Ankylosis

Definition

Classification

A. True Ankylosis (Intra-articular)

• Fibrosis develops between the two articular surfaces following cartilage damage
• Limits movement but complete bony fusion has not occurred
• Commonly follows: tuberculous arthritis, acute pyogenic arthritis, gonococcal arthritis, and rarely rheumatoid arthritis
• Radiograph: joint space may appear preserved; no condyle translation on opening (in TMJ)
• In rheumatoid arthritis: inflammatory pannus invades and destroys cartilage, eventually leading to fibrous ankylosis, which may later ossify

• Bony trabeculae form between the two articular ends following severe destruction of articular cartilage
• Complete fusion of bones - no joint movement possible
• Follows: suppurative (pyogenic) arthritis - occasionally after tuberculous arthritis with secondary infection
• Radiograph: bone proliferation with complete obliteration of joint space
• In rheumatoid arthritis: fibrous ankylosis - bony ankylosis sequence
• In ankylosing spondylitis: sacroiliac joint and spinal ankylosis, progressing caudal to cephalad; classic "bamboo spine"

Note: Tuberculous arthritis generally leads to fibrous ankylosis; bony ankylosis only if secondarily infected. Suppurative arthritis characteristically leads to bony ankylosis. - S Das: A Manual on Clinical Surgery

B. False Ankylosis (Extra-articular)

Sites and Clinical Contexts

1. Temporomandibular Joint (TMJ) Ankylosis

• Most common causes: rheumatoid arthritis, traumatic injury (haemarthrosis or infective arthritis); also congenital abnormalities, infection, neoplasia
• Fibrous TMJ ankylosis: no gross bony changes; condyle fails to translate on opening
• Bony TMJ ankylosis: fusion of mandibular condyle and glenoid fossa; marked mandibular deflection to affected side; trismus
• When it occurs in childhood: hypoplasia of the condyle (concurrent damage to epiphyseal growth center)
• Imaging: CT or CBCT needed to delineate extent (Fig. 61.74)

Bony ankylosis of the left TMJ on axial CT. Bone fragments (arrows) bridge the condyle and glenoid fossa. The patient developed permanent trismus after a childhood accident. - Grainger & Allison's Diagnostic Radiology

2. Ankylosing Spondylitis (AS)

• Progressive inflammatory disease of the spine and sacroiliac joints
• Ankylosis progresses from caudal to cephalad (sacroiliac joints - lumbar - thoracic - cervical)
• After ankylosis occurs, pain symptoms often improve
• Structural remodeling involves osteoproliferation (unlike seropositive RA which is primarily erosive)
• Molecular pathways driving ankylosis:
  • TNF: TNF inhibitors slow but do not completely prevent bone formation, especially effective in early disease/remission
  • IL-17A: elevated in AS sera and synovial fluid; regulates JAK2, promotes osteoblast differentiation, links inflammation to new bone formation
  • Wnt and BMP pathways: key anabolic bone-forming pathways implicated in animal models
  • Bone marrow fat metaplasia on MRI: intermediate step before new bone forms
  • NSAIDs (chronic use): may retard new bone formation in patients with elevated acute phase reactants, though evidence is mixed - Firestein & Kelley's Textbook of Rheumatology

3. Knee Ankylosis

• Extraarticular ankylosis of the knee: some motion preserved; radiographs may show apparently normal joint space
• Management: if extraarticular ankylosis/contracture in extension - quadricepsplasty; in flexion - V-osteotomy (Thompson) can correct flexion deformity

4. Hip Ankylosis (Arthrodesis / Spontaneous Fusion)

• Effects of hip fusion on adjacent joints: ipsilateral knee restricted motion, ligamentous laxity, valgus tendency; increased lumbar spine stress (especially in sitting); increased mechanical stress on contralateral hip
• Poorly positioned fusion (>30° flexion, >10° adduction, any abduction) may require osteotomy
• Conversion to total hip arthroplasty (THA) considered for: disabling back pain, knee or contralateral hip pain, or painful pseudarthrosis - Campbell's Operative Orthopaedics, 15th Ed

5. Elbow Ankylosis

• Bony or fibrous ankylosis in a poorly functioning position is an indication for total elbow arthroplasty
• Severe bony ankylosis is a contraindication to elbow arthroscopy (prevents safe arthroscope introduction)

Pathology (Rheumatoid Arthritis Sequence)

1. Synovial inflammation
2. Synovial hyperplasia - pannus formation
3. Pannus erodes cartilage and bone
4. Articular destruction
5. Fibrous ankylosis (pannus bridges bones)
6. Bony ankylosis (fibrous tissue ossifies)

• Robbins & Kumar Basic Pathology; Grainger & Allison's Diagnostic Radiology

Key Distinguishing Points

Management Principles

• NSAIDs + physiotherapy: first-line in inflammatory causes (AS)
• TNF antagonists (etanercept, infliximab, adalimumab): if NSAIDs fail in AS; slow progression of ankylosis
• IL-17 inhibitors: effective in AS
• Surgical: arthroplasty for severe functional impairment; osteotomy for mal-positioned fusions; release procedures for extra-articular causes; arthroplasty conversion for painful hip fusion