Biomedical subjects

Frederick J Kummer

Publications and source records attributed to Frederick J Kummer.

At least 19 recordsLinked to original sources

PubMed2006

Helical blade versus sliding hip screw for treatment of unstable intertrochanteric hip fractures: a biomechanical evaluation.

OBJECTIVE: To compare the fixation stability in the femoral head with sliding hip screw versus helical blade designs for unstable, intertrochanteric hip fractures. METHODS: A simulated, unstable intertrochanteric hip fracture was created in six pairs of cadaveric femurs. One of each pair was treated using an intramedullary nail with a sliding hip screw (ITST) for femoral head fixation and the other was treated with a nail with a helical blade (TFN). Each specimen was cyclically loaded with 750N vertical loads applied for 10, 100, 1000 and 10,000 cycles. Measurements for femoral head displacement, fracture fragment opening and sliding were made. Specimens were then loaded to failure. RESULTS: There was significantly more permanent inferior femoral head displacement in the ITST samples compared to the TFN samples after each cyclic loading (all p values<0.05). There was significantly more permanent fracture site opening and inferior displacement in the ITST group compared with the TFN group at 1000 and 10,000 cycles (p<0.05). Final loads to failure were not significantly different (p=0.51) between the two treatment groups. Nine specimens demonstrated fracture extension into the anteromedial cortex and subtrochanteric region and three specimens, which had an ITST implant, demonstrated a splitting fracture of the femoral head. CONCLUSION: This study demonstrated that fixation of the femoral head with a helical blade was biomechanically superior to fixation with a standard sliding hip screw in a cadaveric, unstable intertrochanteric hip fracture model.

Biomechanical Phenomena↗

PubMed2006

Arthroscopic rotator interval closure: effect of sutures on glenohumeral motion and anterior-posterior translation.

BACKGROUND: The effect of arthroscopic rotator interval closure on glenohumeral motion and translation is not well understood, nor is the ideal location or number of sutures required for closure. HYPOTHESIS: The number of arthroscopic rotator interval closure sutures and their placement will have a significant effect on glenohumeral range of motion and anterior-posterior translation. STUDY DESIGN: Controlled laboratory study. METHODS: Using a custom testing apparatus, the authors measured range of motion in 12 fresh-frozen cadaveric shoulders; anterior-posterior translation in adduction and neutral rotation was measured in 9. Specimens were initially tested without sutures and then tested after 3 interval closures using a random sequence of (1) an isolated medial suture at the level of the glenoid, (2) an isolated lateral suture 1 cm lateral to the glenoid, or (3) both sutures followed by removal of all sutures. RESULTS: Analysis of variance demonstrated that interval closure had a significant effect on decreasing flexion (mean, 6 degrees), external rotation (mean, 10 degrees), and anterior translation (mean, 3 mm) of the adducted shoulder. There was no significant difference between the 3 interval closures in any of the tests. CONCLUSION: Arthroscopic interval closure produced significant decreases in range of motion and anterior-posterior translation. The effects of single lateral or medial suture closures were similar to the use of 2 sutures. CLINICAL RELEVANCE: This study suggests that the initial effect of arthroscopic rotator interval closure on anterior translation of the shoulder will be similar whether 1 or 2 sutures are used. In vivo studies are necessary to determine if the effect of these 2 methods would be the same over time.

Adult↗

PubMed2006

The olecranon sled--a new device for fixation of fractures of the olecranon: a mechanical comparison of two fixation methods in cadaver elbows.

BACKGROUND: Tension band wiring is the most common surgical procedure for fixation of fractures of the olecranon, but symptomatic hardware prominence and migration of K-wires can cause a high re-operation rate. The olecranon sled has been designed to minimize some of these problems. MATERIAL AND METHODS: Simulated olecranon fractures were created in 6 matched pairs of cadaver arms. Each pair was fixed with tension band wiring used on the one arm and the olecranon sled being used on the other. Mechanical testing was done with the humerus rigidly fixed in a vertical position while the forearm was held at 1 of 3 angles of elbow fixation, 45 degrees , 90 degrees and 135 degrees , respectively. For each angle, the triceps and the brachialis muscles were sequentially loaded with 5 kg (50 N) for 20 cycles and the amount of fracture displacement measured. RESULTS: Loading of the brachialis muscle produced no increase in the fracture gap for either of the two fixation techniques. However, an increase in the fracture gap of up to 0.23 mm was found after cyclic loading of the triceps muscle for both techniques. The amount of increase was not significantly different between the two techniques. INTERPRETATION: The olecranon sled appears to provide as stable fixation as tension band wiring for olecranon fractures.

Adult↗

PubMed2006

A mechanical evaluation of two fixation methods using cancellous screws for coronal fractures of the lateral condyle of the distal femur (OTA type 33B).

PURPOSE: To compare the relative strength and stability of 2 fixation methods for displaced coronal shear fractures of the lateral femoral condyle (Hoffa fractures, OTA Type 33B3). SETTING: University Biomechanics laboratory. DESIGN: Eight matched pairs of embalmed femurs were divided into 2 groups and simulated Hoffa fractures were created. In each pair, 1 of the fractures was fixed with 2 screws placed in an anteroposterior direction, and in the other, the fracture was fixed with 2 screws placed in a posteroanterior direction. METHODS: All specimens were cyclically tested with simulated physiologic loading. Displacement of the femoral condyle was continuously measured to 10 cycles. The specimens were then loaded to failure. RESULTS: Fixation with posterior to anteriorly placed cancellous lag screws was significantly more stable than that with anterior to posteriorly placed screws at 10 cycles (P = 0.05), with 0.67 mm displacement compared to 1.36 mm, respectively. They were also more stable at 10, 100, and 1000 cycles; however, these displacements were not statistically significant. Fixation with posteriorly placed cancellous screws also had significantly higher ultimate strength (P = 0.04), 1700 N compared to 1025 N for anterior placement. CONCLUSION AND SIGNIFICANCE: Lag screws placed posterior to anterior provided more stable fixation of Hoffa fractures in embalmed femurs than anteroposteriorly placed lag screws. This finding may apply in the clinical setting; however, this technique requires that the screw heads be recessed beneath the articular surface. The effects of the cartilage defects so created are not known. The choice of technique is also determined by concomitant fractures and the exposure required for their fixation.

Aged↗

PubMed2006

Fixation of periprosthetic femoral shaft fractures associated with cemented femoral stems: a biomechanical comparison of locked plating and conventional cable plates.

UNLABELLED: To determine which of 2 techniques for the treatment of periprosthetic femoral shaft fractures is of greater stiffness. DESIGN: A laboratory study using 8 pairs of matched, embalmed femurs. METHODS: Femurs implanted with a cemented total hip prosthesis had a simulated periprosthetic femur fracture created distal to the implant. Fractures were fixed with a plate with locked screws or a plate with cables (Ogden construct). Fixation stability was compared in various loading modalities before and after cycling. Failure in torsional loading was then determined. The cement mantle was tested for crack propagation that may have occurred secondary to locked screw insertion and loading. OUTCOME MEASUREMENTS: Fixation stiffness (the ratio of applied load to displacement at the fracture site), torsional strength, mode of failure for each system, and cement mantle evaluation for cracks after screw insertion. RESULTS: Locked plating was stiffer than the Ogden construct in pre- and post-cyclic axial loading and torsion. There was no difference in lateral bending stability or torsional failure loads. CONCLUSIONS: Locked plating constructs were stiffer than the Ogden construct in axial loading and torsion. Although no differences in loads to failure during torsion were noted, locked plating constructs exhibited catastrophic failure not observed with the Ogden construct.

Arthroplasty, Replacement, Hip↗

PubMed2006

Fixation of diaphyseal fractures with a segmental defect: a biomechanical comparison of locked and conventional plating techniques.

BACKGROUND: Locking plates are an alternative to conventional compression plate fixation for diaphyseal fractures. The objective of this study was to compare the stability of various plating with locked screw constructs to conventional nonlocked screws for fixation of a comminuted diaphyseal fracture model using a uniform, synthetic ulna. Locked screw construct variables were the use of unicortical or bicortical screws, and increasing bone to plate distance. METHODS: This biomechanical study compared various construct groups after cyclic axial loading and three-point bending. Results were analyzed via one-way analysis of variance. Displacements after cyclical axial loading and number of cycles to failure in cyclic bending were used to assess construct stability. RESULTS: The constructs fixed by plates with bicortical locked screws withstood significantly more cycles to failure than the other constructs (p < 0.001). Significantly less displacement occurred after axial loading with bicortical locked screws than with bicortical nonlocked screws. Increased distance of the plate from the bone surface, and use of unicortical locked screws led to early failure with cyclic loading for constructs with locked screws. CONCLUSIONS: These results support the use of plating with bicortical locked screws as an alternative to conventional plating for comminuted diaphyseal fractures in osteoporotic bone. Bicortical locked screws with minimal displacement from the bone surface provide the most stable construct in the tested synthetic comminuted diaphyseal fracture model. The results of this study suggest use of plates with unicortical screws for the described fracture is not recommended.

Biomechanical Phenomena↗

PubMed2006

The effect of arthroscopic suture passing instruments on rotator cuff damage and repair strength.

There are a variety of arthroscopic devices used to pass sutures through the rotator cuff for its repair. Because they vary in size and shape, it is possible that they could damage the cuff and affect the integrity of the repair. We chose four devices for assessment--SutureLasso (Arthrex, Naples, FL), straight BirdBeak (Arthrex, Naples, FL), Viper (Arthrex, Naples, FL), and a #7 tapered Mayo needle--and performed cuff reattachments in four paired shoulders using suture anchors. These repairs were cycled and tested to failure. The SutureLasso and Mayo needle repairs failed at approximately 285 N whereas the BirdBeak and Viper failed during cycling at 150 N. It appears that the devices, which made the bigger holes in the cuff, can compromise the integrity of the repair.

Arthroscopy↗

PubMed2006

A biodegradable button to augment suture attachment in rotator cuff repair.

Recent experimental studies suggest that the use of suture anchors for rotator cuff tear (RCT) repair transfers the "weak link" to the suture-tendon interface where failure occurs as the sutures cut through the tendon. The purpose of this study was to evaluate the effect of using a suture augmentation button on the fixation strength of rotator cuff tendon repair. A 1.5 cm by 2 cm defect was created in the supraspinatus tendon of seven cadaveric shoulder pairs and two suture anchors inserted in each humerus for suture attachment. For one of each pair, the defect was repaired with sutures placed in a horizontal mattress configuration. The other side was repaired with the sutures being passed through low profile, bioabsorbable buttons placed on the bursal tendon surface prior to knot tying. The supraspinatus tendon was cyclically loaded at a physiologic rate and load (33 mm/sec and 180 N, respectively). The number of loading cycles was recorded when the specimens developed 0.75 cm and 1.5 cm gaps at the repair site. The specimens were then tested to failure. Specimens in the unaugmented group developed 0.75 cm and 1.5 cm gaps at an average of 135 cycles and 362 cycles, respectively. The button augmented group developed these gaps at average of 420 cycles and 708 cycles, respectively. These differences were statistically significant (p < 0.05). The gaps progressively increased in all specimens, which eventually failed by suture cutting through tendon in all specimens. This study demonstrates that in vitro, suture augmentation with a low profile, bioabsorbable button provides significantly enhanced fixation when using suture anchors to repair torn rotator cuff tendon. This device may be a useful adjunct to current methods of rotator cuff repair.

Absorbable Implants↗

PubMed2006

The effect of interference screw diameter on soft tissue graft fixation.

Tibial fixation of soft-tissue grafts is a weak link in anterior cruciate ligament reconstruction. Previous studies have examined varying interference screw lengths, screw types and tunnel sizes as means to improve graft fixation. We hypothesized that increasing interference screw diameter would significantly increase the maximum load to failure of the graft and decrease the graft's initial slippage. Seventy tibialis anterior and tibialis posterior tendons were divided, looped, trimmed, and sutured to simulate 4-strand hamstring grafts. These grafts were then inserted into composite bone blocks having pre-drilled 8 mm holes and fixed with 8 mm, 9 mm, 10 mm, 11 mm, or 12 mm interference screws. Fourteen grafts were tested for each screw size. The graft was first cyclically loaded from 50 N to 250 N at 0.3 Hz for 100 cycles to measure graft slippage. The graft was then tested to failure at 0.5 mm/sec to determine the maximum load to failure and mode of failure. Graft slippage was not affected by screw diameter. Maximum load to failure increased with increasing screw diameter up to 11 mm; 11 mm screw fixation was 20% stronger than 8 mm screw fixation. In this model, no increase in graft fixation was seen in by increasing interference screw diameter beyond 3 mm of the tunnel diameter.

Adult↗

PubMed2006

The interaction between the whipstitch sutures of multi-strand ACL grafts and interference screw fixation.

In a recent experiment examining the effect of interference screw sizing on the fixation stability of multi-strand anterior cruciate ligament grafts, we noticed a large variation in fixation strengths and attributed it to the suturing of the grafts and its interaction with the screw. We performed an experiment using interference screws for fixation of hamstring grafts within a bone tunnel model to compare how the presence of sutures affected graft fixation. We found that having sutures along the region of the graft that contacts the screw within the bone tunnel can increase graft fixation strength 100%.

Anterior Cruciate Ligament↗

PubMed2005

The role of graft materials in suture augmentation for tendon repairs and reattachment.

Various biomaterials have been used to augment sutures for the repair and reattachment of tendons. This study examined four different graft materials in a simple and reproducible model using chicken Achilles tendons to determine the strength and mechanism of suture reinforcement of tendon repairs. The graft materials tested were Gore-Tex(R) Soft Tissue Patch, Graftjacket, bovine pericardium, and an experimental graft material from Xylos Corporation. Testing was performed in shear to simulate forces on a torn tendon repair and pull-off to simulate those on a tendon reattachment to bone. Compared to unaugmented suture, grafts increased suture fixation strength from 10% to 60% in shear and from 0% to 36% in pull-off with the bovine pericardium graft, providing significant improvement in both tests. In no cases (even unaugmented) did the suture pull directly through the tendon, but instead sliced along it, demonstrating that the interface between the suture and the tendon determines fixation strength. Grafts function by increasing the area, friction, and nature of this interface, not by acting as a barrier for suture pull-through.

Achilles Tendon↗

PubMed2005

Stress risers between two ipsilateral intramedullary stems: a finite-element and biomechanical analysis.

Periprosthetic fracture after total joint replacement predominantly occurs at the stem tip. In this study, the effects of gap size, stem stability and cortical thickness between two press-fit, ipsilateral intramedullary stems on the tensile stresses created in the femur were investigated using finite-element models. The findings were confirmed with strain-gauge tests using a composite Sawbone femur. Gap size did not affect the level of stress on the femur. Cortical thickness had an important effect on stress distribution: peak stresses increased as bone cortical thickness decreased. Irrespective of gap size, the tips of loose stems acted as stress risers particularly with thinner cortices; the tips of well-fixed stems, however, did not.

Biomechanical Phenomena↗

PubMed2005

Bipolar head design: inner bearing range of motion and disassociation.

To address the clinical problems of joint stiffness, acetabular pain, and component wear, recent bipolar heads have been designed to achieve increased inner bearing range of motion. We tested four designs to determine if this compromises component integrity. Inner bearing ranges of motion were determined and the components then mechanically tested to determine inner bearing pull-out disassociation strengths as well as static and dynamic impingement forces for disassociation. Inner bearing ranges of motion with a 22 mm head were between 65 degrees to 84 degrees for the four prostheses. Pull-out forces for disassociation ranged between 700 N to 1475 N; static impingement forces were 20 Nm to 49 Nm and dynamic impingement forces were 5 Nm to 24 Nm. There was no relation between bipolar head inner bearing range of motion and the potential for component disassociation; however, one design modification produced a lowered disassociation strength. Design modifications must be evaluated by a variety of test methods to adequately determine their effects on bipolar head integrity.

Hip Joint↗

PubMed2004

Mismatch of current intramedullary nails with the anterior bow of the femur.

OBJECTIVES: The anterior curvature of the femur affects intramedullary nail insertion, revision prosthesis design, and the biomechanics of the proximal femur. Two previous studies, using small numbers of femurs, determined femoral curvature and showed that it was significantly greater than that of the several intramedullary nails they evaluated. In this study, the curvature of 948 femurs (474 matched pairs) was determined and compared with current intramedullary nails. The correlation of femoral curvature to age, gender, femoral size, and race was also evaluated. SETTING: Museum skeletal collections and a hospital biomechanics laboratory. METHODS: The curvature of 892 femurs (446) from the skeletal collections of 2 museums was measured by processing the digital images of the femurs with a computer curve-fitting program. Fifty-six additional, embalmed femurs (28 pairs) from our collection were also digitally imaged and then radiographed and their medullary curvatures similarly determined for comparison. Curvatures of 8 current antegrade intramedullary nails and 3 long-stemmed femoral hip prostheses were obtained from manufacturers and confirmed by measurements from their templates after digitization. RESULTS: We found the average femoral anterior radius of curvature was 120 cm (+/- 36 cm). There was no effect of age on femoral curvature nor was there a correlation between femoral width or femoral length to curvature. Black donor femurs had less curvature than white donor femurs (P < 0.001). There was close correlation (r = 0.967) between the femoral curvatures determined from the digital images and the radiographs. Radii of curvature of the intramedullary nails ranged from 186 to 300 cm (eg, straighter than the femurs). CONCLUSIONS: There was a large mismatch between the curvature of some current antegrade intramedullary nails and the average femur. Although this is only 1 factor affecting nail insertion, the mismatch warrants a reappraisal of these intramedullary nail designs. CLINICAL RELEVANCE: Because ease of intramedullary nail insertion and possibility of cortical comminution are determined by a number of factors including insertion point and fracture location, it appears that a decrease in radii of curvature (less straight) of current nail designs is warranted, particularly for those larger diameter nails designed for hip fracture stabilization that have greater rigidity due to design or material.

Anthropometry↗

PubMed2004

Biomechanics of locked plates and screws.

OBJECTIVE: To review the biomechanical principles that guide fracture fixation with plates and screws; specifically to compare and contrast the function and roles of conventional unlocked plates to locked plates in fracture fixation. We review basic plate and screw function, discuss the design rationale for the new implants, and examine the biomechanical evidence that supports the use of such implants. DATA SOURCES: Systematic review of the per reviewed English language orthopaedic literature listed on PubMed (National Library of Medicine online service). STUDY SELECTION: Papers selected for this review were drawn from peer review orthopaedic journals. All selected papers specifically discussed plate and screw biomechanics with regard to fracture fixation. PubMed search terms were: plates and screws, biomechanics, locked plates, PC-Fix, LISS, LCP, MIPO, and fracture fixation. DATA SYNTHESIS: The following topics are discussed: plate and screw function-neutralization plates and buttress plates, bridge plates; fracture stability-specifically how this effects gap strain and fracture union, conventional plate biomechanics, and locking plate biomechanics. CONCLUSIONS: Locked plates and conventional plates rely on completely different mechanical principles to provide fracture fixation and in so doing they provide different biological environments for healing. Locked plates may increasingly be indicated for indirect fracture reduction, diaphyseal/metaphyseal fractures in osteoporotic bone, bridging severely comminuted fractures, and the plating of fractures where anatomical constraints prevent plating on the tension side of the bone. Conventional plates may continue to be the fixation method of choice for periarticular fractures which demand perfect anatomical reduction and to certain types of nonunions which require increased stability for union.

Biomechanical Phenomena↗

PubMed2004

Comparison of a sliding hip screw with a trochanteric lateral support plate to an intramedullary hip screw for fixation of unstable intertrochanteric hip fractures: a cadaver study.

BACKGROUND: The lateral trochanteric support plate (LSP) was developed to prevent excessive sliding of unstable intertrochanteric femur fractures fixed with a sliding hip screw (SHS). This study compared the fracture stability and screw sliding characteristics of unstable intertrochanteric femur fractures fixed with either an SHS and LSP or an Intramedullary Hip Screw (IMHS). METHODS: Six matched pairs of cadaveric human femurs with simulated, unstable intertrochanteric femur fractures were stabilized with either an IMHS or a 135-degree SHS with an attached LSP. Inferior and lateral head displacements and lag screw sliding distances were measured for applied static loads of 750 N, before and after cycling. RESULTS: Four-part unstable intertrochanteric femur fractures showed comparable screw sliding characteristics and stability whether instrumented with an SHS and LSP or an IMHS. CONCLUSION: A sliding hip screw with an attached lateral support plate provides stability and ability to resist medial displacement of the femoral shaft similar to that seen with the IMHS.

Biomechanical Phenomena↗

PubMed2004

Treatment of complex tibial plateau fractures using the less invasive stabilization system plate: clinical experience and a laboratory comparison with double plating.

BACKGROUND: Bicondylar tibial plateau fractures are complex injuries, historically associated with high complication rates. The purpose of this study was: 1) to evaluate the clinical use L.I.S.S plating system for stabilization of bicondylar tibial plateau fractures. 2) To compare the biomechanics of this plating system with a double plate construct. METHODS AND MATERIALS: Thirty-eight patients who sustained a complex tibial plateau fracture (OTA type 41C) at one of three level-one trauma centers were stabilized using the Less Invasive Stabilization System (L.I.S.S.). The cohort of patients was evaluated clinically and radiographically for outcomes at a mean 15 months. In phase 2 of this study a model of a bicondylar tibial plateau fractures was made in six matched pairs of embalmed, human tibia and randomized to fixation with either a L.I.S.S plate or a standard double plate construct. The tibias were then subjected to an axial cyclic load of 500N for 10 cycles (3Hz) to approximate 2 months in vivo and displacements measured. RESULTS: Thirty-six of /38 (95%) patients united at 4 months after surgery with no loss of fixation nor infection. Two patients underwent prophylactic autogenous bone grafting for bone loss and united by 3 months postgrafting. Significant loss of knee range of motion (<90) was seen in five patients.Biomechanically, no differences in permanent inferior displacement of the medial fragment were found in initial axial loading and after 10 cycles between the two plate constructs. However, when loaded to 500N the L.I.S.S plate construct demonstrated almost twice the displacement of the medial fragment compared with the dual plate construct. No specimen lost fixation during cycling. CONCLUSION: The L.I.S.S plating system provides stable fixation of complex bicondylar tibial plateau fractures allowing early range of knee motion with favorable clinical results.

Adult↗

PubMed2004

Possible errors in pin insertion positions using the C-arm.

In order to measure errors in pin positions, a tibia with referenced pin insertions was radiographed in various locations using a mini C-arm. Changes in pin position locations up to seven millimeters and twelve degrees were found. To minimize these errors, limbs should be centered and parallel to the plane of the imaging screen of the C-arm. If possible, pin insertions should be made in this plane. Magnification due to the distance from the screen should be determined for precise pin positioning.

Bone Nails↗