This article was authored by Loredana Guetg-Wyatt, Chief Executive of Steps Charity Worldwide, and originally appeared in the British Journal of Child Health, June 2021.
It is only just over a century since Perthes disease (also known as coxa plana, Legg-Calvé-Perthes, Legg-Perthes, and/or Legg-Calvé), a disease which affects the hips in children, was first identified. It remains extremely rare – and indeed it is apparently growing rarer – and many practitioners don’t register that this may be why children are in considerable pain and/or have difficulty walking, sometimes for years. Indeed, even when children are diagnosed they may receive any one of a whole number of treatments.
The patient profile
The disease pattern is still not fully understood; but, very broadly, there seem to be environmental rather than genetic factors involved. It mainly affects boys (around 80 per cent of cases). Worldwide, studies to date show that the greatest incidence is in northern Europe, and within northern Europe the incidence rises sharply – by around nearly 50 per cent – with every 10 degrees further north from the equator. In the UK, it is much more prevalent in the northern regions.
There also appears to be a familial but not a genetic element involved: research on twins has shown that if one twin has the disease, the case of the other twin being affected is no higher in identical twins compared to non-identical twins, but there is a slightly higher likelihood that a family member will be affected compared to the normal population. There is also a link with social deprivation, with deprived children much more likely to develop it.
Children usually first present with pain in their hips, groin, legs and/or knees (this may be referred hip pain). They may also be limping, and/or find it difficult to get the full range of movement with their hips. It may have come on suddenly or have been happening for some time.
They also have other characteristics. They are usually shorter than average, and their growth has usually slowed further in the year before they present; they tend to be more active than other children; and they may also have a genitourinary abnormality such as a hernia, or undeveloped testes or hypospadias.
Perthes affects the blood supply to the hip joint: specifically, to the rounded head of the femur where it fits into the hip socket, and to the growth plate (physis). Over time, this blood loss means that the bone starts to soften and break until the blood vessels regrow and new bone is produced. This may take several years – and importantly, the new bone growth may not be in the ‘right’ shape to fit properly into the hip socket.
The bone changes go through the initial necrosis, sclerosis, fragmentation and reossification phases, before reaching the final ‘healed’ stage. At the very beginning, even though the bone is softening and causing pain it is quite hard to detect under an X-ray and can only be identified using an MRI scan. As the sclerosis progresses the dead bone becomes detectably white under an X-ray, and starts to flatten. After that, as the new blood vessels form the dead bone is broken down and reabsorbed, while new bone is formed from the outside in. In the final reossification stage the central bone of the new femoral head is formed.
There are two main problems. One is the pain and mobility difficulties that the young patients usually experience while the hip is unable to work properly. The other is that the new bone does not always reform into the original rounded shape. It may be a more oval ‘rugby ball’ shape or really quite flat. The more it diverges from a ball shape, the less likely it is to fit properly into the hip socket, affecting mobility permanently and causing pain as well. A significant proportion of adults who had Perthes as children need a hip replacement in later life.
Diagnosis and treatments
Perthes is usually diagnosed by X-ray (occasionally an MRI is also needed). The treatments focus both on pain management and on getting the bone to reform properly. Most children are under some kind of pain management regime; but obviously it’s important to flag up with parents, carers and/or other professionals if they seem to be experiencing a lot of pain despite this.
There is a range of around 10 treatments, from a ‘wait and see’ conservative approach through casts and braces through to different forms of surgery on the hip or pelvis to adjust the positioning and ensure that the hip joint functions as easily as possible. The stages to concentrate on are the early ones, up to the early stages of fragmentation, when the bone is still quite soft and can still be influenced. But the choice of treatment really depends on the unit where the child is being treated. “Some treatments are almost the opposite of another and surgeons may hold completely different beliefs about how a patient should be treated. In practice, we tend to go with the way that historically our unit has practised,” explains Daniel Perry, who is the Associate Professor of Orthopaedics and Trauma Surgery at Oxford University’s Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Science as well as an honorary consultant Children’s Orthopaedic Surgeon at Alder Hey Hospital.
Some children are admitted to hospital for bed rest and/or traction using light weights. However, in the main it’s necessary to keep children as active as possible, in order to maintain a good degree of strength and muscle length in the hip joint. This last is particularly important to avoid pulling the hip into a position where with the increased load the hip joint starts to collapse even further. That means encouraging most movement – football is still an option – but not ones which involve joint force.
Surgical treatment is less common in Europe than North America; the most common operation is femoral osteotomy, but pelvic osteotomy is comparably more common in North and South America and in Australia. Yet the outcomes appear to be fairly similar. Overall, surgery is marginally more likely to result in a well-formed bone shape. The ‘Herring study’, a cohort study conducted in 2004 looking at 438 patients with 451 affected hips, is the main one to date on the effectiveness of different approaches. It found that surgery had a 60 per cent chance of the best (rounded) hip shape and 10 per cent of the worst (flattened), while no surgery was associated with 45 per cent best and 20 per cent worst. Around a third in both cases – 30 per cent with surgery, 35 per cent without – were in the middle, with a shape that was neither round nor flat.
“But these differences aren’t huge,” Perry points out. “Surgery isn’t a miracle cure; the differences are marginal at best. It carries some level of risk and usually involves two operations – one to do the operation, and one later to take the metal plates, screws or wires out. Children usually wear casts for a period afterwards. There’s quite a big insult to the child, but there’s also a duty on the part of the surgeons to do everything you can for that child. Often children undergo surgery primarily because we’re worried about not doing enough if we don’t.”
Research in progress
This is a condition about which there has been relatively little research to date, but this is slowly changing. The James Lind priority-setting partnership of surgeons and families has made research into Perthes a priority , as has the British Society for Children’s Orthopaedic Surgery (BSCOS) .
Perry is designing a randomised control trial, to build on the Herring study which is, as he says, “the best we can hang our hats on” at the moment. This is quite a new move in surgery, but RCTs have been getting under way in areas like fracture and surgical teams are now coming on board with conducting one for Perthes. “All the work I’ve done beforehand combining different trials and research has been pointing towards the ultimate randomised trial in Perthes Disease.”
Adam Galloway, who is a paediatric physiotherapist and Visiting Academic Clinical Fellow at the University of Leeds, has just secured funding from the NIHR to complete a PhD on developing a new complex intervention in the form of an app. “My research is split up into three workstreams,” he explains. “One, speaking to key stakeholders (children and family’s clinicians, clinical nurse specialists, physios, surgeons and so on) to discuss the current experiences of non-surgical care and doing qualitative interviews and identify gaps in non-surgical treatment. In the second, I’ll be working with NHS Digital, and a local app developer to develop the app. We don’t know what that will look like yet, but it should make it possible both for people to access information about the disease and for children to log their exercise and other progress. Finally, we’ll be testing it with a small group and patients and families, to assess how useful it is as a non-surgical treatment.”
“Historically, Perthes Disease is supposed to cause a ‘painless limp’,” Perry concludes. “We know that’s not true. There’s not enough known about the disease at primary care level and there is too much variation at secondary care. We need to change that, because the variation is unacceptable.”
 Metcalfe D, Van Dijck S, Parsons N, Christensen K, Perry DC. A Twin Study of Perthes Disease. Pediatrics. 2016 Mar;137(3):e20153542. doi: 10.1542/peds.2015-3542. Epub 2016 Feb 12. PMID: 26908702.
 Perry DC, Bruce CE, Pope D, Dangerfield P, Platt MJ, Hall AJ. Legg-Calvé-Perthes disease in the UK: geographic and temporal trends in incidence reflecting differences in degree of deprivation in childhood. Arthritis Rheum. 2012 May;64(5):1673-9. doi: 10.1002/art.34316. PMID: 22143958.
 Braito M, Wolf S, Dammerer D, Giesinger J, Wansch J, Biedermann R. Global differences in the treatment of Legg-Calvé- Perthes disease: a comprehensive review. Arch Orthop Trauma Surg. 2021 Jan;141(1):1-16. doi: 10.1007/s00402-020-03392-9. Epub 2020 Mar 14. PMID: 32172318.
 Herring JA, Kim HT, Browne R. Legg-Calve-Perthes disease. Part II: Prospective multicenter study of the effect of treatment on outcome. J Bone Joint Surg Am. 2004 Oct;86(10):2121-34. PMID: 15466720.