Rotating Hinge Distal Femur Replacement: A Turn for the Worse

Discussion

Despite advancements in DFRs and increasing use in the setting of revision TKA, the procedure remains high risk with respect to postoperative complications.^3-7 Vertesich and colleagues demonstrated that 43.3% of patients who underwent DFR for failed TKA developed at least 1 postoperative complication that required a return to the operating room.⁷Physicians need to be aware of the high rate of complications and counsel patients appropriately preoperatively.

Complications after DFR include infection, aseptic loosening, soft tissue failure, and structural failure.^4,7 Soft tissue failures include insufficiency or rupture of the extensor mechanism and patella dislocation.^4,7 Structural failures include fracture of the hinge mechanism, dissociation of the component from the stem, rotating hinge-bushing failure, and dislocation of the hinge.^4,7 In the acute postoperative period, the most common complications are infection and rotating-hinge dislocation/failure.^3,12 There are various component options available for DFRs, including straight vs curved, cemented vs cementless/press-fit, and long vs short stems.¹³ Studies have sought to elucidate the ideal implant to decrease the rate of complications. Lu and colleagues demonstrated that curved press-fit short stems provided a stable interface without loosening over the short term (2 years) in 42 patients.¹³ No implant failures or incidences of aseptic loosening occurred in their study.¹³

The implant used in this case was a curved press-fit short-stem DFR. It was thought that this patient was young and with good enough bone quality that a press-fit short stem would be best in preserving bone stock. Both the technique guide and literature support reaming 0 to 2 mm greater than the planned stem size to accommodate the implant curvature.¹³ In this case, the intramedullary canal was reamed 0.5 mm larger than the curved stem that was implanted (16 mm and 15.5 mm, respectively). Intraoperatively during the index DFR, the component was stable and seemed to have a good press-fit interface. Despite this, obvious loosening of the component occurred with a relatively low-energy mechanism when the patient kicked the leg onto a chair, causing just enough force and femoral rotation to result in 180° rotation of the component.

Conclusions

We present this case report to make surgeons aware of this rare but serious complication. Although the final implant is a porous and curved stem, careful attention should be made during trialing to use the best-fitting implant to prevent this complication. If an adequate interference fit cannot be obtained, cementing the component may be required to prevent its loosening and catastrophic failure.