| Objective: The fracture of calcaneus is common clinically, approximately 2% of the fractures of all over the body,60% of all tarsal bone fractures, 75% of which relate to subtalar joint and the prognosis of which is worse. There are many methods in the management of the calcaneus fracture.The treatment of the calcaneus fracture is operation most, but in the operation, neurovascular injury is iatrogenic, 6%~7% of which are sural nerve injury caused by lateral approach and 25% of which are the branch of the tibial nerve injury caused by medial approach.The major nerve and vascellum are posterior tibial vascellum and its branch(medial and lateral plantar vascellum), tibia nerve and its branch(medial and lateral plantar nerve),sural nerve and its branch(cutaneous dorsalis lateralis nerve).The major neurovascular bundle of the medial calcaneus are tibial nerve and posterior tibial vascellum. The medial plantar nerve is sensus branch, dominating the the skin of the planta and some toes and the lateral plantar nerve is motion branch, dominating the inner muscle of the foot. The posterior tibial artery supplies the skin of two thirds anterior to planta and the bone of posteroinferior of calcaneus. The sural nerve of lateral calcaneus is formed by medial sural cutaneous nerve and communicating branch of peroneal nerve, turnning forward from inferior to lateral melleolus named cutaneous dorsalis lateralis nerve, accompanying the branch of small saphenous vein, which dominates the skin of foot and margines laterales digtorum pedis. Some safe zones of calcaneus have reported in data, but there are no good methods to avoid neurovascular injury exterior and interior of country. L lateral cut and AO plate interal fixation can easily lead to complications such as necrosis of cut margin, infection of incisional wound et al. To reduce operation wound and complications of soft tissue and to promote the union of fracture, minimal technique of reduction and interal fixation develops in the management of the calcaneus fracture. In our study, fresh cadaveric specimens were used and the anatomic study of the hindfoot was done in neutral position. We search the safe zone of placing the internal fixation to avoid the neurovascular and musculotendinous injury through the detailed measure of the medial and lateral neurovascular. We defined a safe zone through the anatomic landmarks of the body surface. We provide the study of the foundational morphology for the application of minimally invasive technique and the plate with micro-cut.Methods: sixteen fresh cadaveric foot specimens containing whole leg were choosen, all of which were gotten from adult patients amputated because of road accident or osteosarcoma and were dissected in neutral position. Several anatomic landmarks were choosen in the medial and lateral calcaneus, on the base of which the reference lines were drawn. The relative safe zone was defined through these landmarks and lines. Therefore, the safe zones can be delineated simplily with palpating. These points and lines were marked by the pins. The soft tissue of medial hindfoot containing the structures in the tarsal tunnel were dissected around these pins. The relationship was measured between the branch of tibia nerve, posterior tibia artery, the distribution of the lateral tendon and these landmarks. The shortest distance was recorded from the branch of the lateral plantar nerve to the line in every specimen. After the medial calcaneus was dissected, the lateral calcaneus was dissected in erery specimen. In the same way, the pins were inserted into these landmarks defined and the soft tissue of lateral calcaneus was carefully dissected. The relationship was found between the sural nerve, peroneal tendon and these landmarks.Results:1 The measure of sustentaculum tali:lenhth(3.3±2.87mm), width(15.1±1.94mm),height(10.36±1.11mm),upward angle (27.82±6.58°),angle lean forward(30.5±5.55°).2 The measure of safe zone in lateral calcaneus2.1 From point A to G: the distance from point A to B: 79.2±4.46 mm2.1.1 LPN: the distance from the point(the lateral plantar nerve crossing line AG)to point G :39.9±3.22mm(50.4±2.22%). 2.1.2 MPN: the distance from the point(the medial plantar nerve crossing line AG)to point G : 48.0±2.96mm(60.7±2.72%)。.2.1.3 PTA: the distance from the point (the posterior tibial artery crossing line AB)to point G.2.2.From point F to G: the distance from pointG to point F : 90.4±4.30mm2.2.1 LPN: the distance from the point (the lateral plantar nerve crossing line FG)to point G: 44.2±2.88mm.(55.7±2.43%)。.2.2.2 MPN: the distance from the point(the medial plantar nerve crossing line FG)to point G: 55.9±4.06mm。(61.8±3.90%)。.2.2.3 PTA: the distance from the point(the posterior tibial artery crossing line FG)to point G:42.9±3.81mm。(47.1±2.95%)。.3 The safe zones of lateral calcaneus3.1.from D to F: the distance from pointD to F:41.5±8.48mm, SN :the distance from the point(the sural nerve crossing line DF)to point D: 12.8±4.37 mm(30.2±4.48%).3.2 from Dto H: the distance from point D to H: 50.4±12.4 mm, SN :the distance from the point(the sural nerve crossing line DH)to point D: 13.5±4.27 mm(26.9±2.55%).3.3 from Dto G: the distance from point D to G: 49.7±13.5mm, SN :the distance from the point(the sural nerve crossing line DH)to point D: 14.0±4.06 mm(27.6±2.35%).3.4 from Dto J: the distance from point D to J: 63.2±9.06mm, SN :the distance from the point(the sural nerve crossing line DJ)to point D: 44.7±4.24 mm(71.4±7.07%)。The safest zone is the posterior tuberosity in medial calcaneus. In all specimens, the major neurovascular structures are anterior to the line CE. The first branch of the lateral plantar nerve was found consistently the most posterior in all structures of ankle tube, all of which were anterior to line CE by a mean distance of 5.33±2.6mm. The safest zone was the posteroinferior of the calcaneus tuberosity or the posteroinferior of the sural nerve and the peroneal tendon. The course of the sural nerve is the posterior to the tip of lateral melleous by a mean distance of 12.8±4.37mm and the inferior to posterior melleous by a mean of distance of 13.5±4.27mm. The sural nerve is named lateral dorsal cutaneous nerve of foot through inferior of lateral melleous and changing the direction to anterior, which is superficial layer of hypoderma. There is relative thick soft tissue between the nerve and facies ossea. Blunt dissection in subperiosteum can avoid the injury of the sural nerve.Conclusion: Through the precision measurement of the relationship between the anatomic landmarks and nerve , vescellum of calcaneus,we find the shadowcasting of nerve ,vescellum of calcaneus and relative safe zones for the choice of operative incision, the placement of interal fixation and the traction pins. Careful blunt dissection can completely avoid neurovascular injury.
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