Weight bearing

Original Editor - Claire Knott Top Contributors - Jeremy Bryan, Claire Knott, Lucinda hampton, Karen Wilson, Rachael Lowe and Kim Jackson

Introduction

In orthopedics, weight bearing refers to how much weight or force is put through a specific limb. It is common for a surgeon or treating physician to prescribing a reduced amount of weight bearing for a specific surgery or injury. Adherence to this reduced weight bearing status is vital for optimal recovery, as prematurely increased weight bearing can delay healing. A reduced weight bearing status can be applied to either an upper or lower limb.

It is important to note that walking is inherently an activity requiring single leg stance and as such, a person with no physical limitations will carry all of their body weight through each leg at different points in the gait cycle. Therefore, having a reduced weight bearing status, for a lower limb, can have wide reaching impacts on walking and ambulation.

Injuries or surgeries most commonly indicating a lower weight bearing status include total or partial joint replacements, bone fractures (surgically and non surgically repaired), and tendon or ligament repairs.

Weight Bearing Status

Non Weight Bearing (NWB)

NWB status means the patient is not to put any weight through the affected limb(s). In the case of a lower limb, this includes not resting the foot on the ground during standing or ambulation.

Toe Touch Weight Bearing (TTWB) or Touch Down Weight Bearing (TDWB)

The definition of TTWB/TDWB is poorly defined in the research literature and is only applied to lower limbs. In clinical practice, it is commonly described as having the ability to touch the foot or toes to the floor without supporting weight from the affected limb, for the purpose of balance. The pressure should be light enough to avoid crushing a potato crisp underfoot.

Partial Weight Bearing (PWB)

PWB is a broad term and can range from anything greater than non-weight bearing to anything less than full weight bearing. This status should be accompanied by a percentage figure to further describe the extent of weight bearing. Most sources define partial weight bearing as being 30% to 50% of a patient’s body weight.

Weight Bearing as Tolerated (WBAT)

WBAT designates that the patient is medically cleared to bear any amount of weight (up to full body weight) through the involved limb. The patient is free to choose how much weight they ultimately bear through the involved limb, within the confines of weakness, pain, balance, etc.

Full Weight Bearing (FWB)

FWB means no restriction to weight bearing.

Safe Mobility

For the lower extremity, NWB, TTWB/TDWB, and PWB require the use of an assistive device to maintain compliance during mobility. In the case of WBAT and FWB, an assistive device may be needed if other impairments (ex. pain, impaired balance, muscle weakness, abnormal tone, etc.) act as barriers to safe ambulation or contribute to significant gait deviations.

Gait Patterns with a Weight Bearing Status

Three-Point Gait Pattern

• Can be used with any weight bearing status.

• Used with two-wheeled walker, standard walker, two crutches, or two canes.
• The assistive device(s) is one point, and each lower limb is one point.

1. The assistive device(s) is moved forward (crutches/canes moved in unison) one step length.
2. The involved limb is moved forward to be even with the back posts of the walker or to be in line with the crutches or canes.
3. The uninvolved limb is moved forward to be even with the involved limb. If needed, some body weight is bore through the arms and assistive device(s) in order offload involved lower limb.

• Note: In the case of NWB, the involved limb should be held in front of or in line with the trunk with the knee straight or slightly flexed and the hip slightly flexed also.

• The above is considered the step to variation. There is also a step through variation, which is a progression of the step too variation. Using the step though variation requires moving the uninvolved lower limb past the involved limb during step three. The goal of the step through variation is to allow for faster, continuous, ambulation without a pause to restart the outlined cycle.

The video below demonstrates a three-point step through pattern with two crutches and partial weight bearing.

Four-Point Gait Pattern

• Can be used with PWB (must be a very high percentage), WBAT (after tolerance to a very high percentage of weight bearing has been demonstrated), or FWB.

• Used with two canes or two crutches
• Each cane or crutch is considered one point and each lower limb is considered one point.

1. One cane or crutch is moved forward one step length.
2. The lower limb opposite the cane or crutch moved in step one is moved forward to be in line with that cane or crutch.
3. The other cane or crutch is moved forward one step length past the cane or crutch moved in step one.
4. The lower limb opposite the cane or crutch moved in step three is moved forward to be in line with that cane or crutch.

• The goal is the repeat steps one through four in a continuous pattern to create smooth ambulation.

Two-Point Gait Pattern

• Can be used with PWB (must be a very high percentage), WBAT (after tolerance to a very high percentage of weight bearing has been demonstrated), or FWB.

• Used with one or two canes as well as one or two crutches
• Each lower limb and the opposite cane or crutch are considered one point. If only one cane or crutch is used, the lower limb without an opposite cane or crutch is a point and the other lower limp plus the cane or crutch is the other point.

1. One combination of a lower limb and the opposite cane or crutch is moved forward one step length.
2. The other combination of lower limb and opposite cane or crutch or the lower limb without the cane or crutch is moved forward one step length past the first combination of lower limb and cane or crutch.

• The goal is the repeat steps one and two in a continuous pattern to create smooth ambulation.

Measures of Adherence

There are a variety of ways to measure adherence to weight bearing restrictions. Clinically, adherence is commonly measured by observation, scales, placing a hand under the foot of an affected limb, and biofeedback.

Little research on been done on the accuracy and reliability of observation and manual assessment. Particularly at lighter weights, the accuracy of scales can be difficult to replicate. Scales appear to be most useful for assessing symmetry in static standing for patients who are WBAT.  Although biofeedback is the most accurate measure of adherence, cost may pose a barrier to clinical use.    

Physical Therapy Applications

Physical therapists need to be aware of patients who have weight bearing restrictions. If restrictions are unclear, they should be clarified with the treating physician. In turn, this will influence the content of patient education, caregiver training, goals of treatment, and the types of devices that may be used for mobility.