Shchepilina O.V., Begun P.I.

Saint Petersburg Electrotechnical University LETI

Method research of the system"thigh-bone graft-implant" in rehabilitation period after osteosynthesis

A hip fracture is a heavy injury to the musculoskeletal system, this type of injury is referred to hip fractures. Rehabilitation after hip replacement surgery depends on many features and do not to say that there is one single program. Modern problems of rehabilitation after hip fracture due to the fact that is not governed by the maximum load, taking into account the recovery of bone regenerate and is not considered a risk of vascular disorders. At the same time during postoperative period after the hip fracture results from the fact that the thighbone traumatic injury affects the locomotor system kinematic reactions in general, thus facilitating associated disorders that do not directly result from the injury, yet worsening the patients life.

Despite new implant designs, improved skills of surgeons, new operation methods implemented, the results stop satisfying patients as the full recovery period reaches half a year. This is because the missing is the individual approach depending on the bone tissue condition, the fracture location. The issue of the bone graft reconstruction at the subcapital fracture location lacks attention.

However, information technologies development in medicine, particularly in trauma surgery, orthopedics and biomechanics allows achieving radically new rehabilitation technology level.

The object of the research is to develop thighbone diagnostic technique after osteosynthesis with muscle activity and elasticity module (E, MPa) taken into account at every bone graft remodeling stage. The algorithm has been developed, the calculations have been carried out and the analysis and the research have been undertaken for the thighbone-bone graft-implant system stress and stain behavior at various rehabilitation stages.

The following assumptions were considered while building the conceptual model: 1) thighbone bone structure is idealized to comprise two isotropic layers: cortical and spongy; 2) within the thighbone, the fissure is located at the thighbone neck cross-section and it has uniform isotropic structure, wherein its mechanical properties change at every osteotylus reconstruction stage and those are localized within the zone that is free of muscular efforts; 3) dynamic stress is applied to the thighbone center by axes X, Y, Z (www.orthoload.com).

Figure 1 represents experimental data of the effective load changes as a function of time (fig.1).

Fig. 1.

As initial data, the thighbone MRT is used (fig.2) to build the object 3d models by means of Mimics, the computer modeling environment. The figure 2 represents the thighbone (1 - spongy layer, 2 - cortical layer).

b

Fig.2

With those models imported into the Solid Works software package, a solid thighbone geometric model was obtained with damages at the area of the greater trochanter.

The considered is the bone recovery via osteosynthesis, with two cannulated titanium screws (fig.3). The figure 3 represents the thighbone osteosynthesis (1 - cortical layer, 2 - spongy layer; 3 - fixing screws, 4 - bone graft).

At every stage, the elasticity module is given according to the diagram of the tab.1 that characterize the graft bone tissue elasticity module change during the postoperative period.

Fig.3.

Tab.1

Time after operation, week

, P

1

before 3

0,0056

2

8-10

7,4

3

14-15

11,4

4

after 20

100

 

In terms of non-linear dynamic analysis, various rehabilitation procedures, relating to the first two rehabilitation stages, were considered. The obtained results are represented via fig.5. Fig. 4 represents dependences of deformations appearing at the first stage with Eper=5.4kPa : 1 allowed deformation, 2 deformation with the thigh aside, 3 deformation for the thigh up 30.

Walking is an important element in the complex process of rehabilitation and positive effect on the work of many organs: cardiovascular system, on the pulmonary system improves joint mobility, prevent muscle degeneration.

Atrophy of muscle tissue influences the distribution of the load on the systemthighbone-bone graft-implant.We have made calculations based on muscle atrophy which have a greater impact on the distribution of the load during walking.

 

Fig.4. The first stage of rehabilitation

In Fig.5. represents dependences deformation of the regenerate (E=6,62 MPa) from time double step when eighty percent of muscle atrophy: 1) the quadriceps muscle of thigh; 2) muscle antagonist synergist; position 3 on the chart of the femur is normal.

Fig.5

Method helps the surgeon in the choice of technology operations and enables them to choose effective implant and method of conducting rehabilitation program, knowing the risks.