Can Diagnostic and Therapeutic Arthrocentesis Be Successfully Performed in the Flexed Knee?

Sabeen Yaqub, MD; Wilmer L. Sibbitt, Jr, MD; Philip A. Band, PhD; James F. Bennett, MD; N. Suzanne Emil, MD; Monthida Fangtham, MD; Roderick A. Fields, MD; William A. Hayward, PhD; Scarlett K. Kettwich, MS; Luis P. Roldan, BS; Arthur D. Bankhurst, MD

Disclosures

J Clin Rheumatol. 2018;24(6):295-301. 

In This Article

Results

The mean age of the extended knee cohort was 62.0 ± 11.3 years, and the flexed knee cohort was 57.6 ± 16.0 years (P = 0.3; 95% CI, −3.5489 < 4.4 < 12.349 [Wald]), indicating similar cohorts. Male-to-female ratios were 7:13 (65% female) in the conventional cohort and 8:27 (75% female) in the compression cohort (P = 0.33, z for 95% CI = 1.96, Pearson), demonstrating an expected general female sex bias in both groups. Preprocedural pain according to the 10-cm VAS was 7.74 ± 1.07 cm in the conventional cohort and 8.45 ± 1.69 cm in the compression cohort (P = 0.07; 95% CI of difference, −1.4394 < −0.70714 < 0.0251 [Wald]), indicating similar degree of preprocedural knee pain. However, procedural pain according to the 10-cm VAS was 2.4 ± 1.5 cm in the conventional cohort and 2.9 ± 1.6 cm in the compression cohort (P = 0.35; 95% CI of difference, −1.2884 < −0.42143 < 0.4455 [Wald]), indicating that constant compression did not seem to appreciably decrease procedural pain. Postprocedural pain according to the 10-cm VAS was 1.3 ± 2.0 cm in the conventional cohort and 1.3 ± 2.0 cm in the compression cohort (P = 0.94; 95% CI of difference, −1.0332 < 0.04286 < 1.1189 [Wald]).

There were no serious adverse events encountered by the 55 patients in the cohort including, but not limited to, reaction to local anesthesia, needlestick, infection, septic joint, hemarthrosis, deep venous thrombosis, pseudoseptic arthritis, dermal atrophy, significant bruising, hemorrhage, or postinjection visits to emergency facilities.

Diagnostic synovial fluid (≥2 mL) was obtained in 19 (95%) of 20 with the extended knee and in 27 (77%) of 35 in the conventional flexed knee cohort, showing a definite trend toward superiority to the extended knee approach for diagnostic arthrocentesis (P = 0.08, z for 95% CI = 1.96, Pearson). Fluid yield for therapeutic arthrocentesis with the extended knee was significantly greater (191% greater) than the flexed knee (extended knee, 16.9 ± 15.7 mL; flexed knee, 5.8 ± 6.3 mL [difference, 11.1 mL; CI, 0.91 < 8.8 < 16.7; P < 0.02, P < 0.007]) (Figure 7), showing clear superiority of the extended knee positioning.

Figure 7.

Arthrocentesis volume with extended and flexed knees. These graphs demonstrate that the conventional superolateral portal extended knee arthrocentesis (Ext Knee) is clearly superior to the conventional anterolateral portal flexed knee arthrocentesis (Flex Knee) (P < 0.007). However, when constant mechanical compression is applied to the flexed knee (Flex Knee With CMC), there is a marked increase in fluid yield, resulting in no difference between the extended and flexed knee fluid yields (P = 0.73). Proportion of effusive knees = patient number/total patient number (20 extended knee with effusion, 35 flexed knee with effusion). Color online-figure is available at https://www.jclinrheum.com.

With mechanical compression in the flexed knee, diagnostic fluid yield (≥2 mL) was increased to 35 (100%) of 35, statistically not different than the extended knee, 19 (95%) of 20 (P = 0.12, z for 95% CI = 1.96, Pearson). After constant compression to the suprapatellar bursa and patellofemoral joint in the flexed knee, quantitative fluid yields were essentially identical (1% different): extended knee, 16.9 ± 15.7 mL; flexed knee, 16.7 ± 11.3 mL (difference, −0.2 mL; 95% CI, −7.6332 < 0.2 < 8.0332; P = 0.96) (Figure 7).

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