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Percutaneous pinning of stable slipped capital femoral epiphysis with Synthes 7.3 mm cannulated screws

    Overview

    Learn the Percutaneous pinning of stable slipped capital femoral epiphysis with Synthes 73 mm cannulated screws surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Percutaneous pinning of stable slipped capital femoral epiphysis with Synthes 73 mm cannulated screws surgical procedure.
    Slipped capital femoral epiphysis (SCFE, SUFE) has an incidence of between 5-10 per 100,000 children per year, generally occurring during the adolescent growth spurt. The majority of slips are slowly progressive over weeks or months.
    It is well accepted that the gold standard of treatment for mild and moderate (grade I/II) SCFE is percutaneous pin stabilisation. The same technique can also be used for grade III severe SCFE although long term results are less favourable.
    For stable SCFE percutaneous pinning can be performed ‘freehand’ on a standard operating table as described here. The image intensifier remains static and the hip is flexed and externally rotated to achieve a lateral view.
    Under X ray guidance a guide wire is passed across the central portion of the physis. A screw is then passed over the guide wire (6.0-8.0mm diameter) with the aim of engaging a minimum of 5 threads past the physis.
    An associated techniques to deal with the later presenting slipped upper femoral epiphysis is dealt with on OrthOracle at https://www.orthoracle.com/library/dunns-osteotomy/

    Indications

    INDICATIONS
    Percutaneous pinning of SCFE is the standard treatment for all grades of slip. It can be used for stable and unstable slips.
    SYMPTOMS & EXAMINATION
    Patients usually present during the adolescent growth spurt (age 11-13 girls, 13-15 boys). Males are more commonly affected than females and obesity is the biggest risk factor. Groin or thigh pain is the commonest complaint although many cases are missed when patients present with referred pain to the knee.
    Symptoms may have been present for weeks or even months. Anything beyond 4 weeks would be considered chronic. Approximately 80% of cases are stable (the patient can weight bear through the leg) but 20% are unstable (can’t weight bear). The later group have a high incidence of damage to the delicate reticular vessels that supply the femoral head. Rates of avascular necrosis of up to 50% have been reported in these cases.
    In the case of a stable SCFE the patient will often have a limp. The more sever the slip the more shortening and external rotation will be noted. When flexed the hip will often turn into obligatory external rotation and attempted internal rotation will be painful.
    IMAGING
    Almost all cases will be diagnosed with plain radiography. Early mild slips can be missed on AP pelvic radiographs. A frog lateral radiograph is mandatory if SCFE is suspected. Classical radiographic signs include a widened physis and a Trethowans sign. This describes the situation where a line drawn up the lateral aspect of the femoral neck, Kiens line, should intersect part of the femoral head, and if it doesn’t, indicates a significantly increased risk of a SCFE being present.
    SCFE can be graded on the degree of displacement (Southwick) or tilt of the femoral head. Grade I <30% displacement, grade II 30-50%, grade III >50%.
    Very early SCFE (pre slip) may be missed on plain radiographs. If so, MRI may be helpful in detecting oedema of the physis.
    ALTERNATIVE OPERATIVE TREATMENT
    For severe SCFE (grade III) there is a growing teen to perform sub capital osteotomy (modified Dunn procedure) since remodelling of deformity is unlikely to be complete.
    NON-OPERATIVE MANAGEMENT
    Non operative treatment is not indicated.
    CONTRAINDICATIONS
    The technique presented here ‘freehand’ employs an image intensifier (II)which is not moved during the operation. The leg is flexed and the hip rotated to obtain a lateral view. An alternative technique is to put the patent on a traction table. The leg is not moved but rather the II is rotated to obtain lateral views. The use of a traction table extends surgical time and also results in higher radiation doses.
    If the patient has an ‘unstable’ SCFE the leg must not be moved and the traction table technique should be employed.

    Setup

    Surgery is performed under general anaesthetic. For many patients it is possible to perform as day case therefore caudal/epidural anaesthetic is not indicated. Patients should have routine blood tests to include thyroid function since ‘atypical’ SCFE can be associated with endocrine abnormalities. The definition of atypical SCFE is children age less than 10 years and weight less than 50th centile.
    Pateint placed supine on radiolucent operating table. Assistant is not mandatory.
    Image intensifier from opposite side of operating table with clear view of image intensifier screens.
    Scrub nurse on same side of operating table as operating surgeon.

    Operation

    Position patient supine on radiolucent operating table
    Surgery is performed with the patent supine on a radiolucent operating table. Notice that the involved (left) leg is externally rotated. This is typical in SCFE and the leg will often be shorter than the non affected side. The degree of shortening and external rotation will vary depending on the severity of the slip.

    The operative limb is draped ‘free’The leg is draped ‘free’.
    Ensure that there is sufficient room to bring the image intensifier ‘C’ arm in under the table and place the screens such that a good view is available.

    Check that a lateral view can be obtained with image intensifierIf the leg is gently flexed and externally rotated (there will be a tendency for the leg to externally rotate with flexion anyway) a ‘frog lateral’ view will be easily obtained.

    Place a straight wire (guide wire) over the hip and using the image intensifier determine the correct path of insertion of the guide wire. This should be along the femoral neck aiming for the centre of the femoral head, crossing the physis at right angles. draw a line along the guide wire with a sterile skin marker.

    Make small stab wound at chosen skin entrance pointWhen using the freehand technique it can be difficult to determine the angle of introduction in the lateral plane. Beware that for severe grade III SCFE entrance point may be so anterior that there is risk of damage to lateral cutaneous nerve or even femoral neurovascular bundle.
    A size 15 blade is used to make a small 2/3mm stab incision. If it is later determined that a different entry point is required this will minimise the amount of scarring.

    Insert guide wire a short distance into the femur under image intensifier controlSeveral different types of cannulated screw system are available. A thicker wire is preferable. The point of the wire is less likely to skid along the anterior cortex of the femoral neck. The guide wire is also less likely to bend when the leg is placed in the ‘frog’ lateral position.
    The Synthes guide wire illustrated is 2.8mm.

    The wire is inserted under II guidance and a check AP view of the guide wire is taken.It is critically important to ensure that the wire has not been passed inadvertently into the joint when one flexes the hip to obtain a frog lateral image.
    This will cause damage to the articular surface, potential wire bending and breakage within the joint.
    It is therefore advisable to leave the wire somewhat short of the articular surface at least until the surgeon is confident that the track of the wire is correct in both AP and lateral planes.

    Gently flex, abduct and externally rotate the hip to achieve lateral view under IIAs the hip is flexed maintain a gentle downward pressure on the guide wire. This reduces the tendency for the wire to be bent if it is tethered by the ileo-tibial band.

    Viewing the frog-lateral X-ray the ideal position for the guide wire is to cross the physis at right angles and aim for the centre of the femoral head.
    Avoid multiple entry points on the lateral cortex of the femur since this will increase risk of iatrogenic subtrochanteric fracture.
    Sometimes the entry point is deemed to be ideal but it is impossible to redirect the guide wire because it keeps following the same track. This problem is more common with thinner guide wires. One solution is to drill over the wire for 1-2cm. The guide wire can then be backed out and redirected along a new path but using the same entrance point.

    Once it has been determined that the guide wire is in a satisfactory position the skin incision can be enlarged to 1.5-2cm which allows passage of a drill guide.A pair of Metzenbaum scissors is run along the guide wire to free up the soft tissues.

    Pass the drill sleeve over the guide wireThe drill guide will vary depending on the system used. However, there are generally at least 2 sleeves, one inside the other. The inner sleeve goes over the guide wire and when removed the drill (and later screw) can be passed through the larger guide.

    Pass depth gauge over wire and through the sleeveA depth gauge is passed over the guide wire to determine the correct length of screw. Always aim to leave the screw 5-10mm proud of the lateral cortex. This will make screw retrieval easier should this be necessary at a later date.
    There are various types of screw design. The Synthes system used here has long and short thread lengths. If threads are crossing the physis this should accelerate physeal closure which is ideal near skeletal maturity. In younger patients (Particularly if more sever slip) continued growth may be desirable to allow remodelling. If so the aim is to pass all threads across the physis (using short thread screw) and into the epiphysis so that the smooth shank of the screw is crossing the physis. In theory the smooth screw shank should not stop physeal growth and the screw should be dragged up the femoral neck with continued growth. If so, it is important to use a screw long enough that the head will not impact against the lateral cortex.

    The cannulated drill is next passed over the guide wire.

    Check advancement of drill using image intensifierIt is common for the drill to cause the wire to advance and there is a danger that the joint will be penetrated. It is thought that joint penetration by wire or screw (even if transient) may increase the risk of chondrolysis.
    The wire will need to be backed out if there is danger of joint penetration.
    The drill must pass the physis but does not need to pass right up to the tip of the guide wire.
    A tap is not necessary in most instances.

    Mount screw onto screwdriverThere are several different screw designs.
    Typically screw diameters should be between 6.5mm and 8.0mm if the plan is to use a single screw. Biomechanically a single screw is sufficient providing positioned in centre of the femoral head. Multiple screws increases risk of joint penetration and should not be used unless first screw is suboptimal.
    The Synthes crew utilised in this case is 7.3mm. It is partially threaded. Thread lengths are either 10mm or 20mm. The 20mm thread will cross the physis and should therefore accelerate physeal closure. The 10mm threads should be distally beyond the physis. In theory this will allow continued growth if a sufficiently long screw is utilised since the smooth ‘shank’ of the screw will be across the physis (see above, step 12).

    The Synthes SCFE screw design incorporates an inner threaded wire which can be passed down the screw driver and locks into the screw itself. This is not used to insert the screw but makes later screw removal easier.

    The selected screw is passed over the guide wire and through the sleeve.

    Check AP position with image intensifier to ensure a minimum of 5 threads across the physis into the epiphysis.
    In this case the patient is approaching skeletal maturity and the screw threads are across the physis to encourage physeal closure.

    The hip is now screened in several positions to ensure that the screw is central and not penetrating the joint.It is not necessary to pass the screw right up to the subcortical bone. The tip of the screw should be at least 5mm from the subchondral bone on all views. Providing well positioned, no more than a single screw is required.

    A spinal epidural needle is passed down the track of the screw to install 15-20ml of dilute local anaesthetic (0.25% bupivocaine).

    Wound closureNo deep sutures requires. Subcuticular absorbable suture e.g. 3/0 monocryl.

    Post Operative

    Patients are allowed to mobilise with crutches. In the case of a stable SCFE partial weight bearing is for 6 weeks. No sport for 6 months or until physeal closure.
    It is important to obtain range of movement early since this is protective against the development of chondrolysis. Providing patients are safe on crutches and can regain good range of movement it is possible for surgery to take place as a day case.
    Unstable SCFE can also be treated with percutaneous pin/screw stabilisation but in this case rehabilitation will have to be much slower and patients should be non/toe touch weight bearing for 6 weeks and then a further 6 weeks partial weight bearing prior to full weight bearing.
    Patients should be warned that SCFE can be bilateral in up to 25% of cases. If the patient is young or has further risk factors (endocrine, unreliable) then prophylactic fixation of the opposite hip should be considered.
    Routine removal of screw following physeal closure is contentious. Removal of screws can be very difficult (especially with certain designs) and associated with morbidity. Overdrilling of a screw that is not move is particularly dangerous and runs the risk of pathological subtrochanteric fracture.
    The most sensible approach is to leave asymptomatic screws in mild grade I SCFE. Patients with more severe slips (gd II/III) are much more likely to run into problems with FAI and routine removal is more easily justified to enable later imaging with MRI and salvage procedures such as hip arthroscopy or intertrochanteric osteotomies.

    Recommended Reading

    The most significant prospective trial into SCFE (The BOSS study) commenced in 2016. This observational study is in the data collection phase and has collected several hundred cases. Preliminary results should be available 2020.
    Percutaneous pinning in situ remains the gold standard of treatment for all grades of SCFE. However, remodelling of severe slips (grade III) is likely to be incomplete and there is therefore a risk of developing femoroacetabular impingement and eventually osteoarthritis. Studies have shown that OA is present in 75% of grade III SCFE at 20 year follow up whilst it is present in less than 5% of grade I slips.
    Risks of managing stable SCFE with percutaneous screw fixation include AVN (less than 10%) and Chondrolysis (less than 2%). Chondrolysis may be associated with transient joint penetration by guide wire/screw. It is more common in females and Afro Caribean races. It is reduced if early joint range of motion is regained.
    Progression of slip is described in 1-2% of cases. This is less common if 2 screws are used rather than a single screw. However, due to the substantial increased risk of joint penetration with 2 screws a single screw fixation is favoured by most surgeons.

    Long term outcomes of slipped capital femoral epiphysis treated with in situ pinning. de Pooter JJ, Beunder TJ, Gareb B et al. Journal Children’s Orthopaedics. 2016. Vol 10 (5)
    The outcome of in-situ fixation of unstable slipped capital femoral epiphysis. Lang P, Panchal H, Delfosse EM, Silva M. J Pediatr Orthop B. 2019 Jan 29; Epub 2019 Jan 29.
    What is the best evidence for the treatment of slipped capital femoral epiphysis? Loder RT, Dietz FR. J Pediatr Orthop. 2012 Sep;32 Suppl 2:S158-65.

    Reference

    • orthoracle.com

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