Search PubMed⌕ Search

Biomedical subjects

F J Kummer

Publications and source records attributed to F J Kummer.

At least 19 recordsLinked to original sources
PubMed1999

The use of an injectable, biodegradable calcium phosphate bone substitute for the prophylactic augmentation of osteoporotic vertebrae and the management of vertebral compression fractures.

STUDY DESIGN: A biomechanical study comparing two materials for augmentation of osteoporotic vertebral bodies and vertebral bodies after compression fracture. OBJECTIVES: To compare an injected, biodegradable calcium phosphate bone substitute with injected polymethylmethacrylate bone cement for strengthening osteoporotic vertebral bodies and improving the integrity of vertebral compression fractures. SUMMARY OF BACKGROUND DATA: Injection of polymethylmethacrylate bone cement into fractured vertebral bodies has been used clinically. However, there is concern about thermal damage to the neural elements during polymerization of the polymethylmethacrylate bone cement as well as its negative effects on bone remodeling. Biodegradable calcium phosphate bone substitutes have been studied for enhancement of fixation in fractured vertebrae. METHODS: Forty fresh osteoporotic thoracolumbar vertebrae were used for two separate parts of this study: 1) injection into osteoporotic vertebrae: intact control (n = 8), calcium phosphate (n = 8), and polymethylmethacrylate bone cement (n = 8) groups. Each specimen then was loaded in anterior compression until failure; 2) injection into postfractured vertebrae: calcium phosphate (n = 8) and polymethylmethacrylate bone cement (n = 8) groups. Before and after injection, the specimens were radiographed in the lateral projection to determine changes in vertebral body height and then loaded to failure in anterior bending. RESULTS: For intact osteoporotic vertebrae, the average fracture strength was 527 +/- 43 N (stiffness, 84 +/- 11 N/mm), 1063 +/- 127 N (stiffness, 157 +/- 21 N/mm) for the group injected with calcium phosphate, and 1036 +/- 100 N (stiffness, 156 +/- 8 N/mm) for the group injected with polymethylmethacrylate bone cement. The fracture strength and stiffness in the calcium phosphate bone substitute group and those in the polymethylmethacrylate bone cement group were similar and significantly stronger than those in intact control group (P < 0.05). For the compression fracture study, anterior vertebral height was increased 58.5 +/- 4.6% in the group injected with calcium phosphate and 58.0 +/- 6.5% in the group injected with polymethylmethacrylate bone cement as compared with preinjection fracture heights. No significant difference between the two groups was found in anterior vertebral height, fracture strength, or stiffness. CONCLUSION: This study demonstrated that the injection of a biodegradable calcium phosphate bone substitute to strengthen osteoporotic vertebral bodies or improve vertebral compression fractures might provide an alternative to the use of polymethylmethacrylate bone cement.

Absorbable Implants↗
PubMed1999

The effect of locking fixation screws on the stability of anterior cervical plating.

STUDY DESIGN: Current anterior cervical plate systems were tested with locked and unlocked fixation screws and with unicortical and bicortical fixation screws to determine fixation rigidity and pull-off strengths. OBJECTIVES: To evaluate the effects of screw-plate locking and screw length on fixation strength and stability of anterior cervical plates. SUMMARY OF BACKGROUND DATA: New plate systems provide for rigid locking of the screw-plate interface, theoretically increasing construct rigidity, allowing unicortical fixation, and preventing screw back-out. There are few data on the effects of locking screws on the stability of anterior cervical plating. METHODS: Eighty fresh lamb vertebrae (C3-T1) were used. Test systems included: Cervical Spine Locking Plate (CSLP; Synthes, Paoli, PA, Orion plate (Sofamor-Danek, Memphis, TN), and Acroplate (AcroMed, Cleveland, OH). The CSLP and Orion plates were tested with fixation screws, locked and unlocked, and the AcroMed plate with unicortical and bicortical screw purchase. Biomechanical testing of the screw-plate constructs was performed to determine the initial bone-plate rigidity and pull-off strength. A 2.5-Nm cyclic bending moment was then applied to additional constructs for 10(5) cycles, and these constructs retested. RESULTS: Locked CSLP and Orion constructs were more rigid than all unlocked unicortical systems initially and after cyclic loading (P < 0.05). After cycling, the rigidity of all unlocked unicortical constructs decreased significantly (P < 0.05). There was no significant difference in pull-off strengths between the CSLP, the Orion, and the unicortical AcroMed plate. However, all had significantly less pull-off strength than the AcroMed plate with bicortical screws. A negative correlation was observed between initial pull-off strength and sagittal vertebral body diameter. CONCLUSIONS: Locking screws significantly increased the rigidity of the tested screw-plate systems initially and after cyclic loading. Because pull-off strength was affected by the vertebral body diameter, use of longer unicortical screws may be clinically beneficial in the patient with larger cervical vertebrae.

Animals↗
PubMed1999

The effect of acetabular cup orientations on limiting hip rotation.

The orientation of the acetabular cup and position of lip augmentation (if present) may improve postoperative total hip replacement stability by decreasing dislocation caused by hip prosthesis impingement during rotation. To determine how these cup parameters affect dislocation, the range and amount of rotation for two standard femoral components was determined in a Sawbones hemipelvis model. The parameters that allowed for maximal range of rotation were a cup angle of inclination between 35 degrees and 45 degrees and cup anteversion between 0 degrees and 10 degrees. Cup anteversion angles greater than 20 degrees and cup angles of inclination greater than 45 degrees significantly limited internal and external rotation, particularly for hip flexion greater than 60 degrees. The position of the cup lip augmentation did not affect the amount of rotation except when the hip was flexed and the lip superiorly oriented. Although there are currently devices to facilitate a particular cup position, hip stem type and orientation are other important factors affecting range of rotation that must be considered.

Acetabulum↗
PubMed1999

Analysis of the heel pad fat in rheumatoid arthritis.

The heel fat pad is organized, both in structure and in composition, to bear the stresses and strains of normal activities and to permit pain-free weightbearing. The fatty acid composition of heel pads in 11 patients with rheumatoid arthritis, a disease process frequently associated with heel fat pad atrophy, was analyzed using gas-liquid chromatography and was compared with that of patients without systemic disease. The heels of patients with rheumatoid arthritis demonstrated a significant change in the composition of saturated fatty acids when compared with heels of nonrheumatoid patients. This composition reflects an increased fat viscosity, which decreases the ability of the heel to absorb and dissipate the energy generated during ambulation. This factor could cause degeneration of the heel septal system, with resulting fat pad atrophy.

Abdomen↗
PubMed1999

Do all hip fractures result from a fall?

Although most fractures of the proximal femur result from a fall and are related to direct loads to the hip, there is evidence that intrinsic factors, such as muscle contraction, can result in a hip fracture and subsequent fall. This paper reviews the current literature on the various mechanisms of femoral neck and intertrochanteric fractures.

Accidental Falls↗
PubMed1998

Optimal selection and preparation of fresh frozen corticocancellous allografts for cervical interbody spinal fusion.

STUDY DESIGN: Iliac crest corticocancellous allografts for anterior interbody fusion were harvested from six cadavers. The grafts were cut sequentially from left and right crests and randomly assigned to tricortical or bicortical preparations. Their compression strengths then were determined and compared by matched pair analysis. OBJECTIVES: To quantify the failure strength of the grafts from different iliac locations and determine the optimal type of preparation of the grafts for anterior interbody fusion. SUMMARY OF BACKGROUND DATA: Iliac crest corticocancellous autografts and allografts commonly are used for interbody cervical fusions. However, graft strengths for specific sites have not been determined fully. METHODS: Six paired, fresh frozen, iliac crests were sectioned using a customized miter box into multiple 1-cm-thick grafts 1.5 cm in depth to simulate cervical interbody grafts. The left and right sides of each pair were randomly assigned to tricortical and bicortical preparations. The samples were tested by applying a compressive load to failure using a specialized fixture to simulate vertebral body loading. RESULTS: The grafts closer to the anterosuperior iliac spine had significantly higher failure loads and failure strengths than those closer to the posterosuperior iliac spine. The strengths of the bicortical grafts were 72 +/- 14% of the strengths of the tricortical grafts (P < 0.001). CONCLUSIONS: Anterior iliac crest grafts were stronger in compression, even after removal of one cortical surface, than posterior iliac crest grafts.

Adult↗
PubMed1998

Crutch handle design: effect on palmar loads during ambulation.

OBJECTIVE: To compare loads, load distributions, pressures, and areas of weight-bearing on the palm for forearm crutches with cylindrical and wide handles during ambulation to determine if one handle type produced greater loads on the carpal tunnel region. DESIGN: Single-group repeated measures of normal adults; descriptive study of patients who were long-term crutch users. Data were collected from six palmar regions using an F-Scan system. SETTING: Center for neuromuscular disorders in a hospital. PARTICIPANTS: Thirty normal volunteers and 6 patients. MAIN OUTCOME MEASURE: Differences in loads for the palmar regions between the two handles, particularly the carpal tunnel region. RESULTS: For the normal adults, significantly greater loads were found in two distal regions for the cylindrical handle and in one proximal region for the wide handle. Distribution of weight-bearing loads showed a similar pattern for both handles with the palm's proximal and distal radial sides having the greatest loads and the carpal tunnel region having the third highest load. The area of weight-bearing was significantly greater for the wide handle than for the cylindrical. CONCLUSIONS: Cylindrical and wide crutch handles have similar load distributions, making it impossible to recommend one type over the other to reduce the occurrence of carpal tunnel syndrome. The wide handle distributes the loads over a greater surface area, producing less focal pressure.

Adult↗
PubMed1998

Postoperative weight-bearing after a fracture of the femoral neck or an intertrochanteric fracture.

Sixty patients who had had operative treatment of a fracture of the femoral neck or an intertrochanteric fracture were allowed to bear weight as tolerated on the injured limb. The average age was seventy-seven years. Computerized gait-testing was performed at one, two, three, six, and twelve weeks postoperatively to quantify weight-bearing. For the purpose of analysis, the patients were divided into three groups according to whether they had internal fixation of a stable fracture, internal fixation of an unstable fracture, or a primary hemiarthroplasty. Thirty-two patients completed the entire twelve-week study. The average amount of weight that these patients placed on the injured limb increased progressively with time. The average load supported by the injured limb was 51 per cent that of the uninjured limb at one week, and it gradually increased to 87 per cent at twelve weeks. During the first three weeks, the patients who had had internal fixation bore substantially less weight than those who had had a hemiarthroplasty. By six weeks, we could detect no significant differences, with the numbers available, among the groups with regard to weight-bearing or other measured gait parameters. We concluded that elderly patients who are allowed to bear weight as tolerated after operative treatment of a fracture of the femoral neck or an intertrochanteric fracture appear to voluntarily limit loading of the injured limb.

Aged↗
PubMed1998

Intramedullary versus extramedullary fixation of subtrochanteric fractures. A biomechanical study.

We compared two different subtrochanteric fracture fixation techniques, an intramedullary hip screw system (IMHS) and an extramedullary, dual sliding screw-plate system (MSP), to determine relative fixation stability. 6 matched pairs of osteosynthesized osteopenic cadaver femurs were axially loaded to 1000 N with concurrent, simulated abductor forces of 0%, 50%, or 86% of the applied head force. The initial loading sequence was made with uniaxial dynamization--the lag screw of the MSP locked and distal locking of the IMHS nail. Femoral head displacement and medial femoral strain were measured for intact femur controls, after fixation of a 2-part reverse oblique subtrochanteric fracture and finally a 3-part reverse oblique subtrochanteric fracture with a lateral wedge defect. The samples were then loaded at 750 N for 10(4) cycles with both devices uniaxially locked, followed by 10(4) cycles with both devices fully biaxially dynamized (unlocked). For the 2-part subtrochanteric fracture pattern, both devices exhibited similar inferior displacements of the femoral head (average 2.0 mm) and medial femoral strain (approximately 70% of intact). Increasing abductor forces decreased medial compressive strain but did not significantly affect head displacement. For the 3-part fracture model, the MSP demonstrated significantly less inferior displacement of the head (1.6 mm vs. 2.1 mm) and both devices demonstrated significantly decreased medial strain. After cycling, head displacement increased approximately 50% in both devices and medial strain increased slightly. After unlocking and cycling, the MSP group showed significant lateral displacement of the proximal fragment. The IMHS and MSP devices provide similar stability for fixation of 2-part and 3-part reverse oblique subtrochanteric fractures. In a biaxially dynamized, 3-part reverse oblique fracture, displacement of the proximal fragment can occur with the MSP.

Aged↗
PubMed1998

The Medoff sliding plate and a standard sliding hip screw for unstable intertrochanteric fractures: a mechanical comparison in cadaver femurs.

The Medoff sliding plate has a dual side capability along both the femoral shaft and neck to increase theoretically interfragmentary compression and load-sharing in hip fractures. We studied intertrochanteric fracture fixation in cadaveric bone to determine whether this device has a mechanical advantage over a standard sliding hip screw. 2-part and 4-part fractures were created in 12 cadaver femurs. The fractures were fixated and sequentially destabilized; bone and plate strains and fragment displacements were determined during testing, as a function of applied physiological loads before and after short-term cycling. The Medoff sliding plate imposed a higher mean medial cortex strain than the sliding hip screw in all fracture models and at all loading levels, and the difference was statistically significant in the 2-part and in the unstable 4-part fracture models. The loading of the medial cortex region after cycling was approximately 50% higher in the Medoff samples than in the sliding hip screw samples. There were no significant differences in plate strains, fracture displacements or load to failure between the 2 devices. These observations favor the dual sliding principle as regards providing fracture compression and load-sharing, which may explain low failure rates in clinical series of unstable intertrochanteric fractures, treated with the Medoff sliding plate.

Aged↗
PubMed1998

Hard bearing surfaces in total hip arthroplasty.

Periprosthetic osteolysis and aseptic loosening are serious problems affecting the outcome of total joint replacement. Polyethylene particulate debris generated from metal-on-polyethylene bearing surfaces and the resulting biologic response to this debris are thought to be largely responsible. As a result, there has been a renewal of interest in hard bearing surfaces for total joint arthroplasty, including both metal-on-metal and ceramic-on-ceramic components. The new-generation all-ceramic and all-metal prostheses have demonstrated, both clinically and in the laboratory, lower friction and wear rates than metal-on-polyethylene bearing surfaces. Theoretically, lower wear rates result in less particulate debris and decreased inflammatory response. Despite excellent tribologic (lubrication, friction, wear) properties, metal-on-metal bearings raise associated issues of metal sensitivity and toxicity. For ceramic-on-ceramic bearing surfaces, issues of ceramic quality and the possibility of brittle fracture must be considered.

Biocompatible Materials↗
PubMed1997

Wurzburg lag screw plate versus four-hole miniplate for the treatment of condylar process fractures.

PURPOSE: The purpose of this study was to compare the biomechanical stability of rigidly fixed condylar neck fractures using either a conventional four-hole miniplate system or the Wurzburg lag screw plate system. MATERIALS AND METHODS: Ten identical synthetic mandibles were used for this study. Simulated bilateral condylar neck fractures were fixed with the lag screw plate system on one side and the miniplate system on the other. The mandibles were loaded with an MTS servohydraulic testing machine at a rate of 1 cm/min until failure was reached. Data for resistance to motion and ultimate strength for each fixation device were compared by paired Student t-tests. RESULTS: The mean resistance to motion for the four-hole miniplate was 64.0 kg/mm (SD = 10.1; range = 52-94) and for the lag screw system was 80.2 kg/mm (SD = 24.0; range = 55 to 126). The mean failure strength was 4.0 kg (SD = 0.9) (range = 2.6 to 5.5) for the miniplate system and 5.0 kg (SD = 2.5; range = 3.4 to 7.2) for the lag screw system. The lag screw system was significantly (P < .05) better than the miniplate for both parameters measured. CONCLUSION: In laboratory testing using synthetic mandibles, the Wurzburg lag screw-plate fixation system proved superior to a four-hole miniplate system in regard to resistance to motion and failure strength. Clinical trials are necessary to substantiate these laboratory data and determine whether the system can be effectively applied by the surgeon.

Bone Plates↗
PubMed1997

A new technique for complex fibula fracture fixation in the elderly: a clinical and biomechanical evaluation.

OBJECTIVE: To determine whether intramedullary fixation could augment plate fixation strength in comminuted and osteopenic fibula fractures. STUDY DESIGN: Retrospective clinical study and biomechanical laboratory study. METHODS: Twenty comminuted or osteopenic fibula fractures in twenty patients age fifty years or older were stabilized using plate fixation augmented with intramedullary Kirschner wires. Nineteen patients were available for follow-up which averaged 15.4 months (range, 6-43 months). In conjunction with this clinical series, a biomechanical evaluation was performed comparing fixation of mildly osteopenic fibulas using this technique to plate and screws alone. The fibulas were first tested non destructively in bending, and then destructively in torsion to determine stability and ultimate strength of the fixation. RESULTS: All nineteen fractures united without loss of reduction: seventeen of nineteen patients (89%) had either no pain, slight or mild pain. Biomechanical testing demonstrated that the resistance to bending of the plated fibulas augmented with Kirschner wires was 81% greater than the fibulas stabilized with a plate alone (p < .05). In torsional testing, the augmented group had twice the resistance to motion than the plate group (p < .002). CONCLUSION: This clinical series and biomechanical study support the use of plate fixation augmented with intramedullary Kirschner wires for the treatment of comminuted and osteopenic fibula fractures in the elderly.

Aged↗
PubMed1997

Use of the Medoff sliding plate for subtrochanteric hip fractures.

OBJECTIVE: To evaluate the effects of dynamization of a sliding hip screw plate on the fixation stability for several types of subtrochanteric fractures. Clinical results of treating reverse oblique fractures occasionally show medialization of the femoral shaft. DESIGN: Two types of plate dynamization were compared using the same test protocol in identically prepared groups of uniform, artificial femurs. METHODS: Sawbones composite femurs (Pacific Research Labs, Vashon, WA) having five orientations of simulated subtrochanteric fractures were used with the Medoff plate (Medpac, Inc., Valencia, CA) either fully dynamized or with the sliding lag screw locked. These specimens were physiologically loaded and cycled and displacements of the proximal femur determined. RESULTS: Significantly more shaft medialization occurred with reverse oblique fracture patterns when the Medoff plate was fully dynamized. CONCLUSION: Clinical treatment of reverse oblique fractures with the Medoff plate should be performed using the lag screw locked and only the plate dynamized.

Bone Plates↗
PubMed1997

Distal femoral fixation: a biomechanical comparison of the standard condylar buttress plate, a locked buttress plate, and the 95-degree blade plate.

OBJECTIVES: This biomechanical cadaver study was performed to compare the fixation stability of a standard lateral condylar buttress plate with a similar condylar buttress plate with the distal screws locked to the plate. Then the study was repeated with six additional matched femoral pairs to compare the locked plate with a standard 95-degree blade plate. DESIGN: Six matched pairs of mildly osteopenic femurs were selected, and each side was assigned randomly to fixation with either a standard lateral condylar buttress plate or a modified lateral condylar buttress plate with locked distal screws. The experiment was repeated with six additional matched pairs of femurs instrumented with either a modified lateral condylar buttress plate with locked distal screws or a standard 95-degree blade plate. INTERVENTION: The femurs were instrumented, and a gap osteotomy was created at the distal femoral metaphysis. The instrumented femurs were then mechanically tested in axial compression and bending/torsional loading to determine fixation stability; then they were loaded at 1,000 newtons for 10(5) cycles and retested for stability. MAIN OUTCOME MEASUREMENT: The displacement across the osteotomy gap at 100-newton and 1,000-newton axial loads was measured directly for each specimen before and after cycling. In addition, resistance to displacement in bending/torsional loading (newtons/centimeter) was determined from load/displacement curves, before and after cycling. RESULTS: The locked buttress plate provided significantly greater fixation stability than the standard plate both before and after cycling in axial loading. The locked buttress plate also proved significantly more stable in axial loading than the blade plate both before and after cycling. CONCLUSION: A condylar buttress plate with locked screws is a valid concept for improving fixation stability.

Biomechanical Phenomena↗
PubMed1997

Equinus deformity in cerebral palsy: recurrence after tendo Achillis lengthening.

Twenty-seven patients with cerebral palsy (CP) were recalled and studied in detail 2 to 9 years post tendo Achillis lengthening (TAL). The recurrence rate of equinus deformity was 22.2%. Multiple clinical characteristics and follow-up examination findings were analyzed to determine their relation to recurrence. The recurrence group had a significantly (P<0.05) smaller preoperative popliteal angle, a greater popliteal angle at follow-up, and a greater change in popliteal angle from preoperative to follow-up than the non-recurrence group. This indicated that increasing hamstring contracture was the major factor influencing recurrence. Spasticity of tibialis posterior and leg-length discrepancy may be related factors as well.

Achilles Tendon↗
PubMed1997

Screw omission and the stability of posterior pedicle screw constructs for short-segment stabilization.

To determine the net contribution of a spinal construct to stability, and whether extending the construct to another level in situations in which a defective pedicle cannot have a screw inserted, we performed biomechanical tests in which we evaluated three-, four-, and five-level synthetic spinal constructs in which the location and number of pedicle screws were varied above and below a vertebrectomy defect. We subjected all constructs to axial, compression, lateral bending, flexion, extension, and torsional forces with the use of an Instron biaxial machine. Left-right symmetrical constructs were more stable than asymmetrical ones. Three-level constructs were statistically stiffer than the longer ones in compression, left bending, and flexion. Torsional stability, however, was greater in the longer constructs. Five-level constructs with both end screws in place had greater torsional stiffness than when they were missing a screw. In vertebrectomy defects, if four screws cannot be placed across it, then the engagement of two screws is indicated. The stability provided by a single screw at a spinal level is minimal. Additional screws augment the purchase of the construct in the bone; however, they do not afford further protection to the defect.

Bone Screws↗