After total knee arthroplasty, quadriceps femoris muscle strength is an important determinant of physical function. Quadriceps weakness is often present in the osteoarthritic limb and worsens after total knee arthroplasty. Although some quadriceps strength is regained, it may take more than 2 years to achieve preoperative levels, and it is unclear if quadriceps strength in the operated limb ever reaches that of the nondiseased contralateral limb or the quadriceps strength of healthy controls. Studies point to volitional muscle activation rather than muscle atrophy or joint pain as the cause of the weakness. The unresolved challenge lies in clarifying the optimal surgical and rehabilitation course that will reverse the weakness early or prevent its occurrence. Studies suggest that progressive resistive strengthening exercises and neuromuscular electrical stimulation, possibly along with "prehabilitation," improve quadriceps volitional force output. Well-designed, controlled studies are necessary to determine efficacy. Because knee osteoarthritis and total knee arthroplasty are highly prevalent, improving quadriceps weakness is an important goal for orthopaedic surgeons and rehabilitation specialists.