Biomechanical comparison of flexible stainless steel and titanium nails with external fixation using a femur fracture model.

There are several options available for surgical stabilization of pediatric femoral shaft fractures. The purpose of this study was to compare the stability afforded by Ender stainless steel nails, titanium elastic nails, and one-plane unilateral external fixators for the fixation using a synthetic adolescent midshaft femur fracture model. The anterior-posterior (sagittal plane) bending, lateral (coronal plane) bending, torsional, and axial stiffness values were calculated using 6 different fixation configurations. These included pairs of 3.5-mm-diameter Ender nails with and without distal locking, 3.5- and 4.0-mm-diameter titanium elastic nails as well as single- and double-stacked monolateral external fixators. Eight synthetic femur models, 4 each with simulated transverse and comminuted fracture patterns, were sequentially tested for stability afforded by the various fracture fixation configurations. External fixation exhibited significantly greater control of anterior-posterior angulation compared with all flexible-nailing systems. Although Ender nails were slightly superior to titanium nails in control of sagittal plane angulation, this was not statistically significant. Compared with the external fixation constructs, all 4 flexible nail constructs demonstrated higher torsional stability. For prevention of axial shortening, all fixation methods were similar for the transverse fracture pattern, whereas external fixation was superior to flexible nails in the comminuted fracture model. No significant benefit was demonstrated with double stacking of external fixators. These findings may help guide clinicians choose the optimal fixation method for treatment of pediatric femoral shaft fractures.

The effect of sacral fracture malreduction on the safe placement of iliosacral screws.

OBJECTIVES: To determine the effects of cranial displacement on the safe placement of iliosacral screws for zone II sacral fractures. DESIGN: Computer imaging and dimensional analysis of a human cadaveric sacral fracture model. SETTING: Cadaveric dissection, Orthopaedic Research Laboratories, Newark, New Jersey. MAIN OUTCOME MEASUREMENTS: Six cadaveric pelves with simulated zone II sacral fractures were imaged with computed tomography at controlled cranial displacements of 5, 10, 15, and 20 mm. The area of contact at the fracture site and volume of bone available for iliosacral screw placement was graphically measured using both two- and three-dimensional computer modeling. Areas of contact were also represented in terms of the maximal number of 7.0 - mm screws that could be simultaneously implanted. RESULTS: Cross-sectional contact area was decreased by 30%, 56%, 81%, and 90% at 5, 10, 15 and 20 mm of displacement, respectively. Volume of bone was decreased by 21%, 25%, 26%, and 34% for 5, 10, 15 and 20 mm of displacement, respectively. In 50% of the specimens at 15 mm and 66% of the specimens with 20 mm displacement, two iliosacral screws could not be contained simultaneously within bone. In 17% of the specimens displaced 15 mm and 50% of the specimens displaced 20 mm, the cross-sectional area was insufficient to contain a single iliosacral screw. CONCLUSIONS: Although previous authors have accepted up to 15 mm of cranial displacement, the data demonstrate substantial compromise of available screw space with displacements greater than 1 cm. Fracture reduction is mandatory, as screw placement with residual displacement of 10 mm or more can endanger adjacent neural and vascular structures.

Neurovascular and tendinous damage with placement of anteroposterior distal locking bolts in the tibia.

OBJECTIVE: To determine the proximity of anteroposterior locking bolts inserted into the distal metaphyseal tibia to nearby neural, vascular, and tendinous structures. DESIGN: A cadaver study. SETTING: University trauma center. METHODS: Sixteen legs (8 matched pairs) were nailed in either neutral (Group 1) or 10 degrees of internal rotation (Group 2) and locked using one anteroposterior bolt. The anterior tibial and extensor hallucis longus tendons and neurovascular bundle were identified, and their respective locations in relation to the bolt head were measured. Average distances were calculated for each structure in each group and statistically compared. Damage to any structure was noted at final dissection. RESULTS: Average distances from the bolt head to the neurovascular bundle, extensor hallucis longus, and anterior tibial tendons were 0.6, 0.5, and 1.6 mm, respectively, for Group 1 and 1.0, 1.5, and 1.8 mm, respectively, for Group 2 legs. Statistical comparison of distances for each anatomic entity for the two groups revealed no detectable significant differences (P = 0.7, 0.4, 0.7, respectively). For all specimens, the rate of nerve, artery, extensor hallucis longus, and anterior tibial tendon injury was 25%, 19%, 0%, and 6%, respectively. However, the incidence of at least one structure damage in Group 1 legs was 63% versus 12% in Group 2 specimens (P = 0.2). CONCLUSION: Anteroposterior distal tibial locking bolts lie in close proximity to the neurovascular bundle. With standard percutaneous techniques, these structures can be damaged. Although 10 degrees of internal rotation does not statistically affect the measured distance of the locking bolt to the neurovascular bundle, it appears to decrease the incidence of neurovascular injury. This difference may best be explained by the necessary path the drill bit must take through the soft tissues to reach the underlying bone. Regardless of nail orientation, larger incisions with careful dissection and clear visualization of the anatomy are recommended to help prevent this complication.

Pseudo os trigonum sign: missed posteromedial talar facet fracture.

BACKGROUND: Posteromedial talar facet fracture (PMTFF) is a rare injury, sparsely reported in the literature. This article proposes that PMTFF is often left undiagnosed by orthopaedic surgeons and suggests the routine application of advanced radiographic studies (i.e., CT scan) in the recognition of PMTFF. It also evaluates nonoperative management of PMTFF. METHODS: After obtaining Institutional Review Board approval, the medical records over a 5-year period (1997-2001) were retrospectively reviewed from the foot and ankle service of a level 1 trauma center, identifying all cases of PMTFF. Charts were reviewed for relevant data. Results of treatment were assessed during follow-up physical examination. RESULTS: Six cases of PMTFF were identified over a 5-year period. All injuries were associated with medial subtalar joint dislocation. Four of six (66%) patients were not initially diagnosed with PMTFF, but instead misdiagnosed as an os trigonum. The remaining two patients had an established diagnosis of PMTFF at the time of initial treatment. All had short leg cast immobilization for medial subtalar dislocation. CT evaluation yielded additional diagnoses in all six patients. All six patients showed a PMTFF. Five patients (83%) revealed persistent subtalar joint subluxation. Five of six (83%) patients required at least one additional procedure as a result of an undiagnosed or nonoperatively treated PMTFF. Four patients underwent subtalar joint fusion, and one patient underwent tibiotalar calcaneal fusion secondary to concomitant ankle/subtalar arthritis. The patient who did not undergo recommended fusion continued to be symptomatic. CONCLUSIONS: Diagnosis of PMTFF necessitates a heightened clinical suspicion, especially when a medial subtalar joint dislocation is present. Proper imaging studies, such as coronal CT scan, should be performed after any subtalar dislocation. Timely treatment, in the form of open reduction and internal fixation for large fragments involving the articular surface or surgical excision for smaller fragments, is recommended in order to restore proper anatomy and function of the subtalar joint. This study verifies the significant morbidity associated with an undiagnosed or nonoperatively treated PMTFF.

The effect of sacral fracture malreduction on the safe placement of iliosacral screws.

OBJECTIVES: To determine the effects of cranial displacement on the safe placement of iliosacral screws for zone II sacral fractures. DESIGN: Computer imaging and dimensional analysis of a human cadaveric sacral fracture model. SETTING: Cadaveric dissection, Orthopaedic Research Laboratories, Newark, New Jersey. MAIN OUTCOME MEASUREMENTS: Six cadaveric pelves with simulated zone II sacral fractures were imaged with computed tomography at controlled cranial displacements of 5, 10, 15, and 20 mm. The area of contact at the fracture site and volume of bone available for iliosacral screw placement was graphically measured using both two- and three-dimensional computer modeling. Areas of contact were also represented in terms of the maximal number of 7.0-mm screws that could be simultaneously implanted. RESULTS: Cross-sectional contact area was decreased by 30%, 56%, 81%, and 90% at 5, 10, 15 and 20 mm of displacement, respectively. Volume of bone was decreased by 21%, 25%, 26%, and 34% for 5, 10, 15 and 20 mm of displacement, respectively. In 50% of the specimens at 15 mm and 66% of the specimens with 20 mm displacement, two iliosacral screws could not be contained simultaneously within bone. In 17% of the specimens displaced 15 mm and 50% of the specimens displaced 20 mm, the cross-sectional area was insufficient to contain a single iliosacral screw. CONCLUSIONS: Although previous authors have accepted up to 15 mm of cranial displacement, the data demonstrate substantial compromise of available screw space with displacements greater than 1 cm. Fracture reduction is mandatory, as screw placement with residual displacement of 10 mm or more can endanger adjacent neural and vascular structures.

Biomechanical consequences of secondary congruence after both-column acetabular fracture.

OBJECTIVES: To create a both-column acetabular fracture model with secondary congruence and to determine the intraarticular loading characteristics present in simulated single-leg stance. HYPOTHESIS: The normal contact pressures on the weight-bearing portion of the acetabulum in simulated single-leg stance are different from those present in a both-column fracture model exhibiting secondary congruence. DESIGN: Cadaveric Biomechanical model. SETTING: Biomechanical testing laboratory. SPECIMENS: Nine fresh frozen cadaveric hemipelves. INTERVENTION: Both-column fracture model with secondary congruence of the acetabular articular surface with respect to the femoral head was created and tested using Materials Testing Machine (MTS Systems Corp., Minneapolis, MN) and Fuji pressure-sensitive film (Sensor Products, Inc., East Hanover, NJ). OUTCOME MEASUREMENTS: Testing data recorded and analyzed comparing the fractured and unfractured states. RESULTS: With respect to the intact specimen, the contact area, mean pressure, and peak pressure in the dome region all increased (p < 0.003) in the both-column model. The contact area in the anterior articular region decreased (p < 0.02) as did the mean pressure (p < 0.032). The posterior articular region demonstrated a trend toward decreased contact area and increased mean and peak pressures. Descriptively, the stress concentration shifted toward the fracture in all cases with the most anterior and most posterior articular regions having little contact in the fracture model. CONCLUSIONS: In the authors' both-column model of secondary congruence, the stress concentration during simulated single-leg stance was increased significantly in the dome of the acetabulum adjacent to the fracture line.