4.6 Human Pelvis - Medical

The hipbone is attached to the vertebral column (backbone) by the five sacral vertebrae, which become fused together in the adult to form the sacrum.

The hip joint is on the side of the hipbone, rather than underneath it. At the hip joint, there is a deep socket for the head of the femur (thighbone). This provides more space for the muscles on the inner side of the thigh.

The knee joints are closer to a middle line drawn vertically through the body. This means the knees are closer to the center of gravity of the body and give more stability. The femur, therefore, has to run inward, as well as downward, to meet the knee joint.

The femur (thighbone) forms the upper part of the leg. It not only supports the body when standing, but is also used when walking, running, jumping, climbing or squatting. Therefore, it is the largest and strongest bone in the body.

The femur is also the longest bone, making up over a quarter of a human being's total height. Its size makes the femur very liable to injury.

The rounded upper end of the femur meets the hipbone at the hip joint, which is a ball-and-socket joint. A narrower neck runs sideways and downward to meet the shaft of the bone. Near the upper end of the femur are two projections, and it is here that muscles attach to the bone. At the lower end of the bone, two rounded surfaces fit into two small hollows on the upper end of the tibia (main shinbone). This forms the knee joint. [36], [37]

Reference [40] p20, recommend 10mm slice thickness with 10mm table feed. Reconstruction to thinner slice thickness will be required for realistic imaging. CAT parameters such as 300mm F.O.V., 120kV and 50 to 100mA can be used.

4.6.1 Background

A male patient required a hip transplant. The orthopedic surgeon was contacted and it was suggested that it will be of great value to capture the geometry of the pelvis to determine if there is sufficient bone structure required for an operation of this nature. The patient was scanned at Morningside clinic with the aid of their Toshiba Spiral X-Vision/GX CAT scanner.

Permission was granted so that this patientís data may be retrieved from the CAT scanner. Please refer to section (3.7.4) for the data retrieval procedures. Morning Side Clinic prepared a 3D visualization of the scanned area. The spiral data was prepared in two sets to evaluate the difference. The radiology firstly prepared one set of 3mm thick slices and 3mm intervals or spacing. The finest possible slice thickness and slice spacing were requested to achieve the best results. In this case it would be better to sample more data than required. The right hand pelvis and femur were in a developed state of deterioration. The orthopedic surgeon was particularly interested in the left-hand pelvis. For a successful hip replacement, sufficient bone structure is required at the back of the pelvis. It was quite clear that the front side of the pelvis did not have sufficient bone structure. The most probable cause of the poor state of the pelvis could be a form of austioporouses. The data processing of this case was particular difficult. The fiber, soft tissue and muscle suspended bone particles. The pelvis needed to separate from the other bone and soft tissue. The pelvis and femur were hardly recognizable in certain areas. It was therefor difficult to decide what bone structure is part of the pelvis and what part is suspended by soft tissue The orthopedic surgeon provide a left-hand side of a real human pelvis for reference. CAT scanned film was also provided with 2D slice information as well as 3D rendering to be used for verification.

The data was then processed and a meeting was arranged with the orthopedic surgeon, to verify the results of the computer screen. He was please with the results and requested that we continue with the next phase of the project.

The next stage was to create a prototype of the pelvis. The 3dd file was used with the Materialise, CTM software to generate a STL format file. The STL file was then used with the Stratasys QuickSlice software. Horizontal slices were created. The software performed support generation, automatically. The SML file was created. The FDM machines use this data to build a prototype. The prototype was grown with the red ABS plastic material and finished by removing the support structure generated by the FDM process.

The prototype of the pelvis was supplied to the orthopedic surgeon. He later fitted temporarily a cup to the pelvis prototype with the aid of a bonding putty called prestik, to display the principle of fitting the cup into the pelvis. Areas where bone and bone cement would normally be filled were left out to view the detail of the pelvisís condition.

4.6.2 Conclusion

Delivery time and cost are again the most important factors. The acceptable delivery time for a pelvis case study would be 3 to 5 days. The cost also needs to be affordable. Some of patients are capable to pay for the cost of this technology themselves, but not all patients are so fortunate.

The finest resolution was selected to produce the prototype. It was the first medical case study and needed to capture as much detail as possible to demonstrate the technology. The time of 110 hours to build the prototype can be reduced to a third. The cost for this phase will drop accordingly. The total project time of 126.7 hours can be reduced to only 53.3 hours in future. It will be very important to deliver prototypes in as short as possible turn around time.

It was of great value to have the 2D and 3D CAT scanned film print outs for verification. It was also used for determining the patient's orientation as well as dimensional inspection.

Data retrieval should be more automated or will need to be performed after hours to avoid any interference with the radiology teamís daily workload.

A fathom need to be obtained for physical data verification in future.

Measurements, in the xy axis, from the CAT scan film at the -133 mm position was compared with the converted Mimics slice at approximately the same position. Measurements were taken with the aid of a caliper, from the CAT scan film, and with the aid of the mouse position from the Materialise software. The scale was determined for the CAT film images to be 4.35:1, thus 1mm on the film represented actually 4.35 mm. Measurements were compared varied 1mm in 45mm or about 2%. A second measurement proved better results, 3.13mm over a 280mm distance, or 1.1% deviation.

Measurements were also taken in the z-axis. A new scale was determined and the deviation proved to be 3.33mm for a distance of 17.53mm, of 19%. It was not easy to find the same position to compare the dimensions and the variation may be due to that. It may also be due to the overlap of the scanned slice data. A comparison of the measurements was taken from the 3D constructions made by Morningside Clinic and compared to the 2D-slice position of the converted Mimics Data. Images




The Human Pelvis and Femur.



The Human Pelvis.




3D reconstruction of the patientís Pelvis.



3D reconstruction of the patientís Pelvis.


FDM prototype of the patientís Pelvis with prosthesis fitted.


FDM prototype of the patientís Pelvis with prosthesis fitted.


4.6.3 Pelvis Data Sheet:
  Description Options (Default) Data


1 CT Image Names   566:227 - 527
2 Patient/Project Name   hip3
3 Number of First Input Image   566:227
4 Number of Last Input Image   566:526
5 Number of First Output Image   hip3.000
7 Horisontal Nr. Of Image Pixels 0 to 65535 (265,512,1024) 512
8 Vertical Nr. Of Image Pixels 0 to 65535 (265,512,1024) 512
9 Number of Images per File (1) 1
10 File Swap Format (0,3) 0,3 0
11 Pixel Type B,UB,S,US,L,UL,F S
12 Header Size *see formula below 8704
13 Inter Image Header Size 0 0
14 Add Value 0 to 4095 2048
15 Scale Value 0 to 4095 1.1
16 Table Position (mm) 0
17 Distance Between Slices (mm) 0.5
18 Slice thickness (mm) 3
19 Pixel Size SQ. F.O.R./Nr. Hor. Pixels (mm) 0.71
20 Gantry Tilt Angle Degrees 0
21 Field of Reconstruction/View (mm) 364
22 Number of Images   257
23 File Size of CAT Image kb 215
24 File Size of Converted Image kb 215
25 .3dd file size Mb 0.742 *.3dd
26 .STL file size Mb 34.62 , pellft.stl
28 .IGS file size Mb -
29 RP Slice file size Mb 34.19, pellft.ssl
30 RP Download File size Mb 34.46
31 Grow Time Hour 109.9
32 Tip size (T12, T25) T12
33 Slice Thickness (0.01", 0.014") 0.01"
34 Finishing Time Hour 6
35 Processing Time Hour 5
36 Data Retrieval Time Hour 4
37 Total Cost Rand =109.9*100+6*55+9*150



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