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Minimally Invasive Medialising Calcaneal Osteotomy (MIMCO)
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Minimally Invasive Medialising Calcaneal Osteotomy (MIMCO) Minimal-Invasive Medialisierende Calcaneus-Osteotomy (MIMCO) Fu-Yuen Thong a,∗, Ewe-Juan Yeap b a b
Department of Orthopaedics, Hospital Raja Permaisuri Bainun, Ipoh, Perak, Malaysia Prince Court Medical Centre. 39 Jalan Kia Peng, 50450 Kuala Lumpur, Malaysia
Received 11 November 2019; accepted 9 January 2020
KEYWORDS Minimally Invasive Surgery; Calcaneal Osteotomy; Adult Acquired Flatfoot Deformity; Tibialis Posterior Tendon Dysfunction; Hindfoot Malalignment
∗
Abstract Background: Medialising calcaneal osteotomy is a common procedure usually done in tandem with other procedures like lateral column lengthening or subtalar arthroereisis, flexor digitorum longus transfer, with or without heel cord lengthening, spring ligament repair and tibialis posterior tendon debridement for the treatment of symptomatic adult — acquired flatfoot deformities (AAFD). The procedure has historically been done via open approaches which are associated with the risk of wound complications and nerve injury. Recently there has been a shift towards more minimally invasive techniques. Methods: Minimally invasive medialising calcaneal osteotomy (MIMCO) is performed percutaneously under fluoroscopy using a high torque, low speed, and saline cooled burr and can be secured with a single cannulated screw, with minimal soft tissue dissection. Results and Conclusions: MIMCO provides surgeons with a safe and reliable tool to correct hindfoot deformities that is comparable to the open procedure but with added potential advantages of decreased postoperative pain, wound complications and iatrogenic injury to neurovascular structures.
Corresponding author. Jalan Raja Ashman Shah, 30450 Ipoh, Perak, Malaysia. Tel.: +605-2087366. fax: +605-2085502. E-Mail: [email protected] (F.-Y. Thong).
https://doi.org/10.1016/j.fuspru.2020.01.005
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F.-Y. Thong, E.-J. Yeap SCHLÜSSELWÖRTER
Zusammenfassung
Minimal-invasive Chirurgie; Calcaneusosteotomie; ErwachsenenPlattfuß; Tibialis posterior Sehnendysfunktion; Rückfußdeformität
Hintergrund: Die medialisierende Calcaneusosteotomie ist eine weit verbreitete Methode zur Korrektur des Knick-Plattfußes, welche üblicher Weise mit anderen Verfahren wie der Verlängerung der lateralen Fußsäule, der Subtalar-Arthrorise, dem Flexor digitorum longus-Transfer, mit oder ohne Achillessehnenverlängerung, Raffung des Spring Ligaments und Debridement der Tibialis posterior-Sehne kombiniert wird. Dieses Verfahren wurde lange Zeit offen durchgeführt, was mit dem Risiko von Wundkomplikationen und Nervenverletzungen einhergeht. In letzter Zeit gibt es einen Trend zu minimal-invasiven Techniken. Methoden: Die minimal invasive medialisierende Calcaneusosteotomie (MIMCO) wird perkutan unter Bildwandlerkontolle mit einer Fräse mit hoher Drehzahl, niedriger Geschwindigkeit und Kochsalzkühlung durchgeführt und kann mit einer einzelnen kanülierten Schraube unter minimaler Weichteildissektion fixiert werden. Ergebnisse und Schlussfolgerungen: Die MIMCO erlaubt eine sichere und effektive Korrektur der Rückfußdeformität beim Knick-Plattfuß vergleichbar der offenen Technik jedoch mit dem zusätzlichen Vorteil verringerter postoperativer Schmerzen, weniger Wundkomplikationen und iatrogener Gefäß- und Nervenverletzungen.
Introduction Tibialis posterior tendon dysfunction results in adult-acquired flatfoot deformity (AAFD). In stage II disease, patients suffer from flexible pes planoabducto-valgus (PPAV) deformity, and those who fail to improve with conservative treatment are often candidates for surgical intervention, most commonly being the medialising calcaneal osteotomy coupled with lateral column lengthening or subtalar arthroereisis, flexor digitorum longus (FDL) tendon transfer, with or without heel cord lengthening, spring ligament repair, and tibialis posterior tendon debridement. The concept of calcaneal osteotomy is an old one. This shifting of the calcaneus or mechanically changing its axis to restore a more neutral position of the hindfoot was first described by Gleich [1] in 1893. Gleich’s technique involved displacement of the posterior fragment forwards, medially and downwards in an attempt to restore the normal angle between the long axis of the calcaneus and the floor. This was achieved by excision of a medial wedge. Koutsogiannis [2] then suggested that sliding the calcaneum medially will improve outcome in flexible pes planus. Biomechanically, the purpose of the osteotomy is two-fold: First it shifts the mechanical pull of the Achilles medially, which supports the relatively weak flexor digitorum tendon transfer and improves inversion power [3]. Secondly, it shifts the valgus heel underneath the mechanical axis of the leg which lowers the risk of valgus deformity after tendon transfer [4]. Traditionally the osteotomy is done using an open approach via a direct oblique or extended lateral approach. This was occasionally associated
with complications including wound breakdown [5], flap necrosis and neurovascular injury. Minimally invasive calcaneal osteotomy is performed percutaneously under fluoroscopy using a high torque, low speed, and saline cooled burr and can be secured with a single 6.5 mm cannulated screw, with minimal soft tissue dissection; with the aim of reducing such complications.
Indications Indications of MIMCO are similar to those of the open approach and are seldom done in isolation. Patients with painful flexible calcaneo-valgus deformities and who have failed conservative management, including medication, physical therapy, shoe wear modification, orthoses, and braces, are candidates for MIMCO. MCO was initially described as an adjunct to offload the flexor digitorum longus (FDL) transfer [3]. The procedure has been shown to be effective in this capacity and is also often combined with additional osteotomies, including lateral column lengthening and/or medial column dorsal opening wedge osteotomies or stabilisation with favorable clinical results [6,7].
Contraindications Contraindications towards MIS MDCO are similar to open techniques and include a rigid flatfoot and symptomatic arthritis of the subtalar, talonavicular, and calcaneocuboid joints, in which triple arthrodesis may be more appropriate. Other contraindications include peripheral neuropathy, infection and a dysvascular foot.
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Minimally Invasive Medialising Calcaneal Osteotomy (MIMCO) The foot should be flexible to proceed. The subtalar joint should allow enough motion (typically cited as 15 degrees) and there should be approximately 10 degrees of adduction motion through the transverse tarsal joints to allow the transferred tendon the ability to lock the joint during motion [8]. Subtalar fusion may an option in place of a joint-sparing reconstruction for obese patients with symptomatic flexible flatfoot because of its durability and dramatically shortened rehabilitation period; however, such an approach is largely based on expert opinion [9—11]. Patients with compromised vascularity are not candidates for elective reconstructive surgery of the foot, including MIS techniques. In addition, patients with poor soft tissue envelope over the lateral heel or those with an active infection of the calcaneus or overlying soft tissue are not candidates for the procedure. Potential risk factors for cases of non-union of the foot and ankle procedures should also be reviewed carefully with each patient before proceeding with any surgery [12]. All attempts should be made to correct or improve the potential effects of these risk factors. The MIS osteotomy should not be used as a means to expand the indications for reconstructive surgery of the foot [9].
Preoperative Planning 1. Perform a comprehensive clinical and radiographic assessment. 2. A comprehensive clinical examination of the foot, with a good understanding of the surface anatomy, is required. (Figure 1) While the patient is standing, valgus malalignment of the subtalar joint is observed. Other symptomatic malalignments like forefoot supination, subfibular impingement should be assessed as it is important that they be corrected intraoperatively in tandem with MIMCO; via procedures such as lateral column lengthening, extraosseous talo- tarsal stabilisation devices and medial column dorsal opening wedge osteotomies. Range of motion of the transverse tarsal and subtalar joints are assessed. If there is any malalignment, check whether it can be passively corrected. Document any sensory deficits. Anteroposterior, oblique, and lateral weightbearing radiographs of the foot are assessed. (Figures 2, 3) In the presence of malalignment, a Saltzman view (hindfoot alignment view, Figure 4) can be
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Figure 1. All patients should undergo routine assessment of perfusion before surgery. Patients with a poor soft tissue envelope over the lateral heel or those with an active infection of the calcaneus or overlying soft tissue are not candidates for surgery.
Figure 2. Weight bearing Ankle Anteroposterior view showing bilateral hindfoot valgus.
used to quantify the deformity. In complex cases (e.g., tarsal coalition, fractures, or large cysts), CT is helpful in surgical planning.
Operative Technique In the authors’ preference, MIMCO is performed under general anesthesia with the C-arm positioned
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Figure 3. Weight bearing lateral view of the foot.
Figure 5. Extent of safe zone is marked, then an incision is made coinciding with the marked location along the intended trajectory of the osteotomy.
Figure 4. Saltzman View.
on the side of the operative limb. The patient is positioned supine on the operating table with bump over the ipsilateral hip to place the lower limb in internal position to facilitate access to the lateral heel. It is also possible to perform this procedure in the lateral position if no medial procedures are planned. A tourniquet is applied on the thigh. Prophylactic antibiotics are administered prior to skin
incision. The limb is prepared with antiseptic solution and draped to the level of the knee. Using fluoroscopy the intended site of osteotomy is first determined. Via a true lateral radiograph of the ankle as indicated by perfect overlap of the medial and lateral talar dome Talusan et al [13] remarked that the safe zone for avoiding the sural nerve can be determined radiographically by tracing a line from the origin of the plantar fascia extending to the posterosuperior aspect of the tuberosity (Landmark line). The burr should be placed in a region between this line and another parallel and 11 mm anterior to it. The proximal and distal extent of the safe zones are marked by placement of needles. The location is marked on the skin over the center of the calcaneal body within the safe zone and a 5-mm skin incision is made coinciding with the marked location along the intended trajectory of the osteotomy (typically 45 degrees to the plantar surface of the hindfoot). (Figure 5) A small artery forceps is used to carefully spread the underlying soft tissues up to cortical bone to retract the sural nerve. A small periosteal elevator is advanced in the trajectory of the intended osteotomy proximally and distally to provide a corridor for the burr. (Figure 6) A 2.5-mm Shannon burr (end- and side-cutting burr) (Figure 7) is advanced across the calcaneus perpendicular to the long axis of the calcaneus. Care should be taken that the limb is maintained in the same position during this phase so as to obtain the most accurate depiction of the osteotomy progress and trajectory. The burr is carefully advanced through the far cortex. The burr can be disconnected from the drive unit while position is checked fluoroscopically. Modification of the direction of the osteotomy allows
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Figure 6. Soft tissue corridor is prepared in the trajectory of the intended osteotomy site.
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Figure 8. Introduction of Shannon burr direct to the lateral calcaneal wall. By changing the anterior or posterior angulation of the osteotomy the surgeon can lengthen or shorten the heel.
Figure 9. The Shannon burr is swept in an arc both dorsal and plantar directions. Fluoroscopic views should be obtained intermittently to ensure that the path of the osteotomy has not shifted. Figure 7. A Shannon burr is an end and side cutting burr designed for percutaneous foot surgery.
the surgeon to shorten or lengthen the heel by angling the osteotomy slightly anterior or posterior respectively. However, the latter may make medial translation more difficult. The earlier will make translation easier but angling to anterior runs a higher risk of neurovascular injury. Decision of which should be made preoperatively. (Figure 8) An axial view of the heel should be obtained to ensure that the osteotomy will be perpendicular to the long axis of the calcaneus. The Shannon burr is swept in a dorsal to plantar direction (Figure 9). A sweeping motion should be used to include the lateral one-third to two-thirds of the calcaneal bone width. The burr may not be easily swept through the
medial aspect of the calcaneus, as the bone there is particularly dense, especially in young individuals. In that case, the medial cortex may require fenestrations with the burr using several careful passes through the medial cortex and then connecting them with a fluid, sweeping motion. Care has to be taken to sweep slowly to avoid breaking the burr. Fluoroscopic views can be obtained intermittently to ensure that the path of the osteotomy has not shifted. The osteotomy site should be intermittently cooled with normal saline to prevent heat necrosis. In addition, an appropriate high-torque (80 Ncm), low-speed (3000 rpm) setting should be used because high speed may also cause heat necrosis. Constant saline irrigation using a syringe is recommended during the procedure.
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Figure 10. The osteotomy is provisionally held with a K-wire and definitively fixed by the insertion of an axially directed cannulated screw perpendicular to the osteotomy site.
Completion of the osteotomy can be determined through tactile sensation and by a change in pitch of the burr. It can be completed with a small osteotome as well. The heel will also be freely mobile, and fluoroscopy will reveal a decreased radiolucent kerf from the burr due to collapse of the fragments onto one another. A lamina spreader is placed to distract the osteotomy site. Care must be taken not to crush the soft bone of the calcaneus especially in older or rheumatoid patients. The knee is then flexed to relax the gastrocnemius tension. This allows medial translation of the tuberosity fragment without superior migration by the pull of the Achilles tendon. The tuberosity fragment is translated medially to obtain the intended correction (usually 10 mm). Medialisation can also be facilitated by levering the fragment within the lateral cortex using a periosteal elevator or small osteotome. The degree of translation is determined using an axial heel fluoroscopic view and direct visualization. Fixation may then proceed with a screw construct. Once the intended medial shift is attained, it is provisionally held with an axially directed percutaneous 1.6 mm K-wire followed by placement of the guidewire from the cannulated screw system. (Figure 10) The guide wire is placed laterally in the posterior tuberosity to accommodate the medial shift and stay within the anterior calcaneus. A lateral and axial fluoroscopic view is used to determine the placement of the screw and that the posterior tuberosity is not superiorly or inferiorly translated. (Figures 11, 12). The cannulated screw is inserted. One large cannulated screw is adequate although some use two smaller screws to control rotation. The osteotomy
Figure 11. A lateral fluoroscopic view shows good compression at the osteotomy site, with no translation of the tuberosity superiorly or inferiorly. In this case there is further use of an extraosseous talo- tarsal stabilisation device inserted into the sinus tarsi to maintain the stability and alignment of the subtalar joint.
Figure 12. Intraoperative image intensification: note the position of the cannulated screw laterally in the posterior tuberosity to accommodate the medial shift and stay central within the anterior calcaneus.
may be performed in a chevron manner to control rotation and translation as well. Partially threaded screws are used, and preferably the threads will all be on the distal part of the osteotomy. During closure, it is important to avoid entrapment
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Figure 13. Patient’s leg after completion of surgery. This patient also underwent endoscopic gastrocnemius release in addition to forefoot surgery for hallux valgus. Figures 13: Post- operative x-ray A, Anteroposterior view showing central placement of cannulated screw within the anterior calcaneus post medialising calcaneal osteotomy; B, Oblique view; C, Lateral view showing good compression over osteotomy site with the use of partially threaded screws with threads on the distal part of the osteotomy.
of the sural nerve. This will create a painful neuroma or sensory deficit (or both) in the lateral foot. Figures 13, 14
Fixation Considerations Screws have been used for fixation of calcaneal osteotomies showing good long-term results [14—16] in terms of patient satisfaction, and union rates. Secondary surgery for removal of hardware, is a known problem when using headed screws; as patients complained of pain over the screw insertion site [14]. In most series the calcaneal sliding osteotomy has been fixed using 2 screws [15], while others used a single screw only [25]. The number of screws used does not appear to affect the union rate, which is similarly high in all series [15,16]. Multiple other methods of fixation have been employed, like headless screws and lateral plating. Abbasian et al [15] showed that regardless of methods of fixation all patients in their series expressed high union rates. As we have found using a headed screw is associated with a higher rate of screw removal, we currently use headless screws.
Postoperative Protocol Sutures used for skin closure are typically removed at 14 days. Calcaneal osteotomy is seldom done in isolation hence the speed of recovery and
Figure 14. 7 weeks post- operative showing: A, Well healed surgical scars; B, Lateral view radiograph, showing correction of Meary’s angle and calcaneal pitch with the insertion of extraosseous talo- tarsal stabilisation device with MIMCO.
rehabilitation would depend on the other procedures done. When a calcaneal osteotomy is the sole bony procedure performed, partial weightbearing can be allowed at 4 weeks postoperatively in a protective walking boot and hindfoot motion can be initiated in physical therapy. Full weightbearing is typically allowed at 6 weeks along with muscle strengthening
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activities. Patients are allowed to gradually discontinue the boot and transition to regular footwear. At this point, patients are encouraged to continue working on range of motion exercises.
Complications Minimally invasive techniques present an opportunity to reduce the risks of hindfoot corrective surgery. However, because there is no direct visualization of the neurovascular structures, precise knowledge of the location and relation to fluoroscopic landmarks are required. Therefore, the main concern in with regards to MIMCO is avoidance of injury to the neurovascular structures. These include the sural nerve, lesser saphenous vein, tibial neurovascular bundle, and the plantar and calcaneal branches of the tibial nerve. Osteotomies of the calcaneus performed through a lateral approach may increase risk to the medial neurovascular structures through direct injury from penetration of the medial cortex. Another speculated mechanism is via the reduction in tarsal tunnel volume from the resulting shift, or compression of by the flexor retinaculum [17,18]; which therefore would not be different with MIS vs open techniques. However, at the time of writing, no comparison study has been noted. Greene et al. [19] studied the medial neurovascular anatomy to determine the structures at risk in open lateral calcaneal osteotomy found that an average of 4 neurovascular structures cross the osteotomy site. These were most frequently branches of the lateral plantar nerve and branches of the posterior tibial artery. The medial plantar branch was not at risk. On the lateral aspect of the heel, the sural nerve and its branches are at risk because they cross the osteotomy site for the open or MIMCO. Despite multiple variations of the nerve and its branches, description of the course of a ‘‘typical’’ nerve trunk was possible. In the hindfoot, the nerve coursed 14 mm posterior and 14 mm inferior to the malleolus. Distally, it crossed superficial to the peroneus longus and brevis tendons. An anastomotic branch coursing into the sinus tarsi area was observed in 24% of specimens. Here, Lawrence [20] reported an average of 3 branches of the sural nerve extending to the lateral heel as lateral calcaneal nerves. These originated a mean distance of 34.7 mm proximal to the tip of the malleolus. Injury to the lateral calcaneal nerves was less frequent using the Shannon burr for an MIS technique than using an open technique [13,21]. Talusan et al. [13] speculated that this may be due to
less soft tissue retraction using the MIS technique, which prevents avulsion of the nerve branches, as well as the rotation of the side-cutting burr being less injurious than the translation motion of a saw.
Discussion Displacement calcaneal osteotomy is a widely used technique in the operative treatment of hindfoot deformity [23]. Open surgical approaches to the calcaneus have traditionally involved variations of a lateral incision situated posterior to the tip of the fibula. The lateral approach originally described by Atkins was developed through anatomical cadaveric and clinical studies to improve wound healing and minimize the disruption to neighboring neurovascular structures [24]; in particular the sural nerve and the perforating branches of the peroneal artery. Nonetheless, the approach is associated with wound complications in 5-10% and sural nerve injury in 7-25% of patients [24—27]. Comparison with a direct lateral direct approach along the line of the osteotomy showed a significant risk of wound complications and sural nerve injury as well [26]. Methods have been sought to reduce the risks of hindfoot surgery, and as such we find a trend towards more minimally invasive approaches [28]. MIMCO as detailed in this article is a representation of the evolution of these approaches. The work of Talusan et al. [13] potentially allows reliable intraoperative assessment of safe zone for osteotomy of the calcaneum via fluoroscopy. MIMCO has been found to be safe and as effective as the open approach but with significantly fewer wound and nerve complications [21,22,24].
Summary MIMCO allows surgeons the means to safely and reliably correct hindfoot deformities comparable to their open counterparts. The MIS calcaneal osteotomy has the added potential advantages of decreased postoperative pain, wound complications and iatrogenic injury to neurovascular structures, while obtaining the same correction afforded by open techniques.
Ethical Approval Not applicable
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Funding The author(s) received no financial support for the research, authorship, and/or publication of this article.
Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
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Minimally Invasive Medialising Calcaneal Osteotomy (MIMCO) Minimal-Invasive Medialisierende Calcaneus-Osteotomy (MIMCO) Fu-Yuen Thong a,∗, Ewe-Juan Yeap b a b
Department of Orthopaedics, Hospital Raja Permaisuri Bainun, Ipoh, Perak, Malaysia Prince Court Medical Centre. 39 Jalan Kia Peng, 50450 Kuala Lumpur, Malaysia
Received 11 November 2019; accepted 9 January 2020
KEYWORDS Minimally Invasive Surgery; Calcaneal Osteotomy; Adult Acquired Flatfoot Deformity; Tibialis Posterior Tendon Dysfunction; Hindfoot Malalignment
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Abstract Background: Medialising calcaneal osteotomy is a common procedure usually done in tandem with other procedures like lateral column lengthening or subtalar arthroereisis, flexor digitorum longus transfer, with or without heel cord lengthening, spring ligament repair and tibialis posterior tendon debridement for the treatment of symptomatic adult — acquired flatfoot deformities (AAFD). The procedure has historically been done via open approaches which are associated with the risk of wound complications and nerve injury. Recently there has been a shift towards more minimally invasive techniques. Methods: Minimally invasive medialising calcaneal osteotomy (MIMCO) is performed percutaneously under fluoroscopy using a high torque, low speed, and saline cooled burr and can be secured with a single cannulated screw, with minimal soft tissue dissection. Results and Conclusions: MIMCO provides surgeons with a safe and reliable tool to correct hindfoot deformities that is comparable to the open procedure but with added potential advantages of decreased postoperative pain, wound complications and iatrogenic injury to neurovascular structures.
Corresponding author. Jalan Raja Ashman Shah, 30450 Ipoh, Perak, Malaysia. Tel.: +605-2087366. fax: +605-2085502. E-Mail: [email protected] (F.-Y. Thong).
https://doi.org/10.1016/j.fuspru.2020.01.005
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Zusammenfassung
Minimal-invasive Chirurgie; Calcaneusosteotomie; ErwachsenenPlattfuß; Tibialis posterior Sehnendysfunktion; Rückfußdeformität
Hintergrund: Die medialisierende Calcaneusosteotomie ist eine weit verbreitete Methode zur Korrektur des Knick-Plattfußes, welche üblicher Weise mit anderen Verfahren wie der Verlängerung der lateralen Fußsäule, der Subtalar-Arthrorise, dem Flexor digitorum longus-Transfer, mit oder ohne Achillessehnenverlängerung, Raffung des Spring Ligaments und Debridement der Tibialis posterior-Sehne kombiniert wird. Dieses Verfahren wurde lange Zeit offen durchgeführt, was mit dem Risiko von Wundkomplikationen und Nervenverletzungen einhergeht. In letzter Zeit gibt es einen Trend zu minimal-invasiven Techniken. Methoden: Die minimal invasive medialisierende Calcaneusosteotomie (MIMCO) wird perkutan unter Bildwandlerkontolle mit einer Fräse mit hoher Drehzahl, niedriger Geschwindigkeit und Kochsalzkühlung durchgeführt und kann mit einer einzelnen kanülierten Schraube unter minimaler Weichteildissektion fixiert werden. Ergebnisse und Schlussfolgerungen: Die MIMCO erlaubt eine sichere und effektive Korrektur der Rückfußdeformität beim Knick-Plattfuß vergleichbar der offenen Technik jedoch mit dem zusätzlichen Vorteil verringerter postoperativer Schmerzen, weniger Wundkomplikationen und iatrogener Gefäß- und Nervenverletzungen.
Introduction Tibialis posterior tendon dysfunction results in adult-acquired flatfoot deformity (AAFD). In stage II disease, patients suffer from flexible pes planoabducto-valgus (PPAV) deformity, and those who fail to improve with conservative treatment are often candidates for surgical intervention, most commonly being the medialising calcaneal osteotomy coupled with lateral column lengthening or subtalar arthroereisis, flexor digitorum longus (FDL) tendon transfer, with or without heel cord lengthening, spring ligament repair, and tibialis posterior tendon debridement. The concept of calcaneal osteotomy is an old one. This shifting of the calcaneus or mechanically changing its axis to restore a more neutral position of the hindfoot was first described by Gleich [1] in 1893. Gleich’s technique involved displacement of the posterior fragment forwards, medially and downwards in an attempt to restore the normal angle between the long axis of the calcaneus and the floor. This was achieved by excision of a medial wedge. Koutsogiannis [2] then suggested that sliding the calcaneum medially will improve outcome in flexible pes planus. Biomechanically, the purpose of the osteotomy is two-fold: First it shifts the mechanical pull of the Achilles medially, which supports the relatively weak flexor digitorum tendon transfer and improves inversion power [3]. Secondly, it shifts the valgus heel underneath the mechanical axis of the leg which lowers the risk of valgus deformity after tendon transfer [4]. Traditionally the osteotomy is done using an open approach via a direct oblique or extended lateral approach. This was occasionally associated
with complications including wound breakdown [5], flap necrosis and neurovascular injury. Minimally invasive calcaneal osteotomy is performed percutaneously under fluoroscopy using a high torque, low speed, and saline cooled burr and can be secured with a single 6.5 mm cannulated screw, with minimal soft tissue dissection; with the aim of reducing such complications.
Indications Indications of MIMCO are similar to those of the open approach and are seldom done in isolation. Patients with painful flexible calcaneo-valgus deformities and who have failed conservative management, including medication, physical therapy, shoe wear modification, orthoses, and braces, are candidates for MIMCO. MCO was initially described as an adjunct to offload the flexor digitorum longus (FDL) transfer [3]. The procedure has been shown to be effective in this capacity and is also often combined with additional osteotomies, including lateral column lengthening and/or medial column dorsal opening wedge osteotomies or stabilisation with favorable clinical results [6,7].
Contraindications Contraindications towards MIS MDCO are similar to open techniques and include a rigid flatfoot and symptomatic arthritis of the subtalar, talonavicular, and calcaneocuboid joints, in which triple arthrodesis may be more appropriate. Other contraindications include peripheral neuropathy, infection and a dysvascular foot.
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Minimally Invasive Medialising Calcaneal Osteotomy (MIMCO) The foot should be flexible to proceed. The subtalar joint should allow enough motion (typically cited as 15 degrees) and there should be approximately 10 degrees of adduction motion through the transverse tarsal joints to allow the transferred tendon the ability to lock the joint during motion [8]. Subtalar fusion may an option in place of a joint-sparing reconstruction for obese patients with symptomatic flexible flatfoot because of its durability and dramatically shortened rehabilitation period; however, such an approach is largely based on expert opinion [9—11]. Patients with compromised vascularity are not candidates for elective reconstructive surgery of the foot, including MIS techniques. In addition, patients with poor soft tissue envelope over the lateral heel or those with an active infection of the calcaneus or overlying soft tissue are not candidates for the procedure. Potential risk factors for cases of non-union of the foot and ankle procedures should also be reviewed carefully with each patient before proceeding with any surgery [12]. All attempts should be made to correct or improve the potential effects of these risk factors. The MIS osteotomy should not be used as a means to expand the indications for reconstructive surgery of the foot [9].
Preoperative Planning 1. Perform a comprehensive clinical and radiographic assessment. 2. A comprehensive clinical examination of the foot, with a good understanding of the surface anatomy, is required. (Figure 1) While the patient is standing, valgus malalignment of the subtalar joint is observed. Other symptomatic malalignments like forefoot supination, subfibular impingement should be assessed as it is important that they be corrected intraoperatively in tandem with MIMCO; via procedures such as lateral column lengthening, extraosseous talo- tarsal stabilisation devices and medial column dorsal opening wedge osteotomies. Range of motion of the transverse tarsal and subtalar joints are assessed. If there is any malalignment, check whether it can be passively corrected. Document any sensory deficits. Anteroposterior, oblique, and lateral weightbearing radiographs of the foot are assessed. (Figures 2, 3) In the presence of malalignment, a Saltzman view (hindfoot alignment view, Figure 4) can be
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Figure 1. All patients should undergo routine assessment of perfusion before surgery. Patients with a poor soft tissue envelope over the lateral heel or those with an active infection of the calcaneus or overlying soft tissue are not candidates for surgery.
Figure 2. Weight bearing Ankle Anteroposterior view showing bilateral hindfoot valgus.
used to quantify the deformity. In complex cases (e.g., tarsal coalition, fractures, or large cysts), CT is helpful in surgical planning.
Operative Technique In the authors’ preference, MIMCO is performed under general anesthesia with the C-arm positioned
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Figure 3. Weight bearing lateral view of the foot.
Figure 5. Extent of safe zone is marked, then an incision is made coinciding with the marked location along the intended trajectory of the osteotomy.
Figure 4. Saltzman View.
on the side of the operative limb. The patient is positioned supine on the operating table with bump over the ipsilateral hip to place the lower limb in internal position to facilitate access to the lateral heel. It is also possible to perform this procedure in the lateral position if no medial procedures are planned. A tourniquet is applied on the thigh. Prophylactic antibiotics are administered prior to skin
incision. The limb is prepared with antiseptic solution and draped to the level of the knee. Using fluoroscopy the intended site of osteotomy is first determined. Via a true lateral radiograph of the ankle as indicated by perfect overlap of the medial and lateral talar dome Talusan et al [13] remarked that the safe zone for avoiding the sural nerve can be determined radiographically by tracing a line from the origin of the plantar fascia extending to the posterosuperior aspect of the tuberosity (Landmark line). The burr should be placed in a region between this line and another parallel and 11 mm anterior to it. The proximal and distal extent of the safe zones are marked by placement of needles. The location is marked on the skin over the center of the calcaneal body within the safe zone and a 5-mm skin incision is made coinciding with the marked location along the intended trajectory of the osteotomy (typically 45 degrees to the plantar surface of the hindfoot). (Figure 5) A small artery forceps is used to carefully spread the underlying soft tissues up to cortical bone to retract the sural nerve. A small periosteal elevator is advanced in the trajectory of the intended osteotomy proximally and distally to provide a corridor for the burr. (Figure 6) A 2.5-mm Shannon burr (end- and side-cutting burr) (Figure 7) is advanced across the calcaneus perpendicular to the long axis of the calcaneus. Care should be taken that the limb is maintained in the same position during this phase so as to obtain the most accurate depiction of the osteotomy progress and trajectory. The burr is carefully advanced through the far cortex. The burr can be disconnected from the drive unit while position is checked fluoroscopically. Modification of the direction of the osteotomy allows
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Figure 6. Soft tissue corridor is prepared in the trajectory of the intended osteotomy site.
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Figure 8. Introduction of Shannon burr direct to the lateral calcaneal wall. By changing the anterior or posterior angulation of the osteotomy the surgeon can lengthen or shorten the heel.
Figure 9. The Shannon burr is swept in an arc both dorsal and plantar directions. Fluoroscopic views should be obtained intermittently to ensure that the path of the osteotomy has not shifted. Figure 7. A Shannon burr is an end and side cutting burr designed for percutaneous foot surgery.
the surgeon to shorten or lengthen the heel by angling the osteotomy slightly anterior or posterior respectively. However, the latter may make medial translation more difficult. The earlier will make translation easier but angling to anterior runs a higher risk of neurovascular injury. Decision of which should be made preoperatively. (Figure 8) An axial view of the heel should be obtained to ensure that the osteotomy will be perpendicular to the long axis of the calcaneus. The Shannon burr is swept in a dorsal to plantar direction (Figure 9). A sweeping motion should be used to include the lateral one-third to two-thirds of the calcaneal bone width. The burr may not be easily swept through the
medial aspect of the calcaneus, as the bone there is particularly dense, especially in young individuals. In that case, the medial cortex may require fenestrations with the burr using several careful passes through the medial cortex and then connecting them with a fluid, sweeping motion. Care has to be taken to sweep slowly to avoid breaking the burr. Fluoroscopic views can be obtained intermittently to ensure that the path of the osteotomy has not shifted. The osteotomy site should be intermittently cooled with normal saline to prevent heat necrosis. In addition, an appropriate high-torque (80 Ncm), low-speed (3000 rpm) setting should be used because high speed may also cause heat necrosis. Constant saline irrigation using a syringe is recommended during the procedure.
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Figure 10. The osteotomy is provisionally held with a K-wire and definitively fixed by the insertion of an axially directed cannulated screw perpendicular to the osteotomy site.
Completion of the osteotomy can be determined through tactile sensation and by a change in pitch of the burr. It can be completed with a small osteotome as well. The heel will also be freely mobile, and fluoroscopy will reveal a decreased radiolucent kerf from the burr due to collapse of the fragments onto one another. A lamina spreader is placed to distract the osteotomy site. Care must be taken not to crush the soft bone of the calcaneus especially in older or rheumatoid patients. The knee is then flexed to relax the gastrocnemius tension. This allows medial translation of the tuberosity fragment without superior migration by the pull of the Achilles tendon. The tuberosity fragment is translated medially to obtain the intended correction (usually 10 mm). Medialisation can also be facilitated by levering the fragment within the lateral cortex using a periosteal elevator or small osteotome. The degree of translation is determined using an axial heel fluoroscopic view and direct visualization. Fixation may then proceed with a screw construct. Once the intended medial shift is attained, it is provisionally held with an axially directed percutaneous 1.6 mm K-wire followed by placement of the guidewire from the cannulated screw system. (Figure 10) The guide wire is placed laterally in the posterior tuberosity to accommodate the medial shift and stay within the anterior calcaneus. A lateral and axial fluoroscopic view is used to determine the placement of the screw and that the posterior tuberosity is not superiorly or inferiorly translated. (Figures 11, 12). The cannulated screw is inserted. One large cannulated screw is adequate although some use two smaller screws to control rotation. The osteotomy
Figure 11. A lateral fluoroscopic view shows good compression at the osteotomy site, with no translation of the tuberosity superiorly or inferiorly. In this case there is further use of an extraosseous talo- tarsal stabilisation device inserted into the sinus tarsi to maintain the stability and alignment of the subtalar joint.
Figure 12. Intraoperative image intensification: note the position of the cannulated screw laterally in the posterior tuberosity to accommodate the medial shift and stay central within the anterior calcaneus.
may be performed in a chevron manner to control rotation and translation as well. Partially threaded screws are used, and preferably the threads will all be on the distal part of the osteotomy. During closure, it is important to avoid entrapment
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Figure 13. Patient’s leg after completion of surgery. This patient also underwent endoscopic gastrocnemius release in addition to forefoot surgery for hallux valgus. Figures 13: Post- operative x-ray A, Anteroposterior view showing central placement of cannulated screw within the anterior calcaneus post medialising calcaneal osteotomy; B, Oblique view; C, Lateral view showing good compression over osteotomy site with the use of partially threaded screws with threads on the distal part of the osteotomy.
of the sural nerve. This will create a painful neuroma or sensory deficit (or both) in the lateral foot. Figures 13, 14
Fixation Considerations Screws have been used for fixation of calcaneal osteotomies showing good long-term results [14—16] in terms of patient satisfaction, and union rates. Secondary surgery for removal of hardware, is a known problem when using headed screws; as patients complained of pain over the screw insertion site [14]. In most series the calcaneal sliding osteotomy has been fixed using 2 screws [15], while others used a single screw only [25]. The number of screws used does not appear to affect the union rate, which is similarly high in all series [15,16]. Multiple other methods of fixation have been employed, like headless screws and lateral plating. Abbasian et al [15] showed that regardless of methods of fixation all patients in their series expressed high union rates. As we have found using a headed screw is associated with a higher rate of screw removal, we currently use headless screws.
Postoperative Protocol Sutures used for skin closure are typically removed at 14 days. Calcaneal osteotomy is seldom done in isolation hence the speed of recovery and
Figure 14. 7 weeks post- operative showing: A, Well healed surgical scars; B, Lateral view radiograph, showing correction of Meary’s angle and calcaneal pitch with the insertion of extraosseous talo- tarsal stabilisation device with MIMCO.
rehabilitation would depend on the other procedures done. When a calcaneal osteotomy is the sole bony procedure performed, partial weightbearing can be allowed at 4 weeks postoperatively in a protective walking boot and hindfoot motion can be initiated in physical therapy. Full weightbearing is typically allowed at 6 weeks along with muscle strengthening
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activities. Patients are allowed to gradually discontinue the boot and transition to regular footwear. At this point, patients are encouraged to continue working on range of motion exercises.
Complications Minimally invasive techniques present an opportunity to reduce the risks of hindfoot corrective surgery. However, because there is no direct visualization of the neurovascular structures, precise knowledge of the location and relation to fluoroscopic landmarks are required. Therefore, the main concern in with regards to MIMCO is avoidance of injury to the neurovascular structures. These include the sural nerve, lesser saphenous vein, tibial neurovascular bundle, and the plantar and calcaneal branches of the tibial nerve. Osteotomies of the calcaneus performed through a lateral approach may increase risk to the medial neurovascular structures through direct injury from penetration of the medial cortex. Another speculated mechanism is via the reduction in tarsal tunnel volume from the resulting shift, or compression of by the flexor retinaculum [17,18]; which therefore would not be different with MIS vs open techniques. However, at the time of writing, no comparison study has been noted. Greene et al. [19] studied the medial neurovascular anatomy to determine the structures at risk in open lateral calcaneal osteotomy found that an average of 4 neurovascular structures cross the osteotomy site. These were most frequently branches of the lateral plantar nerve and branches of the posterior tibial artery. The medial plantar branch was not at risk. On the lateral aspect of the heel, the sural nerve and its branches are at risk because they cross the osteotomy site for the open or MIMCO. Despite multiple variations of the nerve and its branches, description of the course of a ‘‘typical’’ nerve trunk was possible. In the hindfoot, the nerve coursed 14 mm posterior and 14 mm inferior to the malleolus. Distally, it crossed superficial to the peroneus longus and brevis tendons. An anastomotic branch coursing into the sinus tarsi area was observed in 24% of specimens. Here, Lawrence [20] reported an average of 3 branches of the sural nerve extending to the lateral heel as lateral calcaneal nerves. These originated a mean distance of 34.7 mm proximal to the tip of the malleolus. Injury to the lateral calcaneal nerves was less frequent using the Shannon burr for an MIS technique than using an open technique [13,21]. Talusan et al. [13] speculated that this may be due to
less soft tissue retraction using the MIS technique, which prevents avulsion of the nerve branches, as well as the rotation of the side-cutting burr being less injurious than the translation motion of a saw.
Discussion Displacement calcaneal osteotomy is a widely used technique in the operative treatment of hindfoot deformity [23]. Open surgical approaches to the calcaneus have traditionally involved variations of a lateral incision situated posterior to the tip of the fibula. The lateral approach originally described by Atkins was developed through anatomical cadaveric and clinical studies to improve wound healing and minimize the disruption to neighboring neurovascular structures [24]; in particular the sural nerve and the perforating branches of the peroneal artery. Nonetheless, the approach is associated with wound complications in 5-10% and sural nerve injury in 7-25% of patients [24—27]. Comparison with a direct lateral direct approach along the line of the osteotomy showed a significant risk of wound complications and sural nerve injury as well [26]. Methods have been sought to reduce the risks of hindfoot surgery, and as such we find a trend towards more minimally invasive approaches [28]. MIMCO as detailed in this article is a representation of the evolution of these approaches. The work of Talusan et al. [13] potentially allows reliable intraoperative assessment of safe zone for osteotomy of the calcaneum via fluoroscopy. MIMCO has been found to be safe and as effective as the open approach but with significantly fewer wound and nerve complications [21,22,24].
Summary MIMCO allows surgeons the means to safely and reliably correct hindfoot deformities comparable to their open counterparts. The MIS calcaneal osteotomy has the added potential advantages of decreased postoperative pain, wound complications and iatrogenic injury to neurovascular structures, while obtaining the same correction afforded by open techniques.
Ethical Approval Not applicable
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Funding The author(s) received no financial support for the research, authorship, and/or publication of this article.
Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
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