Leaving my local hospital last month, I strode out feeling I was walking normally at last – after years of an unbalanced, awkward gait, where I rocked and then walked forward rather than striding out evenly.

Weeks on and the lower back and sciatic pain that has dogged me for the past four years has gone, too.

There was a simple reason for this pain: like many people, I’d not been told that a knee or hip-joint replacement might alter the length of that leg. In my case it was made even worse because I was using an insole in the wrong shoe.

Most people are born with one leg slightly shorter than the other (up to around 5mm), but I have a measurable difference, what’s known as leg length discrepancy (LLD).

My right leg is, in fact, a whopping 14mm shorter than my left, as a result of my knee replacement operation.

While many of those who have hip or knee replacements have some level of LLD (80 per cent of knee replacement patients have it to some degree, according to a study in The Bone & Joint Journal in 2019) – when it’s more than 10mm it can cause problems such as a changed gait or pain, explains Alex Chipperfield, an orthopaedic surgeon at the private Benenden Hospital in Kent.

In fact, nearly one in ten who have a hip replacement are left with LLD in excess of 10mm, according to a 1997 study in the journal HIP International.

This is hardly news: As many as 27 per cent of patients having a hip replacement had LLD severe enough to require a heel lift, indicating a discrepancy of 10mm, reported The Journal of Bone and Joint Surgery in the 1970s.

My right leg is a whopping 14mm shorter than my left, as a result of my knee replacement operation, writes Lynne Wallis

Signs of leg length discrepancy include lower back pain and a rolling gait

More recently when researchers tracked 100 people who had a knee replacement, around a quarter had a discrepancy of at least 10mm.

The authors of the study, published in 2024 in the journal Orthopaedics & Traumatology: Surgery & Research added that this ‘perhaps explains some patient dissatisfaction’ with their new knee. (A recent review suggested that 10 to 14 per cent of hip and knee patients were dissatisfied, with issues including pain and function.)

Indeed, just last month it was reported that the NHS had to pay out £85,000 to a woman whose leg was left 33mm longer than the other following an operation to replace her arthritic hip.

In a statement her solicitors said the difference was due to the surgeon’s poor planning for the operation and the use of an implant that was too small.

A surgeon, who later assessed her, said if the leg length was not corrected it was likely she would require surgery on her spine.

For the 200,000 or so patients who have a knee and hip replacement in the UK each year, this may come as unwelcome news.

You don’t need to have surgery to develop LLD – some people are born with significant differences in the length of the two femurs (thigh bones) or tibias (shin bones); it can also occur as a result of broken bones, says Mr Chipperfield.

Then there is functional or ‘apparent’ LLD, where the legs are equal in bone length but one seems shorter due to tight muscles, a tilted pelvis (that can be caused by prolonged sitting), weak gluteal or abdominal muscles, flat feet or joint stiffness.

What isn’t much talked about is when LLD can result from hip or knee replacement surgery – and Mr Chipperfield believes all surgeons should warn their patients about the risk. A discrepancy can happen for many reasons after a knee or hip replacement – for example, as in the recent case of the woman given a payout, the size of the implant used, and how deep the implants are put into the bone.

When LLD is more than 10mm it can cause problems such as a changed gait or pain, explains Alex Chipperfield, an orthopaedic surgeon at the private Benenden Hospital in Kent

‘It can be put in too high or too low,’ Mr Chipperfield explains.

In the case of replacement hips, if the ‘cup’ sits slightly higher or lower on the pelvis than the natural joint did, or the stem sits deeper or prouder in the thigh bone, the leg length changes.

And if the patient has arthritis in the other leg or in the back, ‘when you restore one hip to its proper anatomy and the other side is still arthritic, the two legs can end up feeling different because the operated leg is genuinely a touch longer – often simply because the untreated hip is still sitting shortened because of the damage to the cartilage and bone’, he explains.

‘The limbs feel longer even though they’re not – the bone length is the same as before.’

Signs of LLD include lower back pain and a rolling gait, says Liam Stapleton, a sports physiotherapist and orthotics specialist based in London private practice and at NHS hospitals in Kent.

He thinks patients should be screened for LLD after surgery and would like to see better awareness of it within the medical profession. ‘It should be something the physiotherapist includes as part of their screening for problems – everyone has physio after surgery, so they are best placed for this,’ he says.

‘Usually anything over 10mm can lead to difficulties such as lower back problems.

‘The surgeon should not conduct the screening, because they would be keen to avoid pointing out something that may lead to a claim of medical negligence,’ he adds.

Mr Chipperfield says litigation is often due to poor communication between the surgeon and the patient and the risks not being made clear.

It might be listed in potential risks in the information leaflets you’re given prior to surgery, but I don’t recall anyone spelling out the risks to me before my first knee replacement in 2021 – or my second the following year.

At that stage I knew I had LLD – for a different reason. I was first diagnosed with this around 15 years ago due to scoliosis, a curvature in my spine.

It was this, I was told, that had caused the lower back pain on the left side, which I’d had since I was 40.

The curving spine causes the pelvis to lift on one side, which can make one leg seem shorter than the other (even though the bones are the same length). I was told I was probably born with the condition but, as is common, it had no impact until later in life.

I went to see an orthotist who gave me a 1cm insole, a ‘heel lift’, for my left shoe to bring up the short left leg to be the same length as my right.

The shoe reduced the shooting pain that occasionally went down my left leg.

The scoliosis was also a likely contributor to severe osteoarthritis in both knees that began to affect me in my early 40s, not helped by a serious ski accident 16 years ago.

I had my left knee replaced in May 2021, and was confused and disappointed that while my knee became less painful, I developed acute sciatic pain in my lower back and left buttock.

I presumed it was the scoliosis getting worse. I continued to wear my shoe lift in the belief that it must be helping and I would be in a worse state without it.

I had my second knee replacement in October 2022, and the pain level remained the same.

By July this year, the pain was becoming unbearable so I went to see a different NHS orthotist, a specialist who can help improve pain and gait problems with orthotic inserts for shoes.

After measuring me, he told me my right leg was now shorter than my left due to my two knee replacements.

I was making matters worse by using my orthotic insert to prop up what was now the longer leg. I was speechless, eventually managing to exclaim in a dramatic whisper: ‘oh my God’.

When he gave me a 14mm orthotic insert to put in my right shoe the difference was astounding – I felt ‘even’ for the first time in years. I hadn’t realised how uneven I had been, until I wasn’t.

The orthotist said he had watched me walk into his department rocking from side to side, which is the usual gait of someone with LLD.

With the right insert in the correct shoe my awkward rocking gait was gone.

While orthotic inserts are helpful, Liam Stapleton says he always encourages his LLD patients to take up a rehabilitation programme to improve core, hip and leg strength.

‘This can all help to work through the impact of LLD, making the patient more robust so they can withstand a bit of difference in leg length,’ he explains.

In the most severe, disabling cases, a patient with post-operative LLD might have revision surgery to get the joint surgically adjusted or refitted.

Now that my orthotics level me up, my new knees have given me a new lease of life.

My only regret is that I could have enjoyed four pain-free years if I had been made aware of the possibility that my knee replacements could have caused such problems and prompted me to seek help sooner.

So if you’re about to undergo a hip or knee replacement, insist on getting screened for LLD after surgery.