Assessment of commonly used measures of lower extremity swelling following total knee arthroplasty
Authors: Iannitto Johna , Loyd Brian , Johnson Roseann , Eschen Catherine , Levy Daniel , Jennings Jason , Stevens‐Lapsley Jennifer 
Published: November 2023

BackgroundSubstantial swelling commonly occurs after total knee arthroplasty (TKA), however a “gold standard” to accurately quantify swelling post‐operatively has not been identified. This study was designed with two aims: 1) compare the measurements of change in lower extremity swelling from pre‐ to post‐TKA, obtained via circumferential measurement (CM), bioelectrical impedance spectrometry (BIS), and diagnostic ultrasound (US) and 2) examine the relationship of each method of swelling measurement to the clinical outcomes of knee range of motion and patient reports of pain.MethodsMeasurements from fifteen patients undergoing bilateral TKA (30 knees) were collected pre‐TKA, 48 hours post‐TKA, and 6 weeks post‐TKA. Changes in each outcome from baseline to 48 hours and 6 weeks post‐TKA were calculated. Using a tape measure, CM was performed at the superior pole of the patella and at the thigh (10 cm proximal to the patella). A volume was calculated using the frustum created by these CM's. To obtain volume using US, the dimensions of hypoechoic areas within the knee were identified, these were used to calculate volume. BIS was performed by placing two distal electrodes over the ankle and foot and two proximal electrodes on the thigh. The BIS spectrometer passes a 3 mV current through the leg and the change in resistance (Ohms) over time was used to quantify fluctuations in lower extremity swelling. Maximum range of passive and active knee extension and flexion were collected using long arm goniometry and pain levels were recorded using a ten point VAS.ResultsPearson product moment correlations were used to test for relationships in swelling changes collected with each of the three measures. No significant relationships emerged between measures in swelling changes captured using BIS and CM or between US and BIS. However, swelling volume change from baseline to 48 hrs post‐TKA obtained by US was approaching significance to change in volume calculated from CM (0.37; p= 0.06). US measures were correlated to the change in pain from baseline to week 6 (0.45, p=0.01) and negatively correlated to change in extension at week 6 (−0.35, p=0.06), interestingly, the flexion measures were not correlated. Changes from baseline in clinical outcomes did not correlate to changes in any of the measures of swelling at 48 hours post‐TKA.ConclusionChanges in girth, BIS, and US measures of lower extremity swelling were found to have inconsistent relationships to one another. Lack of correlation between these measures may be a result of differing measurement constructs. Placement of BIS electrodes across the limb represents estimates of entire limb swelling, while circumferential measures and US measures represent a localized estimate of swelling. Further work is warranted to determine how measures collected using each method can inform clinical decision making following TKA. Swelling occurring at the knee after TKA may play a role in patient reported levels of pain and knee ROM, however the measures evaluated were not consistently related to these clinical outcome measures. The reliability of these measures remains a subject future research.Support or Funding InformationNIH R01HD065900