This is incorrect
The critic focuses on the verses 86:6-7, especially verse 7 as this is where their contention is directed. The critic claims the Quran (86:7) is telling us that semen is produced between the backbone (sulb) and the ribs (tara’ib). The Arabic words mentioned by the Quran are sulb and tara’ib. Tara’ib is thought to mean ribs, though there is some dispute. However, the chief point of interest is the word sulb. Sulb can be translated as ‘loins’ or ‘backbone’ or ‘lower back’.
The critic favours the translations which use the word ‘backbone’ as they use it to attack the Quran by claiming the Quran teaches that semen is produced between the backbone (sulb) and the ribs (tara’ib).
However, the critic is very selective in deciding which translation to use as he/she avoids the numerous translations which translate ‘sulb’ as ‘loins’. They avoid these translations as they scupper their critical claims straight away as loins. Here, the word loins refers to:
a. The region of the hips, groin, and lower abdomen.
b. The reproductive organs. 
So the critic refrains from using this translation for the word sulb as it is clearly scientifically accurate, ie the semen is produced in the are between the loins and ribs. So, if we translate the Quran (86:7) this way there is no contention.
The misleading methodology of the critic is to avoid mention of the numerous translations which translate the word sulb as loins.Not only do they avoid mentioning the numerous translations using the word ‘loins’ they highlight translations which use the word ‘backbone’.
This is rather deceptive, especially considering a number of non-Muslim translators, including a Christian translator, translates it as ‘loins’ ( A.J Arberry, George Sale, J.M Rodwell and Henry E Palmer) as well as a number of Muslim translators who also use the word loins (Hamid S Aziz, Muhammad M Ghali, Muhammad M Pickthall and Mohammad Asad) . It is unscholarly as well as misleading on the part of the critic not to mention this important fact.
However, the critic does use Abdullah Yusuf Ali’s translation which translates it as ‘backbone’, therefore rendering a meaning of between the backbone and ribs. So the critic understands the Quran as teaching us that semen is produced between the backbone and ribs. In the way of intellectual honesty I do not want the reader to believe that only Abdullah Yusuf Ali translates this verse by using the word ‘backbone’, Shakir and Khan/Hilali also do this. The question still remains; which word should be used in the translation?
Well, the critic does not tell you that Dr Edward William Lane’s Lexicon indicates the word sulb’ to mean ‘loins’ and even refers to the verse in question (86:7) as referring to the ‘loins’. So it does seem that the more accurate translation of this would be “between the loins and the ribs” as opposed to “between the backbone and the ribs” . Hence the critic uses the weaker translation.
However, even if we assume the critic to be correct and take the translation; “between the backbone and the ribs” we still see no scientific error. The critic assumes that the ejaculate (semen) emanates from the testes, this is incorrect. Sperm is produced in the testes and is then transfered to the seminal vesicles awaiting ejaculation, this accounts for 5 % of the ejaculate, the rest of the ejaculate comes from the seminal vesicles (46-80%),with the prostate gland and the bulbourethral and urethral glands producing the rest of the ejaculate . At the time of ejaculation, all this (semen, which contains the sperm) is released
From the seminal vesicles which are in fact between the backbone (coccyx, lower back) and the ribs! So if we run with the translation of the critics we see something that people would describe as a scientific miracle and not a scientific error.
Osama Abdallah says the same thing but goes into a little more detail (bracketing is mine):
“If one was to insist upon the literal meaning (the translation favoured by the critics), one would still find that the Quran is 100% correct literally, too. The seminal vesicles are anterior to the sacrum and coccyx (lower back, loin) and the ribs are anterior to the seminal vesicles. If one was to draw a line from the tip of the coccyx, to the upper portion of the seminal vesicle _ either one of the two_ and extend the line forward it will catch the ribcage.The seminal vesicles from which the semen spurts out during coitus, lies between the ribs and the coccyx (backbone)!” 
The irony is that the critics accuse the Quran of making a scientific error yet the error is on their part as they only believe it to be an error as they wrongly believe semen emanates from the testes, while in fact in emanates from the seminal vesicles which are in between the backbone and the ribs! So now we all know the critics are being unfair, unscholarly and misleading when they claim the Quran (86:6-7) tells us that semen is produced in the kidneys etc.
May Allah guide us all to further Truth. Ameen.
This short article lent very heavily on Fotfoundation’s video presentation on this subject. This two part video presentation (in my view) is the best explanation of this subject and most in depth (all praise is due to Allah) so if the reader wishes to study further then please view:
Part 1 by Fotfoundation
Part 2 by Fotfoundation
Other further readings:
Part 2 by Fotfoundation