Reginald A. Elson

Deep infection of cemented total hip arthroplasties caused by coagulase-negative staphylococci

We reviewed a series of 91 patients with deep infection of a cemented total hip arthroplasty caused by coagulase-negative staphylococci (C-NS). Of these, 72 were treated by one-stage exchange arthroplasty with a failure rate of 13% due to recurrence of infection. The other 19 patients have started or completed treatment by a two-stage exchange without failure to date. In 27 of the 91 patients multiple strains of C-NS were discovered, many being resistant to previously used antibiotics. The use of gentamicin-containing cement in the primary arthroplasty was significantly associated with the emergence of gentamicin-resistant C-NS in subsequent deep infection. Bacteriological diagnosis of such infections must take into consideration the possibility that multiple strains of the organism are involved.

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.

Measuring bone mineral density of the pelvis and proximal femur after total hip arthroplasty

We aimed to evaluate the precision and longitudinal sensitivity of measurement of bone mineral density (BMD) in the pelvis and to determine the effect of bone cement on the measurement of BMD in femoral regions of interest (ROI) after total hip arthroplasty (THA). A series of 29 patients had duplicate dual-energy x-ray absorptiometry (DXA) scans of the hip within 13 months of THA. Pelvic analyses using 3- and 4-ROI models gave a coefficient of variation (CV) of 2.5% to 3.6% and of 2.5% to 4.8%, respectively. Repeat scans in 17 subjects one year later showed a significant change in BMD in three regions using the 4-ROI model, compared with change in only one region with the 3-ROI model (p < 0.05). Manual exclusion of cement from femoral ROIs increased the net CV from 1.6% to 3.6% (p = 0.001), and decreased the measured BMD by 20% (t = 12.1, p < 0.001). Studies of two cement phantoms in vitro showed a small downward drift in bone cement BMD giving a measurement error of less than 0.03 g/cm2/year associated with inclusion of cement in femoral ROIs. Changes in pelvic periprosthetic BMD are best detected using a 4-ROI model. Analysis of femoral ROI is more precise without exclusion of cement although an awareness of its effect on the measurement of the BMD is needed.

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.

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.

Mechanics of Acetabular Fractures

Fractures of the acetabulum occur as a result of force acting between this part and the head of the femur, the last link of a chain of transmission from the greater trochanter, the knee or the foot. Alternatively, a blow on the back of the pelvis can have the same effect.

Early Complications of Operative Treatment Within Three Weeks of Injury

Four of the 569 patients with fractures of the acetabulum operated upon within 21 days after the accident developed pseudarthroses (0.7%). These occurred in two both-column fractures and in two associated transverse and posterior wall fractures. All four cases had a slightly imperfect reduction.

A Comparison of the Performance of Irradiated and Non-Irradiated Bone Graft in Hip Surgery

A retrospective review of notes and radiographs to assess the clinical outcome for two groups of patients undergoing acetabular revision with impacted morsellised allograft bone, was carried out. One group received fresh frozen allograft bone (20 patients, 22 joints), and the other fresh frozen irradiated allograft bone (18 patients, 20 joints). The extent and type of graft used was recorded. Graft performance was assessed radiologically by observing evidence of collapse, incorporation, lucent lines at the site of grafting and component migration. This assessment was repeated by an independent observer. The average follow-up was thirty months for the non-irradiated grafts and fifteen months for the irradiated grafts at the time of this review. The average time taken for the grafts to show signs of incorporation was seven months for non-irradiated grafts and six months for irradiated grafts. The average time for the grafts to show physiological remodelling was similar between groups at sixteen and thirteen months respectively. There was one case of infection after a direct cup exchange with irradiated bone graft. This analysis demonstrated no obvious difference in the clinical performance of irradiated and non-irradiated morsellised bone grafts.

Radiology of the Normal Acetabulum

Since the first edition of this book, the use of CT scanning has become widespread and is now almost routine. At present only a few centres have access to 3-D CT reconstruction; when this is available everywhere, the understanding of acetabular fractures will be much easier. With good 3-D analysis, one just needs to know the classification to be able to link the case being treated to one of the fracture types described. It made us very happy to see that the 3-D images fully confirm the descriptions we gave of the different types of acetabular fracture.