Forward-striking technique in simple femoral shaft fractures: a comparative cohort study.

BACKGROUND: A persistent fracture gap following femoral nailing increases the risk of delayed and nonunion development. A forward-striking technique for reducing the gap in femoral nailing has been described, but its efficacy and therapeutic consequences have not been investigated in comparative studies. We provide the results of a comparative study that investigated the forward-striking technique's efficacy in terms of remaining fracture gaps and surgical outcomes. METHODS: Between 2017 and 2022, a retrospective cohort study was undertaken on 193 skeletal mature patients obtaining reamed femoral nailing for closed femoral shaft fractures. Comparisons of residual fracture gaps, timing to union, complications and re-operation rates were made between 80 patients (41.45%) undergoing femoral nailing with the forward striking procedure and 113 patients (58.55%) undergoing traditional nailing, accompanied by minimal 1-year follow-ups. In addition, the potential difference between fracture gaps before and after applying the forward striking procedure was compared. RESULTS: Both groups had similar age, sex, presence of diabetes, smoking status, body mass index and time to surgery. However, the forward-striking group demonstrated significantly lower rates of postoperative complications, including delayed, nonunion, and the need for re-operation. Conversely, no significant differences were found in time to union (p = 0.222). The forward-striking procedure can significantly reduce residual fracture gaps from 3.99 to 1.66 mm (p < 0.001). No major complications in the forward-striking group including nonunion were observed. CONCLUSION: This study suggests that the forward-striking technique effectively reduces residual fracture gap during femoral nailing. The technique not only could be easily performed but is also reproducible. In addition, it can lower the risk of delayed union, nonunion and obviates the necessity for re-operation. LEVEL OF EVIDENCE: Level III, retrospective cohort study.

Effect of postoperative fracture gap on bone union: A retrospective cohort analysis of simple femoral shaft fractures.

BACKGROUND: Intramedullary nailing (IMN) is considered the gold-standard treatment for femoral shaft fractures. The post operative fracture gap is commonly recognized as a risk factor for nonunion. However, no evaluation standard for measuring the fracture gap size has yet been established. In addition, the clinical implications of the fracture gap size have also not been determined so far. This study aims to clarify how we should evaluate fracture gaps when assessing simple femoral shaft fractures with radiographs and to determine the acceptable cut-off value of the fracture gap size in simple femoral shaft fractures. METHOD: A retrospective observational study with a consecutive cohort was conducted at the trauma center of a university hospital. We investigated the fracture gap using postoperative radiography and the postoperative bone union of transverse and short oblique femoral shaft fractures fixed by IMN. The receiver operating characteristic curve analysis was conducted to obtain the fracture gap's mean, minimum, and maximum cut-off values. Fisher's exact test was used at the cut-off value of the most accurate parameter. RESULTS: In the four nonunions among the 30 cases, the analysis using ROC curves revealed that the maximum value had the highest accuracy among the maximum, minimum, and mean values of fracture-gap size. The cut-off value was determined to be 4.14 mm with high accuracy. Fisher's exact test showed that the incidence of nonunion was higher in the group with a maximum fracture gap of 4.14 mm or greater (risk ratio = not applicable, risk difference = 0.57, P = 0.001). CONCLUSION: In simple transverse and short oblique femoral shaft fractures fixed with IMN, the fracture gap on radiographs should be evaluated by the maximum gap in the AP and lateral views. The remaining maximum fracture gap of ≥4.14 mm would be a risk factor for nonunion.

Fracture gap and working length are important actionable factors affecting bone union after minimally invasive plate osteosynthesis for the treatment of simple diaphyseal or distal metaphyseal tibia fractures.

INTRODUCTION: Indirect reduction of minimally invasive plate osteosynthesis (MIPO) can often result in delayed union in tibia fractures. This study evaluated several factors in MIPO in relation to bone union. HYPOTHESIS: We hypothesized that the fracture gap, plate - tibia distance, or working length would have a substantial effect on the tibia union rate. MATERIALS AND METHODS: Forty-one patients with simple diaphyseal or distal metaphyseal tibia fractures who underwent internal fixation surgery using the MIPO technique were divided into two groups: patients with delayed union and patients without delayed union. Non-actionable factors involving AO/OTA classification, fibula fracture and actionable factors including postoperative fracture gap, plate - tibia distance, working length in relation to parameters of bone union were compared between the two groups. Also cumulative rates of bone union and risk factors of delayed union according to variables of interest were investigated. RESULTS: AO/OTA classification, site of fibula fracture, postoperative fracture gap, working length, and bone union rate of the two groups significantly differed (p<0.05). The cumulative rate of bone union during 1-year follow-up according to 43A tibia fracture, distal fibula fracture, fracture gap, and working length significantly differed between the two groups (p<0.05). By univariate Cox proportional hazards model, 43A tibia fracture, distal fibula fracture, facture gap, and short working length were risk factors for delayed union (p<0.05). DISCUSSION: Non-actionable factors involving AO/OTA classification, distal fibula fracture and actionable factors including postoperative fracture gap, working length were significant factors affecting bone union after MIPO. The present study indicated that small fracture gap and long working length during MIPO might facilitate bone healing in tibia fracture. LEVEL OF EVIDENCE: IV; single-center retrospective cohort study.

Effect of fracture level on the residual fracture gap during tibial intramedullary nailing for tibial shaft fractures.

INTRODUCTION: The development of fracture gap during intramedullary nailing in tibial fractures is associated with poor fracture fragment contact and increased time to union and complications. This study aimed to evaluate the effect of the fracture level in the development of the fracture gap and the effect of the fracture gap on pain, radiologic and functional outcomes, and complication rate. MATERIAL AND METHOD: A total of 45 patients who underwent reamed intramedullary nailing due to closed transverse or short oblique tibial shaft fractures were divided into the proximal fracture group and the distal fracture group. The correlations between the visual analog scale (VAS) score, modified radiograph union score for tibias (RUST), and postoperative 1-year lower extremity functional scale scores, residual fracture gap, and time to union were evaluated. RESULTS: The mean fracture gap amounts in the immediate postoperative anteroposterior and lateral radiographs were 5.6 ± 1.7 and 6.0 ± 1.7 mm in proximal fractures and 0.3 ± 2.4 mm and 0.4 ± 2.3 mm in distal fractures, respectively (p < 0.001 and p < 0.001, respectively). The mean time to union was 21.9 ± 2.9 weeks in the proximal fracture group and 16.7 ± 2.4 weeks in the distal fracture group (p < 0.000). The residual fracture gap amount significantly correlated with the level of fracture (r = 0.811, p < 0.001). DISCUSSION: Tibial shaft fractures proximal to the isthmus level tend to develop significantly larger fracture gaps than distal fractures. It is associated with increased time to union and radiographic union scores as well as slightly higher complication and reoperation rates.

Double lag-screw compression for optimal fixation of intertrochanteric fractures with large fragment gap: A technical note.

Cephalomedullary nailing of unstable intertrochanteric fractures has been established as a fruitful surgical approach with relatively limited complications. Anatomic fracture reduction and proper implant positioning are vital to attaining a favorable long-term surgical outcome. Appropriate intraoperative fracture compression augments stability and invigorates healing. The amount of compression permitted by cephalomedullary nails cannot always adequately reduce large fragment gaps. This paper presents a novel technical trick of double compression of the fracture site, in order to achieve the essential extra compression and reduction when required, thus decreasing the risk of postoperative implant cut-out. The technique was used in 14 out of 277 peritrochanteric fractures treated with cephalomedullary nailing in our trauma center for 12 months, with satisfactory outcomes regarding both fracture site union and postoperative functional capacity.

Fracture Gap Closure and Reduction Are Affected by the Orientation of the Headless Compression Screw.

BACKGROUND: We evaluated the impact of a variable-pitch headless screw's angle of insertion relative to the fracture plane on fracture gap closure and reduction. METHODS: Variable-pitch, fully threaded headless screws were inserted into polyurethane blocks of "normal" bone model density using a custom jig. Separate trials were completed with a 28-mm screw placed perpendicular and oblique/longitudinal to varying fracture planes (0°, 15°, 30°, 45°, and 60°). Fluoroscopic images were taken after each turn during screw insertion and analyzed. Initial screw push-off, residual fracture gap at optimal fracture gap reduction, and malreduction were determined in each trial. Statistical analysis was performed via a 1-way analysis of variance followed by Student t tests. RESULTS: Malreduction was found to be significantly different between the perpendicular (1.88 mm ± 1.38) and the oblique/longitudinal (0.58 mm ± 0.23) screws. The malreduction increased for the perpendicular screw as the fracture angle increased (60° > 45°=30° > 15° > 0°). Residual fracture gap at optimal fracture gap reduction was also found to be significantly different between the perpendicular (0.97 ± 0.42) and oblique/longitudinal (1.43 ± 1.14) screws. The residual fracture gap increased for the oblique/longitudinal screw as the fracture angle increased, although the oblique/longitudinal screw with a 60° fracture angle was the only configuration significantly larger than all the other configurations. Screw push-off was not found to be significantly different between the oblique/longitudinal screw and perpendicular screw trials. CONCLUSIONS: The perpendicular screw had a larger malreduction that increased with fracture angle, whereas the oblique/longitudinal screw had a larger residual fracture gap that increased with fracture angle.

The Effect of Derotational Kirschner Wires on Fracture Gap Reduction With Variable-Pitch Headless Screws.

PURPOSE: We evaluated the impact of angled derotational Kirschner wires (K-wires) on fracture gap reduction with variable-pitch headless screws. METHODS: Fully threaded variable-pitch headless screws (20 and 28 mm) were inserted into "normal" bone models of polyurethane blocks. In separate trials, derotational K-wires were inserted at predetermined angles of 0°, 15°, 30°, and 40° and compared with each other, with no K-wire as a control. Fluoroscopic images taken after each screw turn were analyzed. The optimal fracture gap closure, initial screw push-off, and screw back-out gap creation were determined and compared at various derotational K-wire angles. RESULTS: Initial screw push-off due to screw insertion and screw back-out gap creation were not significantly affected by the angle of the derotational K-wire. With a 20-mm screw, only a 40° derotational K-wire led to significantly less gap closure compared with control and with 0°, 15°, and 30° derotational K-wires. It led to an approximately 60% decrease in gap closure compared with no K-wire. With the 28-mm screw, compared with no K-wire, 15° and 30° derotational K-wires led to statistically significant decreases in gap closure (approximately 25%), whereas a 40° derotational K-wire led to an approximately 60% decrease. With the 28-mm screw, the 40° derotational K-wire also led to a statistically significant smaller gap closure when compared with 0°, 15°, and 30° derotational K-wires. CONCLUSIONS: A derotational K-wire placed in parallel to the planned trajectory of a headless compression screw does not affect fracture gap closure. With greater angulation of the derotational K-wire, the fracture gap is still closed, but less tightly. CLINICAL RELEVANCE: Derotational K-wires can help prevent fracture fragment rotation during headless compression screw insertion. At small deviations from parallel (≤30°), fracture gap closure achieved by the screw is minimally affected. At greater angles (ie, 40°), fracture gap closure may be substantially reduced, preventing fracture compression.

In silico modelling of long bone healing involving osteoconduction and mechanical stimulation.

A lot of evidence has shown the importance of stimulating cell mechanically during bone repair. In this study, we modeled the challenging fracture healing of a large bone defect in tibial diaphysis. To fill the fracture gap, we considered the implantation of a porous osteoconductive biomaterial made of poly-lactic acid wrapped by a hydrogel membrane mimicking osteogenic properties of the periosteum. We identified the optimal loading case that best promotes the formation and differentiation into bone tissue. Our results support the idea that a patient's rehabilitation program should be adapted to reproduce optimal mechanical stimulations.

Fracture gap of the lateral malleolus via posterolateral approach: Improved visualization of the posterior malleolus fracture.

The treatment of posterior malleolar fractures is a popular issue. Anatomic reduction of posterior malleolar fractures is critical for re-establishing the stability of the ankle mortise and ligamentous union after trauma. Inappropriate treatment ultimately leads to poorer functional outcomes and lower quality of life. Open reduction and internal fixation through a posterolateral approach are preferred over indirect reduction and anterior-posterior screw fixation. Although the posterolateral approach, which is more common and direct, provides good exposure to the fracture site, it has some limitations. In this report, we describe the posterolateral approach through the lateral ankle fracture gap for the treatment of posterior ankle fractures. Moreover, we discuss the indications, benefits, and limitations of this approach.

Identifying Predictors of Radiographic Distal Phalangeal Nonunion After Fingertip Replantation.

PURPOSE: This study aimed to estimate the risk factors for distal phalangeal nonunion in cases involving Kirchner wire fixation after successful fingertip replantation. METHODS: This study retrospectively analyzed 116 digits of 111 patients, including 74 and 42 digits with replantation in Tamai zones I and II, respectively. Univariate and multivariable analyses were performed to assess the influences of 15 independent variables on nonunion, including age, sex, medical history of diabetes mellitus, history of smoking, injured hand and digit, injury type (clean, blunt, and crush-avulsion), amputation type (complete or incomplete), length of the distal bone fragment (mm), fracture type (simple or comminuted), presence of a bone defect, length of the fracture gap after fixation (mm), number of Kirchner wires used, evidence of venous repair, and the occurrence of pin tract infections after fixation. RESULTS: At 12 months after replantation, 100 digits showed bony union and 16 (13.8%) digits showed radiographic nonunion or equivalent complications, including 9 digits with asymptomatic nonunion without a secondary operation, 5 that underwent an additional operation for nonunion or a complication, and 2 with distal bone resorption. A multivariable analysis indicated that the postfixation fracture gap was the only significant predictor influencing nonunion (odds ratio, 3.30; 95% confidence interval, 1.92-5.68). CONCLUSIONS: The extent of the postfixation fracture gap had the greatest influence on preventing distal phalangeal nonunion, indicating the importance of reducing the fracture gap in primary fixation as much as possible. TYPE OF STUDY/LEVEL OF EVIDENCE: Prognostic IV.

Letter to the editor: Calcar fracture gapping: a reliable predictor of anteromedial cortical support failure after cephalomedullary nailing for pertrochanteric femur fractures.

A recently published article by Song H et al. investigated the risk factors for anteromedial cortical support loss in pertrochanteric fractures treated with cephalomedullary nails. In this Correspondence, we would like to raise some concerns. Specifically, calcar fracture gap and anteromedial cortical support are different concepts in evaluating reduction quality. In addition, calcar fracture gap using immediate postoperative radiographic images has measurement bias. Lastly, explanatory variables selected for multivariable analysis are inappropriate. We would like to discuss and suggest solutions for these problems.

In response to letter to the editor: calcar fracture gapping: a reliable predictor of anteromedial cortical support failure after cephalomedullary nailing for pertrochanteric femur fractures.

We appreciate the interest by Drs. Hagiyama and coauthors in our work entitled "Calcar fracture gapping: a reliable predictor of anteromedial cortical support failure after cephalomedullary nailing for pertrochanteric femur fractures". They discussed several pertinent points and it is our pleasure to respond their concerns in order. Firstly, we agree that calcar fracture gap and anteromedial cortical support are different concepts, though both of them were used to evaluate the displacement of fracture reduction quality. Secondly, our primary outcome parameter was the threshold distance of calcar fracture gapping in anteroposterior and lateral fluoroscopies, which was calculated based on sensitivity and specificity by receiver operating characteristic curves. Thirdly, we took immediate post-operative fluoroscopic images in 3 views to describe the initial reduction quality as baseline to compare and calculate the changes with three-dimensional computed tomography, which was taken about one week after operation for confirming secondary stability after head-neck sliding and impaction. Lastly, the parameters selected in multivariable analysis. Future work with better study-design is needed to improve the prediction of patient outcomes.

A Mechanical Comparison of the Compressive Force Generated by Various Headless Compression Screws and the Impact of Fracture Gap Size.

Background: There is evidence that interfragmentary fracture gap size may affect the compression achievable with a modern headless compression screw (HCS). This mechanical study compared the compression achieved by 3 commercial HCS systems through various fracture gaps: CAPTIVATE Headless (Globus Medical, Inc, Audubon, Pennsylvania), Synthes (DePuy Synthes, Westchester, Pennsylvania), and Acumed Acutrak 2 (Acumed LLC, Hillsboro, Oregon). Methods: Screws were inserted into a custom test fixture composed of polyurethane synthetic bone foam fragments, separated by a layer of easily compressible polyurethane foam simulating a fracture gap. Compression was measured after final insertion and countersinking. The effect of the interfragmentary fracture gap size on the compression generated was also investigated. Results: The CAPTIVATE Headless 3.0 mm screw (70.1 ± 5.7 N) and the Synthes 3.0 mm screw (64.9 ± 7.3 N) achieved similar compressive forces after final countersink. Similar comparisons were found for the CAPTIVATE Headless 2.5 mm and Synthes 2.4 mm screws, and the CAPTIVATE Headless 4.0 mm and Acutrak 2 Standard screws. The final compression of the CAPTIVATE Headless 2.5 mm and Synthes 2.4 mm screws was not significantly affected when the fracture gap was doubled from 2 to 4 mm, but was reduced significantly by 95.9% with the Acutrak 2 Micro screw. Conclusion: When comparing like-sized screws, the CAPTIVATE, Synthes, and Acutrak 2 HCS systems demonstrated similar potential compressive forces. However, compared with the CAPTIVATE Headless and Synthes HCS systems, which are inserted with a compression sleeve that is not gap distance-dependent, the Acutrak 2 HCS system demonstrated less compression when the simulated fracture gap size was increased to 4 mm.

Outcomes of Patients Undergoing Anterior Screw Fixation for Odontoid Fracture and Analysis of the Predictive Factors for Surgical Failure.

OBJECTIVE: Anterior odontoid screw fixation (AOSF) is a safe and effective treatment for type II and rostral type III odontoid fracture. This study aimed to report the outcomes of the AOSF surgery and evaluate the potential risk factors of surgical failure. METHODS: We enrolled 63 patients who underwent AOSF. Follow-up computed tomography was performed 6 months after the surgery and once a year thereafter to evaluate the union. Clinical data including the age, sex, presenting symptoms, cause of injury, fracture gaps, dislocation position, degree of displacement, screw direction angle, and time interval from injury to operation were collected. RESULTS: Successful fusion was achieved in 55 patients (87.3%) and surgical failure occurred in 8 patients (12.7%). Variables such as age, sex, dislocation position, degree of displacement, screw direction angle, and time interval from injury to operation were not significantly associated with the surgical failure. However, surgical failure was statistically significantly associated with the fracture gap. The overall mean fracture gap at the time of injury was 1.29 mm (range, 0-3.11 mm), and the incidence of surgical failure was 8.3 times higher when the fracture gap at the time of injury was > 2 mm (p = 0.019). CONCLUSION: When performing AOSF in patients with type II or rostral shallow type III odontoid fractures, the displacement of the odontoid fracture fragment should be appropriately reduced to the aligning position before screw insertion and downward reduction should be achieved by perforation of the apical cortex of the odontoid during screw fixation, even if the surgery is delayed.

[Finite element analysis of fixation of U-shaped sacral fractures].

Finite element method (FEM) was used to investigate the biomechanical properties of three types of surgical fixations of U-shaped sacral fractures. Based on a previously established and validated complete lumbar-pelvic model, three models of surgical fixations of U-shaped sacral fractures were established: ① S1S2 passed through screw (S1S2), ② L4-L5 pedicle screw + screw for wing of ilium (L4L5 + IS), and ③ L4-L5 pedicle screw + S1 passed through screw + screw for wing of ilium (L4L5 + S1 + IS). A 400 N force acting vertically downward, along with torque of 7.5 N·m in different directions (anterior flexion, posterior extension, axial rotation, and axial lateral bending), was exerted on the upper surface of L4. Comparisons were made on differences in separation of the fracture gap and maximum stress in sitting and standing positions among three fixation methods. This study showed that: for values of separation of the fracture gap produced by different operation groups in different positions, L4L5 + S1 + IS was far less than L4L5 + IS and S1S2. For internal fixators, the maximum stress value produced was: L4L5 + IS > L4L5 + S1 + IS > S1S2. For the intervertebral disc, the maximum stress value produced by S1S2 is much larger than that of L4L5 + S1 + IS and L4L5 + IS. In a comprehensive consideration, L4L5 + S1 + IS could be prioritized for fixation of U-shaped sacral fractures. The objective of this research is to compare the biomechanical differences of three different internal fixation methods for U-shaped sacral fractures, for the reference of clinical operation.

Analysis of Computed Tomography Scan After Anterior Odontoid Screw Fixation with the Herbert Screw: Is It Effective to Reduce Fracture Gap?

OBJECTIVE: To assess computed tomography scans to evaluate the extent of reduction of fracture displacement and fracture gap after anterior odontoid screw fixation using the Herbert screw. METHODS: Thirty-seven odontoid fractures were reduced and treated by anterior odontoid screw fixation with the Herbert screw. There were 37 patients whose age ranged from 20 to 79 years. Three-dimensional computed tomography scans were obtained for all patients to assess the screw position, the presence of the penetration of superior cortex of dens, the extent of reduction of fracture displacement, and fracture gap. RESULTS: Mean fracture displacement was 2.6 ± 3.2 mm before surgery; after the operation this value was 1.0 ± 1.5 mm. The difference in fracture gap between the preoperative and the postoperative state was -0.1 ± 1.1 mm, which was not statistically significant (P = 0.667). We achieved cortical purchase in only 16 of 37 patients (43.2%); cortical purchase was not obtained in 21 patients (56.7%) due to the fear of the risk of the damage of neural and vascular structures. Of these 21 patients who had no penetration of the superior cortex of dens, widening of the fracture gap occurred in 12 patients (57%), no change in 6 patients (29%), and there was shortening in 3 patients (14%). However, of the 16 patients with penetration of apical dens tip, we achieved significant reduction of fracture gap (P = 0.002). CONCLUSIONS: To maximize reduction of fracture gap using the Herbert screw, it is essential to penetrate the apical dens tip.

Fracture Gap Reduction With Variable-Pitch Headless Screws.

PURPOSE: Fully threaded, variable-pitch, headless screws are used in many settings in surgery and have been extensively studied in this context, especially in regard to scaphoid fractures. However, it is not well understood how screw parameters such as diameter, length, and pitch variation, as well as technique parameters such as depth of drilling, affect gap closure. METHODS: Acutrak 2 fully threaded variable-pitch headless screws of various diameters (Standard, Mini, and Micro) and lengths (16-28 mm) were inserted into polyurethane blocks of "normal" and "osteoporotic" bone model densities using a custom jig. Three drilling techniques (drill only through first block, 4 mm into second block, or completely through both blocks) were used. During screw insertion, fluoroscopic images were taken and later analyzed to measure gap reduction. The effect of backing the screw out after compression was evaluated. RESULTS: Drilling at least 4 mm past the fracture site reduces distal fragment push-off compared with drilling only through the proximal fragment. There were no significant differences in gap closure in the normal versus the osteoporotic model. The Micro screw had a smaller gap closure than both the Standard and the Mini screws. After block contact and compression with 2 subsequent full forward turns, backing the screw out by only 1 full turn resulted in gapping between the blocks. CONCLUSIONS: Intuitively, fully threaded headless variable-pitch screws can obtain compression between bone fragments only if the initial gap is less than the gap closed. Gap closure may be affected by drilling technique, screw size, and screw length. Fragment compression may be immediately lost if the screw is reversed. CLINICAL RELEVANCE: We describe characteristics of variable-pitch headless screws that may assist the surgeon in screw choice and method of use.

Biomechanical Comparison of Inter-fragmentary Compression Pressures: Lag Screw versus Herbert Screw for Anterior Odontoid Screw Fixation.

OBJECTIVE: The purpose of the present study was to compare inter-fragmentary compression pressures after fixation of a simulated type II odontoid fracture with the headless compression Herbert screw and a half threaded cannulated lag screw. METHODS: We compared inter-fragmentary compression pressures between 40- and 45-mm long 4.5-mm Herbert screws (n=8 and n=9, respectively) and 40- and 45-mm long 4.0-mm cannulated lag screws (n=7 and n=10, respectively) after insertion into rigid polyurethane foam test blocks (Sawbones, Vashon, WA, USA). A washer load cell was placed between the two segments of test blocks to measure the compression force. Because the total length of each foam block was 42 mm, the 40-mm screws were embedded in the cancellous foam, while the 45-mm screws penetrated the denser cortical foam at the bottom. This enabled us to compare inter-fragmentary compression pressures as they are affected by the penetration of the apical dens tip by the screws. RESULTS: The mean compression pressures of the 40- and 45-mm long cannulated lag screws were 50.48±1.20 N and 53.88±1.02 N, respectively, which was not statistically significant (p=0.0551). The mean compression pressures of the 40-mm long Herbert screw was 52.82±2.17 N, and was not statistically significant compared with the 40-mm long cannulated lag screw (p=0.3679). However, 45-mm Herbert screw had significantly higher mean compression pressure (60.68±2.03 N) than both the 45-mm cannulated lag screw and the 40-mm Herbert screw (p=0.0049 and p=0.0246, respectively). CONCLUSION: Our results showed that inter-fragmentary compression pressures of the Herbert screw were significantly increased when the screw tip penetrated the opposite dens cortical foam. This can support the generally recommended surgical technique that, in order to facilitate maximal reduction of the fracture gap using anterior odontoid screws, it is essential to penetrate the apical dens tip with the screw.

Effect of Calcaneus Fracture Gap Without Step-Off on Stress Distribution Across the Subtalar Joint.

BACKGROUND: Subtalar arthritis is a common consequence following calcaneal fracture, and its development is related to the severity of the fracture. Previous calcaneal fracture models have demonstrated altered contact characteristics when a step-off is created in the posterior facet articular surface. Changes in posterior facet contact characteristics have not been previously characterized for calcaneal fracture gap without step-off. METHODS: The contact characteristics (peak pressure, area of contact, and centroid of pressure) of the posterior facet of the subtalar joint were determined in 6 cadaveric specimens. After creating a calcaneal fracture to simulate a Sanders type II fracture, the contact characteristics were determined with the posterior facet anatomically reduced followed by an incremental increase in fracture gap displacement of 2, 3, and 5 mm without a step-off of the articular surface. RESULTS: Peak pressure on the medial fragment was significantly less with a 5-mm gap compared to a 2- or 3-mm gap, or reduced. On the lateral fragment, the peak pressure was significantly increased with a 5-mm gap compared to a 2- or 3-mm gap. Contact area significantly changed with increased gap. CONCLUSION: In this study, there were no significant differences in contact characteristics between a <3-mm gap and an anatomically reduced fracture, conceding the study limitations including limiting axial loading to 50% of donor body weight. CLINICAL RELEVANCE: A small amount of articular incongruity without a step-off can be tolerated by the subtalar joint, in contrast to articular incongruity with a step-off present.

The effect of intramedullary pin size and plate working length on plate strain in locking compression plate-rod constructs under axial load.

OBJECTIVE: To investigate the effect of intramedullary pin size and plate working length on plate strain in locking compression plate-rod constructs. METHODS: A synthetic bone model with a 40 mm fracture gap was used. Locking compression plates with monocortical locking screws were tested with no pin (LCP-Mono) and intramedullary pins of 20% (LCPR-20), 30% (LCPR-30) and 40% (LCPR-40) of intramedullary diameter. Two screws per fragment modelled a long (8-hole) and short (4-hole) plate working length. Strain responses to axial compression were recorded at six regions of the plate via three-dimensional digital image correlation. RESULTS: The addition of a pin of any size provided a significant decrease in plate strain. For the long working length, LCPR-30 and LCPR-40 had significantly lower strain than the LCPR-20, and plate strain was significantly higher adjacent to the screw closest to the fracture site. For the short working length, there was no significant difference in strain across any LCPR constructs or at any region of the plate. Plate strain was significantly lower for the short working length compared to the long working length for the LCP-Mono and LCPR-20 constructs, but not for the LCPR-30 and LCPR-40 constructs. CLINICAL SIGNIFICANCE: The increase in plate strain encountered with a long working length can be overcome by the use of a pin of 30-40% intramedullary diameter. Where placement of a large diameter pin is not possible, screws should be placed as close to the fracture gap as possible to minimize plate strain and distribute it more evenly over the plate.