title: Safe Zone for the Plantar Portal: A Cadaveric Study.
abstract: BACKGROUND
  Understanding the plantar nerve anatomy is crucial for safe endoscopic surgery of the sole. We aimed to anatomically dissect the lateral aspect and soles of cadaveric feet to investigate the safety of peroneus longus tendoscopy with a plantar lateral portal and the safe zones for plantar portals.
  
  
  METHODS
  We studied 36 feet of 24 cadavers (mean age, 86.5 years). A cannula for 2.7-mm scope was inserted from the plantar lateral portal to the peroneus longus tendon, and the positional relationship between the cannula and sural nerve was observed. Then, the soft tissue of the sole was dissected, and the relationships between the plantar nerve and flexor digitorum longus tendon and flexor hallucis longus tendon was observed. The plantar nerve course was digitally imaged and uploaded into Image J software to determine nerve position. We further observed the positional relationship between the cannula and plantar nerve.
  
  
  RESULTS
  The mean minimum distance between the cannula and sural nerve was 13.8 mm, and the closest distance was 4.2 mm, allowing for the relatively safe creation of a plantar lateral portal. The use of the plantar lateral portal and evaluation of the peroneal tendon was safe with respect to the lateral plantar nerve as the nerve was in a different tissue layer of the foot. Dissection of the plantar foot demonstrated a relatively safe zone, 36.4% to 56% along a line between the medial aspect of the base of the first metatarsal bone to the proximal tip of the fifth metatarsal. This region may allow for a plantar endoscopic portal; however an anatomic variation may result in the plantar nerve being within this zone. The flexor digitorum longus tendon and peroneus longus tendon passed through the deep layer of the relatively safe zone.
  
  
  CONCLUSIONS
  Peroneus longus tendoscopy was relatively safe to perform from a plantar lateral portal. No neurovascular structure exists on the slightly medial aspect of the central region of the sole, potentially allowing for a relatively safe creation of plantar central portal. An approach from the plantar central portal to the flexor digitorum longus tendon, flexor hallucis longus tendon, and peroneus longus tendon allows for a greater range of vision and treatment options as compared with conventional approaches. The combination of the plantar central portal with portals such as the plantar lateral portal may further the development of endoscopic surgery of the sole.
  
  
  CONCLUSIONS
  We found the anatomic characteristics of a relatively safe zone for the plantar portal for plantar lateral portal.
authors.affiliation: Department of Orthopaedic Surgery, St. Marianna University School of Medicine, Kawasaki, Kanagawa, Japan shingo10082003@yahoo.co.jp.
authors.forename: Shingo
authors.initials: S
authors.lastname: Maeda
authors.affiliation: Department of Orthopaedic Surgery, St. Marianna University School of Medicine, Kawasaki, Kanagawa, Japan.
authors.forename: Hisateru
authors.initials: H
authors.lastname: Niki
authors.affiliation: Department of Orthopaedic Surgery, St. Marianna University School of Medicine, Kawasaki, Kanagawa, Japan.
authors.forename: Takaaki
authors.initials: T
authors.lastname: Hirano
authors.affiliation: Department of Orthopaedic Surgery, St. Marianna University School of Medicine, Kawasaki, Kanagawa, Japan.
authors.forename: Yui
authors.initials: Y
authors.lastname: Akiyama
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002102:Cadaver; D004724:Endoscopy; D005260:Female; D005528:Foot / Q000601:surgery*; D006801:Humans; D007431:Intraoperative Complications / Q000517:prevention & control*; D008297:Male; D059348:Peripheral Nerve Injuries / Q000517:prevention & control*; D013710:Tendons / Q000601:surgery*; D013979:Tibial Nerve / Q000033:anatomy & histology*
keywords: plantar nerve; plantar portal; safe zone; tendoscopy