"Safe dissection parameters of the anconeus rotational flap for soft tissue coverage at the elbow"

The anconeus is a small muscle located on the posterior elbow originating on the lateral epicondyle and inserting onto the proximal-lateral ulna that functions as an elbow extensor as well as dynamic stabilizer. The blood supply is tri-fold: medial/middle collateral artery (MCA), recurrent posterior interosseous artery (RPIA), and less commonly found, the posterior branch of the radial collateral artery. The anconeus has become a popular option for local soft tissue coverage about the elbow (distal triceps, olecranon, proximal forearm). The average defect size for consideration of local anconeus flap coverage is 5-7cm². The aim of the study was to determine safe dissection parameters of the anconeus as well as map arterial pedicles to achieve successful local harvest of the muscle without devascularization.

8 fresh frozen cadaveric arms (all male, average age 63 years - 4 left arms, 4 right arms) from scapula to fingertip were obtained. First, the radial, ulnar and axillary arteries were dissected and isolated. The radial and ulnar arteries were transected. 100cc normal saline was injected through the axillary artery, sequentially clamping the radial followed by the ulnar artery so that adequate flow could be seen through all vessels. 100cc mixture of Biodür and hardener (10:1) was mixed and injected into the axillary artery. We first allowed free flow through both the ulnar and radial vessels followed by clamping of these vessels. This allowed the pressure to build up and fill the smaller vessels in the arms. After injection, the axillary artery was then clamped and the specimens were left to harden for 24-48 h. After hardening, dissection was performed by making a curvilinear incision centred over the lateral epicondyle. The anconeus was identified and the interval between the anconeus and ECU was then confirmed. Measurements of the anconeus muscle were taken. Blunt dissection was carried between anconeus and ECU until the RPIA was identified and protected. We isolated the MCA by dissecting proximally. This was found to run with the nerve to the anconeus. Once this vessel had been protected, the muscle reflected from distal to proximal staying along its ulnar border. The branches of the RPIA were ligated and the dissection was continued proximally. Measurements of the distances of the RPIA, MCA were taken.

The average distance of olecranon to muscle tip was 95.0mm. The average distance of lateral epicondyle (LE) to muscle tip was 90.8mm. The average distance of LE to olecranon was 49.8mm. The average location of the RPIA was 63.mm when measuring LE to vessel, 68.3mm when measuring olecranon to vessel, 18.3mm when measuring RPIA to muscle tip. The average RPIA diameter was 1.1mm and length was 36.4mm from the initial branching of the posterior interosseous artery. The average MCA diameter was 0.7mm. The posterior branch of the radial collateral artery was only found in 3/8 specimens. The RPIA and MCA were constant in all specimens. Dissection was safely carried to the border of the LE and olecranon without disruption of the MCA.

Our conclusions determined that if dissection of the anconeus is undertaken, the RPIA remains constant between the interval of the ECU as well as anconeus at an average distance of 18.3mm from the tip of the muscle measuring proximally; moreover, the MCA was constant in all specimens found directly between the LE and olecranon always running with the nerve to the anconeus. When dissecting and mobilizing to ensure preservation of the MCA, dissection should be taken from distal to proximal as well as dissecting along the ulnar border of the anconeus. Proximal dissection can be taken as proximal as the border of the LE and olecranon as that did not disrupt MCA blood supply.