Background: Chronic low back pain (CLBP) is a predominant cause of disability globally and frequently results from intricate biomechanical interactions rather than solely from disc or nerve-root issues. Variants such as the sacralisation of the fifth lumbar vertebra (L5), patella alta, and pes planus (flat foot) are acknowledged as anatomical and biomechanical contributors; however, their combined occurrence as a contributory triad in CLBP is rarely documented.
Case Presentation: A 23-year-old female patient reported a 4-year history of gradually developing low back pain radiating to the left leg, exacerbated by prolonged standing and heavy lifting, with no prior trauma or neurological deficits. Magnetic resonance imaging of the lumbosacral spine revealed partial sacralisation of L5, a rudimentary L5–S1 disc, and mild degeneration of the L4–L5 disc without nerve-root compression. Radiographs of the knees indicated bilateral patella alta (Insall–Salvati ratio > 1.2). A clinical examination of the feet showed bilateral flat feet (pes planus) with excessive pronation. A multidisciplinary conservative management strategy was implemented, which included core stabilization and lumbar/postural training, custom foot orthoses for flat feet, patellar taping, and quadriceps strengthening.
Discussion: The occurrence of lumbosacral transitional vertebrae varies significantly (4–30%), and sacralisation may influence load distribution across the lumbosacral junction, making adjacent-segment degeneration and mechanical pain more likely. Flat feet lead to excessive internal rotation of the tibia and anterior pelvic tilt, which increases lumbar loading, while patella alta modifies the biomechanics of the knee extensor mechanism and may trigger compensatory postural changes. The simultaneous presence of all three conditions in this patient seems to have caused synergistic disturbances in the kinetic chain, contributing to her CLBP without neural entrapment. Conservative, chain-oriented rehabilitation combined with orthotic intervention was crucial for her clinical improvement.
Conclusion: Healthcare professionals must uphold a heightened level of suspicion for biomechanical variations in the lower limbs and pelvis when assessing chronic low back pain (CLBP), particularly in instances where imaging does not reveal significant neural or discal compression. The uncommon combination of sacralisation of the fifth lumbar vertebra (L5), patella alta, and bilateral flat feet forms a clinically significant “biomechanical triad” that can induce chronic mechanical low back pain due to altered load distribution across the spinal, pelvic, and lower limb structures. Identifying and implementing targeted conservative treatment for this triad can result in both symptomatic relief and functional enhancement.
Keywords: Sacralisation of L5; Patella Alta; Flat Foot (Pes Planus); Chronic Low Back Pain; Biomechanics; Lumbosacral Transitional Vertebra.
Citation: Prakash, S., & Massih, S. (2026). A Rare Biomechanical Triad: Sacralisation of L5, Patella Alta, and Bilateral Flat Foot in a Patient with Chronic Low Back Pain Without Neural Compression – A Case Report. J Prim Health Glob Health 1(1):1-7.