Introduction

Despite the high regenerative capacity of bone, large bone defects often require treatment involving bone grafts. Conventional autografting and allografting treatments have disadvantages, such as donor site morbidity, immunogenicity and lack of donor material. Bone tissue engineering offers the potential to achieve major advances in the development of alternative bone grafts by exploiting the bone-forming capacity of osteoblastic cells. However, viable cell culture models are essential to investigate osteoblast behavior. Three-dimensional (3D) cell culture systems have become increasingly popular because biological relevance of 3D cultures may exceed that of cell monolayers (2D) grown in standard tissue culture. However, only few direct comparisons between 2D and 3D models have been published. Therefore, we performed a pilot study comparing 2D and 3D culture models of primary human osteoblasts with regard to expression of transcription factors RUNX2 and osterix as well as osteogenic differentiation.

Introduction Besides great advances in hip-alloarthroplasty there are still numerous indications for joint saving procedures as correction osteotomies. Often these procedures include complex 3D rearrangements of the proximal femur, which are for the surgeon technically very demanding because of the (1) complexity of a precise 3D planning of the fragment position and as a second step (2) the exact operative realization of the plan.

The project aim was to minimize these two major problems by using computer assisted techniques for exact intraoperative virtual 3D planning including a detailed biomechanical analysis (as change of head offset, torsion, leg length etc.).

Methods A new key feature is that we extended our former developed geometry based approach using 2 fluoro frames from different angles of the proximal femur to inversely reconstruct the femoral head sphere and additionally mark the head-neck axis and the anatomical femur axis. For navigation a passive infrared based optical system was used with a Polaris-camera, a C-arm calibration kit and PC-based developed software. For in vitro evaluation complex osteotomies were performed on 8 femora under simulated OR conditions.

Results The evaluation showed that the difference between the planning and real surgical outcome for the wedge size was less then 3 and for the femur head center position less then 4.1 mm. No implant penetrated the femur neck isthmus, but in 2 femora the position of the plate resulted in a lateral space of maximal 2 mm between the OT-planes, which was by higher plate tensioning completely compensable. The planning process as well as the operative execution was practicable and time efficient.

Discussion The used method demonstrated from a clinical view point a high accuracy. With the described approach it is for the surgeon directly visible during the planning process what biomechanical impacts his planned procedure will have on the femur head offset, torsion, leg length etc.

So without changing the standard operative procedure the method can be of high clinical importance to improve the accuracy of the planning and the consecutive operative realization for a precise fragment positioning and the plate location without penetrating the isthmus of the femoral neck. So it can potentially help to reduce intraoperative complications and the use of the fluoroscope to minimally 4 frames for the whole procedure.

We have to deal with an increasing number of patients who are suffering from a femoral neck fracture. In Ger-many in 1996 135.000 patients with this kind of fracture were treated. These fractures are usually found in old people and have a high complication rate:

Osteonecrosis of the femoral head: 12–43% (Kyle 1994)

Pseudarthrosis: 16–28% (Rogmark 2002)

The indications for a total hip replacement are:

– age > 65years

– presence of osteoporosis (also under 65)

– daily activity possible (otherwise hemialloarthroplasty)

– comorbidity such as osteoarthritis

We have to consider several aspects:

The mortality rate is lower if we use a hip replacement (THR ~6%, osteosynthesis ~10%) The complication rate is lower if we use hip replacement (THR ~2%, osteosynthesis ~5%) In 30% of cases we have to change from osteosynthesis to a total hip replacement due to secondary complications of osteosynthesis in mobile patients If we look at this data, we must conclude that total hip replacement is the goldstandard in the treatment of femoral neck fractures (with Garden III and IV) in the population older than 65 years. Hemialloarthroplasty is only indicated for patients who are more or less immobilized.