Fracture Site Motion Research Articles

Design and validation of finite element models for the assessment of post-fixation distal femur fracture motion.

Fracture site motion is thought to play an important role in the healing of complex fractures of the distal femur via mechanotransduction. Measuring this motion in vivo is challenging, and this has led researchers to turn to finite element modeling approaches to gain insights into the mechanical environment at the fracture site. Developing a systematic understanding of the effect of different model choices for distal femur fractures may allow more accurate prediction of fracture site motion from these types of simulations. In this study, we aim to assess the effect of four different modeling choices and parameters. We looked at the effect of using bone specific density distributions vs generic values, employing landmark-based geometry generation, varying fracture alignment within clinically relevant ranges, and determining whether direct apposition of the fracture to the plate was achieved. For validation, five cadaveric femurs had fractures created and repaired with plated constructs, and these were then loaded and fracture site motion was directly measured. We found that using landmark based bone geometry and patient-specific bone density distributions had a minimal effect on the overall model predictions. Changing the alignment, particularly into varus and procurvatum could have a large (>50%) effect on predicted shear motion, as could direct apposition of the bone to the plate. These findings demonstrate that modeling choices can play an important role in simulating distal femur fracture mechanics, and it is particularly critical that patient customized models attempt to accurately represent alignment of the bone fragments and lateral plate apposition.

Independent volumetric internal fixation reduces posterior column acetabular fracture site motion as compared to plate/screw construct: A biomechanical analysis

Aims & objectivesTo establish whether a suprapectineal pelvic reconstruction plate and posterior column screw (P&S) construct or a single 6.5-mm cannulated posterior column screw (PCS) construct demonstrates greater mechanical stability for fixation of acetabulum fractures involving the posterior column (PC). We hypothesized that the PCS construct would result in less fracture site motion. Materials & methodsTwelve fourth-generation composite hemipelvi were utilized, 6 for each construct. The P&S construct consisted of a suprapectineal pelvic reconstruction plate with two 3.5-mm posterior column screws crossing the fracture site in lag-by-technique fashion and two screws anchoring the plate to the sciatic buttress. The PCS construct consisted of a single 6.5-mm partially threaded cannulated screw placed in an antegrade fashion. Both fixation models were cyclically loaded at 0.5 cycles/second at 400N and 800N, first in a sit-to-stand position that is expected during recovery, and subsequently in a squat-to-stand position to test overload conditions. ResultsUnder sit-to-stand loading, the PCS construct resulted in less motion at the fracture site than the P&S construct (0.06 ± 0.02 mm vs 0.1 ± 0.02 mm at 400N, p = 0.02; 0.13 ± 0.03 mm vs 0.19 ± 0.04 mm at 800N, p = 0.03). The PCS construct also demonstrated less fracture site motion under squat-to-stand loading (0.22 ± 0.13 mm vs 1.9 ± 0.5 mm at 400N, p = < 0.001; 1.48 ± 0.44 mm vs 4.77 ± 0.3 mm at 800N, p = < 0.001). At 800 N, half of the repairs failed during squat-to-stand loading (2 PCS, 4 P&S). ConclusionFixation of the posterior column of the acetabulum with a 6.5-mm cannulated screw demonstrated comparable fracture motion upon loading compared to the plate and screw construct.

Biomechanical Stability of Diaphyseal Ulnar Shaft Fractures and Ulnar Shortening Osteotomies After Fixation.

To determine the amount of micromotion during forearm rotation after diaphyseal ulnar shaft fracture or osteotomy. This was a biomechanical study using 7 paired-matched cadavers. The upper extremity was mounted in a custom rig and the forearm brought through full pronation and supination. A Hall effect sensor was placed at the fracture ends to measure micromotion for all tested conditions. There were 4 conditions tested: (1) intact ulnar shaft with plate to act as a control; (2) transverse fracture/osteotomy without stabilization; (3) fracture/osteotomy with cortical apposition stabilized with plate fixation; and (4) 50% comminuted fracture stabilized with plate. There was a significantly greater amount of fracture site motion in the fracture/osteotomy model without stabilization compared with all other tested conditions (P < .001, .0001, .0003, respectively). The fracture/osteotomy site with cortical apposition and the comminuted fracture models showed no statistically significant differences in the amount of micromotion compared with each another (P = .952) or compared with the intact ulnar shaft (P = .997, .889, respectively). There was no significant difference in the amount of motion between an intact ulnar shaft, an ulnar shaft fracture with cortical apposition stabilized with a plate, and a plated comminuted fracture. These findings may help surgeons decide on their type of postoperative immobilization in the setting of isolated ulnar shaft fractures or ulnar shaft osteotomies stabilized with plate fixation.

Bridge Plate Fixation of Distal Femur Fractures: Defining Deficient Radiographic Callus Formation and its Associations.

To determine whether deficient early callus formation can be defined objectively based on association with an eventual nonunion and specific patient, injury, and treatment factors. Final healing outcomes were documented for 160 distal femur fractures treated with locked bridge plate fixation. Radiographic callus was measured on postoperative radiographs until union or nonunion had been declared by the treating surgeon. Deficient callus was defined at 6 and 12 weeks based on associations with eventual nonunion via receiver operator characteristic analysis (ROC). A previously described computational model estimated fracture site motion based on the construct employed. Univariable and multivariable analyses then examined the association of patient, injury, and treatment factors with deficient callus formation. There were 26 nonunions. Medial callus area at 6 weeks < 24.8 mm2 was associated with nonunion (12 of 39, 30.8%) vs. (12 of 109, 11.0%), p = 0.010. This association strengthened at 12 weeks with medial callus area < 44.2 mm2 more closely associated with nonunion (13 of 28, 46.4%) vs (11 of 120, 9.2%), p < 0.001. Multivariable logistic regression analysis found limited initial longitudinal motion (OR 2.713 (1.12 to 6.60), p = 0.028)) and Charlson Comorbidity Index (1.362 (1.11 to 1.67), p = 0.003) were independently associated with deficient callus at 12 weeks. Open fracture, mechanism of injury, smoking, diabetes, plate material, bridge span, and shear were not significantly associated with deficient callus. Deficient callus at 6 and 12 weeks is associated with eventual nonunion and such assessments may aid future research into distal femur fracture healing. Deficient callus formation was independently associated with limited initial longitudinal fracture site motion derived through computational modeling of the surgical construct, but not more routinely discussed parameters such as plate material and bridge span. Given this, improved methods of in vivo assessment of fracture site motion are necessary to further our ability to optimize the mechanical environment for healing.

A novel way to dynamize a spatial frame and optimize fracture healing

BackgroundFracture site motion creates mechanical strains on the healing tissues which influences bone formation. Axial micro-motion maximizes dilatational strains, whereas shearing motions maximize deviatoric strains on the healing tissues. Dilatational strains optimize bone healing, deviatoric strains retard bone healing. Dynamization of external fixation using either an Ilizarov or Spatial Frame platform is used to increase loading on the limb which increases the mechanical stress and strain on the tissues to improve healing. The scientific literature does not address how dynamization of the spatial frame effects fracture site motion. The purpose of this study is to assess the effect of modified shoulder bolts incorporated into a spatial frame during dynamic loading. MethodsFive identical two-ring spatial frame constructed were mounted on Sawbones tibias with an osteotomy performed distal to the tibial tubercle. Sinusoidal load was applied at a rate of 0.25 Hz. Axial force and displacement, in addition to motion of the proximal and distal tibia segments were recorded. Eight constructs were tested: 1) All struts of the Spatial Frame rigid, 2) Strut #1 loose, 3) Struts #1 and #3 loose, 4) Struts #1, #3 and #5 loose, 5) All struts loose, 6) All struts rigid with dynamization bolts on the proximal end, 7) All struts rigid with dynamization bolts on alternating sides, 8) Threaded rods between the rings with two millimeters of dynamization. ResultsNo difference in vertical displacement was observed between the Ilizarov and all struts locked. No significant difference in shear values between all struts locked and modified shoulder bolt struts was observed. Increase in vertical movement with the modified shoulder bolts was an average of 1.83 mm. Significant shear forces at the fracture site were observed with unlocking single or multiple struts of the spatial frame. ConclusionModified shoulder bolts can be used for spatial frame dynamization without increasing shear motion.

Influence of fracture obliquity and interlocking nail screw configuration on interfragmentary motion in distal metaphyseal tibia fractures.

The indications for the use of intramedullary (IM) nails have been extended to include extra-articular distal metaphyseal tibia fractures. We hypothesize that interfragmentary motion during physiologic compressive loading of distal tibia fractures is influenced by fracture obliquity and can be modulated by interlocking screw configuration. Sawbone specimens were osteotomized with frontal plane obliquities ranging from 0° to 60° and then fixed by IM nailing with six interlocking screw configurations. Interfragmentary motion was evaluated during loading in axial compression to 1000N. Comparisons of interfragmentary motions were made (1) between configurations for the various fracture obliquities and (2) between fracture obliquities for the various screw configurations using a mixed-effects regression model. As the degree of fracture obliquity increased, significantly more interfragmentary displacement was shown in configurations with two distal interlocking screws and one proximal screw set in dynamic mode. Fracture obliquity beyond 30° causes demonstrated instability in configurations with less than two distal locking screws and one proximal locking screw. Optimizing the available screw configurations can minimize fracture site motion and shear in distal tibial fractures with larger fracture obliquities.

Cement Augmentation in Sacroiliac Screw Fixation Offers Modest Biomechanical Advantages in a Cadaver Model.

Sacroiliac screw fixation in elderly patients with pelvic fractures is prone to failure owing to impaired bone quality. Cement augmentation has been proposed as a possible solution, because in other anatomic areas this has been shown to reduce screw loosening. However, to our knowledge, this has not been evaluated for sacroiliac screws. We investigated the potential biomechanical benefit of cement augmentation of sacroiliac screw fixation in a cadaver model of osteoporotic bone, specifically with respect to screw loosening, construct survival, and fracture-site motion. Standardized complete sacral ala fractures with intact posterior ligaments in combination with ipsilateral upper and lower pubic rami fractures were created in osteoporotic cadaver pelves and stabilized by three fixation techniques: sacroiliac (n = 5) with sacroiliac screws in S1 and S2, cemented (n = 5) with addition of cement augmentation, and transsacral (n = 5) with a single transsacral screw in S1. A cyclic loading protocol was applied with torque (1.5 Nm) and increasing axial force (250-750 N). Screw loosening, construct survival, and sacral fracture-site motion were measured by optoelectric motion tracking. A sample-size calculation revealed five samples per group to be required to achieve a power of 0.80 to detect 50% reduction in screw loosening. Screw motion in relation to the sacrum during loading with 250 N/1.5 Nm was not different among the three groups (sacroiliac: 1.2 mm, range, 0.6-1.9; cemented: 0.7 mm, range, 0.5-1.3; transsacral: 1.1 mm, range, 0.6-2.3) (p = 0.940). Screw subsidence was less in the cemented group (3.0 mm, range, 1.2-3.7) compared with the sacroiliac (5.7 mm, range, 4.7-10.4) or transsacral group (5.6 mm, range, 3.8-10.5) (p = 0.031). There was no difference with the numbers available in the median number of cycles needed until failure; this was 2921 cycles (range, 2586-5450) in the cemented group, 2570 cycles (range, 2500-5107) for the sacroiliac specimens, and 2578 cycles (range, 2540-2623) in the transsacral group (p = 0.153). The cemented group absorbed more energy before failure (8.2 × 105 N*cycles; range, 6.6 × 105-22.6 × 105) compared with the transsacral group (6.5 × 105 N*cycles; range, 6.4 × 105-6.7 × 105) (p = 0.016). There was no difference with the numbers available in terms of fracture site motion (sacroiliac: 2.9 mm, range, 0.7-5.4; cemented: 1.2 mm, range, 0.6-1.9; transsacral: 2.1 mm, range, 1.2-4.8). Probability values for all between-group comparisons were greater than 0.05. The addition of cement to standardsacroiliac screw fixationseemed to change the mode and dynamics of failure in this cadaveric mechanical model. Although no advantages to cement were observed in terms of screw motion or cycles to failure among the different constructs, a cemented, two-screw sacroiliac screw construct resulted in less screw subsidence and greater energy absorbed to failure than an uncemented single transsacral screw. In osteoporotic bone, the addition of cement to sacroiliac screw fixation might improve screw anchorage. However, larger mechanical studies using these findings as pilot data should be performed before applying these preliminary findings clinically.

From Bench to Bedside: How Stiff is Too Stiff? Far-cortical Locking or Dynamic Locked Plating May Obviate the Question.

From Bench to Bedside: How Stiff is Too Stiff? Far-cortical Locking or Dynamic Locked Plating May Obviate the Question.

Comminuted olecranon fracture fixation with pre-contoured plate: Comparison of composite and cadaver bones.

To determine whether use of a precontoured olecranon plate provides adequate fixation to withstand supraphysiologic force in a comminuted olecranon fracture model. Five samples of fourth generation composite bones and five samples of fresh frozen human cadaveric left ulnae were utilized for this study. The cadaveric specimens underwent dual-energy X-ray absorptiometry (DEXA) scanning to quantify the bone quality. The composite and cadaveric bones were prepared by creating a comminuted olecranon fracture and fixed with a pre-contoured olecranon plate with locking screws. Construct stiffness and failure load were measured by subjecting specimens to cantilever bending moments until failure. Fracture site motion was measured with differential variable resistance transducer spanning the fracture. Statistical analysis was performed with two-tailed Mann-Whitney-U test with Monte Carlo Exact test. There was a significant difference in fixation stiffness and strength between the composite bones and human cadaver bones. Failure modes differed in cadaveric and composite specimens. The load to failure for the composite bones (n = 5) and human cadaver bones (n = 5) specimens were 10.67 nm (range 9.40-11.91 nm) and 13.05 nm (range 12.59-15.38 nm) respectively. This difference was statistically significant (P ˂ 0.007, 97% power). Median stiffness for composite bones and human cadaver bones specimens were 5.69 nm/mm (range 4.69-6.80 nm/mm) and 7.55 nm/mm (range 6.31-7.72 nm/mm). There was a significant difference for stiffness (P ˂ 0.033, 79% power) between composite bones and cadaveric bones. No correlation was found between the DEXA results and stiffness. All cadaveric specimens withstood the physiologic load anticipated postoperatively. Catastrophic failure occurred in all composite specimens. All failures resulted from composite bone failure at the distal screw site and not hardware failure. There were no catastrophic fracture failures in the cadaveric specimens. Failure of 4/5 cadaveric specimens was defined when a fracture gap of 2 mm was observed, but 1/5 cadaveric specimens failed due to a failure of the triceps mechanism. All failures occurred at forces greater than that expected in postoperative period prior to healing. The pre-contoured olecranon plate provides adequate fixation to withstand physiologic force in a composite bone and cadaveric comminuted olecranon fracture model.

DLS 5.0--the biomechanical effects of dynamic locking screws.

IntroductionIndirect reduction of dia-/metaphyseal fractures with minimally invasive implant application bridges the fracture zone in order to protect the soft-tissue and blood supply. The goal of this fixation strategy is to allow stable motion at the fracture site to achieve indirect bone healing with callus formation. However, concerns have arisen that the high axial stiffness and eccentric position of locked plating constructs may suppress interfragmentary motion and callus formation, particularly under the plate. The reason for this is an asymmetric fracture movement. The biological need for sufficient callus formation and secondary bone healing is three-dimensional micro movement in the fracture zone. The DLS was designed to allow for increased fracture site motion. The purpose of the current study was to determine the biomechanical effect of the DLS_5.0.MethodsTwelve surrogate bone models were used for analyzing the characteristics of the DLS_5.0. The axial stiffness and the interfragmentary motion of locked plating constructs with DLS were compared to conventional constructs with Locking Head Screws (LS_5.0). A quasi-static axial load of 0 to 2.5 kN was applied. Relative motion was measured.ResultsThe dynamic system showed a biphasic axial stiffness distribution and provided a significant reduction of the initial axial stiffness of 74.4%. Additionally, the interfragmentary motion at the near cortex increased significantly from 0.033 mm to 0.210 mm (at 200N).ConclusionsThe DLS may ultimately be an improvement over the angular stable plate osteosynthesis. The advantages of the angular stability are not only preserved but even supplemented by a dynamic element which leads to homogenous fracture movement and to a potentially uniform callus distribution.

The Use of Far Cortical Locking Constructs for Fixation of Periprosthetic Fractures

Locked plate constructs used for fixation of periprosthetic fractures show high rates of healing difficulties. This is especially true in the distal femur, where modern studies show a revision rate of 15% to 22%. The combination of residual fracture gaps created by using biological fixation techniques and the high stiffness of locked plates is thought to result in decreased motion at the fracture site. Concern that the increased stiffness of locked plates contributes to the high nonunion rate lead to changes in the surgical technique (longer working length) and implant materials (titanium). These changes result in plate bending at the fracture site and induce callus at the cortex opposite the plate, with very little callus forming at the cortex near the plate. Far cortical locking (FCL) was developed out of the need to decrease construct stiffness and increase callus formation by allowing symmetric fracture site motion within the optimal range for secondary bone healing. The use of FCL constructs requires only minor changes in surgical technique from standard locked plating. Early outcomes using FCL screws for both nonperiprosthetic and periprosthetic fractures suggest the screws are safe in osteoporotic bone with increased callus formation and no screw breakage or pull out.

Biomechanical Comparison of 4 Different Lateral Plate Constructs for Distal Fibula Fractures

Displaced lateral malleolar fractures are often treated with reduction and surgical stabilization. However, there has not been a comprehensive laboratory comparison to determine the most appropriate device for treating these patients. This study subjected a range of contemporary lateral fibular plates to a series of mechanical tests designed to reveal performance differences. Forty fresh frozen lower extremities were divided into 4 groups. A Weber B distal fibula fracture was simulated with an osteotomy and stabilized using 1 of 4 plate systems: a standard Synthes one-third tubular plate with interfragmentary lag screw, a Synthes LCP locking plate with lag screw, an Orthohelix MaxLock Extreme low-profile locking plate with lag screw, or a TriMed Sidewinder nonlocking plate. Controlled monotonic bending and cyclic torsional loading were applied and bending stiffness, torsional stiffness, and fracture site motion were quantified. Resistance to cyclic torsional loading was determined by quantifying the number of loads withstood before excessive rotation occurred. Correlation between bone mineral density and each of the mechanical measures was determined. There was no difference in angulation or bending stiffness between plates. All plates except the LCP showed greater lateral deflection than in the other bending directions. Bending stiffness was lowest in lateral distal fragment deflection for all 4 plates. There was a positive correlation between bone mineral density and bending stiffness for all plate types. There was no difference in fracture site rotation between plate types in internal or external torsion, but internal rotation of the distal fragment consistently exceeded external rotation. Torsional stiffness in external rotation exceeded stiffness in internal rotation in nearly all specimens. LCP plates performed relatively poorly under cyclic torsion. Significant differences in plate performance were not demonstrated. The effects of bone quality variability and differences in interfragmentary screw purchase resulted in data dispersion that confounded absolute ranking of plate performance. Identification of an optimal lateral fibular plating system has the potential to improve the clinical outcome of malleolar fracture fixation, particularly when patient conditions are unfavorable.

Stabilization of 2-Column Thoracolumbar Fractures With Orthoses

A gross anatomic and motion analysis study in cadavers. Assess spinal motion in a cadaveric spinal fracture model and investigate the ability of external orthoses to control this motion. External orthoses are frequently prescribed for patients who have experienced burst fracture of the thoracolumbar spine. Despite the substantial expense involved, there is little data confirming their value. A T12 burst fracture model was created in 5 lightly embalmed cadavers by resecting the anterior and middle columns of the T12 vertebra through a thoracolumbar anterior approach to the spine. An electromagnetic motion tracking and analysis system was used to track angular and linear displacement at the fracture during routine patient maneuvers. Several commonly used orthoses, including an extension brace and both an "off-the-shelf" and custom-molded thoracic-lumbar-sacral orthosis (TLSO), were applied to the cadavers and the affect on fracture site motion was assessed. Application of all 3 styles of brace resulted in angular motion of 8° to 12° in flexion-extension, 11° to 20° in axial rotation, and 8° to 10° of lateral bending. Brace application resulted in linear displacement of 29 to 46 mm in the medial-lateral plane, 21 to 23 mm in the axial plane, and 21 to 37 mm in the anterior-posterior plane. During logrolling maneuvers, TLSO style braces diminished angular motion, although residual motion in the range of 5° remained. TLSO style braces had little effect on linear translation. When placed in a seated position in bed, TLSO style braces diminished flexion and extension modestly, but did not influence lateral bending or linear translation. Extension style braces had no effect on fracture motion during any activity tested. In a cadaver model of a burst fracture, there is surprising angular and linear motion at the fracture during common hospital activities. TLSO orthoses can decrease angular motion but do not effect translation at the fracture. An extension orthosis had no effect on motion at the spinal fracture site.

Cerclage cable in fracture: frustration or necessity?

Dear Editor, I have read the article “The benefit of wire cerclage stabilisation of the medial hinge in intramedullary nailing for the treatment of subtrochanteric femoral fractures: a biomechanical study” with the great interest [1]. In their article, the authors argue that osteosynthesis frequently fails and a higher rate of nonunion is found in the subtrochanteric region of the femur. As I understand from their article, this nonunion is due to fracture distraction (commonly seen after intramedullary nailing) in the subtrochanteric region, and they believe that supporting the medial column with cerclage wiring can resolve this problem [1]. They concluded that “a mini-open approach to difficult fractures could be helpful in reducing the fracture with a clamp and is sometimes essential. An additional cerclage in oblique subtrochanteric fractures is a good option to ensure the reposition and cortical medial support if appropriate and to decrease osteosynthesis failure and rates of non-unions”. We would like to thank the authors for their invaluable study but do not agree with them. Yes, subtrochanteric fracture of the femur is a very problematic region for orthopaedic surgeons due to the particular anatomical features including high Ratio of cortical bone and to cancellous bone compared to other skeletal regions. These features result in low blood supply which means low union rates compared to other parts of the body. But higher nonunion does not mean more than 10%, but rather means higher compared to the intertrochanteric region. We work at a university hospital and we have faced many nonunions in our clinic, which is why we want to share our experience with cables. Cerclage cable inhibits fracture union in two ways (Fig. 1): (1) it prevents formation of callus and (2) it inhibits local blood supply. Cable is not implantable for transverse fractures and comminuted fractures, as it can only be performed to oblique or spiral fractures. The authors stated that reduction is important and this can be achieved with cable. Most angulation is due to improper nail insertion, and if technical guidelines are followed this problem can be minimised. Intramedullary fixation has biological and biomechanical advantages, but the operation is technically demanding. Gradual learning and great patience is needed in order to make this method truly minimally invasive. Long PFN, long gamma nail or Russell Taylor nail are reliable implants for subtrochanteric fractures, leading to high rates of bone union and minimal soft tissue damage [2]. If angulation still persists, a simple AO screw will suffice. The authors state that if you use clamp for reduction, you can insert a cable [1]. Technically, if you use a clamp, you do not need to cut or devitalize the surrounding tissue. That is why blood supply is not damaged. But if you use cable you need to dissect more tissue. For simple, well-reduced fractures the choice of implant is not critical. If subtrochanteric fractures are unstable (e.g., comminution, segmental bone loss, long spiral), the choice of implant is critical and should be restricted to implants that allow minimal fracture site motion (long gamma and Russell-Taylor) instead of short PFN [3]. Fig. 1 Cable failure and subtrochanteric nonunion In conclusion, in our experience along with other authors, higher union in the subtrochanteric region can be achieved with the last generation intramedullary nail with good technique. Using cable may improve anatomical reduction, but one should not forget that an extra implant may increase operation time, cost, bleeding and nonunion.

Proximal Humeral Fractures

The purpose of our study was to biomechanically compare, under cyclic loading conditions, fracture site motion, humeral head collapse, and intra-articular hardware penetration in simulated 3-part osteoporotic proximal humeral fractures stabilized with 1 of 2 locking-plate constructs. We performed fixation on simulated 3-part proximal humeral fractures in 10 pairs of cadaveric osteoporotic humeri with a Hand Innovations S3 Proximal Humerus Plate (S3 plate) or an LCP Proximal Humerus Plate (LCP plate; 1 each for each pair). The specimens were potted, mounted on a materials testing machine, and subjected to 5000 cycles of abduction in the scapular plane, loading through the supraspinatus tendon. Interfragmentary displacement at 2 virtual points (the most medial aspect of the calcar and the most superior aspect of the osteotomy line between the greater tuberosity and humeral head) was measured using an optical tracking system. Humeral head rotation was also measured. We used a generalized linear latent and mixed model to check for an effect of cyclic loading and treatment on the parameters of interest (significance, P < .05). After cyclic loading, the S3 plate humeri showed significantly greater displacement of the greater tuberosity fragment and rotation of the humeral head and a trend (not a significant difference) toward greater displacement at the calcar. No hardware penetration was noted for either repair. Although the S3 plate repairs resulted in significantly more fracture site motion, it is unknown whether the magnitude of the motion is clinically significant.

Biomechanical Comparison of Three Methods of Sacral Fracture Fixation in Osteoporotic Bone

Biomechanical cadaveric bench study. To measure motion at the fracture site in an osteoporotic cadaveric sacral insufficiency fracture model before and after fracture creation, after fixation (via 1 of 3 fixation techniques), and after cyclic loading and to compare those values with motion of the intact pelvis. Sacral insufficiency fractures occur frequently in the elderly and pose treatment challenges. Screw fixation and sacroplasty have been proposed as possible treatments. There is little information about the stabilization provided by these treatments. We potted 18 osteoporotic cadaveric pelves, mounted them on a materials testing machine, measured sacroiliac (SI) joint motion with a vertical load applied to the lumbar spine, and created simulated sacral insufficiency fractures. Then, we measured fracture site motion under load and repaired the fracture using 1 of 3 techniques: a unilateral SI screw, a bilateral SI screw, or sacroplasty. A vertical compressive load (10-350 N) was applied cyclically at 0.5 Hz to the lumbar spine of the repaired specimens for 5000 cycles. Kinematic analysis was conducted prefracture, postfracture, postrepair, and after cyclic loading. Postfracture, there was a significant increase in motion relative to the intact SI joint. After fixation, the average motion in all 3 groups was similar to that of the intact pelvis. After cyclical loading, motion increased in all groups. No significant differences were found between treatments. All 3 fixation methods resulted acutely in motion similar to that of the intact pelvis. Although motion increased as a function of cyclical loading, no significant differences were found between fixation methods. All 3 repair methods reduced fracture site motion, but clinical studies are needed to determine if each method relieves pain and provides sufficient fixation for fracture healing.

Superior Pubic Ramus Fractures Fixed With Percutaneous Screws: What Predicts Fixation Failure?

The purpose of this study is to present the early complications of percutaneous screw fixation of superior pubic ramus fractures and to present a new classification scheme for superior pubic ramus fractures. Retrospective. Level 1 trauma center. One hundred and twelve patients with pelvic fracture between the ages of 14 to 89 years underwent percutaneous screw fixation of 145 pubic ramus fractures. Eighty-one patients with 107 surgically repaired fractures were followed to fracture union. Follow-up averaged 9 months (range 2-52 months). One additional patient who sustained fixation failure 4 days after surgery was included to yield a study group of 82 patients with 108 surgically repaired ramus fractures. Patients underwent percutaneous screw fixation of a superior pubic ramus fracture. Superior pubic ramus fractures were classified according to a new scheme, the Nakatani system, which categorizes superior ramus fractures according to location with respect to the obturator foramen. Patient radiographs were examined for evidence of loss of reduction, defined as any motion at the ramus fracture site or hardware motion, after fracture surgery. Of the 82 patients followed to union or fixation failure, 12 (15%) had loss of reduction on follow-up radiographs. The average age of patients who lost reduction was 55 years. The most common mechanism of reduction loss was a collapse of the pubic ramus over the screw, with recurrence of an internal rotation deformity of the injured hemipelvis. Ten patients who lost reduction were women, and 11 had undergone ramus screw placement in retrograde fashion. No loss of reduction was seen in Zone III ramus fractures (those that involve the bone lateral to the obturator foramen). No patient sustained recognized neurologic, vascular, or urologic injury as a result of percutaneous screw fixation of a superior pubic ramus fracture. The prevalence of loss of reduction after percutaneous screw fixation of pubic ramus fractures is 15%. Loss of reduction is more common in elderly and female patients and in patients whose ramus screws are placed in a retrograde fashion. Also, loss of reduction appears to be more common in fractures medial to the lateral border of the obturator foramen.

Conversion From Temporary External Fixation to Definitive Fixation: Shaft Fractures

Temporary external fixation is the most common method of initial stabilization of diaphyseal fractures in forward surgical hospitals. Once the patient arrives at a stable environment, usually the United States, the fracture is managed with intramedullary nailing, small-pin external fixation, or a modified external fixator. Future research should be directed toward improving methods of care. It is not precisely known when is the best time to convert to definitive fixation without increasing the risk of infection. The risk factors leading to infection and nonunion are not well-established, making that determination even more difficult. Clinical studies of a suitable size should provide insight into these problems. Although temporary external fixation is commonly used, an optimal construct has not been determined. Data from studies of in vivo fracture-site motion after application of the temporary external fixator should be compared with biomechanical testing of similar constructs. These data could be used to recommend optimal temporary external fixation constructs of tibia, femur, and humerus fractures using currently available devices as well as to provide groundwork for the next generation of fixators.

The Mechanical Behavior of Locking Compression Plates Compared With Dynamic Compression Plates in a Cadaver Radius Model

The purpose of this cadaveric study was to compare the mechanical behavior of a locked compression plate, which uses threaded screw heads to create a fixed angle construct, with a dynamic compression plate construct in a cadaver radius model. Mechanical study with cyclic testing and high-speed optical motion analysis. Biomechanics laboratory at an academic institution. Eighteen pairs of fresh-frozen human cadaver radii were divided into 3 groups of 6 to be tested as a group in each of the following force applications: anteroposterior (AP) bending, mediolateral bending, or torsion. Each bone was osteotomized leaving a 5-mm fracture gap and then fixed with a plate. For each pair, 1 radius received a standard plate (limited-contact dynamic compression plates; LC-DCP), the contralateral radius was fixed with a locking compression plate (LCP), and specimens underwent cyclic loading. Normalized stiffness, average energy absorbed, and Newton-cycles to failure were calculated. In addition, a 3-dimensional, high-speed, infrared motion analysis system was used to evaluate motion at the fracture site. Construct stiffness, fracture site motion, cycles to failure, and energy absorption. Repeated measures ANOVA were used to detect differences between groups with time. In the torsion group, LCP specimens failed at 60% greater Newton-cycles than the LC-DCP (1473 vs. 918; P < 0.05). In the AP group, the LC-DCP absorbed significantly greater energy during 10,000 cycles compared with the LCP group (P < 0.05). The 2 constructs demonstrated different biomechanical behavior with time. As cycling progressed in the LC-DCP specimens under torsion testing, stiffness (measured at the actuator at the bone ends) did not change significantly; however, fracture motion (measured at the fracture surfaces) decreased significantly (P = 0.04). The LCP specimens did not display similar behavior. Our findings indicated that LCP constructs may demonstrate subtle mechanical superiority compared with the LC-DCP. The LCP specimens had less energy absorption in the AP group and survived longer in the torsion group. Discordance of motion between measurement regions was observed only in the LC-DCP torsion group, and may have been caused by plate-bone slippage or bone-screw subcatastrophic failure. However, many other compared parameters were found to be similar, and the clinical significance of the few differences found between constructs mandates further investigation.

A mechanical study of gap motion in cadaveric femurs using short and long supracondylar nails.

To determine the relative stability achieved in unstable supracondylar femur fractures treated with long (36 cm) and short (20 cm) retrograde intramedullary nails using 1 or 2 proximal locking bolts. We hypothesized that longer nails would reduce fracture site motion compared with short nails and that 2 proximal locking bolts would improve stability compared with 1 proximal locking bolt. Nine pairs of matched human cadaveric femurs were instrumented with 20-cm and 36-cm retrograde intramedullary nails (all 12-mm diameter, Biomet, Warsaw, IN) following reaming to 13 mm. Transverse supracondylar gap (6 mm) osteotomies were created. The femurs were mounted and cyclically tested separately in coronal plane bending and sagittal plane bending on a materials testing system. Fracture site translation was measured using a digital caliper in the respective plane. Orthopaedic biomaterials laboratory. With 2 proximal locking bolts, average sagittal translation was 7.2 mm and 1.8 mm, respectively, for the 20-cm and 36-cm nails. Coronal translation was 6.3 mm and 4.3 mm, respectively. With a single proximal locking bolt, average sagittal translation was 7.6 mm and 2.2 mm, respectively, for the 20-cm and 36-cm nails. Coronal translation was 13.6 mm and 4.4 mm, respectively. A statistically significant difference in fracture site translation was found in each pairing by Student t test (P < 0.005), except coronal translation with 2 proximal locking bolts (P = 0.056). Free-body analysis predicts higher local stresses at the proximal interlocks of the shorter nail. Longer nails provide improved initial fracture stability when compared with short retrograde nails for supracondylar femur fractures due to a more stable mechanical interaction between the femoral diaphysis and the nail. A second proximal locking bolt in the long nail provides no additional stability.