Zonal fixation with stems, offset adapters, cones and sleeves in revision total knee arthroplasty · advanced
- Zonal fixation divides the femur and tibia into three zones: Zone 1 (epiphysis), Zone 2 (metaphysis) and Zone 3 (diaphysis). The surgical goal is stable fixation in at least two zones; single-zone (Zone 1) fixation alone is associated with a 25–40 percent failure rate at five years.
- Cemented stems give immediate fixation but risk stress shielding and are difficult to remove; press-fit long diaphyseal-engaging stems achieve biologic fixation with less stress shielding but need adequate canal fill (greater than 80 percent) and cause end-of-stem pain in 10–20 percent of cases.
- Offset adapters (typically 4 mm, 6 mm or 8 mm) reconcile the offset between the intramedullary stem axis and the prosthetic joint line; failure to restore posterior condylar offset to within 3 mm of native increases the risk of flexion instability and limited flexion.
- Metaphyseal cones and sleeves (for AORI Type 2B and 3 defects) provide rotational stability and load transfer in uncontained cavitary defects, achieving 92–98 percent survivorship at 5–10 years when combined with diaphyseal stem fixation.
When & Why
Indication. A painful, failed primary total knee arthroplasty needing revision, where bone loss or poor canal geometry means a standard component will not gain reliable fixation — most commonly aseptic loosening with metaphyseal bone loss, periprosthetic joint infection requiring reimplantation, periprosthetic fracture around loose components, or instability from component malposition. The construct is built around restoring fixation across the deficient bone, not simply swapping the implant. Plan the fixation pre-operatively, zone by zone. Obtain long-leg standing radiographs and a CT to quantify bone loss (AORI grade), measure canal diameter and assess bone quality (Dorr type). The single most important planning decision is which two (or three) zones you will fix in — Zone 1 alone is never sufficient in revision. Indications - Absolute - 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 - 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 a completed antibiotic course and negative aspiration; massive uncontained bone loss (AORI Type 3) with no structural support option available; a patient medically unfit for major revision surgery.
- Relative — isolated polyethylene wear with well-fixed components and adequate bone stock (consider isolated liner exchange); a low-demand patient with tolerable symptoms who declines major surgery. The decision: what kind of stem? Whatever the defect, the construct must achieve fixation in at least two zones. The practical choice is the stem type:
Immediate fixation, easier removal, less stress shielding. The default in poor-quality bone (Dorr C) or a wide canal where canal fill is less than 80 percent.
Biologic diaphyseal fixation with less stress shielding, but needs greater than 80 percent canal fill and carries a 10–20 percent risk of end-of-stem pain.
A Zone 2 metaphyseal cone or sleeve plus a short cemented stem — increasingly favoured for balancing durable two-zone fixation against end-of-stem pain.
Consent specifically for infection (1–2 percent), instability (3–5 percent), aseptic loosening (5–10 percent at 10 years), nerve injury (less than 1 percent), extensor mechanism disruption (1–2 percent) and the possibility of further surgery. Setup. Supine on a radiolucent table with a bump under the ipsilateral hip; a leg holder or sandbag allows 90–120 degrees of flexion. Tourniquet high on the thigh (300 mmHg), inflated after exsanguination. Regional (spinal or epidural) with sedation or a general anaesthetic, with an adductor canal block for post-operative analgesia. Full revision instrumentation available — stems, offset adapters, cones, sleeves, trial components, high-speed burr, flexible reamers, cement-removal instruments and an oscillating saw. Anticipate extensile exposure (needed in roughly 10–15 percent of revisions) and mark the tibial tubercle osteotomy site before component removal.
The Operation
The goal: gain safe exposure of the failed components, remove them preserving host bone, reconstruct the metaphyseal defect with a cone or sleeve, ream the diaphysis to seat an appropriate stem, restore the joint line and posterior condylar offset with offset adapters, then implant the definitive components and balance the knee. The exposure is laid out in full as the first steps below.
Operative sequence
- Supine, radiolucent table, ipsilateral hip bump, leg holder for 90–120 degrees of flexion, tourniquet to 300 mmHg.
- Re-assess the three zones and the planned construct one final time; mark the tibial tubercle osteotomy site now if you anticipate a difficult exposure, before scar tissue distorts the landmarks.
- Most revisions begin with the standard medial parapatellar arthrotomy, extending the previous incision proximally and distally as needed.
- Expose the tibial component by releasing the deep medial collateral ligament fibres and posteromedial capsule in a controlled manner; for the femur, release the posterior capsule as needed.
- If eversion and translation are inadequate, escalate in order: quadriceps snip first, then tibial tubercle osteotomy, rarely a medial epicondylar osteotomy.
- Quadriceps snip — an oblique incision through the quadriceps tendon from the proximal pole of the patella, 3–4 cm proximally and laterally; repair with heavy non-absorbable suture; the post-operative protocol is unchanged.
- Tibial tubercle osteotomy — a 6–8 cm osteotomy with a proximal step-cut to prevent proximal migration, secured with two or three 3.5 mm lag screws or cerclage wires.
- Medial epicondylar osteotomy — for severe varus or a contracted MCL; osteotomise the epicondyle with the attached MCL and posteromedial capsule and repair it with screws or suture anchors.
- Remove the femoral component with an oscillating saw and osteotomes, dividing the implant-cement interface and preserving as much host bone as possible.
- Clear all cement and fibrous tissue from the canal — a clean canal is essential for assessing the true defect and for stem seating.
- Classify the metaphyseal defect using AORI. 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; it should sit flush with the remaining host bone.
- Ream the femoral canal with flexible reamers until cortical chatter — the sign of adequate canal fill.
- 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); prefer a shorter stem when the metaphyseal cone already provides solid Zone 2 fixation.
- Attach trial offset adapters (0 mm, 4 mm, 6 mm, 8 mm) to the stem and rotate the offset to restore the joint line — reference the adductor tubercle (about 10 mm proximal to the medial joint line) or the contralateral knee.
- Confirm posterior condylar offset is within 3 mm of native (measure from the posterior femoral cortex to the posterior condylar surface) and that the epicondylar axis is parallel to the trial's posterior condylar axis.
- With offset and stem length confirmed, impact the final cone or sleeve, then insert the stem (cemented or press-fit) and seat the definitive femoral component.
- Confirm the component sits flush on the cone with no cement or bone interposed at the cone-host interface, and that the knee is stable through a full range of motion.
- Repeat the assessment on the tibia: a tibial cone or sleeve for any metaphyseal defect, with an offset selected to centre the tray on the stem axis.
- Perform ligament balancing and confirm equal flexion and extension gaps before final cementation or impaction.
- Layered closure over a drain as needed; if a quadriceps snip was used, repair it with heavy non-absorbable suture.
- If a tibial tubercle osteotomy was performed, confirm screw fixation of the fragment and protect the patellar tendon insertion.
- Check stability and range of motion on the table before dressing — aim for full extension and at least 110 degrees of flexion.
- Joint-line elevation greater than 5 mm — causes mid-flexion instability and patella baja; correct with a larger offset or a distal augment.
- Offset selected in the wrong direction — produces internal rotation of the femoral component and patellar maltracking; the offset is usually posterolateral on the femur.
- Inadequate diaphyseal engagement (less than 4 cm) — early loosening; the stem must clear the defect by 4–6 cm.
- Over-reaming the canal — loss of press-fit and rotational stability; ream sequentially to cortical chatter, no further.
I reference the adductor tubercle (about 10 mm above the medial joint line) and the posterior femoral cortex to restore posterior condylar offset. If the trial component sits more than 5 mm proximal to the native joint line, I increase the offset or add a distal augment (5 mm or 10 mm). The knee should achieve full extension and at least 110 degrees of flexion on the table before closure — stems are the last step, never cement around a malpositioned trial.
Maintain at least 6–8 cm of osteotomy length with a proximal step-cut, fix it with two or three 3.5 mm lag screws or cerclage wires, and protect the patellar tendon insertion throughout. Non-union runs 2–5 percent and proximal migration or tendon rupture are the feared complications — touch weight-bearing in extension with a brace for six weeks when a tibial tubercle osteotomy has been performed.
Aftercare & Complications
Rehabilitation Weight-bearing and bracing depend on the exposure and fixation. As a guide: | Phase | Timing | Weight-bearing & bracing | Therapy focus | |-------|--------|--------------------------|---------------| | 1 | 0–2 weeks | Weight-bearing as tolerated; if a TTO was performed, touch weight-bearing in a brace in extension | Wound healing, pain control, early quadriceps activation | | 2 | 2–6 weeks | Progress weight-bearing; brace weaning as the TTO fragment unites | Range of motion, patellar mobility, continued regional analgesia | | 3 | 6–12 weeks | Full weight-bearing; brace discontinued | Progressive strengthening and gait re-education | | 4 | 3–6 months | Unrestricted | Return to function; outcomes improve but do not reach primary-TKA levels | 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 stable fixation in at least two zones. Complications
- Rate
- 2–4 percent
- Prevention
- Sequential reaming to cortical chatter and gentle impaction
- Rate
- 1–2 percent
- Prevention
- Careful exposure; extensile osteotomy when eversion is difficult
- Rate
- Less than 1 percent
- Prevention
- Protect the popliteal neurovascular bundle during posterior capsular release
- Rate
- 1–2 percent
- Prevention
- Antibiotic-loaded cement when indicated; meticulous technique
- Rate
- 3–5 percent
- Prevention
- Meticulous haemostasis and layered closure
- Rate
- 5–10 percent
- Prevention
- Aggressive early mobilisation and regional analgesia
- Rate
- 5–10 percent at 10 years
- Prevention
- Two-zone fixation and metaphyseal augmentation
- Rate
- 10–20 percent
- Prevention
- Shorter hybrid constructs
- Rate
- 3–5 percent
- Prevention
- Accurate joint-line and posterior condylar offset restoration
Viva & Exam Focus
ZONALZONAL — zonal fixation concept
STEMSSTEMS — stem selection principles
Relying on Zone 1 alone with short cemented stems in the presence of metaphyseal bone loss fails in greater than 30 percent at five years. Plan fixation in at least two of the three zones.
The stem axis sits 4–8 mm medial and anterior to the native joint-line centre; without an offset adapter the component is medialised and anteriorised, elevating the joint line and losing posterior condylar offset. Always trial offsets before implantation.
Press-fit stems greater than 100–120 mm in the femur (75–100 mm in the tibia) cause end-of-stem pain in 10–20 percent. Prefer shorter cemented or hybrid stems when metaphyseal fixation is solid.
Intra-operative bone loss usually exceeds the radiographic estimate, and cement or small augments alone are then insufficient. Have cones, sleeves and structural options available — underestimating the defect is the commonest cause of early aseptic loosening.
Poor diaphyseal bone (Dorr C femur or a wide tibial canal) makes press-fit fixation unreliable. Use a cemented stem when bone quality is poor or canal fill is less than 80 percent.
Non-union (2–5 percent), proximal migration and patellar tendon rupture are the risks. Maintain 6–8 cm of length with a proximal step-cut, fix with two or three 3.5 mm screws or cerclage wires, and protect the tendon insertion.
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“A 68-year-old man presents with aseptic loosening of a primary TKA performed 12 years ago. Pre-operative radiographs show AORI Type 2B femoral bone loss and a wide femoral canal (Dorr C). Describe your fixation strategy.”
“During revision TKA the trial femoral component with a 6 mm offset adapter sits 8 mm proximal to the native joint line. The patient has limited flexion (90 degrees) and a 10-degree extension lag on the table. What has gone wrong and how do you correct it?”
“A 72-year-old woman with a loose primary TKA has an uncontained medial tibial plateau defect (AORI Type 2A) and a narrow tibial canal. She has 15 degrees of varus deformity. Outline your tibial revision strategy.”
Zonal fixation concept
- Zone 1 (epiphysis) — residual bone or cement; never sufficient alone
- Zone 2 (metaphysis) — critical for load transfer; cones and sleeves restore rotational stability
- Zone 3 (diaphysis) — stem engagement 4–6 cm beyond the defect gives axial stability
- Minimum goal: fixation in at least two zones; single-zone failure exceeds 30 percent at 5 years
- Hybrid constructs (cone plus short stem) preferred over long press-fit stems in poor bone
AORI classification and defect management
- Type 1: contained defect — cement or small augments
- Type 2A: uncontained one-sided defect — unilateral cone or sleeve
- Type 2B: uncontained bilateral defect — bilateral cones or a large sleeve construct
- Type 3: massive uncontained loss — structural allograft, custom implant or endoprosthetic replacement
- Have structural options available — intra-operative defect size often exceeds the radiographic estimate
Stem selection principles
- Cemented short stems (75–100 mm): immediate fixation, easier removal, preferred in Dorr C bone or wide canals
- Press-fit long stems (greater than 120 mm femur): biologic fixation but 10–20 percent end-of-stem pain risk
- Canal fill greater than 80 percent required for reliable press-fit fixation
- Hybrid fixation (cone plus short cemented stem) balances fixation against pain risk
- Stem length should extend 4–6 cm beyond the most distal bone defect
Offset adapters and joint-line restoration
- Offset adapters (4, 6, 8 mm) correct the 4–8 mm mismatch between stem axis and joint-line centre
- Restore the joint line to within 5 mm of native or the contralateral knee
- Adductor tubercle reference: about 10 mm proximal to the medial joint line
- Posterior condylar offset within 3 mm of native — loss causes flexion instability
- Always trial all offsets before final stem implantation
Extensile exposure options
- Quadriceps snip: 3–4 cm proximal-lateral extension; simple repair, no protocol change
- Tibial tubercle osteotomy: 6–8 cm with a proximal step-cut; screws or cerclage; brace 6 weeks
- Medial epicondylar osteotomy: for severe varus or MCL contracture; repair with screws or anchors
- Anticipate extensile exposure in 10–15 percent of revisions; mark the site before component removal
- Protect the patellar tendon insertion throughout exposure
Complications and prevention
- Aseptic loosening 5–10 percent at 10 years — two-zone fixation and metaphyseal augmentation
- End-of-stem pain 10–20 percent with long press-fit stems — shorter hybrid constructs
- Joint-line elevation greater than 5 mm — mid-flexion instability and patella baja; prevented by offset trialling
- Extensor mechanism disruption 1–2 percent — careful exposure and extensile osteotomy when needed
- Infection 1–2 percent — higher than primary TKA; antibiotic-loaded cement in high-risk cases
Background & Evidence
The zonal fixation concept. The dominant framework for fixation planning in revision TKA divides the femur and tibia into three anatomic zones. Zone 1 (epiphysis) is the residual host bone or cement mantle around the original component — it gives immediate but limited fixation and is never sufficient alone when metaphyseal bone loss is present. Zone 2 (metaphysis) is the critical load-transfer zone; its cavitary or uncontained defects are classified by the AORI system, and cones and sleeves restore rotational stability and load sharing with the stem. Zone 3 (diaphysis) is the long intramedullary canal for stem engagement, providing axial and rotational stability when the stem reaches 4–6 cm beyond the defect. The goal is two-zone fixation. The minimum requirement is stable fixation in at least two zones. The preferred modern construct is a Zone 2 cone or sleeve plus a Zone 3 short-to-medium press-fit or cemented stem. Zone 1 plus Zone 3 (a short cemented stem) is acceptable when metaphyseal bone is adequate; Zone 1 plus Zone 2 (a cone without a stem) is rarely sufficient and reserved for very distal femoral or proximal tibial revisions with excellent diaphyseal bone. Single-zone (Zone 1 alone) fixation fails in 25–40 percent at five years, whereas two-zone fixation achieves greater than 90 percent survivorship at ten years.
- Defect
- Contained defect
- Management
- Cement or small augments
- Defect
- Uncontained — one condyle or one plateau
- Management
- Unilateral cone or sleeve
- Defect
- Uncontained — both condyles or both plateaus
- Management
- Bilateral cones or a single large sleeve or cone construct
- Defect
- Massive uncontained loss of the metaphysis
- Management
- Structural allograft, custom implant or proximal tibial or femoral replacement
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; the trade-off is stress shielding and difficult removal. Press-fit long stems achieve biologic fixation with less stress shielding but carry a 10–20 percent risk of end-of-stem pain and need at least 4–6 cm of tight diaphyseal fit (a cemented stem needs a greater than 2 mm cement mantle). Hybrid constructs — a metaphyseal cone plus a short cemented stem — are increasingly favoured for their balance of durable fixation and reduced pain. Offset adapters and joint-line restoration. Offset adapters (4 mm, 6 mm or 8 mm) reconcile the 4–8 mm mismatch between the intramedullary stem axis and the prosthetic joint-line centre; they are required in roughly 60–70 percent of femoral revisions to avoid medialisation and anteriorisation of the component. Restoring the joint line to within 5 mm of native and posterior condylar offset to within 3 mm reduces mid-flexion instability and improves Knee Society scores. Metaphyseal cones and sleeves demonstrate 92–98 percent survivorship at 5–10 years when combined with diaphyseal stem fixation, and modern revision TKA overall achieves 85–95 percent survivorship at ten years — outcomes improve markedly but do not reach primary-TKA levels.
References
Do Porous Tantalum Metaphyseal Cones Improve Outcomes in Revision Total Knee Arthroplasty?
- Porous tantalum metaphyseal cones significantly improved outcomes and reduced aseptic loosening in revision TKA with severe metaphyseal bone loss
- Demonstrated reliable fixation when combined with diaphyseal stems achieving two-zone fixation
The Cost-Effectiveness of Tibial Metaphyseal Cones in Revision Total Knee Arthroplasty
- Tibial metaphyseal cones are cost-effective in revision TKA by reducing re-revision rates for aseptic loosening in bone loss cases
Fixation of revision TKA: a review of the literature
- Cemented and cementless stems achieve comparable fixation when two-zone principles are followed; individualised selection based on bone quality is key
- Long press-fit stems increase end-of-stem pain risk in poor canal fill scenarios
Maintenance of the joint line and posterior condylar offset are the most notable variables for successful outcomes of revision total knee arthroplasty
- Restoration of joint line and posterior condylar offset within narrow tolerances is the strongest predictor of successful clinical outcomes and stability in revision TKA
Surgical exposures in revision total knee arthroplasty
- Tibial tubercle osteotomy with step-cut technique provides safe extensile exposure with low non-union (2-5%) and patellar tendon rupture rates when properly executed