Weight bearing status is a classification used in physical rehabilitation to determine how much force a person can safely place on an injured or surgically repaired lower extremity. Determined by a physician or surgeon, this status protects healing bone, soft tissue, and internal fixations. Partial Weight Bearing (PWB) is a specific stage in this progression, allowing the limb to support only a fraction of the body’s total weight during movement. The goal of controlled weight bearing is to stimulate healing without causing damage or re-injury.
Understanding the Weight Bearing Spectrum
Weight bearing is categorized into a spectrum of five statuses. The most restrictive is Non-Weight Bearing (NWB), which prohibits any contact or weight through the affected limb. Following this is Toe-Touch Weight Bearing (TTWB), sometimes called Touch-Down Weight Bearing (TDWB), which permits the foot to lightly touch the ground for balance only. This contact does not allow the limb to support significant body weight.
Partial Weight Bearing (PWB) is the next classification, where the limb is permitted to bear a specific, measured percentage of body weight. This prescribed percentage commonly ranges from 20% to 50% of the total weight, depending on the stage of healing and the nature of the injury. The purpose of PWB is to gradually introduce load to the recovering structures, encouraging them to strengthen.
The final stages include Weight Bearing As Tolerated (WBAT) and Full Weight Bearing (FWB). WBAT allows a person to place as much weight on the limb as they can comfortably manage, using pain as the limiting factor. FWB signifies no restrictions, meaning the limb can safely support 100% of the body’s weight. Progression is monitored through diagnostic imaging like X-rays to ensure the bone or tissue has reached sufficient stability to handle increased load.
Calculating and Monitoring Partial Weight Bearing
Adhering to a prescribed PWB percentage requires developing a reliable internal sense of the applied force. Therapists often begin training using a standard bathroom scale placed under the injured limb. The individual practices standing and gently shifting weight onto the scale until the display shows the target weight. This repetitive practice helps calibrate the perception of the appropriate pressure.
Once a patient can consistently hit the target weight while looking at the scale, the next step involves closing the eyes to develop an intuitive feel for the required force. For practical estimation outside of therapy, one common analogy is the force needed to hold a gallon of milk, which weighs approximately eight pounds. A more direct visual cue for 50% PWB is to stand with both feet on the ground and distribute the weight equally, as this naturally applies 50% of the body weight to each leg.
Advanced methods for ensuring accuracy involve biofeedback technology, such as specialized sensor insoles that fit into a shoe. These devices measure the real-time pressure applied to the foot and provide immediate feedback (often auditory or haptic) if the user exceeds the prescribed weight limit. While the scale is a temporary training aid, developing consistent sensory awareness protects the healing structures during daily activities.
Essential Tools and Techniques for Safe Execution
Executing partial weight bearing safely necessitates using an assistive device to support the portion of body weight the injured limb cannot bear. The most common tools are crutches, walkers, or sometimes parallel bars in a rehabilitation clinic. The choice of device ensures the load is transferred from the lower extremity to the arms and the device itself, protecting the surgical site or fracture.
The specific movement pattern required for PWB is the modified three-point gait. This technique involves three points of contact with the ground, where the two assistive devices and the injured leg move forward simultaneously. The partial weight is applied through the injured limb as the crutches or walker bear the remaining force. This synchronized step is then followed by the unaffected leg stepping through past the devices.
Proper fit of the assistive device is a safety prerequisite for performing PWB correctly. Crutches must be sized so the top pad sits approximately one to one-and-a-half inches below the armpit, ensuring body weight is supported by the hands, not the armpits. Supporting weight on the armpit can lead to nerve damage. Maintaining a stable tripod stance while resting, with crutches positioned slightly forward at a 45-degree angle, provides a solid base of support and prevents falls.