Kamal Bose

A cadaver study of the function of the oblique part of vastus medialis

Six normal cadaver lower limbs were mounted on a specially designed loading apparatus. Wires were used to simulate the five muscle bellies of the quadriceps, the ratio of their tensions having been determined from that of the anatomical cross-sectional areas of the muscles. A three-camera system was used to track the patella during knee movements from flexion to extension. The patellofemoral contact area was determined by pressure-sensitive film. The limb was loaded with and without tension on the wire which simulated the oblique part of the vastus medialis (VMO). Absence of VMO tension caused the patella to displace laterally (4.2 mm) and increased the load on the lateral patellar facet throughout the range of knee motion. When the tension on the wire simulating vastus lateralis was reduced by 40% to simulate the effect of a lateral release procedure, the abnormal kinematics caused by the absent VMO returned to normal.

Effect of femoral rotation on bone mineral density measurements with dual energy X-ray absorptiometry

Precision in femoral neck scans with dual energy X-ray absorptiometry (DXA) is affected by variability in positioning and subsequent repositioning of the femur for repeated scans. To study the in vitro effect of femoral rotation on the bone mineral density (BMD), four fresh-frozen cadaveric femurs were fixed in a specially designed jig which allows for rotation of the femurs. BMD measurements of the femurs were done in neutral position (0°) i.e., with the femoral neck axis parallel to the surface of the couch and at 15°, 30°, and 45° of internal and external rotation. In vivo precision of the femoral neck scan was determined in five normal male subjects. The scans were first done with the legs positioned using the manufacturers foot block. Five scans were performed, with repositioning, on the left hip of each subject. The procedure was then repeated with the legs positioned using a custom-designed positioning jig to minimize the rotation of the hips during a scan. In the in vitro study, the femoral neck BMD value was minimum at neutral position (0°) and increased when the femur was rotated internally or externally. In vivo precision error of the femoral neck scan was reduced by almost 50% with the use of the positioning jig when compared with the manufacturers foot block. Femoral rotation was shown to have a significant effect on BMD measurements, and proper positioning of the femur during a scan can improve precision significantly.

Effect of preservation medium on the mechanical properties of cat bones.

Mechanical properties of long cat bones after freezing at -20 degrees C and after storage in 10 percent buffered formalin were investigated. The right humeri and femora from 48 adult cats were divided into four groups: Groups 1 and 2 were stored in a freezer at -20 degrees C for 3 and 21 days, respectively, while Groups 3 and 4 were stored in 10 percent buffered formalin for 3 and 21 days, respectively. The control left bones were tested fresh. The humeri were subjected to a torsion test and the femora to a four-point bending test. Freezing had no effect on the mechanical properties evaluated, while formalin storage caused a 50 percent reduction in energy absorption and increased the brittleness of the bones.

Gait analysis study on patients with varus osteoarthrosis of the knee

Biomechanical changes that occur after high tibial osteotomy (HTO) was investigated in 30 patients with osteoarthrosis (OA) of the knee and 11 age-matched normal subjects. Of the 37 knees with varus OA evaluated, 21 were analyzed before and after surgery (average follow-up evaluation, two years). The mean age of the patient group was 58.2 years. Clinical assessment was based on the Hospital for Special Surgery (HSS) knee scoring system. Full-length weight-bearing radiograms were taken for the measurement of the mechanical axis of the lower limb. Results from clinical assessment showed that 90% of the patients had good or excellent postoperative clinical results, as opposed to 9.5% before surgery. An overall improvement in the gait parameters was evident in the group evaluated after surgery, although control levels were not attained. Further analysis based on moments about the knee showed that 57% of the surgically treated knees with good or excellent clinical results had abnormal load distribution. This may lead to deterioration in the future, and further surgery may be required. The abnormal loading was also reflected in the ground-reaction force vector diagram. Therefore, the force vector diagram can be used as a quick screening method to detect abnormal joint loading.

A biomechanical model to determine lumbosacral loads during single stance phase in normal gait

A dynamic biomechanical model to determine loads (joint forces) attained at the lumbosacral joint-centre during the stance phase of normal level walking was developed. The biomechanical model was based on rigid free body-segments; namely, the foot, shank, thigh, pelvis and head, arms and trunk (HAT) segments. In this biomechanical model, the forces and moments acting on the lumbar spine are derived from body-segment mass and movements of the trunk. These external forces and their moments must be equilibrated by internal forces, that is, contributions from the erector spinae or rectus abdominus muscle group, and abdominal pressures from within the trunk together with spine forces. Three-dimensional co-ordinate and ground-reaction force data were captured from five healthy young male subjects performing normal level walking in the motion analysis laboratory of the Department of Orthopaedic Surgery, National University of Singapore. These data were captured using the VICON motion analysis system. Both of these data sets were pre-processed, and together with relevant anthropometric parameters and physical measurements of the subject, were passed into the biomechanical model to compute the resultant loads at the lumbosacral joint-centre. The results of this study showed that the peak resultant loads at the lumbosacral joint-centre were between 1.45 and 2.07 times body-weight.

Biomechanical study on tibialis posterior tendon transfers.

Two methods are used to route the tibialis posterior tendon anteriorly to achieve dorsiflexion: (1) around the medial side of the tibia, or the subcutaneous route; and (2) through the interosseous membrane, or the interosseous route. This study determined the effect of site of tendon insertion on ankle and foot motions and compared the efficacy of both routes. Eleven fresh normal cadaveric legs were used. The detached tibialis posterior tendon was transferred anteriorly through the interosseous membrane and anchored to the first cuneiform along the first metatarsal axis by a barbed staple. The specimen was mounted on a mechanical testing machine. Tension was applied to the tendon and ankle and foot motions were measured. The experimental procedure was repeated with tendon insertion along the second metatarsal axis and serially through to the fifth metatarsal axis. The entire experiment was repeated using the subcutaneous route. The interosseous route was more effective in achieving maximum dorsiflexion with minimal pronation. Shifting the insertion medially caused supination, whereas a more lateral insertion caused pronation.

Effect of decalcification on bone mineral content and bending strength of feline femur

The relationships between bone mineral content (BMC), bone calcium, and bone strength were studied in fractionally demineralized feline femurs. In 44 pairs of cat femurs, the right bones were decalcified in ethylene diaminetetra acetic acid (EDTA) to 20%, 40%, 60%, 80%, and 100% of the mineral content of the intact left bone (=control). The bones were then loaded to failure, and maximum strength values were recorded. The data were then used to calculate the percentage strength of the right relative to the left femurs. A correlation coefficient (r) of 0.970 was found between the percentage decalcification and percentage bending strength. A direct relationship (r=0.876) was also observed between the total calcium extracted and total loss in BMC. The EDTA solutions were spot checked for protein content to determine if the organic matrices had been altered by demineralization. Protein was never detected. Nor did the demineralized tissues display histologic evidence of gross microscopic damage. This study has shown that in cat femurs, 20% decalcification led to about 35% loss in bending strength, and 60% decalcification caused 75% loss in strength. These values are significant as they highlight the importance of calcium to the strength of osteopenic bone.

The results of decompression of cord or cauda equina compression from metastatic extradural tumors.

The role of decompression in spinal metastases with neurologic deficit is controversial. This series demonstrates that the benefit from decompression depends on the nature of the tumor and the neurologic status of the patient. Prognosis is good for patients with incomplete paraplegia, intact sphincter control, a long duration of neurologic deficit and pain, and a gradual onset of compression. The prognosis is poor in cases with complete paraplegia, loss of sphincter control, a short duration of neurologic deficit and pain, and a sudden onset of compression. Surgery is not advocated for all cases, because many patients are already very ill. Surgery is recommended only for selective cases in which the prognosis is good. However, decompression is only palliative. Posterior decompression is preferred, inasmuch as the surgery is less extensive compared to anterior decompression and fusion.

Biomechanical study on axillary crutches during single-leg swing-through gait

This paper describes a kinetic and kinematic study on axillary crutches during one-leg swing-through gait. The primary objective is to evaluate the interplay of forces at the crutch and body interfaces and to relate them in the understanding of problems associated with the use of axillary crutches. Ten normal adult male subjects with simulated left leg impairment participated in the study. For data acquisition, the VICON kinematic system, a Kistler force plate and an instrumented crutch (with force transducers at the two upper struts close to the axillary bar and one near the crutch tip) were used. Results showed that the peak ground reaction force on the weight-bearing leg during lower limb stance increased by 21.6 percent bodyweight. The peak reaction force transmitted to the arm during crutch stancc was 44.4 percent bodyweight. These increased loadings could be detrimental to patients with unsound weight-bearing leg and upper extremities respectively. When the crutches were used incorrectly, 34 percent bodyweight was carried by the underarm. This could cause undue pressure over the neurovascular structures at the axillary region.

Healing of non-vascularised diaphyseal bone transplants. An experimental study

Four different experiments were performed to study the healing of a large, non-vascularised, diaphyseal, bone segment in adult cats. In the first experiment, a 4 cm segment of tibia with its periosteum was excised and replaced in its bed. The other experiments were similar, except that in the second, the periosteum of the segment was removed, in the third its medullary canal was blocked with a Silastic rod, and in the last group the segment was isolated from its muscle bed by a Silastic sheet. The reparative processes were quantified by estimating the resorption index, the cortical new bone formation index, the callus encasement index, and the osteocyte count. Bone resorption and apposition occurred in the segment even when the periosteum was absent or the medullary canal was blocked, with osseous union at both ends by eight to 12 weeks, provided the segment was not isolated from its muscle bed. Thus, the muscle bed played a significant role in these reparative processes.