Total Hip Arthroplasty in Bony Hip Ankylosis and Ankylosing Spondylitis

Preoperative Assessment & Anesthetic Considerations

• Full Spine Imaging: Evaluate the complete spinal axis from the cervical spine down to the sacrum.

• Pseudarthrosis Detection: Screen for occult Andersson lesions or fractures within the rigid, ankylosed spine.

• Spinopelvic Mechanics: Obtain whole-spine lateral radiographs to quantify lumbar lordosis and sagittal balance.

• Sitting Imbalance: Patients with rigid extension cannot sit comfortably. True sitting versus standing functional radiographs show minimal to no pelvissacral tilt changes.

• Spontaneous Spinopelvic Abnormalities: Roughly 15% of patients without previous spinal instrumentation demonstrate abnormal spinopelvic parameters.

• Airway Challenges:

  • Cervical spine ankylosis severely limits neck extension.

  • Temporomandibular (TM) joint involvement restricts mouth opening.

  • An awake fiberoptic intubation setup must be prepared.

• Pulmonary Function: Chest wall expansion is restricted by costovertebral joint ankylosis, causing restrictive lung disease.

Patient Positioning & Surgical Approach Selection

• Positioning Obstacles:

  • Bilateral fixed deformities (such as severe abduction or flexion contractures) make standard lateral decubitus positioning difficult.

  • Direct anterior approaches (DAA) allow supine positioning, easing airway control in patients with fixed cervical spines.

  • Severe flexion contractures impede straight anterior exposure and can prevent primary surgical wound closure in extension.

• The Dual Approach (Ranawat Technique):

  • Useful for complex, fixed flexion-abduction-external rotation deformities.

  • An anterior incision allows an in situ femoral neck osteotomy.

  • The procedure converts to a posterior approach to access the acetabulum and prepare the femur.

• Wound Closure Management in Severe Flexion: Severe contractures may require wound closure in residual flexion, followed by gradual postoperative traction to regain extension safely.

Neck Osteotomy and Acetabular Reconstruction Landmarks

• In Situ Femoral Neck Osteotomy: Mandatory because an ankylosed femoral head cannot be dislocated from the acetabular rim.

• Anatomical Landmarks for the Neck Cut:

  • Identify the abductor insertion at the greater trochanter.

  • Palpate the lesser trochanter.

  • Perform a double neck osteotomy (wafer or dowel cut) to create a bone gap, allowing removal of the neck segment.

• Locating the Native True Floor:

  • Foveal Soft Tissue: Residual pulvinar fat persists within the fovea even in complete bony ankylosis.

  • Central Drill Hole Technique: Drill a 2.5 mm drill bit centrally into the ankylosed head down to the medial wall to measure remaining bone depth (aim for roughly 1 cm of clearance).

  • Intraoperative Fluoroscopy: Verify reamer depth relative to the teardrop and medial cotyloid wall.

• Reaming Strategy in Osteopenic Bone: Disuse osteopenia elevates the risk of medial wall perforation; under-ream by 2 mm to 3 mm and advance cautiously.

Spinopelvic Adaptations (Vigdorchik Hip-Spine Classification)

• Flat-Back Deformities: Loss of lumbar lordosis produces a persistent posterior pelvic tilt, projecting an outlet view on routine AP pelvis radiographs.

• Stuck-Sitting Spine Profile:

  • The pelvis remains permanently tilted posteriorly.

  • Reduces functional native acetabular anteversion.

  • Decreasing prosthetic cup anteversion avoids anterior impingement and posterior instability when standing.

• Stuck-Standing Spine Profile:

  • The pelvis remains fixed in anterior tilt.

  • Requires tailored cup anteversion and inclination to maintain dynamic stability and prevent edge-loading.

High-Yield Clinical Summary

• Always assess the cervical spine and temporomandibular joints; prepare for fiberoptic intubation.

• Severe contractures limit lateral positioning; consider supine anterior or dual-incision approaches.

• Perform an in situ double neck osteotomy to excise a central bone wafer without joint dislocation.

• Rely on persistent foveal fat, central pilot drill depth checks, and fluoroscopy to locate the true medial acetabular floor.

• Adjust acetabular cup anteversion according to the patient’s fixed spinopelvic profile (stuck-sitting vs. stuck-standing).