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Open reduction and internal fixation of acromion fracture with os acromiale using cannnulated screws and box suture

    Overview

    Learn the Open reduction and internal fixation of acromion fracture with os acromiale using cannnulated screws and box suture surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Open reduction and internal fixation of acromion fracture with os acromiale using cannnulated screws and box suture surgical procedure.
    I use the following technique for fixation of displaced acromion fractures that are too small to accommodate fixation using anatomic contoured plates. My first preference would be for plate fixation if the fracture pattern allows, as is also used for surgical management of a symptomatic os acromiale(where the os occurs proximal to the pre-acromion).
    Numerous surgical techniques for management of acromion fractures have been described, which are rare injuries. The main considerations include the location, orientation and size of the fracture fragments, the biomechanical stability of the construct proposed and the amount of associated soft tissue and deltoid stripping. Methods include K-wire fixation, tension band fixation, cannulated screw fixation as well as using pre-contoured plates including lateral end clavicle plates as well as acromion plates.
    In the case described cannulated screws were the only viable option due to the size of the fragments. However to improve the mechanical stability this fixation is augmented with a box suture through the screws to improve the ultimate failure load of the construct, as described by Speigl et al. Fibrewire rather steel wire is used as the suture material because it is less likely to cause soft tissue irritation. Shiu et al have shown there is no significant difference in ultimate load to failure between using stainless steel wire and polyethylene suture.
    K-wire fixation is not recommended due the the risk of early failure and risk of K-wire migration. This is due different planes of action of the deltoid fibres that the construct is unable to counteract.
    Traumatic acromion fractures
    In trauma, fractures involving the scapula usually result from high energy injuries. They commonly involve the scapula body and spine (50%). Associated injuries involving the shoulder girdle have also been commonly reported, including clavicle fractures, vascular injuries, plexus injuries, cuff tear and glenohumeral joint dislocations as well as rib fractures, pulmonary contusions/pneuomothoraces and head and spine injuries. Scapula fractures have a mortality rate of 2-5%.
    Acromion fractures account for 8% of all scapula fractures. They are rare with an incidence of less than 1% of all fractures. As a result, the indications for surgery are not well established. However, concerns with displaced fractures can result in painful non-union and can compromise shoulder function.
    The method of fixation is usually determined by the fracture pattern, with particular reference to the location of the fracture.
    When classifying scapula fractures, they can be subdivided into fractures of the glenoid, acromion and coracoid. The AO classification subdivides scapula fractures into fractures of the process, body or glenoid. Acromion fractures are described as a fracture of the acromion process (14A2), but does not subdivide them into fracture patterns.
    More commonly used classifications include those described by Kuhn et al, Ogawa and Naniwa and Goss et al.
    Kuhn et al. proposed a classification system of acromion fractures and divided them in:
    Type I – Minimally displaced fractures
    IA – avulsion type fracture
    IB – minimally displaced fracture associated with direct trauma
    Type II – fracture with displacement superiorly, anteriorly or laterally
    Type III – fracture with displacement causing a reduction in subacromial space
    Kuhn recommended that type III acromial fractures should undergo surgical fixation.

    Spiegl UJ, Smith SD, Todd JN, Wijdicks CA, Millett PJ. Biomechanical evaluation of internal fixation techniques for unstable meso-type os acromiale. J Shoulder Elbow Surg. 2015 Apr;24(4):520-6.
    Shiu B, Song X, Iacangelo A, Kim H, Jazini E, Henn RF, Gilotra MN, Hasan SA. Os acromiale fixation: a biomechanical comparison of polyethylene suture versus stainless steel wire tension band. J Shoulder Elbow Surg. 2016 Dec;25(12):2034-2039.
    Kuhn JE, Blasier RB, Carpenter JE. Fractures of the acromion process: a proposed classification system. J Orthop Trauma. 1994;8(1):6-13.

    Indications

    INDICATIONS
    Relative indications for surgery include displaced or unstable fractures. There is a lower threshold for surgery if the displacement reduces the subacromial space and predisposes the patient to risk of impingement as well as in patients of high functional demand.
    Associated injuries involving the superior shoulder suspensory complex (SSSC) would also merit surgical consideration if two or more structures are involved. The SSSC comprises of the lateral end of clavicle, acromioclavicular joint, acromion, glenoid and coracoid.
    Symptomatic non-union is also an indication for surgery.
    SYMPTOMS & EXAMINATION
    Scapula fractures usually result from high energy trauma. For acromion fractures, these usually involve a direct blow to the shoulder. There is usually associated bruising and tenderness with associated limitation of shoulder movement due to pain inhibition.
    Careful examination of the shoulder should reveal bony tenderness localised to the fracture site. This should arouse a clinical suspicion of an acromion fracture and correlation by review of imaging may confirm the clinical findings.
    It is also important to assess the shoulder to exclude any associated injuries including a neurovascular assessment, looking for any plexus injury.
    IMAGING
    Anteroposterior and axillary radiographs of the shoulder help to highlight any obvious deformity. Scapula Y views may help in characterising the fracture.
    When assessing the acromion on a radiograph, it may be difficult to clearly identify the fracture due to overlying structures on the different views. If there is a clinical suspicion but no clear fracture or if the fracture pattern is complex, a CT scan with coronal and sagittal reconstructions is helpful in confirming the diagnosis as well as for surgical planning if indicated.
    ALTERNATIVE OPERATIVE TREATMENT
    Due to the rarity of the injury, numerous surgical techniques for management of acromion fractures have been described. The location and orientation of the fracture usually determines the method of fixation. These include K-wire fixation, tension band fixation, cannulated screw fixation as well as using pre-contoured plates including lateral end clavicle plates as well as acromion plates.
    K-wire fixation is not recommended due the the risk of early failure and risk of K-wire migration. The other techniques have reported good results. Plate fixation has reported good to excellent results with good union rates albeit in small case series. Complications of this include metalwork irritation requiring removal.
    Fractures can be located at the tip (pre-acromion region), mid (meso-acromion region) and base (meta-acromion) at the junction with the spine of the scapula.
    NON-OPERATIVE MANAGEMENT
    The majority of acromion fractures are well aligned and minimally displaced. These can be treated in a sling for comfort with early motion as pain allows. Fractures tend to unite at 6-12 weeks with no significant deficit.
    CONTRAINDICATIONS
    Patients of low functional demand or medically unfit or active infection would be relative contra-indications. As part of informed consent, a discussion of outcomes of conservative and operative methods is essential for treatment planning. Surgery is reserved for displaced or unstable fractures.
    Os acromiale
    Os acromiale describes an unfused accessory centre of ossification in the acromion. It is generally asymptomatic but is associated with rotator cuff tears and shoulder impingement. Management of this condition is largely conservative involving anti-inflammatory medications, physiotherapy and corticosteroid injections. Surgery is only considered once conservative measures have failed. Depending on the size of the os, surgical options include subacromial decompression with anterior acromioplasty, reduction and fixation +/- bone grafting or excision of the os.
    The acromion has several ossification centres, with failure to fuse forming an os acromiale at the anterior tip (pre-acromion), mid-body (meso-acromion) and base (meta-acromion). As the ossification centres fuse at different ages, the diagnosis of failure of fusion cannot be made until over the age of 25. The most common type is the meso-acromion.
    There is a higher frequency in Black and male populations.
    The diagnosis can usually be made on plain radiographs but can be easily missed due to the overlapping proximal humerus on the axillary view. A double density sign can also be seen on the AP radiograph of the shoulder. An MRI can be useful in clarifying pathology and also look for associated bony oedema in a suspected symptomatic os.

    Setup

    The patient is placed in a semi-sitting position at around 45 degrees inclination on a shoulder table. The head is secured in the head clamp of the shoulder table in a neutral position, ensuring that the neck is not hyperextended or hyperflexed. A small pad can placed behind the medial border of the scapula to aid retraction of the scapula in relation to the thorax to stabilise the scapula during surgery.
    The shoulder table cut-outs are removed on the operative side to allow unhindered fluoroscopic imaging during the procedure.
    The operative site is prepared in standard sterile fashion and is draped to expose the acromion laterally, to the sternum medially. The lead author does not routinely include the arm in the drapes and is positioned in an adducted position on the the shoulder table.
    Intravenous antibiotics are administered and intermittent calf compression is used for thromboembolic prophylaxis during the procedure unless there is a contraindication.
    Kit required for this case includes:
    Depuy Synthes 4.0mm cannulated screw system incorporating 1.25mm threaded K-wires with cannulated screw measure, 2.7mm cannulated drill, 4mm partially threaded cannulated screws
    Arthrex suture passing wire
    Number 2 Fibrewire

    Operation – 1

    This 18 year old right handed male was involved in a road traffic collision – pedestrian versus car. He sustained a right open acromion fracture (with underlying os acromiale) and associated nerve injury.
    He underwent emergency surgery for debridement and closure of the wound for the open fracture. At the same sitting, an exploration of the nerve in the zone of the injury was performed. The suprascapular nerve was identified but felt to be in continuity.
    After initial management, he was referred for an upper limb opinion for management of the acromion fracture. Post-operatively, his fracture was clinically unstable (due to the underlying os acromiale predisposing him to greater instability) and that he was in significant pain. We therefore felt that this fracture was best managed operatively.

    A CT scan of the right shoulder showing axial (A), coronal (B) and sagittal (C) reconstructions.
    The axial image shows the pre-existing os acromiale at the meso-acromion region. There is a fracture in the sagittal plane splitting the tip of the acromion.
    The fracture can be seen in the coronal image (B).
    The os can be seen in the sagittal image (C).

    The 3D reconstruction of the right shoulder clarifies the orientation and size of the fragments.
    The unfused os is separate from the main body of the acromion (A).
    We can see that the os has been split into a lateral (B) and a medial (C) fragment.

    The patient is set up on a shoulder table inclined at 45 degrees.The head is secured in a head clamp.
    The right shoulder cut-away on the shoulder table is removed to aid fluoroscopic imaging intra-operatively.

    The surgical area is prepped using alcoholic chlorhexidine from the sternum to the proximal half of the humerus.

    A sterile DHS drape is applied exposing the proximal upper limb and shoulder girdle to the sternum.There are advantages to using a DHS drape:
    As it is a single drape, it is quick and easy to apply.
    The DHS drape is transparent, the allows the anaesthetist to check on the patient’s head position intra-operatively.
    The adhesive section of the drape prevents the drape from slipping off and desterilising the operative field.

    A ‘sabre cut’ or superior incision is sited just lateral to the acromioclavicular joint (ACJ).In this case, the incision was made through the old wound. If the exposure was difficult/not appropriate, the incision can be extended anteriorly and posteriorly.
    The ACJ can be located by palpating the ‘V’ formed by the posterior border of the lateral end of clavicle and the spine of the scapula. The posterior limit of the ACJ can be located at the apex of the ‘V’.


    The skin and fat are incised to expose the trapezius and deltoid fascia.Haemostasis is achieved using electrocautery.
    A – Trapezius fascia
    B – Deltoid fascia

    Skin flaps are developed laterally in the plane just superficial to the deltoid and trapezius fascia to expose the acromion.Dissection in this plane is developed until the lateral border of the acromion is exposed.

    Skin flaps are developed medially in the plane just superficial to the deltoid and trapezius fascia to facilitate closure of the layers correctly.Note, the supraclavicular nerves start in the layer beneath platysma and deep cervical fascia but pierce the fascia and platysma around the clavicle to become cutaneous. This is superficial to the deltoid and pectoralis fascia.
    They are normally grouped into an medial, intermedial and lateral supraclavicular nerves.
    The lateral supraclavicular nerves pass obliquely over the outer surface of the trapezius fascia and acromion. The supply sensation to the skin on the upper and posterior parts of the shoulder.
    Transection of these nerves can result in an area of numbness lateral and posterior to the acromion, although usually improves over time and of minimal clinical significance.

    It is helpful to palpate the lateral end of the clavicle to confirm the anatomy and orientation of structures.
    Finger A – posterior border of lateral end of clavicle
    Finger B – anterior border of lateral end of clavicle

    The deltotrapezial fascia is incised in an anteroposterior orientation lateral to the ACJ to expose the acromion body.In this case, the sutures over the fascia are located and removed.

    The fascia is elevated off the bone using a periosteal elvator or using sharp dissection.A – deltotrapezial fascia
    B – body of acromion
    C – site of os acromiale
    D – lateral end of clavicle and ACJ (hidden under fascia)

    The fracture cleavage plane is exposed and fracture surfaces and os acromiale are curetted.The curette is located over the os acromiale in this image.

    In open fractures, the wound and fracture edges are irrigated with normal saline.In this image, the fracture pattern becomes more clear:
    A – lateral fragment of tip of acromion
    B – os acromiale
    C – main body of acromion
    D – medial fragment of tip of acromion still attached to AC ligament and lateral end of clavicle

    The forceps marks the os acromiale (A) more clearly in relation to the lateral tip fragment (B).

    The fibrous articulation at the os acromiale is taken down using sharp dissection.It is important to respect the soft tissue attachments of the os to avoid destabilising the tip of the acromion, as well as preserving the blood supply.

    Both surfaces of the os acromiale on the body and tip are freshened using a burr.If there is any concern that the tip of the acromion is down-sloping and encroaching on the subacromial space, a wedge resection taking more of the superior cortex helps to correct the anterior acromial hook.
    This can be done using the burr or saw.

    The ACJ is located using a hypodermic needle to help orientate the anatomy. A stab incision can be made in the deltoid fascia to allow application of K-wires.Attention is turned to the anteromedial acromial tip fragment (B).
    Care is taken to respect the soft tissue to avoid devitalising the blood supply to the fracture fragments and destabilising the fracture.
    A – ACJ
    C – Deltoid fascia

    A 1.25mm threaded K-wire is passed through the anteromedial tip fracture fragmentThe Kocher is used to manipulate and orientate the anteromedial tip fragment.
    The hypodermic needle acts as an aide for orientation and to avoid the technical error of passing the K-wire through the ACJ.

    The K-wire in the anteromedial tip fragment, along with the Kocher, can be used as a joystick to reduce the fracture.This is aided by the assistant supporting the weight of the arm under the elbow.

    Once reduced, a pointed reduction clamp can be applied from the posterior border of the acromion (A), to the anterior cortex of the lateral end of clavicle (B) to stabilise the reduction.Due to the weight of the arm, the fracture tends to be distracted laterally and posteriorly.

    The K-wire can be driven into the body of the acromion to maintain reduction.

    Having checked the reduction, two 1.25mm threaded K-wires are applied from anterior to posterior, as perpendicular to the os as possible.The K-wires should be as parallel as possible.
    The K-wires are driven in until the far cortex is breached. Once feedback from this is felt, the wires are left in situ to allow measurement off the K-wire.

    In this technically challenging case, each wire has to pass through one of the tip fragments into the body of the acromion, without penetrating the superior or inferior cortex of the acromion.
    Note that in this case, the wires have been directed more posterolaterally than desirable. This is after the first attempt yielding an unsatisfactory K-wire position. Due to the fracture configuration, this was the only trajectory that allowed a K-wire passing from the anteromedial fragment to gain purchase in the body of the acromion.
    As a result, the K-wires tend to exit on the lateral cortex of the acromion, rather than the posterior cortex.

    Operation – 2

    After positioning the K- wires, fluoroscopic images are obtained to ensure the trajectory of the K-wires is acceptable.It is helpful to try to get the x-ray beam in the same plane as the K-wires to allow easy interpretation of the images.

    These fluoroscopic images show that the wires are parallel and have not penetrated the superior or inferior cortex of the acromion, as well as the ACJ.

    The length of screw required can be obtained using the cannulated screw measuring device. This is applied to both K-wires to determine length of both screws.The measuring guide is applied over the wire and should be advanced so that the tip is against the bone.
    The K-wires should have a laser line etched on the shaft so that length of screw can be referenced off the measuring device.
    Note, the measure will place the tip of the screw 5mm short of the position of the tip of the K-wire.

    A 2.7mm cannulated drill bit is applied to the first K-wire and advanced through both cortices.Note, the K-wire can back out when removing the cannulated drill. If this occurs, the K-wire can be re-sited by hand but it is important to check the position using fluoroscopy when in doubt.

    The appropriate length 4.0mm partially threaded cortical screw is applied over the guidewire and advanced until there is good bicortical hold. The K-wire can then be removed by hand.As the screw is advanced and threads engage in the far cortex, it is important to observe that there is compression at the os acromiale.
    It is important not to overtighten to minimise the risk of fracture.

    The second wire is then drilled using the 2.7mm cannulated drill bit and the steps repeated.It is important to sequentially drill and insert the cannulated screw to minimise the risk of losing reduction of the os acromiale or fracture.

    Once the second 4.omm cannulated screw is applied, the 2 cannulated screws are sequentially tightened to ensure good bicortical hold.Again, compression at the os/fracture site should be observed.

    The Arthrex suture passing wire consists of a blunt tipped flexible wire with a nitinol loop at the end (A).
    This helps make passing sutures through cannulated screws a doddle.

    The K-wire is exchanged for an Arthrex passing wire. This is advanced through the screw and exits at the posterior aspect of the acromion at it’s exit point.Before exchanging the K-wire for the suture passing wire, the K-wire can be advanced by hand to confirm the position of the screw tip. This is useful if the screw tip is obscured by soft tissues.
    A – Arthrex suture wire passer tip.

    A number 2 Fibrewire is passed through the nitinol loop of the passing wire.When passing the suture through the loop, there only needs to be sufficient length on one limb of the Fibrewire suture to pass through the cannulated screw. This allows retrieving and unloading from the the passing wire quicker and more efficient once it has been shuttled through the cannulated screw.

    The passing wire is pulled through the cannulated screw from anterior to posterior, taking the Fibrewire suture with it.If there is any snagging on the soft tissues, the passing wire can usually be freed using short, sharp jerks when passing it from anterior to posterior through the screw.

    The Fibrewire suture is unloaded from the wire passer and left in situ, having passed through the first cannulated screw.If there is concern that the Fibrewire can be unloaded from the screw, an artery clip can be applied to the free limb of the Fibrewire suture at the tip of the screw.

    The head of the second screw is located and the free suture wire passer is passed from anterior to posterior with the blunt tip first.

    This is retrieved at its exit point at the tip of the second screw at the posterior aspect of the acromion.A – tip of suture passing wire at tip of second screw.

    The passing wire is pulled through from anterior to posterior through the second cannulated screw.

    The free limb of the Fibrewire suture at the head of the first screw is loaded through the nitinol loop and shuttled through the second screw from anterior to posterior.Before loading onto the suture passing wire, it is important to check that there isn’t any soft tissue bridge between the screw heads anteriorly – particularly fibres of the deltoid muscle.

    The Fibrewire is unloaded from the passing wire and pulled taut.It is important to take all the slack out of the suture before tying.

    The ends of the suture are tied to create a box suture through the cannulated screws.An artery clip can be used to maintain the tension on the Fibrewire suture when tying the first knot.

    Once secure, the stabilising K-wire can be removed.Once removed, check that the fixation has maintained the reduction and that the position is good.

    The deltotrapezial fascia is closed using number 2 Fibrewire.

    The closure of the fascia is important in adding stability to the construct.

    The fat layer is closed using 2-0 vicryl.

    The skin is closed using 3-0 monocryl and dressing using 1/2 inch steristrips.

    The wound is dressed using waterproof dressings.An absorbant pad can be applied for 48 hours to support the dressings.

    This AP radiograph of the shoulder at 6 months shows that the fracture and os acromiale has united and that the position is maintained.
    There is no obvious double density of the acromion on the radiograph.

    Operation – 3

    The axillary view also shows that the fracture and os acromiale has united.
    The screws look to be angled a little laterally and appear to be prominent.
    However, on clinical correlation, the patient has recovered full movement in his shoulder. There is no metalwork prominence clinically and no localised tenderness.
    A CT scan would be indicated if concern remains about implant position.

    Post Operative

    Post-operatively, patients are reviewed by the physiotherapy team before discharge to encourage mobilisation of the elbow, wrist and hand. The arm is supported in a sling for 4-6 weeks. Active assisted shoulder mobilisation is allowed although elevation of arm above shoulder height is restricted for the first four weeks.
    Free active ROM as pain allows is permitted after 4 weeks.
    Patients are reviewed in clinic at two weeks to check the wounds and ensure they are compliant with the rehabillitation programme. Check X-rays are taken at 6-8 weeks in clinic.
    Full active range of motion is initiated at four weeks. When clinical and radiographic signs of union are present (around 6-8 weeks), strengthening exercises of the rotator cuff, deltoid, and trapezius are commenced. Patients usually return to sporting activities by three to four months.

    Recommended Reading

    Spiegl UJ, Smith SD, Todd JN, Wijdicks CA, Millett PJ. Biomechanical evaluation of internal fixation techniques for unstable meso-type os acromiale. J Shoulder Elbow Surg. 2015 Apr;24(4):520-6. doi: 10.1016/j.jse.2014.09.040. Epub 2014 Nov 28.
    Speigl et al. showed there was a significantly higher ultimate load to failure in the cannulated screw with tension band wire group when compared to cannulated screw fixation alone.
    Shiu B, Song X, Iacangelo A, Kim H, Jazini E, Henn RF, Gilotra MN, Hasan SA. Os acromiale fixation: a biomechanical comparison of polyethylene suture versus stainless steel wire tension band. J Shoulder Elbow Surg. 2016 Dec;25(12):2034-2039. doi: 10.1016/j.jse.2016.04.028. Epub 2016 Jul 14.
    Shiu biomechanically tested the same tension band and cannulated screw construct as Speigl et al. and compared constructs using polyethylene suture and steel wire. There was no significant difference in ultimate load to failure between the 2 groups.
    Kuhn JE, Blasier RB, Carpenter JE. Fractures of the acromion process: a proposed classification system. J Orthop Trauma. 1994;8(1):6-13. doi: 10.1097/00005131-199402000-00002.
    Kuhn et al reviewed 27 fractures and proposed a classification involving the level and direction of displacement.
    Surgery was recommended in displaced fractures reducing the subacromial space.
    Hess F, Zettl R, Welter J, Smolen D, Knoth C. The traumatic acromion fracture: review of the literature, clinical examples and proposal of a treatment algorithm. Arch Orthop Trauma Surg. 2019 May;139(5):651-658. doi: 10.1007/s00402-019-03126-6. Epub 2019 Jan 22.
    Hess et al reviewed the current literature on acromion fractures, confirming evidence is limited to small case series due to the rarity of the injury. Surgeons tend to advocate fixation to restore anatomy with good results.

    Reference

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