First, how I would frame this case to the consultant

“I will base correction on a calibrated, full-length weight-bearing AP radiograph with both patellae facing forward, not on the displayed angle alone. I must identify the deformity level with mLDFA, MPTA, joint-line convergence angle, and mechanical-axis deviation.”

Intraoperative viva: MCW distal femoral osteotomy

1. What is the indication?

• Symptomatic valgus malalignment with lateral compartment overload, often lateral compartment chondral disease or osteoarthritis.
• The primary osseous deformity is in the distal femur, commonly an abnormal distal femoral valgus orientation, reflected by a reduced mLDFA.
• Usually a relatively young, active patient seeking joint preservation.
• May be combined with lateral meniscal transplantation, cartilage restoration, or patellofemoral stabilization, depending on pathology.

“The operation is indicated only when symptoms, compartment pathology, alignment, and the location of the deformity are concordant. I am not treating an X-ray alone.”

2. What preoperative imaging and measurements do you require?

Essential studies

1. Weight-bearing full-length AP alignment radiograph
   • Both feet positioned consistently.
   • Patellae forward to avoid rotational error.
   • Hip, knee, and ankle visible.
   • Assess mechanical-axis deviation and where it crosses the knee.
2. Dedicated standing knee radiographs
   • AP, lateral, Rosenberg or PA flexion weight-bearing.
   • Patellofemoral view if symptoms or instability.
3. MRI
   • Cartilage status in all compartments.
   • Lateral meniscus status.
   • Ligament integrity.
   • Bone marrow edema and focal osteochondral lesions.
4. CT rotational profile, only if suspected femoral torsional abnormality, patellar instability, or prior malunion.

Alignment analysis to state in viva

“If MPTA is normal and mLDFA is abnormal, an isolated DFO is logical. If both are abnormal, or correcting only one bone would leave substantial joint-line obliquity, I would consider distributing correction or a double-level osteotomy.”

3. What is your correction target?

“My correction target depends on the clinical objective. In a lateral-compartment overload valgus knee, I aim to restore a physiologic mechanical axis and unload the lateral compartment without overcorrecting the patient into symptomatic medial overload or creating joint-line obliquity.”

Important trap

• Fujisawa is classically applied to valgus-producing HTO for medial compartment varus OA.
• It is not a one-size-fits-all target for varus-producing DFO in a valgus knee.

4. Why medial closing wedge instead of lateral opening wedge DFO?

MCW-DFO advantages

• Bone-on-bone apposition and inherent compression.
• Usually no graft required.
• May be preferable for a larger correction.
• Potentially lower delayed union/nonunion concern than an opening wedge.
• Medial plate lies under more soft tissue coverage than a lateral implant in some patients.
• Shorter lever arm after wedge removal can make fixation stable.

MCW-DFO disadvantages

• Femoral shortening.
• Technically demanding to maintain the lateral hinge and avoid sagittal/rotational malalignment.
• Medial approach requires careful posterior soft-tissue protection.
• If the lateral cortex fractures, correction control can be lost.
• Future TKA may be more complex after any osteotomy because of scars, hardware, and altered anatomy.

5. How do you calculate the wedge?

Principle

• Determine the desired coronal correction angle on calibrated long-leg planning.
• Select the lateral hinge point.
• Plan two converging medial cuts that preserve a 5-10 mm lateral cortical hinge.
• The wedge should be an isosceles triangle to avoid translation or a cortical step-off.

• (R) = distance from the intended lateral hinge to the medial cortical wedge base
• (\theta) = planned correction angle

Example only

“I use a symmetric wedge planned around the lateral hinge. The midline of the wedge is tangent to the medial cortex at its base, minimizing translation and cortical step-off.”

Operative sequence to rehearse

6. Positioning and setup

“The patient is supine on a radiolucent table. I ensure the C-arm can obtain a true AP and lateral distal femoral image, and I prepare the entire limb to allow an intraoperative long alignment check with an alignment rod or cable.”

• Supine, radiolucent table.
• Tourniquet according to local practice, often high thigh.
• Fluoroscopy positioned before skin preparation.
• Prep from iliac crest or hip region to foot if checking mechanical alignment with cable.
• Antibiotics and thromboprophylaxis as per institutional protocol.
• Template implant and have the correct locking plate, guide wires, oscillating saw blades, osteotomes, reduction instruments, and graft/fixation contingency available.

7. Exposure

“I use an approximately 8-10 cm anteromedial distal femoral incision. I expose the medial distal femur, mobilize the vastus medialis anteriorly as needed, and develop a controlled posterior interval for protective retractors.”

• Vastus medialis anteriorly.
• Adductor magnus tendon and adductor tubercle as landmarks.
• Posterior neurovascular structures, especially the popliteal vessels, must be protected with a blunt retractor placed directly on bone.

“My saw and osteotomes are never directed blindly posteriorly. I maintain a subperiosteal posterior retractor directly against bone before completing the posterior cortex.”

8. Where do you put the osteotomy and the lateral hinge?

• The precise level is implant- and plan-specific, generally supracondylar and proximal enough to accommodate distal fixation.
• Place two guidewires under fluoroscopy along the planned proximal and distal osteotomy planes.
• Aim toward the planned lateral hinge.
• Preserve 5-10 mm of lateral cortex.
• Confirm on AP and lateral images that wires:
  • are at the planned level,
  • converge correctly,
  • do not enter the joint,
  • do not produce flexion/extension error,
  • preserve an adequate hinge.

“The hinge must be lateral, controlled, and sufficiently broad. An excessively thin hinge fractures; an excessively medial hinge leaves an unstable osteotomy and alters the intended geometry.”

9. How do you perform the cuts?

1. Insert protective posterior retractors.
2. Use the guidewires as the fluoroscopic template.
3. Cut the posterior cortex first with great care, then progress through the medial and anterior cortices.
4. Stop short of the lateral cortex.
5. Complete carefully with osteotomes if required.
6. Remove the medial bone wedge.
7. Avoid levering that propagates through the lateral hinge.
8. Gradually close the wedge under controlled compression.
9. Check AP and lateral fluoroscopy before definitive fixation.

Key technical priority

• flexion/extension deformity,
• rotational malalignment,
• translation at the osteotomy,
• lateral hinge fracture,
• intra-articular propagation.

10. How do you close and hold the correction?

“I close the wedge gradually while protecting the lateral hinge, using a clamp or the plate construct according to the system. I confirm the correction with fluoroscopy and a long alignment rod before I commit to final fixation.”

• Lateral cortex is intact.
• Osteotomy surfaces oppose fully.
• No medial cortical gap.
• Plate position is correct.
• Distal fixation is adequate.
• Mechanical axis is at the intended target.
• Sagittal plane and rotation are satisfactory.

11. How do you check correction intraoperatively?

“I use a radiopaque cable or alignment rod from the femoral head center to the ankle center, with the limb held in the same rotational position used for planning. I check where that line crosses the knee and correlate it with my preoperative target.”

• Checking alignment with the limb externally rotated.
• Using a non-weight-bearing intraoperative image as though it exactly reproduces standing alignment.
• Blindly matching a numeric angle without examining joint-line orientation.

Common consultant questions and model answers

“What if the lateral cortex breaks?”

“I stop forceful closure, reassess alignment and stability fluoroscopically, then stabilize the hinge. Depending on the fracture pattern, this may include a lateral-to-medial lag screw, supplemental fixation, modification of postoperative weight bearing, and careful assessment that the desired correction has not been lost.”

“What are the important complications?”

Intraoperative

• Popliteal vessel injury.
• Posterior soft-tissue injury.
• Lateral cortical hinge fracture.
• Intra-articular fracture extension.
• Wrong correction or wrong level.
• Flexion/extension or rotational malalignment.
• Inadequate fixation.

Early postoperative

• Hematoma, infection, wound problems.
• DVT/PE.
• Loss of correction.
• Delayed union/nonunion.
• Hardware irritation or failure.
• Knee stiffness.

Late

• Overcorrection with medial compartment overload.
• Under-correction and persistent lateral overload.
• Progression of arthritis.
• Symptomatic implant requiring removal.
• Complexity during later arthroplasty.

“How do you avoid neurovascular injury?”

“I use a controlled medial approach, subperiosteal dissection, a blunt posterior retractor placed on bone under direct control, continuous awareness of saw direction and depth, and fluoroscopic guidance. I do not blindly advance an osteotome or saw toward the posterior cortex.”

“What if the correction needed is large?”

“I reconsider whether this is truly a single-level femoral deformity. I reassess MPTA, mLDFA, joint-line obliquity, and whether a combined or double-level correction is safer and more anatomic. Large single-bone corrections increase the risk of hinge failure, instability, and an oblique joint line.”

“How would you manage an incidental sagittal-plane error?”

“I identify it before final fixation on a true lateral fluoroscopic image. I would correct it before locking the construct, because a coronal correction with residual flexion, extension, or rotational error is not an acceptable result.”

Your 30-second presentation in theatre

“This is a right valgus knee with presumed lateral compartment overload. Before proceeding, I confirm on calibrated full-length standing films that the mechanical axis is lateralized, the mLDFA is abnormal, the MPTA is acceptable, and there is no major intra-articular or rotational contributor that would make isolated DFO inappropriate. My plan is a varus-producing medial closing-wedge DFO around a protected lateral cortical hinge, with a symmetric wedge calculated from calibrated planning. I will use fluoroscopic guidewires, protect posterior structures, preserve 5-10 mm of lateral cortex, close under controlled compression, and confirm the final hip-knee-ankle mechanical axis with a cable before definitive fixation.”