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Biomedical subjects

F J Kummer

Publications and source records attributed to F J Kummer.

At least 37 records · Page 2Linked to original sources
PubMed1996

Flexion failure of posterior cervical lateral mass screws. Influence of insertion technique and position.

STUDY DESIGN: The strength of posterior cervical lateral mass fixation was evaluated in a cadaver model for two techniques of screw insertion. OBJECTIVE: To compare the flexion failure strengths of posterior cervical plate fixation for two techniques of screw placement at the superior and inferior screw hole positions, and to evaluate the effect of bone mineral density on fixation strength. SUMMARY OF BACKGROUND DATA: Biomechanical analyses of various screw insertion techniques for posterior cervical lateral mass fixation have never evaluated the effect of screw position along the plate. METHODS: Individual C3-C6 segments of 24 human cadaveric cervical spines were used. The spinous process and lamina were removed to simulate a postlaminectomy situation. Vertebral body bone mineral density for each specimen was determined by dual-energy radiograph absorption scanning. In each lateral mass, a bicortical 3.5-mm screw was placed using either the Magerl or Roy-Camille insertion technique through an end hole of a titanium bone plate. For "superior" screws, the plate was directed caudally; for "inferior" screws, the plate was directed cranially. Screw violation of the surrounding facet joint was noted. An increasing flexion moment was applied by loading the plate 4 cm from the screw head at a rate of 10 cm/min using a servohydraulic testing machine until screw failure. RESULTS: For the superior screw hole position, the Magerl screw sustained a significantly higher average moment to failure (190.2 Ncm) than the Roy-Camille screw (138.7 Ncm; P < 0.05). For the inferior screw hole position, there was no significant difference in flexion failure strength between the two techniques (Magerl screws, 287.7 Ncm; Roy-Camille screws, 308.2 Ncm). For each insertion technique, inferior screws were nearly twice as strong as superior screws (P < 0.01). Violation of the inferior articular process occurred with 53% of Roy-Camille screws and with none of the Magerl screws. Lateral mass fracture on screw insertion occurred with 6% of the Roy-Camille screws and with 7% of the Magerl screws. Significant correlation between screw path length and load to failure was found only at the superior screw hole position. Correlation with vertebral body bone mineral density was significant at both positions. CONCLUSIONS: The Magerl technique has advantages over the Roy-Camille technique for placing the end screws when performing posterior cervical lateral mass plate fixation, providing greater strength superiorly and not violating unfused facet joints inferiorly. Evaluation of bone mineral density by dual-energy radiographic absorption scanning is predictive of failure strength for both test modes.

Biomechanical Phenomena↗
PubMed1996

Development of a telemeterized shoulder prosthesis.

A telemeterized shoulder prosthesis was developed and tested, first in vitro and then in a cadaver implantation. The prototype prosthesis was instrumented with 3 strain gauges fixed within a hollow, tapered neck element whose output was used to determine the load vectors experimentally applied to the humeral head. Testing demonstrated accuracy of force measurement resolution to within 5% of actual applied forces. This design seems feasible for further investigations to develop a totally implantable telemeterized prosthesis.

Biomechanical Phenomena↗
PubMed1996

Split fractures of the lateral tibial plateau: evaluation of three fixation methods.

A laboratory study was performed to compare the stability and ultimate strength of three standard fixation techniques for split-type lateral tibial plateau fractures. The three methods of fixation were (a) three 6.5-mm cancellous lag screws with washers; (b) two 6.5-mm cancellous lag screws with washers and an additional antiglide 4.5-mm cortical screw with washer; and (c) six-hole L-shaped buttress plate. Twelve pairs of embalmed mildly osteopenic lower extremities were used. Simulated split-type lateral tibial plateau fractures were created, reduced, and then instrumented in a matched pair design. The instrumented specimens were axially loaded to determine resistance to displacement, cyclically loaded to 10,000 cycles to determine dynamic stability, and then loaded to failure. There were no statistically significant differences found between resistance to displacement or failure strength as a function of either fragment size or sample bone density. On the basis of biomechanical stability, there appears to be no difference between the three fixation techniques tested. The results of this study suggest that use of an antiglide screw or buttress plate does not offer an advantage over lag screw fixation alone for the treatment of split type lateral tibial plateau fractures.

Biomechanical Phenomena↗
PubMed1996

Distal femoral fixation: a laboratory comparison of the 95 degrees plate, antegrade and retrograde inserted reamed intramedullary nails.

A biomechanical cadaver study was performed to compare the stability of three standard distal femoral fixation techniques. Eighteen mildly osteoporotic femurs were selected, based on a dual-energy x-ray absorption scanning bone density of 0.3-0.5 g/cm2 and a Singh index of III-IV. After initial mechanical characterization of these intact femurs, a distal femoral osteotomy was created, reduced, and stabilized under compression using random assignment to one of three methods of fixation: (a) six-hole 95 degrees supracondylar plate, (b) retrograde inserted statically locked supracondylar intramedullary nail, and (c) antegrade inserted statically locked Russell-Taylor nail. The instrumented femurs were mechanically tested, a 1-cm gap created, and the femurs retested. The specimens were finally loaded to failure in A-P three-point bending. The 95 degrees plate provided significantly stiffer fixation than the supracondylar intramedullary nail or Russell-Taylor nail in both a compressed transverse and gap distal femoral osteotomy model. The Russell-Taylor nail provided the least rigid fixation. The 95 degrees plate and Russell-Taylor nail had statistically significant greater loads to failure than the supracondylar intramedullary nail. These results support the use of a 95 degrees plate when maximum rigidity of fixation or maximum compression is desired.

Biomechanical Phenomena↗
PubMed1996

Surgical neck fractures of the proximal humerus: a laboratory evaluation of ten fixation techniques.

OBJECTIVE: A biomechanical cadaver study was performed to compare the stability and ultimate strength of ten standard fixation techniques used for the treatment of surgical neck fractures of the proximal humerus. DESIGN: One hundred twenty (60 fresh frozen, 60 embalmed) proximal humerus specimens were selected and divided into two groups: fresh frozen specimens represented a nonosteopenic group and embalmed specimens an osteopenic group. Simulated fractures were created at the level of the surgical neck, reduced, and randomly assigned to one of ten methods of fixation (six fresh frozen and six embalmed specimens per fixation group). These constructs were then mechanically tested with the humeri oriented to create primarily shear loading of the fixation. RESULTS AND CONCLUSIONS: The T-plate and screws provided significantly stronger fixation (p < 0.005) in the fresh frozen specimens than all other methods. The Ender nails/tension band construct was the second strongest fixation technique, providing significantly stronger fixation (p < 0.01) than all the remaining techniques. Four Schanz pins with one pin placed through the greater tuberosity followed by the T-plate and screws provided the strongest fixation in embalmed specimens. Tension band fixation in both humeral groups was shown to provide the least effective fixation.

Biomechanical Phenomena↗
PubMed1996

Cement augmentation of intertrochanteric fracture fixation: a cadaver comparison of 2 techniques.

We evaluated 2 techniques of cement augmentation to enhance fixation of intertrochanteric hip fractures. 4 fixation groups with 6 cadaver femurs in each group were compared: stainless steel lag screw and side plate with and without cement augmentation and a titanium alloy expandable dome plunger and side plate with and without cement augmentation. Gauges were used to establish the mechanical behavior of intact and then fractured femurs to simple uniaxial loads. Subsequent loading to failure allowed determination of maximum fixation strengths and modes of failure. Cement augmentation of each device increased its load to failure. There was no significant difference between the cemented lag screw and the uncemented dome plunger groups with average loads to failure of 4.0 x 10(3) N. The greatest average load to failure was in the cemented dome plunger group (5.6 x 10(3) N) with the lowest in the uncemented sliding hip screw group (3.6 x 10(3) N). Device cut-out as a cause of failure occurred mostly in the uncemented lag screw group. Sliding was enhanced by those methods that increased the fixation surface area within the femoral head, unless cement encroached in the region of the barrel-screw junction. Strain analysis showed that the dome plunger unloaded the bone at the calcar, regardless of cement augmentation, while the sliding hip screw allowed for compressive stresses in this area. Proper cement augmentation increases load to failure and minimizes nail cut-out for both devices studied. However, the dome plunger, a device with a large fixation area in the femoral head, was equally effective and eliminated potential cement encroachment. Failure of intertrochanteric fracture fixation in osteoporotic bone may be minimized by an appropriate choice of device or cement augmentation.

Bone Cements↗
PubMed1996

Coracoacromial ligament function: a phylomorphic analysis.

Various morphologic parameters of the coracoacromial region were quantified for five hominoid genera to examine the evolutionary development of the coracoacromial ligament (CAL) and its significance and relationship to shoulder function. No evolutionary correlation within the family Hominoidea was found for several calculated parameters obtained from osseous dimensions and CAL length. However, from an evolutionary analysis of the order Anthropoidea, it appears that the CAL is not solely a vestigial structure in humans but rather represents a stage in the development of the hominoid shoulder with the function of providing increased mechanical stability to the superior bony vault.

Animals↗
PubMed1996

Fixation stability of olecranon osteotomies.

Eighteen pairs of fresh frozen human upper extremities were selected and each randomized to 2 of 3 olecranon osteotomy and fixation technique groups: (1) transverse osteotomy with 0.062 Kirschner wire and tension band fixation; (2) chevron osteotomy with 6.5-mm cancellous lag screw and tension band fixation; and (3) oblique intraarticular osteotomy with 3.5-mm cortical lag screw and tension band fixation. The arms were mounted with the elbow at 90 degrees flexion and the wrist constrained; a dual linear displacement transducer across the osteotomy was used to determine angulation, translational displacement, and the total gap size. First the brachialis and then the triceps were incrementally loaded to 10 kg using a pulley and cable system to control force direction; the muscle load versus osteotomy displacement was recorded. Cycling with 10 kg was repeated 20 times with the brachialis and triceps alternately loaded and the osteotomy displacement remeasured. There were no statistically significant differences between the amounts of displacement for the 3 osteotomy and fixation techniques caused by either muscle action. The total displacement caused by the brachialis load for all techniques was appreciably greater than that of the triceps load. No significant increase in displacements occurred after 20 load cycles. These results suggest all 3 olecranon osteotomy and fixation techniques offer comparable stability, so the choice of technique should be left to the surgeon's preference.

Biomechanical Phenomena↗
PubMed1995

Effects of supine positioning and fracture post placement on the perineal countertraction force in awake volunteers.

An instrumented traction post was used to determine the magnitude and direction of the countertraction force applied to the perineum of 15 awake volunteers for a series of 12 positions used in fracture surgery and compared with their corresponding neutral position controls. The results demonstrated that adduction of the affected limb and abduction of the contralateral limb applied the greatest force to the perineum with ipsilateral and contralateral placement of the fracture post. These two maneuvers increased the perineal countertraction force 80% above their respective neutral readings. Abduction of the affected limb reduced the traction force by 50% with ipsilateral and contralateral placement of the fracture post. Flexion-abduction-external rotation of the contralateral leg reduced the forces applied to the perineum by 60% when the fracture post was placed contralateral to the affected limb. Contralateral placement of the post decreased the perineal countertraction force 46% below the value for ipsilateral post placement for this maneuver. Internal and external rotation of the affected limb had no effect on the perineal countertraction force for either placement of the post. There was a significant decrease in the perineal forces for the neutral positions after adduction of the affected limb and abduction of the contralateral limb with ipsilateral placement of the post, indicating that the volunteers shifted on the fracture table in response to pain. There was no significant difference in the direction of the countertraction force for the various positions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

The effectiveness of cut-proof glove liners: cut and puncture resistance, dexterity, and sensibility.

Five types of commercial glove liners (within double latex gloves) were compared to single and double latex gloves for cut and puncture resistance and for relative manual dexterity and degree of sensibility. An apparatus was constructed to test glove-pseudofinger constructs in either a cutting or puncture mode. Cutting forces, cutting speed, and type of blade (serrated or scalpel blade) were varied and the time to cut-through measured by an electrical conductivity circuit. Penetration forces were similarly determined with a scalpel blade and a suture needle using a spring scale loading apparatus. Dexterity was measured with an object placement task among a group of orthopedic surgeons. Sensibility was assessed with Semmes-Weinstein monofilaments, two-point discrimination, and vibrametry using standard techniques and rating scales. A subjective evaluation was performed at the end of testing. Time to cut-through for the liners ranged from 2 to 30 seconds for a rapid oscillating scalpel and 4 to 40 seconds for a rapid oscillating serrated knife under minimal loads. When a 1 kg load was added, times to cut-through ranged from 0.4 to 1.0 second. In most cases, the liners were superior to double latex. On average, 100% more force was required to penetrate the liners with a scalpel and 50% more force was required to penetrate the liners with a suture needle compared to double latex. Object placement task times were not significantly liners compared to double latex gloves. Semmes-Weinstein monofilaments, two-point discrimination, and vibrametry showed no difference in sensibility among the various liners and double latex gloves. Subjects felt that the liners were minimally to moderately impairing. An acclimation period may be required for their effective use.

Equipment Design↗
PubMed1995

Biomechanical comparison of the sliding hip screw and the dome plunger. Effects of material and fixation design.

We studied the biomechanical behaviour of three sliding fixation devices for trochanteric femoral fractures. These were a titanium alloy sideplate and lag screw, a titanium alloy sideplate and dome plunger with cement augmentation, and a stainless-steel sideplate and lag screw. We used 18 mildly osteoporotic cadaver femora, randomly assigned to one of the three fixation groups. Four displacement and two strain gauges were fixed to each specimen, and each femur was first tested intact (control), then as a two-part fracture and then as a four-part intertrochanteric fracture. A range of physiological loads was applied to determine load-bearing, load-sharing and head displacement. The four-part-fracture specimens were subsequently tested to failure to determine maximum fixation strengths and modes of failure. The dome-plunger group failed at a load 50% higher than that of the stainless-steel lag-screw group (p < 0.05) and at a load 20% higher than that of the titanium-alloy lag-screw group (NS). All 12 lag-screw specimens failed by cut-out through the femoral head or neck, but none of the dome-plunger group showed movement within the femoral head when tested to failure. Strain-gauge analysis showed that the dome plunger produced considerably less strain in the inferior neck and calcar region than either of the lag screws. Inferior displacement of the femoral head was greatest for the dome-plunger group, and was due to sliding of the plunger. The dome plunger with cement augmentation was able to support higher loads and did not fail by cut-out through the femoral head.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗
PubMed1995

The incidence of full thickness rotator cuff tears in a large cadaveric population.

The incidence of full thickness rotator cuff tears was determined after careful dissection and inspection of 235 male and female cadavers ranging in age from 27-102 years with an average age of 64.7 years. A total of 456 shoulders were examined. Partial thickness tears were excluded from the study. Seventy-eight shoulders, 17% (53 female, 26 male) were found to have full thickness tears. The average age of those cadavers with tears was 77.8 years as compared to 64.7 years in the intact group. The incidence of full thickness tears was also found to increase with increasing age. In cadavers under 60 years of age the incidence of rotator cuff tears was 6% as opposed to 30% in those over 60 years of age.

Adult↗
PubMed1994

Hydroxyapatite enhancement of posterior spinal instrumentation fixation.

STUDY DESIGN: The ability of hydroxyapatite (HA) materials to enhance the fixation strength of posterior spinal instrumentation was examined in 19 adult mongrel dogs. METHODS: Sixteen dogs underwent bilateral placement of lumbar transpedicular screws from L1 to L6, sacral alar screws, and posterior iliac rods. The six transpedicular screw test groups included standard and plasma-sprayed HA-coated screws with the recommended insertion technique, standard and HA-coated screws with a poor initial fit insertion technique using an oversized pilot hole, and HA-grout augmentation of standard and HA-coated screws with a poor initial fit. The sacral alar screws and posterior iliac rods were either uncoated or HA-coated. Six dogs were killed immediately; ten dogs were killed at 6 weeks, and the fixation elements were mechanically tested or histologically examined. Three additional dogs and synthetic bone material were used for additional baseline mechanical testing. RESULTS: The strength of standard screws with recommended insertion did not change after 6 weeks in vivo. HA-coated screws were initially 13% less resistant to pull out than standard screws, but this difference was not significant at 6 weeks. Screws inserted with a poor initial fit technique were significantly weaker initially; at 6 weeks, pull-out strength was similar to the standard screws properly inserted. The HA-grout material significantly enhanced pull-out strength for both screw types at 6 weeks. Sacral alar screw pull-out strength was not significantly different between standard and HA-coated screws initially or at 6 weeks. HA-coated rods were initially twice as resistant to pull out than standard rods and became stronger after 6 weeks in vivo, whereas standard rods became significantly weaker. Histologically, the quantity and morphology of bone around all implants was similar, with HA-coated rods and screws demonstrating regions of direct attachment to bone. An osteoconductive response and new bone formation was observed within the HA-grout material. Scanning electron microscopic observation of mechanically tested implants revealed a shear failure of surrounding bone (and HA if present) at the screw outer thread margin or at the bone-metal or HA-metal interfaces for the posterior iliac rods. CONCLUSIONS: The strength of poorly inserted transpedicular screws was significantly enhanced in vivo by the resorbable HA-grout material. The lower strength of HA-coated screws was attributed to screw geometry changes resulting from the coating process, and modifications of screw coating are recommended.

Animals↗
PubMed1994

Vertical shear fractures of the medial malleolus: a biomechanical study of five internal fixation techniques.

Fifty embalmed human tibias were osteotomized to create a simulated vertical shear (supination-adduction) fracture of the medial malleolus and were stabilized using one of five internal fixation techniques. In offset axial testing, which simulated supination-adduction loading, the fixation strength of tibias stabilized with either cortical or cancellous lag screws placed perpendicular to the osteotomy was over five times greater than the strength of those treated with an antiglide plate and nearly two and a half times greater than those treated with cancellous lag screws placed oblique to the osteotomy. The tibias stabilized with cancellous lag screws placed perpendicular to the osteotomy exhibited twice the fixation strength of the tibias stabilized with an antiglide plate and distal lag screw. The tibias stabilized with an antiglide plate and distal lag screw and perpendicularly placed cortical or cancellous lag screws demonstrated three times greater resistance to displacement to the applied supination-adduction load than those stabilized with an antiglide plate alone. In offset transverse testing, to simulate loading in external rotation, the mean failure load of the tibias stabilized with cancellous lag screws placed perpendicular to the osteotomy was over two and a half times greater than those stabilized with an antiglide plate and distal lag screw. No significant differences were observed in the resistance to displacement for these tests. These results support the use of lag screws placed perpendicular to the fracture surface for stabilization of vertical shear fractures of the medial malleolus and indicate that the use of an antiglide plate, with or without a distal lag screw, does not offer any advantage over lag screw fixation.

Biomechanical Phenomena↗
PubMed1994

The effectiveness of a hospital-based strategy to reduce the cost of total joint implants.

Our hospital implemented an integrated cost-containment program designed to address the increasing disparity between the cost of orthopaedic implants used for total joint replacements and the amount of hospital reimbursement provided for these procedures. This program was divided into four phases: (1) the analysis of the specific usage of total hip and total knee implants at our institution, (2) the development of surgeons' awareness of the problem and the enlistment of their participation in the process of cost containment, (3) the initiation of a competitive bidding system to select standard prostheses that would be available for general use within the institution, and (4) the establishment of a prosthesis-utilization committee to monitor the process and to make decisions concerning the use of non-standard prostheses. Using this cost-containment program, our hospital greatly reduced the number of vendors and implant systems used; all implants were purchased on a consignment basis, which minimized the cost of implant inventory. The average cost reductions in the first year were 14 per cent for total hip implants and 24 per cent for total knee implants. Over-all implant costs were reduced by an estimated $706,477, or 23 per cent of the budget for implants for the previous year.

Competitive Bidding↗
PubMed1993

Repair of peripheral nerve defects by controlled distraction: a preliminary study.

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.

Anastomosis, Surgical↗