The human foot is a biomechanical marvel, capable of absorbing enormous forces while simultaneously providing a rigid lever for propulsion. Central to this dual function is the windlass mechanism — a structural phenomenon that transforms the foot from a flexible shock absorber at heel strike into a rigid platform during push-off. Evaluating the integrity of this mechanism is essential in clinical practice, and one of the most widely used assessments for doing so is Jack’s test, also known as the Hubscher manoeuvre.
The Windlass Mechanism: Anatomy and Function
The windlass mechanism was first described in detail by Hicks in 1954, drawing an analogy to the nautical windlass — a device used to wind rope around a drum to tension and shorten it. In the foot, the plantar fascia (also called the plantar aponeurosis) functions as the rope in this system. This thick band of fibrous connective tissue originates from the medial process of the calcaneal tuberosity and extends distally, fanning out to insert into the plantar plates and proximal phalanges of each toe.
The mechanism works as follows: when the toes are dorsiflexed at the metatarsophalangeal (MTP) joints, the plantar fascia wraps around the heads of the metatarsals, effectively shortening the functional length of the fascial band. This tension raises the medial longitudinal arch, inverts the subtalar joint, and externally rotates the leg. The result is a dramatic stiffening of the foot, converting it into a rigid lever ideal for propulsion during the terminal stance and pre-swing phases of gait. Without an effective windlass mechanism, efficient push-off is compromised, placing abnormal stresses on surrounding structures.
Jack’s Test: Rationale and Clinical Basis
Jack’s test is a simple clinical examination designed to assess whether the windlass mechanism is functioning correctly in a weight-bearing context. First described by Robert Jack in 1953, the test exploits the relationship between great toe dorsiflexion and arch elevation. It is predicated on the principle that if the windlass mechanism is intact, passive dorsiflexion of the hallux (great toe) should produce a visible and palpable rise in the medial longitudinal arch, accompanied by supination of the subtalar joint and external rotation of the lower limb.
The test’s clinical value lies in its ability to differentiate between a functional and a non-functional or impaired windlass mechanism. In conditions such as pes planus (flat foot), hallux limitus, or plantar fasciitis, the mechanism may be compromised. Understanding why and where the breakdown occurs guides diagnosis and informs treatment planning, whether conservative or surgical.
Technique and Interpretation
To perform Jack’s test, the patient stands in a relaxed bilateral stance, ideally on a flat surface. The examiner kneels or crouches in front of the patient to observe the foot from the medial and anterior aspects. The first MTP joint of the hallux is then passively dorsiflexed — typically to approximately 30 to 45 degrees — while the clinician observes the medial longitudinal arch and subtalar joint from the front and side.
A positive test result — indicating a functional windlass mechanism — is characterised by a clear rise in the medial longitudinal arch, visible supination of the subtalar joint (the heel moves into varus), and some degree of external rotation of the tibia. These responses confirm that the plantar fascia is intact and that its tensioning is able to drive the expected kinematic chain. This response is reassuring and suggests that any flatfoot deformity present may be flexible rather than rigid.
A negative test result — where no appreciable arch elevation or subtalar supination occurs upon hallux dorsiflexion — indicates a dysfunctional windlass mechanism. This may result from a range of pathologies including plantar fascia degeneration or tearing, restricted first MTP joint motion (hallux limitus or rigidus), neuromuscular conditions affecting intrinsic foot muscle tone, or a structurally rigid flatfoot. In such cases, the foot is unable to adequately stiffen for propulsion, and compensatory biomechanical patterns are likely to emerge elsewhere in the kinetic chain.
Clinical Significance and Applications
Jack’s test holds considerable diagnostic utility across a range of common musculoskeletal presentations. In the assessment of pes planus, a positive Jack’s test helps to confirm that the deformity is flexible — meaning the arch can be reconstituted — rather than rigid, which would imply structural or osseous pathology. This distinction is clinically important because flexible flat feet may respond well to orthotic interventions and physiotherapy, while rigid flat feet may require surgical consultation.
In cases of plantar fasciitis, a negative or weakly positive Jack’s test may indicate that the plantar fascia’s tensile capacity is reduced due to chronic degeneration, partial tearing, or reactive thickening. Clinicians treating this condition use the test as part of a broader assessment battery, alongside palpation of the fascial band, assessment of ankle dorsiflexion range, and evaluation of footwear and gait. If the windlass mechanism is impaired, rehabilitation strategies must address the underlying cause — whether this is fascial stiffness, hallux mobility restriction, or muscular insufficiency.
The test is also valuable in preoperative assessment for procedures targeting the medial longitudinal arch or first ray. Surgeons performing procedures such as Cotton osteotomy, first MTP arthrodesis, or plantar fascia release need to understand the preoperative windlass function to anticipate postoperative biomechanical consequences. A negative Jack’s test prior to surgery may predict less optimal outcomes following arch-reconstructive procedures if the fascial tensioning system cannot support the corrected position.
Limitations and Considerations
Despite its widespread use, Jack’s test is not without limitations. Its interpretation is inherently subjective, relying on the examiner’s visual assessment of arch elevation and subtalar movement. Inter-rater reliability can vary, particularly among less experienced clinicians. Efforts to improve objectivity have included the use of navicular drop measurement, plantar pressure analysis, and fluoroscopic imaging to quantify arch changes during the test, though these remain largely within research rather than routine clinical settings.
Additionally, the test does not distinguish between the specific structures responsible for a negative result. A failed windlass response could stem from first MTP joint hypomobility, plantar fascial pathology, or poor intrinsic muscle function — each requiring a different management approach. As such, Jack’s test should always be interpreted within the broader clinical context, supplemented by a thorough history, gait analysis, range of motion assessment, and imaging where indicated.
Jack’s test remains one of the most elegant and accessible clinical tools available for assessing the windlass mechanism of the foot. By passively dorsiflexing the hallux and observing the consequent kinematic response, clinicians can rapidly gain insight into the functional integrity of the plantar fascia and the broader arch stabilisation system. Whether evaluating flexible flat feet, diagnosing plantar fasciitis, or planning surgical intervention, the test provides essential information that guides management decisions. While its limitations must be acknowledged, its simplicity, speed, and clinical relevance ensure that Jack’s test continues to occupy an important place in the podiatric and orthopaedic examination repertoire.