The link to the German language 'Focus' story is here.
Here's a link to another story from a local paper that gives more details:
The knife used in the attack was 30cm long with a serrated edge. This was serious.
Also the attacker (the father) shouted 'I am Palestinian! I have stabbed and killed so many Jews!'
No mention whether the attacker thought Dr. Tan was Jewish and whether that was the reason for attacking him.
The incident happened on Monday at a small clinic in Troisdorf. "The patient arrived around 10 o’clock in the evening accompanied by his girlfriend-in full burka. He was very aggressive from the beginning and things got worse when I started treating him", says the doctor to FOCUS Online.
The patient had a broken fibula or calf bone, a leg bone located on the lateral side of the tibia. "I explained everything to him and showed him the exercises he had to do. But he didn’t pay any attention to anything I said." Finally, the 19- year-old rushed out of the clinic only to return shortly thereafter with his brother and father, the latter armed with a knife.
The doctor had just completed surgery on another patient, when his wife called for help at the reception. He ran to her aid and found himself confronted with a man wielding a knife. "He shouted ’Allahu Akbar’ and wanted to behead me!" Recalled the doctor.
Both men immobilized the doctor. "Their father continued to shout at me. ’Apologize to my son, kneel before him and kiss his hand’ he said." In the clinic, panic broke loose.
An 82-year-old patient escaped through a window.
Fortunately, while the three men assaulted the doctor, employees and patients escaped, immediately calling the police, who arrived before the incident could escalate any further.
Police arrested the 19-year-old Muslim and his girlfriend, however the man’s father and brother had escaped before authorities arrived. Later that same evening the father and brother appeared at the police station with a lawyer in tow.
Meanwhile, the doctor’s wife suffered a heart attack due to the sudden shock and is currently recovering in a hospital.