The early functional phase is characterized by an absence of pain, minimal or no effusion, range of motion greater than or equal to 120 degrees and weakness. Isotonic knee extension exercise inside a limited arc is begun with low resistance. Initially, a 90 to 30-degree arc is employed since pattelo femoral forces are displaced over a wider surface area in this range. 

The therapist should palpate for crepitus and note any discomfort throughout the range of motion. The arc of motion should then be modified accordingly. As we function with our feet on the ground, so should we rehabilitate. In this phase, several closed chain exercises are implemented, keeping in mind the functional progression. 

Contralateral theraband exercises provide isometric contraction and Proprioceptive input throughout the involved extremity. The uninvolved extremity attached to theraband at the ankle performs hip extension and flexion and hip abduction and adduction with the involved extremity in a weight-bearing state with the knee slightly flexed. The resultant forces to the involved knee occur in a sagittal and coronal plane, respectively.

The patient is instructed in a proper squatting technique inside a pain-free and crepitus-free arc. The range of motion is limited to no greater than 90 degrees of knee flexion. The use of sports cord assists the patient in maintaining proper form, making sure the knees stay behind the feet, decreasing patellofemoral forces. 

A similar technique is reinforced as the leg press machine is utilized bilaterally progressing to unilateral exercise. Lateral step-ups are added to the program with gradual height increments, starting with a phone book and progressing to a normal step.

BAPS (biomechanical ankle platform system) is started to facilitate proprioception training to the involved knee joint. From the ground up, changes are seen throughout the closed kinetic chain. 

For example, as the foot pronates, the tibia internally rotates, causing a valgus force at the knee. Hence, the knee joint acclimates itself to forces in multiple planes, much like those experienced in sports activity. Proprioception is further challenged by increasing the BAPS level and providing the patient with dumbbells, adding the element of intrinsic loading to the exercise. 

Isokinetic exercise is initiated using short arc, submaximal effort, and intermediate speeds (150 to 210 degrees/sec) and progressing to full arc, submaximal effort, and fast speed.