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Abstract
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Introduction:
Since cementless stems have been introduced for total hip arthroplasty (THA) thigh pain can be a relevant issue. Its main cause is believed to be a mismatch in stiffness between the implant material and the bone leading to pathological stress transfer, but it can also depend on implant design, sizing, surgical technique, component malpositioning and patient anatomy as well as bone mineral density.
Methods:
A 79-year-old female patient with severe osteoporosis, already treated with bisphosphonates, sustained an intertrochanteric fracture of the left femur after a fall. Due to fracture comminution, osteoporosis and concomitant advanced osteoarthritis of the hip joint, THA was preferred over internal fixation. The patient therefore underwent THA over a transfemoral approach with an uncemented, curved, modular, tapered, fluted, titanium-alloy stem. Postoperatively, the patient showed good improvement of hip function but started to develop exertional thigh pain 6 months after surgery. Radiologic follow-up studies showed a correct position of the implant, without any subsidence, and the osteotomy as well as the trochanteric fracture consolidated. However, cortical thickening developed around the tip of the stem along with proximal stress shielding. With the hypothesis of a load transfer in the anchoring area of the stem exceeding resistance of the cortical bone, subcutaneous teriparatide therapy was started for 24 months.
Results:
6 months later the patient was already completely pain free and ambulating without discomfort. Conventional radiographs showed increased bone density in her femur. Within months after discontinuation of teriparatide, the symptoms gradually reappeared. Scintigraphy confirmed relapse of pathological activity at the tip of the stem. The treatment was subsequently changed to denosumab, with moderate improvement of the pain.
Conclusion:
Stem tip pain is a well known complication of distally engaging hip implants. Various surgical options have been suggested over the years to address this condition if conservative treatment fails. Pharmacological treatment has never been tested. Teriparatide is one of the rare truly osteogenic substances available. Its use is restricted to 24 months because of induction of neoplasia. This successful off-label use has not been described so far and might be of interest for the future treatment of this biomechanical complication.
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