Table 4: Distribution of THR Devices Approved by PMA Between 1976-1995

Number of Approvals Held by Manufacturer	Number of Approved Devices	Number of Manufacturers
0 < 10	4 (12%)	2 (50%)
10 to 19	10 (29%)	1 (25%)
≥ 20	20 (59%)	1 (25%)
Total	34	4