Valgus stability is enhanced by flexor digitorum superficialis muscle contraction of the index and middle fingers

Abstract

Background: Flexor digitorum superficialis (FDS) muscle provides dynamic stabilization and medial elbow support for ulnar collateral ligament (UCL). The FDS contraction significantly affects the medial joint distance (MJD) through grip contraction. However, it remains unclear whether FDS activity alone contributes to medial elbow stability, or together with the activation of the flexor digitorum profundus during grip contraction, and which finger's FDS is the main contributor to elbow stability. We investigated the resistive effects of isolated FDS contraction in individual fingers against valgus stress in the elbow joint using stress ultrasonography (US). Methods: We investigated 17 healthy males (mean age, 27 ± 5 years). Valgus stress US was performed using the Telos device, with the elbow at 30°flexion. MJD was measured for each arm during 3 separate conditions: at rest (unloaded), under valgus load (50 N) (loaded), and under valgus load with FDS contracted in individual fingers (loaded-contracted). Results: MJD was significantly longer when loaded (5.4 ± 0.4 mm) than unloaded (4.1 ± 0.2 mm, P = 0.007) or loadedcontracted (4.6 ± 0.3 mm, P = 0.003) for each finger. When loaded-contracted, MJD differed statistically between the index and ring fingers (P = 0.03) and between the middle and ring fingers (P = 0.04). However, the difference between the index and middle fingers was not statistically significant (P = 0.08). Conclusions: Individual FDS contraction, particularly of the index and middle fingers, contributes most to stabilization against valgus stress. Thus, injury care programs should incorporate FDS exercises of these fingers.

Contributions of the Third and Fourth Digits and the Second and Fifth Digits of the Flexor Digitorum Superficialis Muscle to Elbow Valgus Stability

“… 21 A previous study reported that injury care programs should incorporate FDS exercises of these fingers because they, particularly the index and middle fingers, contribute the most to stabilization against valgus stress. 13 However, considering the origin structure of the FDS 21 and the results of the present study, from the viewpoint of transmitting muscle force to the ACT and PCT, it appears necessary to perform exercises for all digits of the FDS in a well-balanced manner, rather than specific finger exercises.…”

“… 4 UCL injury is thought to occur as a result of repeated elbow valgus stress. 15 In anatomical studies, 5 , 8 , 21 , 23 biomechanical studies, 1 , 9 , 20 , 24 , 30 and studies using ultrasonography, 13 , 25 the forearm flexors have been found to be important for reducing elbow valgus stress on the UCL. In particular, the flexor digitorum superficialis (FDS) muscle has been reported to be the most important of the forearm flexors for reducing elbow valgus stress on the UCL.…”

“…In particular, the flexor digitorum superficialis (FDS) muscle has been reported to be the most important of the forearm flexors for reducing elbow valgus stress on the UCL. 13 , 25 , 30 …”

“…In particular, the flexor digitorum superficialis (FDS) muscle has been reported to be the most important of the forearm flexors for reducing elbow valgus stress on the UCL. 13,25,30 With regard to the contribution of the FDS to elbow valgus stability, Hoshika et al 13 measured the ulnohumeral joint space (JS) when elbow valgus stress was applied to humans; in their study, the second, third, and fourth digits of the FDS were contracted individually. The authors reported that all digits were involved in elbow valgus stability, especially the second and third digits.…”

Elbow Ulnar Collateral Ligament Shoelace Repair with Internal Bracing for Treating Throwing Athletes Who Have Ulnar Collateral Ligament Instability

“…Hoshika et al supported this hypothesis and further suggested that valgus stability of the elbows was enhanced by contraction of the flexor digitorum superficialis, especially of the index and middle finger parts of this muscle as revealed by ultrasonography. 13 These findings suggest that the native UCL is an important structure for the dynamic stability of the medial elbow, and its stability should be restored. Further studies are needed to clarify whether this technique has any advantage over traditional UCL reconstruction procedures.…”