An evaluation of the clinical tests and outcome measures used to assess patellar instability

Abstract

A literature review was undertaken to determine which clinical tests and outcome measures have been described to diagnose and evaluate patellar instability, and to assess the literature examining the sensitivity and specificity of these diagnostic tests, or the reliability, validity and responsiveness of the outcome measures identified. An electronic search was undertaken using standard databases as well as a hand search of specialist journals, reference lists and local medical libraries. All English language publications describing and/or evaluating diagnostic tests and outcome measures for patellar instability patients were included.

On review, 104 papers and 64 textbooks were included. Eighteen diagnostic tests and 10 outcome measures were identified. Of these only five diagnostic tests (Bassett's sign; apprehension test; gravity subluxation test; clinical assessment of the tibial tubercle to trochlear groove value; Q-angle) and seven outcome measures (modified International Knee Documentation Committee knee ligament standard evaluation form; Kujala anterior knee pain scale; Fulkerson knee instability scale; Lysholm knee scoring scale; Tegner activity level scale; Short Form-36; Musculoskeletal Function Assessment injury and arthritis survey) had been assessed for accuracy in five studies. The sensitivity, specificity, reliability or validity, of these tests remains unclear for this patient population. Further work is needed to assess the appropriateness of the identified tests and outcomes for patellar instability cohorts.

Introduction

Patellar instability is a generic term encompassing patellar dislocation, patellar subluxation and general symptomatic instability [1]. It is a complex musculoskeletal condition which has been estimated to affect between seven and 49 people per 100,000 [2], [3].

The aetiology of patellar instability is multi-factorial [4]. Factors include biomechanical abnormalities such as excessive foot pronation, femoral anteversion, external tibial torsion, genu valgum, genu recurvatum, trochlear, lateral insertion of the patellar tendon and patellar alta [2], [5], [6], [7]. In addition, other contributing factors may be soft tissue defects such as a rupture of the medial retinaculum or medial patellofemoral ligament (MPFL), hypotrophy of the vastus medialis oblique (VMO), hypertrophy of the vastus lateralis, generalised ligamentus laxity, and tightness of the lateral retinaculum [8], [9], [10], [11], [12], [13].

With such a variety of aetiological factors, the diagnosis and assessment of patellar instability can be difficult and is frequently misdiagnosed [14], [15]. An initial review of the literature suggested that no papers have comprehensively detailed the diagnostic tests or outcome measures used to assess this condition. This is a considerable weakness to the evidence-base since Malanga et al. [16] argued that to ensure the most accurate knee pathology diagnosis, it is imperative that an examiner is aware of each clinical test's sensitivity, specificity and limitations. Accordingly, the objectives of this review are to determine; which clinical tests and outcome measures are used to diagnose and evaluate patellar instability, and to assess the evidence evaluating the sensitivity and specificity of these diagnostic tests, or the reliability, validity and responsiveness of the outcome measures identified.