Tibial shaft fractures require surgical stabilization preferably by intramedullary nailing. However, patients often report functional limitations even years after the injury. This study investigates the influence of the surgical approach (transpatellar vs. parapatellar) on gait performance and patient reported outcome six months after surgery.

Twenty-two patients with tibial shaft fractures treated by intramedullary nailing through a transpatellar approach (TP: n=15, age 41±15, BMI 24±3) or a parapatellar approach (PP: n=7, age 34±15, BMI 23±2) and healthy, matched controls (n=22, age 39±13, BMI 24±2) were assessed by instrumented motion analysis six months after intramedullary nailing. Short musculoskeletal function assessment questionnaire (SMFA) as well as kinematic and kinetic gait data were collected during level walking. Comparisons among approach methods and control group were performed by analysis of variance and Mann-Whitney test.

Six months after surgery, knee kinetics in both groups differed significantly compared to controls (p <.04). The approach method affected gait speed (TP: p = .002; PP: p = .08) and knee kinematics in the early stance phase (TP: p = .011; PP: p = .082), with the parapatellar approach showing a more favorable outcome. However, the difference between patient groups was not significant for any of the assessed gait parameters (p > .2). Also, no differences could be found in the bother index (BI) or function index (FI) of SMFA between surgical approach methods (BI: TP: Mdn = 7.2, PP: Mdn = 9.4; FI: TP: Mdn = 10.3, PP: Mdn = 9.2, p > .7).

Our study demonstrates, that six months after surgery for tibial shaft fractures functional limitations remain. These limitations appear not to be different for either a trans- or a parapatellar approach for the insertion of the intramedullary nail. The findings of this study are limited by the relatively short follow up time period and small number of patients. Future studies should investigate the source of the functional limitation after intramedullary nailing of tibial shaft fractures.

Implant manufacturers develop new products to improve existing fracture fixation methods or to approach new fracture challenges. New implants are commonly tested and approved with respect to their corresponding predecessor products, because the knowledge about the internal forces and moments acting on implants in the human body is unclear. The aim of this study was to evaluate and validate implant internal forces and moments of a complex physiological loading case and translate this to a standard medical device approval test.

A finite elements model for a transverse femur shaft fracture (AO/OTA type 32-B2) treated with a locked plate system (AxSOS 3 Ti Waisted Compression Plate Broad, Stryker, Kalamazoo, USA) was developed and experimentally validated. The fractured construct was physiologically loaded by resulting forces on the hip joint from previously measured in-vivo loading experiments (Bergmann et. al). The forces were reduced to a level where the material response in the construct remained linear elastic. Resulting forces, moments and stresses in the implant of the fractured model were analysed and compared to the manufacturers’ approval data.

The FE-model accurately predicted the behaviour of the whole construct and the micro motion of the working length of the osteosynthesis. The resulting moment reaction in the working length was 24 Nm at a load of 400 N on the hip. The maximum principle strains on the locking plate were predicted well and did not exceed 1 %.

In this study we presented a protocol by the example of locked plated femur shaft fracture to calculate and validate implant internal loading using finite element analysis of a complex loading. This might be a first step to move the basis of development of new implants from experience from previous products to calculation of mechanical behaviour of the implants and therefore, promote further optimization of the implants’ design.

Abstract

Hip osteoarthritis (OA) is a disorder of high socio-economic relevance. The causes of hip osteoarthritis are multifactorial; however, the epidemiological literature regularly cites occupational tasks, such as heavy lifting and carrying, as a risk factor for the development of hip OA. The level of mechanical stresses upon the hip joint caused by occupational tasks remain largely unclear, however. This project sought to quantify the levels of stresses upon the hip joint during occupational tasks. In particular we were interested in comparing load as well as stress levels from everyday activities with occupational tasks typically performed by blue collar workers.

Sectors and occupational activities presenting a high potential for stress upon the hip joint were identified by means of a survey conducted among accident insurance institutions. Lifting, carrying and load transfer (25 to 50 kg), ladder climbing and stair climbing (without additional load and with an additional load of 25 kg) were selected from among these sectors and activities for the purpose of the study. Laboratory measurements were performed in which motion capturing and a range of force measurement apparatus were used to record and evaluate the performance of the selected tasks by 12 skilled workers from a number of sectors. multi-body simulation was used to calculate the stress in the form of hip-joint contact forces. The contact pressures and their geometric distribution on the cartilage surfaces of the hip joint were then calculated from these results by means of finite-element analysis. This produced an indicator for the strain upon the hip joint.

The highest hip-joint forces, at (637±148)% of the body weight, occurred during handling of the 50 kg load. This corresponded to 1.7 times the stress arising during walking, at (368±78)% of the body weight. Significantly higher hip-joint forces compared to those arising during walking were observed for the carrying of loads of 40 kg and 50 kg, the handling of loads of 25 kg, 40 kg and 50 kg, and stair climbing with an additional load of 25 kg. Maximum contact pressures of 24.1 MPa were computed during the finite-element analysis (lifting of 50 kg); only very small regions of the joint surface were however affected by these high pressures. During walking, the maximum pressure reached 15 MPa.

The results obtained provide a quantitative overview of the strains upon the hip joint during occupational and everyday tasks. They constitute an aid to future quantitative exposure assessments in a range of sectors and occupational fields, and thus contribute to improving estimation of the relevance of stresses of occupational origin to the incidence of hip OA.

Introduction

Metabolic disorders are among known risk factors for tendinopathies or spontaneous tendon ruptures. However, the underlying cellular and molecular mechanisms remain unclear. We have previously shown that human and rat tendon cells produce and secrete insulin upon glucose stimulation. Therefore, we hypothesize that nutritional glucose uptake affects tendon healing in a rat model.