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Anatomic Structures at Risk: Curved Hindfoot Arthrodesis Nail—A Cadaveric Approach
The Journal of Foot & Ankle Surgery 53 (2014) 687–691
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Anatomic Structures at Risk: Curved Hindfoot Arthrodesis NaildA Cadaveric Approach Timothy Knight, MBBS 1, Peter Rosenfeld, MBBS, FRCS (Orth) 2, Ioan Tudur Jones, MB, BCh, FRCS (Orth) 3, Callum Clark, MB, BCh, FRCS (Orth) 4, Nick Savva, MBBS, FRCS (Orth) 5 1
Specialist Registrar, West Midlands Deanery, Robert Jones and Agnes Hunt Orthopaedic Hospital, Gobowen, Oswestry, Shropshire, United Kingdom Orthopaedic Consultant Surgeon, St Mary’s Hospital, London, United Kingdom Orthopaedic Consultant Surgeon, St Thomas’ Hospital, London, United Kingdom 4 Orthopaedic Consultant Surgeon, Heatherwood and Wexham Park Hospitals, Berkshire, United Kingdom 5 Orthopaedic Consultant Surgeon, Dorset County Hospital, Dorset, United Kingdom 2 3
a r t i c l e i n f o
a b s t r a c t
Level of Clinical Evidence: 5
Retrograde intramedullary nailing of the hindfoot and ankle is an established procedure for salvage of severe foot and ankle deformity, arthritis, tumor, and instability. In the present study, retrograde hindfoot (tibiotalocalcaneal) arthrodesis nailing was performed using a standardized technique on 7 cadaver specimens by trained senior surgeons. The specimens were then dissected to determine the distance of the subcalcaneal structures at risk from the insertion point of the nail. The findings showed that the distance of the lateral neurovascular bundle from the edge of the nail was 6.5 (range 3.5 to 8, 95% confidence interval 5.9 to 7.1) mm. No neurovascular bundle was compromised, and all were within a previously described “safe window.” Ó 2014 by the American College of Foot and Ankle Surgeons. All rights reserved.
Keywords: ankle arthritis cadaver HAN intramedullary nail tibiotalocalcaneal fusion
Tibiotalocalcaneal arthrodesis is an established treatment option for arthritis of the ankle and subtalar joints. It has been used, but has not been limited to, as treatment of talar avascular necrosis, as salvage treatment in complex trauma, and in the presence of instability or severe deformity, such as from tumor resection (1). It has also been used in failed ankle joint replacement, failed union, and pseudoarthrosis (2–5). Intramedullary nailing has the benefit of not creating the bulky construct seen with plating and avoids the excessive soft tissue dissection associated with wound complications. The concept is not new; however, the fixation design and fixation entry point have been altered in an attempt to achieve maximal fixation and offer protection to the neurovascular structures. The most significant recent changes have been in the curvature of the nail design and claims of improved safety. Moorjani et al (6) undertook a cadaveric study to ascertain the relative anatomic dangers of different theoretical nail entry points of arthrodesis nails with varying curvature designs to the respective neurovascular structures. In their cadaveric study, the distance from
Financial Disclosure: None reported. Conflict of Interest: None reported. Address correspondence to: Timothy Knight, MBBS, Robert Jones and Agnes Hunt Orthopaedic Hospital, Gobowen, Oswestry, Shropshire SY7 10AG United Kingdom. E-mail address: [email protected] (T. Knight).
the center of the nail entry to the respective structures was measured. A distance of less than 10 mm was deemed unsafe when working with a reamer 9 mm in diameter. In all cases, the distance from the medial plantar nerve and artery was greater than 10 mm; however, they identified the lateral plantar nerve and artery as being at the greatest risk. In 1 case, the pin had passed through the lateral plantar artery; in another, the pin and lateral neurovascular bundle were touching; and in a third case, the pin had been inadvertently placed on the medial side of the lateral neurovascular structure, illustrating the potential for injury. The current, newer intramedullary nail designs now require validation and evidence to support their claims of protection of the neurovascular structures in light of the design changes. The structural strength of the nail construct is achieved by driving a bony tunnel of maximal fixation through the calcaneum. The plantar surface of the calcaneum has a sagittal ridge traversing lateral to the mid-axis of the calcaneal body. A curved nail design, therefore, will accommodate an additional valgus nail angulation of 8 , requiring 12 of nail curvature to accommodate a relatively lateral plantar entry point, with a residual valgus alignment of 3 to 5 after insertion. A plantar-lateral entry point will be advantageous, because it is further from the course of the closest neurovascular bundle and the lateral plantar nerve and artery. As used by the AO Foundation, the hindfoot (tibiotalocalcaneal) arthrodesis nailing (HAN), marketed by DuPuy Synthes (Johnson &
1067-2516/$ - see front matter Ó 2014 by the American College of Foot and Ankle Surgeons. All rights reserved. http://dx.doi.org/10.1053/j.jfas.2014.06.005
688
T. Knight et al. / The Journal of Foot & Ankle Surgery 53 (2014) 687–691
Johnson, West Chester, PA) is a retrograde nail with multiple fixation methods (7). The entry of the nail is through the plantar lateral aspect of the body of the calcaneum. Satisfactory retrograde nail results were described with a plantar approach almost 2 decades ago; however, the nail design has been refined in materials, instrumentation, and principles of biology. Previous work has defined a “window of safety” lateral to the midline (6) and supported the design of nails with curvature. The present study examined the anatomic location of the plantar lateral neurovascular bundle to the nail entry point to evaluate the purported benefits of protecting critical neurovascular structures (7). Materials and Methods Using a standard set of instrumentation, 7 experienced orthopedic surgeons familiar with the surgical technique followed a standardized procedure (7) to insert a guidewire for cannulated intramedullary HAN through the heel pad of unembalmed cadaveric lower limb specimens. We elected to examine nail placement of the curved HAN system in 7 below the knee cadavers provided for an industry-sponsored training exercise. Demographic information for the cadaveric specimens was not available; however, we did not believe this would affect the goal of our examination. Live imageintensifier roentgenographic views were available and were used. The equipment was prepared and assembled by trained company representatives. Before performing the technique, the operating team was reminded of the standardized steps for the nail insertion. A fibula osteotomy was performed and, subsequently, the ankle and subtalar joint surfaces were prepared. The entry point for the heel pad was achieved in a training-simulated “real theater” environment. Palpation of the heel pad and surface markings were used to estimate entry. The palpable bony ridge on the plantar lateral aspect of the calcaneum indicates the lateral column of the calcaneum. In accordance with the operational technique guide, which includes illustrations, published by Synthes, “the entry point is in line with the tibial canal and the lateral column of the calcaneus, using a C-arm, identify the center of the tibial canal by placing a 3.2-mm guidewire along the canal. Draw a line (Fig. 1A). Palpate the centre of the lateral column of the calcaneus. Draw a line (Fig. 1B). The entry point is located at the intersection of these two lines, the incision should be in line with the longitudinal axis of the foot” (7). The power-driven guidewire, targeted toward the center of the talus, was advanced. The position was confirmed using live image-intensifier imaging and direct vision. Once a satisfactory guidewire position had been achieved, the wire was advanced into the distal tibia, following the central axis of the tibia. In most cases, this was followed sequentially by measuring, reaming, and introduction of an intramedullary nail using
standardized equipment. As a training session, some surgeons chose not to advance a nail; in these cases, the heel pad was later exposed (Fig. 2) and a reamer placed in situ (Fig. 3) for measurement. A 13-mm protection sleeve was used with the 13-mm cannulated reamer. Subsequent to satisfactory completion of the procedure, the cadaveric feet were examined by the senior authors (N.S. and P.R.). The surgical wounds were extended, and the dissection was made extensile (Fig. 4). The lateral neurovascular bundle was identified between the first muscle layer (abductor hallucis, abductor digiti minimi, and flexor digitorum brevis) and the second muscle layer (flexor digitorum longus, flexor hallucis longus, flexor accessorius, and the lumbricals). Minimizing the damage to the adjacent structural attachments to the neurovascular bundle, it was carefully dissected and exposed. With assistance to hold and document the position, the distance relative
Fig. 1. Anatomic illustration of line markings along the axis of the tibia (A) and lateral column of the calcaneus (B). The entry point is located at the intersection of these 2 lines.
Fig. 3. Reamer and tissue protector positioned to demonstrate the close proximity of the neurovascular bundle.
Fig. 2. Guidewire in situ demonstrating prereamed proximity to the neurovascular bundle.
T. Knight et al. / The Journal of Foot & Ankle Surgery 53 (2014) 687–691
Fig. 4. Dissection of the heel pad in an unreamed cadaveric specimen with forceps identifying the lateral neurovascular bundle.
to the nail entry was measured and confirmed by the senior authors (N.S. and P.R.). The position of the dissected neurovascular bundle was noted during dissection, and dissection was performed to identify the structures while not freeing them more than necessary for identification and measurement. Visual inspection of the structures to identify mechanical injury and the distance from the entry point were used as markers of damage or the potential thereof.
Results All the nails had correctly penetrated the plantar lateral aspect of the body of the calcaneus. All the nails were also correctly situated lateral to the lateral plantar neurovascular bundle. The closest was lying 3.5 mm from the edge of the inserted nail (Table). No neurovascular bundle had been damaged. Moorjani et al (6) reported that the point of safety for insertion of a nail lies lateral to the midline of the heel such “that the distance from the center of the nail to the lateral plantar nerve and artery is greater than 10 mm.” For a 13-mm nail, a safe zone of 10 mm would constitute an additional radius of 3.5 mm from the edge of the nail. No neurovascular structure in the present study crossed this boundary, although one lay on this border. This is represented by the outer dashed line in Fig. 5.
Table Distance from edge of AO hindfoot arthrodesis nail or reamer to lateral neurovascular bundle (13-mm reamer) Cadaveric Specimen No.
Distance (mm) From Edge of AO HAN
1 2 3 4 5 6 7 Mean (mm) Range (mm) 95% CI
7.5 5.5 3.5 6.5 8 7.5 7 6.5 3.5 to 8 5.9 to 7.1
Abbreviations: CI, confidence interval; HAN, hindfoot (tibiotalocalcaneal) arthrodesis nailing.
689
Fig. 5. Scaled representation of observed nail entry position with respect to surrounding anatomy. The 13-mm radius nail edge was marked with the 10-mm “safe zone.” The anatomic line diagram was enlarged from the whole foot (Fig. 6). A, anterior; L, lateral; M, medial; P, posterior.
We measured the distance from the edge of the nail to the lateral plantar neurovascular bundle. A 10-mm window, as previously described by Moorjani et al (6), would consist of the radius of the 9-mm reamer, 4.5 mm, and a safe zone of 5.5 mm. In recognition of the larger reamer used in our study, 13 mm, a safe “buffer” zone of 5.5 mm was considered for completeness. With this revised definition, 1 neurovascular bundle was within this threatened zone (3.5 mm) but had not been injured and another lay on the boundary (5.5 mm). A worst case interpretation of these findings would place 2 of 7 (29%) at risk of injury. Discussion Combined arthrodesis of the hind foot, ankle, and subtalar joints using a curved intramedullary device has become established and increasingly popular for the management of complex cases. A previously described “safe window” (6) has been incorporated into modern nail design to avoid damage to important neurovascular structures. The posterior tibial artery splits into 2 terminal branches, the medial and lateral plantar arteries just posterior to the medial malleolus. Originating at the medial malleolus, the lateral plantar artery passes longitudinally, crossing the long flexor tendons and flexor accessorius to lie close to the base of the fifth metatarsal. At that point, a medial curvature develops, and the artery swings across the foot to form the plantar arch, traversing the metatarsal bases. This establishes the cascade of the metatarsal plantar and digital arteries. The medial plantar artery, a smaller structure, again arising from behind the medial malleolus, takes a different course. It first drops beneath the abductor hallucis and then emerges between the adductor hallucis and flexor digitorum brevis to reach the first metatarsal base. The artery divides into smaller branches that anastomose with the first 3 plantar metatarsal arteries. Thus, the arteries not only derive their name from their relative course, but also from the distribution of the forefoot they supply. In addition to the anastomosis from the terminal medial and lateral plantar artery branches (10), perforating vessels penetrate the metatarsal spaces to communicate with the dorsal blood supply. Injury to 1 or other artery will
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lead to a reduced blood supply to the corresponding area of the foot. Thus, injury to the lateral artery, the dominant supplying artery, could be considered the worse injury of the 2. Anastomosis between the 2 plantar arteries and in the dorsal system has been well described. The corresponding nerves of the plantar arteries run closely. In a similar fashion to the arterial supply, the tibial nerve splits as it passes behind the medial malleolus. In contrast, however, the medial nerve is larger than the lateral nerve. Traveling on the lateral side of the vessel, the medial nerve branches, providing cutaneous innervation to the medial 3.5 toes and sole. It also innervates the adductor hallucis, flexor digitorum brevis, flexor hallucis brevis, and the first lumbrical. The lateral plantar nerve, lying medial to the vessel, traverses the hind foot with the vessel. On reaching the lateral side of the foot, it throws off branches to supply the lateral 1.5 toes and the remaining intrinsic muscles. The combined sensory and motor supply of these nerves make them significant in their deficit. Not only would an injury lead to a corresponding numbness of the foot, but also to a threat of injury, combined with weakness of the intrinsic muscles. In addition, a lateral plantar nerve injury is likely to be associated with a vascular deficit. In a salvage procedure for a deformed and potentially vascularity impaired foot, this will have a significant detrimental effect on the outcome. Snow et al (11) described the sequelae of a single case of iatrogenic injury to the lateral planter nerve as hypoesthesia along the lateral two thirds of the foot, with motor weakness of toe flexion in the third, fourth, and fifth toes and associated pain on walking. Stephenson et al (12) described a technique for straight nail insertion. The entry point was the intersection of the middle and anterior thirds of the heel pad, with a line drawn from the second toe to the heel pad. They reported that of 22 patients, 1 developed lateral plantar nerve paresthesia and 3, calcaneal nerve paresthesia. Flock et al (13) described cadaveric dissection of the heel pad, although no entry incisions were made. They illustrated the vulnerability of the nerve to the abductor digiti minimi, with an estimated rate of injury of 42%. They postulated this as a cause of postoperative neurogenic heel pain. They recommended remaining posterior to the mid-tibial line. Because the lateral plantar nerve and artery have a fairly longitudinal course, anatomic variations, both congenital and acquired, in the sagittal plane will be less significant, because entry point placement in this plane will not threaten the neurovascular bundle to the same extent (6). Pochatko et al (14) performed retrograde straight rodding on 6 cadaveric specimens with subsequent dissection. They concluded that the optimal insertion site was at the junction of the sustentaculum tali and the body of the calcaneus. These earlier studies considered the structures at risk from this procedure (1,12–15); however, the early nail designs were straight nails. Thus, the structures at risk will be subtly different. Subsequent to the work by Moorjani et al (6), the popularity of curved nails, which take a more lateral course through the calcaneus, has increased. No data on the rates of iatrogenic neurovascular injury nail insertion have been published but much speculation has been reported on the potential for injury. A recent large multicenter trial of the outcomes using this nail did not expand on this issue (16). This reflects the current concern of expanding the use of an implant that threatens to put structures at risk by its insertion rather than according to high rates of injury. These concerns have been addressed by the new design changes. The present study sought to more closely examine the structures at risk by making an entry into the fat pad and following this with dissection. This had the inherent advantage that the position of the structures at risk could not be augmented by the dissection. The disadvantage of this approach was the disruption to the anatomic planes that ensued from passing 13-mm instrumentation through small incisions. Thus, it was not possible to comment on smaller structures such as the nerve to the abductor digiti minimi.
The threatened structures can be protected by careful introduction of the reaming protector using blunt dissection and assisted placement. The potential damage from a reamer can be avoided by the methods described. Injury would therefore be most likely result from the initial guidewire placement, a focus of previous studies. In the 1 case in which the nail edge was 3.5 mm from the neurovascular bundle, it was 10 mm (13 mm B nail) from the center of the nail and the initial guidewire entry point. This would have been on the border of the previously described, arbitrary, “safe window,” as illustrated in Fig. 5. In a small anatomic region such as the foot, a 2-cm diameter zone of safe entry can be considered relatively large. Study Limitations The present study was conducted on a small sample group and did not seek to explore any anatomic variations. Arthritic degenerative changes were not searched for in the specimens chosen, and the specimens were generally in good condition. Surgeon experience is likely to have an effect on the reproducibility and accuracy of the entry point. However, our study has endeavored to show the vulnerability of the neurovascular bundle to injury and the improvements made by the design changes regarding the proximity of the neurovascular bundle when following the manufacturer’s surgical technique. We did not explore variations in the described technique. In conclusion, it has been demonstrated that the area of safety must lie lateral to the midline of the heel (6), illustrated in the anatomic diagram shown in Fig. 6. Curved nails have been designed to lateralize the entry point and thus avoid neurovascular injury. Our study sought to confirm the practical reproducibility of entering a curved nail, which is a more complex procedural technique, and avoiding the lateral plantar nerve. Our findings have confirmed this. The present study has shown that slightly less than one third will remain in the zone of danger if careful soft tissue protection has not
Fig. 6. The anatomy of the sole of the foot. The square (shown in Fig. 5) illustrates the field of view for the operative dissections (shown in Figs. 3 to 5). (This image was redrawn from Gray’s Anatomy, edited by Salmons S. Williams P, Plantar arteries of the foot, pp. 15721574, Copyright Elsevier 1995 [Fig. 8.386] [8] and Gray’s Anatomy, edited by Berry LBM. Williams P, Plantar nerves of the foot, pp. 1285-1286, Copyright Elsevier 1980 [Fig. 10.151b] [9].)
T. Knight et al. / The Journal of Foot & Ankle Surgery 53 (2014) 687–691
been observed during reaming. The potential, however, for injury from guidewire positioning has been greatly reduced. Thus, this nail design has achieved a goal of allowing multiple entries of the guidewire within a safe field, with little risk of neurovascular injury. Nail designs with a lateral entry point still place the neurovascular bundle at risk but to a much lesser extent. The curved HAN is one of many designs using this entry point. References 1. Casadei R, Ruggieri P, Giuseppe T, Biagini R, Mercuri M. Ankle resection arthrodesis in patients with bone tumors. Foot Ankle Int 15:242–249, 1994. 2. Pelton K, Hofer JK, Thordarson DB. Tibiotalocalcaneal arthrodesis using a dynamically locked retrograde intramedullary nail. Foot Ankle Int 27:759–763, 2006. 3. Myerson MS, Quill G. Ankle arthrodesis: a comparison of an arthroscopic and an open method of treatment. Clin Orthop Relat Res 268:84–95, 1991. 4. Bluman EM, Chiodo CP. Tibiotalar arthrodesis. Semin Arthrop 21:240–246, 2010. 5. Budnar VM, Hepple S, Harries WG, Livingstone JA, Winson I. Tibiotalocalcaneal arthrodesis with a curved, interlocking, intramedullary nail. Foot Ankle Int 31:1085–1092, 2010. 6. Moorjani N, Buckingham R, Winson I. Optimal insertion site for intramedullary nails during combined ankle and subtalar arthrodesis. Foot Ankle Surg 4:21–26, 1998.
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7. Synthes. Expert hindfoot arthrodesis nail. Cited December 10, 2011. Available at: http:// www.synthes.com/sites/intl/Documents/036.000.980.pdf. Accessed December 10, 2011. 8. Williams P. Plantar arteries of the foot. In: Gray’s Anatomy, pp. 1572–1574, edited by S Salmons, Churchill Livingstone, Edinburgh, 1995. 9. Williams P. Plantar nerves of the foot. In: Gray’s Anatomy, pp. 1285–1286, edited by LBM Berry, S Standring, Churchill Livingstone, Edinburgh, 1995. 10. Williams PWR, Warwick R, Dyson M, Bannister LH. Angiology and neurology. In: Gray’s Anatomy, Churchill Livingstone, Edinburgh, 1980, pp. 734–736. 1113– 1114. 11. Snow DM, Reading J, Dalal R. Lateral planter nerve injury following steroid injection for planter fasciitis. Br J Sports Med 39:e41, 2005. 12. Stephenson KA, Kile TA, Graves SC. Estimating the insertion site during retrograde intramedullary tibiotalocalcaneal arthrodesis. Foot Ankle Int 17:781–782, 1996. 13. Flock TJ, Ishikawa S, Hecht PJ, Wapner KL. Heel anatomy for retrograde tibiotalocalcaneal roddings: a roentgenographic and anatomic analysis. Foot Ankle Int 18:233–235, 1997. 14. Pochatko DJ, Smith JW, Phillips RA, Prince BD, Hedrick MR. Anatomic structures at risk: combined subtalar and ankle arthrodesis with a retrograde intramedullary rod. Foot Ankle Int 16:542–547, 1995. 15. Moore TJ, Prince R, Pochatko D, Smith JW, Fleming S. Retrograde intramedullary nailing for ankle arthrodesis. Foot Ankle Int 16:433–436, 1995. 16. Rammelt S, Pyrc J, Agren PH, Hartsock LA, Cronier P, Friscia DA, Hansen ST, Schaser K, Ljungqvist J, Sands AK. Tibiotalocalcaneal fusion using the hindfoot arthrodesis nail: a multicenter study. Foot Ankle Int 34:1245–1255, 2013.
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Anatomic Structures at Risk: Curved Hindfoot Arthrodesis NaildA Cadaveric Approach Timothy Knight, MBBS 1, Peter Rosenfeld, MBBS, FRCS (Orth) 2, Ioan Tudur Jones, MB, BCh, FRCS (Orth) 3, Callum Clark, MB, BCh, FRCS (Orth) 4, Nick Savva, MBBS, FRCS (Orth) 5 1
Specialist Registrar, West Midlands Deanery, Robert Jones and Agnes Hunt Orthopaedic Hospital, Gobowen, Oswestry, Shropshire, United Kingdom Orthopaedic Consultant Surgeon, St Mary’s Hospital, London, United Kingdom Orthopaedic Consultant Surgeon, St Thomas’ Hospital, London, United Kingdom 4 Orthopaedic Consultant Surgeon, Heatherwood and Wexham Park Hospitals, Berkshire, United Kingdom 5 Orthopaedic Consultant Surgeon, Dorset County Hospital, Dorset, United Kingdom 2 3
a r t i c l e i n f o
a b s t r a c t
Level of Clinical Evidence: 5
Retrograde intramedullary nailing of the hindfoot and ankle is an established procedure for salvage of severe foot and ankle deformity, arthritis, tumor, and instability. In the present study, retrograde hindfoot (tibiotalocalcaneal) arthrodesis nailing was performed using a standardized technique on 7 cadaver specimens by trained senior surgeons. The specimens were then dissected to determine the distance of the subcalcaneal structures at risk from the insertion point of the nail. The findings showed that the distance of the lateral neurovascular bundle from the edge of the nail was 6.5 (range 3.5 to 8, 95% confidence interval 5.9 to 7.1) mm. No neurovascular bundle was compromised, and all were within a previously described “safe window.” Ó 2014 by the American College of Foot and Ankle Surgeons. All rights reserved.
Keywords: ankle arthritis cadaver HAN intramedullary nail tibiotalocalcaneal fusion
Tibiotalocalcaneal arthrodesis is an established treatment option for arthritis of the ankle and subtalar joints. It has been used, but has not been limited to, as treatment of talar avascular necrosis, as salvage treatment in complex trauma, and in the presence of instability or severe deformity, such as from tumor resection (1). It has also been used in failed ankle joint replacement, failed union, and pseudoarthrosis (2–5). Intramedullary nailing has the benefit of not creating the bulky construct seen with plating and avoids the excessive soft tissue dissection associated with wound complications. The concept is not new; however, the fixation design and fixation entry point have been altered in an attempt to achieve maximal fixation and offer protection to the neurovascular structures. The most significant recent changes have been in the curvature of the nail design and claims of improved safety. Moorjani et al (6) undertook a cadaveric study to ascertain the relative anatomic dangers of different theoretical nail entry points of arthrodesis nails with varying curvature designs to the respective neurovascular structures. In their cadaveric study, the distance from
Financial Disclosure: None reported. Conflict of Interest: None reported. Address correspondence to: Timothy Knight, MBBS, Robert Jones and Agnes Hunt Orthopaedic Hospital, Gobowen, Oswestry, Shropshire SY7 10AG United Kingdom. E-mail address: [email protected] (T. Knight).
the center of the nail entry to the respective structures was measured. A distance of less than 10 mm was deemed unsafe when working with a reamer 9 mm in diameter. In all cases, the distance from the medial plantar nerve and artery was greater than 10 mm; however, they identified the lateral plantar nerve and artery as being at the greatest risk. In 1 case, the pin had passed through the lateral plantar artery; in another, the pin and lateral neurovascular bundle were touching; and in a third case, the pin had been inadvertently placed on the medial side of the lateral neurovascular structure, illustrating the potential for injury. The current, newer intramedullary nail designs now require validation and evidence to support their claims of protection of the neurovascular structures in light of the design changes. The structural strength of the nail construct is achieved by driving a bony tunnel of maximal fixation through the calcaneum. The plantar surface of the calcaneum has a sagittal ridge traversing lateral to the mid-axis of the calcaneal body. A curved nail design, therefore, will accommodate an additional valgus nail angulation of 8 , requiring 12 of nail curvature to accommodate a relatively lateral plantar entry point, with a residual valgus alignment of 3 to 5 after insertion. A plantar-lateral entry point will be advantageous, because it is further from the course of the closest neurovascular bundle and the lateral plantar nerve and artery. As used by the AO Foundation, the hindfoot (tibiotalocalcaneal) arthrodesis nailing (HAN), marketed by DuPuy Synthes (Johnson &
1067-2516/$ - see front matter Ó 2014 by the American College of Foot and Ankle Surgeons. All rights reserved. http://dx.doi.org/10.1053/j.jfas.2014.06.005
688
T. Knight et al. / The Journal of Foot & Ankle Surgery 53 (2014) 687–691
Johnson, West Chester, PA) is a retrograde nail with multiple fixation methods (7). The entry of the nail is through the plantar lateral aspect of the body of the calcaneum. Satisfactory retrograde nail results were described with a plantar approach almost 2 decades ago; however, the nail design has been refined in materials, instrumentation, and principles of biology. Previous work has defined a “window of safety” lateral to the midline (6) and supported the design of nails with curvature. The present study examined the anatomic location of the plantar lateral neurovascular bundle to the nail entry point to evaluate the purported benefits of protecting critical neurovascular structures (7). Materials and Methods Using a standard set of instrumentation, 7 experienced orthopedic surgeons familiar with the surgical technique followed a standardized procedure (7) to insert a guidewire for cannulated intramedullary HAN through the heel pad of unembalmed cadaveric lower limb specimens. We elected to examine nail placement of the curved HAN system in 7 below the knee cadavers provided for an industry-sponsored training exercise. Demographic information for the cadaveric specimens was not available; however, we did not believe this would affect the goal of our examination. Live imageintensifier roentgenographic views were available and were used. The equipment was prepared and assembled by trained company representatives. Before performing the technique, the operating team was reminded of the standardized steps for the nail insertion. A fibula osteotomy was performed and, subsequently, the ankle and subtalar joint surfaces were prepared. The entry point for the heel pad was achieved in a training-simulated “real theater” environment. Palpation of the heel pad and surface markings were used to estimate entry. The palpable bony ridge on the plantar lateral aspect of the calcaneum indicates the lateral column of the calcaneum. In accordance with the operational technique guide, which includes illustrations, published by Synthes, “the entry point is in line with the tibial canal and the lateral column of the calcaneus, using a C-arm, identify the center of the tibial canal by placing a 3.2-mm guidewire along the canal. Draw a line (Fig. 1A). Palpate the centre of the lateral column of the calcaneus. Draw a line (Fig. 1B). The entry point is located at the intersection of these two lines, the incision should be in line with the longitudinal axis of the foot” (7). The power-driven guidewire, targeted toward the center of the talus, was advanced. The position was confirmed using live image-intensifier imaging and direct vision. Once a satisfactory guidewire position had been achieved, the wire was advanced into the distal tibia, following the central axis of the tibia. In most cases, this was followed sequentially by measuring, reaming, and introduction of an intramedullary nail using
standardized equipment. As a training session, some surgeons chose not to advance a nail; in these cases, the heel pad was later exposed (Fig. 2) and a reamer placed in situ (Fig. 3) for measurement. A 13-mm protection sleeve was used with the 13-mm cannulated reamer. Subsequent to satisfactory completion of the procedure, the cadaveric feet were examined by the senior authors (N.S. and P.R.). The surgical wounds were extended, and the dissection was made extensile (Fig. 4). The lateral neurovascular bundle was identified between the first muscle layer (abductor hallucis, abductor digiti minimi, and flexor digitorum brevis) and the second muscle layer (flexor digitorum longus, flexor hallucis longus, flexor accessorius, and the lumbricals). Minimizing the damage to the adjacent structural attachments to the neurovascular bundle, it was carefully dissected and exposed. With assistance to hold and document the position, the distance relative
Fig. 1. Anatomic illustration of line markings along the axis of the tibia (A) and lateral column of the calcaneus (B). The entry point is located at the intersection of these 2 lines.
Fig. 3. Reamer and tissue protector positioned to demonstrate the close proximity of the neurovascular bundle.
Fig. 2. Guidewire in situ demonstrating prereamed proximity to the neurovascular bundle.
T. Knight et al. / The Journal of Foot & Ankle Surgery 53 (2014) 687–691
Fig. 4. Dissection of the heel pad in an unreamed cadaveric specimen with forceps identifying the lateral neurovascular bundle.
to the nail entry was measured and confirmed by the senior authors (N.S. and P.R.). The position of the dissected neurovascular bundle was noted during dissection, and dissection was performed to identify the structures while not freeing them more than necessary for identification and measurement. Visual inspection of the structures to identify mechanical injury and the distance from the entry point were used as markers of damage or the potential thereof.
Results All the nails had correctly penetrated the plantar lateral aspect of the body of the calcaneus. All the nails were also correctly situated lateral to the lateral plantar neurovascular bundle. The closest was lying 3.5 mm from the edge of the inserted nail (Table). No neurovascular bundle had been damaged. Moorjani et al (6) reported that the point of safety for insertion of a nail lies lateral to the midline of the heel such “that the distance from the center of the nail to the lateral plantar nerve and artery is greater than 10 mm.” For a 13-mm nail, a safe zone of 10 mm would constitute an additional radius of 3.5 mm from the edge of the nail. No neurovascular structure in the present study crossed this boundary, although one lay on this border. This is represented by the outer dashed line in Fig. 5.
Table Distance from edge of AO hindfoot arthrodesis nail or reamer to lateral neurovascular bundle (13-mm reamer) Cadaveric Specimen No.
Distance (mm) From Edge of AO HAN
1 2 3 4 5 6 7 Mean (mm) Range (mm) 95% CI
7.5 5.5 3.5 6.5 8 7.5 7 6.5 3.5 to 8 5.9 to 7.1
Abbreviations: CI, confidence interval; HAN, hindfoot (tibiotalocalcaneal) arthrodesis nailing.
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Fig. 5. Scaled representation of observed nail entry position with respect to surrounding anatomy. The 13-mm radius nail edge was marked with the 10-mm “safe zone.” The anatomic line diagram was enlarged from the whole foot (Fig. 6). A, anterior; L, lateral; M, medial; P, posterior.
We measured the distance from the edge of the nail to the lateral plantar neurovascular bundle. A 10-mm window, as previously described by Moorjani et al (6), would consist of the radius of the 9-mm reamer, 4.5 mm, and a safe zone of 5.5 mm. In recognition of the larger reamer used in our study, 13 mm, a safe “buffer” zone of 5.5 mm was considered for completeness. With this revised definition, 1 neurovascular bundle was within this threatened zone (3.5 mm) but had not been injured and another lay on the boundary (5.5 mm). A worst case interpretation of these findings would place 2 of 7 (29%) at risk of injury. Discussion Combined arthrodesis of the hind foot, ankle, and subtalar joints using a curved intramedullary device has become established and increasingly popular for the management of complex cases. A previously described “safe window” (6) has been incorporated into modern nail design to avoid damage to important neurovascular structures. The posterior tibial artery splits into 2 terminal branches, the medial and lateral plantar arteries just posterior to the medial malleolus. Originating at the medial malleolus, the lateral plantar artery passes longitudinally, crossing the long flexor tendons and flexor accessorius to lie close to the base of the fifth metatarsal. At that point, a medial curvature develops, and the artery swings across the foot to form the plantar arch, traversing the metatarsal bases. This establishes the cascade of the metatarsal plantar and digital arteries. The medial plantar artery, a smaller structure, again arising from behind the medial malleolus, takes a different course. It first drops beneath the abductor hallucis and then emerges between the adductor hallucis and flexor digitorum brevis to reach the first metatarsal base. The artery divides into smaller branches that anastomose with the first 3 plantar metatarsal arteries. Thus, the arteries not only derive their name from their relative course, but also from the distribution of the forefoot they supply. In addition to the anastomosis from the terminal medial and lateral plantar artery branches (10), perforating vessels penetrate the metatarsal spaces to communicate with the dorsal blood supply. Injury to 1 or other artery will
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lead to a reduced blood supply to the corresponding area of the foot. Thus, injury to the lateral artery, the dominant supplying artery, could be considered the worse injury of the 2. Anastomosis between the 2 plantar arteries and in the dorsal system has been well described. The corresponding nerves of the plantar arteries run closely. In a similar fashion to the arterial supply, the tibial nerve splits as it passes behind the medial malleolus. In contrast, however, the medial nerve is larger than the lateral nerve. Traveling on the lateral side of the vessel, the medial nerve branches, providing cutaneous innervation to the medial 3.5 toes and sole. It also innervates the adductor hallucis, flexor digitorum brevis, flexor hallucis brevis, and the first lumbrical. The lateral plantar nerve, lying medial to the vessel, traverses the hind foot with the vessel. On reaching the lateral side of the foot, it throws off branches to supply the lateral 1.5 toes and the remaining intrinsic muscles. The combined sensory and motor supply of these nerves make them significant in their deficit. Not only would an injury lead to a corresponding numbness of the foot, but also to a threat of injury, combined with weakness of the intrinsic muscles. In addition, a lateral plantar nerve injury is likely to be associated with a vascular deficit. In a salvage procedure for a deformed and potentially vascularity impaired foot, this will have a significant detrimental effect on the outcome. Snow et al (11) described the sequelae of a single case of iatrogenic injury to the lateral planter nerve as hypoesthesia along the lateral two thirds of the foot, with motor weakness of toe flexion in the third, fourth, and fifth toes and associated pain on walking. Stephenson et al (12) described a technique for straight nail insertion. The entry point was the intersection of the middle and anterior thirds of the heel pad, with a line drawn from the second toe to the heel pad. They reported that of 22 patients, 1 developed lateral plantar nerve paresthesia and 3, calcaneal nerve paresthesia. Flock et al (13) described cadaveric dissection of the heel pad, although no entry incisions were made. They illustrated the vulnerability of the nerve to the abductor digiti minimi, with an estimated rate of injury of 42%. They postulated this as a cause of postoperative neurogenic heel pain. They recommended remaining posterior to the mid-tibial line. Because the lateral plantar nerve and artery have a fairly longitudinal course, anatomic variations, both congenital and acquired, in the sagittal plane will be less significant, because entry point placement in this plane will not threaten the neurovascular bundle to the same extent (6). Pochatko et al (14) performed retrograde straight rodding on 6 cadaveric specimens with subsequent dissection. They concluded that the optimal insertion site was at the junction of the sustentaculum tali and the body of the calcaneus. These earlier studies considered the structures at risk from this procedure (1,12–15); however, the early nail designs were straight nails. Thus, the structures at risk will be subtly different. Subsequent to the work by Moorjani et al (6), the popularity of curved nails, which take a more lateral course through the calcaneus, has increased. No data on the rates of iatrogenic neurovascular injury nail insertion have been published but much speculation has been reported on the potential for injury. A recent large multicenter trial of the outcomes using this nail did not expand on this issue (16). This reflects the current concern of expanding the use of an implant that threatens to put structures at risk by its insertion rather than according to high rates of injury. These concerns have been addressed by the new design changes. The present study sought to more closely examine the structures at risk by making an entry into the fat pad and following this with dissection. This had the inherent advantage that the position of the structures at risk could not be augmented by the dissection. The disadvantage of this approach was the disruption to the anatomic planes that ensued from passing 13-mm instrumentation through small incisions. Thus, it was not possible to comment on smaller structures such as the nerve to the abductor digiti minimi.
The threatened structures can be protected by careful introduction of the reaming protector using blunt dissection and assisted placement. The potential damage from a reamer can be avoided by the methods described. Injury would therefore be most likely result from the initial guidewire placement, a focus of previous studies. In the 1 case in which the nail edge was 3.5 mm from the neurovascular bundle, it was 10 mm (13 mm B nail) from the center of the nail and the initial guidewire entry point. This would have been on the border of the previously described, arbitrary, “safe window,” as illustrated in Fig. 5. In a small anatomic region such as the foot, a 2-cm diameter zone of safe entry can be considered relatively large. Study Limitations The present study was conducted on a small sample group and did not seek to explore any anatomic variations. Arthritic degenerative changes were not searched for in the specimens chosen, and the specimens were generally in good condition. Surgeon experience is likely to have an effect on the reproducibility and accuracy of the entry point. However, our study has endeavored to show the vulnerability of the neurovascular bundle to injury and the improvements made by the design changes regarding the proximity of the neurovascular bundle when following the manufacturer’s surgical technique. We did not explore variations in the described technique. In conclusion, it has been demonstrated that the area of safety must lie lateral to the midline of the heel (6), illustrated in the anatomic diagram shown in Fig. 6. Curved nails have been designed to lateralize the entry point and thus avoid neurovascular injury. Our study sought to confirm the practical reproducibility of entering a curved nail, which is a more complex procedural technique, and avoiding the lateral plantar nerve. Our findings have confirmed this. The present study has shown that slightly less than one third will remain in the zone of danger if careful soft tissue protection has not
Fig. 6. The anatomy of the sole of the foot. The square (shown in Fig. 5) illustrates the field of view for the operative dissections (shown in Figs. 3 to 5). (This image was redrawn from Gray’s Anatomy, edited by Salmons S. Williams P, Plantar arteries of the foot, pp. 15721574, Copyright Elsevier 1995 [Fig. 8.386] [8] and Gray’s Anatomy, edited by Berry LBM. Williams P, Plantar nerves of the foot, pp. 1285-1286, Copyright Elsevier 1980 [Fig. 10.151b] [9].)
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been observed during reaming. The potential, however, for injury from guidewire positioning has been greatly reduced. Thus, this nail design has achieved a goal of allowing multiple entries of the guidewire within a safe field, with little risk of neurovascular injury. Nail designs with a lateral entry point still place the neurovascular bundle at risk but to a much lesser extent. The curved HAN is one of many designs using this entry point. References 1. Casadei R, Ruggieri P, Giuseppe T, Biagini R, Mercuri M. Ankle resection arthrodesis in patients with bone tumors. Foot Ankle Int 15:242–249, 1994. 2. Pelton K, Hofer JK, Thordarson DB. Tibiotalocalcaneal arthrodesis using a dynamically locked retrograde intramedullary nail. Foot Ankle Int 27:759–763, 2006. 3. Myerson MS, Quill G. Ankle arthrodesis: a comparison of an arthroscopic and an open method of treatment. Clin Orthop Relat Res 268:84–95, 1991. 4. Bluman EM, Chiodo CP. Tibiotalar arthrodesis. Semin Arthrop 21:240–246, 2010. 5. Budnar VM, Hepple S, Harries WG, Livingstone JA, Winson I. Tibiotalocalcaneal arthrodesis with a curved, interlocking, intramedullary nail. Foot Ankle Int 31:1085–1092, 2010. 6. Moorjani N, Buckingham R, Winson I. Optimal insertion site for intramedullary nails during combined ankle and subtalar arthrodesis. Foot Ankle Surg 4:21–26, 1998.
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7. Synthes. Expert hindfoot arthrodesis nail. Cited December 10, 2011. Available at: http:// www.synthes.com/sites/intl/Documents/036.000.980.pdf. Accessed December 10, 2011. 8. Williams P. Plantar arteries of the foot. In: Gray’s Anatomy, pp. 1572–1574, edited by S Salmons, Churchill Livingstone, Edinburgh, 1995. 9. Williams P. Plantar nerves of the foot. In: Gray’s Anatomy, pp. 1285–1286, edited by LBM Berry, S Standring, Churchill Livingstone, Edinburgh, 1995. 10. Williams PWR, Warwick R, Dyson M, Bannister LH. Angiology and neurology. In: Gray’s Anatomy, Churchill Livingstone, Edinburgh, 1980, pp. 734–736. 1113– 1114. 11. Snow DM, Reading J, Dalal R. Lateral planter nerve injury following steroid injection for planter fasciitis. Br J Sports Med 39:e41, 2005. 12. Stephenson KA, Kile TA, Graves SC. Estimating the insertion site during retrograde intramedullary tibiotalocalcaneal arthrodesis. Foot Ankle Int 17:781–782, 1996. 13. Flock TJ, Ishikawa S, Hecht PJ, Wapner KL. Heel anatomy for retrograde tibiotalocalcaneal roddings: a roentgenographic and anatomic analysis. Foot Ankle Int 18:233–235, 1997. 14. Pochatko DJ, Smith JW, Phillips RA, Prince BD, Hedrick MR. Anatomic structures at risk: combined subtalar and ankle arthrodesis with a retrograde intramedullary rod. Foot Ankle Int 16:542–547, 1995. 15. Moore TJ, Prince R, Pochatko D, Smith JW, Fleming S. Retrograde intramedullary nailing for ankle arthrodesis. Foot Ankle Int 16:433–436, 1995. 16. Rammelt S, Pyrc J, Agren PH, Hartsock LA, Cronier P, Friscia DA, Hansen ST, Schaser K, Ljungqvist J, Sands AK. Tibiotalocalcaneal fusion using the hindfoot arthrodesis nail: a multicenter study. Foot Ankle Int 34:1245–1255, 2013.