Surgical management of rickets

Clinical History

A 52-year-old lady with known history of hypophosphataemic rickets was referred complaining of increasing pain and decreased ability to weight bear.
She presented initially at age 35 with bilateral knee pain. She had a high tibial osteotomy at the age of 37 and then removal of metal work at 46.

Imaging Findings

The lateral image shows she is developing a transverse stress fracture at the junction of the middle and distal 1/3 of the femur.
The femur radiograph shows a varus deformity and a developing fracture in the middle 1/3 and proximal 1/3. A pseudofracture is also present on the medial aspect of the femur in the subtrochanteric area – a Looser’s zone.
18 months post-operative films show the IM nail in correct position and bony union at the osteotomy site.

Discussion

X-linked hypophosphataemic rickets is an x-linked dominant form of rickets that can cause short stature and genu varum (bow-leggedness).
It is due to mutation of the PHEX gene, which causes inactivity of the PHEX protein [1]
Prevalence of this condition is 3.9-5 per 100, 000 live births [2].
Looser’s zones are pseudofractures. They are wide transverse lucencies that traverse partially across a bone, usually at right angles to the involved cortex [4].
Looser’s zones can be seen in a variety of conditions including osteomalacia, renal osteodystrophy, Paget’s disease of the bone, osteogenesis imperfecta and rickets [4].
It was evident from the radiographs of the femur that this patient had Looser’s zones on the medial aspect of the femur and a significant varus femoral deformity. As a result, a stress fracture was also visible affecting the lateral femoral cortex. Due to her increasing symptoms and the appearance of the area on the lateral cortex, it was felt appropriate to intervene before the bone fractured.
Treatment of hypophosphataemic rickets can involve oral phosphate, calcitriol and if bowing is severe such as in this case, an osteotomy may be performed to improve alignment of the leg [3].
The patient underwent intramedullary nailing of the left femur with a wedge osteotomy and plating to allow adequate healing with realignment of the femur. Subsequent radiographs showed bony union and, along with an improved clinical picture, proved the successful management of this condition.

Differential Diagnosis List

Final Diagnosis

Looser’s Zones/pending stress fracture secondary to rickets

URL:	https://www.eurorad.org/case/12919
DOI:	10.1594/EURORAD/CASE.12919
ISSN:	1563-4086