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Porous surface replacement of the hip with chamfer cylinder design
Abstract:
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.