Biological effects of calcium sulfate as a bone graft substitute in ovine metaphyseal defects.

Calcium sulfate has been used as a bone graft substitute in many fields, from dentistry to orthopedics. However, the results of many studies have yielded inconclusive results. In the present study, a sheep model was used with tibial and femoral metaphyseal defects to determine whether calcium sulfate was as effective as autograft and allograft in promoting new bone formation in a critical size defect. Medical-grade calcium sulfate pellets, autograft bone, allograft bone, or nothing was used to fill the metaphyseal defects. The sheep were allowed to heal for 12 weeks. Sagittal sections from the bones were analyzed with high-resolution contact radiographs, backscattered electron microscopy, and light microscopy. The volume fractions of bone within the defect perimeter were determined, and the histologic quality of the bone was observed. The volume fraction of new bone in the autograft, calcium sulfate, and allograft were not statistically different, but all were significantly different than the untreated control. The majority of the calcium sulfate had been resorbed at 12 weeks, and the histologic quality of the bone appeared similar to the autograft-treated bone. Calcium sulfate appears to be a useful biocompatible bone graft substitute that yields results similar to autograft bone in sheep metaphyseal defects.

Tibial component fixation with cement: full- versus surface-cementation techniques.

Despite excellent outcomes with cemented tibial components in total knee arthroplasty, it still is debated whether the tibial stem should be cemented and what the optimal tibial stem design should be. Proponents of full cementation of the tibial stem and component state that better short-term and long-term component fixation is achieved when full cementation is used. Advocates for surface cementation contend that sufficient implant stability is achieved without the increased bone loss that occurs at revision and the stress shielding thought to be linked with cemented stems. This biomechanical cadaver study compared initial fixation and cement penetration depth in fully cemented versus surface cemented tibial trays with two different stem geometries (cruciate and I-beam) and compared two stem designs (cruciate and I-beam) fixed with surface cementation. Under an eccentric load, simulating three times body weight for 6000 cycles, there seems to be no difference in the micromotion of either tibial component implanted with surface or full cementation. Additionally, no difference in the average depth of cement penetration was detected between fixation techniques or stem types. The initial fixation stability of the surface cement technique seems correlated to the depth of cement penetration into proximal tibial surface. The current data support other studies which indicate that stability of surface-cemented tibial components may be related to the depth of cement penetration.