Examining Neuromuscular Adaptation in Foot and Ankle Injuries using Ultrasound Imaging

Background: The plantar intrinsic foot muscles are comprised of four layers of muscles that originate and insert on the planter surface of the feet. Intrinsic Foot Muscles (IFM) form an integral part of the foot. IFM form the base of support, provide attenuation of the forces, and play a critical role in locomotion by providing the necessary propulsive forces. IFM dysfunction can result in neuromuscular deficits that can affect balance, locomotion, sensory input on the planter surface of the feet and may result in functional limitations. Nevertheless, the body of knowledge pertaining to IFMs structure and function is still limited and primarily that is because of lack of valid tools and methods that can be used to assess these muscles where the weakness is suspected. Lately, ultrasound imaging (US) has been shown to be a mainstay for understanding the size, quality and function of these muscles in both non-weight bearing and weight bearing positions. However, we don`t know how these muscles change over the period of time in foot and ankle dysfunctions such as Chronic Ankle Instability (CAI), Patellofemoral Pain Syndrome (PFP), Diabetes Mellitus, 1st Metatarsophalangeal Joint (1st MTPJ) Arthrodesis etc. especially in the functional weight-bearing position. Previous literature using MRI has shown significant decreases in the muscle volume in IFM of patients with CAI. Similar to IFM, there are significant losses found in the muscle size in peroneal muscle group in CAI. However, to date, there are no studies that have examined the changes or gains in the muscle quality and size in IFM and peroneal muscle groups in patients with CAI. The IFM studied in this dissertation are Abductor Hallucis (AbH) and Flexor Digitorum Brevis (FDB).
Purpose: The purpose of Manuscript 1 (M1) was to compare the differences in IFM morphology and tissue quality in patients with CAI, PFP, 1st MTPJ arthrodesis, diabetes, and healthy individuals in weight-bearing functional position. The primary purpose of Manuscript 2 (M2) was to determine IFM size and quality changes using US imaging following impairment-based rehabilitation incorporating IFM exercises in patients with CAI. Peroneal size and quality changes using US imaging following impairment-based rehabilitation in patients with CAI were assessed in Manuscript 3 (M3).
Methods: M1) A case-control study consisting of 119 participants ( PFP=35, CAI=29, Diabetes=9, 1st MTPJ arthrodesis=9, Healthy=38) was performed to assess IFM size muscle size and quality across the spectrum in these pathologies in both non-weight-bearing and functional weight-bearing positions. M2 & M3) A pre-post prospective case-series study of 26 physical active individuals with CAI was performed to assess the improvement and gains in IFM size and quality (M2), and peroneal muscle size and quality (M3) after a 4-weeks of impairment-based rehabilitation program.
Results: M1) There were statistically significant difference (P<0.05) in the CSA of the AbH between all pathology groups when compared to healthy. Post-hoc analysis revealed that it was significantly lower (P<0.01) in every group compared to healthy except 1st MTPJ arthrodesis group. Similarly, significant differences (P<0.01) were found in the CSA of FDB between groups compared to the healthy group and post-hoc analysis revealed group differences in each group except PFP and 1st MTPJ groups. For echogenicity analysis, significant differences (P<0.05) were found between groups for both AbH and FDB. The post-hoc analysis revealed significantly (P<0.05) higher echogenicity in CAI and 1st MTP groups for AbH, and significantly higher (P<0.05) echogenicity in CAI, 1st MTP and PFP for FDB. Large effect sizes were found in both CSA and echogenicity measures when compared to healthy except PFP group for which small to moderate effect sizes were found. M2) A significant (P<0.01) increase was observed after rehabilitation for the normalized CSA with the increase in size of AbH and FDB in both seated and bipedal standing position. There were significant improvements (P<0.05) in CSA observed in the untrained limb for AbH and FDB in the bipedal standing position with moderate to strong effect sizes. However, no significant improvements were seen in the CSA of AbH (P=0.24) and FDB (P=0.19)) in the seated position. There was no significant change seen in the echogenicity measures for both AbH (P=0.26) and FDB(P=0.052) muscles. M3) A significant increase was observed after rehabilitation for the normalize CSA with the increase in size in the peroneal muscle group in lying (pre: 3.44 ± 0.99cm2 , post: 3.72 ± 0.98 cm2, P<0.01) as well as bipedal (pre:3.46 ± 1.05cm2, post: 4.31 ± 0.98cm2, P<0.01 ). There was a significant increase in the CSA on the untrained side as well in both lying (pre:3.34 ± 0.92cm2, post:3.63 ± 1.01cm2, P=0.01) and bipedal (pre:3.59 ± 1.02cm2, post:4.00 ± 1.21cm2, P<0.01). There was a significant decrease in echogenicity measures (pre:70.2 ± 9.91, post:65.7 ± 8.68, P=0.001) in the trained limb post-rehabilitation. There was no significant difference in echogenicity in the untrained limb. Conclusion: This is the first study to collectively analyze multiple clinical groups with suspected IFMs weakness in functional position for both muscle size and quality. We found significant changes in the muscle CSA and tissue quality in the pathological groups compared to a healthy group. These results suggest that clinicians should evaluate lower extremity injured patients to establish the need for rehabilitation of the IFM muscles in an effort to improve foot and ankle function in these populations. The rehabilitation program was administered in the CAI group to address the weakness found in the first manuscript. Normalized CSA of the IFMs increased in both sitting and standing position for the trained leg. However, the CSA of the IFMs increased only in the functional position for the untrained leg. The muscle quality measures did not change for the IFMs before and after rehabilitation which may be need a longer rehabilitation program to produce positive effects. For M3) Normalized CSA of the peroneal muscle group increased in both lying and standing position for the trained leg. However, the CSA of the IFMs increased only in the functional position for the untrained leg. There was a significant increase in the muscle quality as well. Therefore, we observed that there are faster changes in muscle quality in the peroneal muscle group when compared to the IFM and that may be because of different muscle physiology or a because of rehabilitation program that involves more gross motor patterns requiring less motor learning. Over all, the impairment-based rehabilitation was effective in restoring muscle size in IFM, and muscle size and quality in peroneal muscle groups. Rehabilitation programs are recommended for other clinical groups where deficits were observed in this study.