Selection of internal fixation method for femoral intertrochanteric fractures using a finite element method

BACKGROUND Failure to fix unstable intertrochanteric fractures impairs return to daily activities.AIM To simulate five different internal fixation methods for unstable proximal femoral fractures.METHODS A three-dimensional model of the femur was established from sectional computed tomography images,and an internal fixation model was established.Finite element analysis of the femur model was established,and three intertrochanteric fracture models,medial defect,lateral defect,and medial-lateral defects,were simulated.Displacement and stress distribution after fixation with a proximal femoral anti-rotation intramedullary nail(PFNA),integrated dual-screw fixation(ITN),PFNA+wire,PFNA+plate,and PFNA+wire+plate were compared during daily activities.RESULTS The maximum displacement and stress of PFNA and ITN were 3.51 mm/473 MPa and 2.80 mm/588 MPa for medial defects;2.55 mm/288 MPa and 2.10 mm/307 MPa for lateral defects;and 3.84 mm/653 MPa and 3.44 mm/641 MPa for mediallateral defects,respectively.For medial-lateral defects,reconstructing the medial side alone changed the maximum displacement and stress to 2.79 mm/515 MPa;reconstructing the lateral side changed them to 3.72 mm/608 MPa,when both sides were reconstructed,they changed to 2.42 mm/309 MPa.CONCLUSION For medial defects,intramedullary fixation would allow early low-intensity rehabilitation exercise,and ITN rather than PFNA reduces the risk of varus and cut-out;for lateral wall defects or weakness,intram-edullary fixation allows higher-intensity rehabilitation exercise,and ITN reduces the risk of varus.For both medial and lateral defects,intramedullary fixation alone will not allow early functional exercise,but locating lateral or medial reconstruction will.For defects in both the inner and outer sides,if reconstruction cannot be completed,ITN is more stable.

Surgical Fixation of Fourth and Fifth Metacarpal Shaft Fractures with Flexible Intramedullary Absorbable Rods： Early Clinical Outcomes and Implications

Background： To avoid the irritation of tendons and soft tissues as well as hardware-related problems, we designed an intramedullary fixation with bioabsorbable rods for the treatment of the metacarpal shaft fractures. Methods： Five patients with nine shaft fractures of the fourth and fifth metacarpi were treated with intramedullary absorbable implants and followed up with an average of 4.2 months postoperatively. Results： At final follow-up, all patients achieved fracture union with no signs of inflammatory or subcutaneous effusion. There was no shortening, angulatory, or rotatory deformity. There was almost full active extension range of motion （ROM） of the metacarpophalangeal joints while the active flexion ROM of these joints was 80.7 ± 9.6°. hand was 94.0 ± 9.6%. X-rays showed that the arch of the second Compared with the contralateral hand, the grip strength of the injured to fifth metacarpal heads was smooth. There were no intramedullary lytic changes and soft tissue swellings. Conclusion： The intramedullary absorbable implants are a safe, simple, and practical treatment for fourth and filth metacarpal fractures with good early clinical outcomes and no significant complications.

THE MORPHOLOGICAL MEASURE OF THE TIBIAL MEDULLARY CAVITY AND ITS SIGNIFICANCE

Objective To provide morphological reference for the designing of the intramedullary nail fixation which suitable for Chinese by investigating the morphological characteristics of tibial medullary cavity. Methods The morphological parameters of the 113 normal adult tibiale were measured on the X-ray photographs with the image analysis software. Results The total lengths of tibial medullary cavities were 299.49±11.03 mm(male) and 274.60± 6.77 mm(female), and the lengths of the narrow part were 66.36±3.90 mm(male) and 51.57±3.92mm(female). The end-points of narrow part were about 29.9 mm(male) and 26.09 mm(female)below the midpoints of medullary cavities. The radians of the longitudinal axes of medullary cavities were 2.53±1.27°(male) and 2.57±1.16°(female). The proximal opening K were 9.47±2.71(male) and 8.59±2.46(female). The distal opening K were 8.21± 2.93(male)and 7.65±2.87(female). Conclusion The morphology of tibial medullary cavity, the characteristic variety of radian and the opening K were very important references for designing the Chinese intramedullary nail fixation.

A segmental defect adaptation of the mouse closed femur fracture model for the analysis of severely impaired bone healing

Objective: To better characterize nonunion endochondral bone healing and evaluate novel therapeutic approaches for critical size defect healing in clinically challenging bone repair, a segmental defect model of bone injury was adapted from the threepoint bending closed fracture technique in the murine femur.Methods: The mouse femur was surgically stabilized with an intramedullary threaded rod with plastic spacers and the defect adjusted to different sizes. Healing of the different defects was analyzed by radiology and histology to 8 weeks postsurgery. To determine whether this model was effective for evaluating the benefits of molecular therapy, BMP-2 was applied to the defect and healing then examined.Results: Intramedullary spacers were effective in maintaining the defect. Callus bone formation was initiated but was arrested at defect sizes of 2.5 mm and above, with no more progress in callus bone development evident to 8 weeks healing. Cartilage development in a critical size defect attenuated very early in healing without bone development, in contrast to the closed femur fracture healing, where callus cartilage was replaced by bone. BMP-2 therapy promoted osteogenesis of the resident cells of the defect, but there was no further callus development to indicate that healing to pre-surgery bone structure was successful.Conclusions: This segmental defect adaptation of the closed femur fracture model of murine bone repair severely impairs callus development and bone healing, reflecting a challenging bone injury. It is adjustable and can be compared to the closed fracture model to ascertain healing deficiencies and the efficacy of therapeutic approaches.