Data provider Ortex estimated yesterday that 99% of medical tech company MiniMed Group Inc.'s public float was sold short, up from 47.6% on September 15. This anomaly is attributed to an arbitrage play related to parent company Medtronic's offer to exchange 225.3 million MiniMed shares for Medtronic stock. MiniMed's float is only 28.5 million shares, making the swap offer seven times larger than its tradable supply. Arbitrageurs are buying Medtronic stock and shorting MiniMed shares, expecting to use the converted MiniMed shares to close their short positions for a profit. The offer expires this Friday.