Volumetric measurement of periprosthetic bone remodeling: prospective 5 years follow-up after cemented total hip arthroplasty

Mid-term study of bone remodeling after femoral cemented stem implantation: comparison between DXA and finite element simulation

This five-year prospective study was designed to investigate periprosthetic bone remodeling associated with two cemented stem models, ABG-II (Stryker) and VerSys (Zimmer), randomly implanted in patients older than 75 years. The sample consisted of 64 cases (32, ABG-II; 32, VerSys). Inclusion criterion was diagnosis of osteoarthritis recommended for cemented total hip arthroplasty. Besides clinical study, Finite Element (FE) simulation was used to analyze biomechanical changes caused by hip arthroplasty. Bone Mineral Density (BMD) measurements showed a progressive increase in bone mass throughout the entire follow-up period for both stems, well correlated with FE results except in Gruen zones 4, 5, 6 for ABG-II and in zones 4, 5 for VerSys, denoting that remodeling in those zones does not depend on mechanical factors but rather on biological or physiological ones.

Direct evidence of "damage accumulation" in cement mantles surrounding femoral hip stems retrieved at autopsy: cement damage correlates with duration of use and BMI

The "damage accumulation" phenomenon has not been quantitatively demonstrated in clinical cement mantles surrounding femoral hip stems. We stained transverse sections of 11 postmortem retrieved femoral hip components fixed with cement using fluorescent dye-penetrant and quantified cement damage, voids, and cement-bone interface gaps in epifluorescence and white light micrographs. Crack density (Cr.Dn), crack length-density (Cr.Ln.Dn), porosity, and cement-bone interface gap fraction (c/b-gap%) were calculated, normalized by mantle area. Multiple regression tests showed that cement damage (Cr.Ln.Dn. & Cr.Dn.) was significantly positively correlated (r(2)=0.98, p<0.001) with "duration of use" and body mass index ("BMI") but not cement mantle "porosity". There were significant interactions: "duration of use"*"BMI" was strongly predictive (p<0.005) of Cr.Dn.; and "duration of use"*"porosity" was predictive (p=0.04) of Cr.Ln.Dn. Stem related cracks accounted for approximately one fifth of Cr.Dn and one third of Cr.Ln.Dn. The mean c/b-gap% was 13.8% but it did not correlate (r(2)=0.01, p=0.8) with duration of use. We concluded that duration-dependent fatigue damage accumulation occurred during in vivo use. BMI strongly influenced cement crack length and the rate of new crack formation over time. Voids did not increase the rate of crack initiation but appeared to have promoted crack growth over time. Although not progressive, substantial bone resorption at the cement-bone interface appeared to be common.

Periprosthetic bone remodeling using a triple-taper polished cemented stem in total hip arthroplasty

The triple-taper cemented femoral stem was developed to promote proximal femoral and calcar loading to minimize periprosthetic bone loss and aseptic loosening. Periprosthetic changes in bone mineral density in Gruen zones 1 to 7 were analyzed in 103 patients over a 2-year period using dual x-ray absorptiometry. There was a statistically significant decrease in bone mineral density in all Gruen zones, but was most marked in zones 1 and 7. Periprosthetic bone density was reduced significantly in the first 3 to 9 months, after which recovery of bone density occurred. Greater calcar bone loss was seen in women, patients with a low preoperative bone density, and patients with poor postoperative mobility. Age at surgery did not effect calcar bone loss.

Femoral head density on CT scans of patients following hip fracture fixation by expandable proximal peg or dynamic screw

Computed tomography (CT) is currently considered to be an accurate method for evaluating bone density. We evaluated the CT measurements of bone density using the Hounsfield units (HUs) in 23 patients who had been operated in the past for an extra-capsular hip fracture. Twelve patients were treated with a dynamic hip screw and 11 with a proximal femoral expandable hip nail. All the CTs had been performed for non-orthopedic purposes. Bone density with a region of interest (ROI) could be assessed for both hips. We compared the bone density between the operated versus the non-operated sides as well as between the two surgical groups. Bone density was higher in the hip peg (the femoral component of the expandable nail) side 262.5 (range, 169-351) HU, compared to the opposite non-operated side and to the hip screw group 194 (range, 99-283) HU. The hip screw side had decreased bone density compared to the opposite non-operated side. We were able to define a density index and a difference index: both were higher in the hip peg group. These findings persisted over time. It would be interesting to speculate that increased bone density around an expandable peg provides better fracture stabilization and probably faster healing than a dynamic hip screw.