Total Hip Replacement in Special Circumstances

Conversion of a Hip Arthrodesis to THR

Indications

• Pain in other joints due to hip fusion, especially in the other hip and ipsilateral knee
• Previously arthrodesed hip; patient now desires increased range of motion (ROM)

Pre-Op Workup

• Investigate the reason for the original arthrodesis
• Rule out ongoing infection if arthrodesis was due to or complicated by infection

Principles & Potential Problems

1. Proximal femoral deformity
2. Lack of reference for neck cut
3. Lack of reference for cup position (TAL often still present)
4. Bleeding
5. Bone loss (uncommon)

• Functioning abductors are essential for a good outcome
• Assess abductors clinically, using MRI (fatty infiltration) or EMG
• Use retained hardware or visible trochanter as reference for neck cut
• Place retractor in obturator foramen to visualize cup placement
• Intra-operative X-ray can help assess cup position before reaming
• Generally, good bone stock for cup placement
• If proximal femoral deformity or sclerosis is present, consider using burrs, drills, or osteotomy

Paget's Disease

Causes of Hip Pain

• Secondary arthritis
• Deformity
• Stress fracture
• Sarcomatous change
• Referred pain from the spine

Typical Deformities

• Varus neck
• Antero-lateral bowing of the femur
• Protrusio

Possible Problems

• Hypervascular tissues, especially in active disease, leading to significant blood loss
• Risk of intra-pelvic perforation
• Bone may be osteoporotic or sclerotic

Pre-Operative Considerations

• Evaluate for significant proximal femoral deformity; obtain full femur X-rays
• Plan for osteotomy if necessary
• Use burrs and drills to open the canal
• Pre-operative treatment with bisphosphonates and calcitonin to reduce disease activity
• Prepare for protrusio
• Avoid lengthening if the neck is in varus
• Warn the anesthetist about the potential for high output failure in active disease

Gaucher’s Disease

• Commonly presents with AVN; consider in any patient with AVN
• Bone infiltrated with structurally weak Gaucher's cells
• High risk of intra-operative fractures and bleeding
• Post-operative pain is common
• Many patients have had a splenectomy, increasing infection risk

Sickle Cell Anemia

Potential Problems

• AVN and its complications
• Very sclerotic canal due to prior sickle cell crises and infarcts
• Hypervascular tissues leading to bleeding
• Increased infection risk, particularly in asplenic patients
• Pain management challenges due to long-term opioid use

Hemophilia

Characteristics

• Hemophilic arthropathy typically affects the knee and elbow; less common in the hip
• Deformities resemble Perthes disease with a flattened head
• Often associated with acetabular dysplasia

Main Concerns

• Bleeding and infection
• Requires close collaboration with a hematologist in an MDT center

Tumors

Indications for THR

• Metastases
• Low-grade malignancies, such as chondrosarcoma
• Benign aggressive lesions, e.g., PVNS or GCT

Principles

• Determine the nature of the lesion
• Plan surgical margins
• Select the appropriate prosthesis (standard, revision type, or endoprosthesis)
• Preserve abductors if possible
• MDT collaboration is essential for adjuvant or neo-adjuvant therapy

Neuromuscular Disorders

• Examples include Parkinson’s disease
• Instability caused by contractures (flexion, adduction deformities)
• Treatment:
  • Release adductors, rectus femoris, and psoas
  • Use an anterolateral approach and over-antevert the cup
• Patients are prone to skin breakdown and systemic infections post-operatively

Femoroacetabular Impingement (FAI)

Aetiology

• Pain due to a labral tear, caused by acute or chronic trauma
• Often associated with structural issues, commonly CAM lesions
• May be secondary to conditions such as SUFE or Perthes
• Evidence suggests FAI is a leading cause of early-onset OA

Pathophysiology

CAM Impingement

• Mismatch in the radius of curvature between the femoral head and acetabulum
• Labral tear leads to separation at the chondro-labral junction
• Progresses to delamination and unstable chondral flaps

Pincer Impingement

• Femoral neck impinges on the acetabulum during ROM
• Associated with conditions like coxa profunda, protrusio, or acetabular retroversion
• Leads to acetabular lesions with cystic degeneration

Clinical Features

• Deep-seated groin pain exacerbated by hip flexion (e.g., sprinting, kicking, rising from chairs)
• Pincer impingement often causes buttock pain during leg extension
• Associated clicking is common with labral tears

Examination

• Positive impingement sign
• Reduced internal rotation

Imaging

X-Ray (AP and Cross-Table Lateral)

• Evaluate acetabular abnormalities:
  • Centre Edge angle (<15 degrees diagnostic of dysplasia)
  • Protrusio
  • Retroversion
• Evaluate femoral abnormalities:
  • Neck-shaft angle
  • Offset ratio (<0.15 diagnostic of CAM)
  • Alpha angle (>50 degrees diagnostic of CAM)

MRI Arthrogram

• Gold standard for diagnosing labral and chondrolabral tears
• Detects subtle CAM deformities

CT Scan

• Useful for identifying dysplasia and subtle deformities

Management

Non-Operative

• Worth attempting but unlikely to resolve symptoms
• Aim to prevent arthritic changes

Arthroscopic Surgery

• Recommended for isolated CAM deformity with labral tears
• Most common treatment

Open Surgical Dislocation

• Less common due to advancements in arthroscopic techniques

Osteotomy (Periacetabular or Proximal Femoral)

• Used for cases of dysplasia where labral repair alone is insufficient

Arthroplasty

• Suitable for patients with debilitating symptoms and OA
• Options include THR or resurfacing