Complications in Surgical Management of Adolescent Blount Disease

Introduction

Adolescent Blount disease is a developmental disorder of the posteromedial proximal tibial physis. Asymmetric growth results in a classic deformity characterized by tibia vara, internal tibial torsion, and procurvatum. The severity of alignment falls along a spectrum, and appropriate treatment is based on the characteristics of a patient’s particular deformity. Careful analysis of all three dimensions is key to deciding which treatment to prescribe. Achieving perfect limb alignment after treatment requires many key considerations before, during, and after surgery to avoid complications that may compromise outcome. This is especially true when utilizing a circular external fixator to achieve gradual correction of the deformity.

Patient Considerations

Adolescents with Blount disease have specific health concerns that need to be considered to mitigate trouble. As with all elective surgeries, modifiable risk factors detailed here should be optimized prior to surgical intervention.

Patients with adolescent Blount disease are typically obese, with mean body mass index (BMI) found to be 40 kg/m ² or more. Childhood obesity is associated with altered physiology affecting various organ systems. Gordon and Hughes found that 11 of 18 children with Blount disease were diagnosed with sleep apnea. Accordingly, we recommend screening for snoring and morning sleepiness. Precocious puberty can be found as well, affecting skeletal growth and resulting in advanced bone age. Hypertension, diabetes mellitus, and venous thromboembolism are all conditions that warrant consideration.

Prior to any elective osteotomy, it is recommended to screen for smoking and second hand smoke exposure, as these can complicate bone healing and regenerate formation. Despite elevated BMI, relative protein malnourishment can be found on screening labs. As children with Blount disease are 7.33 times more likely to have deficient vitamin D levels, treatment of dietary deficiencies is recommended.

There is no perfect time to insert corrective osteotomy into the life of an adolescent. Strong consideration should be given to social and psychological factors, as treatment with external fixation creates a unique stressor for a child. Treatment with this modality can be lengthy, averaging up to 4.5 months and requiring significant patient and caregiver compliance, which are both decreased if treatment stress is too high. Presurgical psychological therapy for treatment acceptance, as well as postoperative therapy for adjustment, can be useful adjuncts.

Physical Examination

Adolescent Blount disease typically presents as a unilateral genu varum. On exam, ensure that the legs are rotated so that the patella is pointed directly forward to unmask the internal tibial torsion that causes the foot to point inward. The joint line obliquity can make the fibular head appear prominent. Limb length difference should be quantified using radiographs as opposed to physical examination. Note that soft tissue appears at the medial thigh and lateral leg in obese children, obligately abducting the hip. Be sure to observe the limb from the side to see if full extension is present, as the procurvatum deformity can be hidden.

Gait examination may demonstrate waddling or limping. The foot progression angle is negative (internally rotated foot) from the axial plane deformity, and there is increased contact pressure on the lateral side of the foot. Focus your attention on the knee to identify a lateral or varus thrust, which suggests lateral collateral ligament laxity. An obvious varus thrust is likely to be clinically significant and warrant attention during surgical correction, as it may contribute to shear forces that will lead to arthrosis later in life ( Fig. 32.1 ).

Tabletop exam starts with supine evaluation. Ensure full muscle strength and range of motion. Knee extension may be compromised if the proximal tibia has a significant procurvatum deformity. This can be worsened if there is knee flexor contracture, so measure the posterior popliteal angle to quantify hamstrings tightness and compare it to the contralateral side. The gastrocnemius can additionally tighten into equinus to compensate for the limb length difference if the walk is in equinus. Ensure the subtalar joint is supple, as it is forced to evert to compensate for knee varus. Similarly, the forefoot may develop secondary pronation due to overloading the lateral border of the foot.

The final supine maneuver is the assessment of knee stability. This can be challenging due to the large body habitus of some patients. Focus on the lateral collateral ligament by examining the knee for varus laxity in 5 degrees and 30 degrees.

The patient then turns into the lateral position for an Ober test to assess the iliotibial band for contracture. Lastly, the patient turns prone for assessment of rotational profile. Hip internal and external rotation in this position is assessed bilaterally. The thigh-foot angle is assessed and compared between sides; internal tibial torsion is classically observed. Obesity can make it difficult to identify the longitudinal axis of the thigh, so ensure similar landmarks are being used for both sides.

Radiographic Workup

High-quality, biplanar, full-length radiographs are mandatory for accurate evaluation of deformity in the coronal and sagittal planes. Train the radiologic technician to ensure both patellae face straight ahead; the tendency is to focus on getting the foot straight, but it is important to ensure a “knee-centric” approach. Incremental lifts can be placed under the affected side until the pelvis is clinically level, and the total height of the lift should be notated on the image. The lateral view should be performed in full extension to evaluate for any flexion contracture. Advanced imaging such as computed tomography and magnetic resonance imaging is not routinely performed. Additional hand or elbow radiographs can be obtained for skeletal maturity estimation.

Comprehensive deformity analysis is performed on coronal and sagittal images. The mechanical axis is deviated medially due to the genu varum. Joint line angles are used to identify the extent of deviation from population norms. While the tibia is obviously deviated into varus, be sure not to miss concomitant femoral deformity. The femur can contribute up to one-third of the varus deviation. Similarly, the distal tibia may have a compensatory valgus that may need to be addressed. Careful evaluation of the sagittal plane will identify procurvatum deformity. Note that axial plane deformity is not quantitatively measured on radiographs, so do not forget the thigh-foot axis in your physical examination.