Medial Femoral Circumflex Artery: Critical to Safe Hip Dislocation

Introduction and Epidemiology

Surgical dislocation of the hip represents a paradigm shift in the management of complex intra-articular hip pathology. Pioneered by Reinhold Ganz and colleagues in the late 1990s and formally published in 2001, this technique provides complete, 360-degree access to the femoral head and acetabulum while meticulously preserving the blood supply to the proximal femur. The procedure is foundational for the treatment of femoroacetabular impingement (FAI), labral tears, complex chondral injuries, acute severe slipped capital femoral epiphysis (SCFE), Legg-Calvé-Perthes disease, and specific proximal femur or acetabular fractures.

Femoroacetabular impingement is increasingly recognized as a primary etiology of early-onset osteoarthritis in the non-dysplastic hip. The pathogenesis of FAI involves abnormal contact between the proximal femur and the acetabular rim during the terminal arcs of motion, particularly in flexion and internal rotation. This abnormal contact is generally categorized into cam impingement, pincer impingement, or a mixed presentation. Cam impingement is characterized by an aspherical femoral head-neck junction that shears the anterosuperior labrum and adjacent acetabular cartilage. Pincer impingement results from focal or global acetabular overcoverage, leading to linear impact against the labrum.

The epidemiology of FAI indicates a high prevalence in young, active populations, particularly athletes participating in sports requiring repetitive hip flexion and rotation. The natural history of untreated symptomatic FAI is progressive chondral delamination, labral tearing, and eventual end-stage osteoarthrosis. By enabling safe surgical dislocation, orthopedic surgeons can perform comprehensive osteochondroplasty, labral repair or reconstruction, and functional intraoperative assessment of motion, thereby altering the natural history of the disease.

Surgical Anatomy and Biomechanics

Vascular Anatomy of the Proximal Femur

The foundational principle of safe surgical dislocation is the meticulous preservation of the medial femoral circumflex artery (MFCA). Understanding this vascular anatomy is paramount. The blood supply to the femoral head in adults is predominantly derived from the deep branch of the MFCA.

The MFCA originates from the profunda femoris artery and courses posteriorly between the iliopsoas and pectineus muscles. It then passes inferior to the obturator externus tendon and posterior to the tendon of the obturator internus. The deep branch of the MFCA gives rise to the retinacular vessels, which perforate the joint capsule near the superior gemellus and obturator internus tendons. These vessels travel along the posterosuperior aspect of the femoral neck within the retinacular folds to supply the femoral head.

During surgical dislocation, the integrity of the external rotator muscles—most notably the obturator externus—is the key to protecting the MFCA. The obturator externus acts as a protective sling. When the hip is dislocated anteriorly, the intact short external rotators prevent tension on the MFCA, allowing the vascular pedicle to remain completely undisturbed.

Muscular Anatomy and the Digastric Concept

The Ganz approach utilizes a trochanteric flip osteotomy. This creates a digastric muscle flap comprising the gluteus medius proximally and the vastus lateralis distally. The preservation of the tendinous insertions of these muscles on the mobilized greater trochanter fragment ensures that the abductor mechanism remains functional and well-perfused. The short external rotators remain attached to the proximal femur, safeguarding the retinacular vessels.

Biomechanics of Impingement

Normal hip biomechanics rely on a spherical femoral head articulating concentrically within the acetabulum. In cam impingement, the decreased femoral head-neck offset acts as a cam mechanism. As the hip flexes, the non-spherical portion is forced into the joint, increasing tension on the capsule and subjecting the articular cartilage to massive shear forces. This typically leads to an outside-in delamination of the acetabular cartilage.

In pincer impingement, the overhanging acetabular rim acts as an abutment. The femoral neck impacts the labrum directly, crushing it against the rim. This can induce a contrecoup lesion in the posteroinferior acetabulum due to the levering of the femoral head posteriorly during deep flexion.

Indications and Contraindications

Patient selection is critical for the success of surgical hip dislocation. The procedure is primarily indicated for intra-articular pathologies that cannot be adequately addressed via hip arthroscopy, or where a 360-degree view is necessary for complex anatomical restoration.

Operative vs Non Operative Management

Contraindications

Absolute contraindications include advanced osteoarthritis (Tönnis grade 2 or 3), active joint infection, and severe medical comorbidities precluding prolonged anesthesia. Relative contraindications include older age (generally >45-50 years, where arthroplasty yields more predictable outcomes), severe osteopenia affecting trochanteric fixation, and significant obesity, which complicates the approach and increases the risk of trochanteric nonunion.

Pre Operative Planning and Patient Positioning

Imaging Modalities

Comprehensive preoperative imaging is the cornerstone of surgical planning. A standard radiographic series must include an anteroposterior (AP) pelvis, a cross-table lateral, a Dunn 45-degree view, and a false profile view.

On the AP pelvis, the surgeon evaluates the lateral center-edge angle (LCEA), Tönnis angle, and signs of retroversion such as the crossover sign, ischial spine sign, and posterior wall sign. The Dunn 45-degree view is highly sensitive for assessing the anterior femoral head-neck offset and calculating the alpha angle. An alpha angle greater than 50-55 degrees is generally indicative of cam morphology.

Magnetic Resonance Imaging (MRI) or Magnetic Resonance Arthrography (MRA) is essential for evaluating the integrity of the labrum, the articular cartilage, and the subchondral bone. Radial sequence MRI mapping allows for precise localization of cam lesions and chondral delamination flaps.

Computed Tomography (CT) with 3D reconstruction provides an exact topographical map of the bony deformity. This is particularly useful for planning complex osteochondroplasties and assessing femoral version.

Patient Positioning and Preparation

The patient is placed in the lateral decubitus position on a standard radiolucent operating table. Rigid pelvic stabilization using anterior and posterior supports is critical to ensure that the pelvis remains strictly lateral during the procedure, which aids in accurate intraoperative orientation. The entire affected lower extremity must be draped free to allow for full range of motion, which is required for the dislocation and the dynamic assessment of impingement post-correction.

Prophylactic intravenous antibiotics are administered prior to incision. A Foley catheter is typically placed, and sequential compression devices are applied to the contralateral limb.

Detailed Surgical Approach and Technique

Incision and Superficial Dissection

A straight lateral incision (modified Gibson) is utilized, centered over the greater trochanter. The incision extends proximally toward the posterior superior iliac spine and distally along the femoral shaft. The subcutaneous tissues are divided to expose the fascia lata.

The fascia lata is incised in line with the skin incision. Proximally, the dissection splits the fibers of the gluteus maximus, taking care to coagulate branches of the superior gluteal artery. A Charnley retractor is placed to maintain fascial exposure.

Trochanteric Flip Osteotomy

The interval between the posterior border of the gluteus medius and the piriformis is identified. A blunt retractor is placed deep to the gluteus medius, superior to the femoral neck, to protect the superior capsule.

The trochanteric osteotomy is performed using an oscillating saw. The starting point is at the posterior border of the greater trochanter, ensuring a thickness of approximately 1.5 cm. The cut exits proximally just lateral to the piriformis fossa to ensure the piriformis tendon remains on the stable proximal femur.

Once the osteotomy is complete, the vastus lateralis is elevated from the lateral femur, maintaining its continuity with the gluteus medius. This digastric flap is retracted anteriorly, exposing the superior and anterior hip capsule.

Capsulotomy

The exposure of the capsule requires careful mobilization of the overlying musculature. The minimus tendon is sharply elevated from the capsule and retracted with the digastric flap.

A Z-shaped capsulotomy is performed. The first limb runs longitudinally along the anterosuperior axis of the femoral neck. The proximal limb runs parallel to the acetabular rim, staying roughly 1 cm distal to the labrum to preserve capsular tissue for subsequent repair. The distal limb extends inferiorly along the intertrochanteric line.

Great care must be taken during the posterosuperior capsulotomy to avoid injuring the retinacular vessels, which lie immediately outside the capsule in this region.

Safe Hip Dislocation

With the capsulotomy complete, the hip is dislocated anteriorly. This is achieved by placing the leg in flexion, adduction, and external rotation. A bone hook can be placed around the inferior femoral neck to assist with the gentle extraction of the femoral head from the acetabulum.

The ligamentum teres is sharply excised using curved scissors or a specialized ligamentum teres cutter. Once dislocated, the femoral head is covered with a moist sponge, and the leg is placed in a sterile bag or held by an assistant in a figure-of-four position to provide maximum exposure to the acetabulum.

Intraoperative Assessment and Joint Work

The acetabulum is inspected first. In cases of pincer impingement, the labrum is carefully detached from the overhanging rim. The bony rim is then trimmed using an osteotome or a high-speed burr. Following the rim trimming, the labrum is anatomically reattached using suture anchors.

Attention is then turned to the proximal femur. The cam lesion is identified. Osteochondroplasty is performed using a high-speed burr or curved osteotomes to restore the spherical shape of the femoral head and improve the head-neck offset.

Bleeding from the cancellous bone of the femoral neck confirms the preservation of intraosseous blood flow. The extent of the resection is continuously checked using spherical templates to avoid over-resection, which could lead to a femoral neck fracture.

Reduction and Dynamic Testing

The hip is reduced by applying longitudinal traction and internal rotation. A critical step is the dynamic intraoperative assessment. The hip is taken through a full range of motion, specifically deep flexion and internal rotation, to ensure that impingement has been completely eliminated.

If impingement persists, the hip is re-dislocated, and further osteochondroplasty is performed.

Closure and Fixation

The capsule is closed loosely to prevent postoperative stiffness and to avoid constricting the retinacular vessels. Usually, 2-3 interrupted absorbable sutures are sufficient.

The greater trochanter is reduced to its anatomical bed. Fixation is achieved using two or three 4.5 mm fully threaded cortical screws, or 6.5 mm cancellous screws, directed toward the lesser trochanter.

The fascia lata, subcutaneous tissues, and skin are closed in standard layered fashion.

Complications and Management

While surgical dislocation of the hip is a highly successful procedure in experienced hands, it carries specific risks related to the extensive dissection and osteotomy. Meticulous surgical technique is the primary defense against these complications.

Summary of Complications

Avascular necrosis of the femoral head is the most feared complication but is exceedingly rare when the Ganz technique is strictly followed. The intact obturator externus prevents tension on the MFCA, and precise capsulotomy avoids the retinacular vessels.

Trochanteric nonunion or delayed union can cause persistent lateral hip pain and abductor weakness. Meticulous compression of the osteotomy site and avoidance of active abduction against resistance in the early postoperative period mitigate this risk.

Post Operative Rehabilitation Protocols

Postoperative rehabilitation is carefully phased to protect the trochanteric osteotomy and the capsular repair while preventing intra-articular adhesions.

Phase 1 Protection Phase (Weeks 0 to 4)

• Weight Bearing: 20 lbs flat-foot touch-down weight bearing (TDWB) using crutches.
• Range of Motion: Continuous Passive Motion (CPM) machine may be utilized. Passive and active-assisted ROM is encouraged. Flexion is limited to 90 degrees to prevent excessive tension on the posterior capsule.
• Muscle Activation: Isometric quadriceps, hamstrings, and gluteal sets. Strict avoidance of active hip abduction and passive adduction to protect the trochanteric osteotomy.

Phase 2 Early Mobilization (Weeks 4 to 8)

• Weight Bearing: Progression to full weight bearing (FWB) begins at 4-6 weeks, contingent upon radiographic evidence of early trochanteric healing.
• Range of Motion: Progress to full ROM as tolerated.
• Strengthening: Initiate active hip abduction in the supine position. Begin closed kinetic chain exercises (e.g., mini-squats, leg press with light resistance). Pool therapy is highly beneficial in this phase.

Phase 3 Advanced Strengthening (Weeks 8 to 12)

• Weight Bearing: FWB without assistive devices. Normalization of gait mechanics.
• Strengthening: Progressive resistance exercises for the abductors, flexors, and core musculature. Single-leg stance activities to improve proprioception and balance.
• Cardiovascular: Stationary cycling with progressive resistance, elliptical training.

Phase 4 Return to Sport (Months 3 to 6+)

• Criteria for Progression: Pain-free full ROM, abductor strength > 80% of the contralateral side, negative impingement testing.
• Activities: Plyometrics, sport-specific agility drills, cutting maneuvers. Full return to competitive athletics is typically achieved between 6 and 9 months postoperatively, depending on the severity of the initial pathology and the extent of the surgical intervention.

Summary of Key Literature and Guidelines

The foundation of modern hip preservation surgery rests on the anatomical studies and surgical innovations of Ganz and the Bernese group.

1. Ganz R, Gill TJ, Gautier E, Ganz K, Krügel N, Berlemann U. (2001). Surgical dislocation of the adult hip: a technique with full access to the femoral head and acetabulum without the risk of avascular necrosis. J Bone Joint Surg Br. This landmark paper described the surgical technique and reported zero cases of AVN in an initial cohort of 213 hips, establishing the safety and efficacy of the approach.
2. Gautier E, Ganz K, Krügel N, Gill T, Ganz R. (2000). Anatomy of the medial femoral circumflex artery and its surgical implications. J Bone Joint Surg Br. This anatomical study defined the precise course of the deep branch of the MFCA and its relationship to the obturator externus, providing the anatomical rationale for the safe surgical dislocation.
3. Beck M, Kalhor M, Leunig M, Ganz R. (2005). Hip morphology influences the pattern of damage to the acetabular cartilage: femoroacetabular impingement as a cause of early osteoarthritis of the hip. J Bone Joint Surg Br. This paper elucidated the distinct pathomechanical processes of cam and pincer impingement and their direct correlation with specific patterns of labral and chondral injury.
4. Current Consensus: The current consensus among academic orthopedic surgeons emphasizes that while hip arthroscopy has become the standard of care for mild to moderate FAI, surgical dislocation remains an indispensable tool. It is the gold standard for complex deformities, severe SCFE requiring anatomical reduction (modified Dunn procedure), and cases requiring extensive intra-articular access where arthroscopic management is insufficient or technically impossible. Strict adherence to the anatomical principles protecting the MFCA ensures excellent long-term joint preservation outcomes.

Clinical & Radiographic Imaging