Evaluation of the results of closed kinetic chain exercises applied in the conservative treatment of patellofemoral pain syndrome by means of shear wave elastography: A randomized controlled trial

Abstract

Purpose

Non-selective closed kinetic chain exercises (NSKCE) and or selective closed kinetic chain exercises (SCKCE) has been shown to increase Vastus medialis obliquus (VMO) muscle power in patellofemoral pain syndrome (PFPS). However, the superiority of the exercises to each other has not been shown. This study aimed to evaluating the effects of different exercises on the stiffness of the VMO and vastus lateralis (VL) muscles, pain management, functional scores, and thigh circumferences.

Methods

One hundred 60 knees of 80 patients followed up in our outpatient clinic between December 2016 and February 2018 were included in the study. Patients were divided into two groups as 40 patients with single-sided PFPS (20 male and 20 female patients) and 40 healthy controls (20 male and 20 female patients). The patients in each group were divided into subgroups according to NSCKCE or SCKCE. VMO and VL muscles were measured by shear wave elastography (SWE) before and after a 6-weeks therapy.

Results

There was a significant decrease in Visual Analog Scale (VAS) score while a significant increase was found in Lysholm Knee Scale (LKS), however, no statistically difference was found between the two exercise groups in PFPS patients. The effect of both exercises on pain and functional improvement was similar.

Conclusion

Decrease in VAS scores, increase in LKS scores, increase in thigh circumference measurements, and increase in the stiffness of VMO and VL muscles were observed in both groups who received SCKCE and NSCKCE on PFPS patients.

Trial Registration

Study registered at ClinicalTrials.gov (registration number: NCT05427357).

Design

Randomized controlled trial.

Keywords

Elastography exercises non-selective pain patellofemoral

Highlights

- Pre-exercise VMO contraction measurements of the patients in PFPS diseased side knee group were significantly lower than those of healthy control group and PFPS healthy side knee group.

- In the healthy control group, NSCKCE was superior to SCKCE in terms of the increase in thigh circumference.

- Decrease in VAS scores, increase in LKS scores, increase in thigh circumference measurements, and increase in the stiffness of VMO and VL muscles were observed in healthy control and PFPS groups who received SCKCE and NSCKCE.

Introduction

Patellofemoral pain syndrome (PFPS) is one of the most common reason of anterior knee-pain.¹ Etiology of PFPS is multifactorial and includes excessive use of extensor component, patellar instability, chondral and osteochondral injuries.^2,3 Weakness and imbalance of quadriceps muscles are also considered to one of the causes of PFPS.^4–6

The balance between vastus medialis obliquus (VMO) and vastus lateralis (VL) is an important factor for patellar tracking. This balance also plays an important role in patellar stabilization. The imbalance mostly develops due to the atrophy of VMO, hypoplasia of VMO or deficiency of VMO caused by motor inhibition.^6–8 In a study in which evaluations were made by shear wave elastography (SWE), the VMO muscle was shown to be significantly weaker in PFAS patients than in healthy subjects.⁹ Due to its important role in the movement of patella, especially strengthening the quadriceps muscle and more importantly strengthening the VMO muscle are accepted as the mainstay treatment of PFPS.⁸

Superiority of the strengthening exercises described for VMO in particular on each other have not been proven yet.^10–12 Traditional exercise therapy has been shown to be superior to electromyographic biofeedback therapy.¹³ Closed kinetic chain exercises (CKCE) among traditional exercise treatments are more frequently preferred in the treatment of PFPS because they cause less stress on the patellofemoral joint.^14–17 Muscle contraction and VMO/VL ratio were found to be maximum in CKCE performed at 60 degrees of flexion, and it was also found to be more effective than open kinetic chain exercises (OKCE).¹⁸ Although CKCE is recommended in most studies in the treatment of PFPS, in a study with a 5 years follow-up period, it was reported that the long-term results of both exercise types were similar in the evaluation made with VAS scores alone.¹²

It has long been discussion whether selective closed chain exercises (SCKCE) or non-selective closed chain exercises (NSCKCE) are more effective in selective activation of the VMO muscle.^11,19–21 Although there are studies in the literature reporting that NSCKCE is superior to SCKCE, there are also studies that claim the opposite and even report that they are not superior to each other.^11,19,22 In the literature review to demonstrate the effectiveness of PFAS exercise therapy, mostly VAS, Lysholm Knee Scale, Functional Index Questionnaire (FIQ), McGill Pain Questionnaire (MPQ), Modified Functional Index Questionnaire, Short Form-36 Health Evaluation questionnaire, Patient Generated Index, Quality of Life questionnaire scoring systems are used. Although rarely, techniques that require more detailed evaluation such as electromyographic muscle data analysis and SWE have been used.^{8,11,12,18,19,22,23} In our study, SWE, VAS, Lysholm Knee Scale and thigh circumference measurement were used to evaluate the effectiveness of NSCKCE and SCKCE exercises.

There is still no consensus on the treatment of PFPS. One of the main reasons for this controversial situation may be due to the lack of classification systems.²⁴ Although there is a lot of information in the literature about the exercise treatment of PFPS, there are hardly any controlled randomized studies on which exercise is more effective. Our research motivation was to determine the difference between NSCKCE and SCKCE exercise protocols in PFPS using SWE and other parameters with a randomized prospective study. We thought that the information we will gain will be useful for physicians, physiotherapists and patients in PFAS exercise therapy.

Materials and methods

This randomized controlled clinical trial included 40 patients (20 male and 20 female) who were admitted to our hospital and who were clinically diagnosed with single-sided PFPS and 40 healthy controls (20 male and 20 female). The participants in each group were randomized into subgroups according to diseased side of the PFPS group (40 knees), healthy side of the PFPS group (40 knees) and both side of the healthy control group (80 knees). This study is organized according to the CONSORT guidelines. Participants were allocated into two treatment groups: NSCKCE and SCKCE. Randomization was applied with random-number generator (Research Randomizer. Version 4.0). Only one of the authors was aware of randomization. Patient were blind to the relevant group. NSCKCE and SCKCE exercises were applied for 6 weeks in all groups. Thigh circumference measurement was performed 5-10 cm above the upper pole of the patella. In addition, evaluation was made with VAS and LKS.²⁵ Written informed constent was taken from each patient. This study is in line with the Declaration of Helsinki. Approval was obtained by the Local Ethics Committee (17/07/2016-258,642).

Shear wave elastographic ultrasound evaluation

VMO and VL muscles of the participants were measured with SWE just before the therapy and 6 weeks after therapy in hospital. These measurements were performed on the participants in both groups at relaxation and contraction phases of quadriceps muscle before the exercises and after the end of exercises. Values of elastographic analysis on VMO and VL were expressed in kilopascal (kPa).^9,26 Shear wave elastographic ultrasound (ShearWave ™ elastography and 4-15-MHz transducer Supersonic imagine, Aixen-Provence, France) was used in the analysis. The ultrasound probe was placed at the central point of VMO and VL muscles. This point for VMO was determined as approximately 4 cm superior and 3 cm medial to the superomedial border of patella. This point for VL was determined as 10 cm superior and 6 cm lateral to the superolateral border of patella.¹⁹

The measurements were firstly started at relaxation phase. Then, measurements at the contraction phase were performed while the participant was tucking the folded towel placed at the popliteal region and contracting the quadriceps muscle. Ultrasound scanning device gives quantitative values through making rectangular-shaped color flow mapping in the scanned area. Maximum, minimum, standard deviation and mean elasticity values of the muscle were analyzed in kPa through being measured from the region that revealed quantitatively the same values and that was homogenously colored with circular-shaped color box. All the data obtained were recorded into the hard disk of the scanner. This analysis was performed for both the participants diagnosed with PFPS and the healthy controls. Measurements at the relaxation phase were performed while popliteal region was touching to the stretcher. Measurements at the contraction phase were performed during full contraction of quadriceps muscle and when the knee was in the position of full extension. The knee contracted for 5 s until it reached full extension and then slowly relaxed and the measurements were performed at the end of 5 s at maximum contraction. Participants were rested for 5 s between each contraction. The values of elastographic analysis on the muscle were recorded in kPa. Statistical analysis was based on the mean elasticity values. All the measurements were performed 3 times and the mean value of these measurements was recorded.¹⁹

Exercise program

Simultaneous bilateral exercises were applied to the patients in order to prevent a strength asymmetry between the right and left quadriceps muscles. In the study, 20 participants diagnosed with PFPS received closed kinetic chain double-leg semi-squat exercises and the other 20 participants received closed kinetic chain double-leg semi-squat exercises with hip adduction. Similarly, 20 healthy controls received closed kinetic chain double-leg semi-squat exercises and the other 20 healthy controls received closed kinetic chain double-leg semi-squat exercises with hip adduction. The participants received a 6-weeks exercise therapy; 3 days a week at hospital with the guidance of an orthopaedic surgeon and 2 days a week at home. No other therapy in addition to the exercise therapy was applied.

Non-selective closed kinetic chain double-leg semi-squat exercise

In this exercise, the standing patient leans his or her back against the wall and slides down the wall until the knees are about 45° flexed. Daily program was determined as five sessions and 10 repeats. The knee stayed at flexion position for 10 s in each repeat, which aimed the contraction of quadriceps muscle. There is a relaxation period for 5 s between each repeat.

Selective closed kinetic chain double-leg semi-squat exercise with hip adduction

In this exercise, the standing patient leans his or her back against the wall, forces the knees for adduction by squeezing the pillow placed between the knees and slides down the wall until the knees are about 45° flexed.^22,27 Daily program was determined as five sessions and 10 repeats. The knee stayed at flexion position for 10 s in each repeat, which aimed the contraction of quadriceps muscle. There is a relaxation period for 5 s between each repeat.

Inclusion and exclusion criteria

As diagnostic and inclusion criteria, the findings of Insall et al.’s²⁸ study were used. Patients who were diagnosed with PFPS, anterior knee pain lasting longer than 6 weeks and who had at least two of the following conditions; Pain on the back of the patella with compression, pain during isometric quadriceps contraction when the knee is slightly flexed and suprapatellar resistance is applied, pain with direct pressure on the patella when the knee is in full extension and pain on resistant knee extension, and who signed the written informed consents by accepting to participate in the study were included in this study. The conditions for healthy controls to be included in the study were as follows: not having been previously diagnosed with clinically detected PFPS, detection of significant patellofemoral joint cartilage damage in MR images taken during routine controls of patients, not previously having problems with hip or knee, not having bursitis of hip or knee circumference, tendinitis, Osgood-Schlatter Syndrome, traumatic hip or knee injuries, osteoarthritis, plica syndrome or Sinding- Larsen-Johansson syndrome, not having received a knee operation, not having meniscus lesions, ligamentous instability, spinal pain, chondral lesion, patellar tendon pathology, distraction apophysitis of knee circumference or patellar subluxation/dislocation and signing the informed consent form by accepting to participate in the study.

Statistical analysis

NCSS (Number Cruncher Statistical System) 2007 Statistical Software (Utah, USA) program was used for statistical analyses. In addition to descriptive statistical methods (mean, standard deviation, median, frequency, ratio, minimum and maximum), Student t test was used in two-group comparisons of the variables revealing normal distribution in the comparison of quantitative variables and Mann Whitney U test was used in two-group comparisons of the variables revealing non-normal distribution while evaluating the study data. One-Way Anova test was used in comparisons with variance homogeneity in three and more groups which were normally distributed and Bonferroni test was used in the detection of the group causing the difference. Welch test was used in comparisons without variance homogeneity and Tamhane test was used in the detection of the group causing the difference. Kruskal Wallis test was used in comparisons of three and more groups which were not normally distributed and Bonferroni-Dunn test was used in the detection of the group causing the difference. Paired Samples t test was used in intra-group evaluations of normally distributed variables and Wilcoxon Signed-Ranks test was used in intra-group evaluations of non-normally distributed variables. Pearson Chi-Square test was used in the comparisons of qualitative data. Spearman Correlation Analysis was used in the evaluation of the relationships among the variables. Significance was accepted as minimum p < 0.05.

Results

Ages of the participants in the study ranged from 17 to 60 and their mean age was 34.43 ± 10.76 (Table 1).

Table 1.

Evaluation of demographic characteristics by groups.

		Healthy control Group (n = 40)	PFPS Group (n = 40)	^a p
		Mean ± SD (Median)	Mean ± SD (Median)	^a p
Age (Year)		29.08 ± 3.78 (28.5)	39.78 ± 12.71 (40)	0.001**
Height (cm)		173.85 ± 7.18 (173)	171.48 ± 10.06 (172)	0.228
Weight (kg)		71.3 ± 12.69 (75)	72.45 ± 11.29 (75)	0.670
BMI (kg/m2)		23.48 ± 3.24 (23.8)	24.57 ± 2.47 (24.5)	0.094
Follow-up period (day)		45.70 ± 2.99 (45)	45.43 ± 2.26 (45)	0.644
		n (%)	n (%)
Gender	Female	20 (50.0)	20 (50.0)	^b 1.000
Gender	Male	20 (50.0)	20 (50.0)	^b 1.000

Pearson Chi-square test, Studentt test **p < 0.01.

Pre-exercise and post-exercise VAS pain scores and LKS scores of the PFPS knee group were evaluated. A decrease in VAS pain scores and increase in LKS scores were observed both in the group who received SCKCE and in the group who received NSCKCE. When the differences between pre-exercise and post-exercise VAS pain scores and LKS scores of the groups who received SCKCE and NSCKCE exercise were evaluated, no statistical difference was found (p = 0.528; p > 0.05), (p = 0.169; p > 0.05), (Table 2).

Table 2.

Evaluation of pre-exercise and post-exercise VAS and LKS measurements according to the state of SCKCE/NSCKCE.

PFPS group		NSCKCE (n = 20)	SCKCE (n = 20)	^a p
PFPS group		Mean ± SD (median)	Mean ± SD (median)	^a p
VAS	Pre-exercise	5.60 ± 1.05 (6)	4.85 ± 1.09 (5)	0.031*
	Post-exercise	3.05 ± 1.23 (3)	2.45 ± 1.19 (2)	0.091
	^b p	0.001**	0.001**
	Difference between Pre-E and Post-E	−2.55 ± 0.94 (−3)	−2.40 ± 0.82 (−2)	0.528
LKS	Pre-exercise	63.30 ± 9.26 (64)	72.65 ± 4.63 (72)	0.001**
	Post-exercise	72.95 ± 7.77 (75)	80.10 ± 4.68 (80)	0.003**
	^b p	0.001**	0.001**
	Difference between Pre-E and Post-E	9.65 ± 5.59 (7.5)	7.45 ± 3.76 (7)	0.169

^aMann Whitney U test.

^bWilcoxon Signed Ranks test, *p < 0.05, **p < 0.01, Post-E: Post-exercise and Pre-E: Pre-exercise.

A statistical difference was found among the pre-exercise measurements of VMO contraction and relaxation in healthy control, PFPS diseased side and PFPS healthy side groups. Pre-exercise VMO contraction measurements of the patients in PFPS diseased side knee group were significantly lower than those of healthy control group and PFPS healthy side knee group (p = 0.001; p = 0.001; p < 0.01) (Table 3). Increase in stiffness of the VMO with SCKCE was not more than that with NSCKCE (p = 0.766; p > 0.05) (Table 4).

Table 3.

Elasticity measurement results for VMO and VL muscles in the resting and contraction phase before and after exercises of study participants.

		HCG (RS + LS) (n = 80)	PFPS group (DS) (n = 40)	PFPS group (HS) (n = 40)	^a p	Post Hoc
		Mean ± SD (median)	Mean ± SD (median)	Mean ± SD (median)	^a p	Post Hoc
VMO relaxation	Pre-exercise	9.04 ± 1.61 (8.8)	8.73 ± 1.14 (8.8)	8.41 ± 1.15 (8.4)	0.048*	1>3
	Post-exercise	11.42 ± 2.00 (11.4)	10.24 ± 1.17 (10.2)	10.27 ± 1.26 (10.1)	0.001**	1>2, 1>3
	^b p	0.001**	0.001**	0.001**
	Difference between Pre-E and Post-E	2.38 ± 1.48 (2.3)	1.52 ± 0.81 (1.6)	1.87 ± 1.12 (1.6)	^c 0.004**	1>2
VMO contraction	Pre-exercise	194.25 ± 59.18 (202.9)	152.13 ± 42.69 (145.8)	192.91 ± 50.71 (191.7)	0.001**	1>2, 3>2
	Post-exercise	243.81 ± 52.60 (244.6)	193.16 ± 47.70 (177)	247.39 ± 53.62 (247.8)	0.001**	1>2, 3>2
	^b p	0.001**	0.001**	0.001**
	Difference between Pre-E and Post-E	49.56 ± 22.74 (46.4)	41.03 ± 25.29 (36.3)	54.48 ± 49.21 (48.6)	^c 0.048*	1>2
VL relaxation	Pre-exercise	9,05 ± 1,37 (8,9)	8,66 ± 0,95 (8,6)	8,53 ± 0,85 (8,5)	0,040*	1>3
	Post-exercise	11,29 ± 1,83 (11,3)	10,39 ± 1,19 (10,4)	10,68 ± 1,65 (10,3)	0,007**	1>2
	^b p	0,001**	0,001**	0,001**
	Difference between Pre-E and Post-E	2,24 ± 1,58 (2,2)	1,73 ± 1,05 (1,6)	2,15 ± 1,69 (2,2)	^c 0,232	-
VL contraction	Pre-exercise	194,19 ± 54,95 (185,5)	191,35 ± 46,48 (195,5)	191,95 ± 50,26 (190,1)	0,952	-
	Post-exercise	244,85 ± 51,11 (240,5)	242,42 ± 44,63 (244,5)	242,73 ± 48,00 (240,1)	0,957	-
	^b p	0,001**	0,001**	0,001**
	Difference between Pre-E and Post-E	50,66 ± 35,11 (42,7)	51,06 ± 29,12 (51,2)	50,78 ± 35,90 (44,1)	^c 0,906	-

The unit for the mean elasticity is kPa (kilopascal),

^aOneway ANOVA Test

^bPaired Samples T Test

^cKruskal Wallis Test

*p < 0.05, **p < 0.01, DS: Diseased side, HCG: Healthy control group, HS: Healthy side, LS: Left side, Post-E: Post-exercise, Pre-E: Pre-exercise RS: Right side, VL: Vastus lateralis, VMO: Vastus medialis obliquus.

Table 4.

Elasticity measurement results for VMO and VL muscles in the resting and contraction phase before and after exercises of NSCKCE and SCKCE.

PFPS knee group		NSCKCE (n = 20)	SCKCE (n = 20)	^a p
PFPS knee group		Mean ± SD (median)	Mean ± SD (median)	^a p
VMO relaxation	Pre-exercise	8.6 ± 1.22 (8.7)	8.86 ± 1.06 (8.9)	0.485
	Post-exercise	10.27 ± 1.1 (10.3)	10.22 ± 1.27 (10.1)	0.905
	^b p	0.001**	0.001**
	Difference bet boween Pre-E and Post-E	1.67 ± 0.92 (1.9)	1.37 ± 0.67 (1.4)	^c 0.310
VMO contraction	Pre-exercise	150.34 ± 43.16 (137.6)	153.93 ± 43.26 (154.6)	0.794
	Post-exercise	192.08 ± 48.52 (182.5)	194.24 ± 48.1 (176.1)	0.889
	^b p	0.001**	0.001**
	Difference between Pre-E and Post-E	41.75 ± 30.42 (35.3)	40.31 ± 19.64 (36.3)	^c 0.766
VL relaxation	Pre-exercise	8,64 ± 0,67 (8,7)	8,69 ± 1,19 (8,5)	0,871
	Post-exercise	10,26 ± 0,99 (10,4)	10,53 ± 1,37 (10,4)	0,487
	^b p	0,001**	0,001**
	Difference between Pre-E and Post-E	1,63 ± 0,96 (1,5)	1,84 ± 1,15 (1,6)	^c 0,607
VL contraction	Pre-exercise	190,34 ± 43,62 (189,7)	192,37 ± 50,29 (214,5)	0,892
	Post-exercise	243,41 ± 46,86 (243,9)	241,42 ± 43,48 (245,5)	0,890
	^b p	0,001**	0,001**
	Difference between Pre-E and Post-E	53,08 ± 34,41 (47)	49,05 ± 23,41 (55,6)	^c 0,914

Healthy control group		NSCKCE (n = 20)	SCKCE (n = 20)	^a p
Healthy control group		Mean ± SD (median)	Mean ± SD (median)	^a p
VMO relaxation	Pre-exercise	8,14 ± 0,64 (8,2)	8,68 ± 1,46 (8,7)	0,138
	Post-exercise	9,94 ± 1,04 (9,9)	10,61 ± 1,40 (10,3)	0,091
	^b p	0,001**	0,001**
	Difference between Pre-E and Post-E	1,80 ± 1,07 (1,6)	1,94 ± 1,20 (1,7)	^c 0,725
VMO contraction	Pre-exercise	192,49 ± 39,41 (190,9)	193,34 ± 61,03 (191,7)	0,959
	Post-exercise	248,42 ± 51,05 (246,1)	246,37 ± 57,39 (247,8)	0,906
	^b p	0,001**	0,001**
	Difference between Pre-E and Post-E	55,93 ± 64,06 (52,2)	53,04 ± 29,37 (48,6)	^c 0,914
VL relaxation	Pre-exercise	8,43 ± 0,93 (8,4)	8,63 ± 0,77 (8,5)	0,465
	Post-exercise	10,87 ± 1,83 (10,8)	10,49 ± 1,47 (10,1)	0,474
	^b p	0,001**	0,001**
	Difference between Pre-E and Post-E	2,44 ± 1,88 (2,3)	1,86 ± 1,47 (2)	^c 0,261
VL contraction	Pre-exercise	194,23 ± 33,12 (194,2)	189,68 ± 63,85 (171,3)	0,780
	Post-exercise	242,04 ± 45,99 (237)	243,42 ± 51,13 (243)	0,929
	^b p	0,001**	0,001**
	Difference between Pre-E and Post-E	55,93 ± 64,06 (52,2)	53,04 ± 29,37 (48,6)	^c 0,317

The unit for the mean elasticity is kPa (kilopascal)

^aStudent-t test

^bPaired Samples t test

^cMann Whitney U test

**p < 0.01, Post-E: Post-exercise, Pre-E: Pre-exercise, VL: Vastus lateralis, VMO: Vastus medialis obliquus.

In the evaluation of changes in pre-exercise and post-exercise thigh circumference in the healthy control group, a statistical difference was found between the values of change. Difference values of NSCKCE group were significantly higher than those of SCKCE group (p = 0.001; p > 0.01). In the evaluation of changes in pre-exercise and post-exercise thigh circumference measurements in the PFPS diseased side knee group and PFPS healthy side knee group, no statistical difference was found between the values of change according to the SCKCE and NSCKCE groups (p = 0.606; p > 0.05), (p = 0.251; p > 0.05) (Table 5). However, although this difference was not statistically significant in PFPS healthy side and PFPS diseased side knee groups, the changes in pre-exercise and post-exercise thigh circumference in NSCKCE group were higher than those in SCKCE group.

Table 5.

Pre-exercise and post-exercise thigh circumference of healthy control group, PFPS diseased side and PFPS healthy side.

Thigh circumference (cm)		NSCKCE (n = 40)	SCKCE (n = 40)	^a p
Thigh circumference (cm)		Mean ± SD (median)	Mean ± SD (median)	^a p
Healthy control group	Pre-exercise	47,18 ± 7,87 (46)	41,99 ± 5,56 (41)	0,001**
	Post- exercise	49,45 ± 7,60 (48,5)	42,85 ± 5,70 (41,5)	0,001**
	^b P	0,001**	0,001**
	Difference between Pre-E and Post-E	2,28 ± 0,82 (2)	0,86 ± 0,72 (1)	^c 0,001**
PFPS diseased side	Pre-exercise	42,63 ± 4,91 (41,5)	47,70 ± 5,28 (49,5)	0,003**
	Post- exercise	44,55 ± 4,82 (43,5)	49,45 ± 4,97 (51)	0,003**
	^b P	0,001**	0,001**
	Difference between Pre-E And Post-E	1,93 ± 0,69 (2)	1,75 ± 0,97 (2)	^c 0,606
PFPS healthy side	Pre-exercise	43,30 ± 4,52 (41,5)	48,25 ± 5,15 (49,5)	0,003**
	Post- exercise	45,05 ± 4,84 (43,5)	49,65 ± 5,28 (50)	0,007**
	^b P	0,001**	0,001**
	Difference between Pre-E and Post-E	1,75 ± 0,95 (2)	1,40 ± 0,68 (1,5)	^c 0,251

^aStudent-t test

^bPaired Samples t test

^cMann Whitney U test

**p < 0,01, Pre-E: Pre-exercise Post-E: Post-exercise.

Discussion

Decrease in VAS scores, increase in LKS scores, increase in thigh circumference measurements, and increase in the stiffness of VMO and VL muscles were observed in healthy control and PFPS groups who received SCKCE and NSCKCE. In the healthy control group, NSCKCE was superior to SCKCE in terms of the increase in thigh circumference, however, no superiority of selective and non-selective exercises on each other could be revealed in terms of the improvement in these parameters on PFPS patients. There is no consensus in the literature about which exercise would be more effective in the treatment of PFPS. Similar to our findings, according to Syme et al.¹¹ found no significant difference between NSCKCE and SCKCE. They stated that it should not focus on SCKCE in the early phase of rehabilitation, especially in chronic cases. They also questioned the necessity of VMO-specific exercises as they took the extra time and effort. In contrast, Coqueiro et al.²³ recommended that semisquat exercises with hip adduction be used in the conservative treatment of PFPS, as they provide better balance to the medial and lateral portions of the quadriceps muscle. In addition, Miao et al.²² in their study with surface electromyography, stated that the contribution of selective exercises to the development of VMO muscle in PFPS patients is better than non-selective exercises.

Etiology of PFPS is multifactorial. It is considered to be most commonly caused by excessive joint use and malalignments. The balance of the forces affecting patella must be well adjusted for proper development of patellar tracking. These forces are the ones formed by quadriceps muscle, medial and lateral retinaculum, iliotibial band and patellar tendon. The balance among these forces on the patella provides stability and proper development of patellar tracking. The treatment of PFPS is mostly conservative. The key points of the treatment are strengthening, proprioception, increased flexibility and functional training. Exercise programs that include non-steroid anti-inflammatory drugs and aim to strengthen of hip, trunk and knee muscles are considered as the best treatment options.^29–31

Imbalance between VMO and VL may cause the gliding movement of patella in femoral groove to be impaired. Due to its important role in the movement of patella, especially strengthening the quadriceps muscle and more importantly strengthening the VMO muscle are accepted as the mainstay treatment of PFPS.²² In the study by Pattyn et al,⁶ in which they measured VMO size with magnetic resonance imaging, it is not known whether VMO atrophy causes PFPS or whether PFPS causes VMO atrophy, but it is concluded that VMO atrophy is one of the reasons contributing to the development of PFPS. In line with the literature, in our study, pre-exercise VMO contraction measurements in the PFPS group were significantly lower than in the other groups (p < 0,01).

Kinetic chain exercises for knee, which were first defined by Steindler in 1955, are still used in treatments.³² While foot is in constant contact with the ground in closed kinetic chain exercises for knee and it is not in contact with the ground in OKCE. Although both treatment protocols are important, closed chain exercises are the core of treatment in PFPS and have been shown in many studies to be more effective than isokinetic joint isolation and open chain exercises.^14,15,17 In the present study, closed chain semi squat exercises were performed with and without hip adduction. The common protocol of the exercises, which is the protocol used in our study, is five sessions per day, 10 repetitions per session and at least 6 weeks.³³

However, our study has some limitations. In this study, participants who performed selective exercises were instructed about placing a pillow between their knees and forcing their knees for adduction. The possibility that this adduction force may not be effective enough to strengthen VMO should be considered. It should also be considered that studies can be done to strengthen the VMO muscle more specifically by providing the adduction force more effectively. It was thought that more different techniques and equipment could be used in order to make this adduction force to be equal in all patients. In this way, it is possible to strengthen the VMO muscle more effectively with selective exercises. This condition should be considered in future studies on this subject. Matching the younger mean age of the healthy control group with the PFPS group is a limitation, especially in interpreting the SWE results.

Conclusion

Footnotes

Author contributions

The authors confirm contribution to the paper as follows: study conception and design: EH, HB, MRE; data collection: EH, YK, SO, OA, MRE; analysis and interpretation of results: YK, EH, SO, OA, MKO; draft manuscript preparation: YK, EH, SO, OA, MKO, HB. All authors reviewed the results and approved the final version of the manuscript.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Ethical approval

Approval was obtained by the Local Ethics Committee, Cerrahpasa Medical Faculty (17/07/2016-258642).

ORCID iD

Yigit Kultur

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