Hip Range of Motion Measurements
Range of motion measurements were hip flexion, extension, adduction, abduction, internal rotation, and external rotation. Internal and external rotations were measured with the limb at both 0 and 90 degrees of flexion. The pelvis was secured to the examination table with a pelvic strap to minimize confounding pelvic motion or tilt during each measurement. Each side was measured twice, and the mean value was calculated. Examiner reproducibility of measurement performed on 10 healthy people, and was the ICC (1,1): 0.94 to 0.98.
Muscle Strength Assessment
Isometric hip flexor and extensor, and abductor and adductor muscle strength were measured using a handheld dynamometer (μ-TasMF-01; Anima Co. Tokyo).42 The pelvis was stabilized to the examination table using the aforementioned strap. We measured muscle strength twice and adopted the stronger one as each muscle strength and calculated the body weight ratio. Examiner reproducibility of the measurement was carried out with respect to 10 healthy people, and it was the ICC (1,1): 0.87 to 0.92.
Holding time of the side bridge posture in the involved side to the lower side was measured as the trunk muscle strength.30 It was measured once after performing sufficient practice. The examiner checked deflection of the pelvis, defined as the inability to retain initial proper position with excursions of at least 50% of pelvic width in the AP and vertical directions any time during the 60-second testing period.
Femoral Anteversion Angle
Following the method of the Craig test, the involved lower limbs were placed in 0-degree hip extension and 90-degrees knee flexion in the prone position. A digital camera from the foot of the examination table determined the hip rotation position, where the greater trochanter was most prominent laterally.43 Then, the angle between the vertical line and the tibial long axis of the floor was recorded as the femoral anteversion angle using an image analysis software (Image J, National Institutes of Health, USA).
Examiner reproducibility of the measurement carried out with respect to 10 healthy people and was the ICC (1,1): 0.98.
The differences in each item in the preintervention were evaluated by the unpaired t test. The effect of intervention was evaluated by 2-way analysis of variance before and after the intervention. The main effects of each factor were determined by the multiple comparison method of Bonferroni in all combinations. Analysis was performed using IBM SPSS (version 22; SPSS, Inc, Chicago, Illinois), and the level of significance was set at P < 0.05.
Twenty female patients with a mean age of 45.1 ± 8.8 years (range, 29-55 years) and a mean follow-up period of 128.9 ± 82.0 days (range, 71-388 days) formed the substance of this study. There were 2 cases of combined type FAI, 17 cases of isolated cam-type FAI, and 1 case of isolated pincer-type FAI.
There was no significant difference between the respective trunk training group and control group with regard to sex, mean age, height, weight, body mass index, Tegner activity score, femoral anteversion angle, duration from onset pain to the beginning of intervention, MHHS, Vail hip score, and iHOT12 before any intervention, as shown in Table 2. There was a trend toward less duration of pain in the trunk stabilization group (P = 0.19).
The intertester reliability of radiographic parameters ranged from 0.18 to 0.81 (LCEA, 0.69; Tönnis angle, 0.81; alpha angle, 0.18; Sharp angle, 0.48; FNSA, 0.71) (Table 3). The intratester reliability of radiographic parameters ranged from 0.41 to 0.99 (LCEA, 0.99; Tönnis angle, 0.99; alpha angle, 0.99; Sharp angle, 0.41; FNSA, 0.99). There was no significant difference of all radiographic parameters including LCEA, Tönnis angle, alpha angle, Sharp angle, and FNSA between both the groups, as shown in Table 4.
Physical examination demonstrated a significant improvement in hip flexion in the trunk training group detected as early as 4 weeks after the intervention compared with the control group (Bonferroni post hoc test, P < 0.05), whereas there was no significant differences in other hip ROMs between the cohorts (Table 5).
Hip flexor strength significantly improved at 8 weeks after the intervention compared with preintervention in both the groups. In the trunk training group, hip flexor strength significantly improved from 0.74 ± 0.12 N·m/kg to 0.91 ± 0.23 N·m/kg; in control group, it improved from 0.71 ± 0.16 N·m/kg to 0.87 ± 0.14 N·m/kg (Bonferroni post hoc test, P < 0.05). Hip abductor strength also significantly improved in the trunk training group from 1.01 ± 0.24 N·m/kg to 1.16 ± 0.22 N·m/kg at 4 weeks after the intervention (Bonferroni post hoc test, P < 0.05). Hip extension and adductor strength and postural retention time of the side bridge were not significantly different between the cohorts (Table 6).
Patient-Reported Outcome Scores
Patient-reported outcome scores including iHOT12, Vail hip score, and MHHS were obtained at prerehabilitation and 4 weeks and 8 weeks during the intervention. The mean iHOT12 significantly increased from 49.2 ± 18.4 to 68.0 ± 19.4 at 4 weeks of intervention in the trunk training group (Bonferroni post hoc test, P < 0.01) and to 78.7 ± 22.4 at 8 weeks of intervention (Bonferroni post hoc test, P < 0.05) in the trunk training group. There was no improvement in the control group (Figure 3). The mean iHOT12 also significantly increased at 4 and 8 weeks of intervention in the trunk training group compared with the control group (at 4 weeks, trunk training group: 68.0 ± 19.4; control group: 52.8 ± 22.7; P < 0.05: at 8 weeks, trunk training group: 78.7 ± 22.4; control group: 53.0 ± 22.3; P < 0.01) (Figure 3).
The mean Vail hip score significantly increased from 58.9 ± 12.8 to 73.4 ± 17.4 at 4 weeks of intervention in the trunk training group (Bonferroni post hoc test, P < 0.01) to 81.6 ± 18.5 at 8 weeks of intervention (Bonferroni post hoc test, P < 0.01) in the trunk training group. The mean Vail hip score in trunk training group was significantly higher than that in the control group at 8 weeks (trunk training group: 81.6 ± 18.5; control group: 61.1 ± 11.6 points; P < 0.05) (Figure 4).
The mean MHHS significantly improved from 78.5 ± 13.0 to 90.7 ± 11.1 at 4 weeks (Bonferroni post hoc test, P < 0.01) and to 95.0 ± 9.3 points at 8 weeks (Bonferroni post hoc test, P < 0.01) in the trunk training group, although there was no statistically significant difference in MHHS between cohorts at 4 and 8 weeks after the intervention. There was no improvement in the control group (Figure 5).
After the intervention, 4 patients of control group and 7 patients of trunk training group were able to return their previous activities without pain. The other 9 patients (3 from trunk training group and 6 from control group) were unable to completely return to sports activities because of residual hip pain. However, 4 (1 from trunk training group, 3 from control group) of these 9 patients had no symptoms with daily life activities after the intervention. Regarding sports activities, these 9 patients continued cessation of any aggravating activities during the intervention and after the intervention because of residual pain.
To our knowledge, this is the first report of the effect of trunk training on hip ROM, hip muscle strength, and clinical outcome in female patients with symptomatic FAI. In this study, we demonstrated that trunk muscle exercise, when added to hip and pelvic girdle exercise, significantly improved (1) hip ROM, specifically hip flexion, (2) hip strength in flexion and abduction, and (3) PRO scores (Vail hip score and iHot-12) compared with control group with hip muscle exercise only. These findings support the addition of trunk muscle training exercises to a conservative program for female FAI patients.
A recent systematic review demonstrated that physiotherapy and patient education can be effective for managing symptoms of patients with FAI.17 In this review, however, there were few studies detailing the specific treatment regimens. In addition, Yazbek et al28 reported that physical therapy comprising hip and trunk stabilization, correction of hip muscle imbalances, and biomechanical control were effective in 4 cases with FAI and concomitant labral tear, emphasizing the importance of the dynamic stability of the pelvis. In fact, hip pain in those cases significantly decreased in 2 or 3 weeks after dynamic pelvic stabilization exercise and posture guidance, enabling patients to proceed to the next stage of intervention. Similarly, our findings demonstrated that PRO scores in patients who were in the trunk training group improved beyond those in the control group. Furthermore, significantly improved PRO scores are recognized as early as 4 weeks in the trunk training group, similar to the report of Yazbek et al.28
Among a wide variety of trunk stabilization exercises, rehabilitation of the transverse abdominis muscle has been defined as critical for pelvic stabilization.44 Okubo et al45 demonstrated that increased transverse abdominis activity is observed during the plank exercise and bird dog exercise. Thus, we selected plank exercise and bird dog exercise for the trunk stabilization protocol.
On the other hand, the side bridge exercise is also one of the most effective trunk stabilization training exercises.44,46 Side bridging has been demonstrated to be an effective and reproducible trunk stabilization exercise,30,44,47 but difficulty in maintaining proper posture because of pain and dysfunction limits its utility. Hence, we opted to not add the side bridge to our trunk stabilization protocol.
Regarding hip ROM, there was significantly more improvement in flexion in the trunk training group compared with the control group as early as the 4-week time point. Moreside and McGill48 reported that hip ROM improved significantly after the 6-week intervention of motor control exercises for the hip and trunk, such as bird dog and plank, and core endurance exercises compared with the control group. They suggested that the proximal stiffness might affect distal mobility. Hodges and Moseley49 demonstrated that the deep muscles (eg, transverse abdominis) contribute to important spinopelvic stabilization, whereas superficial muscles (eg, biceps femoris and hip adductors) normally do not. However, if the deep muscles are weak, the superficial muscles play a significant compensatory role. Thus, by strengthening the trunk muscles, the superficial pelvic stabilizing muscles (that were compensating for this weakness in female patients with FAI) may become less spastic and painful compared with the control group. This may have contributed to the improved hip flexion range observed in this study with the addition of trunk stabilization. Hip flexor and abductor strength were also significantly more improved in trunk training group than in the control group.
There were significant differences between the trunk training group and the control group at 4 and 8 weeks after treatment in iHOT12 and at 8 weeks after treatment in Vail hip score. However, there were no differences in MHHS. Although PRO scores are useful in the assessment of pain and function,50,51 they vary in their ability to detect athletic or more strenuous function. The iHOT12 has been validated as an instrument to measure health-related quality of life in young, active patients with hip disorders.51 The Vail hip score also assesses hip function in active patients, measuring pain with squatting or during sports activities, or when excessive load is generated in the hip. In contrast, the MHHS assesses primarily sedentary activities of daily living and pain and function during walking, and it has a ceiling effect for more rigorous activities typical of patients with FAI. This may explain our findings of improved iHOT12 and Vail hip scores, which might not have been detected with the MHHS.
We acknowledge that although trunk stabilization significantly benefits short-term clinical outcome in the nonoperative setting, we may not conclude that nonoperative treatment of symptomatic FAI is preferable to surgical treatment. Moreover, the findings of this study may have implications and application beyond nonoperative management. Trunk stabilization may provide incremental improvement to postoperative rehabilitation protocols, which merits further investigation.
There were some limitations for this pilot study including the small number of cases and short-term follow-up. Larger cohorts with longer follow-up may support stronger or different conclusions. Another limitation is that a power analysis was not performed for appropriate sample size. Although this prospective randomized study exhibited no statistically significant differences between cohorts, there was a trend suggesting a shorter duration of pain before the initiation of treatment regimens in the trunk stabilization group. Because the duration of pain in the control group is not a parametric data, the difference in median between the trunk training group (167 days) and the control group (456 days) was evaluated by Mann–Whitney U test. The results were not significant (P = 0.19); however, there was a trend toward less duration in the trunk training group, which we consider a study limitation. Male symptomatic FAI patients were also excluded from this study, so the findings of this study cannot be generalized across genders. Regarding trunk muscle strength, a recent cross-sectional study demonstrated that the thickness of the transverse abdominal and internal abdominal muscles in asymptomatic men is significantly greater than those in women.52 To eliminate a gender influence as a confounding variable, we limited this study to women. Further studies with larger numbers of both men and women are needed to evaluate the effects of trunk training on symptomatic hip FAI.
The activity level as measured by the Tegner activity score in the present study is relatively low: 3.1 to 3.3. Future investigation to evaluate the effect of trunk training for high-level athletes is merited. The MHHS has a significant ceiling effect, limiting its ability to assess athletic performance.50 However, we used 2 additional PRO scores with less ceiling effect. This study did not investigate the relative benefit of formal physiotherapy versus a home exercise program that incorporates trunk stabilization. Moreover, this study does not compare any treatment, home treatment, or surgical treatment to the exercise regimen included in our rehabilitation protocol. It also does not show patients to be completely asymptomatic following rehabilitation, comment on the return to their sports and daily activities, nor does it report patients' ultimate decision for or against surgery ≥2 years after the intervention.
The addition of trunk stabilization to a typical hip rehabilitation protocol improves short-term clinical outcomes and may augment nonoperative and postoperative rehabilitation.
The addition of trunk stabilization exercises to a typical hip rehabilitation program improved short-term clinical outcomes in conservatively managed female patients with symptomatic unilateral FAI.
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Keywords:Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.
femoroacetabular impingement; trunk stabilization exercise; conservative treatment; trunk stabilization