20/11/2022
Windlass and Reverse Windlass Effect: Structural and Functional Hallux Limitus
Hallux limitus has been described as a condition in which the hallux is unable to dorsiflex 65 to 75 degrees at the 1st metatarsophalangeal joint (MPJ) during the propulsive phase of gait (Root, M.L., W.P. Orien and J.H. W**d: Normal and Abnormal Function of the Foot. Clinical Biomechanics Corporation, Los Angeles, CA, 1977, p. 60, 363). In the podiatric medical community, hallux limitus is generally divided into two distinct categories: structural hallux limitus and functional hallux limitus.
Structural hallux limitus is defined as a 1st MPJ that has less than the normal range of dorsiflexion motion in a non-weightbearing setting. Structural hallux limitus may be caused by structural abnormalities in either the soft tissue or osseous components of the 1st MPJ so that there is an actual restriction of normal hallux dorsiflexion when the foot is non-weightbearing. Functional hallux limitus (FnHL) is defined as a 1st MPJ that demonstrates a normal range of hallux dorsiflexion during non-weightbearing examination but which also exhibits a restriction of hallux dorsiflexion during the propulsive phase of gait. In other words, a foot with FnHL will exhibit a reduction in available dorsiflexion of the 1st MPJ when going from a non-weightbearing to a weightbearing setting. It is this “functional” restriction of hallux dorsiflexion during weightbearing activities that occurs with FnHL that has important mechanical implications in the normal and abnormal function of the foot and lower extremity during gait.
John W**d, DPM, was the first person that I heard use the term “functional hallux limitus” when he was teaching my second year biomechanics course at the California College of Podiatric Medicine in 1980. Dr. W**d described hallux limitus deformity and explained the important functional difference between structural and functional hallux limitus and how it could affect the mechanics of the foot. More recently, Howard Dananberg, DPM has published numerous papers on the potential mechanical influences that FnHL may have on the biomechanics of gait that may, in turn, result in a myriad of problems ranging from foot pain to lower back pain (Dananberg, HJ: Functional hallux limitus and its relationship to gait efficiency. JAPMA, 76:648-652, 1986; Dananberg, HJ: Gait style as an etiology to chronic postural pain. Part I. Functional hallux limitus. JAPMA, 83:433-441, 1993). Dr. Dananberg’s pioneering work in correlating the abnormal mechanics of the 1st MPJ to lower back pain has emphasized the importance of recognizing FnHL in the treatment of mechanically based pathologies which are located anatomically quite distant to the foot (Dananberg, HJ, Guiliano, M: Chronic low-back pain and its response to custom-made foot orthoses. 89:109-117, 1999).
In order to fully understand the etiology of FnHL, the clinician must first appreciate the complex mechanical interrelationships between the 1st MPJ and the remainder of the foot and lower extremity. In the foot with an intact plantar fascia, the hallux cannot dorsiflex fully unless other associated motions of the foot also occur simultaneously. The mechanics of this interaction of the 1st MPJ and the remainder of the foot and lower extremity were probably best described by Hicks nearly 50 years ago. Hicks found the following four observations to occur simultaneously in the foot and lower extremity during passive 1st MPJ dorsiflexion: 1) an increase in medial longitudinal arch height (Fig. 1), 2) inversion of the rearfoot, 3) external rotation of the leg, and 4) the appearance of a tight band in the region of the plantar fascia. (Hicks, J.H. The mechanics of the foot. II. The plantar aponeurosis and the arch. Journal of Anatomy. 88:24-31, 1954).
Hicks noted that these motions of the foot and lower extremity that occurred with 1st MPJ dorsiflexion were not necessarily muscular in origin since both paralyzed and cadaver feet showed the same motions. He stated that the four observations listed above also occurred when the individual was asked to stand tip-toe, actively dorsiflexing the 1st MPJ. Hicks found that the same “irresistible” arch-raising effect and plantarflexion of the first metatarsal occurred with 1st MPJ dorsiflexion in a non-weightbearing situation. He noted that the arch-raising effect that occurred with hallux dorsiflexion almost disappeared with transection of the plantar fascia in the cadaver foot (Hicks, 1954).
From his observations in both live subjects and cadaver feet, Hicks described the arch-raising effect that occurred with hallux dorsiflexion as being caused by the plantar fascia being wound, along with the sesamoids, along the plantar and distal aspect of the first metatarsal head during hallux dorsiflexion. He described the unique structural arrangement of the plantar fascia, sesamoids, first metatarsal head and hallux as being mechanically similar to a cable being wound about the drum of a windlass. [A windlass is a revolving lifting device that uses a rope or cable wound around a revolving drum to pull and lift things (Microsoft World Dictionary, 2001).]
Hicks also noted that since the body weight tended to flatten the arch of the foot, that the flattening of the arch tended to cause plantarflexion motion of the hallux and lesser toes, causing the hallux and lesser toes to press with more force on the ground during weightbearing. This effect of the hallux and toes pressing forcefully into the ground with the foot being loaded by body weight was noted also to disappear with transection of the plantar fascia. Hicks described this tendency of the toes to plantarflex at the MPJs with flattening of the arch of the foot as an “unwinding of the windlass” and felt that this effect was at least partially responsible for the “gripping action” of the toes on the ground during weightbearing activities (Hicks, 1954).
The mechanical nature of a non-contractile structure such as the plantar fascia is very important when attempting to understand the mechanics of FnHL since the passively produced tensile forces within the plantar fascia play a major role in the production of FnHL during gait. These important interrelationships of the plantar fascia and FnHL will be explored further in the future newsletters.
[From: Kirby KA: Functional hallux limitus and windlass effect of Hicks. June 2002 Precision Intricast Newsletter. Kirby KA: Foot and Lower Extremity Biomechanics II: Precision Intricast Newsletters, 1997-2002. Precision Intricast, Inc., Payson, AZ, 2002.]
Dr. Kirby's five books may be purchased from Precision Intricast Orthosis Lab at www.precisionintricast.com/shop.
