Frank Linde

AGE VARIATIONS IN THE PROPERTIES OF HUMAN TIBIAL TRABECULAR BONE

We tested in compression specimens of human proximal tibial trabecular bone from 31 normal donors aged from 16 to 83 years and determined the mechanical properties, density and mineral and collagen content. Youngs modulus and ultimate stress were highest between 40 and 50 years, whereas ultimate strain and failure energy showed maxima at younger ages. These age-related variations (except for failure energy) were non-linear. Tissue density and mineral concentration were constant throughout life, whereas apparent density (the amount of bone) varied with ultimate stress. Collagen density (the amount of collagen) varied with failure energy. Collagen concentration was maximal at younger ages but varied little with age. Our results suggest that the decrease in mechanical properties of trabecular bone such as Youngs modulus and ultimate stress is mainly a consequence of the loss of trabecular bone substance, rather than a decrease in the quality of the substance itself. Linear regression analysis showed that collagen density was consistently the single best predictor of failure energy, and collagen concentration was the only predictor of ultimate strain.

Age-related variations in the microstructure of human tibial cancellous bone

A thorough understanding of the microstructure of cancellous bone is crucial for diagnosis, prophylaxis, and treatment of age‐related skeletal diseases. Until now, little has been known about age‐related variations in the microstructure of peripheral cancellous bone. This study quantified age‐related changes in the three‐dimensional (3D) microstructure of human tibial cancellous bone. One hundred and sixty cylindrical cancellous bone specimens were produced from 40 normal proximal tibiae from 40 donors, aged 16–85 years. These specimens were micro‐computed tomography (micro‐CT) scanned, and microstructural properties were determined. The specimens were then tested in compression to obtain Youngs modulus.

Mechanical properties of trabecular bone. Dependency on strain rate

The effect of strain rate (epsilon) and apparent density (rho) on stiffness (E), strength (sigma u), and ultimate strain (epsilon u) was studied in 60 human trabecular bone specimens from the proximal tibia. Testing was performed by uniaxial compression to 5% specimen strain. Six different strain rates were used: 0.0001, 0.001, 0.01, 0.1, 1, and 10 s-1. Apparent density ranged between 0.23 and 0.59 g cm-3. Linear and non-linear regression analyses using strength, stiffness and ultimate strain as dependent variables (Y) and strain rate and apparent density as independent variables were performed using the following models: Y = a rho b epsilon c, Y = rho b(a + c epsilon; Y = (a + b rho)epsilon c, Y = a rho 2 epsilon c, E = a rho 3 epsilon c. The variations of strength and stiffness were explained equally well by the linear and the power function relationship to strain rate. The exponent was 0.07 in the power function relationship between strength and strain rate and 0.05 between stiffness and strain rate. The variation of ultimate strain was explained best using a power function relationship to strain rate (exponent = 0.03). The variation of strength and stiffness was explained equally well by the linear, power function and quadratic relationship to apparent density. The cubic relationship between stiffness and apparent density showed a less good fit. Ultimate strain varied independently of apparent density.

Socket loosening in arthroplasty for congenital dislocation of the hip

Mechanical risk factors in loosening of the socket were radiographically analyzed in 123 Charnley arthroplasties performed during the period 1969-1982 for coxarthrosis secondary to congenital dislocation. The socket was placed as near the true acetabulum as possible without extensive soft-tissue release and without reinforcement of the acetabular roof by bone grafting. The rate of socket loosening was 19 percent using progression of a radiolucent line at the bone-cement interface to a width of greater than 1 mm as the criterion for loosening. Different predictors of loosening were analyzed by stepwise logistic regression analysis. Lack of lateral bony support for the socket was the prime predictor. The next most important predictors were the preoperative degree of hip dislocation and the position of the socket in relation to the true acetabulum.

Fixation of displaced femoral neck fractures. A comparison between sliding screw plate and four cancellous bone screws.

In a prospective, randomized trial, 104 consecutive patients with displaced femoral neck fractures were allocated either to fixation with a sliding screw plate or 4 ASIF cancellous bone screws. The patients were reexamined at fixed intervals to determine the time of union. The 2-year-cumulated rate of union was 64 per cent in the plate group and 84 per cent in the screw group.

Femoral shaft fracture after hip arthroplasty

Femoral shaft fractures after hip arthroplasties were treated in 74 noncemented hemiarthroplasties and 65 cemented arthroplasties. In loose prostheses the best clinical results and the least number of operations were achieved with revision arthroplasty with a long-stem prosthesis, combined with simple internal fixation methods when applicable. In firmly fixed prostheses the results of revision arthroplasty and traction treatment were similar. Cemented revision arthroplasty did not interfere with fracture union. Internal fixation with the prosthesis in situ cannot be recommended because of a large number of secondary revision arthroplasties and nonunions. Removal of the femoral stem prosthesis and internal fixation nearly always require a secondary revision and cannot be recommended.

Ultrasound guidance improves a continuous popliteal sciatic nerve block when compared with nerve stimulation.

Background and Objectives: Continuous sciatic nerve blockade at the popliteal level effectively alleviates postoperative pain after major foot and ankle surgery. No randomized controlled trials have previously compared the success rate of continuous sciatic nerve sensory blockade between ultrasound and nerve stimulation guidance. In the current study, we tested the hypothesis that ultrasound-guided catheter placement improves the success rate of continuous sciatic nerve sensory blockade compared with catheter placement with nerve stimulation guidance. Methods: After research ethics committee approval and informed consent, 100 patients scheduled for elective major foot and ankle surgery were randomly allocated to popliteal catheter placement either with ultrasound or nerve stimulation guidance. The primary outcome was the success rate of sensory block the first 48 postoperative hours. Successful sensory blockade was defined as sensory loss in both the tibial and common peroneal nerve territories at 1, 6, 24, and 48 hrs postoperatively. Results: The ultrasound group had significantly higher success rate of sensory block compared with the nerve stimulation group (94% versus 79%, P = 0.03). Ultrasound compared with nerve stimulation guidance also entails reduced morphine consumption (median of 18 mg [range, 0-159 mg] versus 34 mg [range, 0-152 mg], respectively, P = 0.02), fewer needle passes (median of 1 [range, 1-6] versus 2 [range, 1-10], respectively, P = 0.0005), and greater patient satisfaction (median numeric rating scale 9 [range, 5-10] versus 8 [range, 3-10)] respectively, P = 0.0006) during catheter placement. Conclusion: Ultrasound guidance used for sciatic catheter placement improves the success rate of sensory block, number of needle passes, patient satisfaction during catheter placement, and morphine consumption compared with nerve stimulation guidance.

Mechanical properties of the normal human tibial cartilage-bone complex in relation to age

OBJECTIVE: This study investigates the age-related variations in the mechanical properties of the normal human tibial cartilage-bone complex and the relationships between cartilage and bone. DESIGN: A novel technique was applied to assess the mechanical properties of the cartilage and bone by means of testing the cartilage-bone complex. BACKGROUND: Up to now, mechanical testing of cartilage and bone has been reported separately, and little is known about the mechanical behaviour of both tissues when examined as a unit. METHODS: Cylindrical human proximal tibial cartilage-bone complex specimens from 31 normal donors aged 16-83 years were tested in compression. The deformation was measured simultaneously in bone and cartilage to obtain the mechanical properties of both tissues. RESULTS: The stiffnesses and elastic energies of both cartilage and bone showed an initial increase, with maxima at 40 years, followed by a steady decline. The viscoelastic energy was maximal at younger ages (16-29 years), followed by a steady decline. The energy absorption capacity did not vary with age. Stiffnesses and elastic energies were correlated significantly between cartilage and bone. CONCLUSIONS: The present study demonstrates that similar age-related trends were seen in cartilage and bone, as if they behaved as a single mechanical unit. RELEVANCE: The basic information presented here on the mechanical properties of cartilage and bone and the correlations between them reveals the unit function of both tissues that are of importance for the understanding of the etiology and pathogenesis of degenerative joint diseases, such as arthrosis.

Heterotopic bone formation after total hip arthroplasty in patients with primary or secondary coxarthrosis.

Heterotopic bone formation was investigated in 392 Charnley low-friction total hip arthroplasties. A multivariate linear regression analysis was used to account for the influence of co-variables: sex, age at surgery, postoperative treatment with antiinflammatory drugs during at least the first 2 weeks, and previous ipsilateral hip surgery. A total of 232 hips had been treated for primary coxarthrosis, and 114 and 46 hips for secondary coxarthrosis due to congenital dislocation and fracture-dislocation of the hip, respectively. None of the hips with primary coxarthrosis previously had ipsilateral hip surgery, whereas 41 hips (36%) in patients with congenital dislocation of the hip and 28 hips (61%) in patients with fracture-dislocation of the hip had one or more ipsilateral surgical procedures prior to the arthroplasty. The sex ratio varied between the groups, with a male:female hip ratio of 1:1, 1:10, and 3:1 for the three groups, respectively. The risk of developing grades 2 or 3 heterotopic ossification after total hip arthroplasty were significantly higher in men, patients without postoperative treatment with antiinflammatory drugs, and patients above age 60. In contrast, the analysis documented that previous ipsilateral hip surgery and type of coxarthrosis did not influence lesion development, supporting the theory that a systemic, rather than local factor, is responsible for the development of heterotopic bone formation after total hip arthroplasty.

Changes in the stiffness of the human tibial cartilage-bone complex in early-stage osteoarthrosis

Cylindrical human tibial cartilage-bone unit specimens were removed from 9 early-stage medial osteoarthrotic (OA) tibiae (mean age 74 years) and 10 normal age-matched tibiae (mean age 73 years). These specimens were divided into 4 groups: OA, lateral comparison, medial age-matched, and lateral age-matched and were tested to 0.5% bone strain with a novel technique to obtain the stiffnesses of both cartilage and bone simultaneously. We found a pronounced reduction in the stiffnesses of OA cartilage and subchondral bone when compared with the medial age-matched group. OA cartilage was significantly thinner than that of the lateral comparison and the medial age-matched control groups. However, this reduction in thickness was not correlated with the reduction in stiffness for OA cartilage. The stiffnesses did not correlate between OA cartilage and bone, whereas the stiffness relationships between cartilage and bone remained significant in the three control groups. Our findings suggest that both cartilage and bone in early-stage OA are mechanically inferior to normal, and that OA cartilage and bone have lost their unit function to mechanical loading.