Knees in the Trades

Why this matters

Ask a group of tradespeople over fifty what hurts, and knees come up as often as backs do. Kneeling is so ordinary in the trades that nobody counts it, and it does its damage slowly enough that the bill arrives a decade after the habits that ran it up. A knee worn out at fifty does not just end the kneeling work; it ends ladders, crawlspaces and roofs too. The protection is cheap and the time to start it is the first year, not the first symptom.

What kneeling does to a knee

Kneeling loads parts of the knee that standing does not.

• Upright kneeling (thighs vertical, weight on the kneecaps) puts body weight onto the front of the kneecap and the thin layer of soft tissue over it. There is no muscle there, just skin, a small fluid sac and bone.
• Kneeling back (sitting toward the heels) shifts the load lower, onto the bony bump at the top of the shin, and folds the knee to its limit, which squeezes the cartilage and the menisci (the two crescent-shaped cartilage cushions between thigh and shin bones) at the back of the joint.
• Deep squatting has no pressure on the kneecap but loads the joint surfaces and menisci heavily at full bend.
• Rising from a kneel, especially with a twist or with one hand full of tools, is where the menisci tear. The load is highest at the moment the knee is bent, weighted and rotating.

Two kinds of damage follow. Sharp ones: a meniscus tear on the way up, a kneecap bruised on a stone. Slow ones: inflamed fluid sacs (bursitis) and worn cartilage (osteoarthritis). The slow ones are the career-enders, and they are the ones pads and habits can prevent.

Bursitis: the warning you can see

A bursa is a small fluid-filled sac that lets skin glide over bone. Kneeling presses it repeatedly, and it can inflame and fill with fluid.

• Prepatellar bursitis, a soft swelling directly over the kneecap, comes from upright kneeling. Its old names, "housemaid's knee" and "carpet layer's knee", tell you who gets it.
• Infrapatellar bursitis, a swelling just below the kneecap, comes from kneeling back.

A swollen bursa that is not hot or red usually settles if the pressure stops: better pads, less kneeling time, a different posture for a while. A bursa that is red, hot and painful, or comes with a fever, may be infected, commonly through a small cut or scrape from kneeling on debris, and needs a doctor promptly rather than a better pad. Do not drain one yourself.

Bursitis is useful because it is visible. It is the knee telling you, years before arthritis would, that the kneeling load is more than the tissue can recover from.

Osteoarthritis: the decades-long account

Osteoarthritis is the gradual wearing of the cartilage that lines the joint. It is the condition behind knee replacements, and it has a strong occupational signal: studies of working populations have found knee osteoarthritis risk roughly doubled in people whose jobs involve kneeling or squatting for more than about an hour a day, and higher still when that kneeling is combined with regular heavy lifting. The effect builds with years of exposure, which is why it shows up in the forties and fifties among people who never had a single knee injury.

The useful way to think about it is as a running total. Every hour kneeling unprotected goes on the account, and nothing pays it back.

Worked example: two installers, thirty years

Take two installers who each start at 22 doing work with a lot of floor-level time: tile, under-sink plumbing, low electrical work, a lot of crawlspace. Both kneel about 2 hours a working day, on about 230 working days a year. The figures are illustrative and round, to show the method.

Installer one changes nothing. 2 hours x 230 days = 460 hours of kneeling a year. Over 30 years, 460 x 30 = 13,800 hours, most of it on bare knees or a folded towel, upright on the kneecaps, rising on one leg with a tool in hand.

Installer two changes three things in year one.

• Wears proper pads every time, which does not reduce the hours but spreads the pressure off the kneecap and protects against cuts that seed infected bursitis.
• Uses a low stool or a bucket seat for work between about 12 and 20 in off the floor, which takes roughly a quarter of his kneeling time and turns it into sitting.
• Raises work when it can be raised: assembling the trap on a bench or tailgate, cutting tile on a stand rather than on the floor, prepping fittings at standing height and kneeling only to install. That takes about another quarter.

His kneeling falls from 2 hours to about 1 hour a day, half the exposure. 1 hour x 230 days x 30 years = 6,900 hours, and every one of those hours is padded.

What the numbers say. Installer two has half the kneeling hours, padded, and has dropped from the band the epidemiology flags (over about an hour a day) to its edge. Installer one spent thirty years well inside it. Neither of them felt any difference in year one. That is the whole problem with knees: the decision is made when it costs nothing and feels unnecessary, and the result shows up when it can no longer be changed.

What would change the read. A prior knee injury, especially a meniscus tear or ligament repair, moves a person's knee down the curve, and the same kneeling hours cost them more. So does significant body weight. And installer two's halving depends on the work actually being raisable; a tech who lives in crawlspaces cannot put the crawlspace on a bench, and for them the levers are pads, stints and rotation. See related: Working in a Crawlspace Without Paying for It Later.

Pads and kneelers, by what they actually do

European standard EN 14404 sorts knee protection into four types, and the categories are a useful way to think about pads even though there is no mandatory US standard; a product tested to EN 14404 is at least a signal that someone measured it.

The standard also grades penetration resistance: a level for flat clean floors with no puncture rating, and higher levels for rough ground with stones, screws or debris. For crawlspaces, roofs, unfinished basements and landscape beds, pick pads with a hard outer shell and a puncture rating. A soft gel pad on gravel feels fine for an hour and lets a screw through.

Fit is not optional. A pad that rides up or slides sideways leaves the kneecap bare exactly when the weight goes on. Wide, soft straps sitting below the knee joint are easier on the back of the knee than thin straps sitting in the crease, where they press on the blood vessels and nerve that run behind the joint during a long kneel. People with larger or smaller legs often need different sizes than the default. See related: PPE and Tools That Fit Smaller and Larger Bodies.

What pads do not fix

This is the section most knee advice leaves out. Pads protect the front of the kneecap and the skin. They do almost nothing for:

• The joint itself at full bend. Kneeling back on your heels or deep squatting loads the cartilage and menisci no matter what is strapped on the outside. The fix is posture: a stool, a bucket seat or half-kneeling (one knee down, one foot flat) instead of folding both knees fully.
• Rising with a twist. Get up by planting a hand on something solid and pushing, coming up straight before turning, with tools set down first. A kneeler with handles does this for you.
• Total hours. A padded hour is still an hour on the account. Only raising the work, sitting, or rotating jobs reduces the hours.
• One knee taking all of it. Most people half-kneel on the same knee every time. Swap sides deliberately.

The jobs that are hardest on knees

Look for these in your own schedule. They are where rotation and equipment pay first:

• Tile, flooring, carpet and any finish work at floor level
• Under-sink, behind-toilet and low-cabinet plumbing; dishwasher and range installs
• Crawlspace work of any trade
• Low receptacle, baseboard heater and panel-bottom electrical work
• Roofing on a pitch, where kneeling is combined with balancing
• Landscape bed work, edging and planting; pool tile and waterline cleaning
• Garage door bottom seals and floor-level track work; appliance work behind and under units
• Floor scrubbing and detail cleaning

A shop can write these into its physical demands descriptions so that hiring, rotation and return-to-work plans all start from the same list. See related: Writing a Physical Demands Description for Each Role.

When to get it looked at

Knee pain that lasts into the next morning, a knee that locks, catches or gives way, swelling that comes back after every kneeling day, or any red, hot swelling means see a doctor, and tell them how many hours a day you kneel and in what positions. A knee that locks or gives way often means a mechanical problem like a torn meniscus that will not settle with rest. See related: Talking to a Doctor About What Your Job Actually Involves, and The Early Discomfort Report SOP.

References

• EN 14404, Personal protective equipment: knee protectors for work in the kneeling position (European standard)
• See related: Talking to a Doctor About What Your Job Actually Involves; The Early Discomfort Report SOP
• See related: How Cumulative Strain Injuries Actually Develop; Working in a Crawlspace Without Paying for It Later
• See related: PPE and Tools That Fit Smaller and Larger Bodies; Writing a Physical Demands Description for Each Role