What evaluation and management are indicated for a 75-year-old patient with a right total knee arthroplasty who cannot flex beyond 60 degrees and has persistent pain?

Evaluation and Management of Post-TKA Pain with Limited Flexion

This patient requires immediate systematic evaluation starting with weight-bearing radiographs to exclude infection, aseptic loosening, and component malposition, followed by ESR/CRP testing, as these are the most common causes of persistent pain and stiffness after TKA that require urgent intervention.

Initial Diagnostic Workup

Imaging Protocol

Start with weight-bearing AP and lateral radiographs of the entire prosthesis 1. Look specifically for:

• Periprosthetic lucency (>2mm suggests loosening)
• Component malalignment or malrotation
• Osteolysis (especially around femoral condyles and tibial screw holes)
• Polyethylene wear (manifests as joint space narrowing)
• Patella alta or baja
• Signs of instability

Laboratory Testing

Obtain ESR and CRP immediately to exclude infection, even if clinical signs are subtle 1. In patients >6 months post-TKA with persistent pain, infection must be excluded first:

• CRP >13.5 mg/L has 73-91% sensitivity for infection
• If ≥2 of 3 tests abnormal (CRP >0.93 mg/L, ESR >27 mm/h, fibrinogen >432 mg/dL), sensitivity reaches 93% 1
• Pain at rest or night pain suggests infection; weight-bearing pain suggests mechanical loosening 1

Time-Critical Management Algorithm

If Infection is Excluded and Flexion <90° at 6-8 Weeks:

Manipulation under anesthesia (MUA) is indicated, ideally performed ≤12 weeks post-surgery 2. This is your window of opportunity:

• Mean flexion gains: 30-47 degrees
• Failure rate: ~6%
• Must be followed by immediate aggressive remobilization 2

If Mechanical Causes Identified (Malposition/Overstuffing):

Order 3D-CT to assess component rotation and positioning 2. If confirmed:

• Component malrotation, oversizing, or overhang requires revision surgery
• MARS-MRI can evaluate soft tissue pathology if CT is inconclusive 2

If Aseptic Loosening Suspected:

Aseptic loosening is the leading cause of late TKA failure (>2 years) 1. Radiographic lucency with pain indicates:

• Consider 3-phase bone scan if radiographs equivocal (though limited utility <2 years post-op due to normal bone remodeling) 1
• Large areas of osteolysis require revision surgery 1
• Small osteolysis can be monitored with annual weight-bearing films 1

Management Based on Findings

Mechanical Block (Flexion <60° with Hard End-Point):

1. If <12 weeks post-op: MUA with immediate physiotherapy 2
2. If >12 weeks or MUA fails: Arthroscopic or open arthrolysis 2, 3
3. If component malposition confirmed: Revision arthroplasty with correction of technical errors, possible semi-constrained or hinged implant 3

Pain-Dominant with Preserved Motion:

• Multimodal opioid-sparing analgesia
• Strict edema control with cooling/compression 4
• Consider neuropathic component if burning/shooting pain present (affects 30-50% of chronic post-TKA pain) 5

Combined Stiffness and Pain:

This phenotype requires addressing both mechanical and pain mechanisms 5:

• Rule out infection and loosening first
• If mechanical cause found: surgical correction
• If no mechanical fault: focus on pain management, not repeat surgery 5

Critical Pitfalls to Avoid

1. Do not delay infection workup: 53% of chronic TKA infections are not clinically obvious preoperatively 1
2. Do not perform MUA after 12 weeks: efficacy drops significantly and risk of complications rises 2
3. Do not revise for pain alone without identifying mechanical fault: outcomes are poor when operating on "a nervous system to calm rather than a knee with a mechanical fault to fix" 5
4. Do not rely on bone scan <2 years post-op: 20% of asymptomatic TKAs show uptake at 1 year 1

Expected Outcomes

Set realistic expectations: stiff TKA treatment is prolonged, requires multimodal therapy beyond surgery alone, and results are often imperfect 3. Stiff knees incur 1.5-7.5 times higher two-year costs than non-stiff knees 5.