Patellar chondromalacia is one of the most common syndromes involved in anterior knee pain, especially in youth.1 Patients with patellofemoral joint dysfunction may report pain, atrophy in the vastus medialis (VM) muscles and crepitation.2^–4 Therefore, treatment of this dysfunction, which has been performed conservatively in 80% to 90% of cases,5 is of great importance.

The basis of conservative treatment is strengthening of the VM muscle, which may improve patellar alignment by optimizing muscle performance.6 7 Furthermore, this process may prevent unequal pressure on the patellofemoral joint surface and help to reduce joint inflammation and heal the syndrome by correcting the pattern of load distribution on the joint surface.8^–10 Different techniques have been recommended for VM strengthening, which may be classified as open or closed kinetic chain exercises.[11 12] The general rule in open kinetic chain (OKC) exercises is that the end of the limb moves freely in space. During closed kinetic chain (CKC) exercises, the end of the limb is in contact with a surface or base and the adjacent joints accompany the movement.13 It has been reported that CKC exercises may provide more sensory feedback that might be used to control movement, compared to OKC exercises.14

The common exercise for strengthening the VM muscle in OKC is the straight leg raise (SLR), while the squat is commonly used in CKC.6 15 The results of studies comparing the effects of these exercises are controversial. For example, Witvrouw and colleagues16 showed that there is no difference between these two methods and concluded that both exercises may improve muscle function, relieve pain and optimize performance. They found that CKC exercises produced better results in muscle characteristics and improved signs of disease; however, in a more long-term study, they found neither type of exercise to be preferable.17 Other studies have shown that CKC exercises may improve muscle performance.18 21

According to the results of these studies, it seems that there is no general agreement about the effectiveness of the therapeutic effect of SLR and semi-squat exercises on the patellar chondromalacia syndrome. This study has been designed to investigate the effect of OKC and CKC exercises on patients with patella chondromalacia.

MATERIAL AND METHODS

This study was approved by the ethical committee of the Semnan University of Medical Sciences. Thirty-two female university students suffering from patellar chondromalacia were randomly assigned to one of the two experimental groups (OKC or CKC). Subjects were asked to complete a questionnaire containing the following questions: (a) Do you have any pain during climbing up and down stairs? (b) Do you have any pain after sitting for a long time with the knee flexed? (c) Do you have any problem with knee extension after sitting for a long time with the knee flexed? (d) Does your leg give way during walking? (e) Do you have a history of neuromuscular disease? (f) Do you have a history of musculoskeletal disease? Inclusion criteria included positive answers to questions a to d and a positive Clark test. The subjects who reported a history of neuromuscular or musculoskeletal disorders or who had a deformity in the knee or ankle joint were eliminated from the study.

The statistician for each group drew up a computer-generated randomization list. It was given to the physiotherapy department in a sealed numbered envelope. Once the selected subjects had signed their informed consent forms, they were given the appropriate numbered envelope, which contained the subject’s allocation to either the SLR or semi-squat groups. This information was then given to the physiotherapist to administer the appropriate intervention

Intervention

Subjects in the OKC group followed an SLR exercise programme for 3 weeks (20 times twice daily) with extended knee. The number of exercises was increased by 5 every 2 days, so by the end of the programme (day 21) the subject was performing 70 SLR exercises twice a day. To perform the SLR exercise, the subject should be in a supine position with hip and knee extended in the exercise limb and the nonexercise limb in hip and knee flexion (fig 1A). The subject was asked to lift the lower limb with extended knee until 45° hip flexion and hold it for 3–4 s, and then let it down for a 3–4 s rest.

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Figure 1 (A) Straight leg raise exercise. (B) Semi-squat exercise.

The subjects in the CKC group followed a semi-squat exercise programme for 3 weeks (20 times twice daily). The number of exercises was increased by 5 every 2 days, so by the end of the programme (day 21) the subject was performing 70 semi-squats twice a day. To perform the semi-squat exercise, the subject was asked to stand on the lower limb to be exercised and hold onto a stable surface using their hand, while the nonexercise lower limb was in 90° hip and knee flexion. The subject was then ordered to flex the extended knee 15–20° and hold this position for 3–4 s, then bring it to full extension and remain in this position for a 3–4 s rest (fig 1B).

To ensure the programme was followed, a timetable was given to all subjects and they were asked to tick the appropriate box after each set of exercises.

Measurements

All measurements were performed before the first treatment session, at the end of therapy and 2 weeks following the end of the programme. Measurements included the Q angle, thigh circumference at 5 and 10 cm above patella, degree of anterior knee pain, crepitation, and isometric maximum voluntary contraction force (IMVCF).

In order to measure the Q angle, the subjects were placed in the supine position and asked to relax the quadriceps muscle, then the centre of the patella was marked from the crossing of two horizontal and vertical diameters of patella. Two lines were drawn from the centre of the patella: one line to the anterior superior iliac spine and another line to the tibia tuberosity. The angle between these lines (measured by hand-held goniometer) is considered to be the Q angle, which is normally between 13° and 18°.

The circumference of the thigh 5 and 10 cm from the upper border of patella was measured using a tape measure. The difference between left and right thigh circumference was a measurement of VM atrophy.

Anterior knee pain was measured using a visual analogue scale (VAS), on which the patients could grade their pain along a 10 cm line ranging from 0 ("no pain at all") to 10 ("the most severe pain that I can imagine").

The crepitation sound is usually heard during knee joint movements in the patient with patellar chondromalacia, due to the load of limb and muscle contraction that produces compressing force in the patellofemoral joint and causes crepitation. To assess this sound, the examiner held both sides of patella and the knee was flexed and extended passively; subjects were asked to assist the movement. Any sound heard during this manoeuvre was considered crepitation.

To measure the strength of the quadriceps muscle, a 500 kg load cell, which was connected to a digital monitor (Load cell model BS-7220, Bongshine, Korea), was used with a quadriceps table. The subject was positioned on the quadriceps table so the knee was fixed at 20° of flexion. The trunk was in the upright position and the subject was asked to hold the edge of the table to prevent unwanted movements. The load cell was connected to the distal part of the test leg by a nonstretchable strap at a right angle. After calibration and adjustment of the output to zero, the subject was asked to push the strap by knee extension. The subject was encouraged to produce MIVCF by shouting “more” and “more”. The measurement was repeated three times with a 1 min rest between each record and the maximum value was recorded as the IMVCF.

At the end of each week, we measured the VAS, thigh circumference and crepitation. These were measured again with the Q angle and MIVCF at the end of the exercise programme and 2 weeks later.

Statistics

To compare the effect of SLR versus semi-squat exercises, an intention to treat analysis was used that involved all subjects who were randomly assigned to their group. Student t tests were used to compare the mean changes in the IMVCF, Q angle, thigh circumference and anterior knee pain between the experimental groups.

RESULTS

Thirty-two female university students complaining of patellar chondromalacia were randomly assigned to either the SLR or semi-squat group. Table 1 shows the measured parameters before intervention in both groups; no significant difference was found in the baseline values.

Q angle

Following intervention, the Q angle was reduced in both groups, while the comparison of mean changes showed a significant reduction in the semi-squat group (1.6 (SD 0.4)) compared to the SLR group (0.7 (SD 0.3)) (p = 0.016).

Crepitation

Crepitation was seen in at least 90% of subjects in both groups before the exercise programme began. However, this was reduced to 55.6% in the SLR group and 36.7% in the semi-squat group at the end of the programme. This reduction remained stable 2 weeks after intervention.

MIVCF

After intervention, the comparison of mean changes between experimental groups showed a significantly increased muscle force in the semi-squat group (55.9 N (SD 20.2)) compared to the SLR group (40.1 N (SD 28.5)) (p = 0.01).

Thigh circumference

Figure 2 shows the mean change in thigh circumference 5 and 10 cm above the patella after 3 weeks of intervention in both experimental groups. The results indicate a significant increase of thigh circumference in the semi-squat group at 5 cm (p = 0.002) and 10 cm (p = 0.01) above the patella compared to the SLR group. These results remained unchanged at 2 weeks of follow-up.

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Figure 2 Mean changes of thigh circumference after straight leg raise (SLR) or semi-squat exercises.

VAS

At the end of the 3-week exercise programme, significant pain relief was seen in both SLR (3.1 (SD 1.5)) and semi-squat (2.8 (SD 2.3)) groups, while no significant difference was seen between groups (p = 0.13). This reduction remained unchanged at 2 weeks of follow-up.

DISCUSSION

This study was designed to investigate the effect of open and closed kinetic chain exercises on the treatment of patellar chondromalacia. Our results showed that CKC semi-squat exercises are more effective than OKC SLR exercises. One of the observed effects in the semi-squat group was a reduced Q angle. This was confirmed by Doucette and Child8 who reported that CKC exercises may increase functional ability and activity of VM muscles compared to the vastus lateralis muscle. This increased VM muscle activity may correct the patellar alignment towards medial and reduce the Q angle.6 18

The reduction in crepitation found in our study was also reported by Post (2005) who showed CKC exercise may cause better functional activity and less crepitation compared to the OKC exercises.5 They also showed a greater improvement in muscle strength with CKC exercise, which was confirmed by our results. It seems from these findings that CKC exercises may produce better patellofemoral joint performance during knee flexion and extension.18

Increased thigh circumference after CKC and OKC has not been reported in the literature. However, an increased circumference at 5 and 10 cm above the patella was found in our study, which was accompanied by increased muscle strength after semi-squat exercise. These findings may indicate that CKC exercise is more effective than OKC exercise in producing structural changes in the VM muscle, which is the main muscle controlling the terminal 20° knee extension.2 18

Relief of anterior knee pain has been reported using different exercise protocols such as CKS, OKS or isokinetic exercises.16 19 Such pain relief was also found in our study in both groups. However, long-term rest and avoidance of stressful activities such as stepping up and down may prevent increased pressure on the patellofemoral joint surface, which may account for the same pattern of pain relief seen in both experimental groups.1 5 A similar pattern of pain relief has been reported by other research teams.16 17

Co-contraction of hamstring and quadriceps muscles during CKC exercises has been reported in some studies and it has been suggested that this may improve knee joint performance and so improve patellofemoral joint performance.20 21 While the quadriceps muscles act eccentrically to control knee joint flexion, hamstring muscles act to control hip joint flexion.22 Because the hamstring muscle is a two-joint muscle and its activity affects the knee joint also, the simultaneous activities of quadriceps and hamstring muscles on the knee joint may provide more stability for the knee joint and the patellofemoral joint.9 18 This could be another reason for choosing CKC exercises over OKC exercises. On the other hand, the existence of eccentric activity of quadriceps muscles to control knee flexion may be an effective factor to strengthen the quadriceps muscle by the squat exercise.12 23

CONCLUSION

The results of the present study indicate that CKC exercises within the terminal degrees of knee extension may improve patellofemoral joint performance by increasing quadriceps muscle strength and patellar alignment correction. Our findings showed that semi-squat exercises may be considered as an effective conservative method of treatment for patients with patellar chondromalacia.