Surgical Hip Dislocation (Ganz Trochanteric Flip)

The Ganz surgical dislocation of the hip is a joint-preserving approach that gives 360-degree visualisation of the femoral head and the entire acetabulum while preserving the head's blood supply. Reinhold Ganz and colleagues developed it at the University of Bern (Inselspital) in the 1990s and published it as a reproducible technique in 2001. It has transformed the management of young adult hip pathology, particularly femoroacetabular impingement (FAI).

The principle. A specific anterior trochanteric flip osteotomy preserves the posterior soft-tissue envelope, including the short external rotators and the MFCA retinacular branches. The hip can then be dislocated anteriorly without devascularising the femoral head.

View larger

Indications. The operation is chosen when the femoral head and acetabulum need to be seen and treated in full:

• Femoroacetabular impingement - cam, pincer or mixed, requiring osteochondroplasty, acetabuloplasty, labral repair or refixation
• Intra-articular loose bodies - synovial chondromatosis, fracture fragments, osteochondral loose bodies
• Femoral head fractures - Pipkin type I and II, allowing ORIF with direct joint visualisation
• Acetabular fractures - posterior wall, transverse and T-type fractures where joint surface visualisation is essential for anatomic reduction
• Early avascular necrosis - staging, core decompression or bone grafting under direct vision
• Chondral and osteochondral lesions - assessment and treatment of femoral head defects, and comprehensive evaluation of acetabular and femoral chondral damage, particularly when planning realignment procedures
• Slipped capital femoral epiphysis (SCFE) - the modified Dunn procedure, realigning the epiphysis with vascular protection
• Synovial pathology - pigmented villonodular synovitis (PVNS), other synovial disease and tumours requiring complete synovectomy
• Complex labral and capsular pathology - labral reconstruction with grafts, refixation in the setting of dysplasia or FAI, and capsular plication for instability
• Extra-articular impingement - greater trochanteric and trochanteric-pelvic impingement requiring osteoplasty
• Septic arthritis - formal open debridement in severe septic arthritis when arthroscopic washout is insufficient

Relative indications.

• Legg-Calve-Perthes disease deformity correction in the healed stage
• Post-traumatic deformity of the femoral head or acetabular rim
• Ischiofemoral impingement requiring lesser trochanteric osteoplasty
• Revision after failed hip arthroscopy with residual impingement

Contraindications. Examiners test whether you know when not to open the hip joint.

• Advanced osteoarthritis (Tonnis grade 3)
• Obesity - a BMI greater than 35-40 makes positioning and exposure difficult
• Severe dysplasia, where a periacetabular osteotomy is more appropriate
• Active infection
• Pre-existing femoral head avascular necrosis with collapse, where the head is already unsalvageable

The blood supply. The adult femoral head is supplied predominantly by the deep branch of the medial femoral circumflex artery (MFCA). The artery of the ligamentum teres contributes, but it is variable and usually insufficient to sustain the head alone.

The extracapsular course. The deep branch arises from the profunda femoris, passes posteriorly between the pectineus and iliopsoas tendons, then runs between obturator externus and adductor brevis. It crosses posterior to the obturator externus tendon and anterior to the conjoint tendon of obturator internus and the gemelli, then pierces the capsule at the posterosuperior aspect of the femoral neck. At the base of the neck it forms an extracapsular anastomotic ring with branches of the lateral femoral circumflex and inferior gluteal arteries; staying extracapsular during the approach protects it.

The intracapsular course. At the capsule the MFCA gives off retinacular branches that run along the posterosuperior femoral neck beneath a synovial fold, the retinaculum of Weitbrecht. These superior retinacular arteries, also called the lateral epiphyseal arteries, are its terminal branches and the dominant supply to the weight-bearing segment of the head.

Why the flip is safe. The osteotomy is made anterior to the insertion of the external rotators, so the entire retinacular vascular chain stays within the posterior soft tissues and the retinacular fold on the neck. The short external rotators are left attached in the Ganz technique, but the vessel's shield is obturator externus, not the conjoint tendon it passes in front of: keep obturator externus intact and never divide it. The moments of greatest vascular risk are the osteotomy, which must stay anterior, and the dislocation, which must be gentle.

The greater trochanter. The osteotomy is planned around its attachments:

• Gluteus medius inserts on the posterosuperior and lateral greater trochanter
• Gluteus minimus inserts on the anterior facet
• Vastus lateralis originates from the inferior aspect
• The trochanteric (digital) fossa is the posterior depression where the obturator externus tendon inserts; the osteotomy must not extend into it
• The piriformis fossa is the entry point for the deep branch of the MFCA and must be protected

The capsule. The hip capsule attaches centrally to the acetabular labrum and transverse ligament, and on the femur to the intertrochanteric line anteriorly and to the femoral neck posteriorly at mid-neck level. The inferior capsule is left alone, because additional retinacular vessels may be present there.

The Ganz surgical dislocation does not follow a classic internervous plane. It is a soft-tissue preserving approach that maintains the neurovascular integrity of the posterior structures.

The superficial layer. A lateral or posterolateral incision of approximately 15-20 cm is centred over the greater trochanter, either straight (standard) or slightly curved posteriorly (the modified Gibson approach). The iliotibial band is incised in line with the skin, and in a Gibson-type approach the gluteus maximus fibres are split bluntly along their posterior border.

The deep layer: the trochanteric flip. The osteotomy leaves gluteus medius attached to the fragment superiorly and vastus lateralis inferiorly, creating a mobile fragment that is flipped anteriorly with its muscles. The short external rotators (piriformis, obturator internus, gemelli) are not detached and remain on the intact posterior femur. With gluteus minimus elevated off the capsule, the capsule lies exposed anteriorly, superiorly and posterosuperiorly.

View larger

Position. Lateral decubitus with the affected hip uppermost, stabilised with a peg-board, beanbag or lateral hip positioner. The leg is draped completely free: flexion, adduction and external rotation dislocate the hip, and extension, abduction and internal rotation serve the reduction and the acetabular work.

The dependent side. Make sure the peroneal nerve of the dependent leg is free of pressure at the fibular head, and protect the axilla and brachial plexus of the dependent arm with an axillary roll.

Anaesthesia. General anaesthesia with muscle relaxation is preferred so that the hip dislocates under control and without resistance. Supplemental regional blocks (lumbar plexus or fascia iliaca) may be used for post-operative analgesia.

No traction table. The assistant provides manual traction as needed during dislocation and reduction, and a sterile pocket or leg holder may support the leg while the hip is dislocated.

Fluoroscopy. The C-arm is positioned for AP and lateral views of the hip, to confirm the osteotomy position, the adequacy of the femoral neck osteoplasty, and the reduction and fixation of the trochanteric fragment.

Instruments. Standard hip instrumentation, plus fine osteotomes for the femoral neck osteoplasty, a femoral head sizer or templating guide, suture anchors for labral refixation, and a small fragment set for the trochanter (typically 3.5 mm or 4.5 mm screws).

Trochanteric flip and capsulotomyAnterior dislocation and femoral workAcetabular work and labral repairReduction, trochanteric fixation and closure

Exposure. Through the skin incision the fascia lata and gluteus maximus are split. The anterior border of gluteus medius is identified and the trochanteric bursa is excised.

The osteotomy. It is marked and cut with an oscillating saw, beginning at the posterosuperior aspect of the greater trochanter just posterior to its tip, and directed anteriorly and distally to exit just distal to the anterior trochanteric ridge. The saw must stay anterior to the piriformis fossa.

The flip. The fragment, with gluteus medius superiorly and vastus lateralis inferiorly, is mobilised anteriorly. Gluteus minimus is carefully elevated off the anterior capsule, preserving the muscle belly, and the fragment is flipped to expose the anterior and superior capsule, which is cleaned of overlying tissue.

The capsulotomy. A Z-shaped capsulotomy exposes the femoral head and the labrum. The first limb runs along the anterosuperior acetabular rim, from the anterior margin of the reflected head of rectus femoris towards the posterosuperior rim. The second limb runs from the end of the first along the femoral neck at the head-neck junction.

The dislocation. The hip is gently dislocated anteriorly by flexion, adduction and external rotation. It is done slowly and without excessive force because the retinacular vessels are on stretch: the head is delivered, never pulled or levered, since traction stretches them and risks AVN. The leg then rests in a sterile pocket or is supported by the assistant in the figure-of-four position.

Assessment. With the femoral head fully visualised, assess:

• Chondral integrity of the femoral head (Outerbridge or Beck grading)
• Cam lesion at the anterosuperior head-neck junction (alpha angle assessment)
• Labral integrity and the chondrolabral junction
• Any loose bodies or synovial pathology

Cam osteochondroplasty. When required, the prominence at the head-neck junction is resected with curved osteotomes or a high-speed burr to restore the normal head-neck offset and bring the alpha angle below 50 degrees. The resection is checked with fluoroscopy (Dunn view or frog lateral) and by testing for impingement with the hip reduced. The head is then irrigated and loose bone debris removed.

Assessment. With the head dislocated anteriorly, the acetabulum is fully visualised. The labrum is assessed for tears, degeneration or detachment, and the acetabular cartilage is graded.

Labral repair. A torn but viable labrum is repaired:

• The labrum is taken down from the rim if needed, for access to rim osteoplasty
• Rim trimming of approximately 2-5 mm of the anterosuperior rim is performed if pincer impingement is present
• The labrum is reattached with suture anchors placed at the chondrolabral junction, the sutures passed through the labral substance or around its base
• Typically 2-4 anchors are used along the anterosuperior rim

Labral reconstruction. A deficient or irreparable labrum may be reconstructed with autograft (gracilis or ITB) or allograft. The socket is irrigated and loose debris removed, and focal, contained chondral defects may be addressed with microfracture.

View larger

Reduction. The hip is gently reduced by extension, abduction and internal rotation, smoothly and without force, again protecting the retinacular vessels from stretch.

Trochanteric fixation. The fragment is reduced to its anatomical position and fixed with two or three 3.5 mm or 4.5 mm cortical screws, directed from the fragment into the medial cortex of the femur (bicortical fixation). The screws must not penetrate the medial cortex excessively, which risks the MFCA, and should be angled to avoid the femoral neck, which risks a split. A trochanteric claw plate or cable fixation may be used instead, particularly if bone quality is poor.

Closure. The capsule is loosely closed with absorbable sutures, approximating the edges without making it watertight, to avoid a post-operative haemarthrosis under pressure. The fascia lata is closed over the trochanteric fixation, and the skin in layers.

View larger

Post-operative management.

• Touch-weight-bearing for 4-6 weeks to protect the trochanteric osteotomy
• Passive range-of-motion exercises, avoiding extreme flexion and external rotation for the first 4-6 weeks
• Hip flexion limited to 70 degrees for the first 2-3 weeks
• Abductor strengthening from 6 weeks, with gradual progression to full weight-bearing

The extended retinacular flap. This evolution of the basic technique departs deliberately from the rule above. After the flip and capsulotomy, the synovial retinacular fold carrying the MFCA terminal branches is mobilised off the posterosuperior neck as a soft-tissue flap, and a step of trochanter can be raised with it as a second osteotomy. The vessels then travel with the flap instead of being tethered to the neck, which frees the surgeon to resect the metaphyseal neck and reposition the epiphysis without putting them on stretch.

The modified Dunn procedure. The highest-stakes application of surgical dislocation, and the one that depends on the extended flap. It treats moderate-to-severe and unstable SCFE: the callus and metaphyseal prominence are removed, and the epiphysis is reduced anatomically onto the neck under direct vision and fixed. The deformity is corrected at its source while the flap protects perfusion, which is often monitored intra-operatively.

Relative femoral neck lengthening. A named deformity correction through surgical dislocation, for the coxa breva / coxa magna with a high-riding (over-grown) greater trochanter seen after healed Legg-Calve-Perthes disease or post-SCFE/AVN deformity. The short, wide neck and relatively overgrown trochanter cause abductor weakness (a shortened lever arm, Trendelenburg), extra-articular trochanteric-pelvic impingement, and intra-articular impingement from the aspherical head.

After the trochanteric flip, the redundant lateral femoral neck is resected and contoured down to the head-neck junction (head-neck osteochondroplasty), and the greater trochanter is distalised and advanced, re-fixed more distally and laterally. This lengthens the neck relative to the trochanter, restores the abductor lever arm and offset, and relieves both intra- and extra-articular impingement. The same MFCA-protecting principles apply, with an extended retinacular flap for major neck reshaping, so the head is not devascularised.

The Ganz surgical dislocation has a well-documented safety profile when performed by experienced surgeons, but it carries specific risks from the trochanteric osteotomy, the vascular anatomy and the nearby nerves.

Avascular necrosis. The most feared complication, reported at 0-2% in large series when the technique is performed correctly, and catastrophic in a young patient. When it occurs it is usually technique-dependent: the MFCA or its retinacular branches are lacerated, stretched or thrombosed during the osteotomy or the dislocation. AVN typically declares itself within the first 12-24 months, with progressive groin pain and radiographic change. The risk factors:

• An incorrect osteotomy, too thick or too posterior, entering the piriformis fossa
• Short external rotators divided too close to the femur
• Forceful dislocation, tearing the retinacular vessels
• Pre-existing compromised vascularity, as after SCFE or Perthes disease

Trochanteric nonunion or malunion. Reported in approximately 1-3%, this is the most common mechanical complication. Inadequate fixation, poor bone quality, early weight-bearing and a large fragment all raise the risk. Nonunion or migration of the fragment presents with lateral hip pain, weakness on abduction and a positive Trendelenburg sign; treatment ranges from observation of an asymptomatic fibrous union to revision fixation with bone grafting.

Nerve injury. Sciatic neuropraxia from retraction occurs in approximately 1%, the peroneal division being more susceptible, and most cases resolve within 3-6 months. The nerve is at risk during posterior capsular exposure and acetabular work, and careful retraction, avoiding prolonged posterior retraction, protects it. The superior gluteal nerve is at risk with excessive proximal dissection.

Heterotopic ossification. Reported in approximately 5-8% without prophylaxis, and more common after extensive acetabular rim work or bone grafting. Indomethacin 75 mg daily for 3-6 weeks, or a single post-operative dose of radiation (700 cGy), reduces the risk.

Abductor weakness. Transient weakness of abduction is common after the osteotomy and gluteus medius dissection, and most patients recover strength by 6-12 months. Weakness persists in some, and persistent weakness may indicate trochanteric nonunion or failure of the gluteus medius repair.

Infection. Deep infection is rare (less than 1%) but catastrophic in a young patient with a native hip. Standard peri-operative antibiotic prophylaxis (cephalosporin or clindamycin) is mandatory.

Femoral neck fracture. Rare but reported, particularly after extensive cam osteoplasty, where over-resection of the neck cortex weakens its structural integrity. Resecting more than 30% of the femoral neck diameter significantly increases the risk.

Chondral damage and arthrosis. Intra-operative assessment may reveal more extensive damage than pre-operative imaging suggested, changing the prognosis. Pre-existing chondral damage may progress despite successful impingement correction, leading to early osteoarthritis; the long-term risk depends on the degree of that damage and is a limitation of the underlying pathology rather than a complication of the technique.

Persistent impingement and stiffness. Inadequate resection of the cam or pincer lesion leaves residual impingement and persistent symptoms, so intra-operative fluoroscopic confirmation of adequate resection is essential. Post-operative stiffness and adhesions causing persistent impingement are further sources of ongoing pain.

Reoperation. Hardware removal, trochanteric refixation or progression to arthroplasty are reported in approximately 5-15% of cases at long-term follow-up.

There is no single universal guideline for surgical hip dislocation; practice follows evidence-based principles and surgeon experience. Several international organisations have published guidance relevant to the indications and technique: