A surgical instrument includes a power pack, an outer shell housing configured to selectively encase the power pack, and an adapter assembly configured to selectively couple the outer shell housing to a loading unit. The outer shell housing includes a motor and a drive shaft coupled to and rotatable by the motor. The outer shell housing includes a drive member supported in a distal portion thereof. The drive member is configured to selectively couple to the drive shaft. The adapter assembly has a drive member supported in its proximal end. The drive member of the adapter assembly is configured to selectively couple to the drive member of the outer shell housing such that rotation of the drive shaft actuates movement of the drive member of the adapter assembly via the drive member of the outer shell housing.