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A Controlled Trial of Weight-Bearing Versus Non-Weight-Bearing Exercises for Patellofemoral Pain

Patellofemoral pain syndrome (PFPS) is a common ailment of the knee. It is one of the most frequently presenting complaints in orthopaedic and sports medicine clinics, both in the athletic and nonathletic population. PFPS is characterized by diffuse retropatellar and peripatellar pain resulting from physical and biomechanical changes altering the stress and loading of the patellofemoral joint. Symptoms are exacerbated by activities that strengthen the quadriceps muscle is often prescribed as part of the plan of care. Quadriceps strengthening exercises can be performed as non-weight-bearing single-joint exercises (SJNWBE) or weight-bearing multiple-joint exercises (MJWBE). The clinical use of MJWBE has significantly increased during the past 2 decades. One of the reasons these exercises are commonly used in rehabilitation is that they are similar to many functional movements. In addition, it has been suggested that MJWBE are safer than SJNWBE because the former place lesser stresses on the patellofemoral joint in the functional range of motion of the Itnee. Therefore, patients with PFPS may tolerate M.TWBE better and consequently exhibit better functional results after such a rehabilitation program. Despite the potential significance of quadriceps exercises in the rehabilitation of PFPS, only limited research literature comparing weight-bearing and nonweight-bearing strengthening programs in individuals with PFPS is available.

In a study by Witvrouw 60 patients participated in a 5-week exercise program consisting of either non-weight-bearing or weight-bearing exercises. Both treatment groups reported a significant decrease in pain, increased muscle strength, and increased functional performance after treatment load the patellofemoral joint, such as stair climbing, squatting, running, and kneeling." Thus, this common condition affects many aspects of daily life. The origin and exact pathogenesis of PFPS are unknown" and there is no clear as sociation between severity of the symptoms and radiologic and arthroscopic findings."

Pilot Study
TEST-RETEST RELIABILITY OF THE main outcome measures of peak isometric knee extension using the Cybex 350 dynamometer (Lumex Corp, Ronkonoma, NY), the modified Kujala scale questionnaire and a visual analogue scale (VAS) for pain during isometric quadriceps contraction and stair ascent and descent were established during the clinical trial. Ten male patients with PFPS, ages ranging from IS to 29 years, were assessed on 2 separate occasions no more than 5 days apart.

Subjects
Forty-five male patients (mean ± SD age, 26.9 t 5.6 years; age range, 18-35 years) with a diagnosis of anterior knee pain, patellofemoral joint syndrome, or patellar maltracking were referred to the Physical Therapy Department at Riyadh Armed Forces Hospital (Riyadh, Kingdom of Saudi Arabia) by an orthopaedic surgeon who recruited the patients for this study after obtaining their consent. All participants were further examined to establish that they met the required inclusion and exclusion criteria, which were based on those used by authors of previous studies. The examination was performed by an experienced physical therapist. The study was approVed by the Riyadh Armed Forces Hospital, Riyadh, Kingdom of Saudi Arabia and The Institutional Ethics Committee of Manchester Metropolitan University, UK.

Testing Procedures
All subjects were tested following standardized procedures prior to the start of the rehabilitation Program and after 6 weeks of training. Testing was conducted by an independent assessor (an experienced physical therapist) blinded to intervention group.

Modified Kujala Questionnaire
A combined subjective and functional evaluation of the knee was made with an adapted version (APPENDIX) of the scoring scale described by Kujala et all' This 0- to 100-point scale, with 100 equaling the best score, was specifically designed for patients with patellofemoral pain, to evaluate pain during stair climbing, squatting, running, jumping, and prolonged sitting with the knees flexed, the presence of a limp, swelling, and subluxation, the amount of quadriceps muscle atrophy and knee flexion range-of-motion deficit, and the need for support when walking.

Exercise Intervention
Patients were then randomly assigned by opening a sealed and numbered envelope to 1 of 3 groups: a control group (n. = 15), the SJNWBE group (n -15), and the MJWBE group (n = 15). The patients in the control group participated only in the testing procedures, and all participants were asked to avoid sports or other pain-provocative activities during the exercise intervention period but to participate in their standard army (clerical and administration) duties.

The intervention for both exercise groups consisted of 6 weeks of exercises performed 3 times per week. For each training session, after a 5-minute static-cycle ergometer ride as a warm-up (50-W resistance), the training was carried out with 2-second rest between repetitionsand a 2-minute rest between sets.

Prior to the start of the intervention, the amount of resistance and the number of sets and repetitions were calculated based on the daily adjustable progressive resistive exercise' technique for each participant. The intervention program was based on the maximum amount of resistance the participant could lift for 6 repetitions (6-repetition maximum {6-P311). At the start of each session, the patients performed a first set of 10 repetitions at 50% of the predetermined 6-RM, followed by a set of 6 repetitions performed at 75% of the 6-RM. For the third set, the patient performed as many repetitions as he was able to do using 100% of the 6- RM as resistance. The number of repetitions used for the third set was used to determine the resistance for the fourth set (TABLE 3). For the fourth set, the patient performed as many repetitions as possible using the new adjusted weight. The number of repetitions performed during the fourth set was used to adjust the 6-RM for the next session (TABLE 3). The physical therapist was present during the exercise regimen to monitor that pain-free training occurred. If the load level elicited pain it was immediately decreased.

Patients in the SJNWBE group performed the knee extension exercises in a seated position from 90° of knee flexion to full extension and all subjects were able to complete the 6-week training program. Patients in the MJWBE group performed the leg press exercise in a seated position from 90° of knee flexion to full extensionand all subjects were able to complete the 6-week training program.

Data Analysis
A factorial analysis of variance (AiNOVA) (group, 3 levels; time, 2 levels) was used to compare the baseline results with the 6-week assessments across the 3 groups for each of the outcome measures. Statistical significance was set at P<.05. Paired t tests were used to evaluate specific differences and Bonferroni corrections applied. All statistical tests were performed using SPSS Version 11.0 software.

RESULTS
THE 3 GROUPS WERE OF SIMILAR AGE, height, and body mass (P>.05). The 3 groups were similar at baseline for all outcome measures of function, knee extension strength, and pain (P>.05). All 45 participants completed the study.

Subjective and Functional Assessment
The 2-way ANOVA for the modified Kujala scale (FIGURE 1) indicated a significant interaction (P - .04) for group (SJNWBE, MJWBE, control) by time (preintervention, postintervention). Paired t tests (with Bonferroni corrections) indicated that both the SJNWBE and MJWBE groups demonstrated a significant increase in function (Kujala score) after 6 weeks for the SJNWBE group (P = .03) and for the MJWBE group (P .01). No statistically significant difference was found between the 2 exercise groups postintervention (P>.05). Postintervention, scores on the modified Kujala scale were significantly better for the SJNWBE and MJWBE groups as compared to the control group (PC.001). The control group had a statistically significant decrease in function (Kujala score) over time (P .03).

Knee Extension Strength
The 2-way ANOVA for isometric knee extension strength (FIGURE 2) indicated a significant interaction (P = .03) for group (.5MM-13E, MJWBE, control) by time (preintervention and postintervention). Paired tests revealed that isometric quadriceps muscle peak force increased significantly over tune for the SJNWBE and MJWBE groups (P - .01 and P = .005, respectively). There was no change in knee extension strength for the control group over time (P>.05). Postintervention there were no significant differences between the 2 exercise groups (P>.05), but knee extension strength was greater for both exercise groups than it was for the control group.

Pain During Knee Extension Strength Test
The 2-way ANOVA for the amount of pain perceived during testing of isometric knee extension strength (FIGURE 3) indicated a significant interaction (P = .04) for group (SJNWBE, MJWBE, control) by time (preintervention and postintervention). Paired t tests showed a statistically significant pain reduction in both SJNWBE and NIJWBE, groups (P .005 and P = .025, respectively) following the intervention. No preintervention-postintervention differences were noted for the control group (P>,05). Differences between the 2 exercise groups were not statistically significant (P>.05). Postintervention, both exercise groups had significantly lower level of pain compared to the control group (SJNWBE, P = .015; MJWBE, P = .005).

Pain During Step-up and Step-down Test The 2-way ANOVA for the amount of pain during the step-up and step-down task (FIGURE 4) indicated a significant interaction (P = .03) for group (SJNWBE, MJWBE, control) by time (preintervention, postintervention). Paired tests showed that both exercises group had a significant decrease in pain postintervention (P<.001). However, there was no significant difference between the 2 exercise groups (P>.05). There was no change in pain level in the control group from preintervention to postintervention (P>.05). Postintervention, both exercise groups had lower pain level than the control group (SJNWBE, P = .004; MJWBE, PC.001).

DISCUSSION
IT WAS HYPOTHESIZED THAT THE weight-bearing quadriceps exercise (seated leg press) would be better than a non-weight-bearing strengthening exercise (seated knee extension) to strengthen the quadriceps muscle, decrease pain, and improve function in patients with PFPS. The results of this study revealed that both exercise groups showed a significant and similar improvement in pain, overall function, and knee extension strength after a 6-week intervention. In contrast, the control group showed a significant decrease in function and no change in muscle strength and pain. The results of the study are in agreement with earlier findings of Clark, Hazneci and Witvrouw who all demonstrate an exercise group to have a superior outcome to that of a control (nonexercise) group.

The association between the strength increase, improvement in function, and a decrease in pain observed in this study may be of great importance. This relationship between locomotor function and quadriceps muscle strength was already emphasized by Stiene who along with Heintjes et all° concluded that strengthening exercises can be considered a very effective intervention to restore function in patients with patellofemoral pain. Witvrouw et al24 supported this conclusion by identifying a strong correlation between restoration of quadriceps muscle strength and the functional improvements in patients with patellofemoral pain. Therefore, as this study and others have indicated both weight-bearing and non-weight-bearing quadriceps exercise are equally effective in the treatment of patellofemoral pain,1° they both should be incorporated into rehabilitation programs,14 a conclusion further supported by the overall findings of the systematic (Cochrane) review conducted by Heintjes.

CONCLUSIONS
THIS STUDY DEMONSTRATES THAT there was a similarly significant improvement in pain, knee extension strength, and functionality in patients with PFPS as a result of a 6-week weight-bearing (leg press) or non-weight-bearing (seated knee extension) knee extension strengthening program. As a result of this study, it could be concluded that both weight-bearing and non-weight-bearing quadriceps-strengthening exercises are equally effective for the management of individuals with PFPS.

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