Knee range of motion norms

The CDC measured 674 healthy volunteers aged 2 to 69. Nine physical therapists took passive readings with universal goniometers. It is the closest thing the knee has to a measured population norm, and it sits above the textbook figure in almost every group.

Two things to take from it. Women bend further than men in every adult band, by about four to five degrees. Flexion falls with age in both, so a 60-year-old man at 132° is average for his group, not limited. Children aged 2 to 8 bend furthest of all, and the girls in that band average a few degrees of extension past straight.

Those four bony points are the ones Gogia and colleagues used when they checked goniometer readings against X-rays of the same knee. Agreement was ICC 0.98–0.99, about as good as clinical measurement gets. The knee is the joint where a goniometer earns its place.

Position decides the number. The CDC protocol measured flexion supine, hip and knee bending together with the foot lifting off the table, and stopped when calf met thigh. Prone knee flexion puts rectus femoris on stretch across the hip and reads lower, so pick one position for the episode. For extension the protocol supported the ankle slightly off the table so any hyperextension could show. A heel resting flat on the plinth hides it.

Those are clinic patients, not volunteers (43 of them, measured in a clinical setting). The pattern is the useful part: you re-measuring your own patient is very tight, a colleague re-measuring is looser, and a visual estimate is looser still. The goniometer technique guide covers the error budget across joints, and if you bill the measurement as its own service, read the CPT 95851 guide first.

Patients don't ask for 135°. They ask to manage the stairs at home. Rowe and colleagues strapped flexible electrogoniometers on healthy older adults and sent them round a hospital circuit. Level walking and slopes stayed under 90°, stairs and chairs needed 90–120°, and getting in and out of a bath took about 135°.

Their suggested rehab goal of 110° is a sensible default for a plan of care: it covers stairs and standard chairs, and you can set a bath or low-chair goal when the patient's home needs it. Write the goal as the task, with the degrees beside it, in the plan of care builder.

Cycling is the common ask we can't give a single number for. A full pedal revolution needs more flexion than walking, and a higher saddle reduces how much the knee bends on each stroke, so a stiff knee can often pedal on a raised saddle before it can on a normal one. Raise it, rock the pedals, then try a full turn, and add it to the home programme once it goes round comfortably.

Range is the number everyone asks about after a replacement, and the evidence says not to overrate it. In 684 primary knee replacements followed for a year, patients under 95° of flexion at 12 months had worse WOMAC function scores than those at or above it. Across the whole cohort, though, range correlated only modestly with function (r under 0.34), and flexion was not linked to satisfaction or perceived quality of life. The function score was.

A replaced knee at 100° that climbs stairs is a better result than one at 120° that the patient still doesn't trust.

So chase extension early, because a knee that won't straighten turns every step into a bent-knee step. Work toward the 110° functional mark for flexion and pair each re-measure with a function score. Early-week targets and restrictions belong to the surgeon's protocol, not to a population table.

Use one sign convention and say which. The CDC one works well in a note: a knee that stops short of straight is negative, so “R knee PROM −5° to 118°, supine, firm end-feel” reads the same to the next clinician. Record active range on its own line, and name the gap if active extension falls short of passive.

The SOAP note generator has a slot for this on the objective line. Compare against the patient's other knee before any table. The full ROM chart has every joint, and the neighbouring joints have their own pages: hip norms and ankle norms. A stiff hip or a short calf will show up in knee measurements too.