How Should Surgeons Work Up the Post-TKA Patient with Lingering Knee Pain?
Dr. Samik Banerjee and Dr. Matthew Austin answer ICJR’s questions about their algorithm for determining which of the many possible intrinsic and extrinsic causes is triggering persistent knee pain in patients who have undergone total knee arthroplasty.
ICJR: What are some of the typical causes of pain following primary total knee arthroplasty (TKA)?
Samik Banerjee, MD: Total knee arthroplasty results in significant improvements in pain, function, and health-related quality of life in patients with end-stage degenerative osteoarthritis. However, between 10% and 20% of patients are not completely satisfied with the outcome of the procedure. Many of these patients have residual pain, either localized or globally throughout the knee. This pain is frequently associated with symptoms of swelling, stiffness, and limitations in function. Less commonly, patients report subjective symptoms of instability, clicking, or catching.
A thorough understanding of the clinical presentation – including a focused history and physical examination supported by relevant laboratory investigations, arthrocentesis, diagnostic injections, and imaging – will often aid in determining the etiology of a painful TKA. Unfortunately, in a small percentage of patients, the cause remains unknown despite extensive workup. Nevertheless, a methodical approach avoids errors and helps to improve clinical outcomes and patient satisfaction.
Various intrinsic and extrinsic conditions have typically been described as triggers for persistent pain after TKA. Common intrinsic causes of pain include:
- Infection (25% to 40% of revision TKAs) 
- Instability (10% to 20% of revision TKAs) 
- Component loosening (16% of revision TKAs) 
- Arthrofibrosis (1-2% in primary TKAs) 
- Component malpositioning
Less common intrinsic causes include:
- Extensor mechanism disruption (1-12%)
- Patellar clunk (1-2%) [4,5]
- Patellar osteonecrosis
- Stress fractures
- Bone and soft tissue impingement (eg, fabella, fat pad, retained osteophytes, and extruded bone cement)
- Tendinitis (eg, popliteus tendon snapping) 
- Recurrent hemarthrosis
- Heterotopic ossification (1% to 15%) [7,8]
Extrinsic sources of pain can arise from pathologic conditions in the hip, spine, and vascular system. Less-frequent extrinsic causes of pain include:
- Painful neuromas
- Complex regional pain syndrome (1% to 2%) 
- Metal hypersensitivity 
- Periarticular primary or metastatic bone diseases (rare)
Patients with certain psychiatric diagnoses, worker’s compensation claims, or unreasonable preoperative expectations may experience less pain relief and lower satisfaction after TKA.
ICJR: How do you work up the patient who presents with pain to determine its cause?
Matthew S. Austin, MD: A thorough history and musculoskeletal examination are necessary during the workup of a painful TKA. The history should establish the pain’s:
- Aggravating and relieving factors
- Relationship with activity and movement
It should also include inquiries about extrinsic sources of knee pain, such as spine or hip pathology, as described above.
During the physical examination, the surgeon should determine:
- The presence of swelling, warmth, erythema, or effusion
- Integrity of the surgical incision
- The affected knee’s range-of-motion compared with the contralateral knee
Focal tenderness over soft tissues structures around the knee, specifically over the pes anserine tendons and iliotibial band, may suggest bursitis or flexion instability. Less frequently, it may point to the location of cutaneous neuromas. Varus and valgus stress tests in 0°, 20°, and 90° and seated anterior and posterior drawer tests in 90° of flexion with the leg dangling are essential for evaluating coronal and sagittal plane stability.
Paying special attention to patellar tracking, mobility, and crepitus is important, as the patellofemoral joint can be a pain generator. Assess gait, lower extremity strength, and the presence and equality of pulses in both extremities in the initial evaluation, with particular emphasis on determining if the patient has varus or valgus thrust, antalgia, or Trendelenburg gait. Examine the hip, spine, and foot and ankle to evaluate for extrinsic causes of pain.
A 3-view weight-bearing knee radiographic examination – anteroposterior, lateral, and Merchant’s view – allows for assessment of:
- Implant position and alignment
- Component overhang
- Patellofemoral tilt and tracking
- Posterior condylar offset
- Joint stability
- Presence of lucency, osteolytic lesions, and lateral facet impingement
Consider additional radiographs, including full-length weight bearing hip-knee-ankle scanograms to assess limb alignment and oblique radiographs to detect femoral and tibial component loosening.  Hip radiographs (2 views) and or/ lumbar spine radiographs may be done in the initial visit if the physical examination is suspicious for hip or spine pathology.
Fluoroscopically guided radiographs may be obtained when clinical suspicion of loosening is high or when late posterior cruciate ligament failure is suspected in cruciate retaining knees. [12,13] Consider varus-valgus stress radiographs to objectively determine coronal plane instability. If no cause for the knee pain is found, it may be worthwhile to reassess the preoperative knee radiographs to establish whether an arthroplasty procedure had been warranted based on the degree of degeneration in the patient’s knee.
In some cases, CT scan can be useful to assess rotational alignment of the implants. Using standardized CT protocols, calculate femoral and tibial baseplate axial alignment from the transepicondylar axes and tibial tubercle, respectively. [14,15] CT scans may also be performed to evaluate the extent of osteointegration and component loosening in patients with cementless implants. Nuclear imaging with 3-phase bone scans currently has a limited role in the evaluation of painful TKAs due to the high incidence of false-positive results up to 2 years after the index procedure. [16,17]
All patients should be assessed for periprosthetic joint infection (PJI), with the laboratory workup including inflammatory markers such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). Arthrocentesis, typically indicated if the ESR or CRP is elevated, assesses cell count, differential, crystals, and bacterial (aerobic and anaerobic) culture and sensitivity. Joint aspiration may be performed at the initial visit if the surgeon has a high degree of suspicion that the patient has a PJI.
An elevated ESR or CRP level with synovial fluid cell white blood cell count above 3000/microliter and 80% polymorphonuclear leukocytes has a sensitivity and specificity of 97.7% and 99.5%, respectively, for diagnosing PJI.  The diagnosis of infection is often not straightforward; therefore, the surgeon may order repeat arthrocentesis with more advanced tests, such as synovial alpha defensin, CRP, or leucocyte esterase. [19,20]
Intra-articular hip diagnostic injections may be performed in the presence of mild to moderate hip osteoarthritis to rule out referred knee pain. Similarly, diagnostic foraminal nerve root and epidural injections may be considered after an evaluation by a spine specialist. Knee periarticular steroid injections may be performed cautiously for persistent tendinitis and/or bursitis. Rarely, a lumbar sympathetic blockade may be needed to rule out complex regional pain syndrome and ankle-brachial indices for evaluation of a vascular etiology for painful TKAs.
A summary of our diagnostic algorithm for patients who present with pain following TKA can be found in Figure 1, below.
Figure 1. Diagnostic Algorithm for Post-TKA Pain
Samik Banerjee, MD, is an Adult Reconstruction Fellow at The Rothman Institute, Philadelphia, Pennsylvania. Matthew S. Austin, MD, is Professor of Orthopaedic Surgery at Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania. He is also Adult Reconstruction Division Chief and Adult Reconstruction Fellowship Director at The Rothman Institute, Philadelphia, Pennsylvania.
Disclosures: The authors have no disclosures relevant to this article.
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