Page 7 - JCTR-11-3

Journal of Clinical and

Translational Research

REVIEW ARTICLE
Clinical review and insights into lateral patellar

instability in deep flexion

Roland M. Biedert*
Department of Clinical Research, Faculty of Medicine, University of Basel, Basel, Switzerland

Abstract

Background: Lateral patellar instability in deep knee flexion is a poorly understood
and underreported condition that differs etiologically and biomechanically from the
more common instability near extension. Aim: This paper presents a comprehensive
review combined with clinical experience on lateral patellar instability in deep flexion,
along with insights into the underlying anatomical and biomechanical characteristics.
Methods: A systematic literature search was performed using the terms “patellar
instability” and “knee flexion.” Inclusion criteria included original studies, book
chapters, and reviews in English, whereas computational or biomechanical studies
were excluded. In addition, clinical experience from cases was incorporated into the
considerations and assessments. Results: Nine studies met the selection criteria
consisting of three case reports, three case series, a book chapter, and two reviews. The
analysis of clinical, anatomical, biomechanical, and kinematic factors in patients with
lateral patellar instability in deep flexion did not reveal reliable arguments for the same
etiological factors causing instability near extension. Instead, factors such as changes
*Corresponding author: in the shapes of the lateral and medial condyle during knee flexion, variations in the
Roland M. Biedert
(biedert@sportsclinicnumber1.ch) shape of the lateral femoral condyle, terminal sulcus or false groove, short extensor
muscles, contractures of soft tissues lateral to the patella, and laxity of the medial
Citation: Biedert RM. Clinical
review and insights into lateral ligaments play significant roles in flexion instability. Conclusion: Lateral patellar
patellar instability in deep flexion. instability in deep flexion is a rare but severely disabling condition that often begins
J Clin Transl Res. 2025;11(3):1-13. at a younger age. The etiological factors leading to deep flexion instability differ from
doi: 10.36922/jctr.7131
those causing patellar instability near extension, necessitating a clear distinction
Received: December 9, 2024 between these two types of patellofemoral instability. Accordingly, surgical treatment
Revised: March 24, 2025 should address all documented etiological factors for flexion instability and involve
a combination of procedures. Relevance for patients: Accurate differentiation
Accepted: April 7, 2025
between lateral patellar instability in deep flexion and instability near extension is
Published online: April 25, 2025 essential for devising effective treatment strategies.
Copyright: © 2025 Author(s).
This is an open-access article
distributed under the terms of the Keywords: Patellar instability; Flexion; Etiology; Anatomy; Biomechanics; Treatment
Creative Commons AttributionNon-
Commercial 4.0 International (CC
BY-NC 4.0), which permits all
non-commercial use, distribution,
and reproduction in any medium, 1. Introduction
provided the original work is
properly cited. The American Orthopedic Society for Sports Medicine/Patellofemoral Foundation
Publisher’s Note: AccScience Patellofemoral Instability Workshop defined patellofemoral stability as “constraint by
Publishing remains neutral with passive soft-tissue tethers and chondral/bony geometry that, with muscular forces, guide
regard to jurisdictional claims in
published maps and institutional the patella into the trochlear groove and keep it engaged within the trochlear groove as
affiliations. the knee flexes and extends” [1(p.1)]. Patellofemoral instability is a deficiency of these

Volume 11 Issue 3 (2025) 1 doi: 10.36922/jctr.7131