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Intramedullary fixation of metacarpal fracture using the Acutrak compression screw

    Overview

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    Metacarpal neck fractures are very common in the hand. The “Boxers” fracture of the 5thmetacarpal neck being one of the commonest injuries that presents to a Hand surgeon. Most of these injuries can be treated conservatively and heal satisfactorily with no functional deficit. However, some present with rotational deformities that need correction for an optimal outcome. A handful of these also present with other concomitant injuries in the hand, which cannot undergo appropriate rehabilitation until the metacarpal neck fracture has been adequately stabilized.
    Many surgical techniques have been described for reduction and stabilization of this fracture with varied risks and benefits. Open fixation with plates and screws affords the most reliable reduction and a stable construct for immediate mobilization. However, tendon adhesions and stiffness are a significant potential complication. This is a step-by-step guide of a novel technique to achieve rigid stabilization with a minimally invasive approach and an intramedullary fixation. The procedure is minimally invasive and the intramedullary location of the implant minimises risks of tendon adhesions.

    Indications

    INDICATIONS:
    Intervention with reduction and stabilization of a metacarpal neck fracture is indicated in the following scenarios:
    Open fractures
    Fractures with rotational deformity. No amount of rotational deformity is acceptable as it results in functionally disabling scissoring of the fingers.
    Comminuted and unstable fractures
    Presence of associated injuries in the same hand requiring early rehabilitation
    Angulation more than 70 degrees. Although angulation at fracture site has been extensively studied, this one feature in isolation has not been found to be significant for functional outcome.
    The technique can be used in metacarpal neck fractures of any finger. The following guide describes the procedure for the commonest injury pattern in the 5thmetacarpal.
    SYMPTOMS & EXAMINATION:
    An axial loading force to a clenched fist causes these injuries. This produces a flexion vector on the metacarpal, which succumbs at the neck. The common mechanism is a punching injury and hence the infamous eponym of a “Boxer’s fracture”. They can also coexist with high-energy injuries such as road traffic accidents, as in this case.
    The patient presents with pain and swelling over the dorso-ulnar border of the hand. There is tenderness over the neck of the metacarpus and movements of the finger may be restricted with pain. A common finding is an apparent extensor lag of the small finger at the metacarpophalangeal joint. Presence of any rotational abnormality should be evaluated and documented. Ask the patient to flex all fingers together and look for any scissoring. It is important to remember that the small finger naturally curls radially and points towards the scaphoid tubercle at the wrist. Comparison can be made with the opposite uninjured hand.
    IMAGING:
    Plain radiographs are essential to confirm the diagnosis and plan the management. I always request for three radiographic views of the hand– Antero-posterior, lateral and oblique. The fracture pattern and location, the displacement and the comminution are noted. Associated injuries should always be looked for and are commonly seen involving the base of the 4thand 5thmetacarpals.
    ALTERNATIVE OPERATIVE TREATMENT:
    Conservative with closed reduction followed by plaster immobilisation – Unfortunately, this prevents early rehabilitation of the associated injuries in the hand. In addition, a plaster cast is inadequate to maintain a reduction in comminuted fractures of the neck.
    Percutaneous wiring techniques– These range from longitudinal intramedullary wires, transverse intermetacarpal wires, crossed wires and Bouquet wires. Although these techniques are less invasive, the risk of pintrack infections and the need to eventually remove the wires as a second procedure, make them less favorable. Additionally, the insertion of the bouquet wires can be technically demanding.
    Open reduction and internal fixation with plates and screws – This technique provides reliable stabilization but carries the risk of tendon adhesions and stiffness. However, it is very useful in fracture patterns with comminution.
    CONTRAINDICATIONS:
    Comminuted fractures are a contradiction as compression with the screws can result in a collapse of the fracture fragments.
    Segmental fractures are a relative contraindication as the screw length may not be adequate to effectively straddle both the fracture sites. In addition, the radiographs should be closely examined for any intra-articular extension of the fracture, as this would preclude one from proceeding with this procedure.

    Setup

    Informed consent is an important part of the procedure and the risks and benefits should be clearly explained to the patient. The risk of stiffness at the metacarpophalangeal joint, although reduced, should be discussed. The patient should also be warned of the potential need to convert the procedure to an open reduction and plate fixation if the fracture is irreducible or shows signs of comminution.

    I prefer regional anaesthesia with axillary block for this procedure. However, the newly popular WALANT method of anaesthesia can be used instead. This allows for the patient to retain his motor control during the procedure allowing for better assessment of active scissoring after fixation. The patient is placed supine with the limb extended on an arm table. Upper arm tourniquet is applied and inflated after exsanguination. A prescrub is performed followed by a sterile prep with Chlorhexidine. A lead hand may be used to stabilize the hand. I routinely administer a single dose of antibiotics for this procedure.

    Operation – 1

    A 24 year old right hand dominant man presented with a punching injury. This was an isolated injury with a closed fracture of the metacarpal neck as shown.
    Clinical examination revealed swelling, an extensor lag at the metacarpophalangeal joint and an obvious rotational deformity of the small finger with scissoring.
    The radiographs show a displaced juxta-articular fracture of the neck of the 5th metacarpus. Conventional rigid fixation techniques with plates would place the metalwork adjacent to the articular cartilage and under the closely adherent extensor hood – thereby significantly increasing the risks of tendon adhesions and stiffness.

    The hand is positioned and the landmarks identified.After set-up, the distal end of the metacarpal and the proximal end of the phalanx are marked to identify the location of the MCP joint.

    A 2 cm dorsal longitudinal incision is planned overlying the metacarpophalangeal joint.The skin is incised with a No.15 blade. The subcutaneous tissue is incised with sharp dissection and the skin flaps retracted.

    The extensor hood to the small finger is exposed immediately beneath the subcutaneous tissues. Note the bruising suggestive of the underlying fracture.

    A longitudinal incision is made in the extensor hood to approach the MCP joint.The extensor hood is incised longitudinally to obviate the need for immobilisation for tendon healing in the immediate postoperative period.

    The capsule is identified.
    The split extensor tendon is protected out of the way with a self retaining retractor

    The capsule is incised in line with the longitudinal skin incision.

    The metacarpal head and the base of the proximal phalanx are now revealed.

    The Acutrak 2 Headless Compression screw (Acumed)®system is a cannulated screw of variable thread pitch and self-cutting flutes. The Mini Acutrak screw has a diameter of 3.5 mm and is available in varying lengths of 16-30 mm. The screw is also available in diameters of 2mm (Micro Acutrak), 4mm (Standard Acutrak), 4.5mm, 5.2mm and 7 mm.

    The accompanying set contains the appropriate guide wires as well as the instrumentation for the insertion of the screw.

    A Mini Acutrak screw (3.5mm) was selected as the implant of choice for this procedure. If the medullary canal is larger (as measured on the pre-operative radiographs), a Standard Acutrak Screw (4 mm) can be chosen instead.

    The entry point for the guide wire is identified on the metacarpal head. This is in line with the medullary canal of the metacarpus.A 0.045 mm single trocar guide wire is loaded on to the wire introducer.

    The fractured fragment is always angulated in flexion. A Jahss manoeuvere is performed by flexing the MCP joint and applying an upward pressure along the line of the proximal phalanx.This allows the base of the phalanx to exert an extension force to the flexed fracture fragment. A simultaneous downward counter-pressure on the shaft will assist in reduction.
    Tip – Flexing all fingers together in conjunction with the small finger will prevent rotational misalignment of the affected digit. Some surgeons advocate placing a suture from the tip of the small finger (in a 5th Metacarpal neck fixation) to the hypothenar skin so as to maintain rotational correction.
    Flexion of the MCP joint brings the entire articular surface of the metacarpal head into view.

    This picture shows the guide wire in situ a reduced fracture. Note the entry point of the guide wire on the articular surface of the metacarpal head. Check Xrays with an image intensifier at this stage are essential to confirm the fracture reduction and the wire placement. It is important to ensure that the proximal tip of the guide wire reaches the base of the metacarpus adjacent to the CMC joint. This is to prevent inadvertent removal of the wire during the next stage.

    Once satisfied with the reduction of the fracture and the placement of the guide wire, a 2 mm Mini Acutrak cannulated drill is drilled over the wire.

    A power drill is used to ream upto the desired depth. The markings on the drill help to ensure reaming unto the adequate depth.
    I prefer to choose the longest screw (30 mm). This is shorter than the average length of the metacarpus, but is long enough to ensure that the leading threads are securely engaged in the endosteum of the narrowest part of the medullary canal – thereby allowing for a rigid 3-point fixation of the implant.

    A cannulated profile drill is now threaded over the guide wire to overdrill the entry point. This will allow the screw head to be buried under the articular cartilage.

    Note that the profile drill has been adequately sunk into the articular head of the metacarpal.

    The 2 mm Mini Acutrak screw of appropriate length (30 mm) is now loaded onto the Hex-driver.

    The Acutrak cannulated screw is threaded over the guide wire.

    The screw is inserted taking care that the fracture remains reduced.
    Tip: It is important to ensure that the head fragment does not rotate as the screw head is tightened under the articular surface.

    Radiographs are used to confirm correct screw placement on the table.Check Xrays at this stage will confirm fracture reduction and screw placement.
    Note that although the screw head appears to be immediately subchondral on the fluoroscope, there remains a healthy thickness of cartilage above it – as demonstrated in the next photograph.

    This image shows that the screw head is completely buried under the articular cartilage.
    Note the defect created in the cartilage with this procedure. There is a myth that such a defect can be a precursor to future onset of osteoarthritis. However, CT studies have shown that the surface area affected is an insignificant proportion of the total surface area of the metacarpal head (ten Berg et al 2013).

    Clinical assessment on table is critical to ensure that there is no residual rotational deformity and no scissoring of the fingers.

    The joint capsule and the split extensor hood are allowed to fall back over the MCP joint. I do not routinely repair the capsule.

    Repair of extensor in closure.The extensor hood is repaired with 5’0 Monocryl (absorbable monofilament) sutured in a continuous fashion.

    Operation – 2

    Skin is closed with 5’0 Monocryl (absorbable monofilament) suture in a subcuticular fashion.

    A non-adherent soft dressing is applied. The fixation is stable and rigid and therefore does not require protection in a plaster splint.

    Final fluoroscopic imaging in AP, lateral and oblique planes will confirm satisfactory fracture reduction and the intramedullary placement of the implant.

    Final fluoroscopic imaging in AP, lateral and oblique planes will confirm satisfactory fracture reduction and the intramedullary placement of the implant.

    Final fluoroscopic imaging in AP, lateral and oblique planes will confirm satisfactory fracture reduction and the intramedullary placement of the implant.

    Post Operative

    The dressings are reduced in the clinic in 48-72 hours. Active mobilization exercises are commenced at this stage along with gentle passive exercises. Special emphasis is made to mobilise the MCP joint. A splint is usually not required. Gentle routine activities of daily living can be started as soon as comfortable. Rigorous and heavy activity is avoided.
    Radiographs are repeated at 6 weeks. Once the fracture healing is confirmed, aggressive passive exercises can be instituted. Activities of daily living can be increased at this stage. I advise patients against heavy activities for atleast 3 months until the fracture is consolidated.
    In a personal review of 40 cases over 3 years (unpublished), we have had no significant complications. It is, however, important to realize that this is a notoriously unreliably cohort of patients who are extremely difficult to persuade to return for regular post-operative follow up. Nevertheless, we have had no cases return or referred back to us with complications requiring further surgical interventions.

    Recommended Reading

    Jahss SA: Fractures of the metacarpals: a new method of reduction and immobilization, J Bone Joint Surg Am 20:178-186, 1938.
    Ten Berg PW, Mudgal CS, Leibman MI, Belsky MR, Ruchelsman DE. Quantitative 3-dimensional CT analyses of intramedullary headless screw fixation for metacarpal neck fractures. The Journal of hand surgery. 2013 Feb 1;38(2):322-30.
    This is a simulated study using CT scans to measure articular surface area and volume of metacarpal heads, comparing them to the defects produced with headless screw insertion. This important study confirms the insignificant proportion of defect created with this technique, thereby breaking the myth of significant destruction leading to potential late onset of arthritis.
    del Piñal F, Moraleda E, Rúas JS, de Piero GH, Cerezal L. Minimally invasive fixation of fractures of the phalanges and metacarpals with intramedullary cannulated headless compression screws. The Journal of hand surgery. 2015 Apr 1;40(4):692-700.
    This is one of the earliest publications describing clinical results with this technique. They reported outcomes on 48 metacarpal, 19 proximal phalangeal and 2 middle phalangeal fractures treated with intramedullary headless screws. They reported a 100% rate of union with an average of 249 degrees of TAM for metacarpal fracture fixations.

    Reference

    • orthoracle.com

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