///

5th metatarsal non-union fixation ,using Stryker Asnis cannulated screws

    Overview

    Learn the 5th metatarsal non-union fixation ,using Stryker Asnis cannulated screws surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the 5th metatarsal non-union fixation ,using Stryker Asnis cannulated screws surgical procedure.
    Fractures of the 5th metatarsal (MT) are the most frequently encountered fractures in the foot and more than half of these affect the 5th MT especially after sports trauma and can go onto non-union. These fractures require careful evaluation and classification to ensure selection of the optimum treatment.
    However even classification of these injuries is controversial. The classic thinking relates to the Lawrence and Botte classification which divides the proximal bone into 3 zones (Foot Ankle 1993). Their classification, like so many in those days, was largely based on observation and anecdote.
    Zone 1 fractures are fractures of the styloid, invariably avulsion fractures of the peroneus brevis.
    Zone 2 fractures are metaphyseal fractures involving the joint between the bases of the 4th and 5th metatarsal bases —the so-called Jones fracture (named after Sir Robert Jones, who reported his own injury).
    Zone 3 fractures are diaphyseal and are often stress fractures.
    A more recent paper by Polzer et al (Injury 2012) argued that only 2 zones need to be considered because they believed that the prognosis of fractures in the 2 more proximal zones is identical. Styloid process fractures (Zone 1) and those involving the joint between the bases of the 4th and 5th metatarsal bases (Zone 2) can thus be managed functionally. They argued that zone 3 injuries (from the Lawrence & Botte classification) need operative management.
    So in a nutshell, we tend to think of injuries in the metaphyseal region (call this Zone 3) as being the ones with the poorest blood supply and at the highest risk of delayed or non-union. Type 3 fractures should be considered for operative fixation, particularly if there is any cavus posture of the foot, neuropathy, or if the patient is a competitive sportsperson.
    If surgery is indicated then the argument is that it may reduce the time needed for immobilisation and improve the chance of healing compared to nonsurgical treatment.
    In this case, a 28 year old athlete whom originally had been treated non operatively presented with clinical and radiographic features of a non union 12 months after the original injury.

    Indications

    INDICATIONS
    Type 3 fractures especially those with cavus posture of the foot, neuropathy, or if the patient is a competitive sportsperson.
    Type 2 (Jones type) fractures – some argue these also have a high chance of non-union. Others argue that these do well with non operative management. As with much of orthopaedic surgery, this is a controversial area.
    Other fractures treated non operatively which have gone on to non union.
    SYMPTOMS & EXAMINATION
    Pain and swelling on the outside of the foot. Routine examination should be performed including full neurovascular assessment. Tenderness over the 5th metatarsal is invariably present.
    IMAGING
    Plain radiographic imaging. Three views are taken: dorso-plantar (DP), oblique and lateral. Invariably I arrange a CT scan because it is difficult to appreciate a 3 dimensional injury in 2D images. At the RNOH we use a standing CT scanner (PedCat) as routine imaging for these injuries. Ultrasound or MRI is of benefit in assessing for other injuries such as adjacent joint arthropathy (4/5th TMTJ), or peroneal tendon issues if indicated.
    ALTERNATIVE TREATMENT
    You must always discuss non operative treatment options with the patient and document these discussions. There are other modalities possible like low intensity pulsed ultrasound (eg EXOGEN) bone stimulators, pulsed electromagnetic fields (PEMF), PRP injections, and shockwave therapy. Aside from PEMF which has a small but well constructed study, none of the others have any strong evidence base to support their use in this condition.
    NON-OPERATIVE MANAGEMENT
    Non-operative intervention has a role to play in most fractures of the base of the 5th metatarsal. Remember that some of these fractures go onto heal with a strong fibrous union and are entirely asymptomatic and it is important not to treat an X-ray and deal with the patient in front of you. If surgery is planned, careful consent must be obtained from the patient informing them of the non operative options and potential complications.
    CONTRAINDICATIONS
    Diabetes, vascular disease or metabolic compromise from steroid treatment are relative contra-indications for surgical intervention. Be very cognisant of Charcot disease in a neuropathic foot.
    Always be cautious of non compliant patients and active smokers, as these patients require very careful counselling and consenting if you are considering operating on them.

    Setup

    The patient is positioned supine on the operating table with a padded sandbag (known as a “bump” in the USA) under the ipsilateral buttock. Always assess the patients hips on the wards preoperatively to determine if you are able to swing the foot onto the image intensifier to predictably determine how you will use the II during the case.
    We use a mobile digital mini image intensifier (mini C-arm).
    Antibiotics according to your standard protocol are administered intravenously at induction and a thigh tourniquet set at 280mmHg are applied and inflated. Routine draping and skin preparation is performed with the drapes exposing the knee downwards (like a knee replacement, which is my standard approach as you always need access to the knee when performing foot and ankle procedures).

    Operation

    I try and bring the leg to the II. I do this by abducting the whole leg (as checked preoperatively) and by internally rotating the foot into an oblique position I can view the anatomy. I usually obtain lateral views by external rotation. You will need to develop your own system based on the II you have at your hospital.

    I use the Asnis III Stryker Cannulated Screw System.
    You can use any similar system. The reason I use this system is that the heads are low profile and they have a larger diameter guide wire than other systems. Otherwise a screws a screw and so the other benefits seem to be universal.

    I mark out the anatomy on the foot, obviously technically easier when no swelling is present and the landmarks are palpable. In a swollen foot, I often use the II to assist in drawing my outlines. This enables me to establish where my entry point will be and the trajectory of my screw.
    Remember the peroneus brevis broadly inserts into the base of the 5th metatarsal superiorly, and then the lateral band of the plantar fascia attaches inferior and more lateral than this. Some surgeons try and go between the two, I tend to try and come up slightly higher, often having to pierce through the fascia of the peroneus brevis by coming superomedially (which you need to do if you want to enter the medullary canal) but you really don’t disturb either much.

    I place a K wire on the skin and mark in DP, oblique and lateral images to ensure I can see the fairway and my likely entry point. In this image I am clearly too superior and the wire is repositioned. I want the wire to appear down the fairway on both images.

    Top Tip: A small skin incision is made bearing in mind the distance to the entry point is likely to be more proximal than the actual bone so the trajectory is correct. I tend to make a 1.5cm incision about 2cm proximal to the intersection of a line drawn with my surgical pen.
    The sural nerve usually is encountered directly under the skin incision and must be identified and protected and I use dissection scissors or a clip to split the fascia of peroneus brevis and feel the bone. You may see the lateral band of the plantar fascia attaching just below you.


    A K-wire is inserted into the bone under II control starting in the high and inside position and should not meet any resistance suggesting that the cortex may be penetrated. Stop if you feel resistance and check the imaging as you do not want to penetrate the cortex if possible (unless this is part of your preoperative plan for very proximal fractures). In this case I want my screw to go up the medullary canal.

    Measure the length of your screw.
    Remember that the fifth metatarsal is a curved bone and you are putting in a straight screw. It is therefore important when determining length of screw for all threads of the screw to pass the fracture site but not to extend down the intramedullary canal past 60% of the length of the fifth metatarsal as this can only be achieved by straightening the bone.
    In this case a 55mm screw is chosen.

    Confirm your measurement probe is touching the bone or correct the length appropriately.

    Drill the hole. I am using a 5mm screw and hence using a 3.5mm cannualated drill.
    After tapping I usually add a countersink to ensure the screw is not prominent.
    In cases of non union I ream two or three times to encourage endosteal blood flow. In cases of displaced fibrous union, you may need to open the fracture site and remove the fibrous tissue and freshen the bone ends (and/or apply some local bone graft), but that is not needed in the case of a stress fracture non union as in this case.

    Ream as appropriate across the fracture site.

    I have obtained 2 mls of bone marrow aspirate (BMA) using the aseptic Stanmore Bone Marrow Harvest Technique from the posterior superior iliac crest when the patient arrived in the theatre and was stored with 0.5mls of heparin until this point in a sterile container.
    I then mix the BMA with AlloMatrix Ignite Graft (Wright medical) to produce an injectable paste which I then inject into the 5th metatarsal before inserting the screw.

    I then insert the screw with good compression under II control. You can go up to a 7mm screw in very large patients. It is important however not to put too large a screw in for fear of causing a diaphyseal fracture.

    I try and bury the head so it is not palpable under the skin being cautious not to bury it too far which would make later removal difficult.

    I wash out the wound and then close my small incision using a nylon or monocryl suture (my decision is based on the quality of the skin). If I use a monocryl suture I tend to use Dermabond on top to seal it.

    This is an AP radiograph of this patient pre-operatively demonstrating a non union in Zone 3 of the 5th metatarsal. On a single view it is sometimes difficult to appreciate a non union and so two or three views are essential. In some circumstances an MRI, CT scan or even a Spect CT scan can be useful.

    This is an oblique radiograph of the patient preoperatively where the clear lateral cortical defect is visible.

    This is the postoperative AP radiograph taken at 6 weeks showing fixation and good evidence of healing

    A lateral radiograph showing good fixation and good evidence of healing, which correlates in an improvement in symptoms of the patient

    Post Operative

    My routine dressing is Melolin, natural wool and crepe bandage. Depending on fixation and the patient reliability I may use a below knee backslab.
    I truly dislike Velband, mainly because I had this myself (on several of my numerous operative procedures) and it is minimally expansile and so doesn’t allow swelling easily and is itchy. I therefore use natural wool rolls which are sterile packed and I have never had to split a plaster since.
    The leg is elevated on a Braun Frame or BoneFoam Wedge and neurovascular observations are performed.
    The patient is non weight bearing using crutches for 2 weeks and the decision on weight bearing thereafter depends on the type and nature of the fracture coupled with the progress of the wound healing.
    Thromboprophylaxis is considered as per NICE guidance and discussed with the patient and local thromboprophylaxis protocols should be followed.
    In this patients case, weight bearing began in a short Aircast boot at 6 weeks and physiotherapy focussing on core stability and proximal chain kinetics was initiated. Full weight bearing out of a boot began at 12 weeks as well as initiation of physio to the foot, consisting of joint mobilisations, strengthening exercises for the small muscles of the foot and proximally including wobble board activities etc. Return to competitive sports began at 20 weeks. In some patients I am much less conservative and will allow them to weight bear as comfortable from 2 weeks, but my decision on rehab is very much dependant on the patient characteristics, personality and co-morbidities.

    Recommended Reading

    There is little published evidence on the outcome of 5th metatarsal non unions other than review papers containing level V expert opinion. There are some case reports in the podiatric literature (Chand K 1971 and Rubin LM 1968).
    Habbu et al. 2011 reported a case series (Level IV) of 14 patients with a Jones fracture non union (mean age 49 and mean duration since injury was 28 weeks). All patients were treated with a single intramedullary screw inserted from the base of the fifth metatarsal without opening the nonunion site. Union was achieved in all 14 patients with one delayed union. Mean time to union was 13.3 (range, 8 to 20) weeks. Patients were able to start unassisted full weight bearing without pain at mean 10.2 weeks.
    Foot Ankle Int. 2011 Jun;32(6):603-8. doi: 10.3113/FAI.2011.0603.
    Streit et al 2016 published an interesting study that is described as a level I study but having only included 8 patients cannot really be considered more than a level II study. It is an RCT where 8 patients with established non unions of the 5th MT were randomized to receive either an active stimulation or placebo bone stimulation device. Patients had biopsies prior to and after treatment and ORIF. The authors concluded that adjunctive use of PEMF for fifth metatarsal fracture nonunions produced a significant increase in local placental growth factor although all 8 patients went onto union after ORIF.
    Foot Ankle Int. 2016 Sep;37(9):919-23. doi: 10.1177/1071100716652621. Epub 2016 Jun 10.

    Reference

    • orthoracle.com

    Tags:

    You might be interested in

    Dark mode powered by Night Eye