Identification of subtle residual sacroiliac joint flexion and extension malreductions in AO/OTA 61-C1.2 (APC3) pelvic injuries after provisional anterior ring reduction.

PURPOSE: Hemipelvis reduction in the setting of AO/OTA 61-C1.2 (APC3) pelvic injuries can be challenging. A common strategy is to provisionally reduce or fix the anterior ring prior to definitive fixation of the posterior ring. In this scenario, it is difficult to assess whether residual sacroiliac joint (SIJ) widening is due to hemipelvis flexion/extension or lateral displacement. This simulation sought to identify a radiographic marker for posterior ilium flexion or extension malreduction in the setting of a reduced anterior ring. METHODS: Symphyseal and both anterior and posterior SIJ ligaments were cut in 8 cadaveric pelvis. The symphysis was reduced and wired. One centimeter of posterior flexion or extension at the SIJ was created to mimic the clinical scenario of hemipelvis flexion or extension malreduction, and a lateral compressive force was applied. SIJ widening and the direction of anterior or posterior ileal displacement relative to the contralateral joint were assessed via inlet views. SIJ widening and the direction of cranial or caudal ileal displacement were assessed using outlet views. Comparisons between flexion and extension models used Fisher's exact test. RESULTS: On outlet views, all flexed hemipelvis demonstrated caudal ileal translation at the superior SIJ, in contrast to all extended hemipelvis demonstrated cranial translation (p < 0.0005); the scenarios were easily distinguishable. Conversely, inlet imaging was unable to identify the direction of malreduction. Flexion/extension scenarios resulted in similar amounts of SIJ widening. CONCLUSION: Residual flexion and extension hemipelvis malreductions in APC3 injuries after provisional anterior fixation can be differentiated by the direction of ileal displacement at the superior SIJ on the outlet view.

Fluoroscopic images of the sacroiliac joint alone are unable to identify simulated flexion or extension malreduction of the anterior pelvic ring in AO/OTA 61-B2.3 pelvic injuries.

PURPOSE: Reduction of AO/OTA 61-B2.3 (APC2) pelvic fractures is challenging in the setting of anterior ring comminution. The anterior ring is visually much simpler to evaluate for flexion or extension hemipelvis deformity than the posterior ring, except in the setting of comminution, necessitating some other visual reference to judge hemipelvis reduction. We sought to test whether pelvic inlet and outlet fluoroscopy of the contours of the sacroiliac joint could be used in isolation to judge hemipelvis flexion or extension. METHODS: Symphyseal and anterior SIJ ligaments were cut (6 cadaveric pelvis). The symphysis was held malreduced to produce one centimeter flexion and extension deformity: 1 cm was selected to mimic a maximum clinical scenario. The SIJ was assessed using inlet and outlet fluoroscopy. The scaled width of the SIJ was assessed at the joint apertures and midjoint on both inlet and outlet views. Joint widths in flexion and extension were compared against joint widths measured on the reduced SIJ using paired t-tests. RESULTS: There was no statistical difference in the superior (p = 0.227, 0.675), middle (p = 0.203, 0.693), and inferior (p = 0.232, 0.961) SIJ widths between hemipelvis flexion or extension models against reduced SIJ on outlet views. There was no statistical difference in the anterior (p = 0.731, 0.662), middle (p = 0.257, 0.655), and posterior (p = 0.657, 0.363) SIJ widths between flexion or extension models against reduced SIJ on inlet views. CONCLUSION: Inspection of SIJ width on inlet and outlet fluoroscopy cannot detect up to one centimeter of hemipelvis flexion or extension malreduction in the setting of AO/OTA 61-B2.3 (APC2) pelvic fractures with complex anterior injuries.

Comparison of fibula strut and calcium phosphate cement augmentation of the medial buttress in 2-part proximal humerus fractures reconstruction: a biomechanical study.

PURPOSE: Augmentation strategies for surgical fixation of proximal humerus fractures (PHF) are available to address their relatively high failure rate. The purpose of this study was to compare two medial-buttress augmentation strategies for PHF fixation. METHODS: A two-part PHF model with loss of medial buttress was created in 16 synthetic bones. The PHFs were fixed with locking plates and either calcium phosphate cement (CPC) or fibula strut (FS) augmentation. After cadaveric validations, the fixation constructs were subjected to nondestructive axial compression tests, followed by a cyclic test. Construct stiffness and angular displacement of the humerus head were recorded. RESULTS: Humeral head angular displacement was statistically greater in the CPC group than in the FS group at the applied force of 300 N and higher (p < 0.05). Axial stiffness was statistically greater in the FS fixation group than in the CPC group at initial and final phases of cyclic loading protocol (p < 0.05). CONCLUSIONS: In an osteoporotic cadaveric model of a 2-part PHF with loss of a medial buttress, locked plate constructs augmented with FS have a higher resistance to varus collapse compared to those augmented with CPC.

A Biomechanical Comparison of Fiberglass Casts and 3-Dimensional-Printed, Open-Latticed, Ventilated Casts.

Background: The aim of this study was to quantify the stabilizing properties of a 3-dimensional (3D)-printed short-arm cast and compare those properties with traditional fiberglass casts in a cadaveric subacute distal radius fracture model. Methods: A cadaveric subacute fracture model was created in 8 pairs of forearms. The specimens were equally allocated to a fiberglass cast or 3D-printed cast group. All specimens were subjected to 3 biomechanical testing modalities simulating daily life use: flexion and extension of digits, pronation and supination of the hand, and 3-point bending. Between each loading modality, radiological evaluation of the specimens was performed to evaluate possible interval displacement. Interfragmentary motion was quantified using a 3D motion-tracking system. Results: Radiographic assessment did not reveal statistically significant differences in radiographic parameters between the 2 groups before and after biomechanical testing. A statistically significant difference in interfragmentary motion was calculated with the 3-point bending test, with a mean difference of 0.44 (±0.48) mm of motion. Conclusions: A statistically significant difference in interfragmentary motion between the 2 casting groups was only identified in 3-point bending. However, the clinical relevance of this motion remains unclear as the absolute motion is less than 1 mm. The results of this study show noninferiority of the 3D-printed casts compared with the traditional fiberglass casts in immobilizing a subacute distal radius fracture model. These results support the execution of a prospective randomized clinical trial comparing both casting techniques.

Acetabulum Cup Stability in an Early Weight-Bearing Cadaveric Model of Geriatric Posterior Wall Fractures.

BACKGROUND: Primary total hip arthroplasty (THA) has been suggested for posterior wall (PW) fractures with unfavorable features in the geriatric population. There is a paucity of studies reporting on postoperative protocols for primary THA after PW fractures. The purpose of this study was to test the biomechanical effect of immediate assisted weight-bearing on acetabulum THA cup fixation in an osteoporotic PW fracture model. METHODS: Computed tomography scans of 18 geriatric PW fractures (mean age, 77 ± 8 years) were used to generate representative PW fracture. This fracture pattern, comprising 50% of the PW and 25% of the acetabulum rim, was then created in 6 female cadaveric pelves. A multihole acetabulum THA cup was implanted with line-to-line reaming and fixed with four 5-mm screws. The pelves were cyclically loaded to up to 1.8× body weight (BW) in the intact form, after fracture creation and fracture fixation. Optical markers were used to determine acceptable cup motion of less than 150 µm. RESULTS: Five specimens withstood 3.6× BW loading after implantation and before fracture creation. At 1.8× BW load, cup motion was nonfractured: 50 ± 24 µm (range, 5-128 µm), fractured with no fixation: 37 ± 22 µm (range, 8-74 µm), or fractured with fixation: 62 ± 39 µm (range, 5-120 µm) (P = 0.0097). Cup motion was <150 µm for all groups. CONCLUSION: This study supports the practice of allowing immediate assisted weight-bearing in patients undergoing THA with PW fractures involving up to 50% of the PW and up to 25% of the acetabular rim, with or without fixation of the PW fragment.

Mapping of the Stable Articular Surface and Available Bone Corridors for Cup Fixation in Geriatric Acetabular Fractures.

BACKGROUND: The optimal treatment of acetabular fractures in the senior cohort is undetermined. Total hip arthroplasty in the setting of an acetabular fracture is increasing in popularity. However, there is concern regarding the fixation of a prosthetic cup in a fractured acetabulum. The purpose of this study is to map the area of stable articular surface and bone corridors available for cup fixation in this fracture cohort. METHODS: CT scans of acetabular fractures in 131 consecutive geriatric patients older than 65 years from two level 1 academic trauma centers were analyzed. Acetabular fractures were classified using the Letournel classification, the available stable articular surface, and the bone corridors available for fixation. RESULTS: Fractures involving the anterior column were the most common fracture type seen. The dome only pattern was the most common stable articular surface pattern. The sciatic corridor was available for fixation in all fracture types, followed by the gluteal pillar corridor. Most fractures had at least two corridors (93%) available for screw fixation. CONCLUSIONS: The findings of this study may aid in the development and evaluation of fixation strategies for acetabular cups allowing geriatric acetabular fracture patients earlier weight bearing after primary hip arthroplasty.

Use of standard musculoskeletal ultrasound to determine the need for fasciotomy in an elevated muscle compartment pressure cadaver leg model.

INTRODUCTION: Acute compartment syndrome (ACS) is a limb-threatening condition often associated with leg injury. The only treatment of ACS is fasciotomy with the purpose of reducing muscle compartment pressures (MCP). Patient discomfort and low reliability of invasive MCP measurements, has led to the search for alternative methods. Our goal was to test the feasibility of using ultrasound to diagnose elevated MCP. METHODS: A cadaver model of elevated MCPs was used in 6 cadaver legs. An ultrasound transducer was combined with a pressure sensing transducer to obtain a B-mode image of the anterior compartment, while controlling the amount of pressure applied to the skin. MCP was increased from 0 to 75 mmHg. The width of the anterior compartment (CW) and the pressure needed to flatten the bulging superficial compartment fascia (CFFP) were measured. RESULTS: Both the CW and CFFP showed high correlations to MCP in the individual cadavers. Average CW and CFFP significantly increased between baseline and the first elevated MCP states. Both Inter-observer and intra-observer agreements for the ultrasound measurements were good to excellent. DISCUSSION: Ultrasound indexes showed excellent correlations in compartment pressures, suggesting that there is a potential for the clinical use of this modality in the future.

The influence of mini-fragment plates on the mechanical properties of long-bone plate fixation.

OBJECTIVE: Mini-fragment plates (MFPs) are increasingly used in fracture surgery to provide provisional fixation. After definitive fixation, the surgeon decides whether to remove the plates or leave them in place as additional fixation, based on the perceived biomechanical influence of the MFP. However, there are no current biomechanical studies to guide this decision. Therefore, the purpose of this study was to evaluate the influence of MFPs on the four-point bending and torsional stiffness of long bone transverse and simple wedge fracture fixation constructs. METHODS: Fourth-generation composite bone cylinders were cut to produce transverse (AO-OTA classification 12-A3) and simple wedge (AO-OTA classification 12-B2) fracture models. The specimens were fixed using a low-contact dynamic compression plate (LC-DCP) and MFPs. Specimens were tested in four-point bending and torsion utilizing 3 different MFP orientations. RESULTS: No statistically significant differences in bending stiffness were found between control and MFP groups for transverse fracture constructs. MFPs significantly increased the bending stiffness for wedge fracture constructs under certain loading conditions. This increase was observed when MFPs were positioned both orthogonal (85.1% increase, P = .034) and opposite (848.2% increase, P < .001) to the LC-DCP. MFPs significantly increased the torsional stiffness for both transverse and wedge fracture constructs when MFPs were positioned both orthogonal (transverse: 27.7% increase, wedge: 16.7% increase) and opposite (transverse: 28.4%, wedge: 24.2% increase) to the LC-DCP. CONCLUSIONS: Our results indicate that including MFPs in definitive fixation can increase the bending and torsional stiffness of a long-bone fracture fixation construct. This suggests that the biomechanical influence of MFPs should be considered. However, clinical studies will be required to test the applicability of these findings to the clinical setting.