A Mini-Invasive Internal Fixation Technique for Studying Immobilization-Induced Knee Flexion Contracture in Rats

This simple and effective muscle-gap separation model technique combine the ways of mini-invasion method is the best internal fixation in our rat knee joint contraction model. The main advantage of this technique is that it's process are reproducible and the minimally invasive alternative to inducing contracture of the knee joint in animals. Demonstrating the procedure will be Shihai Jiang and Fei Zhang, graduate student from my laboratory.

After confirming a lack of response to toe-pinch, shave the lower body of the anesthetized rat, including the two hind limbs. Disinfect the exposed skin with tincture of povidone iodine two times and 75%ethanol three times. Apply ointment to the animal's eyes and place the rat laterally under a surgical drape with one hind limb and hip exposed.

Disinfect the surgical area with additional povidone iodine. At the distal end of the femur greater trochanter, draw a line along the body surface projection of the muscle gap between the vastus lateralis and biceps femoris to mark the direction of the skin incision. Next, make a 1.5 centimeter incision in the epidermis along the line.

Use tissue forceps to bluntly dissect the muscle gap between the vastus lateralis and biceps femoris until approximately one centimeter of the femoral shaft is exposed. Use a retractor to facilitate a continuous separation of the muscle gap. Make a one centimeter incision in the epidermis along the body surface projection of the muscle gap between the tibialis anterior and fibularis longus on the distal lower extremity.

Bluntly dissect the muscle gap until approximately one centimeter of the tibia is exposed. Use the retractor and smooth forceps to separate the soft tissues. Holding a drill perpendicular to the bone, drill a one millimeter diameter hole into the femoral shaft at 1, 500 rotations per minute approximately eight millimeters below the lower edge of the greater trochanter.

Quickly press the wound to stop the bleeding and drill a 0.9 millimeter diameter hole into the tibia approximately four millimeters below the edge of the tibiofibular fusion. Use a straight mosquito-type hemostatic clamp to form a submuscular course from the tibia hole to the femur hole, passing below the gastrocnemius in the tibia end and above the gluteus medius below the biceps femoris in the femur end. Then use one m1.4 by eight millimeter steel screw to secure one end of a plastic plate in the proximal femur.

Use one m1.2 by six millimeter steel screw to secure another end of the plastic plate in the distal tibia. When the plate has been secured, use 4-0 absorbable sutures to close the myofascia, deep fascia, and subcutaneous tissue. Close the skin with silk sutures.

X-ray imaging reveals a correct placement of the steel screws in the femur or the tibia. Three-dimensional reconstruction analysis after high-resolution microcomputed tomography scanning demonstrates the lateral placement of the screws approximately eight millimeters below the lower edge of the greater trochanter at the proximal femur and about four millimeters below the edge of the tibiofibular fusion at the distal tibia. The arthrogenic deficits in the the range of motion increase during immobilization in a time-dependent manner.

As demonstrated by the higher average arthrogenic deficits measured for the immobilized knee joint compared to the control knee joint at 56 days of immobilization. On day one of the immobilization, no adhesion is observed by elastic staining of the posterior-superior knee joint capsule in the joint space between the posterior-superior joint capsule in the femur in the immobilized or the contralateral side knee joint. By 28 days of immobilization however, fibroadipose tissue deposits and adhesion develop in the joint space of the immobilized knee.

After 56 days of immobilization, the fibrous tissues are partially replaced by the deposition while this type of adhesion is not observed in the contralateral knee joint. This method is modified from that used by Professor Trudel and colleagues from the University of Ottawa. It is key to identify and separate the muscle gaps during the surgery.

Following different immobilization techniques other experimental process such as the culture of the knee joint capsule can be performed to study the underlying molecular mechanisms.