The human foot is a marvel of engineering, and much of the art of Podiatry and sports medicine is focused on understanding how it bears weight. Perhaps one of the most useful clinical test for assessing foot mechanics, the Jacks test for windlass mechanism, is one of the simplest, and perhaps one of the most useful, contemporary tests available. Easy to perform and based on sound biomechanical principles, this test affords clinicians a direct insight into how the ‘should be’ arch support system is actually working.
This article will unpack the test, explaining what it assesses, how it should be conducted, and what the results reveal to those in pain, or walking funny, in layman’s terms.
Understanding Jacks Test for Windlass Mechanism
Fundamentally, the windlass mechanism is the foot’s tensioning mechanism. As the big toe dorsiflexes while walking, the plantar fascia, the central band of tissue that extends along the sole of the foot, winds like a cable around a drum, thereby stiffening the plantar fascia, lifting the medial longitudinal arch and stiffening the entire foot for effective push-off. When the windless mechanism is not functioning, the gait cycle becomes mechanically inefficient and abnormal stress is redistributed to cause long-term problems.
Windlass Mechanism Basics
The plantar fascia attaches inferiorly at the heel and fans anteriorly to attach on the plantar aspect of the base of each toe. When the hallux dorsiflexes, (i.e. bends dorsally), the fascia is tensioned as it loops around the head of the first metatarsal like a cable around a capstan. This is the windlass effect.
The arch is elevated, the subtalar joint supinates and the foot is transformed into a rigid lever for pushthe failure of this chain of events to occur results in a relatively planar flexible foot when it should be becoming rigid-an inefficient system that predisposes to conditions as diverse as plantar fasciitis to posterior tibial tendon dysfunction.
Jack’s Test vs. Hubscher Manoeuvre
This is where the terminologies become a little muddled. Jacks test and the Hubscher manoeuvre refer to essentially the same clinical test and are used interchangeably by different clinicians and in different countries. Some clinicians and podiatrists use Hubscher in the literature but others use the more common term Jacks test in their routine podiatric practice.
The test itself is the same: dorsiflexion of the hallux in a weight bearing position, watching for an arch response.
Performing Jacks Test for Windlass Mechanism
It’s easy to underestimate the importance of executing the evaluation accurately. Slight inaccuracies in technique – excessive application of force, inappropriate foot placement, patient anticipatory guarding – can compromise the validity of the results. Its weight-bearing intent is central to its clinical relevance.
Recreating the load environment present during normal stance means the fascia receives the same tensile loading experienced when walking, as opposed to the lax unloaded state present in the supine position.
Patient Position and Setup
The patient should have their feet placed flat on a hard level surface with weight evenly distributed. The patient should be relaxed and in a normal stance. The examiner should crouch/kneel in front of the patient to observe the medial arch profile before any movement has taken place.
Resting arch height is important, so observe the resting arch height, a flat arch at rest and a neutral arch will respond differently so this may influence your response. It can be beneficial to test both feet in turn as differences may be detected that are missed when testing just a single foot.
Step-by-Step Test Procedure
Lightly stabilize the midfoot with one hand and passively dorsiflex the hallux, lifting the big toe upwards with the other hand. Remember the passive – don’t let the patient do the work. Watch the medial arch as the toe is dorsiflexed; a normal windlass mechanism will produce a visible increase in arch height while the heel inverts very slightly and the toe joint offers little resistance.
Movement should be fluid – any stiffness, lack of arch change, or discomfort should all be noted.
How to Interpret Jacks Test Results
Having the test performed is only 50% of the work. Interpreting what the results actually mean – and what they don’t – requires some clinical judgment. The findings are always on a continuum rather than a clear pass/fail and context is essential when drawing conclusions from a solitary orthopaedic test.
Normal vs. Abnormal Findings
Normal performance would demonstrate a defined, proportional increase of the medial arch as the hallux is dorsiflexed with the heel deviated slightly into inversion and the forefoot feeling reasonably stiff. Both abnormal patterns may be described into two categories; lack of or minimal arch raising which would indicate that the windlass mechanism is not being properly actuated; or dorsiflexion of the hallux which is uncomfortable which would indicate that the first MTP is limited. These two pattern’s should not be confused.
What a Positive Test May Suggest
A positive test- where the arch is not responding as it should- is more indicative of a flexible flatfoot with an arch present at rest but collapsing under load as the windlass is unable to produce the necessary tension. Positive tests may also indicate hallux limitus as decreased range of motion of the first MTP joint physically limits tensioning of the fascia. Decreased windlass efficiency – due to any cause – is usually associated with increased stresses through the plantar fascia itself and altered loading patterns through the ankle and knee.
Clinical Uses and Limitations
Jacks test is not a diagnostic test but a part of a wider assessment of foot function. It will be used in conjunction with gait analysis, muscular strength and joint range-of-motion tests to provide a clearer assessment of foot function. The test has value in its own right but limitations.
Where the Test Helps Most
This assessment is especially beneficial when assessing the stability of an arch in patients with plantar heel pain, excessive pronation, or forefoot pressure problems. It is a great means to distinguish between a fixed or mobile flatfoot deformity, which in turn guides the intervention by means of orthotics, footwear modification or rehab exercises to strengthen intrinsic foot muscles.
Common Pitfalls and Reliability Issues
Tester technique is also a major factor. Overly dorsiflexing the hallux will give the appearance of arch movement, less will fail to elicit one. Pain, fear, guarding by the patient can inhibit the windlass mechanism.
The inability of the static exam to translate into real time gait may mean static findings are not reflective of real life walking or running (hence why combining it with a functional gait assessment makes for a far more complete clinical picture).
Related Conditions and Practical Considerations
Getting a sense of how the findings of Jacks test relate to the wider picture of foot health provides a more realistic outlook on what the results will mean on a daily basis for clinicians and patients alike.
Flexible Flatfoot and Plantar Fascia Issues
A no or sluggish windlass response in a flexible flat is indicative of the arch not being dynamically supported during push-off. This results in repetitive overload to the plantar fascia, spring ligament and posterior tibialis over time. Typical complaints include medial arch fatigue, heel pain that increases with prolonged standing, or pain after the initial few steps in the morning, the classic signs of a fascial loading system not dispersing force efficiently.
When Jacks Test Results Need Further Assessment
Abnormal findings do not necessarily equate to pathology- but they should always trigger further investigation. Weight bearing X-rays can measure the degree of arch collapse more objectively. Ultrasound can be used to determine the thickness of the plantar fascia, as well as the quality of its structure.
Finally, a full gait analysis- either visual or through pressure plate techniques- will observe foot behavior throughout an entire gait cycle, something that a clinical test on its own cannot achieve. Jacks test for the windlass mechanism – explained. How is it performed, normal and abnormal results and indications for further assessment.