Safe Zone At The Medial And Lateral Calcaneus And The Proximal Tibia For Percutaneous Pin Placement: An Anatomical Study

Objective: To mark off the safe zone at the medial and lateral calcaneus and the proximal tibia for percutaneous pin placement and provide the clinical surgeon the basic information for safe operation to reduce clinical complications.Methods: Eight cadaveric legs specimens of four male adult unembalmed cadavers were used in this study.The knee joint capsules,deep neurovascular structures in the ankle joint and both medial and lateral calcaneus of all specimens were intact.No trauma and malformation in the knee and ankle joint was found.On the medial calcaneus,three palpable anatomic landmarks were identified on each ankle and labeled as Point A (posteroinferior medial calcaneus), Point B (inferior medial malleolus), and Point C(navicular tuberosity). The medial neurovascular bundle was carefully dissected, and the medial calcaneal nerve(MCN), the most posterior branch of the lateral plantar nerve(MPLPN), the lateral plantar nerve(LPN), the medial plantar nerve(MPN), and the posterior tibial artery(PTA) (or the lateral plantar artery(LPA) and the medial plantar artery(MPA)) were identified. The length of line AB and AC and the distance from the points at which the neurovascular structures transected line AB and AC to the point A were measured. And then calculate the percentage of these distances respectively on the line AB and AC to mark off the relative safe zone at medial calcaneus. On the lateral calcaneus,two palpable anatomic landmarks were identified on each ankle and labeled as Point D (posteroinferior lateral calcaneus), Point E (inferior lateral malleolus). The lateral calcaneal nerve,sural nerve and the trunk of the small saphenous vein were carefully dissected and identified.The lenghth of line DE and the distance from the points at which the neurovascular structures transected line DE to the point D were measured. Calculate the percentage of these distances respectively on the line DE to mark off the relative safe zone at lateral calcaneus.On the proximal of the tibia, the knee joint was dissected and the line where the knee joint capsule attaches to the tibia was exposed. We assume the tibial plateau surface as a dial plate.Each time point represents a position where the distance was to be measured. The distance from the attachment point of the knee joint capsule to the articular surface on each time point were measured.All the data were based on the right knee in clockwise to determine the attachment line of the knee joint capsule where the safe zone was marked off.Results: On the AB line of the medial calcaneus, the distance from the point at which the medial calcaneal nerve, the most posterior branch of the lateral plantar nerve, the lateral plantar nerve, the medial plantar nerve, and the posterior tibial artery transected line AB to point A account for 22%,50%,55%,64%,58% the length of line AB respectively.Most of the important neurovascular structures located at the 1/2 anterior superior part of line AB. On the AC line of the medial calcaneus, the distance from the point at which the medial calcaneal nerve, the most posterior branch of the lateral plantar nerve, the lateral plantar nerve, the medial plantar nerve, the lateral plantar artery and the medial plantar artery transected line AC to point A account for 14%,38%,48%,64%,41%,58% the length of line AC respectively.Most of the important neurovascular structures located at the 2/3 anterior superior part of line AC. On the DE line of the lateral calcaneus, the distance from the point at which the lateral calcaneal nerve,sural nerve and the trunk of the small saphenous vein transected line DE to point D account for 20%,66%,62% the length of line DE respectively. Most of the neurovascular structures located at the 2/5 anterior superior part of line DE.On the lateral knee joint,the lowest point of the knee joint capsule attached to tibia located at near 5 o'clock.The mean depth is 10.27mm and its 95% IC is (8.18～12.36). On the medial knee joint,the lowest point of the knee joint capsule attached to tibia located at near 10 o'clock.The mean depth is 5.94mm and its 95% IC is (5.25～7.6).Conclusions:On the medial calcaneus,the region posterior to 1/2 of the line AB and 1/3 of line AC was considered as the relative safe zone for percutaneous pin placement,the more posterior areas were safer; On the lateral calcaneus,the region posterior to 3/5 of the line DE was considered as the relative safe zone for percutaneous pin placement; On the lateral knee joint,the lowest point of the knee joint capsule attached to tibia located at near 5 o'clock. On the medial knee joint,the lowest point located at near 10 o'clock. The distal region of 12.36mm below the tibial plateau articular surface on the lateral and 7.6mm on the medial of the knee joint was considered as the relative safe zone for percutaneous pin placement.