Malalignment of knee Epidemiology and Biomechanic H.Mousavi,MD Deprtment of Orthopaedic Surgery Esfahan University of Medical Sciences Jan.2016, Esfahan H

Epidemiology of Knee Alignment Mechanical axis : Alignment of the lower extremity is defined as a line drawn from the centre of the femoral head to the centre of the talus. The hip-knee- ankle alignment(HKAA) is best assessed with long leg films . This line passes close to the centre of the tibial head between the eminentia tibiae, approximately 1° in varus (neutral alignment 0–2°)

Epidemiology of Knee Alignment  Moreland et al. reported a mean of 1.3° varus alignment in normal western males . Hsu et al. noted a mean of 2.3° varus alignment in western males and 1.3° varus alignment in western females. Tang et al. reported that a mean of 2.2° varus alignment was observed in a Chinese population regardless of gender.

Incidence of constitutional varus alignment was 20.34%. Coronal Alignment of the Lower Limb and the Incidence of Constitutional Varus Knee in Korean Females Moo-Ho Song, MD,1 Seong-Ho Yoo, MD,1 Suk-Woong Kang, MD,1 Yeong-Joon Kim, MD,1 Gyu-Taek Park, MD,1 and Yong-Seon Pyeun, MD Knee Surg Relat Res. 2015 Mar;27(1):49-55 The mechanical axis of the lower limb (HKAA) was in slight varus (1.35°±2.04°) in the 118 Korean females in their 20s and 30s . Incidence of constitutional varus alignment was 20.34%.

Is Neutral Mechanical Alignment Normal for All Patients Is Neutral Mechanical Alignment Normal for All Patients?: The Concept of Constitutional Varus Clin Orthop Relat Res (2012) 470:45–53 Johan Bellemans, MD, PhD,corresponding author1,2 William Colyn, MD,2 Hilde Vandenneucker, MD,2 and Jan Victor, MD, PhD2 32% percent of men and 17% of women had constitutional varus knees with a natural mechanical alignment of 3° varus or more. Constitutional varus was associated with increased sports activity during growth spurt. Restoration of mechanical alignment to neutral in these cases may not be desirable and would be unnatural for them.

Constitutional varus alignment According to Bellemann et al.Constitutional varus alignment was associated with increased sports activity during the growth spurt in the teenage years, whereas no significant correlation was established with weight, body type, and BMI. In particular, intense sports activity at the end of the growth spurt (range, 14 to 16 years) imposes biomechanical overload on the medial physis in the proximal tibia, resulting in the development of varus knees Hueter-Volkmann's law :Growth at the physes is retarded under increased compression, whereas accelerated under reduced loading. Such unbalanced stress on the epiphysis has also been associated with tibia vara in children

Epidemiology Some studies also suggested that vitamin D insufficiency in children could cause coronal bowing of the femoral shaft, coxa vara, and proximal tibia vara, eventually resulting in constitutional varus alignment. Nagamine et al. reported that medial torsion of the proximal tibia during kneeling and squatting in childhood in Asian countries with floor-sitting lifestyle resulted in high prevalence of varus alignment compared to that in the Western countries.

Biomechanic In the normally aligned knee, the center of pressure of tibiofemoral force passes slightly through the medial side of the knee during stance (average of 4–8 mm medial to the knee joint center). the medial compartment of the knee sustains 60–70% of the load

Joint Reaction Force GRF + AMF = JRF The combination of ground reaction force (GRF) plus the antagonist muscle force (AMF) on the knee is what causes the joint reaction force (JRF), or the compressive force within the knee: GRF + AMF = JRF

GRF At neutral varus/valgus angulation,there is almost twice the compressive force across the medial joint as across the lateral joint. This is a result of the medially directed component of the GRF.

Biomechanic average peak force of about 3 times body weight (BW) during walking and of about 6 times BW during stair climbing. During flexion, this center of pressure lies even more medial. Varus or valgus malalignment of the lower extremity results in an abnormal load distribution across the medial and lateral tibiofemoral compartment For example, a 4–6% increase in varus alignment increases loading in the medial compartment by up to 20%

Varus Deformity With increased amounts of varus deformity, forces increase in the medial compartment and proportionally decrease in the lateral compartmen lateral compartment begins to separate unless the quadriceps and hamstrings produce augmented compressive forces or the LCL is tensioned

Varus Deformity Primary varus: Double varus: Triple varus: 1. Physiologic tibiofemoral angulation and osteocartilagenous (narrowing) of the medial tibiofemoral compartment. Double varus: 1.Tibiofemoral osteocartilagenous and geometric alignment. 2. Separation of the lateral tibiofemoral compartment from moderate deficiency of the posterolateral structures Triple varus: 1. Tibiofemoral osteocartilagenous and geometric alignment. 2. Separation of the lateral tibiofemoral compartment. 3. Varus recurvatum in extension, severe deficiency of posterolateral ligamentous structures

Valgus Angulation In a valgus knee, the force on the lateral compartment increases, and the force on the medial compartment decreases but proportionally less than for same angulation in the varus knee.

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