The influence of proximal stem geometry and surface finish on the fixation of a double-tapered cemented femoral stem

A novel intramedullary nail to control interfragmentary motion in diaphyseal tibial fractures

Numerous animal and human studies have demonstrated the benefit of controlled interfragmentary motion on fracture healing. In this study, we quantified interfragmentary motion and load transfer in tibial fractures fixed using a novel intramedullary nail (IMN) that allows controlled axial motion. Fifty composite tibias with various fracture patterns were utilized. For all test conditions, two interlocking screws were used to fix the nail in the proximal metaphysis, and two interlocking screws through the distal metaphysis. The nail allowed either no motion (static mode) or 1 mm (dynamic mode) of cyclic axial motion between the two fracture fragments for every fracture pattern tested. As expected, strain shielding was more prominent under static nail conditions. In contrast, specimens tested under dynamic nail conditions transferred axial load between the fracture fragments such that strains near the fracture site were generally similar to those measured on an intact tibia. Maximum shear strains proximal to the fracture were significantly lower in specimens with oblique or butterfly fracture patterns (p < 0.01) compared to intact specimens. This decrease in shear strain indicates that strain shielding effects were likely present due to the implant. However, strain shielding appeared to be reduced in tensile and compressive principal strains. In summary, the novel IMN allowed controlled axial motion between the fragments in a variety of common diaphyseal tibial fracture patterns. Clinical Significance: The present in vitro biomechanical study investigated a novel intramedullary nail capable of controlled axial interfragmentary motion which may potentially enhance fracture healing.

Biomechanical Comparison of Fixation Devices for First Metatarsocuneiform Joint Arthrodesis

Common surgical treatment of first tarsal-metatarsal arthritis is by first metatarsocuneiform joint arthrodesis. While crossed-screw and locking plate fixation are the most widely used methods, a novel construct was designed to alleviate soft tissue irritation while still providing stable fixation. Using anatomic first metatarsal and medial cuneiform composites, we compared 3 arthrodesis implants (crossed-screw, dorsal locking plate, and IO Fix) under 2 cyclic bending loading scenarios (cantilever and 4-point bending). Additionally, the optimal orientation (plantar-dorsal or dorsal-plantar) of the IO Fix construct was determined. Failure load, diastasis, joint space angle, and axial and angular stiffness were determined. Both crossed-screw fixation and the IO Fix constructs experienced significantly higher failure loads than the dorsal locking plate during both loading scenarios. Additionally, they had lower plantar diastasis and joint space angle at failure than the plate. Moreover, the plantar-dorsal IO Fix construct was significantly stiffer than the crossed-screw during cantilever bending. Finally, the plantar-dorsal orientation of the IO Fix device had higher failure load and lower diastasis and angle at failure than in the dorsal-plantar orientation. The results suggest that the IO Fix system can reduce motion at the interfragmentary site and ensure compression for healing comparable to that of the crossed-screw fixation.

LEVELS OF EVIDENCE

Level V: Bench testing.

Fixation of non-cemented total hip arthroplasty femoral components in a simulated proximal bone defect model

An accelerated sequential proximal femoral bone loss model was used to measure the initial stability of three noncemented femoral stem designs: fully porous-coated, proximally porous-coated, and dual-tapered, diaphyseal press-fit (N=18). Only dual-tapered, diaphyseal press-fit stems remained stable with as much as 105 mm of bone loss, with average cyclic micromotion remaining below 25 μm in ML and below 10 μm in AP planes. In contrast, with proximally coated and fully coated stem designs with circular or oval cross-sections, 60mm of bone loss, resulting in lower than 10 cm of diaphyseal bone contact length, led to gross instability, increasing average cyclic micromotions to greater than 100 μm prior to failure. Therefore, the results provide support for using a dual-tapered stem in revision cases with proximal bone loss.