Ultrastructural changes in muscle following freezing in situ by a surface applied cold probe

Freezing of tissues under the conditions of cryosurgery resulted in changes in the muscles shortly after thawing occurred. The changes were progressive and included dilatation of mitochondria and sarcoplasmic reticulum, loss of glycogen, disruption of myofilaments and pyknotic changes in the nuclei. The progression of events is similar to other diseases of muscle but is structurally and chronologically unique. It does not appear to be typical of the early stages of ischaemia of muscle. It is suggested that the rapid onset of fibre damage following thawing is consistent with progressive alterations caused by ice-crystals at the time of freezing.