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Core decompression is a common treatment for early stage osteonecrosis of the femoral head due to the simplicity of the procedure and the positive results of this intervention. A number of different core decompression methods exist: including methods backfilled by a bone graft material and those without filling. Due to the inherent desire that the core decompression defect regenerate healthy bone, reduce pain, and stave off the need for total hip arthroplasty for some period of time, this surgically created defect is an excellent application for the use of a bone graft substitute.

Recently, an injectable calcium sulfate (CaSO4)/calcium phosphate (CaPO4) composite graft has become available for use in the treatment of surgically created defects. The synthetic graft is an injectable composite of CaSO4, tricalcium phosphate (TCP) granules, and brushite that hardens in situ. The triphasic resorption pattern exhibited by this material in vitro and in pre-clinical canine studies has indicated that the CaSO4 matrix resorbs at early time points to reveal a longer resorbing CaPO4 scaffold for bone onlay. In a canine proximal humerus model, the use of this material in a critical bone defect has demonstrated a regenerate with higher compressive strength at 13 week time points than defects treated with CaSO4 alone, defects treated with autograft, and normal untreated bone. By 26 weeks, the regenerated bone within the defect resembled normal bony architecture with similar mechanical properties.

Early clinical series have indicated similar results to the canine studies. Reports of early clinical findings have included a 12 patient benign bone tumor series with 4–12 month follow up and a core decompression series of 38 Ficat stage I–III hips with 6–16 month follow up. Preliminary radiological results in the bone tumor series showed peripheral resorption of the injectable CaSO4/CaPO4 composite with new bone formation along the resorbing edge. Clinically, patients in the bone cyst series have not experienced fractures or additional surgery and all patients have displayed full functional recovery. In the core decompression series, 32 of the 38 hips experienced pain relief and within the subset of 30 symptomatic hips, 24 had pain relief. These results, although preliminary, are promising outcomes.

Collectively, the pre-clinical and preliminary clinical results indicate that the use of an injectable CaSO4/CaPO4 composite could prove to be of benefit in core decompression of the femoral head. The staged resorption and dense bone formation evidenced in canine studies would be desirable in core decompression techniques where healthy bony ingrowth is the goal. Due to the straightforward compilation and use of this composite, the incorporation of this material as a backfill matrix into the core decompression procedure is technically simple. Although additional studies are certainly merited, these early clinical results are encouraging.

The abstracts were prepared by Lynne C. Jones, PhD. and Michael A. Mont, MD. Correspondence should be addressed to Lynne C. Jones, PhD., at Suite 201 Good Samaritan Hospital POB, Loch Raven Blvd., Baltimore, MD 21239 USA. Email: ljones3@jhmi.edu