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Joint replacement- Swansons silicone MCP joint

    Overview

    Learn the Joint replacement: Swansons silicone MCP joint surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Joint replacement: Swansons silicone MCP joint surgical procedure.

    Swanson’s joint replacement was described in the mid-1960s. The silicone-rubber implant was designed to improve the alignment of the fingers by active as an internal splint and stimulate a pseudo capsule formation. Swanson termed this implant a ‘load-bearing flexible hinge’. This is still the most commonly performed prosthetic arthroplasty for rheumatoid arthritis.
    There are three major designs of the implant available. The original Swanson design (Wright Medical), the Small Joint Innovations flexible implant and NeuFlex (DePuy).

    Indications


    INDICATIONS: MCP joint replacements are usually indicated in rheumatoid arthritis when the joints are subluxed and painful. The goals of the operation are to relieve pain, correct deformity and improve function and appearance of the hand.
    SYMPTOMS & ASSESSMENT: A detailed history including the progression of disease, medical treatment and functional limitation due to the hand problem need to elicited. Patients also need a detailed clinical examination starting with neck, shoulder, elbow, wrist, thumb and fingers to assess the extent and severity of their inflammatory arthropathy. While examining the metacarpophalangeal joints (MCPJs), one should make a note of ulnar drift and ulnar or volar subluxation. Passive correction of the deformity is attempted which is possible with ulnar drift. A functional assessment with a specialist hand therapist will provide useful information regarding impairment and allow early intervention on other joints for splinting pre-subluxation.
    INVESTIGATION: X-Rays are essential to assess the changes in the joint and should include AP, Lateral and Oblique images. The radiographs will assess the degree of deformity, joint subluxation, bone erosion and cavitation with fracture risk during the procedure. More sophisticated imaging techniques are usually not indicated in these patients.
    OPERATIVE ALTERNATIVES: The alternative to arthroplasty is a joint fusion which works well for index finger MCPJ. There are alternatives to the silicone implants such as pyrocarbon implants. However the use of a semiconstrained or unconstrained implant carries a high risk of complications including dislocation for the inflammatory arthritis patient who has ligament insufficiency. The Swanson implant or variations of this constrained hinge remains the most popular choice.
    NON-OPERATIVE ALTERNATIVES: Splints are useful to correct ulnar drift and is a good alternative to surgery. A detailed assessment by the Occupational Therapist helps to decide on splintage and also to help with activities of daily living.
    CONTRAINDICATIONS: The main contraindication to arthroplasty is acute infection. Relative contraindications include inadequate soft tissue coverage, compromised neurovascular status and severe progressive rheumatoid arthritis where bone stock is not sufficient to insert the implant.

    Setup

    MCP joint replacements can be performed under regional or general anaesthetic. It is preferably performed in a laminar flow theatre. The hand is positioned on a hand table with an upper arm tourniquet applied. Fluoroscopy is not usually required. A single dose of pre-operative antibiotic is given intravenously.

    The trial implants are required for sizing the defect and specific proximal and distal medullary canal reamers. A suitable range of implant sizes should be available in the operating theatre.

    Operation

    The joints to be replaced are marked on the hand. This patient had her middle finger replaced in the past through a vertical incision.

    Incisions are marked over the MCP joints. A single transverse incision works well for replacing all four MCP joints. However as this patient already had a vertical incision for the middle finger, separate vertical incisions are used.

    Incision is made with a No.15 blade. The skin in these patients are very thin from long term steroid use and it is important not to make the cut too deep.

    Skin hooks are placed on either skin edges by the assistant which the tissue planes are developed. It is important to protect the small dorsal digital nerves. The dorsal vein branches are diathermised.

    The extensor hood in exposed. The extensor tendon is usually subluxed and is lying in the gutter between the metacarpals on the ulnar side. Incision is placed in the midline and extensor hood opened.

    Once the joint is exposed, the metacarpal head is osteotomised using an oscillating saw. The cut is made at 90 degrees to the long axis of the metacarpal.

    The metacarpal is now prepared for the implant. Most text books mention reaming the proximal phalanx before the metacarpal. This is thought to be due the fact that the size of the implant is decided by the proximal phalanx size and avoids over-reaming of the metacarpal. However I haven’t found this to be a significant problem and have often done the metacarpal first as in this case.
    Reaming starts with a sharp entry broach which is a sharp awl.

    Reaming of the metacarpal head is done. In the Swanson’s tray the reamers for the metacarpal are marked at P for proximal. With the soft bones in Rheuamtoid arthritis a mallet is often not necessary in the beginning and reaming can be done by hand.

    As we change to larger reamers one may need to use the mallet.

    The proximal phalanx is prepared best using a burr. The base is squared off and the burr is used to create the hole for subsequent reaming.

    The reamers for the proximal phalanx are marked as D for distal.

    Once the joint surfaces are prepared a trial sizer implant is used. They are colour coded for the sizes and largest fitting trial implant is chosen. It is important to flex and extend the finger with the trial implant in place to check that the joint has stability.

    The definite implant is chosen based on the sizer. The implants are numbered and an appropriate one is chosen. The implants come with metal grommets but most surgeons have stopped using them as they don’t seem to provide any extra stability nor prevent breakage.

    Once the implant is positioned the capsule is closed using 4-0 PDS running sutures.

    The extensor tendon is closed using 4-0 PDS running sutures. At this point it is important to release the subluxed tendon from the ulnar side. If there is redundancy of the extensor hood, the tendon can be double breasted.

    Extensor hood repair is completed.

    Skin in closed in layers. It is often difficult to get good dermal sutures in the thin skin. In that case, a single layer interrupted suture using 4-0 or 5-0 Nylon can be used.

    Wounds were closed using 5-0 Nylon interrupted sutures. Picture shows the closed wounds.

    A multi-layered dressing is used. The first layer can be a non-adherent dressing such as jelonet or mepitel. This is then covered with dressing gauze.

    Velband and cotton wool bandage is used next.

    A POP volar slab is used to keep the wrist extended and MCP joints in 30 degrees flexion.

    Dressings are completed and the vascularity of the fingers checked after releasing the tourniquet.

    Post Operative

    The hand is elevated in a sling and patients are often discharged home the same day. Elderly patients with poor social support may need one night’s overnight stay.
    Dressing are changed between 5-7 days and if wounds are satisfactory an outrigger thermoplastic splint is made to start mobilising the fingers. If non-absorbable sutures are used, they are removed at 2 weeks.
    The outrigger splint is used for 5-6 weeks during which the patients regain movements at MCP joints. At this points, patients are monitored for a recurrence of ulnar drift and if needed splintage continued for two to three weeks more.
    Early complications include bleeding, infection and wound breakdown. Late complications include recurrence of ulnar drift and implant failure.

    Recommended Reading

    Wilson YG, Sykes PJ, Niranjan NS. Long-term follow-up of Swanson’s silastic arthroplasty of the metacarpophalangeal joints in rheumatoid arthritis. J Hand Surg Br. 1993 Feb;18(1):81-91
    Delaney R, et al. A comparative study of outcome between the Neuflex and Swanson metacarpophalangeal joint replacements. Randomized controlled trial. Delaney R, et al. J Hand Surg Br. 2005 Feb;30(1):3-7.
    Wilson YG, Sykes PJ, Niranjan NS. Long-term follow-up of Swanson’s silastic arthroplasty of the metacarpophalangeal joints in rheumatoid arthritis. J Hand Surg Br. 1993 Feb;18(1):81-91
    Delaney R, et al. A comparative study of outcome between the Neuflex and Swanson metacarpophalangeal joint replacements. Randomized controlled trial. Delaney R, et al. J Hand Surg Br. 2005 Feb;30(1):3-7.

    Reference

    • orthoracle.com

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