Using a Knee Arthrometer to Evaluate Tissue-specific Contributions to Knee Flexion Contracture in the Rat

Summary

The goal of the protocol is to measure the extension range of motion of the rat knee. The effects of various diseases that increase the stiffness of the knee joint and the effectiveness of treatments can be quantified.

Abstract

Normal knee range of motion (ROM) is critical to well-being and allows one to perform basic activities such as walking, climbing stairs and sitting. Lost ROM is called a joint contracture and results in increased morbidity. Due to the difficulty of reversing established knee contractures, early detection is important, and hence, knowing risk factors for their development is essential. The rat represents a good model with which the effect of an intervention can be studied due to the similarity of rat knee anatomy to that of humans, the rat's ability to tolerate long durations of knee immobilization in flexion, and because mechanical data can be correlated with histologic and biochemical analysis of knee tissue.

Using an automated arthrometer, we demonstrate a validated, precise, reproducible, user-independent method of measuring the extension ROM of the rat knee joint at specific torques. This arthrometer can be used to determine the effects of interventions on knee joint ROM in the rat.

Introduction

Having full range of motion (ROM) of the joints is critical for health and well-being¹. A loss in joint passive ROM is called a contracture². Joint contractures may arise from numerous conditions, including prolonged bedrest, paralysis, joint arthroplasty, burns, infection, and neurologic conditions^1,3,4,5. A contracture of the knee can be disabling as it accelerates joint degeneration, increases the risk of falls and detrimentally affects a person's ability to perform basic functional task....

Protocol

The rat knee immobilization model used has been approved by the University of Ottawa Animal Care and Veterinary Service and the local ethics committee.

1. Animal Preparation

1. At the end of the predetermined immobilization period, euthanize the rats by administration of carbon dioxide.
   NOTE: Here we used an immobilization model with a plate and 2 screws (one inserted in the proximal femur and the other in the distal tibia), which avoids violation of any knee joint structures, and maintains a knee-flexed position of 135° as described previously⁶. Over a period of time, this produces a kne....

Results

The amount of knee extension determined for various periods of immobility are summarized for increasing durations of immobility and show that more severe contractures were produced following increasing lengths of immobilization. Representative results using ImageJ are shown in Figure 3.

The ability to measure maximum extension of rat knees in a valid, precise and reproducible, user-independent manne.......

Discussion

The rat knee arthrometer was developed to reproducibly and reliably determine the maximum extension of the rat knee following an intervention. Advantages of this device include the consistent generation of torque across the knee joint with a constant arm length and extension force. Another advantage includes the ability to set the torque at a level that allows repetitive testing on the same joint to evaluate the influence of different articular structures on knee ROM, such as muscle, capsule, or ligament. For example, fo.......

Materials

Name	Company	Catalog Number	Comments
Arthrometer	The Ottawa Hospital Rehabilitation Centre - Rehabilitation Engineering	N/A
Camera	Canon	EOS-500D	Commonly known as EOS Rebel T1i
ImageJ	National Institutes of Health	Version 1.45s
Absotbent Underpads	VWR	820202-845
Dissection Kit	Fisher	08-855	Kit Includes:  Forceps: medium points, nickel-plated  Scissors: 1.5 in. (40mm) blades, stainless steel  Dissecting knife handle: nickel-plated  Knife blades: stainless steel, pack of 3  Dropping pipet: glass  Bent dissecting needle: stainless steel with plastic handle  Straight dissecting needle: stainless steel with plastic handle Vinylite Ruler 6 in. (15cm)
Precision Screw Driver	Mastercraft	057-3505-8
Scalpel Blades - #10	Fine Science Tools	10010-00
Screwdriver	Stanley	057-3558-2
Hex Keys	Mastercraft	058-9684-2
Universal AC to DC powder adapter	RCA	108004951