Correlation of Technetium-99m scintigraphy, progressive acetabular osteolysis and acetabular component loosening in total hip arthroplasty.

In total hip arthroplasty (THA) Technetium scintigraphy can help to diagnose a loose implant by detecting elevated osteoblastic activity. It has been used for timing the revision of cemented implants. In uncemented cups progressive radiological acetabular osteolysis can be present before loosening accurs, but it is probably unwise to await cup loosening before embarking on revision. We explored the possible relationship between such osteolysis and positive findings on technetium scintigraphy, to see if the technique could predict the need for revision. Between 1990 and 1996 500 hydroxyapatite-coated hip prostheses were implanted (follow-up range: 9-15 years), and technetium scintigraphy and plain radiography were performed annually postoperatively. 32 cups were revised for progressive acetabular osteolysis. We compared the introperative findings at revision with the pre-operative scintigraphic and radiographic results. The sensitivity and specificity for diagnosing progressive acetabular osteolysis by technetium scintigraphy were 34% and 0% respectively. The sensitivity and specificity of the technique for detecting loosening were 38% and 73% respectively. The sensitivity and specificity of technetium scintigraphy for detection of a either loosening or progressive acetabular osteolysis are worse than reported for plain radiography. Despite negative scintigraphy, there may be progressive bone loss at a critical level. Scintigraphy has no additional value to plain radiography as a reliable indicator for timing cup revision in the process of progressive acetabular osteolysis.

Cross-linked compared with historical polyethylene in THA: an 8-year clinical study.

UNLABELLED: Wear particle-induced osteolysis is a major cause of aseptic loosening in THA. Increasing wear resistance of polyethylene (PE) occurs by increasing the cross-link density and early reports document low wear rates with such implants. To confirm longer-term reductions in wear we compared cross-linked polyethylene (irradiation in nitrogen, annealing) with historical polyethylene (irradiation in air) in a prospective, randomized clinical study involving 48 patients who underwent THAs with a minimum followup of 7 years (mean, 8 years; range, 7-9 years). The insert material was the only variable. The Harris hip score, radiographic signs of osteolysis, and polyethylene wear were recorded annually. Twenty-three historical and 17 moderately cross-linked polyethylene inserts were analyzed (five patients died, three were lost to followup). At 8 years, the wear rate was lower for cross-linked polyethylene (0.088 +/- 0.03 mm/year) than for the historical polyethylene (0.142 +/- 0.07 mm/year). This reduction (38%) did not diminish with time (33% at 5 years). Acetabular cyst formation was less frequent (39% versus 12%), affected fewer DeLee and Charnley zones (17% versus 4%), and was less severe for the cross-linked polyethylene. The only revision was for an aseptically loose cup in the historical polyethylene group. Moderately cross-linked polyethylene maintained its wear advantage with time and produced less osteolysis, showing no signs of aging at mid-term followup. LEVEL OF EVIDENCE: Level I, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Bone remodeling and hydroxyapatite resorption in coated primary hip prostheses.

Hydroxyapatite coatings for THA promote bone ongrowth, but bone and coating are exposed to stress shielding-driven osteoclastic resorption. We asked: (1) if the resorption of hydroxyapatite coating and bone ongrowth correlated with demographics; (2) if the resorption related to the stem level; and (3) what happens to the implant-bone interface when all hydroxyapatite coating is resorbed? We recovered 13 femoral components from cadaveric specimens 3.3 to 11.2 years after uneventful primary THA. Three cross sections (proximal, medial, distal) of the hydroxyapatite-coated proximal implant sleeve were analyzed by measuring the percentage of residual hydroxyapatite and bone ongrowth on the implant perimeter. Hydroxyapatite resorption was independent of patient age but increased with time in vivo and mostly was gone after 8 years. Bone ongrowth was independent of time in vivo but decreased with aging patients. Only in the most proximal section did less residual hydroxyapatite correlate with less bone ongrowth. Hydroxyapatite resorption, which was more proximal than distal, showed no adverse effects on the implant-bone interface.

Preoperative bone quality as a factor in dual-energy X-ray absorptiometry analysis comparing bone remodelling between two implant types.

Recently it was shown that the design changes from the ABG-I to ABG-II hip stem resulted in a better, although not significant, proximal bone preservation. Our hypothesis was that by matching patients for preoperative bone quality, statistical power would increase and that the trend of better proximal bone preservation in ABG-II might become significant. Twenty-four ABG-II patients were compared to two different ABG-I groups: (1) 25 patients from our earlier prospective study and (2) a group of 24 patients selected to perfectly match the ABG-II group regarding gender, age and preoperative bone quality. Postoperative changes in periprosthetic bone mineral density (BMD) were quantified at 2 years postoperatively using DEXA scanning. Bone preservation (less BMD loss) was better for the ABG-II than the ABG-I (all two groups) in the proximal zones 1 and 7. In Gruen zone 7, a statistically significant difference was found for group B (p = 0.03). By matching patients for preoperative bone quality and gender, a statistical significant difference was found in proximal bone preservation in favour of ABG-II. In future comparative bone remodelling studies using DEXA, patients should be matched for preoperative bone quality and gender.

Cementless hemispheric hydroxyapatite-coated sockets for acetabular revision.

This study describes our experience with a hydroxyapatite-coated uncemented hemispherical component used for revision of 72 patients with aseptic loosening of the acetabular component. Preoperative Paprosky classification of the acetabular defects was 1 type I, 35 type II, and 36 type III; according to American Academy of Orthopaedic Surgeons, 14 segmental, 10 cavitary, and 48 combined. The mean follow-up was 7.6 years (range, 5.0-13.0). Complications were seen in 7 cases (9.6%). Seventy acetabular components (97.2%) showed bone ongrowth on the radiographs. The survival rate was 90.8% after a mean follow-up of 7.6 years (range, 5.0-13.0) when revision for any reason is the end point (confidence interval, 80.5%-100%) and 98.1% (confidence interval, 94.5%-100%) when aseptic loosening of the cup is the end point. We conclude that hydroxyapatite-coated cups for acetabular revision show promising results.

Crosslinked polyethylene compared to conventional polyethylene in total hip replacement: pre-clinical evaluation, in-vitro testing and prospective clinical follow-up study.

BACKGROUND: Polyethylene wear-induced osteolysis is a major cause of implant loosening in total hip arthroplasty. New crosslinked polyethylenes are presumed to give lower wear rates, but no long-term clinical results are available yet. PATIENTS AND METHODS: We compared basic material characteristics and MTS hip joint simulator wear rates of a crosslinked polyethylene (Duration) to those of conventional polyethylene. In a randomized double-blind 5-year clinical follow-up study, 133 hips (67 conventional, 66 Duration) in 127 patients were followed-up for an average of 5 (3-6) years. Wear rates were measured using a computer-based edge detection method. The radiographic appearances of wear-related phenomena were recorded. RESULTS: The Duration polyethylene showed a significantly lower in-vitro wear rate in the simulator study (mean 22 (SD 2.3) vs. 40 (SD 1.5) mm3/106 cycles). Also, the in-vivo wear was lower for Duration (mean 0.083 (SD 0.056) mm/year) than for conventional polyethylene (mean 0.123 (SD 0.082) mm/year). All radiographic signs of osteolysis were less frequent in the Duration group. INTERPRETATION: Our study has given a substantial body of evidence--from lower wear rates, less frequent signs of osteolysis, and higher survival rates after a mean follow-up of 5 years--that Duration provides better clinical outcomes than conventional polyethylene.

Seven to 10 years followup of an anatomic hip prosthesis: an international study.

Hypothetically, hydroxyapatite-coated anatomic-shaped femoral stems and hemispheric acetabular cups should improve biologic fixation of the implant and strength transmission to the bone, improving unsatisfactory results of the first cementless hip prosthesis focused on the stress-shielding phenomenon at the femur and failure of the threaded acetabular cups. A consecutive series of 312 patients who had primary Anatomique Benoist Giraud hip prostheses unilaterally implanted were followed up. We analyzed the clinical and radiographic results and report the outcomes 7-10 years after implantation. Two hundred thirty-two patients were assessed at 7-10 years. The survival rate for the implant was 96.8%; 77.2% of patients had no pain, 72.4% maintained total mobility, and 62.9% were able to walk without restrictions. However, radiologic assessment shows that problems improved but did not disappear. More than 55% of femurs had signs of proximal stress-shielding develop. More important, substantial polyethylene wear was observed in at least 62% of the acetabular inserts at 7-10 years followup.

High survival rate of hydroxyapatite-coated hip prostheses: 100 consecutive hips followed for 10 years.

We followed 100 consecutive primary total hip replacements with a proximal hydroxyapatite coating for 10 years. No patient was lost to follow-up. 29 patients (32 hips) died before the 10-year follow-up was done; none of their hips had been revised. Thigh pain on activity occurred in 3 hips. We found no radiographic signs of loosening of the femoral components. In course of time the location of dense bone around the femoral stem, which would suggest implant/bone stress transfer, moved distally in 51 of 67 stems after 10 years. No linear or distal osteolysis occurred around the stem. Revision of 1 stem was performed because of thigh pain, but it was found fixed to bone proximally, while 3 cups were revised because of acetabular osteolysis. The 10-year survival of the stem and cup, using revision or pending revision as endpoint, was 100% (95% CI: 99-100) and 97% (95% CI: 94-99), respectively.