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Dunns osteotomy

    Overview

    Learn the Dunns osteotomy surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Dunns osteotomy surgical procedure.
    Severe grade II/III unstable slipped upper femoral epiphysis (SUFE/SCFE) is associated with high rates of avascular necrosis (AVN). Historically rates as high as 50% have been quoted. In view of this there has been a tendency to perform the simplest and (perceived) least risky operation. This is generally held to be pinning in situ.
    The Dunn osteotomy was described for stable and unstable SUFE. The osteotomy is performed at the level of the physis. Subsequent authors generally failed to match the results of the original author. However, the advent of the trochanteric flip osteotomy and extended reticular flaps as described by Ganz has reignited interest and the ‘modified’ Dunn osteotomy has had encouraging results in the hands of high volume surgeons.
    The classic modified Dunn osteotomy requires division of the ligament trees and dislocation of the femoral head. We describe an alternative method where by the femoral head is not dislocated and the ligamentum trees is preserved.

    Indications

    Indications:
    Pinning in situ remains the gold standard for grade I and grade II SUFE. Patients need to be consented regarding risks of AVN but modified Dunn osteotomy is an acceptable treatment option for grade III SUFE (both stable and unstable) providing the physis is open.
    Investigation:
    Pre operative plain X ray should be sufficient to determine whether modified Dunn osteotomy is indicated. If in doubt CT can be helpful but the affected leg should not be placed in frog lateral position if the SUFE is thought to be unstable since this will cause further damage to the reticular vessels.
    MRI has not been shown to be accurate in predicting vascularity of femoral head pre operatively. If SUFE is unstable there is a trend toward 1-2 weeks of skin traction prior to surgery to allow inflammation and vascular spasm to settle.
    In patients with atypical SUFE endocrine work up is recommended particularly checking thyroid function.
    Operative alternatives:
    The classical alternative for all grades of SUFE is pinning in situ. World wide this remains the gold standard but does not allow restoration of normal anatomy. Pinning in situ is definitely the procedure of choice for grade I and mild grade II SUFE. In these cases there may be some remodelling with further growth particularly if a ‘growing’ pin/screw is used. Grade III SUFE may also be pinned in situ if surgeon is not experienced in technique of modified Dunn osteotomy.
    In patients with a closed physis intertrochanteric osteotomy (Imhauser/Southwick) is the preferred treatment for severe grade II/III SUFE. Intertrochanteric osteotomies have lower risk of AVN but are less powerful in terms of degree of correction because they are further from the physis. Intertrochanteric osteotmy also creates deformity of the proximal femur which can be problematic if arthroplasty is required at a later stage. Milder slips may be treated arthroscopically to remove the metaphyseal ‘bump’ once the physis has closed.
    Hip spicas have been used but this form of treatment is now historical.
    Contraindications:
    A closed capital femoral physis would be considered a contraindication by most surgeons since the risks of AVN are elevated.

    Setup

    General anaesthetic. Indwelling epidural catheter and urinary catheter. Prophylactic antibiotics. Experienced surgical assistant is necessary.

    Operation – 1

    Surgery is performed with the patient in a lateral position. In the case of unstable SUFE the delicate reticular vessels are all that holds the femoral head to the metaphysis. They are at significant risk of injury if the leg is moved without care. It is the responsibility of the operating surgeon to hold the leg whilst skin prep is applied. The leg should be abducted without letting the knee ‘buckle’ into flexion in which case the hip is at danger of suddenly collapsing into flexion and internal rotation.

    Lateral approach is utilised. This should be marked and centred over the greater trochanter. An incision of 15-20cm will usually be sufficient.

    Maintaining haemostasis during the operation is important as the delicate later steps require good visualisation of the tissues. Once the fascia has been cleared the gluteus maximus is split in line with its fibres to access the greater trochanter.

    Having cleared any bursal tissue tissue from the greater trochanter the level of the trochanteric flip osteotomy has to be judged. If too deep there is risk of damaging the reticular vessels. If too superficial the osteotomy will be performed through the gluteus medius.
    The osteotomy should be marked with diathermy. Place a finger in the piriformis fossa (1). This must not be entered. It might mean that a small cuff of gluteus medius is left attached to the neck but this will not affect later function. The osteotomy should aim to exit distally just below the flare of the trochanter so that part of vastus laterals is attached to the trochanter.
    The thickness of the trochanteric fragment should be approximately 1.5cm.

    The osteotomy is performed using a broad approximately 4cm saw.

    The osteotomy can be completed with a broad osteotome. The trochanteric fragment should be levered forward using the osteotome. There will be remaining fibres of gluteus medius and also some fibres of gluteus minimus inserting into the free fragment and these too will need to be released to allow enough mobility to displace the trochanter with its attached glut medius and vastus lateralis forwards. The piriformis tendon (1) should remain attached to the main body of the femoral neck. The reticular vessels will be below this.
    The trochanteric physis will be seen running from poster inferior to anterior superior (2).

    Gluteus minimus (1) runs from posterior to attach into the superior and anterior capsule. Some fires will also run into the trochanter itself. It is possible to pass a right angle retractor underneath the muscle and tendon using blunt dissection. A suture (1 vicryl) is then passed through the tendon.

    Once gluteus minimus has been released it needs to be reflected backwards to access the capsule of the joint. this will require blunt dissection with either a cobb elevator or swab on a stick.

    The next stage is to perform the capsulotomy. This can be marked out with diathermy. The cut is made in a ‘Z’ shape with the longitudinal limb running from the anterior superior neck level with the anterior edge of the trochanteric osteotomy. It is critical that the anterior (inferior) limb runs along the femoral edge of the capsular attachment and the posterior limb along the acetabular attachment. The capsule MUST NOT be cut where it attaches to the trochanter around the pirifomis fossa.

    Care must be taken not to damage the acetabular labrum (2) with the posterior (acetabular) limb of the capsulotomy which should extend over a length of approximately 3cm. This would be to a 10 o’clock position if the acetabulum is considered as a clock face.
    Once the capsulotomy has been performed a Lanes lever can be inserted anteriorly in front of the femoral neck to retract the capsule forwards (1).

    The next step is to raise the periosteum off the front of the femoral neck (1). A midline cut can be made along the neck in the same plane as the longitudinal limb of the capsulotomy. Again, this must not pass past the 12 o’clock position to avoid damage to the superior reticular vessels.
    In the case of an acute SUFE the periosteal attachment will be ripped at the level of the head neck junction and the bare end of the metaphysics will be visible where the head has sheared off at the level of the physis. A Watson Cheyne elevator is ideal for raising the periosteum off the bone.

    The key step to this operation is raising of the extended reticular flap. This involves elevating the entire periosteum off the superior and posterior neck in continuity with the posterior superior aspect of the greater trochanter and the femoral head.
    The first step is to elevate the periosteum off the posterior aspect of the trochanter. This is easily achieved with a Watson Cheyne elevator.

    Elevation of the superior periosteum with he trochanter requires extreme care. A fine Lambotte osteotome is used to remove a ‘V’ shaped segment of bone.

    The aim is not to enter the the piriform fossa but rather to create a situation where by the poster superior aspect of the trochanter can be gentley separated taking the periosteum and reticular vessels with it.

    Fine instruments including Watson Cheyne, Kerazon and small curved curette are useful to gently remove the posterosuperior aspect of the trochanter without ripping the underlying periosteum and vessels.

    With care the loose fragment will separate from the main body of the trochanter. The whole of the soft tissue envelope around the superior and posterior femoral neck can then be peeled off in continuity with the femoral head.

    The bare femoral neck is exposed as the soft tissues are lifted away. The femoral head is still not visible but in the case of an unstable SUFE will be loose.

    With extreme care a spinal cobb elevator can be inserted between the femoral head and neck. The periosteum and reticular vessels will be behind the cobb (1).

    The hip is gently flexed and externally rotated and at the same time the cobb is used to elevate the femoral neck away from the femoral head which remains enlaced in the acetabulum (the physis is visible on the femoral head). The ligamentum teres remains intact which decreases risk of dislocation in post operative period. Any posterior ‘beak’ of bone can be removed from the femoral neck with fine bone nibblers or curved osteotome.

    If necessary the femoral neck can be shortened using a saw and/or nibblers. Care is required not to damage the vessels behind the femoral head. In the case of acute unstable SUFE minimal shortening (0.5-0.75cm) should be sufficient.

    Once the posterior beak of bone has been removed and the neck shortened (if necessary) and chamfered the femoral neck can be reduced back onto the femoral head (which has remained within the acetabulum throughout). This manoeuvre is done with care. Longitudinal traction applied to the leg by the assistant and gentle internal rotation.The reticular vessels should be visualised and protected by the operating surgeon whilst the reduction is performed. Once complete the anterior and lateral aspect of the epiphysis will be clearly visible. The reticular vessels should be intact (1)

    The femoral head, reticular vessels and posterior capsule should form one single continuous envelope.Drilling of the head of the femur with a 2mm drill can be performed. If the femoral head bleeds this is reassuring that the vascular supply is intact. However, failure to bleed is not necessarily a sign of avascularity.

    The next step is to stabilise the femoral head. I prefer one or two 7.0mm cannulated screws. Image intensifier is set in a horizontal position allowing an AP view of the hip since the patient is lying on their side. By carefully moving the hip into a frog lateral position and lateral projection is obtained.

    When inserting the screws ensure that the entry point is below the trochanteric osteotomy. Ideally the screws should be anterior enough in the femoral neck to allow the passage of a screw at right angles to stabilise the trochanter.

    Once the guide wire is in place position can be checked by gently flexing and abducting the hip (frog lateral position) without moving the image intensifier. Take care not to pass wire too far and risk joint penetration.

    Operation – 2

    Once screws have been inserted the capsule is repaired with interrupted 1 vicryl sutures along with gluteus minimus tendon.

    The trochanteric osteotomy is reduced and stabilised temporarily with a stout K wire. Position is checked with image intensifier and then definitive fixation with single 6.5mm partially threaded screw plus washer. The screw will generally pass behind the femoral neck screws.

    Interuppted 1 vicryl sutures are used to complete the trochanteric repair. Followed by repair of TFL, fat and skin (3/0 subcutucular monocryl).

    Pre operative AP pelvis radiograph demonstrating severe unstable SUFE left hip

    Radiograph 12 months post operative. No evidence of AVN. Physis has closed.

    Post Operative

    Patients should have 2 doses of post operative antibiotics. Skin traction of 4Kg is applied for 4 days.
    It is important to ensure that passive hip movement is restored prior to discharge since there is a risk of chondrolyisis. This is more common in females. Ideally passive hip flexion to 90 degrees prior to discharge. Active hip movements should be avoided in first 2 weeks.
    Anteroposterior radiograph of pelvis prior to discharge but avoid placing hip in frog lateral position.
    Patients should be non weight bearing for 6 weeks and then partial weight bearing for a further 6 weeks.
    Follow up is required until closure of the proximal femoral physis. If there are no radiological features of AVN after 12-18 months the complication should not occur.

    Recommended Reading

    SUFE is a rare condition affecting 1:1000 children. Surgeons will treat relatively few cases each year. For this reason there are very few published series with significant numbers of patients. The BOSS study (British Orthopaedic Surgery Surveillance) started in 2016 with the aim of capturing all cases treated in the UK. At present over 600 have been collected.
    Pinning in situ remains the gold standard of treatment for all cases of SUFE. However there is an increasing recognition that severe SUFE will inevitably result in hip impingement and early onset of osteoarthritis. For this reason modified Dunn osteotomy is gaining popularity.
    The technique was first described by Ganz (2008). In 2017 the same group published long term results for the procedure. The overall rate of AVN of 2% is the lowest in the published literature. Ten year survival in this cohort is 93%. Other authors have struggled to match these results with rates of AVN varying between 3% and 26%. It is clear thatAVN rates are much higher in unstable SUFE compared to stable slips.

    Reference

    • orthoracle.com

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