When the Tibia Hurts: Pain and Revision After Extendable Distal Femoral Endoprostheses in Young Patients

En-bloc excision with limb salvage is the gold standard for aggressive bone tumors around the knee, but up to 15% of cases occur in skeletally immature patients, creating a risk of limb-length discrepancy. Growing distal femoral prostheses with passive sliding tibial components address this issue but introduce unique mechanical challenges and potential complications. This study aimed to evaluate the incidence of tibial pain and complications beneath extendable distal femoral endoprostheses, and to correlate clinical symptoms and revision surgery.

The study comprised a retrospective review of 31 extendible distal femur endoprostheses from a single tertiary institution between 2008 and 2018. Measurements of radiographic parameters included coronal alignment, cortical thickness, cortical stem distances, stress shielding, and pedestal and periosteal reaction. The radiographic features were correlated with clinical evidence of tibial pain and the need for subsequent revision of the tibial component.

17 patients reported tibial pain during the follow-up period, with a mean time of onset of 62.2 months (range, 27-132). There were 14 revisions in 12 patients, 4 revisions for tibial pain. Stress shielding and pedestal formation were seen in all patients after 28 months following insertion. Lateral cortical hypertrophy was more prominent in the group with pain with a mean thickness of 5.8 mm (range, 4-9.8). Varus shift of the tibial stem was radiographically evident during follow-up (n = 18). 95% of the patients with tibial pain had radiographic evidence of stem migration, 88% showed a periosteal reaction, and 76% had varus malalignment. In 13 patients (76%) with pain, all three of these parameters were present.

There is a strong correlation between radiographic evidence of tibial stem migration and periosteal reaction and the development of symptoms. Patients should be warned of the need for revision of the tibial component for pain during the lifetime of the implant.

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