感染性關節炎為關節腔受微生物侵犯，視為臨床急症。由於滑膜之充血反應，典型感染性關節炎可由三相骨酪掃描中發現三相皆出現關節處示蹤劑聚集。然而，當關節腔內有大量的積液(膜液)時，會造成滑膜下血管受壓迫;若不進行緊急減壓術，將造成關節腔內骨組織之缺血性壞死。是以，此狀況下之三相骨儲掃描反而為關節腔內於三相皆有示蹤劑低下之情形。我們的病例報告為一位四歲之小女孩，有發燒、左側體部痛、紅血球沈降速率及血清C反應蛋白上升之情形。三相骨骷掃描發現左側價部於三相中皆呈現示蹤劑低下。體關節切開術確認左側體關節感染性關節炎伴隨大量關節腔內積液(膜液)及關節腔內壓力上升。雖給予病人左側體關節腔減壓術及靜脈內抗生素治療，依舊發生左側股骨頭壞死。為了能及早發現感染性關節炎及給予適當的治療，核子醫學科醫師及臨床醫師必須熟悉感染性關節的這些非典型但重要之三相骨酪掃描發現。

Septic (infectious)arthritis refers to invasion of synovial space by microbes and is a clinical emergency. Due to hyperemia of synovial vessels， the characteristic finding of也ree phase bone scan is increased甘acer ac世前ty around the involved joint in all three phases. However， when there is prominent effusion (pus)inside the synovial cavity， tamponade of subsynovial vessels occurs， followed by avascular necrosis of in個-capsular bony structures if without urgent decompression. In也issituation，也e scintigraphic findings of也ree phase bone scan may turn to be intra-capsul訂photopenia恆all three phases. We r<叩ort a 4-year-old girl with fever， left區p pa尬， elevated CRP and ESR. The three phase bone scan showed intra-capsular photopenia of left 趾pin all也ree phases. Septic arthri世s of left hip joint wi也prominent joint effusion (pus)and high intracapsular pressure were con:finned by arthrotomy. Avascular necrosis of left femoral head developed despite of the operation and antibiotic仕ea虹nent. For early identification and proper仕間位nent， it is important for nuclear medicine physicians and clinical doctors to be familiar with these important scintigraphic fmdings in septic訂也ritis.