After a hip replacement and a return home, many patients suddenly feel, in front of the mirror or after a few steps, that the operated leg seems to have become longer. This worry is very common and easily grows. Is the artificial joint in the wrong position? Does the patient need to go back to hospital for an X-ray straight away? Before worrying, the first step is to settle a basic question: is the length of the two legs really different when measured, or is it only a feeling of asymmetry? The causes, how often each occurs and the way each is managed are quite different.
The conclusion first: in the early period after a hip replacement, about 30% of patients feel they have a leg length difference, but only about one third of them have a real difference on imaging. Most cases come from a tilted pelvis or muscles that have not regained balance, and improve after a few months of rehabilitation. Only patients whose feeling stays clear or affects daily walking need to consider a shoe lift or a further assessment (Wylde 2009; Konyves 2005). In other words, feeling that the legs are unequal is far more common than the legs actually being unequal, and for most people the feeling of asymmetry fades with time and rehabilitation training.
Telling a real leg length difference from a perceived one
To manage a leg length difference well, it must first be established which type it is. Clinically there are two main types. The first is a real leg length difference, where the bones really differ in length, for example because the prosthesis has actually made the operated leg longer or shorter. The second is a perceived or functional leg length difference, where the bones are in fact of similar length and the patient feels asymmetry because of a tilted pelvis or tight soft tissues around the hip. Literature reviews show that 6% to 32% of patients perceive a leg length difference, and that when the operated leg is shortened by more than 10 mm or lengthened by more than 6 mm, almost all patients notice it (Desai 2013). Separating the two types decides whether the next step is to focus on rehabilitation training, or to use a shoe lift or arrange imaging.
- The bones (lower limb) really differ in length, and this can be measured and confirmed on imaging
- Often related to the position of the prosthesis and the height at which the femoral component was placed
- When large enough (shortening over 10 mm or lengthening over 6 mm) it is almost certain to be noticed
- Only a difference that stays clear is considered for compensation with a shoe lift or a further assessment
- The bones are in fact of similar length and only the feeling is asymmetric
- Mostly caused by a tilted pelvis, or by tightness or weakness of the muscles around the hip
- A clinical relative limb length check matches the actual sensation better than a pelvic X-ray
- Mostly improves naturally over months as muscle balance and rehabilitation progress
The distinction matters because the asymmetry felt in the early period after surgery often does not mean a real gap in bone length. Rebuilding weight-bearing and a symmetrical gait after a hip replacement happens step by step, and the sense of asymmetry is one of the things that rehabilitation addresses along the way.
How common the feeling is and what imaging shows
The statistics show a clear gap between what patients feel and what is objectively present. A study of more than a thousand hip replacement patients found that about 30% of respondents reported a leg length difference, but only about one third of them had an anatomical difference in length confirmed by imaging. Conversely, some patients who did have a length difference on imaging had no abnormal sensation in daily life (Wylde 2009). The subjective perception and the anatomical structure are thus not equivalent:
Another study that followed patients with relative measurements after surgery also found that about 39% felt they had a leg length difference (Mavčič 2019). This agrees broadly with the 30% reported by Wylde and with the 6% to 32% range of perception in the review by Desai. Three independent sets of data reach the same conclusion: feeling a leg length difference after a hip replacement is quite common, but only a minority of cases involve a real difference in bone length.
Causes of an apparent leg length difference
If the bones are of similar length and the legs still feel uneven, the source of the problem must lie outside the bones, in the position of the pelvis and the tension of the muscles around the hip. Long-standing degeneration of the hip, or a protective posture after surgery, easily tilts the pelvis to one side and leaves the hip abductors tight on one side and weak on the other. When the two sides of the pelvis stand at different heights, one leg feels longer (Desai 2013). This kind of functional difference often improves naturally with the surgery itself and with rehabilitation training afterwards:
Common mechanisms behind an apparent leg length difference
- Pelvic tilt: one side of the pelvis is raised, so the leg on that side feels longer.
- Muscle imbalance around the hip: the abductors, which move the thigh outwards, are too tight on one side and not strong enough on the other, so the pelvis stands unevenly.
- Soft tissue tightness: the operated hip has been held tight for a long time and does not relax straight after surgery.
- Protective compensation: after surgery, fear of pain shifts the body weight towards the good leg, which makes the feeling of asymmetry more obvious.
Why measurement and feeling can differ
- A pelvic X-ray measures bone structure only and does not reflect the sense of leg length difference that comes from movement or a tilted posture.
- A clinical check in which the patient lies flat and the relative length of the two legs is measured reflects what the patient actually feels better.
- For the same difference in length, smaller people notice it more easily (see the section below).
- As the pelvis and muscles regain balance, the patient’s subjective feeling of leg length difference changes with them.
How the feeling changes with time and rehabilitation
It is reassuring that a perceived leg length difference mostly fades or disappears with time. A study that specifically followed patients who felt a leg length difference after surgery found that at one year, the feeling had disappeared completely in about 45% of cases and improved clearly in 18%, so more than 60% of patients improved in all (Adams 2021). Together with the Konyves 2005 figures in the section above, where the proportion feeling the leg was longer fell from 43% to 33%, this supports the view that the body adapts slowly and rebuilds its balance. The usual course of recovery is as follows:
Who is more likely to feel a leg length difference
Even when the objectively measured difference is exactly the same, the subjective experience of different patients can be very different. Research shows that patients with a smaller build (shorter and with a lower BMI) feel a leg length difference more readily for the same objective difference, and that a clinical relative measurement predicts the patient’s subjective sensation more accurately than a pelvic X-ray (Mavčič 2019). This explains why some patients whose legs measure almost the same still strongly feel an asymmetry:
Situations in which a leg length difference is more easily perceived:
- Smaller build (shorter, low BMI)—People with a smaller build notice the same objective difference more easily. Research shows that the combination of BMI below 26 and height below 1.75 m is an independent risk factor for patients feeling a leg length difference (OR 2.49; Mavčič 2019).
- A larger relative difference after surgery—Measured as the relative length after surgery, each additional 5 mm of difference between the legs raises the risk of the patient feeling a leg length difference (OR 1.38). This shows that a clinical relative length measurement is closer to the patient’s true feeling than a pelvic X-ray (Mavčič 2019).
- Pelvis or hip muscles not yet back in balance—When the pelvis is still tilted to one side, or the hip abductors are too tight on one side and not strong enough on the other, the body’s sense of left-right asymmetry is magnified. This kind of functional problem can mostly be improved by rehabilitation training (Desai 2013).
Warning signs and steps for a review
Most perceived leg length differences do not need undue worry, but that does not mean they can be left entirely alone. A feeling of leg length difference that lasts for years is often linked to poorer function and lower satisfaction with surgery. A six-year follow-up study found that patients who reported a leg length difference had about twice the risk of poor function (OR 2.00) and about twice the risk of being dissatisfied with the operation (OR 2.24) (Iversen 2011). If the feeling of asymmetry is persistent and obvious, it should therefore be dealt with early. The common clinical warning signs and the order of management are as follows:
- The feeling of leg length difference has lasted several months without improving, or has even become worse.
- It affects balance when walking, or there is an obvious limp.
- There is still pain in the hip joint, or the patient often needs a shoe lift to walk comfortably.
- After buying a shoe lift on one’s own, walking has become less steady.
- Using a shoe lift too early or too much without a professional assessment, in an attempt to correct a functional difference that would improve by itself over time.
Clinical management follows an order. The first step is for a physiotherapist to carry out a relative limb length check and to see whether the two sides of the pelvis are level, so as to tell first whether the problem is real or functional, and then decide what follows. If it is a functional difference, management is mainly rehabilitation training, including stretching, strengthening of the hip abductors and gait training. Only a patient with a real difference and symptoms that stay clear needs to consider a shoe lift as compensation, and clinically over-lengthening of the operated leg is avoided as far as possible (Mahmood 2015 found that the group with a “longer” operated leg had smaller improvements, more remaining hip pain and more frequent use of shoe lifts). If the main cause of a limp is weakness of the hip abductors, targeted hip abductor training often addresses the root of the problem better than simply adding a lift.
Recovery timing in Hong Kong and home follow-up
In Hong Kong, a hip replacement patient’s worry about leg length often appears after returning home from hospital, in the ordinary days while waiting for the follow-up appointment. The role of home physiotherapy is to turn the anxiety of feeling that one leg is longer into a clinical assessment that can be clearly sorted out at the bedside at home:
- A relative limb length check at home—A physiotherapist can visit and measure the relative length of the two legs with the patient lying flat, and see whether the two sides of the pelvis are level. This tells a real difference in the bones from a perceived or functional one, and the patient does not need to rush around for an X-ray.
- Treating pelvic tilt and muscle imbalance—For pelvic tilt and for hip abductors that are too tight or not strong enough, the therapist designs suitable stretching, strengthening and gait training to suit the home environment. The therapist also checks the height of any shoe lift the patient already uses, so that over-lifting does not get in the way of a functional difference that would improve by itself with time.
- Accompanying gait training during capsule healing—During the capsule healing period of about 6 weeks after surgery, the home therapist accompanies the patient in practising a balanced walking pattern with the walking aid, to reduce the guarded walking that comes from fear of pain and makes the leg length illusion more obvious.
- Local resources—The patient information on total hip replacement from the Hong Kong College of Orthopaedic Surgeons (HKCOS) (orthoinfo-hkcos.org) contains information on returning to daily activities 3 to 6 weeks after surgery, rehabilitation exercises and the use of shoe lifts. For booking surgery and public sector referral, visit the Hospital Authority website (ha.org.hk).
In home assessments, the most common situation is a patient who, around the follow-up visit two or three weeks after surgery, says anxiously that the operated side seems longer, while on measurement the difference between the legs is tiny. The therapist first does a relative limb length check lying down and looks at whether the pelvis is level, and then explains in detail how a tilted pelvis and unbalanced muscle tone can create an apparent leg length difference. After a few weeks of stretching and strengthening and a reassessment, the great majority of patients do not need to rush into a shoe lift. Another common situation is a patient who has bought a shoe lift and found that walking is less steady, because using a lift too early or too much can backfire on a functional difference that would improve as the muscles regain balance. The therapist first checks whether there is a real difference in length and then decides whether to adjust the height of the lift or remove it. If it is still unclear whether the leg length difference is real or apparent, or the odd feeling has not faded, Nova Health’s registered physiotherapists can visit to carry out a relative limb length check to clarify the cause, draw up a stretching, strengthening and gait training plan to suit the individual, or assess whether a shoe lift and further imaging are needed.
In summary, feeling a leg length difference after a hip replacement is mostly a subjective sensation more than the legs really being one long and one short, and it often improves with time and rehabilitation training. When in doubt, the first step is therefore not to panic or rush to add a shoe lift, but to have a therapist tell first whether the problem is real or functional, and then manage it accordingly. Only when the feeling lasts for years and affects daily function is a further assessment needed.