Anterior knee pain after total knee arthroplasty: does it correlate with patellar blood flow?

Purpose Total knee arthroplasty (TKA) disturbs patellar blood flow, an unintended accompaniment to TKA that may be a cause of postoperative anterior knee pain. We examine whether disrupted patellar blood flow correlates with anterior knee pain following TKA. Methods In 50 patients (21 men, 29 women) undergoing TKA, we compared patellar blood flow at flexions 0 to 30, 60, 90, and 110 before and after medial parapatellar arthrotomy to pre- and postoperative anterior knee pain scores by means of a laser Doppler flowmeter (LDF) probe. Anterior knee pain was assessed using the pain intensity numeric rating scale (NRS) of 0–10 (0-no, 10-worst pain). Based on the NRS pain values, patients were divided into two main groups: group A (n = 34) with no pain or discomfort (NRS range 0–4) and group B (n = 16) with anterior knee pain (NRS range 5–10). Results Patients of group B demonstrated a significant decrease in blood flow before arthrotomy at flexions from 0 to 90, and 110 and from 0 to 60, 90, and 110 after arthrotomy. For group A, a significant decrease in blood flow was detected at flexions from 0 to 90, and 110 before and after arthrotomy. For both groups, medial arthrotomy did not have a statistically significant influence on patellar blood flow (margin of significance P\0.05). Prior to TKA, 16 of the 50 patients of group B (32%) complained of anterior knee pain (mean NRS 7.1 ± 1.7). At 2-year follow-up, pain significantly decreased (NRS 3.1 ± 2.1) and only 4 of the 16 patients (25%) complained of moderate anterior pain (average NRS 5.7 ± 0.5), while 8 of 16 (50%) patients reported discomfort (mean NRS 3.5 ± 1.8) around the patella. Patients in group A also demonstrated a significant decrease in pain intensity (from NRS 1.5 ± 1.4 preoperatively to NRS 0.4 ± 1.5 at 2-year follow-up). Statistical analysis demonstrated no statistically significant correlation between pre-arthrotomy/ post-arthrotomy patellar blood flow and the presence of preoperative and postoperative anterior knee pain. Only the degree of flexion had an influence on patellar blood flow. Conclusion Medial arthrotomy had no direct significant effect on patellar blood flow, and the diminished blood flow did not correlate with postoperative anterior knee pain. However, a significant correlation was revealed between patellar blood flow and the degree of flexion: in almost a quarter of patients, blood flow dropped to zero at flexions of 100 and above. Level of evidence II.