Percutaneous Antibiotic Delivery Technique (PAD-T)
The PAD-T is indicated for osteomyelitis involving the Cierny Mader anatomical classification types I, II, and III. Classification type IV can be treated on a case-by-case basis. The PAD-T may be beneficial in type IV osteomyelitis when there is not significant loss of bone integrity. Spongiosa cavity defects up to a two to three cubic centimeters can be filled with the PAD-T and larger defects may have to be addressed through an open technique with possible external fixation. In regards to infected bone voids larger than three cubic centimeters, bone grafting is required once the bone infection is resolved otherwise a sterile cavity remains, which may be acceptable as well. Approximately two to three weeks after delivery of the BVF with antibiotics, there is no organized presence of the bone void filler in that cavity. This occurs because when you add the antibiotic, the antibiotic disrupts the ability of the bone void filler to set properly and maintain its structural integrity and thus the BVF quickly reabsorbs.
A thorough familiarization of the three-dimensional anatomy of the area of osteomyelitis is paramount to successful percutaneous antibiotic delivery. The set up for this procedure is fairly simple and is illustrated in the tab labeled "Instrumentation layout for the PAD-T" to the left. A tourniquet should be utilized to minimize medullary bleeding. Only utilize antibiotics in powder form. Using antibiotics in liquid form will over dilute the bone void filler and render the mixture difficult to handle and there may be excessive leakage of the BVF. Unless pre-operative culture results are available or drug allergies contradict their use, the antibiotics used are vancomycin and tobramycin. If a substitution for tobramycin is needed ceftazipime 1 gram can be used.
A simple percutaneous skin incision is completed near to the area of osteomyelitis. An exception is with metatarsal and phalangeal bone. In this case, a small incision to the effected bones is made to visualize the bone cortex. This allows an easier bone cortex incision on a small bone. Also, when the metatarsal and phalanx are involved around a joint, the incisional approach allows you to visualize the integrity of the joint and bone to see if bone resection is needed instead. The bone cortex incision is made with a steinmann pin as close in diameter to the kyphon needle as possible to allow a snug purchase of the kyphon needle to the bone cortex to minimize BVF leakage. This tight purchase between the bone and the kyphon needle cannot be over emphasized. If a bone cortex incision is made that the kyphon needle is loose at the bone, the BVF will leak out at the bone cortex incision and not travel into the bone. The steinmann pin is then advanced to the far bone cortex without far bone cortex violation. Usually a single plane pass of the steinmann is sufficient. Multiple passes of the steinmann pin in long bones can unnecessary increase the risk of stress risers and should be avoided. After the bone cortex incision is completed, bone irrigation and biopsies for culture can be completed with a curved curette. For all lower leg, tarsal, and lesser tarsal bones use a number three kyphon needle. For the smaller bones, i.e. phalanxes and metatarsals, a number two kyphon needle is used.
1.2 grams of tobramycin and 1 gram of vancomycin are placed in basin. A 10 cc kit of the BVF is added to the antibiotics in the basin and mixed, then placed into a 20 cc syringe. This loaded syringe is then connected to the kyphon needle. Under intra-operative fluoroscopy the kyphon needle is then advanced through the bone cortex incision into the spongiosa bone. The kyphon needle is then slowly withdrawn under intra-operative fluoroscopy while delivering the BVF and antibiotics. Under intra-operative fluoroscopy there should be a nice filling effect seen as the BVF and antibiotics fill the infected bone. Stop injecting when the bone defect is filled. This can be identified when you meet resistance in placing the product into the bone, i.e. there is product ooze through the bone cortex incision, small cortical defects, or some product is seen in the soft tissue or vasculature on intra-operative fluoroscopy. Stop when you visualize any product in the vasculature. You do not need to place a lot of BVF to be successful, especially in small bones. In a smaller void or small bone, only 1-2 cc's of product is needed. In the situation where a two-plane delivery is planned, after the first pass of the BVF with antibiotics the percutaneous soft tissue incision should be closed before the second pass is initiated. This is done so there is no leakage out of the first cortex bone incision from the second pass. Even though the delivery BVF is not cytotoxic in vitro to fibroblast, a large amount of BVF into soft tissues may cause an immune reaction, compartment syndrome, or excessive leakage through the incision or ulcer.