Introduction to Chronic Posterior Hip Dislocation
Chronic or neglected posterior hip dislocations represent one of the most formidable challenges in orthopedic trauma and reconstructive surgery. Defined generally as a dislocation that has remained unreduced for more than three weeks—though often presenting months or even years post-injury in developing healthcare systems—these injuries are associated with profound pathoanatomical changes. The natural history of an unreduced posterior hip dislocation involves severe soft tissue contracture, superior migration of the proximal femur, filling of the acetabulum with dense fibrofatty scar tissue, and a high probability of femoral head osteonecrosis (avascular necrosis, AVN).
The management of these complex injuries requires a highly individualized approach, dictated by the chronicity of the dislocation, the presence of associated acetabular or femoral head fractures (e.g., Thompson-Epstein Types IV and V), the viability of the femoral head, and the patient's age and functional demands.
Clinical Pearl: The timeline of the dislocation is the primary driver of surgical decision-making. Dislocations less than 3 months old with a viable femoral head may be amenable to open reduction and internal fixation (ORIF). Conversely, dislocations older than 3 months, or those with established osteonecrosis, almost universally require primary reconstructive procedures such as Total Hip Arthroplasty (THA).
Pathoanatomy and Biomechanics of the Neglected Dislocation
Understanding the altered biomechanics and distorted anatomy is critical for preoperative planning. When the femoral head remains dislocated posteriorly and superiorly over the ilium, several predictable changes occur:
- Soft Tissue Contracture: The pelvifemoral musculature, particularly the abductors (gluteus medius and minimus), iliopsoas, and adductors, undergo severe adaptive shortening.
- Acetabular Dysplasia and Scarring: The empty acetabulum rapidly fills with a dense, adherent fibrocartilaginous scar (the pulvinar hypertrophies). Over time, the articular cartilage undergoes fibrillation and necrosis due to the absence of synovial fluid nourishment and mechanical loading.
- Neurovascular Compromise: The sciatic nerve is frequently tethered or draped over the displaced femoral neck or posterior acetabular wall fragments. Superior migration of the femur places chronic tension on the nerve, increasing the risk of iatrogenic injury during reduction.
- Osteonecrosis: The medial circumflex femoral artery (MCFA) is invariably stretched or torn during the initial trauma. The incidence of AVN approaches 100% in dislocations left unreduced for several months.
Preoperative Evaluation and Imaging
A meticulous preoperative workup is mandatory to formulate a safe and effective surgical strategy.
Radiographic Assessment
Standard anteroposterior (AP) pelvis and Judet views (iliac and obturator obliques) are required to assess the position of the femoral head and identify posterior wall or column fractures.
Advanced Imaging
- Computed Tomography (CT): A fine-cut CT scan with 3D reconstructions is the gold standard for evaluating acetabular bone stock. It precisely delineates posterior wall defects, intra-articular incarcerated fragments, and the degree of superior femoral migration.
- Magnetic Resonance Imaging (MRI): MRI is critical for assessing the vascularity of the femoral head. If the femoral head is deemed avascular on MRI or a technetium-99m bone scan, joint-preserving procedures (ORIF) are contraindicated, and primary reconstruction should be pursued.
Preoperative Skeletal Traction
If the head of the femur is displaced superiorly, preoperative skeletal traction is a necessary and invaluable adjunct. Immediate acute reduction of a chronically migrated femur carries an unacceptably high risk of sciatic nerve palsy and catastrophic vascular compromise.
Technique and Protocol
- Pin Placement: A heavy, threaded Steinmann pin is placed either in the distal femur or proximal tibia, depending on the status of the ipsilateral knee ligaments.
- Weight Application: Traction is initiated at 10% to 15% of the patient's body weight.
- Vector: The traction vector should be longitudinal, combined with gradual abduction to bring the femoral head down to the level of the true acetabulum.
- Duration: Traction is typically maintained for 1 to 3 weeks. Serial radiographs are obtained every 3 to 5 days to monitor the descent of the femoral head.
Surgical Warning: Monitor the patient's neurological status daily during the traction phase. If signs of sciatic nerve neuropraxia develop (e.g., foot drop, paresthesias), the traction weight must be immediately reduced.
Surgical Strategies and Decision-Making
1. Open Reduction and Internal Fixation (ORIF)
Indications: Injuries less than 3 months old, viable femoral head on MRI, and reconstructable acetabular bone stock.
If the posterior acetabular rim is fractured, it must be anatomically reduced and rigidly fixed to restore posterior stability.
Surgical Approach:
The Kocher-Langenbeck approach is the workhorse for posterior fracture-dislocations.
* The patient is positioned in the lateral decubitus position.
* The sciatic nerve must be identified early and protected throughout the procedure. It is often encased in dense scar tissue and displaced from its normal anatomical bed.
* The short external rotators (if still intact) are tagged and released.
* The acetabulum is meticulously cleared of all fibrofatty tissue, organized hematoma, and labral debris.
* The femoral head is gently reduced into the true acetabulum using a Schanz pin in the greater trochanter as a joystick.
* The posterior wall fragment is reduced and fixed using a combination of interfragmentary lag screws and a contoured pelvic reconstruction plate spanning from the ischium to the ilium. Spring plates may be utilized for comminuted marginal fragments.
2. Total Hip Arthroplasty (THA)
Indications: Dislocations older than 3 months, Thompson-Epstein Type IV (fracture of the acetabular rim and floor) or Type V (fracture of the femoral head), or any case with established osteonecrosis.
Total hip arthroplasty is the gold standard for chronic posterior dislocations and yields the most predictable, satisfactory results, as demonstrated in landmark series by Garrett et al. and Ilyas & Rabbani. However, these are highly complex arthroplasties.
Technical Challenges and Solutions:
* Acetabular Bone Stock: The primary challenge is creating adequate acetabular coverage when the posterior lip is fractured, displaced, or resorbed.
* Structural Grafting: If the posterior wall defect is massive, the native, excised femoral head can be utilized as a structural autograft. The graft is fashioned to fit the defect, temporarily fixed with Kirschner wires, and then definitively secured with cancellous lag screws. The acetabulum is then reamed, incorporating the graft, to accept a hemispherical multi-hole component.
* Impaction Bone Grafting: For cavitary defects, morselized autograft or allograft can be impacted into the defect before cup placement.
* Component Selection: A highly porous, multi-hole titanium shell is recommended to allow for multiple screw fixations into the intact ilium, ischium, and pubis. In cases of severe pelvic discontinuity or uncontained defects, an anti-protrusio cage or custom triflange component may be required.
* Femoral Preparation: Due to chronic superior migration, the femur may require a subtrochanteric shortening osteotomy to allow reduction of the prosthetic joint without placing undue tension on the sciatic nerve. However, successful preoperative skeletal traction often obviates the need for this osteotomy.
Pitfall: Attempting to place the acetabular component in the "false" superior acetabulum (high hip center) leads to poor biomechanics, increased wear, and high rates of aseptic loosening. The cup must be placed in the true anatomical acetabulum, utilizing bone grafts to manage uncontained defects.
3. Arthrodesis (Hip Fusion)
Indications: Young, heavy laborers with unilateral disease, where THA may fail prematurely due to high functional demands.
Considerations:
Successful fusion is notoriously difficult to achieve in the presence of osteonecrosis, as the avascular bone lacks the biological capacity to consolidate.
* Prerequisites: As with any hip arthrodesis, the surgeon must rigorously evaluate the status of the ipsilateral knee, the contralateral hip, and the lumbar spine. A fused hip places immense compensatory stress on these adjacent joints; pre-existing degenerative changes in these areas are an absolute contraindication to arthrodesis.
* Technique: A cobra-head plate or dual-plate construct is typically utilized, often requiring extensive autogenous bone grafting (iliac crest) to bridge the necrotic segments and promote osteogenesis.
4. Subtrochanteric Osteotomy (Salvage Procedure)
Indications: Late, unreduced dislocations in resource-stratified areas where arthroplasty or endoprosthetic replacements are not readily available.
This procedure is reserved for patients who are relatively pain-free and possess a reasonable range of hip flexion but suffer from severe joint contracture (adduction/internal rotation) or debilitating limb-length inequality.
Biomechanics:
Based on the principles of the Schanz osteotomy, a valgus-producing subtrochanteric osteotomy realigns the mechanical axis of the lower extremity. By creating a valgus angulation at the osteotomy site, the femur is brought out of its adducted position, effectively equalizing limb length and improving the abductor lever arm. While it does not restore the joint, it significantly improves gait mechanics and functional independence in a low-resource setting.
Postoperative Protocols and Rehabilitation
The postoperative regimen must be tailored to the specific reconstructive procedure performed.
Following ORIF or THA with Structural Grafting
- Weight-Bearing: Patients are typically restricted to toe-touch weight-bearing (TTWB) or non-weight-bearing (NWB) for 8 to 12 weeks to allow for fracture consolidation or structural graft incorporation.
- Dislocation Precautions: Strict posterior hip precautions are enforced. An abduction brace may be utilized in non-compliant patients or those with severe abductor insufficiency.
- Prophylaxis:
- Venous Thromboembolism (VTE): Chemical prophylaxis (e.g., Low Molecular Weight Heparin or direct oral anticoagulants) is mandatory for a minimum of 28 to 35 days.
- Heterotopic Ossification (HO): Given the extensive soft tissue dissection and prior trauma, HO prophylaxis with Indomethacin (75 mg sustained release daily for 3-6 weeks) or a single dose of localized radiation therapy (700 cGy) is highly recommended.
