Was it widely known during his reign that Kaiser Wilhelm II had a deformed arm?

Alas, after couple hours of strenuous research yesterday, I admit that this question is hard to answer but is capable of being deduced upon since one cannot speak for the general public. Thus, I came down with the similar conclusion as CDR.

Unfortunately, I was only able to find French and English articles instead of the desired German articles. Below are three quotes from articles published around 1888-1918 which alludes to the Kaiser's crippled arm before his abdication.

In the first article seemingly published in 1918, the article states:

The last time I saw Dick we decided the best way to end this war was for us to challenge the Kaiser and the Crown Prince to a doubles match in Berlin. We figured this out after learning that the Kaiser had a crippled arm and the Crown Prince never played the game. Dick says that with a month's hard practice we could give them a hell of a run for it.

The second article created in 1894 states:

The Kaiser's crippled arm does not prevent his being an excellent shot, and he takes great pride in bringing in a fine bag of game.-Harper's Bazar.

The French article created in 1888 states:

Wilhelm a l'uniforme des hussards rouges, dont il est le colonel effectif. Il est grand et fort, mais du tronc robuste, désagréable surprise, se détache un bras d'infirme, atrophié par suite d'un arrêt de développement et qu'il porte généralement devant lui comme s'il était paralysé."

"Wilhelm wears the uniform of the Red Hussars, of which he is the effective colonel. He's tall and strong, but from the robust trunk, an unpleasant surprise, stands out a crippled arm, atrophied as a result of arrested development and which he generally carries in front of him as if paralyzed."

Excerpts from a letter by Charles Gibson (1867-1944) to American journalist George Creel (1876-1953) in February 1918:

“Charles Dana Gibson enthusiastically passed on a suggestion to Creel: too many pictures in the press presented a youthful, vigorous kaiser; better to show his crippled left arm and “sinister countenance.” “Flattering pictures of the Kaiser,” he advised, “should be discouraged.” Creel agreed.”

Source: Manipulating the Masses by John Maxwell Hamilton pg. 236

Conclusion: People were cognizant of Wilhem’s arm, however to try to answer for the general public would be fatuous since there’s not much sources willing to help us on that. It would thus seem that majority of the people would've known that he had a crippled arm by the virtue of those sources above. Thus, as CDR said, it would seem that "it was definitely common knowledge by the time his reign came to an end."

I'm going to say that, yes, it must have been fairly well-known. For instance, a number of (American) newspapers in 1893/4 quote Harper's Bazar in saying:

The Empress of Germany shares her husband's taste for hunting, and frequently accompanies him upon his shooting expeditions. [...] The Kaiser's crippled arm does not prevent his being an excellent shot, and he takes great pride in bringing in a fine bag of game.

Meanwhile, a 1909 issue of the Staunton Spectator cites Dr. William Lee Howard as having said this:

Much has been said about the Kaiser's crippled arm. It is not a crippled arm- when an infant he suffered from an attack of infantile paralysis. This was merely a temporary injury to the nerves supplying the left arm, probably due to some pressure upon the delicate infantile shoulder.

Moving on, though, we find a 1915 issue of the Bamberg Herald explaining the story in detail. It frames itself as a tell-all, and after the following opening lines, it claims that "the circumstances attending the unfortunate happening may not be known generally." But it's unclear whether the not-generally-known part is the hand's crippled-ness itself, or if it's the reason for its being crippled:

Readers of current literature must observe a peculiarity in the pose of the pictures representing the German emperor. The peculiarity is this- the left hand is always seen thrust into the side pocket of his coat. The reason for this is that the member is useless and has been so all his life, the affliction having had its origin at his birth through the blunder of the attending physician.

All that said, it was definitely common knowledge by the time his reign came to an end.