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Biomedical subjects

F J Kummer

Publications and source records attributed to F J Kummer.

108 records · Page 6Linked to original sources
PubMed1981

Biological effects of magnetic fields generated with CoSm magnets.

Experiments were conducted to determine whether any observable short-term biological effects were caused by a static magnetic field created with CoSm magnets similar to those used in the elbow prosthesis described on pages 69-80. Tissue culture studies of several cell lines showed no obvious effects on cell growth rate, morphology, or the ability to grow and remain confluent; and no deleterious effects of the magnetic field were evident as a result of an in-vivo study of wound and bone healing in rats. Long-term effects, if any, have yet to be determined.

Animals↗
PubMed1979

An uncemented total hip replacement: experimental study and review of 300 madreporique arthroplasties.

Mafreporique arthroplasty is not intended as a bustitute for acrylic cement stabilized arthroplasty but is available as an effective alternative. An experimental and clinical investigation including radiological analysis of 300 madreporique arthroplasties has convinced us of the reality and reliability of biological anchoring by endosteal osteogenesis. The madreporique method does not result in any local or general complications usually associated with the cement technique. Full weight-bearing is permitted at the same postoperative time as the cemented prosthesis. The results at early and interim follow-up periods compare favorably with cemented hip arthroplasties. Living bone that undergoes remodelling provides for long-term anchor of the prosthesis and eliminates the chemical intermediary which leads, more or less, with time to loosening of the implant in a significant number of cases.

Aged↗
PubMed1976

Studies of the corrosion susceptibility of metallic cement restrictors: comparative corrosion behavior of stainless steel and cobalt-chromium alloys.

Passive film and accelerated corrosion tests were performed on both wrought AISI 316L stainless steel and wrought Vitallium (Haynes Stellite 25) Charnley Type cement restrictors. The morphology and incidence of corrosion at the wire-wire crevices and the methacrylate-metal crevices were determined by scanning electron microscopy. The results are interpreted in view of the previously-documented crevice corrosion susceptibility of these two alloys.

Bone Cements↗
PubMedDate not supplied

Interobserver reliability of acromial morphology classification: an anatomic study.

One hundred ten acromial anatomic specimens were classified by three shoulder surgeons with the classification system described by Bigliani et al. to determine the interobserver reliability. These results demonstrated a fair to poor level of interobserver reliability. Given this relatively low level of agreement, the diagnosis of impingement and rotator cuff tears should be based on clinical findings supplemented, when indicated, by rotatory cuff imaging with less diagnostic reliance placed on the assessment of acromial morphology.

Acromion↗
PubMedDate not supplied

The influence of acromioclavicular joint morphology on rotator cuff tears.

A detailed anatomic study of 123 shoulders was performed to define the location of the acromioclavicular (AC) joint within the supraspinatus outlet and to determine the correlation of AC joint morphologic characteristics with the presence of full-thickness rotator cuff tears (RCTs). The presence, location, and extent of RCTs were first documented for each shoulder, and 2 anatomic landmarks consisting of the anterolateral acromial corner and the inferior midpoint of the AC joint were identified and their positions digitized in 3 dimensions to calculate outlet space and clearance and AC joint locations. High resolution x-ray films were then obtained to determine the extent of degenerative changes including the location and size of inferior osteophytes and joint space. These specimens were cleaned of all soft tissues, and additional measurements were made. All data were entered into a computerized database and analyzed with respect to age, sex, and the presence of RCT. Comparison of age-matched RCT versus non-RCT groups revealed no significant differences in the position of the AC joint within the supraspinatus outlet. When AC joint morphologic characteristics were compared with those of a nontear, age-matched group, no significant differences with regard to joint space narrowing were found, but significantly larger and greater number of osteophytes were identified on both sides of the joint in the RCT group. In conclusion, the position of the AC joint is fairly constant within the supraspinatus outlet and does not appear to predispose to RCTs. The morphology of the AC joint contribution of the tears seems to be acquired in nature rather than inherent in its location within the outlet.

Acromioclavicular Joint↗
PubMedDate not supplied

The use of the bicipital groove for alignment of the humeral stem in shoulder arthroplasty.

Four hundred twenty humeri were measured to determine humeral head retroversion and its relation to the location of the bicipital groove. Average head retroversion was found to be 28.3 degrees (+/- 13.2 degrees), and the angular orientation of the bicipital groove referenced to the transepicondylar axis was 55.5 degrees (+/- 13.8 degrees). The average difference between these angular orientations was 27.3 degrees (+/- 14.2 degrees). This result implies that the bicipital groove can be used as a landmark for prosthetic stem positioning in shoulder arthroplasty if the center of the lateral aspect of the stem is posteriorly offset approximately 30 degrees from the center of the groove. However, because of the appreciable variation in these averages, the use of the bicipital groove as a reference can result in a significant error of humeral stem alignment, which should be considered when determining the retroversion for a particular patient.

Aged↗
PubMedDate not supplied

A simple technique for assessing heel contact in orthoses.

Orthoses are used by patients with neuromuscular disorders to control their ankle and foot position. Heel contact inside an orthosis is difficult to determine. A simple, inexpensive device was constructed that could be positioned between the heel and the inside of the orthosis. It consists of a thin, single-cell pressure sensor connected to a low-cost, digital multimeter. The resistance reading was used to determine the presence or absence of heel contact during a controlled standing protocol. The device was evaluated in 23 patients. The majority of patients did not weightbear on their heels. The heel contact of five patients was reassessed by using a computerized F-scan system, which determines plantar weightbearing forces. A 100% agreement was found between the single-cell sensor and the F-scan system. This single-cell sensor is a simple, inexpensive, and easily used device to determine the presence or absence of heel contact within an orthosis.

Equipment Design↗
PubMedDate not supplied

Internal fixation of femoral neck fractures with posterior comminution: a biomechanical study.

OBJECTIVES: This study was performed to determine whether four cancellous lag screws provide significantly improved rigidity and fixation strength compared with three screws for fixation of displaced femoral neck fractures with posterior comminution. DESIGN: Biomechanical cadaver study. INTERVENTION: Eight pairs of mildly osteopenic femurs were selected, and each pair was fixed with three or four cancellous lag screws (randomly assigned) after the creation of a simulated femoral neck fracture with posterior comminution. A separate comparison with an unmatched group of six similar femurs with a simulated femoral neck fracture without posterior comminution and instrumented with three screws was performed to investigate the effect of posterior comminution. MAIN OUTCOME MEASUREMENT: The specimens were non-destructively tested to determine fixation rigidity in axial and anterior loading. Cyclic axial loading was then performed for 10,000 cycles; the femurs were retested for rigidity and finally were axially loaded until failure. RESULTS: The femurs with a posterior defect stabilized with three screws had significantly less resistance to axial and anterior displacement and sustained significantly lower axial loads to failure than those stabilized with four screws. The specimens instrumented with three screws without a posterior defect exhibited greater resistance to displacement in anterior loading and sustained greater axial loads to failure than those with a posterior defect stabilized with three screws. CONCLUSION: This study suggests that there are benefits to using four screws for fixation of femoral neck fractures with posterior comminution.

Biomechanical Phenomena↗
PubMedDate not supplied

Schuhli augmentation of plate and screw fixation for humeral shaft fractures: a laboratory study.

OBJECTIVES: Schuhli locking nuts provide a mechanism to lock 4.5-millimeter bone screws to a standard dynamic compression plate (DCP plate). It has been proposed that Schuhlis can provide increased fixation stability in areas of a proximal cortical defect or osteopenic bone and may keep screws from loosening and backing out from the plate. A biomechanical study was performed to investigate the effect of Schuhli augmentation of a ten-hole broad DCP plate for fixation of a simulated humeral shaft fracture versus standard DCP plate fixation. DESIGN: Biomechanical cadaver study. INTERVENTION: Six pairs of cadaveric humeri from elderly individuals were tested in offset axial loading, torsion, and four-point bending to obtain load versus deformation curves and baseline mechanical properties. Each pair of humeri was then instrumented with a ten-hole broad DCP plate on one side and a DCP plate augmented with Schuhlis at each screw hole on the contralateral side. All screws were placed in cortical bone. The constructs were retested in all three modalities. The humeri were then cycled in torsion for 1,000 cycles and retested in all three modalities. Each humerus was then loaded to failure in torsion to determine the ultimate load and rotational displacement. MAIN OUTCOME MEASUREMENTS: Resistance to displacement was determined from the load versus deformation curves in each testing modality before and after cycling; these data were normalized to the intact values determined prior to instrumentation. Paired Student's t tests were performed to determine statistically significant differences between the two modes of fixation. RESULTS: There were no significant differences in stability between the two fixation techniques in all three testing modalities both before and after cycling. However, the Schuhli augmented constructs sustained significantly greater loads and rotational deformations prior to failure. CONCLUSIONS: In this model of humeral shaft fractures in the elderly, the addition of Schuhlis did not significantly change the mechanical stability of plate and screw fixation. However, load and angular deformation at failure were significantly greater in the Schuhli augmented specimens.

Aged↗
PubMedDate not supplied

Fixation of periprosthetic femoral shaft fractures: a biomechanical comparison of two techniques.

OBJECTIVE: To determine which of two currently used techniques for the treatment of periprosthetic femoral shaft fractures provides the greater fixation rigidity and strength. DESIGN: A laboratory study using six matched pairs of femurs. METHODS: Embalmed femur prosthesis constructs had a simulated periprosthetic fracture created and were fixed with a plate with proximal cables and distal bicortical screws (Ogden concept) or two allograft struts and cables. Fixation stability was compared in various loading modalities before and after cycling. They were then tested to failure. OUTCOME MEASUREMENTS: Fixation rigidity was defined as the ratio of applied load to the amount of displacement at the fracture. RESULTS: In all loading modalities, the Ogden construct was more rigid than the allograft strut fixation. The Ogden construct required 1,295 newtons for failure and the allograft strut fixation required 950 newtons (p < 0.05). CONCLUSION: The Ogden construct provided a more rigid and stronger initial fixation of a periprosthetic fracture than did the allograft construct.

Arthroplasty, Replacement, Hip↗
PubMedDate not supplied

Alternative bearing surfaces for total joint arthroplasty.

The biologic response to polyethylene particulate debris generated from metal-on-polyethylene bearing surfaces is thought to be largely responsible for periprosthetic osteolysis and aseptic loosening in total joint arthroplasty. As a result, there has been an interest in developing polyethylene with improved wear characteristics, as well as a renewed interest in alternative bearing surfaces for total joint arthroplasty, including ceramic-polyethylene, metal-metal, and ceramic-ceramic articulations. These alternative surfaces have demonstrated less friction and lower wear rates than metal-on-polyethylene bearing surfaces in both clinical and laboratory experiments. Clinical results, although only short- to mid-term, have been encouraging. Alternative bearing surfaces, with lower wear rates and less particulate debris formation, may have the potential to improve total joint arthroplasty survivorship by decreasing periprosthetic osteolysis, especially in younger, high-demand patients.

Arthroplasty, Replacement, Hip↗
PubMedDate not supplied

Effect of piriformis versus trochanteric starting point on fixation stability of short intramedullary reconstruction nails.

Recently, a new, shorter IM nail using two 6 mm reconstruction screws for proximal fixation was introduced in two versions for femoral insertion: piriformis fossa (FAN) and greater trochanter (TAN). These nails were compared experimentally for their fixation stability, proximal load transmission, and failure strength in an unstable intertrochanteric fracture model in cadaveric femurs. Vertical and axial loads were first applied to the intact femurs. Fractures were created, subsequent fixation applied, and the femurs underwent a series of both vertical and axial loading tests. There was no significant difference in strain readings between the nails for either axial loading or cyclical loading. There was no statistically significant difference between the loads to failure for the trochanteric nails and the standard antegrade nails. The average ultimate loadfor the FAN and TAN nails were 3010 N and 2830 N respectively. These two nails performed very similarly throughout our testing.

Biomechanical Phenomena↗
PubMedDate not supplied

The effect of screw type on the fixation of depressed fragments in tibial plateau fractures.

The ability of various screw types to stabilize depressed tibial plateau fractures was determined in a biomechanical study using a Sawbones model. Two sizes of both cancellous and cortical screws were evaluated for both supportfrom below and through the depressed fragment. As a general trend, cancellous bone screws provided a greater resistance to fragment displacement than cortical bone screws, and screws with a smaller thread diameter provided greater resistance to displacement than screws of the same thread type with a larger diameter. These results agree with the accepted standard that cancellous screws provide better fixation for tibial plateau fractures, but also are counterintuitive in that smaller screws provided greater fixation than larger screws of the same type.

Analysis of Variance↗
PubMedDate not supplied

The effect of distal screw orientation on the intrinsic stability of a tibial intramedullary nail.

To compare the intrinsic stability of two distal interlocking screw orientations for tibial nailing of distal third tibial diaphyseal fractures without isthmal support, six Depuy (Warsaw, Indiana) tibial intramedullary nails were implanted in simulated distal tibiae. The constructs received both two parallel (medial to lateral) and two perpendicular (one medial to lateral, one anterior to posterior) distal interlocking screws in a random order Angular, translational, and torsional displacements of the nails were measured in response to 70 N proximal applications of anterior, posterior, medial, and lateral loads, and a 7.7 Newton-meter torsional load. There were no differences in medial or lateral angulations between the screw orientations (average: 2.5 degrees, p > 0.8). Angulation in the sagittal plane (anterior and posterior) was slightly less for parallel screw fixation (1.6 degrees versus 2.4 degrees), but this was not statistically significant (p > 0.1). Rotational angulation was higher in the parallel (average: 9.9 degrees) versus the perpendicular (average: 8.1 degrees) screw orientation, but these results were not statistically significant (p > 0.1). Pure translation did not occur in either the parallel or perpendicular screw orientations. These results indicate that fixation stability of these tibial intramedullary nails is not significantly influenced by distal interlocking screw orientation in response to sagittal, coronal, or rotational forces.

Bone Nails↗
PubMedDate not supplied

The effect of immobilization devices on the load distribution under the foot.

The load distribution under the foot was investigated under various conditions by means of pressure-sensitive transducers. Weight-bearing pressures at the first and third metatarsal heads and at the heel were measured while subjects ambulated barefoot and while wearing numerous immobilization devices. The proportion of body weight imposed on the plantar surface of the foot is dependent on the specific gait pattern displayed during barefoot walking. Maximum reduction of forefoot loads was achieved by means of a short-leg walking cast or an ankle boot cast with a posteriorly placed flat rubber heel. A centrally placed rocker heel leads to increased forefoot loads, especially under the first metatarsal head. Casting devices used in conjunction with cast shoes were not as effective in pressure reduction as the same cast with a posteriorly placed heel, but they were more effective than the rocker heel. The height of the cast and configuration of the sole of the cast shoe had little effect on the observed patterns of force distribution. The wooden-soled post-operative shoe did decrease weight-bearing pressures as compared with barefoot walking and casts with a rocker heel but was less effective than the other devices studied. Peak loads measured at the sole of the foot were dependent on the position of the ankle and subtalar joints at the time of cast application.

Adolescent↗
PubMedDate not supplied

Biomechanical determination of the optimal number of fixation screws for the sliding hip screw plate.

Laboratory measurement of the tensile forces on the plate fixation screws of the sliding hip nail demonstrated that most of the force is borne by the proximal three screws in an intertrochanteric fracture model. Testing of an intact femur, which simulate a healed femur, demonstrated a proximal shift of the screw forces. Four screws appear adequate for fixation if screw torque is controlled.

Biomechanical Phenomena↗