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. 2010 Aug;81(4):427-35.
doi: 10.3109/17453674.2010.501748.

Uncemented custom femoral components in hip arthroplasty. A prospective clinical study of 191 hips followed for at least 7 years

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Uncemented custom femoral components in hip arthroplasty. A prospective clinical study of 191 hips followed for at least 7 years

Pål Benum et al. Acta Orthop. 2010 Aug.

Abstract

Background and purpose: We have developed an individually designed, uncemented femoral component for achievement of improved strain distribution and fixation to the bone, to make uncemented stems more applicable in femurs of abnormal size and shape, and to improve the joint mechanics. Here we describe the design of the implant and present the results of a prospective clinical study with at least 7 years of follow-up.

Patients and methods: The prostheses are produced by CAD-CAM technique. The design of the stem is based on CT information, and the neck design is based on the surgeon's planning of the center of rotation, femoral head offset, and leg length correction. The first-generation stem produced before 2001 had a proximal HA coating and a sand-blasted distal part that was down-scaled to avoid contact with compact bone. The second-generation stem had a porous coating beneath the HA layer and the distal part of the stem was polished. The implant was used in 762 hips (614 patients) from 1995 until 2009. 191 of these hips were followed for 7 years and 83 others were followed for 10 years, and these hips are included in the present study. Mean age at surgery was 48 (20-65) years. Congenital dysplasia of the hip was the reason for osteoarthritis in 46% and 57% of the hips in respective groups. Merle d'Aubigné score was recorded in 152 and 75 hips in the two groups. Prostheses followed for 10 years, and almost all in the 7-year group, were first-generation stems.

Results: The 7- and 10-year cumulative revision rates were 1.1% and 2.4%, respectively, with stem revision for any reason as endpoint. The clinical results were similar at 7 and 10 years, with Merle d'Aubigné scores of 17. Intraoperative trochanteric fissures occurred in 2 of the 191 operations (1.0%); both healed after wiring. In hips followed for 7 years, 2 periprosthetic fractures occurred; exchange of the stem was necessary in both. One additional fracture occurred between 7 and 10 years, and it was treated successfully with osteosynthesis. The rate of dislocation was 1.6% and 2.4%, respectively. There was no radiographic loosening at follow-up.

Interpretation: Use of a custom femoral stem gives a reliable fixation and promising medium-term clinical results in femurs of normal and abnormal shape and dimension. The individual design, which enables optimized joint mechanics, gives a low risk of mechanical complications.

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Figures

Figure 1.
Figure 1.
A. CT scans of the proximal femur, with 5-mm distance between each section. B. Digital template of the suggested stem design. C. Use of the template for determination of ideal medial femoral head offset and leg length. Information about medial femoral offset and leg length correction is automatically shown during use of the template. (The arrows show the text box where this information is given).
Figure 2.
Figure 2.
A. Adjustable resection guide. B. The prosthesis produced after the planning shown in Figure 1 has been inserted into the right femur. A custom prosthesis has also been implanted into the left femur.
Figure 3.
Figure 3.
A. Scanogram of the right femur in a case of femoral head necrosis with high dislocation of the hip. B. Radiograph after subtrochanteric resection osteotomy and insertion of the custom stem. The osteotomy has healed.
Figure 4.
Figure 4.
A. Bilateral hip dysplasia with valgus deformities after earlier subtrochanteric osteotomies. B. Radiograph after insertion of custom femoral stems bilaterally.
Figure 5.
Figure 5.
Preoperative (A) and postoperative (B) images in a case of bilateral CDH with osteoarthritis. Note that adequate medial femoral offset has been obtained despite the extremely narrow intramedullary cavities.
Figure 6.
Figure 6.
Preoperative (A) and postoperative (B) images of a case of dwarfism treated with custom stems. On the left side, an intraoperative fissure was treated with wires.

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