Computer-assisted surgery planner and intra-operative...

Details Computer-assisted surgery planner and intra-operative... Computer-assisted surgery planner and intra-operative...

1998-11-12

2001-03-20

Teska, Kevin J. (Department: 2763)

Data processing: structural design, modeling, simulation, and em

Simulating nonelectrical device or system

Biological or biochemical

C703S007000, C623S019140, C623S020230, C623S021180, C623S022290

Reexamination Certificate

active

06205411

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention is directed generally to the implantation of artificial joint components, osteochondral grafts, and osteotomy and, more particularly, to computer assisted surgical implantation of artificial joint components during replacement and revision procedures, computer-assisted osteochondral grafts, and computer-assisted osteotomy.
Total hip replacement (THR) or arthroplasty (THA) operations have been performed since the early 1960s to repair the acetabulum and the region surrounding it and to replace the hip components, such as the femoral head, that have degenerated. Currently, approximately 200,000 THR operations are performed annually in the United States alone, of which approximately 40,000 are redo procedures, otherwise known as revisions. The revisions become necessary due to a number of problems that may arise during the lifetime of the implanted components, such as dislocation, component wear and degradation, and loosening of the implant from the bone.
Dislocation of the femoral head from the acetabular component, or cup, is considered one of the most frequent early problems associated with THR, because of the sudden physical, and emotional, hardship brought on by the dislocation. The incidence of dislocation following the primary THR surgery is approximately 2-6% and the percentage is even higher for revisions. While dislocations can result from a variety of causes, such as soft tissue laxity and loosening of the implant, the most common cause is impingement of the femoral neck with either the rim of an acetabular cup implant, or the soft tissue or bone surrounding the implant. Impingement most frequently occurs as a result of the malposition of the acetabular cup component within the pelvis.
Some clinicians and researchers have found incidence of impingement and dislocations can be lessened if the cup is oriented specifically to provide for approximately 15° of anteversion and 45° of abduction; however, this incidence is also related to the surgical approach. For example, McCollum et al. cited a comparison of THAs reported in the orthopaedic literature that revealed a much higher incidence of dislocation in patients who had THAs with a posterolateral approach. McCollum, D. E. and W. J. Gray, “Dislocation after total hip arthroplasty (causes and prevention)”, Clinical Orthopaedics and Related Research, Vol. 261, p.159-170 (1990). McCollum's data showed that when the patient is placed in the lateral position for a posterolateral THA approach, the lumbar lordotic curve is flattened and the pelvis may be flexed as much as 35°. If the cup was oriented at 15-20° of flexion with respect to the longitudinal axis of the body, when the patient stood up and the postoperative lumbar lordosis was regained, the cup could be retroverted as much as 10°-15° resulting in an unstable cup placement. Lewinnek et al. performed a study taking into account the surgical approach utilized and found that the cases falling in the zone of 15°±10° of anteversion and 40°±10° of abduction have an instability rate of 1.5%, compared with a 6% instability rate for the cases falling outside this zone. Lewinnek G. E., et al., “Dislocation after total hip-replacement arthroplasties”, Journal of Bone and Joint Surgery, Vol. 60-A, No.2, p. 217-220 (March 1978). The Lewinnek work essentially verifies that dislocations can be correlated with the extent of malpositioning, as would be expected. The study does not address other variables, such as implant design and the anatomy of the individual, both of which are known to greatly affect the performance of the implant.
The design of the implant significantly affects stability as well. A number of researchers have found that the head-to-neck ratio of the femoral component is the key factor of the implant impingement, see Amstutz H. C., et al., “Range of Motion Studies for Total Hip Replacements”, Clinical Orthopaedics and Related Research Vol. 111, p. 124-130 (September 1975). Krushell et al. additionally found that certain long and extra long neck designs of modular implants can have an adverse effect on the range of motion. Krushell, R. J., Burke D. W., and Harris W. H., “Range of motion in contemporary total hip arthroplasty (the impact of modular head-neck components)”, The Journal of Arthroplasty, Vol. 6, p. 97-101 (February 1991). Krushell et al. also found that an optimally oriented elevated-rim liner in an acetabular cup implant may improve the joint stability with respect to implant impingement. Krushell, R. J., Burke D. W., and Harris W. H., “Elevated-rim acetabular components: Effect on range of motion and stability in total hip arthroplasty”, The Journal of Arthroplasty, Vol. 6 Supplement, p. 1-6, (October 1991). Cobb et al. have shown a statistically significant reduction of dislocations in the case of elevated-rim liners, compared to standard liners. Cobb T. K., Morrey B. F., Ilstrup D. M., “The elevated-rim acetabular liner in total hip arthroplasty: Relationship to postoperative dislocation”, Journal of Bone and Joint Surgery, Vol 78-A, No. 1, p. 80-86, (January 1996). The two-year probability of dislocation was 2.19% for the elevated liner, compared with 3.85% for standard liner. Initial studies by Maxian et al. using a finite element model indicate that the contact stresses and therefore the polyethylene wear are not significantly increased for elevated rim liners; however, points of impingement and subsequent angles of dislocation for different liner designs are different as would be expected. Maxian T. A., et al. “Femoral head containment in total hip arthroplasty: Standard vs. extended lip liners”, 42nd Annual meeting, Orthopaedic Research society, p. 420, Atlanta, Ga. (Feb. 19-22, 1996); and Maxian T. A., et al. “Finite element modeling of dislocation propensity in total hip arthroplasty”, 42nd Annual meeting, Orthopaedic Research society, p. 259-64, Atlanta, Ga. (Feb. 19-22, 1996).
An equally important concern in evaluating the dislocation propensity of an implant are variations in individual anatomies. As a result of anatomical variations, there is no single optimal design and orientation of hip replacement components and surgical procedure to minimize the dislocation propensity of the implant. For example, the pelvis can assume different positions and orientations depending or whether an individual is lying supine (as during a CT-scan or routine X-rays), in the lateral decubitis position (as during surgery) or in critical positions during activities of normal daily living (like bending over to tie shoes or during normal gait). The relative position of the pelvis and leg when defining a “neutral” plane from which the angles of movement, anteversion, abduction, etc., are calculated will significantly influence the measured amount of motion permitted before impingement and dislocation occurs. Therefore, it is necessary to uniquely define both the neutral orientation of the femur relative to the pelvis for relevant positions and activities, and the relations between the femur with respect to the pelvis of the patient during each segment of leg motion.
Currently, most planning for acetabular implant placement and size selection is performed using acetate templates and a single anterior-posterior x-ray of the pelvis. Acetabular templating is most useful for determining the approximate size of the acetabular component; however, it is only of limited utility for positioning of the implant because the x-rays provide only a two dimensional image of the pelvis. Also, the variations in pelvic orientation can not be more fully considered as discussed above.
Intra-operative positioning devices currently used by surgeons attempt to align the acetabular component with respect to the sagittal and coronal planes of the patient. B. F. Morrey, editor, “Reconstructive Surgery of the Joints”, chapter Joint Replacement Arthroplasty, pages 605-608, Churchill Livingston, 1996. These devices assume that the patient's pelvis and trunk are aligned in a known orientation, and do not take into account

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