We present the case of a 13-month-old girl on cyclical bisphosphonate therapy who had unusual sclerotic lines throughout the metaphyses of her long bones.
A 13-month-old girl, with known osteogenesis imperfecta (type III), presented to the Emergency department with a painful right leg.
The child had previously presented on multiple occasions with long bone fractures. Medical therapy with cyclical bisphosphonates had been instigated.
Plain radiograph revealed a right proximal femoral fracture. Multiple transverse sclerotic lines were also noted through the metaphyses of the long bones. The aetiology and nature of these lines was unfamiliar to the orthopaedic team.
The fracture was successfully treated in a hip spica.
Bisphosphonates have been at the cornerstone of cyclical OI management. Pamidronate in particular has been associated with improved clinical outcomes, reduced bone resorption, and increased bone density (1). The mechanism of action involves inhibition of bone resorption and stimulation of PTH-mediated anabolic effects on osteoblastic processes (2).
Numerous papers throughout the literature have reported similar sclerotic lines associated with cyclical bisphosphonates therapy in the immature skeleton (3,4,5) – recently termed ‘Zebra Lines’ (6). Each line represents a bisphosphonates treatment cycle and between these bands linear growth is demonstrated. Banding intervals are dependant upon patient age, bisphosphonate dosing regimen and rate of growth. The band is thought not to represent growth arrest but to to represent a layer of primary spongiosa from developing bones which has failed to appropriately remodel due to osteoclast inhibition (6). Another reported change associated with bisphosphonate is a subtle metaphyseal undertubulation (7)
The key differential with such sclerotic lines are those of Harris growth arrest lines (7). These occur in the immature skeleton during periods of systemic illness such as malnutrition, infection or chemotherapy. During this time bone growth ceases and the trabeculum thicken and fuse to form a dense band which becomes apparant once normal bone growth has resumed.
Both Harrison growth arrest lines and Zebra lines undergo remodelling and therefore disappear with progression into the disphysis. Owing to their nature zebra lines are more easily remodelled and hence with growth their presence is usually restricted to the metaphysis, whereas growth arrest lines may extend further in the diaphysis (6).
Other sclerotic lines with appear in the metaphysis may arise from trauma, lead poinsoning, healing rickets and chronic anaemia.
Bisphosphonate associated sclerotic bands - "Zebra Lines"
On the patient’s skeletal X-ray films, multiple relatively parallel, well-defined dense lines can be observed at both proximal and distal metaphyseal regions of the long bones (appearing as band-like high-density areas). These dense lines are relatively evenly distributed between the metaphyses. Overall, the bone density is relatively increased, and the degree of osteoporosis is less severe compared to peers of the same age, consistent with the commonly observed “zebra lines” following bisphosphonate therapy.
In addition, there is some degree of curvature deformity in the arrangement of the patient’s limbs, suggesting possible underlying skeletal developmental abnormalities, which are not uncommon in conditions such as osteogenesis imperfecta (OI). No obvious fresh fracture lines were noted, and no significant soft tissue thickening or swelling was observed.
The patient has a history of osteogenesis imperfecta and is undergoing periodic bisphosphonate therapy. Combined with the typical band-like dense lines near the metaphyses, this finding corresponds to common bisphosphonate deposition features on imaging.
In cases of systemic disease (such as malnutrition, infection, or chemotherapy) that lead to growth arrest, similar dense bands at the metaphyses can also appear. However, their distribution pattern during the recovery phase, along with the absence of significant systemic stress history in this patient, makes this possibility relatively low.
Chronic lead poisoning, post-traumatic changes, healing phase of rickets, or chronic anemia, among others, can also lead to increased density at the metaphyses. However, given the patient’s previous medical history and clinical presentation, these etiologies are relatively less likely.
Considering the patient’s history of osteogenesis imperfecta (OI), the ongoing periodic bisphosphonate therapy, and the characteristic multiple dense metaphyseal banding (“zebra lines”) observed on X-ray, the most likely diagnosis is bisphosphonate therapy-related “zebra lines.”
Treatment Strategy:
Rehabilitation and Exercise Prescription:
FITT-VP Principles:
This report provides a preliminary analysis based on the provided imaging and medical history and is for reference only. It does not replace in-person medical consultation or professional medical advice. Please combine it with the actual clinical situation and consult a specialist before finalizing any specific treatment plan.
Bisphosphonate associated sclerotic bands - "Zebra Lines"
