Revision Total Knee Replacement - Femoral Component

In a stiff knee with less than 70 degrees of flexion, release the lateral gutter before attempting eversion and score adhesions in the suprapatellar pouch. If the patella will not evert safely, a quadriceps snip (45 degrees from the lateral border of the VMO, proximally) adds 10-15 degrees of flexion; a V-Y turndown is for severe stiffness (risk of avulsion); a tibial tubercle osteotomy is the last resort for an ankylosed knee.

Document the wear pattern systematically — asymmetric wear suggests instability or malalignment; anterior wear in a PS design suggests cam-post impingement or excessive posterior slope; medial wear suggests varus malalignment or MCL insufficiency. Send explanted components for analysis and photograph them for medicolegal documentation.

Indications: malalignment (greater than 3 degrees varus/valgus or greater than 10 degrees rotation), flexion-extension mismatch, osteolysis needing access, polyethylene wear into the component, need for higher constraint, or instability not correctable by tibial revision alone. If retaining it, clean the surfaces thoroughly and check for damage or metallosis.

This is the most challenging step; a well-fixed cemented component may take 30-45 minutes to remove safely. For an ingrown cementless component an oscillating saw or a Gigli saw passed under the component is safer than osteotomes (less bone loss). Create small windows in the anterior flange if needed to access cement. Preserve bone stock — patience is critical. Consider ultrasonic cement removal for a well-fixed cement mantle.

Complete cement removal is essential to assess the true bone defects and achieve fixation of the revision component. Use a headlight and magnification; pulsatile lavage after gross cement removal. A cement restrictor deep in the femoral canal may need a flexible drill or osteotome. Send 5-6 tissue samples for culture and histology even in presumed aseptic cases (occult infection in 7-10 percent).

Distal uncontained defects arise from loosening or osteolysis; posterior notching from a malpositioned component or osteolysis. Uncontained defects greater than 5mm need metal augments (screw-fixed where possible); contained defects less than 5mm can use cement or impaction grafting. Check the posterior condyles carefully — they are often underestimated.

Short stems (50-75mm) for AORI 1-2 give rotational control and reduce stress shielding; long stems (100-150mm) for AORI 3 or a deficient metaphysis give fixation and load transfer. Press-fit is preferred (better long-term fixation). Offset stems are available for canal deformity or malunion. Start small — you can always ream larger but cannot make the canal smaller. Fluoroscopy helps confirm alignment.

Perpendicular to the mechanical axis (coronal), neutral flexion-extension (sagittal), minimal bone resection. Use the intact condyle as the reference (usually lateral in varus knees, medial in valgus knees). With massive asymmetric bone loss, use an asymmetric resection or augments. Avoid notching the anterior cortex (supracondylar fracture risk). The resection level sets the extension gap — balance it against the flexion gap later.

Internal rotation causes patellar maltracking and medial polyethylene wear; external rotation causes lateral polyethylene wear and PCL tightness. Use the transepicondylar axis if the landmarks are visible, otherwise 3 degrees external to the posterior condylar axis; in revision with bone loss Whiteside line is most reliable. Avoid oversizing (notching, overstuffing) and undersizing (instability, poor coverage). Restoring posterior condylar offset maintains the flexion gap.

Metal augments are modular blocks or wedges that fill specific defects; they must be fully supported by host bone at the periphery (no cantilever), with screw fixation into host bone preferred. They are cemented to both bone and prosthesis at final implantation. Modular systems offer built-in augmentation. Avoid structural allograft for femoral defects where possible (high resorption rate).

The extension gap is set by the tibial and distal femoral cuts; the flexion gap by the posterior femoral cuts and condylar offset. Tight extension: recut the tibia or downsize the femur. Tight flexion: add a posterior augment or increase the tibial slope. If the gaps differ by greater than 2mm, revise the cuts or use constraint (CCK). Assess the joint line — it should be 2-3cm distal to the medial epicondyle.

CCK has a taller post and wider box than PS and gives 3-7 degrees of varus/valgus constraint; RHK allows axial rotation but prevents varus/valgus tilting. Higher constraint needs longer stems for load transfer. Use the least constraint that achieves stability.

Clean dry bone, pressurization, cement-gun application, component insertion during the dough phase, and removal of excess before polymerization. Hybrid fixation (press-fit stem, cemented metaphyseal component) combines biological fixation with immediate stability. Use antibiotic cement in all revisions (even aseptic) to reduce infection risk. Apply cement to the augments and the bone-augment interface.

Rotation 3 degrees external to the posterior condylar axis or parallel to the transepicondylar axis; flexion neutral (0 degrees or slight flexion acceptable, avoid extension); sizing to maximize coverage without notching and to restore condylar offset. Polyethylene thickness: minimum 10mm for PS, 12-15mm for CCK (taller post), 15-20mm for RHK. Lock the insert securely and confirm it cannot be removed by traction.

Tranexamic acid 1g IV at induction and at closure; ice and elevation; TED stockings and chemical thromboprophylaxis (LMWH or DOAC) for 35 days; IV antibiotics 24h; early mobilization on day 1 with physiotherapy, weight-bearing as tolerated with a frame; CPM if available (0-60 degrees advancing to 0-90 degrees by week 2); remove the drain at 24-48h; radiographs AP/lateral/skyline to check alignment, component position and the absence of fracture; discharge day 4-7 to rehabilitation; follow up at 6 weeks, 3 months, 1 year, then annually.