Tiptoeing Through Time: A Rare Variant of the Quadratus Plantae Muscle with Evolutionary Implications
Location
D.P. Culp Center Ballroom
Start Date
4-5-2024 9:00 AM
End Date
4-5-2024 11:30 AM
Poster Number
105
Name of Project's Faculty Sponsor
Jonathan Millard
Faculty Sponsor's Department
Biomedical Sciences
Competition Type
Competitive
Type
Poster Presentation
Presentation Category
Health
Abstract or Artist's Statement
INTRODUCTION: The quadratus plantae muscle is an intrinsic muscle of the second layer of the sole of the foot believed to influence the gait cycle and flexion of the distal interphalangeal joint of pedal digits 2-5. Typically, the muscle arises from the calcaneus bone and inserts into the tendon(s) of the flexor digitorum longus muscle. Previous reports on quadratus plantae muscle variation have focused on its highly variable origin, which can occur as one, two, or three heads. Here we report an unusual insertion pattern of the quadratus plantae muscle. METHODS: During the routine cadaveric dissection of the right foot of a 95-year-old formalin-fixed whole-body female donor, the flexor digitorum longus muscle with associated lumbrical muscle bellies was identified without an attached quadratus plantae muscle. Upon reflection of the flexor digitorum longus muscle, a variation of quadratus plantae muscle was found arising from the calcaneus bone with four tendinous extensions, each with an additional associated lumbrical muscle, inserting onto the distal phalanges. RESULTS/CONCLUSIONS: Early descriptions of the quadratus plantae muscle, often termed “flexor accessorius”, proposed the muscle facilitated in-line flexion of the pedal digits in the sagittal plane by redirecting the force vector of the flexor digitorum longus muscle. Later, electromyographic studies suggested the muscle was most frequently recruited to supplement flexor digitorum longus muscle force production during bipedal progression. This influence would likely peak during toe purchase, transitioning between stance phase and toe off. In African apes, the quadratus plantae muscle is typically absent, whereas the lumbrical muscles tend to be larger and better developed than in humans. In our donor, pedal flexion would have been directly reinforced by this hybrid quadratus plantae muscle, instead of indirectly via its insertion in the flexor digitorum longus tendon. Interestingly, the tendons of the muscle originated its own lumbricals in addition the lumbricals found on the flexor digitorum longus tendons. This finding is congruent with the suggestion that the primary utility of the muscle is to maximize pedal flexion force during the bipedal gait cycle, although it is unclear if this morphological arrangement is a product of selection pressures or isolated congenital anomaly. As this is an understudied feature, future directions should include larger studies to assess the prevalence of this variation.
Tiptoeing Through Time: A Rare Variant of the Quadratus Plantae Muscle with Evolutionary Implications
D.P. Culp Center Ballroom
INTRODUCTION: The quadratus plantae muscle is an intrinsic muscle of the second layer of the sole of the foot believed to influence the gait cycle and flexion of the distal interphalangeal joint of pedal digits 2-5. Typically, the muscle arises from the calcaneus bone and inserts into the tendon(s) of the flexor digitorum longus muscle. Previous reports on quadratus plantae muscle variation have focused on its highly variable origin, which can occur as one, two, or three heads. Here we report an unusual insertion pattern of the quadratus plantae muscle. METHODS: During the routine cadaveric dissection of the right foot of a 95-year-old formalin-fixed whole-body female donor, the flexor digitorum longus muscle with associated lumbrical muscle bellies was identified without an attached quadratus plantae muscle. Upon reflection of the flexor digitorum longus muscle, a variation of quadratus plantae muscle was found arising from the calcaneus bone with four tendinous extensions, each with an additional associated lumbrical muscle, inserting onto the distal phalanges. RESULTS/CONCLUSIONS: Early descriptions of the quadratus plantae muscle, often termed “flexor accessorius”, proposed the muscle facilitated in-line flexion of the pedal digits in the sagittal plane by redirecting the force vector of the flexor digitorum longus muscle. Later, electromyographic studies suggested the muscle was most frequently recruited to supplement flexor digitorum longus muscle force production during bipedal progression. This influence would likely peak during toe purchase, transitioning between stance phase and toe off. In African apes, the quadratus plantae muscle is typically absent, whereas the lumbrical muscles tend to be larger and better developed than in humans. In our donor, pedal flexion would have been directly reinforced by this hybrid quadratus plantae muscle, instead of indirectly via its insertion in the flexor digitorum longus tendon. Interestingly, the tendons of the muscle originated its own lumbricals in addition the lumbricals found on the flexor digitorum longus tendons. This finding is congruent with the suggestion that the primary utility of the muscle is to maximize pedal flexion force during the bipedal gait cycle, although it is unclear if this morphological arrangement is a product of selection pressures or isolated congenital anomaly. As this is an understudied feature, future directions should include larger studies to assess the prevalence of this variation.