The flexor digitorum profundus tendon is inserted into the distal phalanx, while the flexor digitorum superficialis tendon is inserted into the middle phalanx. The flexor digitorum profundus tendons extend to the long, ring, and small finger and have a common muscle belly. They may also be interconnected to the separate tendon that runs to the index finger. The interconnection of the flexor digitorum profundus tendons resembles how the reigns connect to a chariot. These tendons will not be able to move independently. If one tendon gets shorter, the other tendons will not have full excursion.
Quadriga is usually the result of adhesion or scarring of the flexor digitorum profundus tendons. This may also result from over tightening or distal advancement of the tendon after rupture and repair. Quadriga may also be seen after amputation with suturing of the profundus tendon to the extensor tendons. This condition results in a weak grasp in the remaining fingers and the patient will be unable to make a full fist. If one tendon is shortened, the others will not shorten and there will be a loss of flexion in the other digits.
The difference between Quadriga and Lumbrical Plus Finger is that Quadriga occurs from the overtightening or scarring of the flexor digitorum profundus (weak grasp), while Lumbrical plus finger occurs from a lax FDP tendon which results in tension in the lumbricals. During Lumbrical plus finger, one finger sticks out when attempting to hold an object such as a can.