Rat Model of Adhesive Capsulitis of the Shoulder

This method can help answer key questions in the orthopedic surgery field, such as, Would relaxing to improve the range of motion in patients suffering from arthrofibrosis? The main advantage of this technique is that it avoid the section of shoulder girdle muscles and any intra-articular trauma, thus preserving capsular and articular continuity and anatomic integrity. Before beginning the procedure, connect the microcontroller of a Stepper Motor to a computer and set up an in-house-developed Matlab code to control the microcontroller.

Next, position a 13-week-old, 250 to 300 gram Sprague Dawley rat in a customized range of motion device with the aid of a laser guide. Then, position the left forelimb of the rat on the arm clamp in 90 degrees forward flexion with the sensing axis aligned with the long axis of the humerus and secure the forelimb by the wrist and elbow. Then, use the microcontroller to control the passive forelimb rotation and cycle the sensor assembly three times between 60 degrees of external rotation and 80 degrees of internal rotation to obtain baseline torque measurements using inputs from the inclinometer in conjunction with those from a torque sensor to indicate the start and end of the measurements.

To perform the surgical immobilization of the shoulder joint, after confirming a lack of response to toe pinch, make a posterior longitudinal incision parallel to the humeral shaft starting just below the shoulder joint and extending for about three centimeters. Using two braided polyester sutures, pierce through the medial edge of the scapula and around the distal two-thirds of the humeral shaft. And subsequently tighten the sutures to immobilize the shoulder joint.

Use wound clips to close the incisions and monitor the incision sites for infection daily during the first post-operative week. Eight weeks after the immobilization, make an incision on top of the scar from the previous procedure and remove the sutures from humerus and the scapula. Then close the incision with fresh wound clips and measure the passive shoulder mechanics as demonstrated.

To measure the range of motion, use the torque values at baseline as preset input variables in the program to detect changes in the rotation range of motion with a 0.2 degree resolution. For stiffness measurements, use the original rotation angles of 60 degrees external rotation and 80 degrees internal rotation as the preset inputs in the program to detect the changes in torque with a resolution of 0.01 newton millimeters. Weigh the animal on the same day as each range of motion assessment as one of the tools for evaluating animal health status during the study.

Then return the animal to its cage with daily monitoring during the first week for signs of infection, pain, or distress, and removing the wound clips on the 10th day after the second surgery. The intact group displays a proper separation between the capsule and the articular surface of the humeral head as well as a normal cellular organization in the synovial tissue and articular cartilage. The surgically immobilized group, however, exhibits evidence of capsular adhesions in the inferior aspect of the shoulder joint.

Moreover, the surrounding tissue appears to be denser as compared to the intact shoulders, leading to a tighter capsule with a decreased joint space. While attempting this procedure, it’s important to remember to position the animals correctly. Following this procedure, other methods like intraperitoneal injection of Relaxin-2 can be performed to answer additional questions about the systemic effects of Relaxin-2.

After its development, this technique paved the way for researchers in the field of orthopedic surgery to explore the use of Relaxin-2 in reversing fibrosis in different joints due to various underlying pathologies. Don’t forget that working with animals can be dangerous and that precautions such as proper animal handling and wearing personal protective equipment should always be taken while performing this procedure.