title: The split portal: Description of a new accessory posterior portal for arthroscopic shoulder instability procedures.
abstract: OBJECTIVE
  Open approach to the posterior shoulder during bone block for posterior shoulder instability is challenging. Anatomical study was performed to identify landmarks of a portal, avoiding soft tissue damage, between the infraspinatus (IS) and teres minor (TM) muscles and distant from the supra-scapular nerve (SSN) for arthroscopic shoulder bone block.
  
  
  METHODS
  Eight fresh-frozen cadaveric shoulder specimens were used. The arthroscope was introduced through the soft point (SP). A guide wire was placed through the SP, in the rotator interval direction. A posterior open dissection exposed the split between the IS and TM. A new guide wire was placed into the split, parallel to the first wire, to locate the new posterior arthroscopic approach. Ten distances were measured to define the safe position.
  
  
  RESULTS
  The mean values were: SP to split IS-TM: 2 ± 0.2 (2-2.8); spinal bone to split IS-TM: 5 ± 0.5 (3-6.2); split IS-TM to posterior glenoid 6 o'clock: 1.3 ± 0.3 (0.6-1.6), 9 o'clock: 1.5 ± 0.3 (1-1.9), and 12 o'clock: 2 ± 0.1 (2.1-2.4); SSN to posterior glenoid 6 o'clock: 2.4 ± 0.2 (2.1-2.6), 9 o'clock: 1.7 ± 0.1 (1.5-1.8), and 12 o'clock: 1.5 ± 0.3 (1.2-2.1); and SSN to split IS-TM: 2 ± 0.3 (1.2-2.1).
  
  
  CONCLUSIONS
  This preliminary anatomical study described a posterior arthroscopic portal located 2 cm under the SP, parallel to the SP portal direction, and finishing between 7 and 8 o'clock at the posterior rim of the glenoid. For arthroscopic shoulder bone block, this portal can avoid muscle and SSN lesions.
authors.affiliation: Service de Chirurgie Orthopédique-Traumatologique, Hôpital Henri-Mondor, 51 Avenue du Maréchal De Lattre de Tassigny, 94010, Créteil, France.|Université de Médecine Paris-Est Créteil, Créteil, France.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Mirouse
authors.affiliation: Groupe Maussins, Groupe Ramsay Générale de Santé, Clinique des Maussins, 67 rue de Romainville, 75019, Paris, France. gnourissat@wanadoo.fr.
authors.forename: Geoffroy
authors.initials: G
authors.lastname: Nourissat
mesh_terms: D000369:Aged, 80 and over; D001182:Arthroscopy / Q000379:methods*; D016025:Bone Transplantation; D002102:Cadaver; D006801:Humans; D007593:Joint Instability / Q000601:surgery*; D008297:Male; D012782:Shoulder / Q000033:anatomy & histology / Q000601:surgery*; D012785:Shoulder Joint / Q000033:anatomy & histology* / Q000601:surgery*
keywords: Arthroscopy; Posterior bone block procedure; Posterior shoulder instability; Supra-scapular nerve