An assembly for surgery in a patient, comprising: an elongate support member extending between a first end and an opposite second end; a first arm member including an external housing extending along a longitudinal axis between a proximal end engageable with said elongate support member and an opposite distal end, said distal end including a first engagement portion rotatably coupled to said first arm member and structured to engage with a first retractor portion; a second arm member including an external housing extending along a longitudinal axis between a proximal end engageable with said elongate support member and an opposite distal end, said distal end including a second engagement portion rotatably coupled to said second arm member and structured to engage with a second retractor portion; wherein said external housing of each of said first and second arm members defines an elongated receptacle extending along said longitudinal axis from a distal opening at said distal end, said elongated receptacle including a locking element releasably biased into engagement with a respective engagement portion; a first retractor portion including a first end engaged with said first engagement portion and a second end positionable in an incision; and a second retractor portion including a first end engaged with said second engagement portion and a second end positionable in the incision opposite said second end of said first retractor portion; characterised in that said engagement between said locking element and said respective engagement portion allows rotation of said engagement portion in a first direction about the longitudinal axis of a respective arm member and prevents rotational movement of said engagement portion in a second direction about the longitudinal axis of said respective arm member; and in that rotation of said first and second engagement portions about said longitudinal axes of said first and second arm members in said respective first directions (R 1, RR 1) increases a separation distance between said second ends of said first and second retractor portions. an elongate support member extending between a first end and an opposite second end; a first arm member including an external housing extending along a longitudinal axis between a proximal end engageable with said elongate support member and an opposite distal end, said distal end including a first engagement portion rotatably coupled to said first arm member and structured to engage with a first retractor portion; a second arm member including an external housing extending along a longitudinal axis between a proximal end engageable with said elongate support member and an opposite distal end, said distal end including a second engagement portion rotatably coupled to said second arm member and structured to engage with a second retractor portion; wherein said external housing of each of said first and second arm members defines an elongated receptacle extending along said longitudinal axis from a distal opening at said distal end, said elongated receptacle including a locking element releasably biased into engagement with a respective engagement portion; a first retractor portion including a first end engaged with said first engagement portion and a second end positionable in an incision; and a second retractor portion including a first end engaged with said second engagement portion and a second end positionable in the incision opposite said second end of said first retractor portion; characterised in that