loss modulus increased over the loading cycles at all energies. Severe fissures were observed across the cartilage surface and through its thickness at levels of impact energy equal or greater than 1.472 J. CONCLUSIONS: This study identified thresholds for the strain rate, impact stress and impact energy, which caused permanent changes in the mechanical properties and damage to structure of cartilage.

Computer-assisted total knee arthroplasty using patient-specific templating.

Current techniques used for total knee arthroplasty rely on conventional instrumentation that violates the intramedullary canals. Accuracy of the instrumentation is questionable, and assembly and disposal of the numerous pieces is time consuming. Navigation techniques are more accurate, but their broad application is limited by cost and complexity. We aimed to prove a new concept of computer-assisted preoperative planning to provide patient-specific templates that can replace conventional instruments. Computed tomography-based planning was used to design two virtual templates. Using rapid prototyping technology, virtual templates were transferred into physical templates (cutting blocks) with surfaces that matched the distal femur and proximal tibia. We performed 45 total knee arthroplasties on 16 cadaveric and 29 plastic knees, including a comparative trial against conventional instrumentations. All operations were performed using patient-specific templates with no conventional instrumentations, intramedullary perforation, tracking, or registration. The mean time for bone cutting was 9 minutes with a surgical assistant and 11 minutes without an assistant. Computer-assisted analyses of six random computed tomography scans showed mean errors for alignment and bone resection within 1.7 degrees and 0.8 mm (maximum, 2.3 degrees and 1.2 mm, respectively). Patient-specific templates are a practical alternative to conventional instrumentations, but additional clinical validation is required before clinical use.

Conditioning of cartilage during normal activities is an important factor in the development of osteoarthritis.

Mechanical factors have long been implicated in the aetiology of osteoarthritis (OA). The two most popular hypotheses regarding the mechanism of cartilage damage are: the application of too high a stress and the mechanism of fatigue. Mechanical failure in any material, however, can be caused by either or both of these mechanisms. It is hypothesized that, because cartilage is a living tissue, the threshold at which it fails by either mechanism is regulated by the prevalent stresses arising in a joint. As these stresses are determined by activities and lifestyles, a low failure threshold can be the result of prolonged periods of low-level activity, which, if interrupted with short periods of intense activities, can subject weakened cartilage to damaging stresses. Were this hypothesis proven, it would address difficulties encountered with these hypotheses and explain some clinical observations. It would also have implications for the activities and lifestyles of individuals.

Personalised image-based templates for intra-operative guidance.

The high rate of unplanned perforation, poor fixation, and nerve injury with freehand pedicle screw insertion has led to the use of image-guided navigation systems. Although these improve accuracy, they have several drawbacks that could be overcome by using image-based drilling guide templates. The accuracy of such templates was tested in a cadaveric study of screw placement in the lumbar, thoracic, and cervical regions of the spine. The dimensional stability with autoclaving of duraform polyamide, to be used for manufacturing the guides, was first determined using test specimens. Computed tomography (CT) images were acquired of 4 cadaveric spines, and placement of 4 cervical, 32 thoracic, and 14 lumbar screws was planned. Eighteen personalized drilling guide templates, in four different designs, were built. Orthopaedic surgeons experienced in the freehand techniques used the templates. CT images were acquired to assess placement position with respect to the pedicle. Duraform polyamide was found to be unaffected by sterilization. Two of the template designs facilitated the placement of 20/20 screws without error. Templates can lead to successful screw placement, even in small pedicles, providing their design is optimized for the application area, e.g. with enhanced rotational stabilization.

Zonal and directional variations in tensile properties of bovine articular cartilage with special reference to strain rate variation.

UNLABELLED: THE AIMS of this study were: (i) to investigate the variation in the tensile properties of articular cartilage with depth through cartilage thickness and fibre orientation; (ii) to determine the effect of strain rate on tensile properties of articular cartilage. MATERIALS AND METHOD: All experimental work was performed on cartilage specimens taken from two bovine knee joints. Osteochondral plugs 12 mm in diameter were harvested with a special reamer from the femur and the tibial plateaux of each knee. Slices (0.2 mm thick), of articular cartilage were cut from the plug with a microtome. The predominant orientation of the collagen fibres on the cartilage surface was determined using the pinpricking technique. Each specimen used for the tensile test was cut, so as to produce a dumbbell shape, with a gauge length of 6 mm. Uniaxial tensile tests were performed on each specimen in order to determine the tensile Young's modulus, and ultimate tensile strength (UTS). In this investigation, these tensile tests were carried out at different strain rate: 1, 20, 50 and 70%/sec. RESULTS: As regards the zonal properties, it was found that tensile stiffness was greater in the superficial layer than in deep layer. However, a few specimens from the deep layer displayed similar or greater stiffness compared to the superficial layer. With respect to the directional properties, the specimens oriented parallel to the predominant alignment of collagen, were stiffer than those, which were perpendicular to it in each layer. However, only the results regarding the deep layer can be considered statistically significant. In regard to the variation of modulus with the strain-rate, the results showed that there is no significant increase of the modulus with increasing strain rate from 20 to 50% per second. However, at 70% per second, articular cartilage stiffness considerably increased by up to one order of magnitude greater than that determined at lower strain rates in both the superficial and deep layer. Moreover, the UTS of cartilage specimens tested at 70% per second showed a significant rise, reaching values of four to five times that of those measured at 1, 20 or 50% per second. CONCLUSION: The steep increases in both the stiffness and ultimate tensile strength of cartilage at high strain rates point to the existence in cartilage of a mechanism for its protection from damage by stresses arising in trauma, which are usually applied at high rates. This mechanism needs to be elucidated. The reduced anisotropy found in the present study pointed out that collagen is likely to be less organized in bovine cartilage than in the human and therefore, a study of its ultra-structure would be appropriate.

The longitudinal Young's modulus of cortical bone in the midshaft of human femur and its correlation with CT scanning data.

This study was concerned with establishing the regional variations in the magnitude of the longitudinal Young's modulus of the cortical bone in the femoral midshaft and with investigating whether a relationship existed between the Young's modulus of bone and the CT number. Were such a relationship to exist this would provide a noninvasive method of assessing the quality of bone in the regions of fixation of implants to bone. The data would be of considerable aid to designers of implant stems to withstand the stresses arising at its interface with the bone. Five pairs of fresh frozen human femora were used. Several beam-shaped small specimens were methodically harvested from each pair and were used to measure the longitudinal modulus adopting the three-point bending test, which was carried out with a specially constructed and validated apparatus. CT scans of the bone were obtained, prior to harvesting the specimens, and the CT number was measured at locations corresponding with the specimen sites. The results indicate that in the femoral midshaft the cortical bone has an average Young's modulus value of 18600 +/- 1900 MPa. This agrees well with data obtained by other researchers using different experimental methods. Statistical analyses revealed no regional variations in the value of the longitudinal modulus of the bone. No correlation was found between the bone modulus and the CT number. Thus a noninvasive method for establishing the bone properties still remains a challenge.

Quality assessment of the cortical bone of the human mandible.

This study is the first to investigate simultaneously both the regional and the directional variations in mechanical properties and computed tomography (CT) numbers of the fresh mandible bone and to explore the correlation between the two sets of data with a view to provide a noninvasive method for determining the bone quality for designers of dental implants. Using a three-point bending test the regional variation of Young's modulus of bone in the human mandible was determined from five fresh specimens from donors representative of patients in need of dental implants in that some of the mandibles were fully dentulate, some partly so, and some fully edentulate. While a pattern of the modulus distribution was evident in the mandibles we tested, these mandibles did have, as a result of their respective states, their own peculiarities. We determined also the directional variations of the modulus for the mandible, which are due to the anisotropic nature of bone. The modulus values obtained in our study were much lower than those listed in the only other published study, which was conducted on dry mandibles. These differences in the modulus data from the two studies were attributed partly to the differences in condition of the bone and differences in the dimensions of specimens tested in the two studies. Because the values of the modulus obtained in this study are lower than those previously published, they would be safer as a basis for implant designs. A weak correlation was found between the modulus values and the CT number of the mandible. This would not be sufficient for accurate predictions of the bone properties from CT scans. The development of a noninvasive method for determining the bone quality in various patients thus remains a challenge for researchers.

Mechanical behaviour of articular cartilage under tensile cyclic load.

INTRODUCTION: Although fatigue has been implicated in cartilage failure, there are only two published studies in this area, by the same author. However, in these previous studies cartilage was tested in the direction parallel to that of collagen orientation in the superficial layer, where it possesses greater tensile strength. In the present work, articular cartilage was also tested along the direction perpendicular to that of the collagen. Furthermore, the study investigated topographic and zonal variations in the fatigue behaviour of cartilage from the human knee. METHODS: Specimens were tested in a specially constructed apparatus that allowed the number of cycles at specimen failure, as well as the load and elongation of the specimen, to be monitored for each specimen. To date, some 72 specimens have been tested, all from the same knee joint, though from different sites and at different depths within the cartilage layer. RESULTS AND CONCLUSIONS: The most impressive of the outcomes of this study is the scatter of the data. Considering all the specimens used, the range of number of load cycles to failure was between 2 and 1.5 million. The zonal variation in fatigue behaviour was similar to that in tensile modulus reported previously; the surface and deep layers seemed to have better fatigue properties whether tested in the direction parallel or perpendicular to that of the collagen in the superficial layer. The middle layer was far weaker, suggesting that highly packed and ordered fibres in the surface and deep zones have better mechanical properties than the more random and loose fibres in the middle zone. The variation in fibre organization through the cartilage thickness was also reflected in the differences observed in the elongation of the specimen during the test. The surface and deep zones had a higher stiffness than the middle zone. Cartilage had better fatigue resistance when the specimen was loaded in a direction parallel rather than perpendicular to the collagen within the surface layer. This was true whether specimens were harvested from the superficial, intermediate or deep layer. There were many factors that confounded attempts to estimate the likely fatigue life from the data obtained in such a study.

Effect of implant lengthening and mode of fixation on knee laxity after ACL reconstruction with an artificial ligament: a cadaveric study.

An "apparent" lengthening of the ligament implant, which causes an increase in knee laxity after the reconstruction of the anterior cruciate ligament (ACL) may be due to either slippage of the implant from under the fixation devices, or tunnel migration (due to bone resorption). These two mechanisms are related to the initial ligament placement, implant tensioning, and fixation modes. This cadaveric study simulates, in a controlled experimental situation, the postoperative lengthening of artificial ACL implants, and seeks to quantify the consequent increase in joint laxity. Eight cadaveric right knees, in which the Leeds-Keio artificial ligament was implanted, were tested in a specially constructed apparatus, which allowed the knee joint six degrees of freedom. In each of the tested joints the laxity was measured under several test conditions for two final fixation modes of the implant. The difference between the fixation modes was the application (as in mode B) or not (as in mode A), of a posteriorly directed force of 50 N on the tibia, at the moment of final fixation of the ligament. In both cases a tensile load of 50 N was maintained along the implant. All measurements were taken at flexion angles of 20 degrees and 90 degrees and with controlled implant lengthening of up to 3 mm in 0.5-mm increments. After implantation, adopting fixation mode B resulted in the knee exhibiting an anterior laxity considerably less than the original physiological laxity, compared with that measured after using fixation mode A. Thus at 20 degrees of knee flexion, under an anterior load of 100 N applied on the tibia, adopting fixation mode B, the joint laxity was 2.8 mm smaller than the natural laxity, whereas, for fixation mode A, it was 1.4 mm larger. At 90 degrees of knee flexion, the situation was similar, but with smaller differences. However, the situation was overturned as the implant length was increased. Thus, at 20 degrees of knee flexion, when the implant was lengthened in a range of 1--2 mm, the laxity observed with fixation mode B was similar to that recorded when the ACL was intact, whereas the laxity observed with fixation mode A was about 3--4 mm greater. Similar data were observed at 90 degrees of knee flexion. It appears that fixing the implant finally by applying a tensile load on it while simultaneously pushing the tibia posteriorly could be an effective measure against the possible return of joint laxity.

Modelling femoral curvature in the sagittal plane: a cadaveric study.

This study examined the possibility of representing the mid third of the human femur with two straight sections. This portion of the femur visually has a distinct curvature, which can potentially present problems when considering implant stem designs to be introduced in this region. Sixteen femora were sectioned at 10 mm intervals along the femoral shaft in the mid third region (35-65 per cent of femoral length). Photographic records were obtained of each section against a consistent axis system to which all coordinates were referenced. The position of the centre of the medullary canal cross-sectional area along the femur, in relation to fixed orthogonal planes, has been analysed; the outer anterior cortex was also modelled. The results showed that the medullary centre of area plots and the anterior cortex coordinates are suitably modelled as two straight lines. For each bone it was possible to define the intersection point between the two straight sections (point of angulation), and the subtended angle between these sections (angle of incidence). The average point of angulation for the medullary plots occurred at 57 per cent along the femur, while the mean angle of incidence was 6.5 degrees. The anterior surface had an average point of angulation at 58 per cent along the femur with the mean angle of incidence being 22.2 degrees. The centre-line of the medulla was also found to be almost parallel to the outer anterior surface for sections distal to the point of angulation. It is proposed therefore, that this difference in angulation is the result of medullary expansion/cortical thinning towards the proximal extremity of the femur, causing the straight-line model of the medulla to angulate less than the outer anterior cortex.

The relationship of the compressive modulus of articular cartilage with its deformation response to cyclic loading: does cartilage optimize its modulus so as to minimize the strains arising in it due to the prevalent loading regime?

AIM: To investigate the relationship of the instantaneous compressive modulus with its deformation response to cyclic loading typical of that encountered at the knee joint during level walking. METHOD: The study was performed on 24 osteochondral plugs taken from three unembalmed cadaveric knees. As the compressive modulus of cartilage has been shown to vary topographically across the knee in an established manner, the specimens were taken from specific sites on the femur and tibia of each knee. All the cartilage specimens were immersed in Hanks' salt solution at 37 degrees C and were subjected to the same cyclic loading regimen that was representative of a typical walking cycle in a specialized indentation apparatus, for over 1 h. RESULTS AND CONCLUSION: The viscous and elastic components of matrix strain, the creep rate and the cartilage compressive modulus were measured. The latter was found to be significantly related to the strain response of cartilage to cyclic loading. Elastic strain varied exponentially with the compressive modulus; specimens with a modulus less than 4 MPa experienced elastic strains in the range 0.18-0.36, whereas stiffer specimens experienced strains between 0.05 and 0.13. Viscous strain varied linearly with cartilage stiffness and was as low as 0.02 at the lower values of the compressive modulus but increased to 0.22 for a compressive modulus of 18 MN/m(2). The rate of creep under cyclic load was inversely linearly related to cartilage stiffness. The strain response of soft specimens approached steady state by 200 cycles but that of stiff specimens did not approach it until 1300 cycles. It was hypothesized that the viscous strain response of cartilage can be explained in terms of differences in permeability between specimens of different compressive modulus, stiffer cartilage having a lower permeability than soft cartilage.

Roles of the anterior cruciate ligament and the medial collateral ligament in preventing valgus instability.

Both the medial collateral ligament (MCL) and the anterior cruciate ligament (ACL) are reported to prevent valgus instability of the knee. In this study, the anatomical mechanisms by which these ligaments prevent valgus instability were experimentally investigated. The valgus rotation angle and the magnitude of the medial joint space opening were measured in six cadaveric knees, using biplanar photography before and after the MCL and/or the ACL were severed. A significant increase in the valgus rotation angle and a large medial joint space opening were observed when the MCL was severed. An increase in the valgus rotation angle was also observed when the ACL was severed, but only a small medial joint space opening was present. The increase in the valgus rotation angle after ACL severance was nearly parallel to the increase in the internal rotation of the tibia. Thus, we concluded that both ligaments function to prevent valgus instability, but that the anatomical reasons for their function are different. The MCL prevents valgus instability by stopping an opening in the medial joint space. The ACL, on the other hand, prevents the internal rotation of the tibia. When the ACL is severed, the internal rotation increases, and causes the valgus rotation angle to also increase, despite the presence of only a small medial joint space opening.

Axis location of tibial rotation and its change with flexion angle.

The magnitude and location of the axis of tibial rotation were measured at 15 degrees increments between 0 degree and 90 degrees flexion using 24 normal anatomic knee specimens, and their changes with flexion angle were investigated. The magnitude of tibial rotation was small (8.3 degrees) at 0 degree flexion, but increased rapidly as the flexion angle increased and reached a maximum rotation (31.7 degrees) at 30 degrees flexion. It then decreased again with additional flexion (24.8 degrees at 90 degrees flexion). The location of the axis was close to the tibial insertion of the anterior cruciate ligament at 0 degree flexion, gradually moving toward insertion of the posterior cruciate ligament (observed at 45 degrees and 60 degrees flexion), and then moved anteriorly again with additional flexion: the axis was approximately equidistant from the two cruciate insertions at 90 degrees flexion. The results showed that a relatively large degree of tibial rotation was possible in a normal knee and that the location of the axis remained approximately in the area between the two cruciate ligament insertions throughout the range of flexion. However, the location of the axis changed with the flexion angle within this area according to the changes in direction and tension of the cruciate ligaments and the surrounding soft tissues.

Reconstructive treatment of posterolateral rotatory instability of the knee: a biomechanical study.

Twelve cadaveric knees were tested to determine effective reconstructive treatment for severe chronic posterolateral rotatory knee instability accompanied by excessive varus and posterior laxity. Posterolateral, varus, and posterior laxity were measured, first with the ligaments intact, then after complete sectioning of the posterior cruciate ligament (PCL) and posterolateral structures, and finally after reconstruction of these structures in different orders. The increases in those laxities were produced following the sectioning of all of the structures and disappeared throughout the flexion range after combined reconstruction of the PCL, lateral collateral ligament (LCL), and popliteus tendon. However, some residual increase in the laxity was always observed if any of the three structures were excluded from reconstruction. Therefore, combined reconstruction of the PCL, LCL, and popliteus tendon is essential and adequate for treating severe chronic posterolateral rotatory instability.

Anterior cruciate ligament reconstruction with the Leeds-Keio artificial ligament.

The Leeds-Keio (L-K) artificial ligament, developed for knee ligament reconstruction, is made of polyester with a maximum tensile strength of 2200 N. This implant works not only as a ligament but also as a scaffold onto which natural tissue grows from synovium. In an animal experiment, each strand of the L-K ligament was covered with new tissue by 2-3 weeks after anterior cruciate ligament reconstruction. Eight weeks postoperatively, abundant fibrous tissue with extensive vascularity covered the implant, which was still histologically immature. After 16 weeks, vascularization and tissue induction began to subside, and histologic analysis showed dense fibers running longitudinally and parallel. By 36 weeks, the new ligament looked like a natural anterior cruciate ligament, although histologically more cells could be seen than in the natural ligament. This maturation was observed only when the substitute was implanted under good tension. Clinically, the surgical procedure has been improved over the past 10 years, to the current practice in which the tape-in-tube double L-K ligament employs a small piece of autogenous tissue to promote early tissue induction and maturation. Using this practice (n = 135), more than 85% of the patients were satisfied subjectively, objectively, and arthroscopically at the 5-year postoperative FU period. Few patients had joint effusion postoperatively. Sacrifice of autogenous tissue is minimal. The patient can return to activities of daily living within 2 weeks, and more than 50% of them to sports within 10 weeks, and the new ligament is expected to keep its function for a long period as ingrowth completes the structure biologically.

Ultrasonic measurement of the thickness of human articular cartilage in situ.

OBJECTIVE: The objective of the present study was to explore the possibility of using the ultrasonic pulse-echo technique for the non-invasive measurement of cartilage thickness in situ during a joint arthroscopic examination. The accuracy of the ultrasonic measurement was assessed in vitro against that of an established needling technique which is destructive. METHODS: The velocity of sound in articular cartilage was measured in an in vitro study of one set of ipsilateral human ankle and hip joints at 69 test sites. Its variability was determined. RESULTS: The velocity of sound in human articular cartilage measured in situ varied widely (1419-2428 m/s; mean: 1892 m/s; S.D. 183 m/s) and therefore the error in the thickness of cartilage obtained from ultrasonic measurement based upon a constant velocity of sound could be as large as 33.6% (mean 7. 38%; S.D. 6.25%). CONCLUSIONS: The ultrasonic pulse-echo technique is not accurate for the measurement of the thickness of cartilage in situ. An alternative (albeit minimally invasive) would be the needling technique. This requires the development of a specialized probe.