Three dimensional imaging techniques for the reconstruction of a complex hip problem. A case report.

This report illustrates the use of three-dimensional imaging techniques to solve a difficult reconstruction problem of the hip. Custom prosthetic components manufactured by a computer-assisted design process are used in this procedure.

Porous surface replacement of the hip with chamfered-cylinder component.

One hundred porous surface replacements (PSR) were performed in 92 patients (63 men and 29 women) with a mean age of 53 (range 17-76). Follow-up times range from 1 to 4 years, with 48 patients having a follow-up of at least 2 years. Preoperative diagnoses were osteoarthritis (OA) 63, osteonecrosis (ON) 13, dysplasia 9, rheumatoid-ankylosing spondylitis 6, and other 9. Seventeen hips had metal-backed acrylic-fixed THARIES acetabular sockets, nine hips had a porous cobalt chrome hemispheric beaded acetabular component with adjuvant fixation screws and externally protruding screw hubs, and 74 hips had a porous chamfered cylinder-design acetabulum. Pain relief had been immediate and more complete than with acrylic-fixed or biologic-ingrowth stem-type replacement with comparable walking and function improvements. There have been no major systemic complications, sepsis, or loosening. There have been two transient peroneal nerve palsies and three trochanteric fibrous unions. There have been three reoperations, one for subluxation, one for "metalosis" due to mesh pad loosening, and one femoral neck fracture. Examination of one removed femoral surface component which has been histologically sectioned revealed excellent (90%) bone in-growth. Circumferential progressive radiolucencies developed at the bone-cement interface by 1 year in all of the 17 acrylic-fixed acetabular components. Reaming or seating defects were noted in 25% of the ingrowth components on postoperative radiographs. Radiographic analysis of immediate postoperative films of the chamfered cylinder design acetabular components frequently demonstrated bone-component interface radiolucencies which represented component seating defects. These initial interface radiolucencies became progressively more narrow over the first six months postoperatively suggesting "healing" of the reamed bone-component interface with trabecular bone around the chamfered cylinder acetabular components. Partial healing of initial interface voids with residual narrow radiolucencies were typical of the nine hemispheric-design acetabula with adjuvant screws and screw hubs. This new porous surface replacement (PSR) of the hip using porous ingrowth fixation avoids the major disadvantages of acrylic-fixed SR: excessive acetabular reaming and difficulty with acetabular revision. (When conversion to stem-type replacement is necessary the modular polyethylene socket liner can be exchanged.) The PSR has the prospect of enhanced fixation and improved longterm durability.

Porous surface replacement of the hip with chamfer cylinder design.

Fifty-seven porous surface replacements (PSR) were performed in 53 patients (36 men and 17 women) with a mean age of 54 years (range, 19-75 years). Follow-up examination times ranged from one year to 2.5 years with 33 patients having follow-up periods of at least two years. Preoperative diagnoses were osteoarthritis (OA), 37; osteonecrosis (ON), six; dysplasia, nine; rheumatoid ankylosing spondylitis, three; and other, two. Sixteen hips had metal-backed acrylic-fixed THARIES (total hip articular replacement by internal eccentric shells) acetabular sockets, nine hips had a cobalt chrome hemispherical beaded acetabular component with adjuvant screws, and 32 hips had a chamfer-cylinder designed acetabulum. Pain relief has been immediate and more complete than with acrylic-fixed or biologic-in-growth stem-type replacements with comparable walking and function improvements. There have been no major systemic complications, sepsis, or loosening. There have been two transient peroneal nerve palsies and three trochanteric fibrous unions. There has been one subluxation requiring reoperation. Histologic sections of the removed femoral surface component showed excellent (90%) bone ingrowth. Circumferential progressive radiolucencies developed at the bone-cement interface by one year in all of the 16 acrylic-fixed acetabular components. Reaming or seating defects were noted in 25% of the patients on postoperative radiographs. Serial radiographic analyses demonstrate progressive narrowing of all of the chamfered cylinder design and less in hemispherical design with screw fixation. These observations are encouraging and suggest healing of the bone-component interface with bony trabeculae in the porous-coated acetabular design. This new surface replacement (SR) of the hip uses porous-ingrowth fixation to overcome the major disadvantages of acrylic-fixed SR which are as follows: (1) excessive acetabular reaming, (2) poor long-term fixation, and (3) difficulty with acetabular revision.

Bony ingrowth fixation of newly designed acetabular components in a canine model.

Implantation of a newly designed acetabular component with a porous coating has resulted in superior fixation when compared with acrylic cementation in the short term. Experiments in dogs demonstrate rapid ingrowth within the porous layers, resulting in rigid fixation of the acetabular components despite defects in the prepared bony bed. Acute infection prevents bony ingrowth and causes loosening. The absence of any foreign-body response to the titanium fiber mesh components suggests that this is a biocompatible metal. The fixation has been excellent; progressive or delayed loosening is not encountered once successful ingrowth is achieved. Progressive radiolucent zones generally do not appear in the short term but when visible soon after surgery, may consolidate and disappear. Ingrowth fixation of acetabular components appears to offer an attractive alternative to the use of acrylic cement and may even be feasible in patients with periarticular bony abnormalities.