Slipped capital femoral epiphysis
BMJ 2009; 339 doi: https://doi.org/10.1136/bmj.b4457 (Published 06 November 2009) Cite this as: BMJ 2009;339:b4457
- N M P Clarke, consultant orthopaedic surgeon,
- Tony Kendrick, associate dean for clinical research, professor of primary medical care
- Correspondence to: N M P Clarke ortho{at}soton.ac.uk
- Accepted 12 October 2009
Case scenario
A 13 year old boy visited the general practitioner because of a six week history of intermittent limp and pain in the left lower thigh and knee, which was exacerbated by playing sports. On examination he was overweight, but he had no abnormality in the knee. “Knee strain” was diagnosed, and he was advised to take ibuprofen and abstain from sports. Four weeks later he returned with worsening more persistent pain, now in the thigh as well as the knee. Careful examination of the hip elicited a degree of restriction of flexion and rotation, both internal and external, with 2 cm shortening of the affected leg. Radiography of the left hip showed a slipped capital femoral epiphysis.
Slipped capital (or upper) femoral epiphysis occurs during periods of rapid growth in adolescence, when shear forces, particularly in obese children, increase across the proximal femoral growth plate, leading to displacement of the epiphysis. The typical patient is obese. In a recent case study of 54 patients with this condition, all had body mass indexes in the overweight or obese ranges.1 In boys, accompanying hypogonadism implicates possible endocrine causes.2 A chronic slip is the most common presentation, with symptoms present for weeks or months as the slip progresses. An acute slip occurs after a traumatic event and prevents weight bearing, whereas in an acute on chronic slip, prodromal symptoms are followed by a sudden exacerbation of pain. The last two types of slip usually present to the emergency department rather than the general practitioner.
Why is it missed?
The indolent nature of the symptoms in a chronic slip and pain referred to the knee often mislead the doctor. Examination of the hip may be overlooked and the diagnosis missed. In a review of 106 patients, those (n=14) who had pain in the knee or distal thigh only were more likely to be misdiagnosed, have unnecessary radiographs, and have more severe slips on confirmation of the diagnosis.5
Why does this matter?
Chronic slippage will gradually progress in terms of severity of displacement and deformity, with increasing limb shortening and external rotation, as confirmed by a recent case series.6 Alternatively, after prodromal symptoms, sudden severe pain may occur with minor trauma such as a fall. This indicates an acute on chronic slip, with major epiphyseal displacement and an increased risk of ischaemic injury and avascular necrosis, which can have devastating consequences. Major surgery may also be needed. Residual deformity causes femoro-acetabular impingement and premature osteoarthritis.7
How is it diagnosed?
Clinical features
Any child or adolescent who presents with knee pain must undergo careful examination of the hip. Loss of internal rotation of the leg in flexion, with pain at the extreme of movement, is the key physical sign.
Investigations
Anteroposterior and lateral radiographs of both hips on the same film are the primary (and usually the only) imaging needed to diagnose and evaluate the condition. Klein’s line drawn parallel to the superior neck on the anteroposterior view will normally intersect the lateral portion of the femoral epiphysis but not if slipped (Trethowan’s sign; fig 1⇓).8 Slipped capital femoral epiphysis must be excluded before investigation for other pathology.
Fig 1 Anteroposterior radiograph of the hips and pelvis showing a minor left slipped capital femoral epiphysis. Klein’s line drawn along the superior femoral neck does not intersect the lateral portion of the epiphysis
How is it managed?
Once the diagnosis has been confirmed the usual treatment—based on expert consensus and experience—is to admit the patient urgently to hospital and place on bed rest to avoid acute displacement of a chronic slip, which can have a catastrophic affect on prognosis (fig 2⇓).9 Surgery is needed to stabilise a displaced capital femoral epiphysis and prevent further displacement and increasing deformity. This is achieved by single cannulated screw fixation under image intensifier control (fig 3⇓). The more severe the deformity the more challenging the procedure, necessitating different entry points. Very severe displacement may necessitate femoral neck osteotomy or subsequent salvage procedures for persistent deformity. Remodelling can occur in younger patients.10 Avascular necrosis and chondrolysis (chemical necrosis of articular cartilage) are the most common complications, the first usually after acute displacement (up to 35% of cases), but both may occur after surgery. Reports of the incidence of chrondrolysis after screw fixation vary, but some are as low as 1.5%.11
Fig 2 The same patient two weeks later, after an exacerbation of pain. The radiograph shows increased slip of the left capital femoral epiphysis, with further displacement
Key points
Knee pain in adolescents should trigger a careful examination of the hip because it may be caused by slipped capital (or upper) femoral epiphysis
Delayed diagnosis is associated with an increased slip and hence deformity and morbidity
Radiography in anteroposterior and lateral planes confirms the diagnosis
Surgical treatment of an early slip leads to an almost normal outcome
Notes
Cite this as: BMJ 2009;339:b4457
Footnotes
This is a series of occasional articles highlighting conditions that may be commoner than many doctors realise or may be missed at first presentation. The series advisers are Anthony Harnden, university lecturer in general practice, Department of Primary Health Care, University of Oxford, and Richard Lehman, general practitioner, Banbury. If you would like to suggest a topic for this series please email us (easilymissed.bmj{at}bmjgroup.com)
Contributors: NMPC was the main author of this article and TK contributed. NMPC is guarantor.
Funding: No special funding received.
Competing interests: None declared.
Provenance and peer review: Not commissioned; externally peer reviewed.
Patient consent not required (patient anonymised, dead, or hypothetical).