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Excision of accessory navicular(os naviculare) with release of the medial head of gastrocnemius

    Overview

    Learn the Excision of accessory navicular(os naviculare) with release of the medial head of gastrocnemius surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Excision of accessory navicular(os naviculare) with release of the medial head of gastrocnemius surgical procedure.
    Under normal circumstances the navicular ossifies from a single ossification centre early in childhood. This usually occurs around 3-5 years in girls and boys with fusion occurring by the age of about 13. An accessory navicular, also variously called the Os Tibiale Externum or Os Navicularum, is an extra bone that lies adjacent to the parent navicular and is a variation of the embryological origin of the navicular bone. It occurs because the medial navicular tuberosity can have its own ossification centre and it is this that develops as a separate fragment of bone, with a variable pattern of what happens to it by the time of skeletal maturity.
    An Os Naviculare develops as either a sesamoid in the substance of the tibialis posterior (which attaches to the medial tuberosity of the navicular), a separate fragment of bone and cartilage which forms a synchondrosis with the parent navicular, or it can fuse completely with the parent bone as a synostosis leading to a plantar medial elongation of the navicular bone. These variations form the basis for a radiological classification of the anomaly(Geist, 1914).
    The condition is asymptomatic in most, occurring in about 5-14 % of the population. The commoner causes of the onset of pain are overuse, ill fitting or nonconforming shoes, stress fractures, tibialis posterior tendinopathy or synovitis at its insertion to the accessory navicular. Rarely fracture or arthropathy effecting the synchondrosis can occur. Many patients have significant pes planus which also makes the medial side of the navicular more prominent and prone to injury.

    Indications

    INDICATIONS
    The typical patient is an adolescent female with a history of flat feet which have become symptomatic following an index incident, either during sport or a minor injury, and which does not settle with conservative treatment. The patient often is unaware of the bony prominence prior to presentation, which is ususally bilateral but can be symptomatic on only one side.
    The excision of the accessory navicular is only reserved for patients who have pain and not just pes planus with a medial prominence, which is not an indication for the surgery.
    SYMPTOMS & EXAMINATION
    Common presenting symptom is pain either with wearing footwear or with running sport. Rarely it can present as an acute and severe flare up of pain either from a fracture of the synchondrosis, a tear of the tibialis posterior in the vicinity of the accessory bone or simply after an ankle sprain that fails to settle. Patients often have had some physiotherapy but are unable to perform the exercises due to pain or weakness of the tibialis posterior tendon.
    Clinical examination reveals the bony prominence which can be exquisitely tender. Tests for tibialis posterior function are often positive not because of the tendon itself being pathological but usually because the accessory navicular is too painful to allow single heel raise test or direct testing of the tib post against resistance.
    Tests must include the Silfverskiold test for gastrocnemius tightening which is very often present to a significant degree as many of the patients have had a valgus hind foot with a medial collapse of the arch and gastrocnemius tightness for many years. This is an important aspect of the treatment of the condition and has to be carefully examined for. Tightness of the gastrocnemius predisposes to a vagus positioning of the foot relative to the midline to allow the ankle and midfoot joints to dorsiflex and can be a significant contributor to pes planovalgus deformity. This may accentuate pre-existing pes planus in the presence of an accessory navicular. For a fuller explanation of this see step 6 of the operative technique that follows.
    The other tests include range of movement of the ankle and subtalar joints along with joints of the midfoot. The difficulty with diagnosis is the confusion about what actually causes pain the accessory navicular or the tibialis posterior tendon? it is therefore important to be thorough with clinical examination to analyse the symptoms carefully and to arrive at the right diagnosis if possible.
    IMAGING
    Plain radiographs of the foot weight bearing anteroposterior and lateral of the foot are essential as well as a lateral oblique view which will show the plantar medial prominence of the accessory navicular.
    MRI scans will clearly demonstrate pathology in the tibialis posterior tendon which will help with the diagnostic conundrum
    It will also show oedema in the accessory navicular or arthritic changes in the articulation if present.
    Rarely an isotope bone scan or CT SPECT may be necessary particularly if there have been previous operations which can cause diagnostic difficulties..
    ALTERNATIVE OPERATIVE TREATMENT
    Simple excision of the accessory navicular particularly if it is a sesamoid in the tendon often is adequate to give excellent symptomatic relief
    NON-OPERATIVE MANAGEMENT
    Injections into the synchondrosis are often effective particularly if there are arthritic changes.
    The use of rest, activity and shoe modification for short periods with simple analgesia is often helpful. A period of watchful expectancy, especially in the young patient close to skeletal maturity, is sometimes rewarded by the cessation of symptoms. A semi rigid orthosis to buttress the medial arch assists this process.
    CONTRAINDICATIONS
    Asymptomatic prominent accessory naviculars should not be excised for cosmesis . The area can become painful as a result of the operation!
    The other contraindications are infection or vascular insufficiency: these are rare in the age group that presents with symptomatic accessory naviculars.

    Setup

    Typically the patient is in their late adolescence or early adulthood. This particular patient had undergone a previous procedure for similar complaints and had a deprofiling of the prominent bony bump on the medial aspect of the navicular. She was complaining of a recurrence of the bony lump along with pain proximal to it . She also had difficulty with footwear.
    There are 2 components to this operation . Both occur on the medial side of the limb.
    The first is a proximal gastrocnemius release just distal to the popliteal skin crease and medial to the midline. The second is the excision of the accessory navicular and repair of the bed of the accessory navicular in the tibialis posterior tendon. I DO NOT advance the tibialis posterior as it does cause a significant tension in the tendon and I have not had good results with advancement. Persistent medial pain has been a significant problem in patients with advancement of the tendon and this is a difficult problem to resolve especially if there are degenerative features developing in the tendon.
    It is of paramount importance to mark the posterior landmarks behind the knee to plan the incision to isolate the medial head of Gastrocnemius muscle. I do this before the tourniquet is applied so as to not distort the anatomy behind the knee. The midline of the popliteal fossa behind behind the knee is marked longitudinally as well as the popliteal crease . The incision is marked 1 inch from the midline and 1 inch below the popliteal crease and stops short of the medial hamstrings as felt through the skin. If the limb is very large it may be necessary to extend the incision medially but I do not cross the midline laterally. The structures of importance are clearly confined to the midline especially the neurovascular bundle which lies deep to the interval between the 2 heads of gastrocnemius. It is also important to know the anatomy of the medial hamstrings which travel just medial to the medial border of the medial head of gastrocnemius and indeed forms the medial boundary of the same. For most patients with a tight gastrocnemius merely release the aponeurosis of the medial head is adequate to correct the deformity whilst not weakening the muscle: sometimes the lateral head aponeurosis may also require to be released in which case it is best done with the patient prone.
    The second is the excision of the accessory navicular and reattachment of the tibialis posterior if required. The anatomy of the medial side of this region has clear landmarks. The area between the medial malleolus and the medial navicular tuberosity is devoid of any bony prominence usually and this is the region where an accessory might present itself. if it is well plantar and does not present as a bony prominence, then sometimes it can be impalpable and only visible on a radiograph. The tibialis posterior the medial navicular tuberosity and the medial malleolar profile form the boundaries of the area to be explored for an excision. The saphenous vein and nerve lie dorsal to this region whilst the posterior tibial neurovascular bundle las inferior and posterior to it. The spring ligament is the floor in this region.
    I use a sand bag or a bolster under the buttock on the opposite side so as to make the process of gaining good visualisation of the posteromedial part of the knee easier. It also helps with the medial approach to the accessory navicular.
    An above knee tourniquet is used and inflated to 300 mm of mercury. If a hindfoot osteotomy or flat foot correction surgery is contemplated then the position of the patient will have to be changed when this part of the operation has to be performed.

    Operation – 1

    The standing AP radiograph of the foot confirms the presence of the accessory navicular proximal t the medial tuberosity of the parent bone.
    There is an irregularity on the medial pole cortex where previous surgery was attempted although the actual accessory is well proximal and plantar to the area that was excised.
    The patient continued to get severe symptoms and then sought a second opinion from me.
    Accessory navicular
    Site of previous attempted excision of accessory navicular

    The lateral standing radiograph also shows the accessory navicular (1) which as seen here clearly lies proximal to the medial navicular tuberosity.
    The position variety and articulation with parent navicular are of 3 types.
    a) A sesamoid in the tibialis posterior tendon which is usually asymptomatic unless traumatised.
    b)A larger fragment which articulates with the parent bone usually with fibrocartilage (synchondrosis). This accounts for about 55% of cases.
    c) A fused accessory navicular where it is part of the parent bone but has a hook like abnormal prominence in the plantar medial aspect of the foot also called the cornuate navicular. This can be seen on plain radiographs and forms the basis of the Geist classification.
    Geist ES (1914) Supernumerary bones of the foot: A roentgen study of the feet of 100 normal individuals. Am J Orthop Surg 12:403

    The medial aspect of the midfoot clearly demonstrates an abnormal bony prominence with the scar of the previous surgical procedure.
    The patient had a pes planus deformity which did not worsen significantly on standing. The hindfoot was in 10 degrees of valgus and symmetrical to the opposite side which also had an accessory navicular prominence .

    The plantar view clearly demonstrates the medial bony prominence of the accessory navicular. It is clear that this can be a significant impediment to shoe wearing especially in the younger population. In this patients case there had been a previous attempt to remove the prominence but it still persisted as the accessory fragment was missed on initial operation and instead the parent navicular was shaved down.

    The skin incision is marked in the line of the tibialis posterior tendon, beneath the medial malleolus and to its insertion.
    The tibialis posterior tendon and the medial tuberosity of the navicular are marked in addition

    The incision for the for proximal gastrocnemius release is sited just below the transverse popliteal crease, in the interval between the two heads of gastrocnemiusThe 2 heads of gastrocnemius can be made out in thinner patients and by dorsiflexing the ankle with the knee extended.
    I use the interval between the two heads of gastrocnemius as my landmark for the midline of the fossa.
    The incision is centred just below the transverse popliteal crease and just medial to the midline. It is necessary to remember not to cross the midline , or extend too far medially for fear of damaging the medial hamstrings.
    This patient had isolated gastrocnemius shortening with a positive Silfverskiold test. This contributes to the planovalgus deformity and hence the need to rectify by releasing the medial head. This alone is more often than not adequate to render the Silfverskiold test negative.
    This patient had no tightness of the soleus as the ankle could be dorsiflexed past 90 degrees with the knee flexed. If there is only minimal tightness of the tendon with the knee extended, this can be accepted . Thus if the ankle can be dorsiflexed past 90 degrees with the knee flexed and can be brought to plantigrade with the knee straight, I do not perform the medial gastrocnemius release (but do instruct the physiotherapists to stretch the gastrocnemius with the knee extended and the heel in neutral postoperatively).
    If indeed the ankle is unable to be brought past neutral both in the knee bent and knee straight positions then it is the case that the patient suffers from true equinus due to gastrosoleus contracture and will need a tendo achilles lengthening.

    The skin and the subcutaneous tissue are incisioned in line with the popliteal marking. Small veins are cauterised carefully as they can bleed quite profusely marring good vision of the structures in this region.The popliteal fossa is a diamond shaped space and is bordered by muscles on all sides. Its superomedial boundary is the semimembranosus tendons. Its superolateral boundary is the biceps femoris muscle and tendon. The inferomedial and inferolateral boundaries are the 2 heads of gastrocnemius. Within this quadrilateral space lie the popliteal artery vein and tibial nerve whilst the common peroneal nerve borders its superolateral border along with biceps femoris. also within this fossa lies the popliteal pad of fat. The small saphenous vein lies between the 2 heads of gastrocnemius whilst the lateral and medial cutaneous sural nerves traverse its inferolateral border. It is vital to understand this anatomy before making the incision as there are only small margins for error.

    A self retaining retractor is used to widen the popliteal exposure and the deep fascia is divided in line with the skin incision.Just lateral to the midline is the medial sural cutaneous nerve which can be at risk if one strays too far across the midline.

    Division of the deep fascia exposes the medial head of the muscle whose identity is confirmed by extending the knee and moving the ankle to demonstrate stretching of the muscle belly.One should avoid crossing the tendinous band that separates the medial from the lateral head or cross the midline with the incision, both superficial and deep.
    The aponeurosis is characterised by its tough texture and white sheen. This must be differentiated from the epimysium more towards the midline which is a much thinner structure, lacks the sheen, and which does not need to be divided.
    The knee is flexed to about 30 degrees and a sandbag placed under the contralateral buttock so that the popliteal fossa can be better accessed by externally rotating the hip and relaxing the popliteal fascia and muscles. This facilitates retraction as well.

    Overlying the gastrocnemius is the aponeurosis whose medial and lateral extent are now defined by retractionIt is important to isolate the aponeurosis only for division and to protect the hamstring tendons which lie in the medial border of this exposure.

    The gastrocnemius aponeurosis is carefully divided with a knife, taking care to avoid cutting into the muscle below as it will cause significant bleeding.The division must extend to the medial border of the aponeurosis so that the maximum benefit of the release can be achieved.
    Whilst there are no neurovascular structures over the medial head, it is important not to traverse the midline as the popliteal neurovascular bundle lies in the fossa along with the cutaneous sural branches further laterally , whilst medial transgression may result in injury to the medial hamstring tendons.

    The release is tested by assessing the correction of the equinus deformity previously seen. The cut edges of the aponeurosis will be seen to retract with dorsiflexion of the ankle which confirms a satisfactory release.by assessing the correction of the equinus deformity previously seen. The cut edges of the aponeurosis will be seen to retract with dorsiflexion of the ankle which confirms a satisfactory release.
    This patient had a 15 degree lack of dorsiflexion with the knee straight and up to 20-25 degrees of contracture can be corrected by this procedure as long as there is no contribution by the soleus to the deformity.

    The wound is irrigated with saline and only the superficial fascia with the fatty layer is closed with interrupted Vicryl Sutures
    A subcuticular Vicryl Rapide stitch or interrupted mattress suture ( as in this case)completes the closure

    The wound is infiltrated with 10 mls of 0.5% Chirocaine for analgesia

    The skin incision is marked in the line of the tibialis posterior tendon, beneath the medial malleolus and to its insertion.The surface marking is important to avoid damage to structures in the vicinity. These include the saphenous vein and nerve anteriorly, the posterior tibial neurovascular bundle plantar to the tibialis posterior, and the flexor digitorum longus immediately behind the tibialis posterior.

    The skin is carefully incised to avoid damaging deeper structures especially subcutaneous veins which traverse the area. In this case the old scar was reopened. The fat is carefully excised in line with the incision

    Plantar to the line of incision lies the tendon of tibialis posterior which is exposed at its distal endFollowing the tendon distally will lead one to the medial navicular tuberosity and the accessory navicular. The sheath of the tendon is often deficient here and if present is densely adherent to the tendon. It must not be dissected free of the tendon to avoid damage to the tendon itself.

    The accessory navicular is identified lying in the substance of the tendon and it is useful to remember that it lies proximal and plantar to the parent bone.In the younger age group this might be largely made up of cartilage and a synchondrosis is often present.
    In this patient identification is all the more important, and mapping of the extent of the bony fragment paramount, as there was a previous attempt to remove the fragment and one can find multiple fragments on occasion because of previous surgery. It is therefore important to understand the anatomy and position of the accessory relative to the tendon of tibialis posterior.

    The bony fragment is carefully dissected out of its tendinous bed taking care not to compromise the tendon not in the immediate surgical fieldThe medial tuberosity sometimes in in close proximity to the fragment and forms a pseudoarthrosis with the parent bone. In this situation the medial tuberosity requires to be shaved down too as it is often hypertrophied and irregular

    The accessory navicular is shelled out of its bed and sent for microbiology
    Although it is not done routinely, this patient had a post operative infection the last time she was operated on and hence as a precautionary measure a pus swab and the accessory navicular were sent off for culture to ensure no residual infection was present.

    The bed of the accessory navicular now is a void which requires to be obliterated. This bone is then freshened with a rasp to bleeding bone to receive the tibialis posterior.This is not a defect in the tibialis posterior length and therefore the tibialis posterior is not discontinuous and therefore does not need reattachment to the medial navicular tuberosity nor does it need advancement.
    I do not advance the tendon routinely as it can cause a focus of pain and may cause tendinopathic features in the distal tendon if the tension on the tendon is significant. This is a problem when there is a large accessory navicular that is synchondrous to parent bone, to which is attached the entire tendon. Excising the accessory here will leave a large gap in the tendon and tensioning it to close the gap will do 2 things. Firstly it will cause significant tension in the tendon which may result in painful symptoms. Secondly it will shorten the medial column, compared to the preoperative situation, by adducting the foot.
    It is therefore important to balance closing any gap produced with the potential resulting tension placed on the tendon. An advancement of up to a centimetre is reasonably well tolerated if the associated planovalgus deformity is not severe but if there is severe hindfoot valgus with pes planus and an unstable medial ray, then appropriate measures need to be taken. This may include a hindfoot osteotomy to medialise the os calcis as well as stabilising the medial ray with fusion at the appropriate level. Attempts to make a tunnel in the navicular to re-insert the tendon )the Kidner procedure) may result in an unacceptable amount of tension in the tendon and produce an adduction deformity of the foot.


    The spring ligament(1)is inspected and appears intact with no slackness or tear.
    The spring ligament (inferior calcaneonavicular ligament) is an important ligament in the foot and serves to maintain the arch in conjunction with the tibialis posterior and the plantar fascia. It consists of 3 portions the superomedial (dorsal) and the intermediate and lateral which are plantar. The ligament takes origin from the sustentaculum tali of the os calcis and is attached to the plantar aspect of the navicular to form a hammock-like structure to house the talar head. Proximally the superomedial blends with the anterior / superior fibres of the the deltoid ligament(tibiospring) whilst dorsally it presents a fibrocartilaginous surface to articulate with the talar head as part of the ‘Acetabulum pedis’. This arrangement is vital for the integrity of the arch and therefore essential for the normal functioning of the midfoot during propulsive ambulation. This must always be inspected for thinning or tears especially in patients with severe flat foot as it may require augmentation or repair.

    The dedicated drill is used to make a hole in the medial navicular tuberosity, the guide having at its end an arresting collar that stops the drill from advancing too far into the bone.The defect in the tendon bed needs to be obliterated and the tendon re-apposed to the medial tuberosity of the navicular without significant advancement, so as to not alter the biomechanics of the tendon
    It is to be reiterated that the tension in the tendon does not change significantly with excision of the accessory navicular but it does lose some of the connections to the parent bone . Thus the aim is to hitch the tendon bed on to the parent bone whilst not altering its tension or shortening the tendon. This is done by using suture anchors plumbed into the medial tuberosity of the navicular.
    I use Arthrex Mini Biocomposite SutureTac with Fibre wire to facilitate this. The SutureTac comes with preloaded fibre wire with needles and an anchor that has ridges for strong purchase in bone. The unique ‘suture on suture’ eyelet avoids the wear that is often the case with a ‘suture on anchor’ eyelet. The braided polyblend Fibrewire suture offers a unique tensile strength that is not afforded by non or semi absorbable sutures.
    The first step consists of using the dedicated drill to make a hole in the medial navicular tuberosity. The SutureTac is then impacted into the hole and the needles freed from their carrier cartridge. The drill has a drill guide that prevents over-drilling with an arresting collar (1) that stops the drill from advancing too far into the bone.

    The SutureTak is then threaded into its prepared hole.It is necessary to ensure that the correct guide with the right collar is used to sink the suture in. The suture anchor is impacted to the laser line on the introducer to ensure that it is well buried .

    The needles are then released from their carrying cartridge. A further SutureTac is then inserted plantar and distal to the first. Both sets of sutures are tugged by hand to ensure that they are securely fixed to the bone. This is especially important to check in osteoporotic bone.
    A larger anchor may be required under such circumstances.

    Operation – 2

    Aim to get a second SutureTak in place by using one that travels plantar lateral from the tip of the medial tuberosity, and a second one at least 7-10 mm distally and travelling laterally and slightly dorsal.It is important not to put the anchors too close to each other due to the risk of fracturing the bone in between with resultant failure of the anchors. Sometimes there is only space for 1 anchor and it would not be wise to crowd the area with 2 .

    Thus two SutureTaks are now ready to be utilised in hitching the tendon on to the medial tuberosity of the navicular.
    The tendon is carefully hitched on to the medial tuberosity without tensioning it. It is to be remembered that the tendon has extensive connections to the medial cuneiform and even the base of the first metatarsal as well as to the surrounding tissues. If there is a significant gap in the tendon then one can try several methods of trying to minimise the gap.
    An advancement of about a cm works well in my hands with no significant tension providing the preoperative deformity is not severe. This can be tested intraoperatively by simulated weight bearing
    it is possible to gather the connections of the tibialis posterior to the cuneiform and and using this to bolster and close the bed in the tendon from where the accessory navicular was excised in order to strengthen it. This can then be hitched on to the parent navicular on its plantar medial side with anchors.
    If there is significant deformity preoperatively with an uncovered talar head, and as significant gap in the tendon after excision, then a lateral column lengthening with an Evans calcaneal osteotomy +/- a medializing calcaneal osteotomy works well to bring the medial pole of the navicular closer to the tendon end and avoid severe tensioning of the tendon. This may have to be coupled with a spring ligament augmentation or repair if indicated This my preferred method of treating gaps and has worked well in my hands although I do not believe there is published evidence for the same. However it stands to logic that the primary deformity needs to be address if severe in order to normalise forces going through the tendon

    The sheath if present is closed with Vicryl

    The wound is then closed in layers with Vicryl to the subcutaneous tissue and Vicryl Rapide to the skin in a subcuticular stitch.

    The wound is infiltrated with 20 ml of Chirocaine 0.5%
    A short below knee non weight bearing plaster is applied with the foot in neutral dorsiflexion and 10 deg of inversion
    Adequate analgesia and Dalteparin is prescribed for the patient

    Post Operative

    The patient is advised to mobilise non weight bearing for 4 weeks. Then plaster taken off and patient is then mobilised in a walker boot with a semi-rigid medial arch support for a further 4 weeks with physio assistance to regain range of ankle and subtalar movement. Finally the patient is allowed to walk and return to normal activity thereafter. However I advice my patients to wear the insole for about 3-4 months post op.

    Recommended Reading

    The results of simple excision of the accessory navicular deprofiles the foot and relieves pain of pressure over a bony prominence . It does not correct deformity of pes planus. Therefore patients must be counselled about the outcomes of the procedure to synchronise objectives and expectations.
    The use of tibialis posterior tendon advance has variable outcomes with many authors not satisfied with procedures such as the Kidner procedure. I do not perform advancement as in my experience, patients have been unhappy with residual pain brought on either because of traction pain along an over tensioned tendon due to attempting to bridge a gap between tendon and parent navicular. Others have returned with frank degeneration, occasionally even warranting a tendon transfer. The deformity of pes planovalgus cannot be corrected by simply pulling the tendon on to the navicular by dynamically trying to shorten the medial column. I have tended to do a minimally invasive medializing calcaneal osteotomy and/or an Evans anterior calcaneal osteotomy to lengthen the lateral column and rotate the navicular on its articulation with the talar head in order to attach the tendon without tension to the medial pole.
    It is also the case that attempting to plumb the tendon into a drill hole in the navicular with an interference screw by definition will shorten the tendon significantly. I therefore hitch the tendon on to the navicular with as little tension as possible and use bony procedures to achieve deformity correction to facilitate this.
    Suggested reading:
    Surgical Treatment of Symptomatic Accessory Navicular in Children and Adolescents. Juan Pretell-Mazzii et al: The American Journal of Orthopedics. March 2014: (110-114)
    Comparison of Outcomes of Arthrodesis and reconstruction(advancement) posterior tibial tendon with excision of accessory tarsal navicular in Type 2 accessory navicular. Gang Zeng et al. Journal of Foot and Ankle surgery
    https://doi.org/10.1016/j.fas.2019.12.005
    Revision surgery for Recurrent Pain after excision of the Accessory Navicular and Relocation of the Tibialis posterior tendon. Hong Joon Choi, MD and Woo Chun Lee, MD
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5435664/#

    Reference

    • orthoracle.com

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