once？

Other observations undermine the basic premise of the biomedical model. For example, when a pathological cause of chronic pain is purportedly identified, such as a herniated lumbar disk on MRI, attempts to eliminate this pathology (e.g., back surgery) often fail to provide pain relief. These failures are not surprising, since radiologic studies of the lumbar spine demonstrate that up to 35% of persons with no pain symptoms show significant pathology on MRI (92–95). Confounding this model further, patients with the same diagnosis and level of pathology often respond differently to the same treatment, so the physician is left to ponder the other factors contributing to the patient’s suffering. To reiterate, usually there is an initiating somatic cause to persistent pain (e.g., neuropathic, nociceptive, myofascial, or central), but once this initiating cause is found, often it is resistant to conventional medical treatment.

其他观察结果也不符合生物医学模式的基本前提。例如，当据称确定了慢性疼痛的病因时（例如MRI上的腰椎间盘突出），试图消除这种病理（例如，腰部手术）往往不能提供疼痛缓解。这些不符合并奇怪，因为腰椎的放射学研究表明：高达35%的没有疼痛症状的人在MRI上显示出明显的病变(92-95)。而且具有相同诊断和病理水平的患者往往对相同的治疗反应不同，这就进一步质疑了这一模式，因此医生不得不思考导致患者痛苦的其他因素。需要重申的是:持续性疼痛通常有始发的躯体原因(例如，神经性、伤害性、肌筋膜性或中枢性)，但一旦发现这种始发原因，通常会对常规药物治疗产生抵抗力。

这里的once翻译成一旦，似乎不通，可翻译成即使吗？

medical treatment是 药物治疗？

谢谢