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Internal fixation of metacarpal shaft fractures using Synthes® 2.0 mm Modular Hand System

    Overview

    Learn the Internal fixation of metacarpal shaft fractures using Synthes® 20 mm Modular Hand System surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Internal fixation of metacarpal shaft fractures using Synthes® 20 mm Modular Hand System surgical procedure.
    Metacarpal fractures are amongst the commonest injuries in the hand and if either malunited or managed sub-optimally can result in significant disability. Internal fixation of these injuries allows more rapid rehabilitation, so important in the recovery of dexterous hand function.
    Conventional wisdom has always advocated a minimum of three bicortical screws on either side of the fracture for a stable construct. However, penetration of the drill across the opposite cortex can cause iatrogenic injuries to the closely associated soft tissue structures in the hand. Recent biomechanical studies by Liodaki et al showed that unicortical plating in the metacarpals might provide adequate strength and stability based on cyclical loading. This technique can avoid the risk of drill and screw penetration across the far cortex. Similar biomechanical studies have confirmed the utility of unicortical screws in the cervical spine (Muffoletto AJ et al), the sacrum (Smith SA et al), femur (Beingessner D et al) and the clavicle (Croley JS et al).
    This is a step-by-guide for unicortical fixation of a metacarpal fracture using the Synthes ®2.0 mm Modular Hand System.

    Indications

    INDICATIONS
    Metacarpal fractures, when they occur in isolation, can be treated in a multitude of ways – both conservative and surgical. However, indications for surgical fixation include the following:
    Open fractures
    Fractures with rotational deformity
    Comminuted and unstable fractures
    Presence of associated injuries in the same hand requiring early rehabilitation
    The stabilising effects of the interossei muscles are disrupted in multiple metacarpal fractures. Together with the severity of the injury force, this produces significant deforming vectors on the fracture fragments – resulting in considerable displacements and rotations. Internal fixation, therefore, remains the treatment of choice.
    SYMPTOMS & EXAMINATION
    The patient presents with pain and swelling over the dorsum of the hand. There is tenderness over the metacarpals and movements of the finger may be restricted with pain. A common finding is an apparent extensor lag of the fingers 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– Anteroposterior, lateral and oblique. The fracture pattern and location, the displacement and the comminution are noted. Associated injuries should always be looked for.
    ALTERNATIVE TREATMENT
    Conservative with closed reduction followed by plaster immobilisation – Unfortunately, this prevents early rehabilitation of the hand. In addition, a plaster cast is inadequate to maintain a reduction in these unstable fractures.
    Percutaneous wiring techniques– These range from longitudinal intramedullary wires, transverse intermetacarpal wires, crossed wires and Bouquet wires. Although these techniques are less invasive, they do not provide a very stable construct and can be technically demanding in multiple metacarpal fractures.
    Open Reduction & Internal Fixation. Internal fixation with plates and screws is perfectly suitable for these injuries. Conventional wisdom has always advocated a minimum of two bicortical screws on either side of the fracture for a stable construct. However, penetration of the drill across the opposite cortex can cause iatrogenic injuries to the closely associated soft tissue structures in the hand. Recent biomechanical studies by Liodaki et al showed that unicortical plating in the metacarpals might provide adequate strength and stability based on cyclical loading. This technique can negate the risk of drill and screw penetration across the far cortex. Similar biomechanical studies have confirmed the utility of unicortical screws in the cervical spine (Muffoletto AJ et al), sacrum (Smith SA et al), femur (Beingessner D et al) and the clavicle (Croley JS et al).

    Setup

    Informed consent is an important part of the procedure and the risks and benefits should be clearly explained to the patient. The metalwork lies in close proximity to the extensor tendons. The patient should, therefore, be always counseled regarding the risk of tendon adhesions and stiffness necessitating removal of metalwork after the fracture is healed.
    I prefer regional anaesthesia with axillary block for this procedure. 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 is used to stabilize the hand. I routinely administer a single dose of antibiotics for this procedure.

    Operation – 1

    The hand is laid prone and stabilized in the lead hand for a dorsal exposure.
    Note that the fractured fingers are marked with skin marker to prevent exposure of the incorrect metacarpals

    The 4thand 5thmetacarpals are marked on the skin and a single straight dorsal incision is planned between the 2 metacarpals. If the metacarpals are fractured at different levels I use an S-shaped incision for optimal exposure.

    The skin is incised with a No.15 blade. The subcutaneous tissue is incised with sharp dissection and the skin flaps retracted.

    The dorsal cutaneous nerve lies in the subcutaneous plane just ulnar to the 4thmetacarpal. This is identified, dissected and protected. Injury to this cutaneous nerve will result in a painful neuroma, which can be functionally debilitating.

    The extensor tendons are now exposed. Note the bruising suggestive of the underlying fractures.

    There is no significant proven benefit of the order of fixation. I prefer to stabilize the 4thmetacarpus first as I believe that it has lesser mobility due to the attachment of the interossei and can be better manipulated when fixed before the 5thmetacarpus.
    The bone is exposed on the ulnar border of the extensor to the metacarpus. You may need to divide the juncture tendinae – which is repaired at the end of the procedure. Alternatively, you can split the extensor tendon in the midline for exposure of the fracture site.

    A periosteal elevator is used to elevate the periosteum off the bone. Care should be taken to prevent devitalizing any small, comminuted fragments. I always attempt to retain the soft tissue attachments to these fragments.

    Reduction bone clamps (available on the set) are applied on either side of the fracture. This provides better control of the fragments during manipulation for reduction.

    The fracture is reduced, taking care that the interdigitations match for an anatomical reduction.

    The Synthes®2.0 mm Modular Hand System has a variety of plate lengths and designs. These are low contact dynamic compression plates and do not accommodate screws in locking mode. A straight plate of appropriate length is chosen from the set. The plate length should allow for atleast 2 screws on either side of the fracture.
    The plate is contoured to allow for the dorsal bow in the metacarpal bone. It is important to remember that the tensile surface of the metacarpal bone is on the dorsum, which is the ideal surface for placement of the osteosynthesis plate.

    The plate is placed on the realigned metacarpus, bridging the fracture. The appropriate placement of the plate on the surface of the bone and the alignment of the screw holes are checked before commencing fixation. Plate holding forceps are available on the set to aid this process if required

    The drill guide facilitates the drilling of a pilot hole in the distal fragment. This is done with a 1.5 mm drill. The near cortex is drilled. The far cortex is left intact.

    The depth gauge is advanced into the pilot hole until it abuts the intact far cortex. The screw length is measured.

    A cortical screw of the appropriate length is chosen and mounted on the screwdriver.
    Tip: Always ensure the appropriate screw length by checking it again after mounting on the screwdriver. This can be done on the measuring scale provided on the set. Changing screws multiple times can distort the pilot hole, thereby reducing the engagement of the screw threads.

    The reduction is checked. The position of the plate on the bone is confirmed. A proximal pilot hole is now drilled through the plate in the same manner – using a standard drill guide and a 1.5 mm drill bit. The near cortex is drilled leaving the far cortex intact. A screw of the appropriate length is inserted.
    It may be useful at this stage to do preliminary radiographs to confirm fracture reduction and the plate placement if required.

    If the reduction is satisfactory, the remaining screws can now be inserted in the same manner as above.

    The reduction, if visible, is confirmed to be anatomical. Moving the fingers through a passive range can allow you to assess the fracture stability. Check radiographs at this stage will confirm the reduction and the appropriateness of the screw lengths.

    The 5thmetacarpal can now be exposed, reduced and stabilized using the same principles as above.

    Clinical rotation is crucial for satisfactory outcome and should always be assessed before wound closure. A tenodesis test with dorsiflexion of the wrist allows the fingers to curl into flexion in a cascade. A normal cascade will reveal a typical pattern wherein the amount of finger flexion increases from radial to ulnar – with the small finger appearing most flexed and the index finger least. In addition, the fingertips will appear to point towards a definite location on the wrist – the scaphoid tubercle. Any deviation from this is suggestive of a rotational abnormality.
    ST – scaphoid tubercle

    Final radiographs confirm anatomical reduction along with satisfactory plate placements. Note that none of the screws engage or penetrate the opposite cortex. This is a unicortical fixation.
    A randomized controlled trial comparing this unicortical fixation with the standard bicortical screws is currently underway at the University Hospitals Birmingham (SUBMIT Trial). Preliminary unpublished results suggest no significant differences in healing times, fracture stability or complications. In addition, there is the theoretical advantage of preventing iatrogenic damage with the penetration of the drill bit across the far cortex. In balance, this appears to be a very attractive alternative to the standard fixation techniques.

    After a thorough lavage, the periosteum is closed over the plate with interrupted monofilament absorbable sutures. I believe this creates a layer underneath the tendon, minimizing the risk of adhesions. It is not always possible to obtain a watertight closure as the presence of the plate stretches the periosteum, making its closure difficult.

    The tendons are approximated with monofilament absorbable sutures. The juncture tendinae is repaired.

    A subcutaneous closure may be performed to reduce the tension on the skin sutures.

    Skin is closed with interrupted monofilament nonabsorbable sutures. I have used 5’0 Nylon in this instance.

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

    Operation – 2
    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 needed to mobilise the MCP joint. A splint is usually not required.
    Sutures are removed in 2 weeks. 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.

    Stiffness and tendon adhesions may sometimes necessitate a secondary procedure of tenolysis. This is best delayed for 3 months following the initial procedure to allow for the fracture site to become well consolidated.

    Recommended Reading

    Curtis BD, Fajolu O, Ruff ME, Litsky AS. Fixation of Metacarpal Shaft Fractures: Biomechanical Comparison of Intramedullary Nail Crossed K‐Wires and Plate‐Screw Constructs. Orthopaedic surgery. 2015 Aug;7(3):256-60. This is a biomechanical study comparing the strengths of different methods of fixation in synthetic bones. A 3 point bending load confirmed that the load to failure was significantly higher in the group treated with plates and screws as compared to K wires or intramedullary devices.
    Dona E, Gillies RM, Gianoutsos MP, Walsh WR. Plating of metacarpal fractures: unicortical or bicortical screws?. Journal of Hand Surgery. 2004 Jun;29(3):216-9. This is a biomechanical study on 18 fresh frozen cadaveric models. These were randomly divided into 2 groups. One had bicortical screws in plate fixation of artificially created shaft fractures. The other group had unicortical fixation. The authors found that the stiffness and the load to failure were similar in both groups. In addition, they noted that none of the screws pulled out.
    Khalid M, Theivendran K, Cheema M, Rajaratnam V, Deshmukh SC. Biomechanical comparison of pull-out force of unicortical versus bicortical screws in proximal phalanges of the hand: a human cadaveric study. Clinical biomechanics. 2008 Nov 1;23(9):1136-40. This biomechanical study was performed on phalanges of the hand. The study revealed that unicortical screw fixation at the diaphyseal level is actually stronger than biocortical screw fixation at the metaphyseal level.
    Ochman S, Doht S, Paletta J, Langer M, Raschke MJ, Meffert RH. Comparison between locking and non-locking plates for fixation of metacarpal fractures in an animal model. The Journal of hand surgery. 2010 Apr 1;35(4):597-603. This is a biomechanical study to compare the strengths of metacarpal fixation in different surgical techniques. 40 samples from pig metacarpals were randomly divided into 4 groups with monocortical/bicortical nonlocking fixation and monocortical/bicortical locking fixation. The monocortical screw fixation group had similar stiffness and no significant difference in load to failure.
    Liodaki E, Wendlandt R, Waizner K, Schopp BE, Mailänder P, Stang F. A biomechanical analysis of plate fixation using unicortical and bicortical screws in transverse metacarpal fracture models subjected to 4-point bending and dynamical bending test. Medicine. 2017 Jul;96(27). This biomechanical study confirms that unicortical plating method may provide adequate strength and stability to metacarpal fractures based on the results of the cyclical loading representative of physiological loading.

    Reference

    • orthoracle.com

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