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Biomedical subjects

H A Jacob

Publications and source records attributed to H A Jacob.

At least 55 records · Page 3Linked to original sources
PubMed1980

The mechanical response of the neural arch of the lumbosacral vertebra and its clinical significance.

To investigate the effect of mechanical stresses in the aetiology of spondylolisthesis a study of the behaviour of the lumbar spine under load has been carried out. The loading tests on the lumbo-sacral segment, both with and without the dorsal elements present, showed that generally the disc only transmitted axial loads whereas transverse loads are resisted by the dorsal processes. Only after simulating a spina bifida, by splitting the lamina, was it possible to initiate a fracture in the isthmus by means of force applied in the transverse direction. Measurement of the stress behaviour in the neural arch shows that with transverse loading alone the pedicle can be just as heavily stressed as the pars interarticularis. Strain gauge measurements were performed on a macerated fifth lumbar vertebra to determine the manner in which loading forces must act to provide the greatest effect upon the region of the pars interarticularis. This was found to occur with vertical loading of the hyperextended spine. The vulnerability of the vertebra under these conditions was confirmed with further tests upon fresh cadaver specimens when it was found that the pars interarticularis of the fifth lumbar vertebra, when impinged upon by the caudal joint edges of the fourth lumbar vertebra, could be fractured with a vertically applied load of about 200 kp.

Humans↗
PubMed1980

A new approach towards hip-prosthesis design.

A new femoral prosthesis with a stemless design, different from conventional types, has been conceived in an effort to preserve the physiological stress distribution in magnitude and direction within the living bone as far as possible. The most important feature is that the hip joint forces are transmitted directly to the cortical bone of the resected femoral neck by means of a thrust plate, which maintains the physiological stress an the proximal end of the femur. The prosthesis, the instruments required for its implantation and the surgical technique are described in detail. Up to now, 3 patients have received this new prosthesis.

Hip Joint↗
PubMed1979

Histomorphological investigations of coxa femoral ends following double-cup arthroplasty according to Freeman.

Of 20 shell prostheses inserted in cases of early coxarthrosis in our clinic during the period from mid-1976 to the end of 1978, three had to be removed. Morphological examinations, employing different techniques, were made of the coxa femoral ends which were removed. The foreign body reaction of the bone tissue beneath the cement within the prosthetic shell and the biomechanical response were investigated on the basis of macroscopic and microscopic structural analyses. Dependent upon the time elapsed, the exposed spongiosa surface was observed to have become remodeled to a thin cortical protective layer. Independent of time between insertion and removal of the prosthetic shell, a continuous wide layer, consisting of cellular and fibrous tissue, was formed between the bone and the cement (which remained intact) even after the formation of the above-mentioned cortical bone substrate.

Adult↗
PubMed1979

[Comments on the double-cup hip endoprosthesis according to Freeman (author's transl)].

Histological examinations (including tetracycline labelling) of preparations of the neck of the femur which had to be removed 1 1/2, 3 and 14 1/2 months subsequent to double-cup arthroplasty according to Freeman, prove that the bone tissue can remain vital under the solidly cemented metal cup. A thick layer of connective tissue with bundles of collagenous fibres running parallel to the surface, is temporarily formed between the cement layer and the prepared spongiosa of the neck of the femur. It is possible that this layer of connective tissue is replaced within about a years' time by a thin, lamellar cortex layer, which is then covered only by a thin layer of connective tissue which is rich in fibres. Below this layer, the spongiosa spaces are definitely widened and filled with fibrotic fat marrow; vascularisation decreases, whereas osteoporosis increases.

Adult↗
PubMed1978

[Biomechanical analysis of the loosening of the femur prostheses (author's transl)].

A comparison of the stresses determined in an expoxy model of the human femur both with and without an intramedullary endoprosthetic replacement indicates how loosening of the implant could occur due to inappropriate mechanical loading of the bone. The stress pattern explains the manner in which the prosthesis stem is loaded and also indicates how hip-joint forces are transmitted from the prosthesis to the bone. The results obtained were verified by strain measurements on prostheses implanted within fresh human cadaver femora.

Biomechanical Phenomena↗
PubMedDate not supplied

[Stiffness of the AO spinal external fixator. Experimental results of stiffness of the AO spinal external fixator with 3 different pedicle screw systems].

The stiffness of the AO external pedicular fixator was analysed in an experimental laboratory study using three different sets of pedicle screws and different configurations of the implant. The experiments were performed with a wooden model as well as with bi-segmental human lumbar spine specimens with disc and ligaments intact. The capacity of the AO external pedicular fixator to compensate axial load, transversal- and torsion forces was compared to physiological requirements. Of particular interest was the effect of preload on the axial stiffness. It is demonstrated that the axial stiffness of the AO external pedicular fixator is so low that the axial load on the lumbar spine level in humans cannot be influenced by the fixator even when preloaded. However the resistance against torsion and transversal slipping is probably higher than required in vivo. No significant differences were found between the three types of pedicular screws. The effect of the triangular counter nuts of the AO external pedicular fixator on the transversal- and torsion stability was important. The presented results suggest that the AO external pedicular fixator can be of significant value in segmental rotation- and translocation pathologies of the lumbar spine and that the effect of isolated segmental distraction has probably been overestimated.

Bone Screws↗
PubMedDate not supplied

[Synergism between joint mechanics and stump muscles in upper leg amputees. Arguments for a myotenodesis of the greater adductor muscle].

Stance- and swing-phase control of AK prostheses due to the development of new knee joint mechanics has been frequently discussed in the recent past. The functional anatomical principles of the thigh muscles will be presented, including the results of the most recent neurophysiological and biomechanical investigations. These conclusions lead to the discovery of obvious consequences in the modification of the above-knee amputation technique such as the fitting of AK prostheses.

Amputation, Surgical↗
PubMedDate not supplied

[The self-locking Balgrist hip socket for cement-free fixation--history of its development and clinical experience to date].

In March, 1981, development of a hip socket for implantation without the use of bone cement was begun in the Biomechanics Research Laboratory of the Department of Orthopaedic Surgery of the University of Zurich, Balgrist. Already in March, 1982, the first artificial socket with selflocking action, the Balgrist Hip Socket, was successfully implanted in a patient. Following some design modifications, a series of 287 hip sockets were implanted before April, 1986; all of them being made entirely of high density polyethylene. In an attempt to improve the anchoring of the prosthesis within the bone, the outer surface of polyethylene that faced the bone was furnished with a thin coating of titanium and in this form the socket was used 63 times. In the meantime, a model with the outer split shell made of titanium was designed so that in this presently used form, from November, 1987, up to August, 1989, 133 of these hip sockets have been implanted. With the removal or replacement of only 29 sockets, which amounts to 6% (2.7% aseptic and 0.8% septic loosenings, 1.3% removed because of technical mistakes made in the early stages, and 1.3% removed because of suspected low grade infection) the results up to now might well be considered most encouraging.

Acetabulum↗
PubMedDate not supplied

[Mobility of the sacroiliac joint in vitro].

A photogrammetric method was used to measure the range of motion of the iliosacral joint in a two-dimensional in-vitro model. The results were compared with values reported in the literature. The influence of morphological and histopathological parameters was simultaneously studied on the same objects. This method which does not use radiation or metal implants leads to comparable values. Three-dimensional in-vivo studies using similar photogrammetric methods can achieve the required accuracy in a less invasive way.

Adult↗
PubMedDate not supplied

[The Balgrist hip cup--a 4-to-10-year survival analysis of cement-free hip cups].

The results of 715 cement-free acetabular sockets used in primary total hip arthroplasties are shown according to a survivorship analysis after Kaplan-Meier. The survival probability of the examined cement-free polyethylene sockets after 5 years lies between 88.1% and 93.6% (Endler screw socket of polyethylene: 93.6%; Balgrist socket of polyethylene: 88.1%; Balgrist socket of polyethylene with titanium coating: 90.6%). The survival probability of the Endler socket after ten years is only 44.2%. No statistically significant difference in the survival curves of the polyethylene socket models could be found (p logrank 0.797). The Balgrist sockets with the outer split ring made of titanium show a far better survival rate (98.8% after 4 years) than those made of polyethylene. This result justified the further development of a Modular Revision socket made of titanium so that the original idea could be extended to revision interventions where large acetabular defects have to be coped with.

Acetabulum↗
PubMedDate not supplied

[Freeman's double-cup total hip endoprosthesis. Clinical results and biomechanical studies].

From July 1976 up to the end of 1979 forty-three Double Cup hip replacements of the Freeman type were implanted in thirty-seven patients at the Department of Orthopaedic Surgery, Balgrist, of the University of Zurich. Now, four to seven years after implantation, 15% of early complications have developed and only 25% of all the hips are free of pain. Radiographically, every second femoral cup shows migration of about 2 mm. pro year at an average. Clinical and radiographical investigations, as well as biomechanical experiments and calculations show the possible reasons for the unsatisfactory results. Subsequently, we are now very cautious when considering the indications for the implantation of Double Cups.

Adult↗
PubMedDate not supplied

[Erosion with loosening of an aluminum oxide ceramic acetabulum. Case report].

The arthrodised hip of a 52 year-old female patient that had been absolutely trouble free for 9 years was remobilised by implanting a Mittelmeier, Autophor prosthesis (Al2O3 socket, Al2O3 head). Two years later, the hip joint had to be revised because of loosening of the socket. Since the shaft of the prosthesis was still firmly anchored within the femur, only the socket und the head were replaced. About three years following this revision, signs of loosening of the acetabular component again developed. Finally 4 1/3 years after the first revision (6 1/3 years after primary implantation) the hip was again revised. A polyethylene socket was then cemented into an acetabulum supporting shell and the prosthesis shaft furnished with a ceramic head of 32 mm diameter. Possible disadvantages of ceramic-ceramic bearing surfaces in patients with an altered bone structure of the pelvis and with a high risk of subluxation, due to weakened pelvi-trochanter muscles, are discussed.

Acetabulum↗
PubMedDate not supplied

[Biomechanics of the metatarsophalangeal joints].

Koehler-Freiberg's disease is found to most commonly manifest itself in the metatarsal head of the second ray. Occasionally it is observed to occur in the metatarsal head of the third and less commonly it is seen to appear in the other rays of the foot. An investigation into probable causes of the disorder calls for consideration of the biomechanical conditions in the region of the metatarsophalangeal joints. A review of the literature pertaining to this matter has failed to reveal any detailed information in this respect and therefore a series of experiments have been conducted involving determination of a) the ground force under the metatarsophalangeal joints and under the toes in normal barefoot walking b) the direction of the flexor tendons and such others that cross the joint and that might play an important role in exerting force between the toes and the ground, c) the geometry of the articulating surfaces and d) the forces that act between the metatarsal head and the corresponding phalangeal joint surface. It is shown that the specific loading of the MP-II joint (due to forces acting across the joint) could amount to nearly twice that to which MP-I is subjected to. This might explain the more frequent occurrence of osteonecrosis of the second metatarsal head as compared to that observed within the head of the first. Furthermore, the direction of the joint resultant force in the MP-II joint is seen to be more dorsally inclined than that in MP-I, which agrees well with clinical findings regarding the site of localized lesions. Lastly, a hypothesis which still requires closer investigation is presented to explain the development of the bone lesions that are known to occur just below the subchondral cortex.

Biomechanical Phenomena↗