Three-step technique for implantation of rotating hinge knee prostheses : Demonstration using the Enduro prosthesis

Implantation of an axis-guided knee prosthesis with consideration of the joint line and balanced flexion and extension gap to reduce the mechanical load on the prosthesis axis and to improve the movement of the prosthesis.

Distinct unilateral instability due to ligament insufficiency in association with knee prostheses. Primary implantation of axis-guided knee prostheses with pronounced axial malalignment (>20-25° valgus or varus malalignment) or/and severe flexion contracture > 40°. Replacement of prosthesis with nonsignificant imbalance between flexion and extension gap.

Clearly unstable flexion gap such that the extension gap cannot be adjusted appropriately. Significant femoral bone defects requiring distal femoral replacement prostheses.

Reconstruction of the tibial platform with the trial prosthesis with regard to height in relation to the tip of the fibula. Determination of the femoral prosthesis size. Adjustment of the anteroposterior (AP) cutting block of the selected size, referenced anteriorly and in correct rotation. Determination of the flexion gap with spacers using the stable side of the collateral ligaments. Positioning the distal cutting block and determination of the height of the extension gap. Moving the distal cutting block until the same height of spacer as used in the flexion gap fits into the extension gap, taking into account the stable side of the collateral ligaments. The extent of the displacement D1 is noted. Reverse displacement of the distal cutting block by the distance D2 until a satisfactory bony contact surface for the femoral component in the distal femur can be created. The thickness of the required distal augments on the following chamfer-cutting guide (4-in‑1 cutting block) and thus on the femoral prosthetic component is the sum of D1 + D2. The chamfer-cutting guide (4-in‑1 block) with distal augments of the calculated height (D = D1 + D2) is placed in position. Definition and preparation of the posterior contact surface with positioning of any necessary posterior augments. Completion of the femoral preparation taking into account the distal and posterior augments. Assembly of the trial prostheses with a trial inlay having the height of the spacers used. Implantation of the selected prosthesis components.

Thrombosis prophylaxis, physiotherapy under full weight-bearing and mobility exercises.

After implantation of 104 axis-guided Enduro™ knee prostheses (Aesculap AG, Tuttlingen, Germany) (73 knee prosthesis revisions and 31 primary implantations), the Knee Society Score increased from 42.8 ± 18.8 preoperatively to 84.8 ± 13.9 after 24 months. Complications comprised one deep vein thrombosis and one periprosthetic infection.