A posterior medial portal is not often used as it would lie very close to, or directly over the ulnar nerve.
In the study by Stothers et al., they found that the proximal approaches (proximal medial and proximal lateral), are safer than the traditional anteromedial and anterolateral approaches.
Unlu et al describe the relative distances from portals to the neurovascular structures. Their measurements are included under each potential response below.
1. The anterolateral portal is 1cm anterior to the lateral epicondyle at the level of the joint line. The posterior antebrachial cutaneous nerve is an average of 12.6mm away and the radial nerve is an average 4.8mm away.
2. The anteromedial portal is placed 2cm distal and 2cm anterior to the medial epicondyle. The medial antebrachial cutaneous nerve is an average of 8.9mm away, the median nerve is an average of 12.9mm away, and the ulnar nerve is an average of 22.1 mm away.
3. The posterolateral portal is located 2 cm proximal to the tip of the olecranon and adjacent to the lateral edge of the triceps tendon and is a safe distance from the medial brachial cutaneous nerve, posterior antebrachial cutaneous nerve and the ulnar nerve.
5. The direct posterior (straight posterior) portal is located midway between the condyles about 3 cm proximal to the tip of the olecranon. It is 15-25mm from the ulnar nerve.
Unlu MC, Kesmezacar H, Akgun I, Ogut T, Uzun I. Anatomic relationships between elbow arthroscopy portals and neurovascular structures in different elbow and forearm positions. J Shoulder Elbow Surg. 2006;15:457-462.
PMID:16831651 (Link to Abstract)
Stothers K, Day B, Regan WR: Arthroscopy of the elbow: Anatomy, portal sites, and a description of the proximal lateral portal. Arthroscopy 1995;11:449-457.
PMID:7575879 (Link to Abstract)