DES for low back + bilateral knees: how do they decide fitting/unfitting, and how hard is LDES vs IDES?

The Physical Evaluation Board (PEB) determines a condition "unfitting" if it directly prevents you from performing the duties of your office, grade, rank, or rating, per 38 CFR 4.1 and the principles in *DeLuca v. Brown*. They absolutely can deem your low back unfitting while finding your bilateral knees fitting; each condition is assessed individually for its specific impact on your military duties. However, the PEB can consider the combined effect of multiple conditions if they collectively render you unfit, even if individually they might not, as supported by case law like *Buchanan v. Nicholson*. For your second question, the Integrated Disability Evaluation System (IDES) is generally more advantageous if you already have a VA rating, as it generates a single, binding VA rating used for both separation and veteran benefits, streamlining the process. The Legacy DES (LDES) is faster (6-8 months) but results in two separate ratings—a DoD rating for unfitting conditions only and a later VA claim for all conditions—often leading to a lower separation payment and a prolonged post-service VA process. Your actionable next step is to immediately consult with your assigned Physical Evaluation Board Liaison Officer (PEBLO) and a Military Legal Assistance attorney to review your Medical Evaluation Board (MEB) narrative summary and strategize, ensuring all duty-limiting impacts of your back and knee conditions are thoroughly documented to support an unfitting determination. **Disclaimer: This is educational information for veterans regarding VA claims processes and is not intended as legal, medical, or official advice.**