Can diminished knee reflex be a result of total knee replacement (TKR) surgery?

Diminished Knee Reflex Following Total Knee Arthroplasty

Yes, diminished knee reflex is directly caused by total knee arthroplasty (TKA). Research demonstrates that patients who have undergone TKA experience a significant reduction in patellar tendon reflex compared to their non-operated knee.

Evidence for Diminished Knee Reflex After TKA

• Patients who have undergone unilateral TKA show a patellar tendon reflex (PTR) that is on average only 55.1% of the response seen in their contralateral uninvolved knee 1
• This reduction in reflex response is statistically significant when compared to patients with knee arthritis awaiting TKA (96.03% reflex symmetry) and patients without knee arthritis (102.2% reflex symmetry) 1
• The diminished reflex persists at least 6 months postoperatively, indicating this is not a temporary phenomenon 1

Mechanism and Clinical Implications

• The altered knee anatomy following TKA affects the normal biomechanics of the knee joint and the function of the extensor mechanism 2
• Component positioning and rotation can affect patellar alignment and tracking, which may contribute to changes in reflex response 2
• Patellofemoral instability occurs in 1-12% of TKA patients, often due to internal malrotation of femoral and/or tibial components, which may further impact reflex mechanisms 2
• Extensor mechanism alterations following TKA can include changes to the quadriceps and patellar tendons, potentially affecting the reflex arc 2

Differential Diagnosis Considerations

• When evaluating patients with diminished knee reflexes after TKA, it's important to recognize that the reflex asymmetry is likely due to the knee replacement itself rather than lumbar radiculopathy 1
• This finding is particularly important for spine specialists who use reflex testing as part of their neurological examination 1
• Clinicians should be aware that diminished knee reflex in a patient with TKA does not necessarily indicate a new neurological problem 1

Other Potential Complications of TKA to Consider

• The most common complications following TKA include loosening (39.9%), infection (27.4%), instability (7.5%), periprosthetic fracture (4.7%), and arthrofibrosis (4.5%) 2
• Patellar complications occur in approximately 3.6% of TKA cases and include subluxation, dislocation, fracture, component loosening or wear, impingement, and osteonecrosis 2
• Reflex sympathetic dystrophy (complex regional pain syndrome) has been reported in 0.8% of TKA patients and can present with excessive pain and cutaneous hypersensitivity 3

Evaluation of TKA Patients with Knee Symptoms

• Radiographs remain the initial imaging modality for evaluation of a patient with TKA concerns, typically consisting of anteroposterior, lateral, and axial views 2
• CT is the modality most commonly used for measuring axial malrotation of knee prosthesis components when alignment issues are suspected 2
• MRI with metal artifact reduction techniques can be used to assess soft tissue complications and component rotation 2

In conclusion, the diminished knee reflex observed in your patient with bilateral TKA is an expected finding directly related to the knee replacement surgery itself, rather than indicating a new pathological process.