Considering the Intrinsic Foot Musculature in Evaluation and Rehabilitation for Lower Extremity Injuries
Abstract
The intrinsic foot musculature may have an important, stabilizing role in the foot during weight bearing, dynamic activities. The purpose of the article is to discuss a clinical test for evaluating the intrinsic foot muscles following lower extremity injuries and to describe a rehabilitation exercise targeting the intrinsic foot muscles in rehabilitation.
Introduction
Altered neuromuscular control and activation of lower extremity musculature has been associated with acute and chronic lower extremity musculoskeletal injuries from ankle sprains to patellofemoral pain, but neuromuscular changes in the intrinsic foot muscles have not been documented.1–4 Rehabilitation focuses on restoring strength, neuromuscular control, and activation of the muscles influencing the injured area. Typically, clinicians prescribe exercises targeting hip, thigh, and lower leg muscles proximal to the injured joint to improve strength and postural stability and to restore normal movement patterns following injury.5–7
It is plausible that there may be altered neuromuscular recruitment and activation of the intrinsic foot muscles distal to the injured area. The intrinsic foot musculature makes a significant contribution for maintaining a stable base of support during dynamic activity.8 It has been suggested that intrinsic foot musculature is essential to stabilize tarsal bones in the foot.8 Poor activation and function of the intrinsic foot muscles may lead to altered distribution of forces through the foot during gait or landing. Diminished strength or control of the foot muscles following injury may increase stress on static stabilizers in the foot. Activation and strength of the intrinsic foot musculature are not routinely evaluated in the presence of lower extremity injuries.
The intrinsic foot muscles stabilize the foot at segmental levels, with attachment sites on the tarsals, metatarsals, and phalanges.8 Jam8 suggested that proper neuromuscular control of these muscles in the foot is essential to stabilize the foot and control motion through the stance phase of the gait cycle. A similar concept targets muscles that stabilize the spine at a segmental level to improve global movement patterns and has been previously addressed in core stability literature. Tsao and Hodges9 described training to activate the transverse abdominus, a stabilizer of the spinal segments, which improved activation and function of the muscle, motor control during gross movement patterns, self-reported pain, and function during dynamic tasks. It may also be important to focus on the intrinsic foot muscles in rehabilitation as local stabilizers in the foot while they work in coordination with the extrinsic foot muscles as global movers to control foot motion during weight bearing and dynamic activities.
For clinicians to effectively focus on the intrinsic foot muscles in rehabilitation, it is important to appreciate and be familiar with the underlying anatomy. The foot yields a complex set of musculature with 4 layers on the plantar aspect deep to the plantar fascia and plantar aponeurosis. The first layer of plantar muscles is the most superficial and includes the abductor hallucis, flexor digitorum brevis, and abductor digiti minimi.10 The abductor hallucis abducts the great toe and the abductor digiti minimi abducts the fifth toe. The flexor digitorum brevis flexes the lesser toes. The second layer contains the quadratus plantae and lumbricals.10 The quadratus plantae assists with flexion of the lesser toes. The lumbricals are flexors of the proximal phalanges and extensors of the middle and distal phalanges of the lesser toes. The third layer of plantar muscles contains the flexor hallucis brevis, adductor hallucis, and the flexor digiti minimi brevis.10 The flexor hallucis brevis flexes the proximal phalanx of the great toe. The adductor hallucis adducts the great toe. The flexor digiti minimi brevis flexes the fifth toe in combination with the flexor digitorum brevis and flexor digitorum longus. The fourth layer of plantar muscles contains 3 plantar interossei and 4 dorsal interossei.10 The plantar interossei adduct the second, third, and fourth digits and assist with flexion of the metatarsophalangeal joints. The dorsal interossei abduct the second, third, and fourth digits and assist with flexion of the metatarsophalangeal joints. The 4 layers of muscles in the foot aid in supporting the foot, on a segmental level, during weight-bearing activities.11,12
Intrinsic Foot Muscle Test
The intrinsic foot muscle test is a clinical test for evaluating the intrinsic foot muscles during the single-limb stance.8 This test evaluates the patient’s ability to maintain a neutral foot position and height of the medial longitudinal arch without compensatory movements or muscle involvement. To start the test, the neutral foot position is set as the test foot is extended while metatarsal heads and calcaneus remain on the ground (Figure 1A). This neutral foot positioning technique is suggested as an active positioning into subtalar joint neutral.8 As the patient maintains the neutral foot position, the toes are lowered back to the floor. Once the toes are back to the floor, the patient is asked to maintain the foot position in the single-limb stance for 30 seconds (Figure 1B).
Intrinsic Foot Muscle Test. The Patient Demonstrating Setting the Foot in a Neutral Position (A), Maintaining the Foot Position in the Single-Limb Stance (B), Demonstrating a Correct Technique to Maintain Foot Position Without Overactivity of the Extrinsic Foot Muscles (C), and Demonstrating Incorrect Technique with Overactivity of the Extrinsic Foot Muscles to Maintain the Foot Position (D).
During the test, the evaluating clinician gives the patient a performance classification of poor, fair, or satisfactory.8 The grade is assigned based on the patient’s ability to maintain a steady navicular height and the presence of overactivity of the extrinsic foot muscles during the test (Table and Figure 1C). When monitoring steadiness of the navicular height, the clinician is subjectively observing gross changes in the navicular height. Overactivity of the extrinsic foot muscles is indicated by flexion or extension of the toes in an effort to maintain the height of the arch8 (Figure 1D). It is important to note that, currently, this clinical test does not have psychometric properties established regarding its validity and reliability.
| PERFORMANCE GRADE | CRITERIA TO DETERMINE PERFORMANCE GRADE DURING THE TEST |
|---|---|
| Poor | The patient demonstrates consistent unsteadiness of the navicular height, consistent overactivity of extrinsic foot musculature, or both. |
| Fair | The patient demonstrates inconsistent unsteadiness of the navicular height, inconsistent overactivity of extrinsic foot musculature, or both. |
| Satisfactory | The patient demonstrates consistent steadiness of navicular height without overactivity of the extrinsic foot musculature. |
Short Foot Exercise
The short foot exercise (SFE) has been previously described in rehabilitation therapy textbooks.13,14 The SFE is a sensorimotor training technique used to enhance proprioception, as well as improve postural alignment and stability. The name of the exercise, also known as the small foot, describes the specific foot positioning and involves a shortening and narrowing of the medial longitudinal and transverse arches, respectively.13 Janda et al14 described the exercise increasing afferent input from the sole of the foot. The goals of the SFE include correctly aligning the position of body segments, promoting stability of the body in an upright position, and improving the springing moment of the foot during walking. Greenman13 described the primary goal as stimulating proprioceptors of the sole of the foot by attempting to grasp the floor without excessive curling of the toes. Both sources recommend incorporating the SFE in all closed-kinetic chain rehabilitation.
Janda et al14 described a progression for teaching a patient the SFE beginning with passive foot modeling. In this technique, the patient is in a sitting position with a relaxed foot (Figure 2A), and the clinician cups the heel and compresses the metatarsal heads as he or she shortens the foot and medial longitudinal arch with vibratory movements (Figure 2B). This is thought to stimulate the patient’s foot muscles used in the SFE. Following passive modeling, the patient pushes the plantar aspect of the foot into the ground and pulls the metatarsal heads back to the calcaneus without clinching the toes as the clinician guides the motion with the active-assistive level of the exercise (Figure 2C).14 As the patient understands the concept, he or she can progress to active modeling of the foot (Figure 2D). The active position of the SFE will be initiated in a sitting position progressing to a double-limb stance followed by a single-limb stance.14
Short Foot Exercise. A Patient Performing the Short Foot Exercise with a Relaxed Foot (A), Passive Foot Modeling with Help from a Clinician (B), Active-Assisted Modeling with Help from a Clinician (C), and an Active Contraction of the Short Foot Exercise (D).
Once the patient can perform the foot positioning exercise in single-limb stance, it can be incorporated into all weight-bearing and dynamic activities during a rehabilitation session or a home exercise program, such as balancing exercises, 4-way hip strengthening, or single-limb hopping activities. Actively performing the SFE during dynamic activities, such as lunges, jumping, and landing, allows the opportunity to strengthen and reinforce neuromuscular patterning of the intrinsic foot muscles during daily and sports activities. During these activities, the SFE assists with better control and function of the intrinsic foot muscles during pronation and supination rather than creating a rigid, supinated foot. Recent research has objectively evaluated the influence of the SFE on lower extremity rehabilitation outcomes.
Michell et al6 compared individuals with healthy ankles and individuals with functionally unstable ankles before and after a functional balance training program. Within each population, half of the participants were assigned to a group who wore exercise sandals for all balance training and the other half of participants wore standard athletic shoes. All participants performed the SFE during training sessions proceeding additional exercises. In addition, the exercise sandals were meant to encourage performance of the SFE and were used during all rehabilitation exercises. Results indicated that all participants improved their postural stability following the training program, although the specific contribution of the SFE to the improvement in postural stability was unclear. Further research in this area is warranted to evaluate the specific contribution of the SFE to an improved functional performance in an injured population. A possibility exists that rehabilitation with the exercise sandals should be implemented as a method of training and improving the function of the intrinsic foot muscles.
Rothermel et al15 studied the effects of the foot positioning SFE on a 4-week balance training program in healthy participants. The foot positioning group was compared with the traditional rehabilitation and control groups regarding center of pressure velocity measures during static balance. Balance performance improved following the foot positioning intervention; however, the changes were not significant compared with the control or balancing training groups that did not perform SFE. Although this study did not show a significantly greater improvement with the foot positioning intervention, it is important to note that it was completed in a healthy population that did not have balance deficits. Changes following rehabilitation in healthy individuals may not represent the responsiveness to change that would occur in a population sustaining a lower extremity injury. In addition, the foot positioning group was asked to practice the SFE at home. Correctly performing the exercise requires practice and feedback from a clinician. It is possible that participants were not practicing the exercise on a daily basis or that they were practicing incorrect technique. The authors discussed that their participants complained of foot cramping during the exercise. Foot muscle cramping is expected as patients are learning the SFE, but it will subside as strength and activation of the foot muscles improves with practice. It is important to monitor and encourage patients to practice the exercise and use proper technique.
Conclusion
Lower extremity injuries may affect the neuromuscular control or activation of the intrinsic foot muscles. The intrinsic foot musculature may have an influential role on postural stability and control of the foot during dynamic activities. In our case review, we have presented techniques for evaluation and rehabilitation targeting the intrinsic foot muscles. The intrinsic foot muscle test is a brief clinical test that can be easily incorporated into an initial evaluation for any lower extremity injury. The activation and neuromuscular function of the local stabilizing muscles should be routinely evaluated in a population with lower extremity injury. The SFE may be an effective rehabilitation strategy in a patient with decreased control or activation of the intrinsic foot musculature following lower extremity injury. The improvement of foot muscle function and control may ultimately improve balance and risk of reinjury.
Implications for Clinical Practice
The intrinsic foot muscles stabilize the foot on a segmental level and inevitably support the foot during dynamic activities. It may be beneficial for clinicians to more closely evaluate the intrinsic foot muscles during activities and rehabilitation to best care for patients with lower extremity injuries. The intrinsic foot muscle test is one simple test that could be implemented into an evaluation of lower extremity injuries. In addition, the short foot exercise can be incorporated into rehabilitation programs to improve upon activation and strength of the intrinsic foot muscles. Improved function of the foot muscles may better stabilize the foot on a segmental level and improve outcomes for patients recovering from lower extremity injuries.
- 1.Delahunt E, Monaghan K, Caulfield B. Changes in lower limb kinematics, kinetics, and muscle activity in subjects with functional instability of the ankle joint during a single leg drop jump. Orthop Res. 2006; 24:1–10.
10.1002/jor.20235 > CrossrefGoogle Scholar - 2.Freeman M, Dean M, Hanham I. The etiology and prevention of functional instability of the foot. J Bone Joint Surg Br. 1965; 47:678–685. > Google Scholar
- 3.Anderson G, Herrington L. A comparison of eccentric isokinetic torque production and velocity of knee flexion angle during step down in patellofemoral pain syndrome patients and unaffected subjects. Clin Biomech. 2003; 18:500–504.
10.1016/S0268-0033(03)00054-8 > CrossrefGoogle Scholar - 4.Madeley LT, Munteanu SE, Bonanno DR. Endurance of the ankle joint plantar flexor muscles in athletes with medial tibial stress syndrome: A case-control study. J Sci Med Sport. 2007; 10:356–362.
10.1016/j.jsams.2006.12.115 > CrossrefGoogle Scholar - 5.Hale S, Hertel J, Olmsted-Kramer L. The effect of a 4-week comprehensive rehabilitation program on postural control and lower extremity function in individuals with chronic ankle instability. J Orthop Sports Phys Ther. 2007; 37:303–311. > Google Scholar
- 6.Michell T, Ross S, Blackburn J, Hirth C, Guskiewicz K. Functional balance training, with or without exercise sandals, for subjects with stable or unstable ankles. J Athl Train. 2006; 41:393–398. > Google Scholar
- 7.van Linschoten R, van Middelkoop M, Berger MY, Supervised exercise therapy versus usual care for patellofemoral pain syndrome: An open label randomised controlled trial. BMJ. 2009; 339: b4074–b4081.
10.1136/bmj.b4074 > CrossrefGoogle Scholar - 8.Jam B. Evaluation and retraining of the intrinsic foot muscles for pain syndromes related to abnormal control of pronation. http://www.aptei.com/articles/pdf/IntrinsicMuscles.pdf. Accessed February 27, 2008. > Google Scholar
- 9.Tsao H, Hodges P. Persistence of improvements in postural strategies following motor control training in people with recurrent low back pain. J Electromyogr Kinesiol. 2008; 18:559–567.
10.1016/j.jelekin.2006.10.012 > CrossrefGoogle Scholar - 10.Moore K, Dalley A. Lower limb. In: , ed. Clinically Oriented Anatomy. 4th ed. Baltimore, MD: Lippincott Williams & Wilkins; 1999:503–663. > Google Scholar
- 11.Fiolkowski P, Brunt D, Bishop M, Woo R, Horodyski M. Intrinsic pedal musculature support of the medial longitudinal arch: An electromyography study. J Foot Ankle Surg. 2003; 42:327–333.
10.1053/j.jfas.2003.10.003 > CrossrefGoogle Scholar - 12.Headlee D, Leonard J, Hart J, Ingersoll C, Hertel J. Fatigue of the plantar intrinsic foot muscles increases navicular drop. J Electromyogr Kinesiol. 2008; 18:420–425.
10.1016/j.jelekin.2006.11.004 > CrossrefGoogle Scholar - 13.Greenman P. Exercise principles and prescription. In: , ed. Principles of Manual Medicine. 2nd ed. Baltimore, MD: Williams and Wilkins; 1996:449–524. > Google Scholar
- 14.Janda V, Vavrova M, Herbenova A, Veverkova M. Sensory motor stimulation. In: , ed. Rehabilitation of the Spine: A Practitioner’s Manual. 2nd ed. Baltimore, MD: Lippincott Williams & Wilkins; 2007:513–530. > Google Scholar
- 15.Rothermel S, Hale S, Hertel J, Denegar C. Effect of active foot positioning on the outcome of a balance training program. Phys Ther Sport. 2004; 5:98–103. > Google Scholar
