Malunion Correction — Principles

Malunion is defined as fracture healing in a position that is functionally or cosmetically unacceptable. It differs from nonunion (failure to heal) and delayed union (slow healing). Correction of malunion requires careful preoperative planning, understanding of the deformity, and selection of the appropriate surgical technique to restore alignment, length, and rotation.

• Malunion may be angulatory, rotational, translational, or involve shortening — often in combination
• Clinical significance depends on location, magnitude, patient age, and functional demands
• Upper limb tolerates greater deformity than lower limb due to compensatory motion at shoulder and elbow
• Lower limb malunion: even small rotational or angular errors can cause abnormal gait, joint overload, and early arthritis
• Goals of correction: restore mechanical axis, joint orientation angles, length, and rotation

Malunion deformity is described across four planes. Accurate characterisation is essential before planning correction.

• Deformities are often multiplanar — must assess all planes systematically
• CORA (Centre of Rotation of Angulation) is the key concept in planning osteotomy level and orientation
• The CORA is the point where the mechanical or anatomical axis lines of the proximal and distal segments intersect
• Osteotomy at the CORA corrects angulation without creating translation
• Osteotomy away from the CORA corrects angulation but introduces secondary translation (must be compensated)

Thorough preoperative evaluation is the cornerstone of successful malunion correction. Both clinical and radiographic assessments are mandatory.

• History: original injury, prior surgery, healing time, functional complaints, pain, limb use
• Clinical exam: gait analysis, rotational profile, limb length, joint range of motion, neurovascular status
• Scanogram (long-leg alignment film): essential for lower limb — measures mechanical axis deviation (MAD)
• CT scan: mandatory for rotational malunion — compare femoral anteversion and tibial torsion bilaterally
• Joint congruency: assess for secondary articular changes or intra-articular malunion
• Bone quality: osteoporosis affects implant choice and osteotomy technique

Key radiographic measurements for lower limb:

The CORA method (Paley) is the gold standard for planning corrective osteotomy. It provides a systematic geometric approach to identify where and how to cut.

• Step 1: Draw the mechanical or anatomical axis of the proximal and distal bone segments
• Step 2: The intersection of these two lines is the CORA
• Step 3: The bisector of the angle at the CORA defines the axis of correction (the hinge axis)
• Rule 1: Osteotomy at the CORA and angulation around the bisector = pure angular correction, no translation
• Rule 2: Osteotomy away from the CORA = angular correction + secondary translation; requires intentional shift
• Multiplanar deformities require simultaneous or staged corrections in each plane
• Oblique plane deformities are best corrected with oblique osteotomies aligned to the true CORA in 3D space

The choice of osteotomy depends on the bone, the deformity type, the need for lengthening, and surgeon expertise.

• Opening wedge osteotomies risk non-union at the graft site — bone graft or substitute required
• Closing wedge osteotomies shorten the limb — consider if LLD acceptable or to be corrected later
• Dome osteotomy (e.g. proximal tibia) allows correction in any plane without changing length significantly
• Rotational osteotomies must be combined with axial compression fixation to prevent secondary angulation

Stable fixation after corrective osteotomy is mandatory to maintain correction and allow bone healing.

• Plate and screw fixation: most common; locking plates preferred in osteoporotic bone or periarticular osteotomies
• Intramedullary nail: ideal for diaphyseal deformity correction; allows early weight bearing
• External fixator (Taylor Spatial Frame / Ilizarov): for gradual correction, infected nonunion-malunion, or when simultaneous lengthening required
• Staples/screws alone: used for small corrections in cancellous bone (e.g., proximal tibia opening wedge)
• Hexapod frames (Taylor Spatial Frame) allow six-axis deformity correction gradually with daily strut adjustments
• Acute correction is faster; gradual correction via distraction osteogenesis safer for large corrections (>30°) or when lengthening needed

Malunion correction principles vary by anatomical location. Accepted thresholds for intervention differ across bones.

• Distal radius malunion: correct within 1 year for best results; late correction still valuable if symptomatic
• High tibial osteotomy (HTO): used for varus malunion and medial compartment OA — offloads medial compartment
• Femoral malunion: rotational errors >15° cause patellofemoral problems and gait disturbance — correct with derotation
• Intra-articular malunion (e.g., tibial plateau) may require articular osteotomy, distraction, or eventual arthroplasty

• Nonunion of osteotomy site: risk increased with opening wedge without graft, infection, or poor fixation
• Neurovascular injury: especially with acute lengthening or osteotomy near neurovascular structures
• Compartment syndrome: risk after acute correction of long-standing deformity — monitor postoperatively
• Overcorrection or undercorrection: technical error in planning or execution
• Hardware failure: fixation failure before consolidation — more common with poor bone quality
• Joint stiffness: prolonged immobilisation, periarticular scarring
• Infection: especially with external fixation pin-sites or revision in previously infected bones
• Loss of correction: inadequate fixation or early weight bearing

• CORA is the intersection of proximal and distal bone segment axes — osteotomy at CORA corrects angulation without translation
• Osteotomy away from CORA introduces translation — must plan intentional shift to compensate
• Taylor Spatial Frame allows six-axis simultaneous correction via daily strut adjustments
• Distal radius malunion: dorsal tilt >10° or shortening >2 mm with symptoms = indication for correction
• Rotational malunion of femur: CT required — compare anteversion bilaterally; >15° difference = clinically significant
• HTO for proximal tibia varus malunion: aim for 3–5° of overcorrection into valgus for medial compartment OA
• Dome osteotomy allows correction in multiple planes with minimal length change — ideal for proximal tibia
• Intramedullary nail exchange is the preferred method for diaphyseal malunion correction
• Always assess and correct rotational deformity separately — it cannot be inferred from plain films alone
• Leg length discrepancy >2 cm in adults is generally symptomatic and may require simultaneous lengthening