Ankylosing Spondylitis: Joint Stiffness and Total Hip Arthroplasty Outcomes
Yes, ankylosing spondylitis (AS) causes generalized joint stiffness as a hallmark feature of the disease, and total hip arthroplasty remains highly successful in this population despite technical challenges. 1, 2, 3
Understanding Generalized Joint Stiffness in AS
Ankylosing spondylitis is fundamentally a disease characterized by progressive stiffness affecting multiple joints:
- Axial involvement is universal, with sacroiliac joint inflammation and spinal fusion being defining features 1, 2
- Peripheral joint stiffness occurs commonly, with hip involvement representing the most severe peripheral manifestation 1
- Pain and stiffness are the primary symptoms requiring first-line treatment with NSAIDs 1, 3, 1
The disease causes stiffness through chronic inflammation leading to:
- Enthesitis (inflammation at tendon/ligament insertions)
- Progressive ankylosis (bony fusion) of affected joints
- Structural damage including syndesmophyte formation
- In severe cases, complete bony ankylosis with total loss of joint motion 4
Treatment should be tailored according to current manifestations including axial symptoms, peripheral joint involvement, structural damage, and hip involvement 1. The optimal management requires combining non-pharmacological treatments (patient education, regular exercise, physical therapy) with pharmacological interventions 1, 3.
Total Hip Arthroplasty Success in AS
Total hip arthroplasty should be strongly recommended for AS patients with advanced hip arthritis causing refractory pain or disability, independent of age 2, 3, 1, 2. This is a strong recommendation with 100% expert agreement despite very low-quality evidence, because observational studies consistently demonstrate excellent outcomes 2.
Evidence of Success:
Mid-to-long-term outcomes are excellent:
- 90% prosthesis survival at 10 years and 65% at 20 years 5
- Significant improvements in pain (VAS scores dropping from 6.5 to 2.5) 6
- Harris Hip Score improvements from 22-37 preoperatively to 89-92 postoperatively 4, 7, 6
- Range of motion improving from 0° (complete ankylosis) to 100-110° 4, 7
- 87% patient satisfaction rates 4, 6
Critical Timing Consideration:
Perform THA before complete bony ankylosis occurs. Recent evidence demonstrates that bony ankylosis adversely affects postoperative outcomes 4:
- Hips with bony ankylosis achieve lower postoperative ROM (100° vs 110°) compared to stiff but not ankylosed hips
- Lower Harris Hip Scores (89 vs 92) in ankylosed hips
- Higher WOMAC scores (worse function: 43 vs 31) in ankylosed hips
- Poor hip flexion is the main complaint among dissatisfied patients (58.5% of those dissatisfied) 4
The shorter the disease duration before surgery, the better the postoperative Harris scores and total hip ROM 7.
Technical Recommendations:
Surgery must be performed by orthopedic surgeons and at hospitals highly experienced in joint replacement for AS patients 2. Key technical considerations include:
- Use larger diameter femoral heads (36mm vs 28mm) to reduce dislocation risk and improve ROM 7
- Consider dual mobility cups in patients with spinal fusion to mitigate instability risk from absent spinopelvic motion 8
- Prefer ceramic-on-ceramic bearings over metal-on-polyethylene to reduce osteolysis (0% vs 50% osteolysis rates) 7
- Direct anterior approach (DAA) is feasible even with concomitant spinal ankylosis, allowing supine positioning and fluoroscopic guidance 8
- Biological (cementless) fixation is standard, particularly in younger AS patients 7, 6
Complication Profile:
While THA is successful, AS patients face higher complication rates than osteoarthritis patients 9, 10:
Common complications include:
- Dislocation: 2.6% (lower with larger femoral heads) 9, 7
- Heterotopic ossification: 4-15% (much lower with modern techniques and NSAID prophylaxis) 5, 9, 6
- Infection: 5.1% 9
- Periprosthetic fracture: 1.4-2.7% 4, 9
- Revision rate: 4% 9
NSAIDs do not need to be discontinued for THA surgery and actually help prevent heterotopic ossification 1. Early studies reported high rates of heterotopic bone formation, but contemporary studies show much lower rates 5.
Perioperative Medication Management:
For AS patients on biologic therapy undergoing THA, follow the 2022 ACR/AAHKS perioperative guidelines 11:
- Specific recommendations exist for timing of withholding and restarting DMARDs and biologics
- TNF inhibitors and other biologics require careful perioperative management
- The primary concern is balancing infection risk against disease flare
Key Pitfall to Avoid:
Do not delay THA until complete bony ankylosis develops. The evidence clearly shows that operating before complete ankylosis results in superior functional outcomes, better ROM, and higher patient satisfaction 4, 7. Waiting too long compromises the functional benefit that makes surgery worthwhile.
The main cause of patient dissatisfaction after THA in AS is poor hip flexion function 4, which is directly related to operating after complete ankylosis has occurred. Early surgical intervention, before complete joint destruction, maximizes the functional gains from arthroplasty.