Ⅰ Introduction
The number of lumbar spinal fusions performed has increased recently. Posterior lumbar interbody fusion (PLIF) is one of the most commonly performed types of lumbar fusions (Miosz A). PLIF has been reported to support the weight of the vertebral body, recover tension in the annulus fibrosus, fix the vertebral body with instability due to degenerative changes, and decompress lesions associated with diseases (Choi, Y. J., Lee, M. S., Kim, D. H., Kim, Y. G., & Min, K. S., 1996). However, lumbar spinal fusions can cause structural damage, trunk muscle weakness, and chronic low back pain (LBP) (Kawaguchi, Y., Matsui, H., & Tsuji, H., 1994). After lumbar spinal fusion, patients should perform variable exercises, including motor control, aerobic, deep breathing, strengthening, stabilization, and neuro-mobilization exercises; among them, walking is the most important single activity (Miosz A). Early walking exercises yield better results in terms of cognitive function and muscle strength in elderly patients after low back surgeries (Kiribayashi, M., Inagaki, Y., Nishimura, Y., Yamasaki, K., Takahashi, S., & Ueda, K., 2010).
Elderly individuals with back pain have a higher risk of knee pain because of the impact of the changes in the biomechanics of axial movements, and chronic LBP inhibits the movements of the knee extensor muscles, which could lead to prolonged weakness and possibly structural changes in the affected muscle group (Weiner, D. K., Haggerty, C. L., Kritchevsky, S. B., Harris, T., Simonsick, E. M., Nevitt, M., & Newman, A., 2003; Suter, E., & Lindsay, D., 2001). This phenomenon could be caused by weakness generally or a muscular psychologic factor (Lee, J. H., Ooi, Y., & Nakamura, K., 1995). A sufficient quadricep muscle strength maintains a good dynamic stability and prevents falls during activities of daily living in the elderly (Scarborough, D. M., Krebs, D. E., & Harris, B. A., 1999). Isokinetic knee strength can potentially reflect the functional status of the elderly (Hartmann, A., Knols, R., Murer, K., & De Bruin, E. D., 2009).
An anti-gravity treadmill is a device that allows changing the gravity by reducing the weight of an individual up to 80% while walking and running. A special chamber is installed outside the normal treadmill, and the individual moves into the chamber; the pelvis and lower extremity are then zipped in the chamber. Thereafter, the air circulation inside the chamber temporarily reduces the body weight during walking or running while lifting the body of the individual (Saxena, A., & Granot, A., 2011). Unlike underwater walking, anti-gravity treadmill walking can elongate the stride while maintaining normal walking and reduce ground reaction force without changing the ankle and knee joint ranges of motion Grabowski, A. M., 2010). In addition, it can be used for early rehabilitation, since it reduces the amount of impact force in the knee, ankle, and pelvis during walking or running. Furthermore, the metabolic activity generated does not differ between antigravity treadmill and normal treadmill exercises (Figueroa, M. A., Manning, J., & Escamilla, P., 2011).
After PLIF, patients usually experience higher pain intensities during walking. Thus, its application is limited to aerobic walking exercises, and it could weaken the lower extremity muscles, especially the knee muscles. However, we thought that as an anti-gravity treadmill reduces the ground reaction force and amount of impact force in the pelvis during walking, it could be applied as aerobic walking exercises for patients who undergo PLIF. Therefore, the main purpose of this research was to investigate the effect of anti-gravity treadmill exercises on knee muscle strength and LBP status. Our hypotheses were that anti-gravity treadmill exercises have no negative effect on the patient’s LBP status and improve the knee muscle functions.
Ⅱ Case Description
1 Participant and History
The patient was a 77-year-old man (height, 173.2 cm; weight, 68.3 kg; body mass index, 22.7 kg/m2) who underwent an L2-4 PLIF on August 3, 2015. Approximately 20 years prior, the patient experienced his first symptom, which was LBP. At that time, he received an epidural steroid injection at both L3-4 and L4-5 foramen. However, his symptom worsened, his pain radiated to the left lower extremity, and he developed paralysis with muscle weakness. Furthermore, lumbar spinal magnetic resonance imaging revealed that he had many conditions: lumbar spondylosis, retrolisthesis at L2-3 and L3-4, facet arthrosis of the L spine, symmetrical disc bulging at L2-S1, degenerative central canal stenosis at L3-4 and L4-5, and degenerative neural foraminal stenosis at the right L3-4. Four weeks after surgery, he participated in a rehabilitation program with anti-gravity treadmill gait exercise.
2 Rehabilitation Program
After 2 postoperative weeks, the patient was discharged from the hospital where he underwent PLIF and visited our rehabilitation center. He participated in our rehabilitation program, which consisted of two sessions per week [a total of 80 therapy sessions (10 months)], supervised by one physical therapist who had 8 years of experience. A physical therapist educated the patient regarding the importance of maintaining a neutral position of the lumbar and informed him about the precautions to be taken in the activities of daily living. Basically, the rehabilitation program consisted of low back, pelvic, hip jointstretching, core stabilization (using a gym ball), and aerobic exercises (using anti-gravity treadmill). Low back, pelvic, hip joint-stretching, and core stabilization exercises were conducted every session for 10 minutes in a similar manner (Table 1). However, anti-gravity treadmill exercise was conducted progressively, while changing the velocity and applying gravity (Fig. 1). We designed the anti-gravity treadmill exercise such that it consisted of 10 levels. The patient participated in this program on the first visit, and we increased the program’s level every 4 weeks (Table 2). We considered the patient’s back pain and health status on the day of exercise.
3 Evaluation of Outcomes
1) Isokinetic Knee Strength Evaluation
To assess the strength of the knee extensor and flexor muscles of the patient, we used the Biodex Multi-Joint System 4 (Biodex System 4, Biodex Medical Systems Inc., Shirley, New York, USA). The patient sat on the chair of the machine, and we put the straps across his chest. He flexed his hip and knee at 90ﾟ on the chair, and the thigh to be tested was bounded by straps. The patient performed reciprocal maximum concentric contractions of the hamstring/ quadricep muscle at an angular velocity of 60ﾟ/second for five repetitions, which were recorded as Nm/kg, and 180ﾟ/second for 15 repetitions, which were recorded as J. Higher scores indicate a good muscle function. To prevent injury and muscle fatigue, the patient performed warm-up exercises using a stationary cycle for approximately 10 minutes and rested for 30 seconds between sets and tests. The Biodex system is a reliable device used to measure isokinetic maximal concentric contraction of the quadriceps muscles and strength of the hamstring muscles of the elderly and demonstrated excellent (Hartmann, A., Knols, R., Murer, K., & De Bruin, E. D., 2009; Drouin, J. M., Valovich-mcLeod, T. C., Shultz, S. J., Gansneder, B. M., & Perrin, D. H., 2004) (Fig. 2).
2) Oswestry Disability Index (ODI)
To evaluate LBP and functions, we used the ODI. The ODI is used to assess pain-related disability in patients with LBP. This index is widely used for determining functional disability due to LBP and is a simple, inexpensive method, which can be easily administered. Further, the ODI is a valid, vigorous, and worthwhile outcome measure. It consists of a 10-item scale, with a score ranging from 0 to 5; the final score is presented as a percentage, with higher scores indicating greater disability. Section 7 pertains to sex life, and the patient had no response in this section.
Ⅲ Results
1 Isokinetic Knee Strength
The isokinetic knee strength values of the patient are presented in Table 3. All isokinetic knee strength values increased gradually after surgery. His isokinetic knee extension peak torque (Rt. 75.4Nm/kg (31.7%↓), Lt. 51.2Nm/kg (36.6%↓)) and total work (Rt. 694.5J (36.8%↓), Lt. 401.4J (56.8%↓)) decreased 12 weeks after surgery. However, after 40 weeks, his isokinetic knee extension peak torque (Rt. 94.2Nm/kg, Lt. 77.2Nm/kg) and total work (Rt. 969.4J, Lt. 834.3J) recovered back to their preoperative values. The subject’s isokinetic knee flexion peak torque and total work further improved compared with those before surgery.
2 ODI
The ODIs of the patient are presented in Table 4. His ODIs, specifically pain intensity score, decreased progressively over time. Furthermore, his personal care and sleeping scores reached zero points 24 weeks after surgery. Finally, his total score was 36 points, which indicated that he had moderate disability with higher pain intensities and difficulties in sitting, lifting, standing, travelling, social living, personal care, sleeping, and performing activities of daily living before surgery. However, the total score decreased to 14 points after 40 weeks; this score indicated that he had minimal disability, that is, he could perform most activities of daily living.
Ⅳ Discussion
This study was designed to investigate the effect of aerobic exercises using an anti-gravity treadmill for rehabilitation after PLIF. After the 40-week intervention, we found that the subject’s isokinetic knee extension peak torque and total work recovered to their preoperative status and that the isokinetic knee flexion peak torque and total work recovered further compared to those before surgery. In addition, the subject’s ODI decreased progressively over time, and his ability to perform activities of daily living improved compared to that before surgery.
In the isokinetic knee extension strength evaluation, the peak torque and total work of the subject grossly decreased 12 weeks after surgery and gradually recovered over time until the last evaluation period. The isokinetic knee strength has a potentially important role in the functional status assessment of the elderly (Hartmann, A., Knols, R., Murer, K., & De Bruin, E. D., 2009). Further, their quadricep muscle strength has an important role for good dynamic stability for preventing falls during activities of daily living (Scarborough, D. M., Krebs, D. E., & Harris, B. A., 1999). However, patients with LBP have been reported to experience weakness not only in the trunk muscle but also in the lower extremity muscle. Lee et al. reported that the knee extension and flexion muscle strength was lower in their group with LBP than in their group without LBP. They suggest that muscle weakness results from disuse atrophy or poorly developed musculature by nature or fear of injury during the test (Lee, J. H., Ooi, Y., & Nakamura, K., 1995). Our subject also stated that he had a fear of re-injury and pain. Although the subject’s pain slightly decreased after surgery, the scores for sleeping, walking, lifting, and standing before surgery were similar to those 12 weeks after surgery. This could indicate that the subject’s functional status and movement did not recover completely yet. Moreover, our subject, who underwent PLIF, had 2 weeks of bed rest for recovery. Berg et al. reported that the knee extension isokinetic strength of their cohort decreased by approximately 25-30% after 6 weeks of bed rest owing to factors resulting in a decreased neural input to and specific tension in the muscle (Berg, H. E., Larsson, L., & Tesch, P. A., 1997). Mulder et al. also reported that 8 weeks of bed rest significantly improved quadriceps femoris muscle weakness and atrophy over time (Mulder, E. R., Stegeman, D. F., Gerrits, K. H. L., Paalman, M. I., Rittweger, J., Felsenberg, D., & De Haan, A., 2006). We thought that the pain experienced by our subject was relieved; however, his knee strength decreased owing to the postoperative bed rest and fear of re-injury and pain. This result influenced his physical functions. This is the reason why the subject’s ODIs before and 12 weeks after surgery were similar. However, his functional status gradually improved as his isokinetic knee extension strength recovered. Therefore, not only core muscle-strengthening and flexibility exercises but also knee extension-strengthening exercises should be included in rehabilitation programs for elderly patients who undergo back surgeries.
However, patients who underwent back surgeries rarely participate in general resistance exercises or normal gait exercise programs because they easily feel pain related to surgery or weight bearing. Our subject also developed pain and feared normal gait and resistance exercises; however, when he participated in the gait exercise program using anti-gravity treadmill, he did not feel pain or discomfort. This was because the anti-gravity treadmill decreased the ground reaction force and risks for pain and re-injury Grabowski, A. M., 2010). Gait exercises are useful exercises that can strengthen the lower extremity muscle in the elderly as much as resistance exercises. Simons and Andel reported that compared with resistance exercises, gait exercises significantly increased the leg strength in their elderly cohort (Simons, R., & Andel, R., 2006). Moore et al. reported the case of a 52-year-old marathoner with an HNP who participated in a gait exercise program using an anti-gravity treadmill and found that it improved the leg strength without symptoms and positively changed the emotion felt by the patient; the patient returned successfully to marathon running after approximately 5 weeks (Moore, M. N., Vandenakker-Albanese, C., & Hoffman, M. D., 2010). The limitations of this study were that it could not be generalized because it has proceeded to one subject and the subject needed a longer period to recover his knee strength because the anti-gravity treadmill gait exercise supported the weight differently from the normal walking exercise. However, the anti-gravity treadmill gait exercise has an advantage in that it could manage the pain and fear of symptom recurrence after surgery. Therefore, it may be possible for patients to participate more actively in rehabilitation programs.
Ⅴ Conclusion
Anti-gravity treadmill exercises can positively affect the conditions of patients after PLIF; it can recover knee muscle strength and low back functional status to patients who undergo PLIF. Further studies in larger patient cohorts to develop anti-gravity treadmill exercise programs for back surgery patients are needed.
