Calcium sulfate (or calcium sulphate) is the inorganic compound with the formula CaSO4 and related hydrates. One particular hydrate is better known as plaster of Paris, and another occurs naturally as the mineral gypsum. All forms are white solids that are poorly soluble in water. Calcium sulfate causes permanent hardness in water.
Mixed with polymers, it has been used as a bone repair cement.
Amy L. Ladd MD, Kimberly Wirsing MD, in Principles and Practice of Wrist Surgery, 2010, (Excerpt)
Calcium sulfate, better known as plaster of Paris, results from the calcination of gypsum (CaSO4, 2H2O), which partiallydehydrates to produce a hemi-hydrate (CaSO4, ½H2O).
The large deposits of gypsum around Paris permitted its widespread use in the 18th century to plaster walls for fire protection. Plaster of Paris became popular as an orthopedic dressing in the mid 19th century by a Dutch surgeon named Mathysen. In Germany, Dreesmann was able to document healing in six of eight bone defects using plaster of Paris and phenol, but its use was slow to develop despite acceptances of asepsis and sterile technique in the 20th century. Peltier and colleagues29 wrote a landmark article on its usefulness with bone defects in 1959, documenting the bone activity in animal studies and correlating it with clinical cases. Since the clinical use of calcium sulfate predated the existence of the FDA, it was designated a class II special controls device in 1998, requiring institution of voluntary consensus standards for its use. This consensus is known as “surgical grade,” reflecting purity and consistency of the material. The first calcium sulfate marketed was Osteoset, available in pellet form, and more recently as an injectable (Minimally Invasive Injectable Graft, MIIG). Both preparations are compatible with antibiotic powder and are therefore useful in the local delivery of antibiotics for the treatment of infected bone nonunions. Other marketed calcium sulfate products include Calceon (Synthes USA) in pellet form, and BonePlast (Interpore Cross, now Biomet), which is moldable and injectable. Jax-CS (Smith & Nephew, Memphis, Tennessee) comes in granular form but can be administered manually or with a syringe.
Resorption of calcium sulfate is rapid, with total resorption observed as early as a few weeks to potentially longer times. Manufacturers’ information is scant on the rate of resorption, but it depends on the formulation and configuration of the material, size, and local environment of the defect and potentially the formulation. Whereas fast resorption occurs by dissolution and arguably renders no advantage to bone healing, replacement with trabecular bone has been shown. It is currently approved for filling metaphyseal defects. Calcium sulfate potentially renders immediate stability, but augmented fixation is required because of its rapid resorption.
ROSS K. LEIGHTON BSc, MD, FRCSC, FACS, … KELLY TRASK MSc, 2009
Evidence for the use of calcium sulfate is extremely poor. In a study done by Petruskevicius and coworkers looking at OsteoSet (Wright Medical Technology, Arlington, TN) on bone healing and tibial defect in humans, OsteoSet was compared with no bone graft in the substitution of anterior cruciate ligament repairs. Computed tomographic scans of the defect were taken on the first day after the operation, at 6 weeks, 3 months, and 6 months. No difference was found in the amount of bone in the defect in the OsteoSet and control groups, and indeed, in the control group (no bone graft or pellets), the bone volume increased from 6 weeks to 3 months. A study looking at the use of calcium sulfate in nonunions, presented at the OTA in 2004, demonstrated no improvement in bone healing, an increased infection rate, and increased wound drainage. The authors’ conclusion was to suggest calcium sulfate should not be used in the treatment of nonunions. Despite excellent efforts, there is no Level I or II evidence that the healing is enhanced, and indeed, healing may be worse in periarticular injuries or nonunions with the addition of calcium sulfate.
With the increasing popularity of calcium sulfate, there have been some cases of severe inflammatory response particularly in tumor cases. It has been hypothesized that the rapid absorption of the calcium sulfate pellets into a calcium-rich fluid stimulates inflammation.