The relative timing of VMO and VL in the aetiology of anterior knee pain: a systematic review and meta-analysis

Abstract

Background: Anterior knee pain (AKP) is a common musculoskeletal complaint. It has been suggested that one factor that may contribute to the presence of AKP is a delay in the recruitment of the vastus medialis oblique muscle (VMO) relative to the vastus lateralis muscle (VL). There is however little consensus within the literature regarding the existence or nature of any such delay in the recruitment of the VMO within the AKP population. The purpose of this systematic review and meta-analysis was to examine the relative timing of onset of the VMO and VL in those with AKP in comparison to the asymptomatic population.

Methods: The bibliographic databases AMED, British Nursing Index, CINAHL, EMBASE, Ovid Medline, PEDro, Pubmed and the Cochrane Library were searched for studies comparing the timing of EMG onset of the VMO and VL in those with AKP versus the asymptomatic population. Studies fulfilling the inclusion criteria were independently assessed. Heterogeneity across the studies was measured. A meta-analysis of results was completed for those studies where adequate data was supplied. Where comparable methodologies had been used, results were pooled and analysed.

Results: Fourteen studies met the inclusion criteria; one prospective and thirteen observational case control. Eleven compared VMO and VL EMG onset times during voluntary active tasks while four investigated reflex response times. All used convenience sampling and did not state blinding of the assessor. Study methodologies/testing and assessment procedures varied and there was considerable heterogeneity within individual samples. Whilst a trend was identified towards a delay in onset of VMO relative to the VL in the AKP population during both voluntary active tasks and reflex activity, a substantial degree of heterogeneity across the pooled studies was identified (I2 = 69.9-93.4%, p < 0.01).

Conclusion: Findings are subject to substantial and unexplained heterogeneity. A trend was demonstrated towards a delayed onset of VMO relative to VL in those with AKP in comparison to those without. However not all AKP patients demonstrate a VMO-VL dysfunction, and this is compounded by normal physiological variability in the healthy population. The clinical and therapeutic significance is therefore difficult to assess.

Figure 1

QUORUM flow chart.

Figure 2

The results of meta-analysis of studies investigating stair ascent and descent. A negative VMO-VL value indicates VMO activation before VL activation. 2. Data for the mean and standard deviation was extracted from charts rather than the text for Cowan et al [5, 20] and standard deviation for Cowan et al [16]. 3. Standard deviation for Brindle et al [21] is an average estimate using data from other studies. 4. Small study bias: Stair ascent studies: Begg's test p = 0.71; Egger's test p = 0.40. Stair descent studies: Begg's test p = 0.09, Egger's test p = 0.04.

Figure 3

Results from four studies that measured onset timing of the VMO and VL during different activities. A negative VMO-VL value indicates VMO activation before VL activation. 2. Standard deviation for the study by Earl et al [17] is an estimate based on data from other studies. 3. Results from individual studies are not quantitatively combined since the onset timing was measured during different tasks.

Figure 4

The results for onset timing of VMO and VL during the patellar tendon reflex reaction. A negative VMO-VL value indicates VMO activation before VL activation. 2. Data for mean was extracted from charts rather than the text for Voight and Weider [6]. 3. Standard deviation for Voight and Wieder [6] and Witrouw et al [18] is an estimate based on data from Karst and Willet [30] and Witrouw et al [13]. 4. Small study bias: Begg's test p = 0.73, Egger's test p = 0.11.