Andrew J. Hamer

BIOMECHANICAL PROPERTIES OF CORTICAL ALLOGRAFT BONE USING A NEW METHOD OF BONE STRENGTH MEASUREMENT: A COMPARISON OF FRESH, FRESH-FROZEN AND IRRADIATED BONE

There have been conflicting reports on the effects of gamma irradiation on the material properties of cortical allograft bone. To investigate changes which result from the method of preparation, test samples must be produced with similar mechanical properties to minimise variations other than those resulting from treatment. We describe a new method for the comparative measurement of bone strength using standard bone samples. We used 233 samples from six cadavers to study the effects of irradiation at a standard dose (28 kGy) alone and combined with deep freezing. We also investigated the effects of varying the dose from 6.8 to 60 kGy (n = 132). None of the treatments had any effect on the elastic behaviour of the samples, but there was a reduction in strength to 64% of control values (p < 0.01) after irradiation with 28 kGy. There was also a dose-dependent reduction in strength and in the ability of the samples to absorb work before failure. We suggest that irradiation may cause an alteration in the bone matrix of allograft bone, but provided it is used in situations in which loading is within its elastic region, then failure should not occur.

Effect of pamidronate in preventing local bone loss after total hip arthroplasty: a randomized, double-blind, controlled trial.

Acute periprosthetic bone loss occurs after total hip arthroplasty. Bone loss undermines the support of the implant and may contribute to prosthetic failure. At present, there is no established prophylaxis for this process. We studied the effect of a single‐dose infusion of 90 mg of pamidronate on early periprosthetic bone mineral density (BMD), biochemical markers of bone turnover, radiological, and clinical outcome in a 26‐week, prospective, randomized, double‐blinded study of 47 men and women undergoing total hip arthroplasty. Pamidronate therapy led to a significant reduction in bone loss compared with placebo for both the proximal femur and the pelvis (repeated measures analysis of variance [ANOVA]); p = 0.001 and p = 0.01, respectively). Pamidronate therapy was associated with suppression of all biochemical markers of bone turnover compared with placebo (repeated measures ANOVA; p < 0.05 for all comparisons), with the exception of urinary free deoxypyridinoline. Pamidronate did not interfere with the clinical improvement in symptoms after total hip arthroplasty, or radiological outcome, and was not associated with an increase in adverse events. This study provides clinical data on the efficacy and safety of bisphosphonates for the prevention of bone loss after total hip arthroplasty and supports the establishment of larger‐scale clinical trials to determine the long‐term clinical efficacy of this intervention using implant failure as the primary endpoint.

Changes in allograft bone irradiated at different temperatures

Secondary sterilisation of allograft bone by gamma irradiation is common, but the conditions under which it is performed vary between tissue banks. Some do so at room temperature, others while the bone is frozen. Bone is made brittle by irradiation because of the destruction of collagen alpha chains, probably mediated by free radicals generated from water molecules. Freezing reduces the mobility of water molecules and may therefore decrease the production of free radicals. We found that bone irradiated at -78 degrees C was less brittle and had less collagen damage than when irradiated at room temperature. These findings may have implications for bone-banking.

Bone mineral density and biochemical markers of bone turnover in aseptic loosening after total hip arthroplasty.

The aims of this study were to determine whether subjects with aseptic loosening after total hip arthroplasty (THA) have regional differences in periprosthetic bone mineral density (BMD) and systemic biochemical markers of bone turnover compared to subjects with successful implants.

Variation in the TNF Gene Promoter and Risk of Osteolysis After Total Hip Arthroplasty

Genetic factors may influence implant failure caused by osteolysis after THA. In an association study of 481 subjects after THA, we found that carriage of the TNF‐238A allele was associated with an increased incidence of osteolysis versus noncarriage (odds ratio, 1.7) and was independent of other risk factors. Genetic and environmental factors influence implant survival after THA.

Intraoperative red blood-cell salvage in revision hip surgery. A case-matched study.

BACKGROUND Revision hip arthroplasty is commonly associated with substantial blood loss and the subsequent need for transfusion. This leads to an increased risk of blood-borne infection and hemolytic reactions. The purpose of this study was to demonstrate whether the use of intraoperative red blood-cell salvage in revision hip arthroplasty reduces the overall rate of allogeneic transfusion. METHODS Forty-seven patients who had undergone revision hip arthroplasty with the use of intraoperative cell salvage were identified. A computer database was used to individually match these patients, for age, sex, and eleven operative variables, to control patients who had undergone revision hip arthroplasty in the same unit without intraoperative cell salvage. Data gathered included the total allogeneic transfusion requirement for each patient, preoperative and postoperative hemoglobin levels, and operative time. RESULTS The total allogeneic transfusion requirement was significantly lower in the group that had intraoperative cell salvage than in the control group (median, 2 compared with 6 U of packed red blood cells, p = 0.0006), with a median reduction in allogeneic transfusion of 4 U. There was no significant difference in preoperative or postoperative hemoglobin levels between the groups. CONCLUSIONS The use of intraoperative cell salvage significantly lowered the allogeneic transfusion requirement, which can lead to substantial cost savings. To our knowledge, this is the first study in which the use of intraoperative red blood-cell salvage in revision hip arthroplasty was evaluated by matching patients on the basis of age, sex, and operative variables.

Irradiated allograft bone for acetabular revision surgery: RESULTS AT A MEAN OF FIVE YEARS

We report the results of the revision of 123 acetabular components for aseptic loosening treated by impaction bone grafting using frozen, morsellised, irradiated femoral heads and cemented sockets. This is the first large series using this technique to be reported. A survivorship of 88% with revision as the end-point after a mean of five years is comparable with that of other series.

Biochemical markers of bone turnover and development of heterotopic ossification after total hip arthroplasty

We studied biochemical markers of bone turnover markers in 20 men and women over 26 weeks after total hip arthroplasty (THA) in order to characterize the changes in bone metabolism associated with developing heterotopic ossification (HO). Transient increases in biochemical markers of both osteoclast and osteoblast activity occurred after surgery. Subjects developing HO (n = 9) had greater rises in the osteoclast marker C‐telopeptide of type‐I collagen (CTX‐I; ANOVA P = 0.004), and the osteoblast markers N‐terminal propeptide of type‐I procollagen (PINP; ANOVA P − 0.01) and osteocalcin (OC; ANOVA P − 0.02) than those who did not develop HO. A rise of > 42% in CTX‐I at one week after surgery had a sensitivity of 89% and a specificity of 82% for predicting HO development at week 26 (P < 0.05). Rises of > 57% in PINP and > 13% in OC at week 6 had sensitivities of 89% and 56%, and specificities of 82% and 91%, respectively for development of HO. Transient increases in osteoblast and osteoclast activity occur after THA. These changes are greater in patients developing HO than in those who do not develop HO. The potential applications of these markers are as a non‐invasive, radiation‐free tool for investigating the pathogenesis of HO, and as an early surrogate outcome marker for HO development in clinical trials of novel prophylaxis regimes for its prevention.

BIOMECHANICAL PROPERTIES OF CORTICAL ALLOGRAFT BONE USING A NEW METHOD OF BONE STRENGTH MEASUREMENT

There have been conflicting reports on the effects of gamma irradiation on the material properties of cortical allograft bone. To investigate changes which result from the method of preparation, test samples must be produced with similar mechanical properties to minimise variations other than those resulting from treatment. We describe a new method for the comparative measurement of bone strength using standard bone samples. We used 233 samples from six cadavers to study the effects of irradiation at a standard dose (28 kGy) alone and combined with deep freezing. We also investigated the effects of varying the dose from 6.8 to 60 kGy (n = 132). None of the treatments had any effect on the elastic behaviour of the samples, but there was a reduction in strength to 64% of control values (p < 0.01) after irradiation with 28 kGy. There was also a dose-dependent reduction in strength and in the ability of the samples to absorb work before failure We suggest that irradiation may cause an alteration in the bone matrix of allograft bone, but provided it is used in situations in which loading is within its elastic region, then failure should not occur.

Long-term outcome of a cementless, hemispherical, press-fit acetabular component: SURVIVORSHIP ANALYSIS AND DOSE-RESPONSE RELATIONSHIP TO LINEAR POLYETHYLENE WEAR

Between 1988 and 1998 we implanted 318 total hip replacements (THRs) in 287 patients using the Plasmacup (B. Braun Ltd, Sheffield, United Kingdom) and a conventional metal-on-polyethylene articulation. The main indications for THR were primary or secondary osteoarthritis. At follow-up after a mean 11.6 years (7.6 to 18.4) 17 patients had died and 20 could not be traced leaving a final series of 280 THRs in 250 patients. There were 62 revisions (22.1%) in 59 patients. A total of 43 acetabular shells (15.4%) had been revised and 13 (4.6%) had undergone exchange of the liner. The most frequent indications for revision were osteolysis and aseptic loosening, followed by polyethylene wear. The mean Kaplan-Meier survival of the Plasmacup was 91% at ten years and 58% at 14 years. Osteolysis was found around 36 (17.1%) of the 211 surviving shells. The median annual rate of linear wear in the surviving shells was 0.12 mm/year and 0.25 mm/year in those which had been revised (p < 0.001). Polyethylene wear was a strong independent risk factor for osteolysis and aseptic loosening. The percentage of patients with osteolysis increased proportionately with each quintile of wear-rate. There is a high late rate of failure of the Plasmacup. Patients with the combination of this prosthesis and bearing should be closely monitored after ten years.