and Treatment of Angular Deformities

Fig. 37.1

Examples of (a) genu varum and (b) “windswept” limb deformities

Limb bowing can be generalized or focal. The differential diagnosis of the cause of genu varum or genu valgum includes physiologic, posttraumatic (malunion, sequelae of physeal fractures), postinfectious, inflammatory (juvenile arthritis), and systemic diseases (rickets), generalized bone disorders (skeletal dysplasias, osteogenesis imperfect, enchondromatosis, osteochondromatosis, neurofibromatosis), and congenital causes such as limb deficiencies. Tibial deformity can be anterolateral (apex anterior and lateral – associated with congenital pseudarthrosis), anteromedial (apex anterior and medial – associated with fibular hemimelia), and posteromedial (apex posterior and medial – associated with a calcaneovalgus foot deformity).

Recognizing that many deformities are multiplanar and that planning complex limb realignment is beyond the scope of this book, the authors’ goal is to provide a basic understanding of (1) lower limb malalignment, (2) how to identify components of the deformity, and (3) surgical options for achieving correction.

Clinical Evaluation of Limb Deformities

The history should identify previous traumatic injuries or infections and/or medical or nutritional issues, suggesting an underlying metabolic problem. A family history can identify similar limb malalignment in other family members and familial bone diseases. Ask how the patient and family perceive the “problem”: is it purely cosmetic, or is there pain or limitation in activities?

The physical assessment begins with general health and nutrition. Height and weight should be measured and compared with normative data. The lower extremity exam includes observational gait analysis and focuses on limb alignment and leg lengths, both assessed while standing with the patellae facing forward. Hip, knee, and ankle range of motion are measured, as contractures can be sources of apparent limb length discrepancy. Knee joint stability is tested, as ligamentous laxity can contribute to a varus or valgus moment with weight-bearing, often associated with a “thrust” during ambulation. The spine should be examined to rule out associated spinal deformity or pelvic obliquity, which can contribute to apparent limb shortening and gait deviations.

Radiographs are essential when evaluating a limb deformity, ideally as standing full-length AP (patella pointing forward) and lateral radiographs of both lower extremities. If long cassettes are unavailable, consider separate standing AP and lateral films of both the femur and the tibia/fibula, including the proximal and distal joints in each film. When weight-bearing views are unavailable, knee laxity must be inferred from the clinical exam. Look for physeal widening and other abnormalities seen in rickets or certain skeletal dysplasias. Upper extremity and spine x-rays may be necessary to confirm underlying diagnoses and optimize the patient preoperatively.

Preoperative Planning

In general, the mechanical axis of the leg passes from the center of the femoral head through the medial tibial spine and the center of the ankle joint (Fig. 37.2). The anatomic axes of the femur and tibia are drawn parallel to the shaft of each bone. The mechanical axis of the femur is a line from the center of the femoral head to the center of the knee. The mechanical and anatomic axes of the tibia are identical. Tibiofemoral angles can either be anatomic – an angle formed by the intersection of the anatomic axes – or mechanical, an angle formed by the intersection of the mechanical axes. When using the anatomic axes, the value is normally 5–7° valgus. In the sagittal plane, the mechanical axis runs from the center of femoral head to the center of the ankle, passing anterior to the knee joint. This facilitates locking the knee in extension during stance and minimizes the work of the knee extensors.

../images/270913_2_En_37_Chapter/270913_2_En_37_Fig2_HTML.png — Fig. 37.2

A patient with Blount’s disease is shown illustrating the mechanical axis and both the mechanical and anatomic tibiofemoral axes. Note that the left patella faces forward, while the right is medial and the limb is slightly rotated. The blue circles indicate the location of the patellae

Preoperative planning should:

Identify the mechanical axis deviation (in mm from the center of the knee joint)
Determine the source of malalignment – femur, tibia, joint laxity, or any combination
Define the planes and levels of deformity

For simplicity, we will discuss coronal malalignment at the knee, recognizing that varus or valgus deformities of the proximal femur or the ankle can also play a role.

When a deviation in the mechanical axis has been identified, the location of deformity (femur, tibia, and/or joint) can be determined by comparing selected radiographic measurements with normal values or with the contralateral extremity in patients with unilateral involvement (Fig. 37.3a, Table 37.1). These include the tibiofemoral angle, the mechanical (or anatomic) lateral distal femoral articular angle (mLDFA, aLDFA), and the mechanical proximal tibial angle (MPTA). Normative values are also available for sagittal alignment about the knee (Fig. 37.3b), including the anatomic posterior distal femoral angle (aPDFA) and the posterior proximal tibial angle (PPTA). Most deformities are in fact multiplanar.

../images/270913_2_En_37_Chapter/270913_2_En_37_Fig3_HTML.png — Fig. 37.3

(a) This radiograph of a patient with rickets demonstrates the anatomic (aLDFA) and the mechanical (mLDFA) distal femoral articular angles, as well as the mechanical medial proximal tibial angle (MPTA). (**b, c**) Measurements used to assess deformity in the sagittal plane include the anatomic posterior distal femoral angle (aPDFA) and the posterior proximal tibial angle (PPTA)

Table 37.1

Analysis of coronal and sagittal alignment

Joint	Measurement	Description	Normal values	Pathologic deviation
Joint	Measurement	Description	Mean (range)	Pathologic deviation
Coronal alignment	Mechanical lateral distal femoral angle (mLDFA)	Angle between the mechanical axis of the femur (center of hip to center of knee) and a line drawn along the distal femoral condyles	88° (85–90°)	↑ = Femoral varus ↓ = Femoral valgus
	Anatomic lateral distal femoral angle (aLDFA)	Angle between the anatomic axis (midshaft) of the femur and a line drawn along the distal femoral condyles	81° (79–83°)	↑ = Femoral varus ↓ = Femoral valgus
	Medial proximal tibial angle (MPTA)	Angle between tibial mechanical (same as anatomic) axis and a line drawn across the proximal tibial joint surface	87° (85–90°)	↑ = Tibial valgus
	Medial proximal tibial angle (MPTA)		87° (85–90°)	↓ = Tibial varus
	Joint line congruence angle (JLCA)	Angle between a line drawn along the distal femoral condyles and a line drawn along the proximal tibial joint surface	2° (1–3°) apex medial	↑ =Varus (wider laterally)
	Joint line congruence angle (JLCA)		2° (1–3°) apex medial	↓ =Valgus (wider medially)
Sagittal alignment	Posterior distal femoral angle (PDFA)	Angle between the mid-diaphyseal line of the distal femur and the sagittal distal femoral joint line (physis or physeal scar)	83° (79–87°)	↑ = Recurvatum
Sagittal alignment	Posterior distal femoral angle (PDFA)		83° (79–87°)	↓ = Procurvatum
	Posterior proximal tibial angle (PPTA)	Angle between the proximal tibial articular surface and the mid-diaphyseal line of the tibia	81° (77–84°)	↑ = Recurvatum (more anterior slope)
	Posterior proximal tibial angle (PPTA)		81° (77–84°)	↓ = Procurvatum (more posterior slope)