J. C. Mulier

The mechanical characteristics of cancellous bone at the upper femoral region

Mechanical behaviour of trabecular bone at the upper femoral region of human bones has been studied by compression tests on trabecular bone specimens removed from normal femora obtained at autopsy. Compression tests were performed along three different axes of loading on wet specimens and high loading rates. Femoral head specimens proved to be the strongest for any axis of loading. Large variation in compressive strength and modulus of elasticity is seen within and between femoral bone samples. Anisotropy and differences in anisotropy for the different regions have been observed. A significant correlation between mechanical properties (sigma max - E) and bone mineral content of the specimen was found. Tests on whole bone structures demonstrate that removal of the central part of the trabecular bone at the proximal femur reduces the strength for impact loading considerably (+/- 50%).

Patellar tendinitis (jumper's knee)

A jumpers knee is an overload lesion of patellar or quadriceps tendon near its insertion at the lower or upper pole of the patella. If conservative treatment fails, an operation can be performed in Phase 3 where disabling symptoms, are present. The necrotic tissue in the patellar tendon is excised. The early results of this surgery are encouraging.

Comparison of conservative and operative treatment of Achilles tendon rupture

The surgical repair of a ruptured Achilles tendon has been the generally accepted method of treatment for the last decade. A controversy has arisen more recently since the conservative treatment has been advocated by Lea and Smith in 1968.1 Conservative treatment has also been recommended by Gillies and Chalmers and others.2,3 3 In contrast to earlier publications on conservative treatment4--6 when rest, taping, or short periods of casting were applied, it is based today upon the results of animal experimentS7, 8 and the better management of casting.1-3 Clinical data and objective assessment of the results comparing both methods are scanty and the conclusions on the treatment of choice are contradictory. 2, 4· 9

Chronic leg pain in athletes due to a recurrent compartment syndrome

A series of 29 patients, all engaged in sports activity on a regular basis, suffering from recurrent compart mental syndrome, is reported. The syndrome is not restricted only to long distance runners but to athletes involved in a variety of sports activities (soccer, volley ball, cycle racing, gymnastics, judo, physical education, and long distance running). Although most patients presented activity-related leg pain, some patients mainly complained of ankle weakness and recurrent ankle distortions at fatigue. The wick catheter technique proved to be most useful to determine which compartments were involved. The severity of clinical symptoms correlated highly with the anomalies of the tissue pressure measurements. The predominance of deep posterior compartment and mul tiple compartment involvement are in contrast with most previous reports. Conservative treatment was unsuccessful in every patient, whereas surgical de compression of the involved compartments yielded fa vorable results in those cases where all the involved compartments were released.

The mechanical behaviour of intracondylar cancellous bone of the femur at different loading rates

The compressive properties of human cancellous bone of the distal intracondylar femur in its wet condition were determined. Specimens were obtained from six cadaveric femora and were tested at a strain rate of 0.002, 0.10 and 9.16 sec−1. It was found that the compressive strength decreases with an increasing vertical distance from the joint. The highest compressive strength level was recorded in the posterior medial condyle. Correlations among the mechanical properties, the bulk specimen density and the bone mineral content yield (i) highly significant correlations between the compressive strength and the elastic modulus (ii) highly significant correlations between the compressive strength or the modulus of elasticity and the bulk specimen density (iii) a doubtful correlation between the compressive strength and the bone mineral content. All recorded graphs of the impact loaded specimens displayed several well defined stress peaks, unlike the graphs recorded at low loading rates. It can be concluded that upon impact loading the localized trabecular failure which is associated with each peak, does not affect the spongy bones stress capacity in a detrimental way.

The mechanical characteristics of the long bones of the lower extremity in torsional loading.

Abstract Human femoral and tibial whole bone specimens have been subjected to torsional loading at high strain rates. Torque versus angular deflection were recorded. Strain energy before fracture and torsional stiffness were calculated, and the following mean values obtained. Mean torsional stiffness for femoral bones: 562 Nm/r and for tibial bones: 101 Nm. Mean maximum torque for femoral bones: 183 Nm and for tibial bones: 101 Nm. Mean ultimate deflection: 20° for femoral bone specimens and 23°7 for tibial bone speciments. Mean energy absorption for femoral bone specimens: 35 joule and for tibial bones: 25 joule. A high variability of these mechanical parameters had been observed. It is postulated that the variation in geometry of the bone structures accounts for the variation of the mechanical behaviour of bony structures.

Recurrent dislocation of the peroneal tendons: Results of rerouting the tendons under the calcaneofibular ligament

Nine patients (11 cases) with recurrent dislocation of the peroneal tendons who were treated by surgically rerouting the tendons under the calcaneofibular liga ment were reviewed. Mean follow-up time was 30.5 months. An excellent or good result was obtained in all cases. This operative technique was previously de scribed in 1975, by Sarmiento and Wolf, in a case report.

Identification of In-Vivo Vibration Modes of Human Tibiae by Modal Analysis

When attempting to evaluate the mechanical properties of human bones in vivo by mechanical vibration analysis, some essential requirements must be met. A quantitative relation between measured vibration parameters (e.g., natural frequency) and mechanical bone properties must be available, in-vivo vibration modes should correctly be identified and the associated natural frequencies reproducibly and accurately measured, the influence of joints and soft tissues must be known. These problems were addressed by modal analysis (i.e., experimental determination of natural frequencies, mode shapes and damping ratios) of human tibiae in the following situations: 1) dry excised tibiae, 2) fresh excised tibiae, 3) in-vivo tibiae, 4) tibiae in an amputated leg, in different steps of dissection. In the in-vivo measuring conditions used by the authors, the tibia vibration is practically free-free. Two single bending modes (at +/- 270 Hz and +/- 340 Hz, respectively), each of them corresponding with one principal direction for bending, were identified. The difference between the natural frequencies observed in vivo and those of fresh excised tibiae is almost completely caused by the effect of muscles (added mass and damping), whereas joints and skin play only a minor role. Frequency differences between fresh and dry excised tibiae are largely accounted for by the absence of bone marrow in the latter.

The geometrical properties of human femur and tibia and their importance for the mechanical behaviour of these bone structures

SummaryA series of non pathological human tibial and femoral bones have been tested in torsional loading at high strain rates.Elastic (torsional stiffness) and ultimate properties (Tmax) have been determined. A geometrical description of the individual bone structures has been performed by determination of the polar moment of inertia (assuming axial symmetry), variation of this parameter along the long axis of the bone and length of the specimen between the grips.A fairly accurate prediction of mechanical behaviour of bone structures could be obtained using these geometrical parameters.The high variation of elastic and ultimate properties of whole bone structures in torsional loading is primarily the result of the high variation of polar moment of inertia for the different bone specimens.

Experimental study on internal fixation of femoral neck fractures

The relative strength and the failure mode of internal fixation by multiple pinning and nailing was investigated on 35 specimens. Internal fixation consisted of 3, 5 and 7 Knowles pins, a Smith-Petersen nail or a sliding nail plate. The strength of a specimen with a triflanged nail is only half of that with multiple Knowles pins. There is no significant difference in strength of 3, 5, or 7 pin specimens. The strength of an internal fixation with a sliding nail plate is not superior to the strength of multiple pinning. The mode of failure for the different types of internal fixation is primarily a crush fracture of the supporting trabecular bone at the femoral neck with downward and outward migration of the pins or nail. Except with the fixation with 3 pins where an initial bending could be observed, failure is not a plastic deformation of the internal fixation device.