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Arthroscopic subtalar fusion

    Overview

    Learn the Arthroscopic subtalar fusion surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Arthroscopic subtalar fusion surgical procedure.
    Arthroscopic subtalar fusion may be performed to treat subtalar pain due to arthritis, instability , and deformity – when this is passively correctible.
    In common with other arthroscopic fusions, it preserves the tissue envelope, with perceived advantages of rapid and reliable union.
    It is particularly useful in cases with poor lateral skin due to valgus deformity, burns or previous scars.
    The Orthosolutions titanium cannulated screw system provide the surgeon with a comprehensive range of large screw diameters and pitch lengths with excellent on-table compressive performance. They make dealing with a multitude of fixation situations during subtalar fusion as straight-forward as it can be and are what I have come to rely on.

    Indications

    Subtalar fusion is indicated by pain, instability or deformity arising from the joint.
    Surgery is only indicated when appropriate corrective and stabilising orthotics, and appropriate medical treatment (up to injection of the joint) has been undertaken.
    Before surgery the patient should be examined standing, walking and on the couch, noting range of active and passive movement of the subtalar joint and surrounding joints, and noting the state of the surrounding skin and any sensory or motor loss in the foot.
    When deformity is present, it is important to note whether this is passively correctable – or fixed. In general fixed deformity is a contra-indication for arthroscopic fusion in this joint.
    Plain films should be taken, and if needed MRI or Ct to assess the joint and the surrounding joints.
    Arthroscopic surgery to the subtalar joint is an advanced arthroscopic procedure, and should only be undertaken by surgeons who are experienced in arthroscopic ankle fusion.

    Setup

    Antibiotic prophylaxis is administered according to local protocols.
    A thigh tourniquet is applied.
    The patient is positioned in lateral position with a firm support under the calf, so that the foot hangs over the end of the support, and as the foot falls medially, the lateral side of the joint is opened. Suitable anterior and posterior props should be adjusted to secure the patient on the table (as per lateral hip approach). Check that the position does not result in the foot being over any radio-opaque bar on the table, and adjust to avoid this.
    In most cases (except when the joint is very loose) it is helpful to apply a Hintermann distractor across the joint. To do this a wire is passed into the talus (above the joint, and the calcaneum (below the joint, before injecting the joint with saline and distracting using the Hintermann distractor. The wires can be positioned using the image intensifier if required, and care should be taken to avoid breaching the medial cortex of either bone – as a precaution against damaging the nmedial neurovascular bundle.
    Equipment used for arthroscopic subtalar fusion is : 1.a large (knee -6-6.5mm) arthroscope, cannula etc,2. A pressure regulating pump 3. A set of arthroscopic instruments – source, handle and minimum of 3.5mm burr and 4mm soft tissue rejector. 4.A Hintermann distractor, wires and power driver to insert them.5. a small curette 6. A large 6.5mm or 8.mm cannulated self cutting screw set (Ortosolutions), with appropriate power instruments 7. waterproof drapes with fluid collection.8. Image intensifier.
    A plaster cast or synthetic cast is applied at the end of the operation.
    Post operative thromboembolic prophylaxis is administered for the duration of cast (6-8/52)

    Operation

    With the patient in lateral position, and after skin preparation and draping,wires are inserted to distract the subtalar joint.
    under the image intensifier, the location of the talus is defined, and a point identified which will allow passage of the wire into the talus, but which is at the posterior end of the sinus tarsi (if you pass the wire at the level of the sinus tarsi the retractor will get in the way of the arthroscope and instruments).
    Then after making a small skin incision, a 2mm wire is passed well into (but not right through) the talus – so that ideally its tip just touches the medial cortex.

    A second wire is inserted into the calcaneum, after checking position using the image intensifier. Again it is passed to but not through the medial cortex.

    The Hintermann retractor is then passed over the wires, and after injecting the joint with saline solution, distraction is applied.Position the handles of the retractor over the heel, not towards the front of the foot, so that it does not impede access.
    Two incisions will be made- one towards the front of the sinus tarsi, and one half way back along the sinus tarsi (both on the lateral side of the foot). Note that the Hintermann retractor has been positioned so that it allows free access to the sinus tarsi from an anterolateral direction.

    The arthroscopic cannula is first inserted into the posterior of the two incisions, and with the trochar still in place it is swept across the anterior aspect of the posterior facet of the subtalar joint. In most cases when the joint has been inflated and distracted, the trochar can the be advanced easily,and will enter the posterior facet.

    Insert a soft tissue resector into the anterior incision…….

    Here is the view into the posterior subtalar joint. It is cloudy with synovial fluid, and capsule partly obscures the view (on the right). The fluid should be turned on (with a pump pressure of about 50mmHg), and the anterior capsule cleared using a soft tissue resector.

    The view clears as the synovial fluid is washed out through the suction portal of the resector. Clearance of the anterior capsule allows a clear view of the posterior facet of the subtalar joint.

    Residual areas of carilage are excised using a soft tissue resector. Alternatively a small mastoid or spinal curette (5mm or less) can be used to remove any cartilage, and the loose fragments then removed using the resector and suction.

    Then after removal of the soft tissue resector, a burr is introduced. A 3.5mm spherical burr is typically used as it allows pressure to be applied to the surface which is sometimes necessary if the talar or calcaneal chonral and subchondral areas are hard.
    When using the burr, start medially and prepare the bone surfaces using sweeps of the burr laterally (starting medially avoids accidental damage to the main neurovascular structures if the burr skids forwards whilst being advanced).When a full sweep across the joint is complete, advance the burr and reposition it medially again before making a second cut more deeply into the joint. This is repeated making cuts further and further back in the joint until the surfaces are prepared.
    Technical tip:It is easiest to prepare the bony sufaces starting at the front on the upper (talar) suface, and working backwards to clear the whole talar surface first. This leaves a better access to clear the calcaneal bone.

    It is important to clear the cartilage and bone down to a bleeding subchondral or cancellous layer. Usually ,as here, where the burr has cleared the first few millimetres of the talar bone, it can clearly be seen that the burr is deep enough, as cancellous bone is visble.

    If the bone is more sclerotic, then being sure of adequate clearance and sufficient depth of burring is more difficult. If there is doubt, turn off the pressure at the arthroscope, and apply suction via the burr (suction test). This may cause small artefacts such as the air bubble seen on this image, but more importantly the bone surface will visibly bleed.
    Technical tip: this test can only be performed two or three times in each procedure, as it becomes unreliable once subchonral bone has been emptied by suction.

    Resection is continued until a minimum of 70% of each surface is prepared – preferably more.
    It is more important to have well prepared surfaces into bleeding bone. The surfaces do not need to be smooth or matching.


    It is not usually necessary to prepare the middle facet joint, unless the fusion is being performed for severe arthritis mainly affecting these joints. However if there is severe arthritis of this part of the joint, the facet can be prepared by passing a burr anteriorly from the medial corner of the posterior facet. If this is done, great care must be taken not to burr right through and damage the neurovascular bundle.

    At the end of the procedure, once the joint surfaces have been prepared, the instruments and wires are removed, and the wounds sutured.

    An incision is made over the tip of the heel (do not drift into the plantar fat pad). Placement of the incision may, if desired, be located under image intensifier control.

    Under image intensifier control pass a wire from the Orthoslutions large fragment cannulated set centrally through the tip of the heel (calcaneum) across the fusion site and into the body of the talus using a power drill.

    Guide this into into position carefully, periodically rotating the foot to allow AP views as well. Great care should be taken to make sure the wire remains intraosseous and does not enter the ankle, or penetrate anteriorly and risk damaging nerves, tendons etc).
    Technical tip:It is easier and quicker to rotate the foot (which is easy provided the patient does not have a stiff hip) than to rotate the image intensifier, but either method can be used.

    The tip of the wire should stop around (but no closer than) 5mm from the ankle joint suface or suoerior cortex of the talus (to allow for a safety zone andcompression). Measure the wire length – being certain (using the image intensifier) that the tip of the measure is against the surface of the calcaneum. Remove a further 5mm from the measured length to allow for countersinking the screw.

    Countersinking the screw reduces the risk of the patient getting symptoms from screw head prominence, but overdoing the countersink reaming may lead to weakness of grip of the screw head and subsequently poor fixation.
    Avoid this problem by advancing the countersink under the image intensifier until it presses against the bone of the calcaneum, then using a marker to mark the reamer circumferentially 3-4 mm above the skin. If you then ream til this mark is at the level of the skin, you will avoid over reaming.

    A screw is then inserted by power, finishing insertion by hand – and under image control to ensure it is advanced to the correct depth.
    Technical tip: If the patient is elderly or has some disbility which mkes it unlikely or impossible to non-weight bear, then a second screw can be inserted to give greater stability.

    Postoperative AP and lateral views should be taken at the end of the operation. here two screws (A) have been inserted. The continuously threaded screws remain in situ from an ankle fusion performed 15 years previously.
    The purpose of the radiographs is to document accurate screw placement and make any adjustments needed. It is very common to see a gap of a few mms remaining at the site of the posterior facet after subtalar fusion. This is normal and will fill with marrow from the patient – proceeding to union. It does not need grafting (a a gap would after open fusion).

    Post Operative

    A cast or a removable boot is applied for 8 weeks.
    Sutures are removed at 10 days and the cast or boot reapplied.
    Ideally the patient should remain non-weight bearing for 8 weeks, then progress to partial weight bearing after a check hindfoot ap and lateral xray at 8 weeks.
    Weight bearing should progressively increase over a further 8 weeks, when the cast or boot can be removed after an xray shows union.
    These periods should be increased in patients with diabetes
    However many patients needing this surgery are elderly, frail or disabled, and unable to fully weight relieve. In this case provided two screws have been used with good fixation and the patient is not neuropathic, the patient may be allowed limitted mobility with weight applied through the leg from an early stage – using either crutches or frame for supprot.
    Physiotherapy should be started after removal of cast – to restore movement to remaining unfused joints, and an assessment made at around 6 months to determine whether orthotics are needed.

    Recommended Reading

    This is a relatively new procedure, and results are not widely available.
    However El Shazly et al ( El Shazly O et al, Arthroscopic subtalar fusion for post-traumatic subtalar arthritis. Arthroscpy 2009 July;25(7) 783-787) showed that posterior facet arthrodesis was succesful when performed arthroscopically in 10 patients with post calcaneal fracture arthritis. The mean time to fusion was 11.44 weeks, and the only complication noted was a neuroma at the site of the antero-lateral portal. After a mean of 28 months, there was significant improvement in total AOFAS scores, and individually in the domains for pain and walking distance.
    Vila-Rico (Vila-Rico et al, Subtalar arthroscopic arthrodesis and outcomes. Foot and Ankle 2017 23, 9-15)with a mean follow up of 57.5 months, showed a 95.4% union rate at 12 weeks in a cohort of 65 patients with differing aetiologies. They had significant improvement in AOFAS scores, with a complication rate of 12.3% – including superficial infection, non-union and need for hardware removal.

    Reference

    • orthoracle.com

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