Many active and passive rehabilitation programs are applied in the rehabilitation processes after flexor tendon repair. There is no clear rehabilitation program accepted by the whole world. An accurate understanding of these injuries at the histological and biomechanical level is necessary to improve rehabilitation outcomes. Mechanical properties of tendons, such as their viscoelasticity, are affected by the increase in stiffness caused by the rupture, repair, and healing process. Previous studies have shown that the mechanical properties of a repaired tendon, such as stiffness, material properties and functionality of tendon tissue Shear-wave elastography can detect pathological changes in tendinopathy before they are visible on conventional Ultrasonography imaging. In addition, shear wave elastography allows the evaluation of quantitative measurements and is considered more objective because it provides reproducible results. Our aim in this study is to evaluate the changes in the mechanical properties of the hand flexor tendons repaired using shear wave elastography (SWE) during the rehabilitation process and natural process and their effect on functionality.

Patients' affected tendons will be evaluated by shear wave elastography within 3 - 5 days after surgery. The tendons of the healthy hands of the patients will also be evaluated as the control group.

Afterwards, patients will be randomized into two groups by computer-assisted randomization.

Group 1: early passive mobilization Within 3 to 5 days following surgery, patients will begin using a dorsal forearm-based orthosis with 30* flexion of the wrist, 70* flexion of the metacarpophalangeal (MCP) joints, full extension of the interphalangeal (IF) joints. Home exercises will be performed as passive flexion and active extension exercises with rubber band 10 times per hour on the postoperative 3rd day for 3 weeks. Passive flexion and extension exercises will be performed ten times a day, four times a day, on the MCP + Proximal Interphalangeal (PIP) + IF joints. The bands will be removed at night and the fingers will be kept in full extension. In 3 weeks, the orthosis will be modified so that the wrist is in a neutral position and the MCP joints are extended a little more. Approximately 3 weeks after the repair, the dorsal orthosis will be removed during the exercises, and non-resistance active movement and tenodesis exercises will be started in the presence of a physiotherapist. From the 6th week, the dorsal orthosis will be worn only at night, tendon gliding exercises and blocking exercises will be started.

Group 2: early active mobilization Patients will begin to use a dorsal forearm-based orthosis that positions the wrist in a neutral position, metacarpophalangeal (MCP) joints 50* -70* flexion, IF joints in full extension within 3 to 5 days after surgery. After the flexion active extension exercises, full passive flexion of the fingers with the other intact hand and then gently keeping the fingers in the flexion position for 3-5 seconds when the contralateral hand is raised will be performed for 3 weeks, no force will be applied on the fingers. Passive flexion and extension exercises will be performed ten times a day, four times a day, on the MCP + PIP + IF joints. These exercises will be organized as a home exercise program. The patients will be evaluated by the physiotherapist and clinician once a week in the first two weeks of the exercises, and 3 days a week in the third week, in terms of monitoring the exercises, and the exercises will be shown again. The bands will be removed at night and the fingers will be kept in full extension. Approximately 3 weeks after the repair, the dorsal orthosis will be removed during the exercises, and the patients will be started with non-resistance active movement and tenodesis exercises in the form of a home exercise program 3 days a week with a physiotherapist on the remaining days. From the 6th week, the dorsal orthosis will be worn only at night, tendon gliding exercises and blocking exercises will be started.

Patients will be evaluated by an investigator blinded to the treatment groups at week 8 and week 12 using the following methods.

1. Tendon elasticity will be evaluated with shear wave elastography
2. Measurements of hand grip strength and pinch strength (only at 12 weeks) will be evaluated with a dynamometer device.
3. Duruoz Hand Index will be filled.
4. Total active movements of the fingers will be calculated.

Inclusion Criteria:

• Forty patients aged 18-75 years who had flexor tendon injury and underwent primary surgical repair (within the first 10 days after injury) will be included in the study

Exclusion Criteria:

• Patients with a history of previous hand trauma, neurological or systemic disease affecting the hand, patients with a history of upper extremity surgery, concomitant extensor tendon injury, fracture and amputation will be excluded from the study.

The patients were randomized into two groups as active and passive rehabilitation groups by computer program. Patients, shear wave elastography practitioner and data evaluator were blinded to the treatment administered to the patient.