Biomechanical and Functional Improvements Gained by Proximal Tibia Osteotomy Correction of Genu Varum in Patients with Knee Pain

Abstract

Background: Mechanical axis malalignment contributes to abnormal forces across the knee joint. Genu varum, or increased medial mechanical axis deviation (MAD), increases force transmission and contact pressures to the medial compartment. With increasing MAD and femoral-tibial mechanical axis angle (MAA), contact forces within the medial or lateral compartment of the knee significantly increase with increasing deformity. This may lead to knee pain, further deformity, and medial compartment degenerative joint disease, which can interfere with participation in sports and diminish quality of life.

Purposes/questions: We sought to evaluate patients with knee pain with bilateral genu varum and determine the effect of bilateral proximal tibial osteotomies on knee biomechanics, deformity correction, and functional outcomes.

Methods: This was a single-center, prospective study of eight limbs in four patients. Consecutive patients presenting with knee pain and bilateral genu varum originating from the proximal tibia were included. All patients underwent staged bilateral proximal tibial osteotomies with gradual deformity correction with an external fixator. Subjects underwent a three-dimensional (3D) instrumented motion analysis during level walking. A 3D lower extremity model was built and bilateral knee frontal plane kinematics and kinetics during the stance phase of gait were determined. Radiographic analysis was performed including assessment of MAD, MAA, and medial proximal tibial angle (MPTA). Functional outcomes were assessed with the Knee Injury and Osteoarthritis Outcome Score (KOOS), the 36-item Short-Form Survey (SF-36), the Lower Limb Questionnaire (LLQ), and a visual analog scale (VAS) for pain.

Results: The average time in the external fixator for a single limb was 97 days. The average follow-up period was 310 days. All biomechanical outcomes significantly improved, including knee adduction angle (7.8° to 1.8°), knee adduction moments (first peak, - 0.450 to - 0.281 nm/kg, and second peak, - 0.381 to - 0.244 nm/kg), and knee adduction moment impulse (- 0.233 to - 0.150 nm s/kg). There was a significant improvement in MAA, MAD, and MPTA. All patients showed qualitative improvement in mean scores on VAS (11.8 to 0.0), LLQ (77 to 93), KOOS (64 to 84), and SF-36 (71 to 88).

Conclusion: These findings suggest that bilateral proximal tibial osteotomy may be effective in improving knee biomechanics during gait and correcting mechanical alignment in patients with bilateral genu varum. Patients also demonstrated improvement in functional outcome scores. This technique should thus be considered in patients with varus knee osteoarthritis in the setting of genu varum to alleviate symptoms and potentially decrease further clinical deterioration.

Keywords: external fixation; gait biomechanics; knee pain; osteoarthritis; proximal tibial osteotomy; varus.

Fig. 1

a, b Radiographic pre-operative assessment of mechanical axis deviation (MAD) (a) and medial proximal tibial angle (MPTA), lateral distal femoral angle (LDFA), and mechanical axis angle (MAA) (b). m MAD, F Femur mechanical axis, T Tibia mechanical axis, a MPTA, b LDFA, c MAA.

Fig. 2

Standing hip-to-ankle radiograph showing neutral alignment once full correction was achieved with bilateral hexapod external fixators in place.

Fig. 3

a, b Standing hip-to-ankle radiograph showing maintenance of correction and neutral alignment once complete consolidation was achieved and bilateral external fixators removed. a shows neutral mechanical axis deviation and b shows neutral mechanical axis angle and normalization of the medial proximal tibial angle.

Fig. 4

Average pre- and post-operative knee kinetics normalized to stance phase and as compared to controls. Highlighted kinetic outcomes are first and second knee adduction moment peaks.

Fig. 5

Average pre- and post-operative knee kinematics through the gait cycle and as compared to controls.