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The safety of the posterior ankle arthroscopy in management of posterior ankle impingement: A cadaveric study
The Foot 27 (2016) 4–9
Contents lists available at ScienceDirect
The Foot journal homepage: www.elsevier.com/locate/foot
The safety of the posterior ankle arthroscopy in management of posterior ankle impingement: A cadaveric study T.H. Lui a,∗ , L.K. Chan b a
Department of Orthopaedics and Traumatology, North District Hospital, 9 Po Kin Road, Sheung Shui, NT, Hong Kong SAR, China Institute of Medical and Health Sciences Education and Department of Anatomy, The University of Hong Kong, Li Ka Shing Faculty of Medicine, Hong Kong SAR, China b
h i g h l i g h t s • • • •
Posterior ankle arthroscopy can manage posterior ankle impingement in supine position. Associated intra-articular pathology and anterior ankle impingement can be dealt with without the need of change of patient positioning. Posteromedial portal is just anterior to the posterior tibial tendon and posterolateral portal is just posterior to the peroneal tendons. The coaxial portals are not suitable for treating the Achilles tendon pathology especially the insertional problem.
a r t i c l e
i n f o
Article history: Received 20 June 2015 Received in revised form 3 September 2015 Accepted 4 September 2015 Keywords: Posterior ankle impingement Anterior ankle impingement Os trigonum Ankle arthroscopy Endoscopy
a b s t r a c t Background: Arthroscopic management of the posterior ankle impingement with the patient in supine position has the advantage of dealing with anterior ankle pathology at the same time without the need to change position of the patient. This study aims at evaluation of the safety of portal establishment and instrumentation of this technique. Methods: Sixteen fresh-frozen cadaver specimens were used. The relationships of the posteromedial and posterolateral portals to the adjacent tendons and nerves and the relationship of the coaxial portal tract with the posterior ankle capsule and the flexor hallucis longus tendon were studied. Result: Angle 1 between the intermalleolar line and the posterior ankle coaxial portal tract averaged 1◦ (−10◦ to 22◦ ). Angle 2 between the intermalleolar line and the metal rod where the neurovascular bundle started to move averaged 19◦ (10◦ to 30◦ ). Angle 3 between the intermalleolar line and the metal rod where it reached the lateral border of the Achilles tendon was larger than angle 2 in all specimens. The angle of safety ( s ) averaged 18◦ (−1◦ to 26◦ ). Conclusions: Injury to the tendon, nerves or vessels is possible during establishment of the portals and resection of the os trigonum. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction Posterior ankle impingement is a common cause of chronic ankle pain and results from compression of an os trigonum, prominent Stieda’s process, the posterior tibiotalar ligament or the intermalleolar ligament during ankle plantarflexion [1–6]. Traditional surgical treatment of posterior ankle impingement using posteromedial or posterolateral arthrotomy has been shown to be effective; however, wound problems and substantial recovery periods have been reported [5]. Arthroscopic treatment
∗ Corresponding author. Tel.: +86 852 26837588. E-mail addresses: [email protected] (T.H. Lui), [email protected] (L.K. Chan). http://dx.doi.org/10.1016/j.foot.2015.09.004 0958-2592/© 2015 Elsevier Ltd. All rights reserved.
through the posteromedial and posterolateral portals at either side of the Achilles tendon with the patient in prone position has gained popularity in recent years [5–9]. It has been shown to be safe and effective in treating posterior ankle impingement with less tissue disruption, less symptomatic scar formation and speedier recovery [5,10]. However, in the rare cases when anterior ankle pathologies e.g. anterior ankle impingement or osteochondral lesion coexist with posterior ankle impingement, combined anterior and posterior arthroscopic approaches are needed on the same patient [11]. This requires either change of patient position; posterior ankle endoscopy with the patient in prone position followed by anterior ankle arthroscopy with the knee flexed [12,13] or combined procedures with the patient in the prone position, knee flexed and ankle distracted [14]. These approaches have problem of
T.H. Lui, L.K. Chan / The Foot 27 (2016) 4–9
intra-operative contamination, prolonged operating time and confusing arthroscopic orientation [12–14]. Lui has described a technique of treating posterior ankle impingement with coaxial posterior ankle portals [15]. This allows treatment of both anterior ankle and posterior ankle pathologies at the same time with the patient in the supine position [15]. The posteromedial portal is anterior to the posterior tibial tendon (PTT) and the posterolateral portal is behind the peroneal tendons. The portal tract is at the posterior recess of the ankle joint. In order to deal with the pathologies associated with posterior ankle impingement which are extra-articular, posterior capsulotomy is needed. After capsular release is completed, the arthroscopic instruments can go extra-artciularly to deal with the bony and soft tissue pathologies of posterior ankle impingement. The author has recommended that the instrument through the posteromedial portal should go extra-articularly at the lateral side of the FHL tendon to protect the posterior tibial neurovascular bundle. In this study, the safety of this procedure including establishment of the portals and instrumentation was evaluated.
2. Methods Sixteen fresh-frozen cadaver specimens in 8 cadaver bodies were used for this study. The average age of succumb was 71.5 year old (59–88). None of the cadavers had deformity, trauma or any surgery of their foot and ankle regions. The posteromedial portal was made by a stab wound just posterior to the medial malleolus at the ankle level. A metal rod was inserted and entered the posterior ankle recess and exited posterior to the peroneal tendons. The posterolateral portal was then made at the exit point of the rod [15,16]. The rod represented the coaxial posterior ankle portal tract. The medial and lateral malleolar tips were marked by needles. The intermalleolar line was projected to the sole and an incision represent the line was made and stained with methylene blue. The angle between the intermalleolar line and the posterior ankle coaxial portal tract ( 1 ) was measured (Fig. 1). The skin of the lateral ankle was removed and the relationships of the posterolateral portal to the sural nerve, peroneal tendons and peroneal tendon sheath
5
were studied (Fig. 2). The medial skin and the upper portion of the tarsal tunnel retinaculum were removed. The relationship of the posteromedial portal to the PTT was studied. The tibial neurovascular bundle was retracted posteriorly to expose the posterior ankle. The rod was examined whether it was intra-capsular and deep to the FHL tendon. Posterior ankle capsulotomy was done. The rod was retrieved so that the tip was in the retrocalcaneal space and deep to the FHL tendon (Fig. 3). The rod was then tilted posteriorly and stopped once the neurovascular bundle was noted to move. The angle 2 between the rod and the intermalleolar line was then recorded. The rod was tilted further posterior until the lateral border of the Achilles tendon was reached. The angle 3 angle between the rod and the intermalleolar axis was also recorded (Fig. 4). The ankle was kept in neutral position during the whole procedure and measurements.
3. Results The results of the cadaveric study were summarized in Table 1. The rod was posterior to the peroneal tendons and the tendons were intact in all specimens. The sural nerve was at average 6 (0–12) mm posterior to the posterolateral portal. The rod (represented the portal tract) was within the peroneal tendon sheath in 15 specimens. The rod is outside the tendon sheath in specimen number 7 and has direct contact with the sural nerve. The rod was inserted straightly into the posterior ankle recess through the posteromedial portal in the first three specimens. The rod passed through the PTT in specimen number 2 and 3. Starting from specimen number 4, the rod was inserted proximally into the PTT sheath between the tendon and the distal tibia (Fig. 5). The rod was then slide distally to the ankle joint level deep to the PTT. The PTT was intact in the subsequent specimens. The rod was intra-capsular in 15 specimens and extra-capsular in one specimen. The rod was deep to the FHL tendons in all specimens. Angle 1 ranged from −10◦ to 22◦ and averaged 1◦ . Angle 2 ranged from 10◦ to 30◦ and averaged 19◦ . Angle 3 was larger than angle 2 in all specimens. It ranged from 16◦ to 45◦ and averaged 31◦ . The angle of safety ( s ) was calculated by subtracting 1 from
Fig. 1. The metal rod passed through the posteromedial and posterolateral portals and represented the coaxial portal tract. The medial and lateral malleolar tips were marked by needles (A). These was joined by a rod (B), followed by a skin incision at the sole and stained with methylene blue (C). This represented the intermalleolar axis. The angle 1 between the intermalleolar line and the posterior ankle coaxial portal tract was measured (D).
6
T.H. Lui, L.K. Chan / The Foot 27 (2016) 4–9
Fig. 2. (A) The distance between the sural nerve (SN) and the posterolateral portal was measured. (B) The portal passed through the peroneal tendon sheath in this case.
Fig. 3. (A) The posteromedial portal was anterior to the PTT (a) in this case. (B) The rod was confirmed to be intra-capsular. (b) flexor digitorum longus tendon; (c) posterior tibial neurovascular bundle. (C) Posterior ankle capsulotomy. (D) The rod can go extra-articularly.
2 . This is the angle that the instrument can be mobilized before impinging the neurovascular bundle. Angle s ranged from −1◦ to 26◦ and averaged 18◦ . 4. Discussion Acevedo et al. [16] conducted a study of the coaxial posterior ankle portals. Results of the anatomic study showed that the posterior tibial nerve and posterior tibial artery were located a mean distance of 5.7 mm and 6.4 mm from the edge of the cannula, respectively. Neither penetration nor contact of nerve or vessel was observed at either posterior portal. They also presented a series of 29 clinical cases. Posterior capsular synovectomy was performed arthroscopically with no detectable complications. Gui et al. [17]
conducted another anatomical study of coaxial posterior ankle portals with the lateral portal just behind the lateral malleolus. They studied the portion of posterior talar dome that can be reached through the coaxial posterior portals. There was no nerve, vessel or tendon injury reported. In contrast to these two reports which focused on the intra-articular procedures, our study focused on the extra-capsular procedure of the posterior ankle. From the results of this study, the surgeon should pay attention on the details of the technique in order to ensure a safe procedure. The procedure starts from establishment of the posteromedial portal. The metal rod was inserted straightly into the posterior ankle recess in the first 3 specimens. Posterior tibial tendon injury was noted in specimen number 2 and 3. This was because the tendon turned forwards around the medial malleolus at this point and
T.H. Lui, L.K. Chan / The Foot 27 (2016) 4–9
7
Fig. 4. The stained sole incision represented the intermalleolar axis. (A) The rod represented the coaxial portal tract and angle 1 was measured. (B) The rod stopped at the point where the neurovascular bundle started to move and angle 2 was measured. (C) The rod touched the lateral border of the Achilles tendon and angle 3 was measured. Table 1 Summary of the findings of the cadaveric study. Specimen number
Laterality
Medial portal
Anterior to PTT
Lateral portal
Trans-PTT
Portal tract
Angle 2
Angle 3
Angle s ( 2 − 1 )
Posterior to peroneals
Trans peroneal tendon sheath
Distance from the sural nerve (mm)
Intracapsular
Deep to FHL tendon
11 12 8 5 2 7 0
+ + + + + + +
+ + + + + + +
−5 −4 6 4 −10 6 22
20 15 20 30 10 24 21
25 35 32 45 16 32 36
25 19 14 26 20 18 −1
+ +
5 −6
20 15
30 33
15 21
3 6 6 5 6 11 9
+ Posterior to the capsule + + + + + + +
+ + + + + + +
−3 −4 4 −7 3 −3 5
15 16 19 17 20 16 22
28 30 30 29 34 29 31
18 20 15 24 17 19 17
1 2 3 4 5 6 7
L R L R L R L
+
+ + + +
+ + + + + + +
8 9
R L
+ +
+ +
+ + + + + + Posterior to the tendon sheath + +
10 11 12 13 14 15 16
R L R L R L R
+ + + + + + +
+ + + + + + +
+ + + + + + +
+ +
Angle 1
6 5
L: left, R: right, PTT: posterior tibial tendon, FHL: flexor hallucis longus, Angle 1 : the angle between the intermalleolar line and the posterior ankle coaxial portal tract, Angle 2 : the angle between the intermalleolar line and the metal rod where the neurovascular bundle started to move, Angle 3 : the angle between the intermalleolar line and the metal rod where it reached the lateral border of the Achilles tendon, Angle s = 2 − 1 and represented the angle that the instrument can be mobilized through the posteromedial portal before impinging on the posterior tibial neurovascular bundle, laterally opened angle is defined to be positive angle and medially opened angle is defined to be negative angle.
the tendon is relatively immobile and stuck to the bone. This complication can be avoided by insertion of the rod proximally between the tendon and the tibia and then turning distally to the ankle level. The tendon is more mobile at the proximal level and the rod can be easily placed anterior to the tendon. Moreover, the ankle can be plantarflexed to reduce the forward turning and tension of the tendon. In case of obese or edematous patient, the landmark of the posterior border of medial malleolus may not be palpated well.
A larger portal wound should be made to identify the PTT before insertion of instrument. The rod was outside the posterior ankle capsule in one specimen (6%). This would not be a problem in vivo as this can be detected arthroscopically. The surgeons can either reinsert the instrument into the posterior ankle recess or start the procedure with the instruments in the extra-articular space. If one chooses to start the procedure extra-articularly, the surgeon should identify the FHL
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T.H. Lui, L.K. Chan / The Foot 27 (2016) 4–9
Fig. 5. In specimen number 3, the PTT was injured by the metal rod (A). In order to avoid this complication, the rod can be inserted proximally between the tendon and tibia (B) and then turning distally to the ankle level (C).
tendon as it is the landmark to the location of the neurovascular bundle. It is recommended only for the surgeons that are familiar with the hindfoot endoscopy. The rod exited posterior to the peroneal tendons in all specimen and remained inside the peroneal tendon sheath in 15 specimens (94%). The sural nerve was safe in these specimens. For the one that the rod is outside the peroneal tendon sheath, the sural nerve is at risk. It is recommended that the posterolateral portal (that was established with an inside-out technique) should be just posterior to the peroneal tendons. This can be achieved by palpation of the peoneal tendons by the tip of the arthroscopic trocar. Moreover, the surgeon should be aware of the problem if the trocar is more than 20◦ from the intermalleolar axis. It has been proposed that the neurovascular bundle will be protected if the instruments stay at the lateral side of the FHL tendon [11,15]. However, although the FHL may prevent direct contact of the instrument with the neurovascular bundle, the rod can push the FHL toward the neurovascular bundle and press it onto the flexor retinaculum causing neurovascular damage. Therefore, we performed limited dissection to preserve the tendons and most of the flexor retinaculum in order to preserve the local soft tissue condition and examine the effect of the motion of instrument through the posteromedial portal on the movement of neurovascular bundle. Because of the minimal dissection, we cannot examine whether the bundle was pushed by the FHL tendon or the rod. This is not a concern whether the bundle was pushed by the tendon or the rod but the common outcome that the bundle would be impinged from inside. We tried to identify the angle of safety in order to allow pre-operative assessment of the risk of neurovascular injury by means of computed tomogram with the ankle in neutral position and intra-operative guidance of the safe zone where the instrument of the posteromedial portal can move before impinging the neurovascular bundle. The safe zone cannot be determined because of the wide range of the angle of safety ( s ) in this study. We recommend resection of the posterior portion of the os trigonum/Steida’s process by arthroscopic burr in the posterolateral portal with the posteromedial portal as the visualization portal. Moreover, angle s of specimen number 7 was −1◦ . This implied that the bundle can be impinged during establishment of the coaxial
portals even the trocar was deep to the FHL tendon if the trocar was pointing too posteriorly. The measurements in this study were made with the ankle in neutral position. Ankle dorsiflexion and plantarflexion can affect the tension of the tendons, flexor retinaculum and neurovascular bundle and the position of the bundle in the tarsal tunnel. These have conflicting effects on the angle of safety. For example, ankle plantarflexion will relax the retinaculum and the neurovascular bundle and may decrease the risk of impingement. However, the FHL tendon will also relax and the role as a restraint to the posterior motion of the instrument will be lost. The coaxial portals are not suitable for treating the Achilles tendon pathology especially the insertional problem. Instrumentation through the posteromedial portal will damage the neurovascular bundle as angle 3 was larger than angle 2 in all specimens. Moreover, extensive soft tissue resection of the retrocalcaneal space is needed before the Achilles tendon can be reached and resection of the posterosuperior calcaneal process is not effective through these portals. Additional portals at the sides of the Achilles tendon for endoscopic calcaneoplasty in supine position [18]. Clinical relevance of this study is to identify the safety precautions of this new technique.
5. Limitations The study was limited by the error of measurement and the small sample size and statistical analysis was not possible. The actual incidence of damage to the posterior tibial neurovascular bundle cannot be evaluated because of the subjective assessment of the motion of the bundle.
6. Conclusions Injury to the tendon, nerves or vessels is possible during establishment of the portals and resection of the os trigonum. The surgeon should pay attention of the every technical detail during
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arthroscopic management of posterior ankle impingement in order to ensure a safe procedure. References [1] Fiorella D, Helms C, Nunley II JA. The MR imaging features of the posterior intermalleolar ligament in patients with posterior impingement syndrome of the ankle. Skeletal Radiol 1999;28:573–6. [2] Giannini S, Buda R, Mosca M, Parma A, Di Caprio F. Posterior ankle impingement. Foot Ankle Int 2013;34:459–65. [3] Golanò P, Mariani PP, Rodríguez-Niedenfuhr M, Mariani PF, Ruano-Gil D. Arthroscopic anatomy of the posterior ankle ligaments. Arthroscopy 2002;18:353–8. [4] Rosenberg ZS, Cheung YY, Beltran J, Sheskier S, Leong M, Jahss M. Posterior intermalleolar ligament of the ankle: normal anatomy and MR imaging features. AJR 1995;165:387–90. [5] Willits K, Sonneveld H, Amendola A, Giffin JR, Griffin S, Fowler PJ. Outcome of posterior ankle arthroscopy for hindfoot impingement. Arthroscopy 2008;24:196–202. [6] Yilmaz C, Eskandari MM. Arthroscopic excision of the talar Stieda’s process. Arthroscopy 2006;22:225.e1–3. [7] Gasparetto F, Collo G, Pisanu G, Villella D, Drocco L, Cerlon R, et al. Posterior ankle and subtalar arthroscopy: indications, technique, and results. Curr Rev Musculoskelet Med 2012;5:164–70. [8] van Dijk CN, Scholten PE, Krips R. A 2-portal endoscopic approach for diagnosis and treatment of posterior ankle pathology. Arthroscopy 2000;16:871–6.
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[9] van Dijk CN, van Dyk GE, Scholten PE, Kort NP. Endoscopic calcaneoplasty. Am J Sports Med 2001;29:185–9. [10] Calder JD, Sexton SA, Pearce CJ. Return to training and playing after posterior ankle arthroscopy for posterior impingement in elite professional soccer. Am J Sports Med 2010;38:120–4. [11] Henderson I, La Valette D. Ankle impingement: combined anterior and posterior impingement syndrome of the ankle. Foot Ankle Int 2004;25: 632–8. [12] Lui TH. Ankle arthroscopy with patient in prone position. Arch Orthop Trauma Surg 2008;128:1283–5. [13] Lui TH, Chan WK, Chan KB. The arthroscopic management of frozen ankle. Arthroscopy 2006;22:283–6. [14] Kim HK, Jeon JY, Dong Q. Ankle arthroscopy in a hanging position combined with hindfoot endoscopy for the treatment of concurrent anterior and posterior impingement syndrome of the ankle. J Foot Ankle Surg 2013;52: 704–9. [15] Lui TH. Arthroscopic treatment of posterior ankle impingement in the supine position using coaxial posterior portals. Foot Ankle Int 2014;35:834–7. [16] Acevedo JI, Busch MT, Ganey TM, Hutton WC, Ogden JA. Coaxial portals for posterior ankle arthroscopy: an anatomical study with clinical correlation on 29 patients. Arthroscopy 2000;16:836–42. [17] Gui JC, Gao F, Wang LM, Gu XJ, Shen HQ, Yu Z, et al. Anatomical study about the posterior coaxial portals via posterior tibial tendon sheath for ankle arthroscopy. Zhonghua Wai Ke Za Zhi 2005;43:1587–9. [18] Kaynak G, Ogut T, Yontar NS, Botanlioglu H, Can A, Unlu MC. Endoscopic calcaneoplasty: 5-year results. Acta Orthop Traumatol Turc 2013;47: 261–5.
Contents lists available at ScienceDirect
The Foot journal homepage: www.elsevier.com/locate/foot
The safety of the posterior ankle arthroscopy in management of posterior ankle impingement: A cadaveric study T.H. Lui a,∗ , L.K. Chan b a
Department of Orthopaedics and Traumatology, North District Hospital, 9 Po Kin Road, Sheung Shui, NT, Hong Kong SAR, China Institute of Medical and Health Sciences Education and Department of Anatomy, The University of Hong Kong, Li Ka Shing Faculty of Medicine, Hong Kong SAR, China b
h i g h l i g h t s • • • •
Posterior ankle arthroscopy can manage posterior ankle impingement in supine position. Associated intra-articular pathology and anterior ankle impingement can be dealt with without the need of change of patient positioning. Posteromedial portal is just anterior to the posterior tibial tendon and posterolateral portal is just posterior to the peroneal tendons. The coaxial portals are not suitable for treating the Achilles tendon pathology especially the insertional problem.
a r t i c l e
i n f o
Article history: Received 20 June 2015 Received in revised form 3 September 2015 Accepted 4 September 2015 Keywords: Posterior ankle impingement Anterior ankle impingement Os trigonum Ankle arthroscopy Endoscopy
a b s t r a c t Background: Arthroscopic management of the posterior ankle impingement with the patient in supine position has the advantage of dealing with anterior ankle pathology at the same time without the need to change position of the patient. This study aims at evaluation of the safety of portal establishment and instrumentation of this technique. Methods: Sixteen fresh-frozen cadaver specimens were used. The relationships of the posteromedial and posterolateral portals to the adjacent tendons and nerves and the relationship of the coaxial portal tract with the posterior ankle capsule and the flexor hallucis longus tendon were studied. Result: Angle 1 between the intermalleolar line and the posterior ankle coaxial portal tract averaged 1◦ (−10◦ to 22◦ ). Angle 2 between the intermalleolar line and the metal rod where the neurovascular bundle started to move averaged 19◦ (10◦ to 30◦ ). Angle 3 between the intermalleolar line and the metal rod where it reached the lateral border of the Achilles tendon was larger than angle 2 in all specimens. The angle of safety ( s ) averaged 18◦ (−1◦ to 26◦ ). Conclusions: Injury to the tendon, nerves or vessels is possible during establishment of the portals and resection of the os trigonum. © 2015 Elsevier Ltd. All rights reserved.
1. Introduction Posterior ankle impingement is a common cause of chronic ankle pain and results from compression of an os trigonum, prominent Stieda’s process, the posterior tibiotalar ligament or the intermalleolar ligament during ankle plantarflexion [1–6]. Traditional surgical treatment of posterior ankle impingement using posteromedial or posterolateral arthrotomy has been shown to be effective; however, wound problems and substantial recovery periods have been reported [5]. Arthroscopic treatment
∗ Corresponding author. Tel.: +86 852 26837588. E-mail addresses: [email protected] (T.H. Lui), [email protected] (L.K. Chan). http://dx.doi.org/10.1016/j.foot.2015.09.004 0958-2592/© 2015 Elsevier Ltd. All rights reserved.
through the posteromedial and posterolateral portals at either side of the Achilles tendon with the patient in prone position has gained popularity in recent years [5–9]. It has been shown to be safe and effective in treating posterior ankle impingement with less tissue disruption, less symptomatic scar formation and speedier recovery [5,10]. However, in the rare cases when anterior ankle pathologies e.g. anterior ankle impingement or osteochondral lesion coexist with posterior ankle impingement, combined anterior and posterior arthroscopic approaches are needed on the same patient [11]. This requires either change of patient position; posterior ankle endoscopy with the patient in prone position followed by anterior ankle arthroscopy with the knee flexed [12,13] or combined procedures with the patient in the prone position, knee flexed and ankle distracted [14]. These approaches have problem of
T.H. Lui, L.K. Chan / The Foot 27 (2016) 4–9
intra-operative contamination, prolonged operating time and confusing arthroscopic orientation [12–14]. Lui has described a technique of treating posterior ankle impingement with coaxial posterior ankle portals [15]. This allows treatment of both anterior ankle and posterior ankle pathologies at the same time with the patient in the supine position [15]. The posteromedial portal is anterior to the posterior tibial tendon (PTT) and the posterolateral portal is behind the peroneal tendons. The portal tract is at the posterior recess of the ankle joint. In order to deal with the pathologies associated with posterior ankle impingement which are extra-articular, posterior capsulotomy is needed. After capsular release is completed, the arthroscopic instruments can go extra-artciularly to deal with the bony and soft tissue pathologies of posterior ankle impingement. The author has recommended that the instrument through the posteromedial portal should go extra-articularly at the lateral side of the FHL tendon to protect the posterior tibial neurovascular bundle. In this study, the safety of this procedure including establishment of the portals and instrumentation was evaluated.
2. Methods Sixteen fresh-frozen cadaver specimens in 8 cadaver bodies were used for this study. The average age of succumb was 71.5 year old (59–88). None of the cadavers had deformity, trauma or any surgery of their foot and ankle regions. The posteromedial portal was made by a stab wound just posterior to the medial malleolus at the ankle level. A metal rod was inserted and entered the posterior ankle recess and exited posterior to the peroneal tendons. The posterolateral portal was then made at the exit point of the rod [15,16]. The rod represented the coaxial posterior ankle portal tract. The medial and lateral malleolar tips were marked by needles. The intermalleolar line was projected to the sole and an incision represent the line was made and stained with methylene blue. The angle between the intermalleolar line and the posterior ankle coaxial portal tract ( 1 ) was measured (Fig. 1). The skin of the lateral ankle was removed and the relationships of the posterolateral portal to the sural nerve, peroneal tendons and peroneal tendon sheath
5
were studied (Fig. 2). The medial skin and the upper portion of the tarsal tunnel retinaculum were removed. The relationship of the posteromedial portal to the PTT was studied. The tibial neurovascular bundle was retracted posteriorly to expose the posterior ankle. The rod was examined whether it was intra-capsular and deep to the FHL tendon. Posterior ankle capsulotomy was done. The rod was retrieved so that the tip was in the retrocalcaneal space and deep to the FHL tendon (Fig. 3). The rod was then tilted posteriorly and stopped once the neurovascular bundle was noted to move. The angle 2 between the rod and the intermalleolar line was then recorded. The rod was tilted further posterior until the lateral border of the Achilles tendon was reached. The angle 3 angle between the rod and the intermalleolar axis was also recorded (Fig. 4). The ankle was kept in neutral position during the whole procedure and measurements.
3. Results The results of the cadaveric study were summarized in Table 1. The rod was posterior to the peroneal tendons and the tendons were intact in all specimens. The sural nerve was at average 6 (0–12) mm posterior to the posterolateral portal. The rod (represented the portal tract) was within the peroneal tendon sheath in 15 specimens. The rod is outside the tendon sheath in specimen number 7 and has direct contact with the sural nerve. The rod was inserted straightly into the posterior ankle recess through the posteromedial portal in the first three specimens. The rod passed through the PTT in specimen number 2 and 3. Starting from specimen number 4, the rod was inserted proximally into the PTT sheath between the tendon and the distal tibia (Fig. 5). The rod was then slide distally to the ankle joint level deep to the PTT. The PTT was intact in the subsequent specimens. The rod was intra-capsular in 15 specimens and extra-capsular in one specimen. The rod was deep to the FHL tendons in all specimens. Angle 1 ranged from −10◦ to 22◦ and averaged 1◦ . Angle 2 ranged from 10◦ to 30◦ and averaged 19◦ . Angle 3 was larger than angle 2 in all specimens. It ranged from 16◦ to 45◦ and averaged 31◦ . The angle of safety ( s ) was calculated by subtracting 1 from
Fig. 1. The metal rod passed through the posteromedial and posterolateral portals and represented the coaxial portal tract. The medial and lateral malleolar tips were marked by needles (A). These was joined by a rod (B), followed by a skin incision at the sole and stained with methylene blue (C). This represented the intermalleolar axis. The angle 1 between the intermalleolar line and the posterior ankle coaxial portal tract was measured (D).
6
T.H. Lui, L.K. Chan / The Foot 27 (2016) 4–9
Fig. 2. (A) The distance between the sural nerve (SN) and the posterolateral portal was measured. (B) The portal passed through the peroneal tendon sheath in this case.
Fig. 3. (A) The posteromedial portal was anterior to the PTT (a) in this case. (B) The rod was confirmed to be intra-capsular. (b) flexor digitorum longus tendon; (c) posterior tibial neurovascular bundle. (C) Posterior ankle capsulotomy. (D) The rod can go extra-articularly.
2 . This is the angle that the instrument can be mobilized before impinging the neurovascular bundle. Angle s ranged from −1◦ to 26◦ and averaged 18◦ . 4. Discussion Acevedo et al. [16] conducted a study of the coaxial posterior ankle portals. Results of the anatomic study showed that the posterior tibial nerve and posterior tibial artery were located a mean distance of 5.7 mm and 6.4 mm from the edge of the cannula, respectively. Neither penetration nor contact of nerve or vessel was observed at either posterior portal. They also presented a series of 29 clinical cases. Posterior capsular synovectomy was performed arthroscopically with no detectable complications. Gui et al. [17]
conducted another anatomical study of coaxial posterior ankle portals with the lateral portal just behind the lateral malleolus. They studied the portion of posterior talar dome that can be reached through the coaxial posterior portals. There was no nerve, vessel or tendon injury reported. In contrast to these two reports which focused on the intra-articular procedures, our study focused on the extra-capsular procedure of the posterior ankle. From the results of this study, the surgeon should pay attention on the details of the technique in order to ensure a safe procedure. The procedure starts from establishment of the posteromedial portal. The metal rod was inserted straightly into the posterior ankle recess in the first 3 specimens. Posterior tibial tendon injury was noted in specimen number 2 and 3. This was because the tendon turned forwards around the medial malleolus at this point and
T.H. Lui, L.K. Chan / The Foot 27 (2016) 4–9
7
Fig. 4. The stained sole incision represented the intermalleolar axis. (A) The rod represented the coaxial portal tract and angle 1 was measured. (B) The rod stopped at the point where the neurovascular bundle started to move and angle 2 was measured. (C) The rod touched the lateral border of the Achilles tendon and angle 3 was measured. Table 1 Summary of the findings of the cadaveric study. Specimen number
Laterality
Medial portal
Anterior to PTT
Lateral portal
Trans-PTT
Portal tract
Angle 2
Angle 3
Angle s ( 2 − 1 )
Posterior to peroneals
Trans peroneal tendon sheath
Distance from the sural nerve (mm)
Intracapsular
Deep to FHL tendon
11 12 8 5 2 7 0
+ + + + + + +
+ + + + + + +
−5 −4 6 4 −10 6 22
20 15 20 30 10 24 21
25 35 32 45 16 32 36
25 19 14 26 20 18 −1
+ +
5 −6
20 15
30 33
15 21
3 6 6 5 6 11 9
+ Posterior to the capsule + + + + + + +
+ + + + + + +
−3 −4 4 −7 3 −3 5
15 16 19 17 20 16 22
28 30 30 29 34 29 31
18 20 15 24 17 19 17
1 2 3 4 5 6 7
L R L R L R L
+
+ + + +
+ + + + + + +
8 9
R L
+ +
+ +
+ + + + + + Posterior to the tendon sheath + +
10 11 12 13 14 15 16
R L R L R L R
+ + + + + + +
+ + + + + + +
+ + + + + + +
+ +
Angle 1
6 5
L: left, R: right, PTT: posterior tibial tendon, FHL: flexor hallucis longus, Angle 1 : the angle between the intermalleolar line and the posterior ankle coaxial portal tract, Angle 2 : the angle between the intermalleolar line and the metal rod where the neurovascular bundle started to move, Angle 3 : the angle between the intermalleolar line and the metal rod where it reached the lateral border of the Achilles tendon, Angle s = 2 − 1 and represented the angle that the instrument can be mobilized through the posteromedial portal before impinging on the posterior tibial neurovascular bundle, laterally opened angle is defined to be positive angle and medially opened angle is defined to be negative angle.
the tendon is relatively immobile and stuck to the bone. This complication can be avoided by insertion of the rod proximally between the tendon and the tibia and then turning distally to the ankle level. The tendon is more mobile at the proximal level and the rod can be easily placed anterior to the tendon. Moreover, the ankle can be plantarflexed to reduce the forward turning and tension of the tendon. In case of obese or edematous patient, the landmark of the posterior border of medial malleolus may not be palpated well.
A larger portal wound should be made to identify the PTT before insertion of instrument. The rod was outside the posterior ankle capsule in one specimen (6%). This would not be a problem in vivo as this can be detected arthroscopically. The surgeons can either reinsert the instrument into the posterior ankle recess or start the procedure with the instruments in the extra-articular space. If one chooses to start the procedure extra-articularly, the surgeon should identify the FHL
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T.H. Lui, L.K. Chan / The Foot 27 (2016) 4–9
Fig. 5. In specimen number 3, the PTT was injured by the metal rod (A). In order to avoid this complication, the rod can be inserted proximally between the tendon and tibia (B) and then turning distally to the ankle level (C).
tendon as it is the landmark to the location of the neurovascular bundle. It is recommended only for the surgeons that are familiar with the hindfoot endoscopy. The rod exited posterior to the peroneal tendons in all specimen and remained inside the peroneal tendon sheath in 15 specimens (94%). The sural nerve was safe in these specimens. For the one that the rod is outside the peroneal tendon sheath, the sural nerve is at risk. It is recommended that the posterolateral portal (that was established with an inside-out technique) should be just posterior to the peroneal tendons. This can be achieved by palpation of the peoneal tendons by the tip of the arthroscopic trocar. Moreover, the surgeon should be aware of the problem if the trocar is more than 20◦ from the intermalleolar axis. It has been proposed that the neurovascular bundle will be protected if the instruments stay at the lateral side of the FHL tendon [11,15]. However, although the FHL may prevent direct contact of the instrument with the neurovascular bundle, the rod can push the FHL toward the neurovascular bundle and press it onto the flexor retinaculum causing neurovascular damage. Therefore, we performed limited dissection to preserve the tendons and most of the flexor retinaculum in order to preserve the local soft tissue condition and examine the effect of the motion of instrument through the posteromedial portal on the movement of neurovascular bundle. Because of the minimal dissection, we cannot examine whether the bundle was pushed by the FHL tendon or the rod. This is not a concern whether the bundle was pushed by the tendon or the rod but the common outcome that the bundle would be impinged from inside. We tried to identify the angle of safety in order to allow pre-operative assessment of the risk of neurovascular injury by means of computed tomogram with the ankle in neutral position and intra-operative guidance of the safe zone where the instrument of the posteromedial portal can move before impinging the neurovascular bundle. The safe zone cannot be determined because of the wide range of the angle of safety ( s ) in this study. We recommend resection of the posterior portion of the os trigonum/Steida’s process by arthroscopic burr in the posterolateral portal with the posteromedial portal as the visualization portal. Moreover, angle s of specimen number 7 was −1◦ . This implied that the bundle can be impinged during establishment of the coaxial
portals even the trocar was deep to the FHL tendon if the trocar was pointing too posteriorly. The measurements in this study were made with the ankle in neutral position. Ankle dorsiflexion and plantarflexion can affect the tension of the tendons, flexor retinaculum and neurovascular bundle and the position of the bundle in the tarsal tunnel. These have conflicting effects on the angle of safety. For example, ankle plantarflexion will relax the retinaculum and the neurovascular bundle and may decrease the risk of impingement. However, the FHL tendon will also relax and the role as a restraint to the posterior motion of the instrument will be lost. The coaxial portals are not suitable for treating the Achilles tendon pathology especially the insertional problem. Instrumentation through the posteromedial portal will damage the neurovascular bundle as angle 3 was larger than angle 2 in all specimens. Moreover, extensive soft tissue resection of the retrocalcaneal space is needed before the Achilles tendon can be reached and resection of the posterosuperior calcaneal process is not effective through these portals. Additional portals at the sides of the Achilles tendon for endoscopic calcaneoplasty in supine position [18]. Clinical relevance of this study is to identify the safety precautions of this new technique.
5. Limitations The study was limited by the error of measurement and the small sample size and statistical analysis was not possible. The actual incidence of damage to the posterior tibial neurovascular bundle cannot be evaluated because of the subjective assessment of the motion of the bundle.
6. Conclusions Injury to the tendon, nerves or vessels is possible during establishment of the portals and resection of the os trigonum. The surgeon should pay attention of the every technical detail during
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