Computer-aided bone distraction

Details Computer-aided bone distraction Computer-aided bone distraction

2000-04-07

2004-03-02

Lateef, Marvin M. (Department: 3737)

Surgery

Diagnostic testing

Detecting nuclear, electromagnetic, or ultrasonic radiation

C600S425000, C600S429000, C382S128000, C382S131000, C382S132000, C378S098120, C378S021000, C378S062000, C378S063000, C606S091000

Reexamination Certificate

active

06701174

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
(Not Applicable)
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
(Not Applicable)
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention broadly relates to the field of orthopedic surgery, and more particularly, to computer assisted orthopedic surgery that uses two or more X-ray images of a patient's bone to generate a computer-based 3D (three dimensional) model of the patient's bone and a computer-based surgical plan for the doctor.
2. Description of the Related Art
Bone distraction in orthopedic surgery might well be considered one of the earliest successful forms of tissue engineering. Bone distraction is a therapeutic process invented in Russia in about 1951 for treating fractures, lengthening limbs and correcting other skeletal defects such as angular deformities. In bone distraction, external fixators are used to correct bone deformities and to lengthen bones by the controlled application of ‘tension-stress’, resulting in natural, healthy tissue.
FIG. 1
illustrates a prior art Ilizarov fixator
20
attached to a bone
22
. The external Ilizarov fixator
20
is constituted of a pair of rings
24
separated by adjustable struts
28
. The rings
24
are mounted onto the bone
22
from outside of the patient's body through wires or half-pins
26
as illustrated in FIG.
1
. The lengths of the struts
28
can be adjusted to control the relative positions and orientations of the rings
24
. After the fixator
20
is mounted to the patient's bone
22
, the bone
22
is cut by osteotome (i.e., surgical cutting of a,bone) as part of the bone distraction process. Thereafter, the length of each individual strut
28
is adjusted according to a surgical plan. This length adjustment results in the changing of the relative position of the rings
24
, which then forces the distracted (or “cut”) bone ends to comply and produce new bone in-between. This is termed the principle of “tension-stress” as applied to bone distraction.
The bone distraction rate is usually controlled at approximately 1 mm (millimeter) per day. The new bone grows with the applied distraction and consolidates after the distraction is terminated. Thereafter, the fixator
20
can be safely removed from the bone
22
and, after recanalization, the new or “distracted” bone is almost indistinguishable from the old or pre-surgery bone. The bone
22
may be equipped with other units, such as hinges, to correct rotational deformities about one or a few fixed axes. Thus, controlled application of mechanical stress forces the regeneration of the bone and soft tissues to correct their own deformities. The whole process of deformity correction is known as “bone distraction.”
At present, the following nominal steps are performed during the bone distraction process: (1) Determine an appropriate frame size for the fixator (e.g., for the Ilizarov fixator
20
); (2) Measure (e.g., from X-rays) the deformity of bone fragments (or the anticipated fragments after surgically cutting the bone) and obtain six parameters that localize one fragment relative to the other; (3) Determine (or anticipate) how the fixator frame should be mounted on the limb; (4) Input the parameters and measurements to a computer program that generates the strut lengths as a function of time required to correct the deformity; (5) Mount the fixator frame onto the bone fragments; and (6) Adjust the strut lengths on a daily basis according to the schedule generated in step (4).
The steps outlined in the preceding paragraph are currently executed with minimal computerized assistance. Typically, surgeons manually gather or determine the required data (e.g., fixator frame size, bone dimensions, fixator frame mounting location and orientation, etc.) and make their decisions based on hand-drawn two-dimensional sketches or using digitized drawings obtained by tracing X-ray images For example, a computerized deformity analysis (CDA) and pre-operative planning system (hereafter “the CDA system”) developed by Orthographics of Salt Lake City, Utah, USA, rates the boundary geometry of bones using X-ray images that are first digitized manually, i.e., by placing an X-ray image on a light table and then tracing the outline with a digitizing stylus, and then the digital data are fed into the CDA system. Thereafter, the CDA system assists the surgeon in measuring the degree of deformity and to make a surgical plan. The entire process, however, is based on two-dimensional drawings and there is no teaching of showing or utilizing three-dimensional bone deformity or bone geometry.
It is observed that in the complex area of bone distraction surgery, it is difficult, if not impossible, to make accurate surgical plans based solely on a limited number of two-dimensional renderings of bone geometry. This is because of the complex and inherently three-dimensional nature of bone deformities as well as of fixator geometry. Furthermore, two-dimensional depictions of surgical plans may not accurately portray the complexities involved in accessing the target positions of the osteotome and fixator pins surrounding the operated bone. Lack of three-dimensional modeling of these geometric complexities makes it difficult to accurately mount the fixator on the patient according to the pre-surgical plan.
After a surgeon collects the requisite data (e.g., fixator frame size to be used, patient's bone dimensions, fixator frame mounting location and orientation, etc.), the surgeon may use the simulation software accompanying commercially available fixators (such as the Taylor Spatial Frame distributed by Smith & Nephew Inc. of 1450 Brooks Road, Memphis, Tenn., USA 38116) to generate a day-by-day plan that shows how the lengths of the fixator struts should be adjusted. Such a plan is generated after the initial and target frame positions and orientations are specified by the surgeon. However, the only functionality of the simulation software is a simple calculation of the interpolated frame configurations. The software does not provide any assistance to the surgeon about making surgical plans nor does it provide any visual feedback on how the fixator frame and bone fragments should be moved over time.
The Taylor Spatial Frame (shown, for example, in
FIG. 16
) with six degrees of freedom (DOF) is more versatile, flexible and complex than the Ilizarov fixator
20
in FIG.
1
. Because of the sophistication of modern fixators (e.g., the Taylor Spatial Frame) and because of the limitations of the presently available bone distraction planning and execution systems, current computerized bone distraction procedures are error-prone, even when performed by the most experienced surgeons. As a result, the patients must typically revisit the surgeon several times after the initial operation in order for the surgeon to re-plan and refine the tension-stress schedule, or even to re-position the fixator. Such reiterations of surgical procedures are not only time-consuming, but incur additional costs and may lead to poorer therapeutic results while unnecessarily subjecting patients to added distress. It is therefore desirable to generate requisite bone and fixator models in three-dimensions prior to surgery so as to minimize the surgery planning and execution errors mentioned hereinbefore.
The discussion given hereinbelow describes some additional software packages that are available today to assist in the simulation and planning of bone distraction. However, it is noted at the outset that these software packages are not based on three-dimensional models. Further, these software packages are quite limited in their capabilities to assist the surgeon in making important clinical and procedural decisions, such as how to access the site of the osteotomy or how to optimally configure fixator pin configurations. Additional limitations of the present software systems include: (1) No realistic three-dimensional view of a bone and a fixator; (2) No usage of motion in surgical simulation; (3) Lack of an easy-to-use graphical user

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