Possibly heard of, rarely implicated and not often treated, this is one muscle you should consider taking a look at.
The quadratus plantae is generally considered to arise from two heads of differing and variable fiber type composition, with the lateral head having slightly more Type 1 endurance fibers (1) The two heads are separated from each other by the long plantar ligament, though it can arise from from one (somewhat more common) to 3 heads (very rare). The attachments can be variable, The medial head is larger and more muscular, attached to the medial calcaneus, lateral aspect of the long plantar ligament and often from the plantar calcaneocuboid ligament (2); the lateral head is smaller and more tendinous, attaching to the lateral border of the inferior surface of the calcaneus and the long plantar ligament. The two portions join and end in a flattened band which inserts into the lateral, upper and under surfaces of the muscles, tendons or aponeurosis of predominantly the flexor digitorum longus and usually of the second and third, and sometimes fourth toes (2,3).
Its action can be equally as variable. In addition to augmenting the pull of the long flexor tendons along the long axis of the foot and so that the 3rd and 4th toes do not curl under the foot, the tendinous slips of the FHL may distribute the load of the great toe to the second toe to the third or fourth toe in the forefoot, especially during toe-off (3).
The main attachment of the QP to the tendinous slips of the FHL may provide more efficient control of the long flexor tendons in comparison with that of the QP to the tendon of the FDL (3). EMG studies suggest it resists extension of the toes during the stance phase of locomotion, which serves to increase the stability of the foot. Additional EMG studies suggest it actually acts as a primary toe flexor in voluntary movements, being preferentially recruited over flexor digitorum longus and from comparative anatomical considerations it also seems likely that quadratus plantae may be an intrinsic evertor of the foot (4).
This muscle is a major player in gait and rehabilitation of this muscle should not be overlooked. I could only find one study looking at exercise activation of the QP (5) . It was examined along with the abductor hallucis, flexor digitorum brevis, abductor digiti minimi, flexor digiti minimi, adductor hallucis oblique, flexor hallucis brevis, interossei and lumbricals during rehabilitative the short-foot exercise, toes spread out, first-toe extension, second- to fifth-toes extension.
So, what else can you do?
- you could ignore the muscle and hope it gets better. (in all likelihood it will worsen)
- you could give them long flexor, toe scrunching towel-curling, marble-grasping exercises, like you see all over the internet…and give the flexor digitorum longus even more of a mechanical advantage, and make the problem worse
- you could give them exercises to increase the function of the long extensors, which would increase the mechanical advantage of the quadratus plantae. like the shuffle walk; lift, spread and reach and tripod standing exercises
- look north of the foot to see what might be causing the problem (loss of ankle rocker, insufficient gluteal activity, loss of internal rotation of the hip, etc)
Check out the QP on your next foot pain patient, or whenever you see the toes trying to crawl under the foot. You may be surprised at your results.
1. Schroeder KL, Rosser BW, Kim SY. Fiber type composition of the human quadratus plantae muscle: a comparison of the lateral and medial heads. J Foot Ankle Res. 2014 Dec 13;7(1):54. doi: 10.1186/s13047-014-0054-5. eCollection 2014.
2. Pretterklieber B1. Morphological characteristics and variations of the human quadratus plantae muscle. Ann Anat. 2017 Nov 21;216:9-22. doi: 10.1016/j.aanat.2017.10.006. [Epub ahead of print]
3. Hur MS, Kim JH, Woo JS, Choi BY, Kim HJ, Lee KS. An anatomic study of the quadratus plantae in relation to tendinous slips of the flexor hallucis longus for gait analysis. Clin Anat. 2011 Sep;24(6):768-73. doi: 10.1002/ca.21170.
4. Sooriakumaran P, Sivananthan S. Why does man have a quadratus plantae? A review of its comparative anatomy. Croat Med J. 2005 Feb;46(1):30-5.
5. Gooding TM, Feger MA, Hart JM, Hertel J. ntrinsic Foot Muscle Activation During Specific Exercises: A T2 Time Magnetic Resonance Imaging Study. J Athl Train. 2016 Aug;51(8):644-650. Epub 2016 Oct 3.