Faculty Bibliography

One hundred twenty-three consecutive primary total hip arthroplasties in 107 patients were performed with the insertion of a cemented, all polyethylene, flanged acetabular component. At a minimum of 20 years, 66 patients had died (75 hips) and 8 patients (8 hips) were lost to follow-up evaluation, leaving 40 hips in 33 patients. At a mean of 21.1 years, 2 cups had been revised for aseptic loosening, one well-fixed cup was revised at the time of femoral component revision, and 4 additional cups had definite evidence of radiographic loosening. Survivorship analysis revealed a 77.3% survivorship for the component at 21 years, with revision or definite loosening as an endpoint (95% confidence interval, 67.8%-86.8%).

BACKGROUND: Debonding of the cement from metal implants has been implicated in the loosening of cemented total hip prostheses. Strengthening of the stem-cement interface has been suggested as a way to prevent loosening of the component. Previously, it was reported that preheating the stem to 44 degrees C reduced the porosity of the cement at the stem-cement interface. The purpose of this study was to determine the effect of stem preheating on the characteristics of the stem-cement interface. METHODS: The effects of stem preheating, at temperatures of 37 degrees C, 44 degrees C, and 50 degrees C, on the stem-cement interface were studied in a test model and a preparation that closely simulated the clinical situation. Static interface strength was determined initially and after the stems had been kept in isotonic saline solution at 37 degrees C for two weeks. Fatigue lifetimes were measured, and the nature and extent of porosity at the interface were quantified. RESULTS: Stem preheating had significant effects on the stem-cement interface. Stems preheated to 37 degrees C had greater interface shear strength than stems at room temperature both initially (53% greater strength) and after simulated aging (155% greater strength). Fatigue lifetimes were also improved, and there was a >99% decrease in interface porosity. The setting time of the cement decreased 12%, and the maximum temperature at the cement-bone interface increased 6 degrees C. Similar effects were found after preheating to 44 degrees C and 50 degrees C. CONCLUSIONS: Stem preheating had significant effects on the stem-cement interface, with significant improvements in the shear strength and cement porosity of the interface. Also, polymerization temperatures at the cement-bone interface increased. The possible biological effects of these increased interface temperatures at the cement-bone interface require further study

In October of 1992, Medicare reimbursement decreased by 50% for a second total hip or knee arthroplasty performed as part of a simultaneous bilateral procedure. The Medicare records of 67726 patients who underwent total hip and knee arthroplasty were reviewed using data from the New York State Department of Health in the period from October 1, 1989, to September 30, 1996. Simultaneous bilateral total hip arthroplasties represented 1.8% of the total number of total hip replacements performed in fiscal year 1991 (60 of 3418) compared with 1.7% (77 of 4547) performed in fiscal year 1994 (P=.902). Similarly, the number of simultaneous bilateral total knee arthroplasties did not change significantly, with simultaneous bilateral procedures representing 5.9% of the total number of total knee replacements performed in fiscal year 1991 (214 of 3620) compared with 6.2% (369 of 5,931) performed in fiscal year 1994 (P=.568).

Because of several failures by dissociation of a redesigned bipolar prosthesis, a new, dynamic test was developed. This dynamic cam-out test represents a closer simulation of one possible clinical mechanism of bipolar disassociation. The results of dynamic testing are affected by the bipolar design, particularly the locking mechanism that was the problem with the redesigned prosthesis

Determination of the cause of groin pain after total hip arthroplasty can be difficult. The case of a patient with an unusual cause of groin pain after total hip arthroplasty, iliopsoas tendinitis, is presented. The patient failed nonoperative treatment and underwent surgical release of the iliopsoas tendon with complete resolution of symptoms

Patients at high risk for osteoporosis and its associated morbidity, including postmenopausal women, are being pharmacologically managed to stabilize and improve bone mass. Alendronate sodium (Fosamax) is a commonly used antiresorptive agent effective in osteopenic women for reducing bone resorption, increasing bone density, and decreasing fracture incidence. With the increased incidence of alendronate-treated women who are undergoing hip replacement or fracture repair by prosthesis placement, data are needed to predict how alendronate affects host bone integration with uncemented surfaces. The aim of this study was to determine the effect of alendronate on new bone formation and attachment to implant surfaces in a normal and simulated estrogen-deficient, calcium-deficient canine model, using an implantable bone growth chamber. Alendronate did not affect host bone integration to surfaces commonly used in uncemented total joint arthroplasty, but there were significant differences dependent solely on the type of surface

Polyethylene wear is a major contributor to osteolysis and subsequent aseptic loosening of prosthetic components in total hip arthroplasty. Use of ion implantation as a surface modification to the metallic bearing component of orthopaedic implants may be an effective means of reducing wear debris at the bearing interface. In July 1991, low friction ion treated femoral heads were introduced. This study evaluates the effect of the low friction ion treated femoral head on polyethylene wear. Fifty-five total hip arthroplasties (53 patients) with low friction ion treated femoral heads followed up a minimum of 3 years were matched with 55 total hip arthroplasties (47 patients) without low friction ion treated femoral heads for the same postoperative period. Socket wear was evaluated radiographically. Case matching and strict inclusion criteria were used to control for known factors influencing polyethylene wear. These criteria included: (1) cases matched for gender and age within 2 years; (2) diagnosis limited to osteoarthritis or avascular necrosis of the femoral head only; (3) femoral head diameter limited to 26 or 28 mm only; (4) hydroxyapatite coated femoral stem of the same design and a metal backed socket of the one of two designs with the same polyethylene insert; and (5) minimum followup of 3 years. The linear wear rate of polyethylene was 0.161 +/- 0.095 mm per year in the group without the low friction ion treated heads and 0.116 +/- 0.101 mm per year in the low friction ion treated group. The volumetric wear rates were 74.5 +/- 44.3 mm3 per year for the group without the low friction ion treated heads and 57.8 +/- 51.1 mm3 per year for the low friction ion treated group. Assuming the sensitivity of these measurements can detect these small differences in wear accurately, these results suggest low friction ion treated prosthetic heads are useful in reducing polyethylene wear at 3-year minimum followup.

High rates of aseptic loosening have been reported for microstructured hydroxyapatite-coated acetabular components. A macrostructured component surface (arc-deposition) not only improves resistance to shear forces experienced by the acetabular component and increases initial stability, but also provides channels for bone ingrowth. The purpose of this investigation was to radiographically compare a series of grit-blasted (microstructured) and arc-deposited (macrostructured) hydroxyapatite-coated acetabular components. A minimum 4-year retrospective radiographic analysis of acetabular components was performed on a total of 50 total hip arthroplasties. At 4 years, arc-deposited components were associated with fewer radiolucent lines in all Charnley zones, particularly Charnley zone III. While the 4-year results for arc-deposited hydroxyapatite acetabular components are superior to their microstructured predecessors, long-term results are still unknown