Revision TKA — Stems, Offsets and Metaphyseal Fixation Principles

Indications for Stemmed Revision Constructs

Absolute Indications

• Aseptic loosening with metaphyseal bone loss (AORI Type 2B or 3)
• Periprosthetic joint infection requiring component removal and reimplantation
• Periprosthetic fracture with loose components and bone loss
• Instability with component malposition requiring revision of both femoral and tibial components
• Massive osteolysis or contained cavitary defects requiring metaphyseal augmentation

Relative Indications

• First-time revision with poor bone quality (Dorr C femur, wide tibial canal)
• Conversion of unicompartmental to total knee arthroplasty with significant bone loss
• Staged reimplantation after infection with residual metaphyseal defects

Contraindications

Absolute:

• Active infection without completed antibiotic course and negative aspiration
• Massive uncontained bone loss (AORI Type 3) without structural support options available
• Patient medically unfit for major revision surgery

Relative:

• Isolated polyethylene wear with well-fixed components and adequate bone stock (consider isolated liner exchange)
• Low-demand patient with tolerable symptoms who declines major surgery

Evidence for Zonal Fixation

• The zonal fixation concept (Zones 1-3) is the dominant framework for stem selection in revision TKA.
• Achieving fixation in two zones yields greater than 90 percent survivorship at 10 years; single-zone fixation (Zone 1 alone) is associated with 25-40 percent failure at 5 years.
• Metaphyseal cones and sleeves demonstrate 92-98 percent survivorship at 5-10 years when combined with diaphyseal stem fixation.

Evidence for Offset Adapters and Joint Line Restoration

• Restoration of the joint line to within 5 mm of native and posterior condylar offset to within 3 mm significantly reduces mid-flexion instability and improves Knee Society scores.
• Offset adapters are required in approximately 60-70 percent of femoral revisions to avoid medialisation and anteriorisation of the component.

Evidence for Cemented versus Press-Fit Stems

• Cemented stems provide immediate fixation and are preferred in poor-quality bone or when canal fill is less than 80 percent.
• Press-fit long stems achieve biologic fixation with less stress shielding but carry a 10-20 percent risk of end-of-stem pain.
• Hybrid constructs (metaphyseal cone plus short cemented stem) are increasingly favoured for their balance of fixation and reduced pain.

The Three-Zone Concept

The femur and tibia are divided into three anatomic zones for fixation planning:

Zone 1 — Epiphysis

• Residual host bone or cement mantle around the original component.
• Provides immediate but limited fixation.
• Never sufficient alone in revision TKA when metaphyseal bone loss is present.

Zone 2 — Metaphysis

• Critical load-transfer zone in revision.
• Cavitary or uncontained defects classified by AORI system.
• Metaphyseal cones and sleeves restore rotational stability and allow load sharing with the stem.

Zone 3 — Diaphysis

• Long intramedullary canal for stem engagement.
• Provides axial and rotational stability when the stem is 4-6 cm longer than the defect.
• Press-fit stems require at least 4-6 cm of tight diaphyseal fit; cemented stems require adequate cement mantle (greater than 2 mm) around the stem.

Goal of Two-Zone Fixation

• Minimum requirement: stable fixation in at least two zones.
• Preferred modern construct: Zone 2 metaphyseal cone or sleeve plus Zone 3 short-to-medium press-fit or cemented stem.
• Zone 1 plus Zone 3 (short cemented stem) is acceptable when metaphyseal bone is adequate.
• Zone 1 plus Zone 2 (cone without stem) is rarely sufficient and reserved for very distal femoral or proximal tibial revisions with excellent diaphyseal bone.

AORI Classification and Metaphyseal Augmentation

• Type 1: contained defect, managed with cement or small augments.
• Type 2A: uncontained defect involving one femoral condyle or one tibial plateau — cone or sleeve on the affected side.
• Type 2B: uncontained defect involving both condyles or both plateaus — bilateral cones or a single large sleeve/cone construct.
• Type 3: massive uncontained defect with complete loss of metaphyseal bone — structural allograft, custom implant or proximal tibial/femoral replacement.

Standard Medial Parapatellar Approach

• Most revision TKAs begin with the standard medial parapatellar arthrotomy.
• Extend the incision proximally and distally as needed.
• Release the medial collateral ligament and posteromedial capsule in a controlled manner to expose the tibial component.
• For the femur, release the posterior capsule and perform a medial epicondylar osteotomy if needed for exposure.

Extensile Exposure Options

Quadriceps Snip

• Oblique incision through the quadriceps tendon from the proximal pole of the patella extending 3-4 cm proximally and laterally.
• Allows additional eversion and translation of the patella.
• Repair with heavy non-absorbable suture; post-operative protocol identical to standard approach.

Tibial Tubercle Osteotomy

• Indicated when patellar eversion is impossible or when extensive tibial exposure is required.
• Osteotomy length 6-8 cm with a proximal step-cut to prevent proximal migration.
• Secure with two or three 3.5 mm lag screws or cerclage wires.
• Weight-bearing as tolerated with brace in extension for 6 weeks; active quadriceps exercises begin immediately.

Medial Epicondylar Osteotomy

• Useful for severe varus deformity or when MCL is contracted.
• Osteotomise the medial epicondyle with attached MCL and posteromedial capsule.
• Repair with screws or suture anchors; protects the MCL while allowing exposure.

Positioning and Preparation

Patient position: Supine on radiolucent table with a bump under the ipsilateral hip. Leg holder or sandbag used to allow 90-120 degrees of flexion. Tourniquet applied high on the thigh (300 mmHg) and inflated after exsanguination.

Anaesthesia: Regional (spinal or epidural) plus sedation or general anaesthesia. Consider adductor canal block for post-operative analgesia.

Equipment: Full revision instrumentation set including stems, offset adapters, cones, sleeves, trial components, high-speed burr, flexible reamers, cement removal instruments and oscillating saw.

Consent: Discuss risk of infection (1-2 percent), instability (3-5 percent), loosening (5-10 percent at 10 years), nerve injury (less than 1 percent), extensor mechanism disruption (1-2 percent), and the possible need for further surgery.

Step-by-Step Technique — Femoral Component Revision with Stem and Offset

Step 1: Exposure and Component Removal

Perform medial parapatellar arthrotomy. If exposure is inadequate, perform quadriceps snip or tibial tubercle osteotomy. Remove the femoral component with an oscillating saw and osteotomes, preserving as much bone as possible. Remove all cement and fibrous tissue from the femoral canal.

Step 2: Metaphyseal Assessment and Cone/Sleeve Preparation

Assess the metaphyseal defect using AORI classification. For Type 2B defects, prepare the metaphysis with a high-speed burr or dedicated reamer to accept a cone or sleeve. Impact the trial cone until it achieves rotational stability. The cone should sit flush with the remaining host bone.

Step 3: Diaphyseal Reaming and Stem Length Selection

Ream the femoral canal with flexible reamers until cortical chatter is achieved. Select a stem length that engages 4-6 cm of diaphyseal bone beyond the metaphyseal defect. Trial short (75-100 mm) versus long (greater than 120 mm) stems. Prefer shorter stems when metaphyseal cone provides adequate Zone 2 fixation.

Step 4: Offset Adapter Trialling and Joint Line Restoration

Attach trial offset adapters (0 mm, 4 mm, 6 mm, 8 mm) to the stem. Rotate the offset to restore the joint line (reference adductor tubercle or contralateral knee radiographs). Confirm posterior condylar offset is within 3 mm of native by measuring from the posterior femoral cortex to the posterior condylar surface. Verify that the epicondylar axis is parallel to the posterior condylar axis of the trial component.

Step 5: Final Implantation

Once the offset and stem length are confirmed, impact the final cone or sleeve, then insert the stem (cemented or press-fit) and attach the definitive femoral component. Ensure the component sits flush on the cone and that no cement or bone interposes at the cone-host bone interface. Confirm stability through full range of motion.

Step 6: Tibial Side and Balancing

Repeat the process on the tibial side if required. Use a tibial cone or sleeve for metaphyseal defects and select an offset if needed to centre the tray on the stem. Perform ligament balancing and confirm equal flexion-extension gaps before final cementation or impaction.

Intra-operative Complications

• Extensor mechanism disruption (1-2 percent) — prevented by careful exposure and extensile osteotomy when needed.
• Intra-operative fracture during stem insertion (2-4 percent) — avoid by sequential reaming and gentle impaction.
• Nerve injury (less than 1 percent) — protect the popliteal neurovascular bundle during posterior capsular release.

Early Post-operative Complications

• Infection (1-2 percent) — higher than primary TKA; use antibiotic-loaded cement when indicated.
• Wound dehiscence or haematoma (3-5 percent) — meticulous haemostasis and layered closure.
• Stiffness (5-10 percent) — aggressive early mobilisation and regional analgesia.

Late Complications

• Aseptic loosening (5-10 percent at 10 years) — reduced by two-zone fixation and metaphyseal augmentation.
• End-of-stem pain (10-20 percent with long press-fit stems) — mitigated by shorter hybrid constructs.
• Instability (3-5 percent) — prevented by accurate joint line and posterior condylar offset restoration.

Outcomes

Modern revision TKA with zonal fixation, metaphyseal cones or sleeves and appropriate stem selection achieves 85-95 percent survivorship at 10 years. Patient-reported outcomes (Knee Society Score, WOMAC) improve significantly but do not reach primary TKA levels. The most important predictor of success is achieving stable fixation in at least two zones.