The Study of Morphology of supinator muscle and the arcade of Frohse

Abstract               Background: Supinator muscle is important from surgical point of view. Sometimes, the superior border is thick and fibrous as described by Frohse. This is an anatomic variation and not so common. The Deep Branch of Radial Nerve (DBRN) enters deep to the superior border border of supinator and passes between the two heads of supinator. The DBRN nerve is called posterior interosseous nerve (PIN) at the lower border of supinator muscle. Radial Tunnel Syndrome and PIN Syndrome both have same medical and surgical treatment. Surgical exploration is by three method or approaches. For this few parameters, distance from radial head and lateral epicondyle of humerus to the entry and exit of DBRN respectively are of paramount importance. Material and Methods: 22 upper limbs were dissected to explore the radial tunnel and supinator muscle. Superior border, superficial and deep head of supinator were observed. The superior border of the supinator for the arcade of Frohse. The composition of the superficial and deep head was noted. The entry and exit of the DBRN was observed and was measured from the lateral epicondyle of humerus and radial head. These landmarks are important to explore the DBRN or PIN in surgical approach as a treatment for decompression. Lengthening of the supinator and splitting of arcade of Frohse is done to relieve the Radial Tunnel Syndrome or PIN Syndrome. Result:  Superficial head of supinator: 1 muscular, 13 fibrous and 6 musculofibrous, and 2 fibrousmuscular.  The arcade of Frohse was observed in only one cadaver out of 22. The breadth of the supinator muscle is 4.41 cm. The distance between the lateral epicondyle to the entry of the DBRN is 4.46 cm. The distance between lateral epicondyle to exit of DBRN is 7.72 cm. The distance between radial head and entry of DBRN is 2.98 cm. The distance between radial head and exit of DBRN is 6.5 cm. Conclusion: The arcade of Frohse is the variation at the superior border of the supinator. The superficial head of supinator is of different composition either muscular or fibrous or intermediate. The distance between lateral epicondyle of humerus, radial head and entry and exit of DBRN at superior border and at lower border of supinator respectively are important landmarks during surgical intervention as a treatment of Radial Tunnel Syndrome or PIN Syndrome.

Key Word: supinator muscle, arcade of Frohse.