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Irrigating allograft bone with saline reduces infection risk
Warming saline irrigation fluid to 60�C can help melt fatty marrow and provide a more rapid cleansing of allograft bone.
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Thoroughly washing nonirradiated allograft bone before implantation can effectively reduce bacterial infection risk while maintaining allograft structural integrity, according to a study by British researchers.
Previous studies have shown mechanical methods that remove blood and marrow content from bone also reduce bacterial contamination. Removing fat and marrow content also produces a stronger and more compacted graft with better shear resistance. However, the risk of possible graft contamination during processing at a bone bank makes it necessary to irradiate tissue secondarily. This, either alone or in combination with freeze-drying, affects the structural integrity of the bone, although the clinical relevance of the effect has not been proven, according to the study.
“We believe that thorough washing of the bone immediately before implantation reduces the risk of bacterial cross-contamination and avoids the need for irradiation,� the authors said in the study.
To test this, Richard A. Power, FRCSEd(Orth), and colleagues at the Glenfield Hospital in Leicester, England, retrospectively evaluated the infection rate among 138 patients (144 procedures) who received nonirradiated impaction bone grafts during revision hip arthroplasty.
The study included 62 men and 76 women with a mean age of 67 years. Surgeons grafted the acetabulum alone in 99 cases, the femur alone in 23 cases and both the acetabulum and femur in 22 cases.
All patients received prophylactic antibiotics before surgery and another two doses postoperatively. Patients also had an average of four years’ follow-up, with one-year minimum.
Surgeons implanted a mean of 1.7 femoral heads during surgery, ranging from one to eight. They also actively looked for signs of infection during follow-up.
Postoperatively, four patients (2.9%) developed superficial wound infections, all of which were successfully treated.
Of 124 available culture swabs taken from grafts before cleansing, 17 (14%) tested positive for microbial contamination. However, no patients implanted with grafts that yielded positive swab cultures developed a deep infection, the authors noted.
Only one patient (0.7%) developed a deep infection with methicillin-resistant Staphylococcus aureus, they said. The source of the infection, though unclear, was likely hospital-acquired, they noted.
Bone graft preparation
In preparing for implantation, OR staff first thawed the bone grafts at room temperature for one hour. Surgeons then milled the femoral heads to remove any remaining soft tissue and sclerotic subchondral bone. They then used a pneumatic mill (Leer Mill, DePuy Ltd.) to create 2 to 5 mm bone chips.
The surgeons next placed the bone chips in a standard metal sieve and irrigated them using normal saline solution (without antibiotics) pulsed at 7 bar pressure, according to the study.
In most cases surgeons used saline solution at normal room temperature. Later, they began warming the solution to 60°C, which helped to melt fatty marrow and provide a more rapid cleansing, the authors noted.
The Leicester Bone Bank supplied the morcellised femoral head bones used in all procedures. This bone bank follows British Association of Tissue Banking guidelines for storage and irradiates any graft material it believes to be contaminated based on microbiological cultures. However, no femoral heads used in the study had positive cultures and thus were not irradiated prior to use, according to the study.
For more information:
- Kwong FNK, Ibrahim T, Power RA. Incidence of infection with the use of non-irradiated morcellised allograft bone washed at the time of revision arthroplasty of the hip. J Bone Joint Surg Br. 2005;87-B:1524-1526.