To specifically answer your question. If more than 12 months since your ACL surgery and your knee has fully recovered than you should be qualified. Chances of a waiver, if necessary, would be very high. But get into the weeds and read on below.
My typical answer is to reference the DoDMERB standard which you should look at and review for yourself. For Knee look around page 32-34
http://www.dtic.mil/whs/directives/corres/pdf/613003p.pdf
d. Leg, Knee, Thigh, and Hip
(1) Current loose or foreign body in the knee joint (717.6). (
2) History of uncorrected anterior (717.83) or posterior (717.84) cruciate ligament injury.
(3) History of surgical reconstruction of knee ligaments (P81.4) (CPT 27427-27429) DOES meet the standard if 12 months has elapsed since reconstruction, and the knee is asymptomatic and stable.
(4) Recurrent ACL reconstruction (CPT 27427, 27407).
(5) Symptomatic medial (717.82) or lateral (717.42) meniscal injury. The following DOES meet the standard if asymptomatic and released to full and unrestricted activity: (a) Meniscal repair (CPT 27403), more than 6 months after surgery. (b) Partial meniscectomy (CPT 27332-27333) more than 3 months after surgery.
(6) Meniscal transplant (CPT 29868).
(7) Symptomatic medial (844.1) and lateral (844.0) collateral ligament instability.
If you had ACL surgery more 12 months ago and everything is fine you should not have any issues.
Your response on your medical history form (as long as it is true) should be something like. Anterior cruciate ligament injury on xx/xx/xx to my right knee. Surgically repaired on xx/xx/xx. After surgery my knee is asymptomatic and stable with full range of motion. Released to full and unrestricted activity on xx/xx/xx.
It would be helpful if you had documentation that states the information above. You could gather that information prior to filling out your medical questionnaire, but that is not totally necessary. If is something that you could put together if DodMERB requests remedial information.