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Biomedical subjects

Frederick J Kummer

Publications and source records attributed to Frederick J Kummer.

36 records · Page 2Linked to original sources
PubMed2003

The effect of an attachable lateral support plate on the stability of intertrochanteric fracture fixation with a sliding hip screw.

BACKGROUND: Use of a sliding hip screw (SHS) alone for some unstable intertrochanteric femur fractures can allow excessive medial shaft displacement during impaction. This study evaluated the effect of an attachable lateral support plate on these fractures after loading. METHODS: Unstable, three-part intertrochanteric fractures were created in 10 matched pairs of embalmed femurs that were instrumented with 135-degree SHSs with or without an attachable lateral support plate. Under physiologic loading, inferior and lateral head displacements and lag screw sliding distances were measured. RESULTS: After 10,000 cycles at 750 N, all measurements for femurs with the lateral support plate were significantly less than for the femurs with the SHS alone: mean lateral difference was 1.7 mm (34%) (p < 0.05), mean inferior difference was 3.0 mm (38%) (p < 0.05), and mean lag screw sliding difference was 4.5 mm (58%) (p < 0.05). CONCLUSION: The addition of an attachable lateral support plate to an SHS significantly decreased displacement of the femoral head after cyclic loading.

Bone Screws↗
PubMed2003

Effects of preheating of hip prostheses on the stem-cement interface.

BACKGROUND: Debonding of the cement from metal implants has been implicated in the loosening of cemented total hip prostheses. Strengthening of the stem-cement interface has been suggested as a way to prevent loosening of the component. Previously, it was reported that preheating the stem to 44 degrees C reduced the porosity of the cement at the stem-cement interface. The purpose of this study was to determine the effect of stem preheating on the characteristics of the stem-cement interface. METHODS: The effects of stem preheating, at temperatures of 37 degrees C, 44 degrees C, and 50 degrees C, on the stem-cement interface were studied in a test model and a preparation that closely simulated the clinical situation. Static interface strength was determined initially and after the stems had been kept in isotonic saline solution at 37 degrees C for two weeks. Fatigue lifetimes were measured, and the nature and extent of porosity at the interface were quantified. RESULTS: Stem preheating had significant effects on the stem-cement interface. Stems preheated to 37 degrees C had greater interface shear strength than stems at room temperature both initially (53% greater strength) and after simulated aging (155% greater strength). Fatigue lifetimes were also improved, and there was a >99% decrease in interface porosity. The setting time of the cement decreased 12%, and the maximum temperature at the cement-bone interface increased 6 degrees C. Similar effects were found after preheating to 44 degrees C and 50 degrees C. CONCLUSIONS: Stem preheating had significant effects on the stem-cement interface, with significant improvements in the shear strength and cement porosity of the interface. Also, polymerization temperatures at the cement-bone interface increased. The possible biological effects of these increased interface temperatures at the cement-bone interface require further study.

Arthroplasty, Replacement, Hip↗
PubMed2003

Two or three screws for fixation of femoral neck fractures?

This study compares the stability of 3 cannulated cancellous lag screws with that of 2 cannulated cancellous lag screws for fixation of subcapital femoral neck fractures. Using 10 matched pairs of human cadaveric femurs, subcapital femoral neck osteotomies were created, reduced, and then randomized to 1 of the 2 fixation methods. The constructs were tested with anterior loading to 500 N, incremental axial loading from 100 N to 1000 N, and cyclic loading at 1000 N. The specimens stabilized using 3 screws showed greater resistance to anterior loading, less inferior femoral head displacement, and less superior gapping at the osteotomy site. Although 2 screws may be an acceptable fixation method for this fracture type, the addition of a third screw provides supplemental stability and appears justified.

Absorptiometry, Photon↗
PubMed2003

Interobserver reliability and intraobserver reproducibility in suprascapular notch typing.

The size and shape of the suprascapular notch may be a factor in suprascapular nerve entrapment. The suprascapular notches of 623 scapulae were digitally photographed and used to determine notch type and area. Three researchers used to different classification systems for suprascapular notch typing. These systems were compared for interobserver reliability and intraobserver reproducibility using the kappa test. The mean kappa value for the classification used by Rengachary and colleagues was 0.468 and for the classification used by Ticker and associates was 0.531 for the inferior border of the notch and 0.736 for the superior border of the notch. The classification system used by Ticker and associates was more reliable and reproducible and produced both a superior and an inferior classification, making it possibly more clinically relevant than the classification system used by Rengachary and colleagues.

Adolescent↗
PubMed2003

Comparison of two headless screw designs for fixation of capitellum fractures.

In order to determine the effects of two different headless screw designs on fixation of simulated capitellum fractures six matched pairs of embalmed humeri had simulated capitellum fractures created. Fixation with Acutrac compression screws was compared to Herbert screws in a matched pair experimental design. All specimens were cyclically tested with simulated physiologic loading. Both displacement of the capitellum as a function of the number of cycles and failure loads were determined. Fixation by the Acutrac screws was significantly more stable than Herbert screws at 2000 cycles, 0.17 mm wersus 1.57 mm (p < 0.02) The Acutrac fixation also had a higher failure load, 154 N versus 118 N (p < 0.05). The Acutrac screws tested in this biomechanical study provided more stable fixation of simulated capitellum fractures than Herbert screws. This appears to be related to the design of these screws.

Biomechanical Phenomena↗
PubMed2003

Loading of the acetabulum by polyethylene and all-ceramic inserts in metal-backed acetabular cups.

Both static and dynamic loads were applied to metal-backed acetabular cups with ceramic or polyethylene inserts and the resulting load transmissions at a simulated bone interface were determined. Perfect fit and under-sized and over-sized cavities were prepared in simulated bone substrates, lined with Fuji pressure sensitive film, and acetabular cups inserted with physiological loads. The magnitude and location of contact forces between the cup and bone were measured. These cups were then subjected to a controlled impact load and the intensity and frequency of the loads transmitted to the substrate were determined. The results suggest that a polyethylene backing for ceramics is not necessary as there were no major differences in the static and dynamic stresses transmitted to the cup-bone interface with all polyethylene or ceramic inserts.

Acetabulum↗
PubMed2002

Comparison of the LISS and a retrograde-inserted supracondylar intramedullary nail for fixation of a periprosthetic distal femur fracture proximal to a total knee arthroplasty.

Simulated supracondylar fractures were created proximal to posterior cruciate ligament-retaining total knee arthroplasty components in paired human cadaver femora and stabilized with either a retrograde-inserted locked supracondylar nail or the Less Invasive Stabilization System (LISS; Synthes USA, Paoli, PA). Loads were applied to create bending and torsional moments on the simulated fracture stabilized with either no gap or a 10-mm gap. The LISS exhibited less torsional stability with anterior (P<.001) and posterior loads (P<.01). When varus loads were applied to 10-mm-gap specimens, the specimens stabilized with a retrograde nail had an 83% reduction in fracture displacement (P<.001) and 80% less medial translation of the distal fragment (P<.001). The samples stabilized with the LISS had a 93% reduction in fracture gap displacement when a valgus load was applied with a 10-mm gap (P<.001). Overall, these results suggest that the retrograde-inserted nail may provide greater stability for the management of periprosthetic supracondylar femur fractures in patients with a posterior cruciate ligament-retaining femoral total knee arthroplasty component.

Arthroplasty, Replacement, Knee↗
PubMed2002

Revision of polyethylene acetabular liners with a cemented polyethylene cup: a laboratory study.

Various technique parameters for the revision of failed polyethylene acetabular liners using a cemented polyethylene cup were evaluated in this laboratory study. The effects of cement mantle thickness and roughening the inner surface of the shell or outer surface of the cup were determined by measuring cup dissociation strength from the metal shell after cyclic loading of the cup. The use of a cement mantle thickness of 2 to 4 mm provided dissociation strengths 3 to 4 times greater than that of the original, press-fit polyethylene liner. If a failed acetabular liner is revised by a cemented cup within the existing, well-fixed, metal shell, the size of the cup selected should create a cement mantle of <4 mm. Roughening the inside of a smooth shell or one with few screw-holes increases fixation strength approximately 20% but also creates particulate debris.

Arthroplasty, Replacement, Hip↗
PubMed2002

Capitellum fractures: a biomechanical evaluation of three fixation methods.

OBJECTIVE: To determine the relative stability of three fixation methods for displaced capitellum fractures. DESIGN: Twelve matched pairs of embalmed humeri were divided into two equal groups and simulated capitellum fractures created. The first group compared cancellous lag screws placed in an anteroposterior direction to screws placed in the posteroanterior direction. The second group compared the Acutrac compression screw, inserted anteroposteriorly, to the more stable construct from the first test group. METHODS: All specimens were cyclically tested with simulated physiologic loading. Both displacement of the capitellum over a range of cycles and the number of cycles to failure were recorded. RESULTS: Fixation with posteroanteriorly directed cancellous lag screws was significantly more stable than anteroposteriorly directed screws at 2000 cycles (p = 0.007); loads to failure were not statistically different. Fixation by the Acutrac screws was significantly more stable than posteroanterior cancellous screws at 2000 cycles (p = 0.03). The Acutrac fixation had a higher failure load; however, this was not statistically significant. CONCLUSION: The headless screws tested in this biomechanical study provided more stable fixation of capitellum fractures in the cadaveric specimens than four-millimeter partially threaded cancellous lag screws and may do so in the clinical setting. When the cancellous lag screws were tested, insertion in the posteroanterior direction provided more stable fixation than the anteroposterior direction and has clinical benefit of not violating the articular surface. Ultimately, the decision of which method to use lies with the attending surgeon and the technique with which he or she feels most comfortable.

Biomechanical Phenomena↗
PubMed2002

The effect of posterior sag on the fixation stability of intertrochanteric hip fractures.

BACKGROUND: This study evaluates the effects of posterior sag on the fixation stability of intertrochanteric hip fractures. METHODS: A simulated, two-part intertrochanteric fracture was created in human cadaveric femurs. One of each pair was stabilized using a sliding hip screw in anatomic reduction and the other in 30 degrees of posterior sag. Measurements for load versus inferior head displacement, gapping, and shearing were made in axial and torsional loading. RESULTS: Initial axial and torsional loading showed no significant differences between the two groups. During cyclic loading, the osteotomy gap in the posteriorly angulated specimens decreased by 0.11 cm at 10 cycles (p = 0.006) and by 0.22 cm at 10,000 cycles (p = 0.33), corresponding to a 2-degree and 6-degree reduction in sag angle. Axial stiffness differed between the two groups: 10.3 N/mm for anatomic versus 6.7 N/mm (p = 0.002) for posteriorly angulated specimens. Loading to failure demonstrated no significant differences between the two groups. CONCLUSION: This study demonstrated that 30 degrees of posterior sag does not result in a significant difference in construct strength or stability.

Biomechanical Phenomena↗
PubMed2002

Fixation stability of comminuted humeral shaft fractures: locked intramedullary nailing versus plate fixation.

BACKGROUND: This study compared the fixation stability of two treatments for humeral shaft fractures with segmental bone loss during cyclic, physiologic loading. METHODS: Six matched pairs of human humeri received either a 10-hole broad dynamic compression plate or a locked antegrade inserted humeral nail applied to a humeral diaphyseal osteotomy with a 1.5-cm gap defect. The bone-implant humeral constructs were axially loaded for 10,000 cycles at 250 N and 500 N, with measurements of gap displacement and calculation of construct stiffness. The specimens were then loaded to failure. RESULTS: Cyclic loading showed no difference between the two groups for average gap displacement or construct stiffness. The intramedullary nail constructs failed by humeral shaft splitting (n = 4) or head cut-out (n = 2) at an average of 958.3 N, whereas the plate constructs failed by humeral shaft splitting and screw pull-out (n = 3) or plate bending (n = 3) at an average of 641.7 N (p < 0.001). CONCLUSION: Although both methods offer similar fixation stability under physiologic loads, the higher load to failure demonstrated by intramedullary nail fixation may have implications for the patient with multiple injuries for whom partial weightbearing on the injured upper extremity may be necessary.

Adult↗
PubMed2002

Toe flexor forces in dancers and non-dancers.

Toe flexor force (hallux and second toe) was determined in the right and left feet of 24 dancers and 29 non-dancers (sitting and standing positions) using a commercially-available pressure sensor connected to a voltmeter. For the hallux and second toe combined (all trials combined), average toe flexor force was slightly greater for dancers than non-dancers (dancers, 7 +/- 4 N; non-dancers, 6 +/- 4 N; P<0.049). For dancers and non-dancers combined (all trials), the average toe flexor force of the hallux was more than twice that of the second toe (hallux, 9 +/- 4 N; 2nd toe, 4 +/- 1 N; P<0.0001); average toe flexor force was slightly greater in standing than sitting positions (standing, 7 +/- 4 N; sitting, 6 +/- 3 N; P<0.0001); and the average toe flexor force was slightly greater for the right than left foot (right, 7 +/- 4 N; left, 6 +/- 4 N; P<0.012). The average toe flexor force was greatest for the first repetition and slightly decreased for the second and third repetitions (first repetition, 7 +/- 4 N; second and third repetitions each, 6 +/- 4 N; P<0.0013). Toe flexor force measurement may potentially be applicable to clinical practice as a guide to rehabilitation after injury or as a screening parameter for readiness to advance dance or other athletic training, performance, or competition.

Adult↗
PubMedDate not supplied

The effect of end screw orientation on the stability of anterior instrumentation in cyclic lateral bending.

BACKGROUND CONTEXT: Screw pullout at the proximal or distal end of multilevel anterior instrumentation can occur clinically. Previous laboratory studies have shown that angulation of vertebral body screws increases screw pullout strength and stability in toggling. PURPOSE: To determine the effect of end screw angulation on instrumentation construct stability after cyclic, lateral bending. STUDY DESIGN: A biomechanical study in calf spines comparing two anterior spinal instrumentation constructs, one with parallel polyaxial screws and the other with angled polyaxial end screws. METHODS: Sixteen instrumented constructs were made from eight thoracic (T8-T12) and eight lumbar calf spines (L1-L5). Eight (four lumbar specimens and four thoracic specimens) had five bicortical screws inserted mid-body and parallel to the end plates. The other eight specimens had two screws angled toward the superior end plates of the top two vertebrae; the middle vertebra had a mid-body screw parallel to the end plate, and the bottom two vertebrae had screws angled towards their inferior end plates. The constructs were then cycled in lateral bending, and the displacements of the two instrumentations with a 10 N-m bending load were compared. RESULTS: After 10,000 cycles, constructs with parallel end screws exhibited twice the average displacement than those with angled screws: 5.4 mm versus 2.9 mm (p=.031). CONCLUSION: The use of angled screws at the ends of anterior constructs demonstrated increased construct stability after cycling compared with traditional transverse screws. Although angled screw insertion is technically more difficult and is possible only with specific screw designs, its use might increase instrumentation longevity.

Animals↗
PubMedDate not supplied

Treatment of acromioclavicular joint separation: suture or suture anchors?

This investigation compared the stability of 2 methods of fixation for acromioclavicular (AC) joint separations. A complete AC joint separation was simulated in 6 matched pairs of fresh-frozen human cadaveric shoulders. One specimen from each pair was repaired with two No. 5 nonabsorbable braided sutures passed around the base of the coracoid and the other with 2 suture anchors preloaded with the same suture material placed into the base of the coracoid process. The specimens were cyclically loaded for 10(4) cycles to simulate our early postoperative rehabilitation protocol for coracoclavicular repairs. Before cycling, the repairs had a mean superior laxity of 1.68 +/- 0.44 mm for the sutures alone and 1.23 +/- 0.31 mm for the suture anchors. After 10(4) cycles, the laxity was 1.32 +/- 0.59 mm and 1.33 +/- 0.94 mm, respectively. These differences were not statistically significant (P =.2). This study demonstrated that similar stability can be achieved for coracoclavicular fixation with suture anchors or with sutures placed around the base of the coracoid for the treatment of AC joint separations. The clinical relevance includes the following: (1) the potentially diminished risk of neurovascular injury with the use of suture anchors compared with the passage of sutures around the base of the coracoid and (2) the potentially reduced surgical time associated with the use of suture anchors.

Acromioclavicular Joint↗
PubMedDate not supplied

Fit of current glenoid component designs: an anatomic cadaver study.

The glenoids of 412 scapula specimens were templated with the use of 6 currently available glenoid systems to determine the goodness of fit for the various designs. When a fitting criterion of a mismatch of less than 2 mm between the template and the actual glenoid periphery for 8 radial locations was used, the various designs fit from 0% to 48% of the glenoids. Because glenoid component fixation longevity can depend on the degree of osseous support, these results indicate that glenoid component design and sizing can be improved.

Adult↗
PubMedDate not supplied

Posterior olecranon plating: biomechanical and clinical evaluation of a new operative technique.

The purpose of this investigation was to compare the biomechanical analysis of a new plating technique for olecranon fractures to tension band wiring, and review early clinical results. Six matched pairs of cadaveric ulnae were used for the biomechanical analysis. A transverse osteotomy of the mid part of the olecranon was made. One ulna of each pair was stabilized using a tension band and the other with a posterior hook plate. The ulnae were mounted and loaded, and displacement at the osteotomy site recorded. Twenty patients treated with this new technique (14 fractures and 6 osteotomies) were reviewed at one year (range: 8 to 18 months) for infection, union rate, hardware related complaints. and removal. Statistical analysis showed significantly less displacement occurred at the osteotomy site in the plating group. Clinically, all patients had fracture union, and there were no hardware related problems. Posterior plating with this technique achieves greater stability compared to tension band wiring. Early clinical results indicate a low level of hardware related complications.

Adult↗
PubMedDate not supplied

Biomechanical comparison of five external wrist fixators.

The relative stiffness of five different external wrist fixators currently in use for distal radius fractures was determined using a uniform fracture model consisting of wood dowels to isolate the effects of the fixators themselves. Each construct was loaded in axial compression, eccentric and cantilever modes of bending, and torsion. The stiffest of the fixators varied by a factor of three in compression, five in bending, and three in torsion. Although the ideal stiffness of a wrist fixator is unknown, there is a large variation in the stiffness of existing devices.

Biomechanical Phenomena↗