Biomedical subjects
Publications and source records attributed to F J Kummer.
Although device failure in intramedullary (IM) nailing of subtrochanteric fractures is uncommon, breakage of the nail can occur. Following a review of the literature on this subject, a case is reported that illustrates the surgical and biomechanical factors that can lead to nail failure.
Five cats underwent a 3.0-cm removal of their ulnar nerves followed by delayed repair. One limb received a standard cable grafting procedure, and the other side had the proximal nerve stump lengthened by controlled distraction and a subsequent direct anastomosis. Histological examination of the lengthened nerves revealed better quality than the grafted nerves in all cats. Nerve conduction velocity of the lengthened side was greater than the graft side in three cats. It appears that this technique of nerve lengthening and direct repair might have clinical applicability.
Cyclic loading of Ti-6-4 and Co-Cr-Mo (cast) test samples with grit-blasted or waffle-textured surfaces coated with a plasma-sprayed 50-mum HA layer was performed in air, Ringer's solution (5% dextrose), 0.9% NaCl (Tris buffer, pH 7.40), and balanced Hank's solution. Maximum interfacial stresses in bending of 40 ksi (280 MPa) and 20 ksi (140 MPa) were utilized, and the specimens tested to 10 6 cycles at 5 Hz with a MTS servohydraulic machine. Tested samples were examined by optical microscopy to determine coating integrity and thickness and by scanning electron microscopy (electron backscatter mode and EDAX) to determine surface morphology and chemical changes. The following observations were made: (1) Samples cyclically tested in solutions showed a general thinning of the coating, accentuated in the higher-stressed regions. (2) Samples tested with an equivalent static load in the solutions did not show this centralization. (3) Bare metal interface surfaces were noted on most of the edges of highly stressed central specimen regions, in several entire central regions, and on the upper surfaces of some of the waffled samples. (4) The specimens tested in Ringer's solution (pH 4.70 initially) demonstrated the most dramatic coating deterioration. (5) The coatings on titanium appeared more stable than these on Co-Cr as tested in all solution environments for both surface types. The HA coating evaluated in this experiment demonstrated increased instability when cyclically loaded in in vitro solutions of lowered pH and depleted cations (Ca 2+) at stress levels of 280 MPa.(ABSTRACT TRUNCATED AT 250 WORDS)
Mechanical tests were performed to characterize the initial stability of press-fit cups as a function of cup design, surface structure, and surgical preparation. Eight cups from six manufacturers were press-fit into acetabular cavities prepared in two densities of Sawbones polyethylene foam and in bovine knee trabecular bone. Cavity sizes and cup loading forces were varied. Acetabular defects were simulated in the Sawbones model. Preparations were tested to determine axial-rotatory and tangential ("levering-out") stability. Results suggested that cup geometry and proper surgical technique--in particular, proper sizing and depth of the acetabular cavity--are important in determining initial cup stability independent of adjuvant screw or spike fixation. Stability is a function of the area of interface contact between the cup rim and the substrate. If the cavity is too small or too shallow, and the substrate too dense, the cup will not seat to the rim and stability will be compromised. If there are defects in the rim, the area of interface contact will be diminished and stability compromised. Cups with a true hemispherical design have a greater area of rim interface contact than "low-profile" cups and are therefore more stable. 1 mm undersizing of the cavity (or 2 mm undersizing in less dense substrate) appears to provide optimal stability.
We examined the effect of the Gamma nail on strain distribution in the proximal femur, using ten cadaver femora instrumented with six unidirectional strain gauges along the medial and lateral cortices. The femora were loaded to 1800 N and strains were determined with or without distal interlocking screws before and after experimentally created two-part and four-part fractures. Motion of the sliding screw and the nail was also determined. Strain patterns and screw motion were compared with previously obtained values for a sliding hip screw device (SHS). The Gamma nail was shown to transmit decreasing load to the calcar with decreasing fracture stability, such that virtually no strain on the bone was seen in four-part fractures with the posteromedial fragment removed; increasing compression was noted, however, at the proximal lateral cortex. Conversely, the SHS showed increased calcar compression with decreasing fracture stability. The insertion of distal interlocking screws did not change the pattern of proximal femoral strain. The Gamma nail imparts non-physiological strains to the proximal femur, probably because of its inherent stiffness. These strains may alter bone remodelling and interfere with healing. Distal interlocking screws may not be necessary for stable intertrochanteric fractures.
Although there is a potential hospital cost savings in reusing Ilizarov frame components, such reuse must be carefully considered in view of the deterioration of the parts during clinical use. A study is presented that addresses this issue through examination of clinically removed frames, laboratory testing, and engineering calculations.
The mechanical properties of canine tibias lengthened by the Ilizarov method as well as the degree of healing--as determined by the osseous appearance of the limbs using three imaging modalities--were examined as a function of fixator application time. Sixteen mongrel dogs had right tibial lengthening using a two-ring Ilizarov external fixator. The average lengthening was 27 mm. Four groups of four animals were killed at four, six, eight, and ten weeks after the completion of lengthening. The operated and contralateral tibias were examined with biplanar roentgenography, computerized tomography, and technetium scintigraphy. The torsional strengths of the tibias were then determined and histologic analysis was performed. There was considerable variation in the healing rate of the lengthening sites, both within and among groups. Histologic analysis and results of the imaging modalities revealed different degrees of development of the lengthening sites among members of the same group. Two types of mechanical behavior were seen, corresponding to completely and incompletely ossified lengthening zones. The strongest samples were those that had ossified across their lengthening sites by four or six weeks. The degree of recorticalization of the new bone and the extent of formation of a marrow space correlated well with increased torsional strength. The average strength of the fully ossified bones decreased progressively with time, paralleling a decrease in cortical thickness outside the lengthening zone. This seems to be a consequence of stress shielding by the fixator and disuse by the animal.
The stability of the basic unit for fixation of the Ilizarov external fixation system was tested in several loading modes. The effects of varying the number of wires and the orientation of wire placement were studied. The fixation units were mounted on a plastic, simulated, long bone and tested by loading in several directions. The Ilizarov fixation ring was found to be relatively stiff in axial compression and torsion. Its stiffness in this mode was directly proportional to the number of wires in the system and independent of the configuration of wire placement. Loading in bending and in shear provided much lower levels of stiffness, and this was dependent on the angles formed between the wires. The addition of a wire at a minimum distance of 4 cm from the primary ring significantly improved bending stiffness. The use of opposed olive wires also improved shear stiffness.
The Ilizarov external fixator exhibits more isotropic mechanical properties in bending and nonlinear axial stiffness than do unilateral and bilateral external fixators. Each frame element--wire size, tension, and orientation, as well as ring type--contributes to overall frame rigidity and stability. These factors and the specific clinical situation must be considered for the successful application of the Ilizarov fixator.
Hardware failure of the sliding screw system used in hip fracture fixation is rare. The fatigue failure of the sliding screw is always related clinically to nonunion or refracture along the path of the screw. In both situations, cyclic loading of the implant exceeds its endurance limit, and failure can ensue. Three cases of failure of the sliding screw are presented: a nonunion of a basicervical fracture, a nonunion secondary to stress fracture at the plate-barrel junction, and a refracture through the femoral neck after healing of an intertrochanteric fracture. A biomechanical analysis of the stresses on the sliding screw focuses on design features such as the internal threaded region used for the compression screw or the barrel length that creates increased stresses in the screw, thus lowering the number of cycles to failure. Based on this analysis, recommendations are made concerning implant design and surgical technique.
Five different types of osteotomies for the correction of the hallux valgus deformity were performed on dried human first metatarsal bones. These included the step-cut Mitchell osteotomy, a distal transverse osteotomy, a distal biplanar osteotomy, the Chevron osteotomy, and a basilar osteotomy. Each type of procedure was then fixed using a variety of clinically appropriate techniques including single K-wires, crossed K-wires, a single A-0 cancellous screw, a single A-0 cortical screw, and three different types of sutures. Specimens were placed in a test jig and physiological loads applied with a Materials Testing Systems servohydraulic testing machine (Minneapolis, Minnesota). No difference in stability was observed between the various types of osteotomies, except for the Chevron osteotomy, which did possess greater inherent stability. Fixation by screws or multiple K-wires provided the most stable configuration when compared to other methods. The postoperative regimen following first metatarsal osteotomy should take into account the relative stability of fixation. Cast immobilization and a nonweight-bearing status may be preferable after procedures characterized by less mechanical stability.
The extraosseous and intraosseous vascular anatomy to the fifth metatarsal as visualized in a group of below-the-knee amputation specimens has been described. The extrinsic circulation to the area is provided by the dorsal metatarsal artery, the plantar metatarsal arteries, and the fibular plantar marginal artery. These three source arteries supply branches to the metatarsal and adjacent joints. The intraosseous vascularity consists of a periosteal plexus, a nutrient artery, and a system of metaphyseal and capital vessels.
This paper reports the initial and long-term results of 45 Akin procedures done at the Hospital for Joint Diseases/Orthopaedic Institute from 1966 to 1985. Indications for 36 of the 45 operated feet were for an essentially asymptomatic great toe valgus deformity which caused symptoms to develop in the second toe and in 9 of 45 feet for residual hallux valgus after previous hallux valgus surgery. Excellent and good results were reported in 89% of the patients. The most common technical problem reported in 22% of the patients was plantar angulation at the osteotomy site. The only technical problem that was associated with long-term complications was bone apposition of less than 50% which may have lead to a nonunion in one case and recurrence of deformity in another. Shortening of the hallux was observed in all cases secondary to the closing wedge osteotomy. Shortening can be limited if a minimum of bone is removed from the proximal phalanx. A mathematical analysis is presented in this paper which can be used to provide guidelines to osteotomy size so that a minimum of bone necessary for correction can be removed. The Akin procedure should be performed within certain guidelines. Rarely is an Akin procedure alone indicated for the correction of a hallux valgus deformity. In most patients the proximal phalangeal osteotomy needs to be performed in combination with some other procedure to correct all components of the hallux valgus deformity. Furthermore the procedure can be used with success in those patients who present with an essentially asymptomatic great toe valgus deformity at the metatarsophalangeal joint or the interphalangeal joint which causes symptoms and/or deformity to develop in the second toe.(ABSTRACT TRUNCATED AT 250 WORDS)
Although the experience of the Hospital for Joint Diseases is unique in terms of size of market controlled, the cost-containment techniques described above are applicable to almost any hospital. A crucial factor in any such process is enlisting the active participation of the surgical staff at every stage. On the basis of the success, this cost-containment procedure is being applied to other components of the medical device purchases.
Six Autophor alumina ceramic total hip arthroplasty components (5 removed for stem loosening and 1 for cup loosening) were evaluated to determine the nature and extent of wear by direct measurement, scanning electron microscopy of wear debris, and histology. Component implantation averaged 29 months (range, 8-54 months). All components had evidence of marked wear, including gross loss of material, which increased with the duration of implantation.
Two cases of polyethylene bearing failure in the Triaxial elbow are presented. Although these were low-demand patients with the prostheses properly aligned, the severity of the wear suggests inadequate prosthesis design.
There is general agreement that the implant of choice for intertrochanteric fractures is the sliding hip screw (SHS). However, considerable differences of opinion exist as to which plate angle--varying from 130 to 150 degrees--is preferred. Thus far there has been no cadaver-based biomechanical analysis of this problem. To examine these questions, we determined the effect of plate angle on plate strain and proximal medial femoral strain distribution in cadaver femurs fixed with 130, 135, 140, 145, and 150 degrees SHS after experimentally produced stable and unstable intertrochanteric fractures. Twenty-four fresh adult cadaver femurs were assigned randomly to either the 130, 135, 140, 145, or 150 degrees SHS group. Each femur was radiographed and bone mineral density was determined by dual-photon absorptiometry. Multiple-strain gauges were affixed to the femur, with specific focus on the proximal femur and plate. Femurs were loaded at 25 degrees adduction in increments of 70 N from 0 to 1,800 N in a servohydraulic testing machine. Femurs were tested in a progressive manner: (a) intact femur; (b) intact femur with SHS inserted; (c) a stable two-part intertrochanteric fracture reduced with SHS; (d) a four-part fracture with the posteromedial fragment (PMF) reduced anatomically by a lag screw; (e) the same fracture with the PMF rotated 180 degrees and held in place by a lag screw to approximate a "near-anatomic" reduction; and (f) the same fracture with the PMF discarded. Screw sliding measurements were determined at regular intervals throughout each test.(ABSTRACT TRUNCATED AT 250 WORDS)
This study compares the standardized measurements of the foot in nonweight-bearing and weight-bearing radiographs. Both normal and hallux valgus patients were studied. The results show that some changes thought to occur with weight-bearing cannot be consistently demonstrated. Obtaining both weight-bearing and nonweight-bearing views may not be routinely indicated in all patients.