Coronoid fractures account for 2 to 15% of the cases with elbow dislocations and usually occur as part of complex injuries. Comminuted fractures and non-unions necessitate coronoid fixation, reconstruction or replacement. The aim of this biomechanical study was to compare the axial stability achieved via an individualized 3D printed prosthesis with curved cemented intramedullary stem to both radial head grafted reconstruction and coronoid fixation with 2 screws. It was hypothesized that the prosthetic replacement will provide superior stability over the grafted reconstruction and screw fixation. Following CT scanning, 18 human cadaveric proximal ulnas were osteotomized at 40% of the coronoid height and randomized to 3 groups (n = 6). The specimens in Group 1 were treated with an individually designed 3D printed stainless steel coronoid prosthesis with curved cemented intramedullary stem, individually designed based on the contralateral coronoid scan. The ulnas in Group 2 were reconstructed with an ipsilateral radial head autograft fixed with two anteroposterior screws, whereas the osteotomized coronoids in Group 3 were fixed in situ with two anteroposterior screws. All specimens were biomechanically tested under ramped quasi-static axial loading to failure at a rate of 10 mm/min. Construct stiffness and failure load were calculated. Statistical analysis was performed at a level of significance set at 0.05. Prosthetic treatment (Group 1) resulted in significantly higher stiffness and failure load compared to both radial head autograft reconstruction (Group 2) and coronoid screw fixation, p ≤ 0.002. Stiffness and failure load did not reveal any significant differences between Group 2 and Group 3, p ≥ 0.846. In cases of coronoid deficiency, replacement of the coronoid process with an anatomically shaped individually designed 3D printed prosthesis with a curved cemented intramedullary stem seems to be an effective method to restore the buttress function of the coronoid under axial loading. This method provides superior stability over both radial head graft reconstruction and coronoid screw fixation, while achieving anatomical articular congruity. Therefore, better load distribution with less stress at the bone-implant interface can be anticipated. In the clinical practice, implementation of this prosthesis type could allow for early patient mobilization with better short- and long-term treatment outcomes and may be beneficial for patients with irreparable comminuted coronoid fractures, severe arthritic changes or non-unions.
Treatment of comminuted intraarticular calcaneal fractures remains controversial and challenging. Anatomic reduction with stable fixation has demonstrated better outcomes than nonoperative treatment of displaced intraarticular fractures involving the posterior facet and anterior calcaneocuboid joint (CCJ) articulating surface of the calcaneus. The aim of this study was to investigate the biomechanical performance of three different methods for fixation of comminuted intraarticular calcaneal fractures. Comminuted calcaneal fractures, including Sanders III-AB fracture of the posterior facet and Kinner II-B fracture of the CCJ articulating calcaneal surface, were simulated in 18 fresh-frozen human cadaveric lower legs by means of osteotomies. The ankle joint, medial soft tissues and midtarsal bones along with the ligaments were preserved. The specimens were randomized according to their bone mineral density to 3 groups for fixation with either (1) 2.7 mm variable-angle locking anterolateral calcaneal plate in combination with one 4.5 mm and one 6.5 mm cannulated screw (Group 1), (2) 2.7 mm variable-angle locking lateral calcaneal plate (Group 2), or (3) interlocking calcaneal nail with 3.5 mm screws in combination with 3 separate 4.0 mm cannulated screws (Group 3). All specimens were biomechanically tested until failure under axial loading with the foot in simulated midstance position. Each test commenced with an initial quasi-static compression ramp from 50 N to 200 N, followed by progressively increasing cyclic loading at 2Hz. Starting from 200 N, the peak load of each cycle increased at a rate of 0.2 N/cycle. Interfragmentary movements were captured by means of optical motion tracking. In addition, mediolateral X-rays were taken every 250 cycles with a triggered C-arm. Varus deformation between the tuber calcanei and lateral calcaneal fragments, plantar gapping between the anterior process and tuber fragments, displacement at the plantar aspect of the CCJ articular calcaneal surface, and Böhler angle were evaluated. Varus deformation of 10° was reached at significantly lower number of cycles in Group 2 compared to Group 1 and Group 3 (P ≤ 0.017). Both cycles to 10° plantar gapping and 2 mm displacement at the CCJ articular calcaneal surface revealed no significant differences between the groups (P ≥ 0.773). Böhler angle after 5000 cycles (1200 N peak load) had significantly bigger decrease in Group 2 compared to both other groups (P ≤ 0.020). From biomechanical perspective, treatment of comminuted intraarticular calcaneal fractures using variable-angle locked plate with additional longitudinal screws or interlocked nail in combination with separate transversal screws seems to provide superior stability as opposed to variable-angle locked plating only.
Distal radius fractures have an incidence rate of 17.5% among all fractures. Their treatment in case of comminution, commonly managed by volar locking plates, is still challenging. Variable-angle screw technology could counteract these challenges. Additionally, combined volar and dorsal plate fixation is valuable for treatment of complex fractures at the distal radius. Currently, biomechanical investigation of the competency of supplemental dorsal plating is scant. The aim of this study was to investigate the biomechanical competency of double-plated distal radius fractures in comparison to volar locking plate fixation. Complex intra-articular distal radius fractures AO/OTA 23-C 2.1 and C 3.1 were created by means of osteotomies, simulating dorsal defect with comminution of the lunate facet in 30 artificial radii, assigned to 3 study groups with 10 specimens in each. The styloid process of each radius was separated from the shaft and the other articular fragments. In group 1, the lunate facet was divided to 3 equally-sized fragments. In contrast, the lunate in group 2 was split in a smaller dorsal and a larger volar fragment, whereas in group 3 was divided in 2 equal fragments. Following fracture reduction, each specimen was first instrumented with a volar locking plate and non-destructive quasi-static biomechanical testing under axial loading was performed in specimen's inclination of 40° flexion, 40° extension and 0° neutral position. Mediolateral radiographs were taken under 100 N loads in flexion and extension, as well as under 150 N loads in neutral position. Subsequently, all biomechanical tests were repeated after supplemental dorsal locking plate fixation of all specimens. Based on machine and radiographic data, stiffness and angular displacement between the shaft and lunate facet were determined. Stiffness in neutral position (N/mm) without/with dorsal plating was on average 164.3/166, 158.5/222.5 and 181.5/207.6 in groups 1–3. It increased significantly after supplementary dorsal plating in groups 2 and 3. Predominantly, from biomechanical perspective supplemental dorsal locked plating increases fixation stability of unstable distal radius fractures after volar locked plating. However, its effect depends on the fracture pattern at the distal radius.
