Ian Stockley

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.

Reconstruction of massive bone defects with allograft in revision total knee arthroplasty

Allograft bone was used to reconstruct a defect in the proximal aspect of the tibia or the distal aspect of the femur, or both, in thirty knees of twenty-eight patients who had a revision total knee arthroplasty. The average age of the patients at the time of the index procedure was 65.8 years (range, twenty-four to eighty-nine years). At an average of fifty months (range, twenty-four to 132 months; median, thirty-six months) postoperatively, the score for twenty-three knees (twenty-one patients) had increased by at least 20 points, and these knees did not need additional operative treatment. Thus, the rate of success was 77 per cent. The procedure was considered a failure for the remaining seven knees because of infection (three), loosening of the tibial component (two), fracture of the graft (one), and non-union at the allograft-host junction (one). Properly applied allograft can be used to reconstruct massive bone defects, provide stability and support for implants, and restore bone stock in the event that additional operative treatment is necessary.

Fractures of the distal radius. Intermediate and end results in relation to radiologic parameters

The purpose of this study was to quantify the functional impairment following distal radial fractures and to identify the factors affecting prognosis. One hundred fifteen patients were assessed six months and two years following initial injury. On final assessment, subjectively, 56% had good, 39% had fair, and 5% had poor results. Median grip strength improved from 51% to 78%, range of movement from 87% to 94%, and wrist torque from 93% to 100%. Redisplacement occurred in 59%; only 33% clinically and 19% radiologically had perfect cosmetic results. Radial malunion was important functionally. Only when the dorsal angle exceeded 20° or the radial angle fell below 10° with a 30° mean was there reduction in grip strength (p = 0.05). Comminution and intraarticular involvement predisposed to a median loss of movement of 15% and 11%, respectively (p = <0.05). Patients requiring physiotherapy formed a poor prognostic group. A combination of factors is responsible for poor results. Attention should be directed toward early and adequate rehabilitation of the injured hand and wrist.

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.

Is there a role for extended antibiotic therapy in a two-stage revision of the infected knee arthroplasty?

All major studies have incorporated the use of prolonged courses of parenteral or oral antibiotic therapy in the management of two-stage revision of an infected total knee arthroplasty. We present a series of 59 consecutive patients, all with microbiologically-proven deep infection of a total knee arthroplasty, in whom a prolonged course of antibiotic therapy was not routinely used. The mean follow-up was 56.4 months (24 to 114). Of the 38 patients who underwent a staged exchange, infection was successfully eradicated in 34 (89%) but recurrent or persistent infection was present in four (11%). Our rate of cure for infection is similar to that reported elsewhere. We conclude that a prolonged course of antibiotic therapy seems not to alter the incidence of recurrent or persistent infection. The costs of the administration of antibiotics are high and such a regime may be unnecessary.

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.

Simultaneous or staged bilateral total knee replacements in rheumatoid arthritis. A prospective study

In a prospective study of 100 knee arthroplasties in patients with rheumatoid arthritis, simultaneous bilateral surgery was compared with staged bilateral replacements. All patients had improved function following their operations but those who had staged surgery only achieved maximum benefit after the second knee had been replaced. The complication rate was no greater for simultaneous surgery and we therefore advocate the method for those patients who require bilateral replacements.

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.