The spring ligament is a band of tough connective tissue on the underside of your foot that connects your heel bone (calcaneus) to the navicular bone, a small bone near the top of your arch. Its formal name is the plantar calcaneonavicular ligament, and it serves as the primary structural support for the arch on the inner side of your foot. Without it, your arch would gradually collapse under your body weight every time you stand or walk.
Where the Spring Ligament Sits
The spring ligament runs along the inner (medial) side of your foot, deep beneath the skin, bridging the gap between two key bones. The calcaneus, your largest foot bone, anchors the back end. The navicular, a smaller boat-shaped bone that sits at the peak of your arch, anchors the front. Together, this connection forms a kind of sling that cradles the head of your talus, the bone that sits on top of your foot and connects to your ankle.
It doesn’t work alone. The spring ligament has direct attachments to the deltoid ligament on the inner side of your ankle, and it lies just beneath the posterior tibial tendon, a major tendon that runs down from your calf. A thin gliding layer, only 1 to 3 millimeters thick, separates the tendon from the ligament, allowing them to slide against each other during movement. This close relationship means that problems in one structure often affect the other.
Three Bundles, Not One
Despite being called a single ligament, the spring ligament is actually a complex made up of three distinct bundles, each with a slightly different orientation and job:
- Superomedial bundle: The largest and most clinically significant of the three. It sits on the upper-inner portion of the complex and has fibers running in multiple overlapping directions, giving it broad, multi-directional strength. This is the bundle most commonly injured.
- Medioplantar oblique bundle: Positioned in the middle, with fibers running horizontally along the length of the foot.
- Inferoplantar bundle: The deepest layer, with fibers oriented vertically along its short axis.
The superomedial bundle contains fibrocartilage, a dense tissue similar to what you’d find in your knee’s meniscus. This cartilage-like surface directly supports the head of the talus bone, cushioning it as weight transfers through the foot.
How It Supports Your Arch
Your medial longitudinal arch, the curve along the inner side of your foot, is essential for absorbing shock, distributing your body weight across the foot, and providing a rigid lever for pushing off the ground when you walk or run. The spring ligament is the primary “static stabilizer” of this arch, meaning it holds the arch’s shape even when muscles aren’t actively contracting.
Think of it this way: your muscles and tendons are the active, dynamic supports for the arch, adjusting in real time as you move. The spring ligament is the passive safety net, maintaining the arch’s structural integrity at rest and preventing the bones from shifting out of alignment under load. When you’re standing still, or when your muscles fatigue during long periods on your feet, the spring ligament bears much of the responsibility for keeping the arch from flattening.
The Connection to Flatfoot
When the spring ligament stretches, tears, or weakens over time, the arch on the inner side of the foot loses its primary support. The talus bone drops downward, the arch flattens, and the heel tilts outward. This is the hallmark of adult-acquired flatfoot deformity, a progressive condition that typically develops in middle age and worsens without treatment.
In most cases, the process begins with dysfunction of the posterior tibial tendon rather than the spring ligament itself. As that tendon weakens or tears, it places greater stress on the spring ligament. Over time, the ligament stretches beyond its capacity and can no longer hold the arch in place. Once both structures fail, the deformity accelerates. However, spring ligament failure can also occur on its own in patients whose posterior tibial tendon appears normal on imaging, suggesting it can be an independent cause of flatfoot in some people.
Symptoms of a Spring Ligament Injury
A damaged spring ligament typically causes pain and tenderness along the inner side of the foot, concentrated under the arch. You may notice swelling in the same area, difficulty putting full weight on the foot, or a gradual flattening of the arch that you can see when standing. Pain often worsens with walking, standing for long periods, or pushing off the ground during a stride. Some people first notice the problem when their shoes begin wearing unevenly or their ankle seems to roll inward more than usual.
Because the spring ligament sits so close to the posterior tibial tendon, the symptoms of injury in either structure overlap significantly. Distinguishing between the two often requires imaging.
How Injuries Are Diagnosed
MRI is the standard tool for evaluating spring ligament damage. Radiologists look at the superomedial bundle in particular, checking for signs like unusually bright signal on certain MRI sequences (indicating fluid or inflammation within the tissue), a wavy or irregular contour, thinning below 2 millimeters, thickening above 5 to 6 millimeters, or a visible gap in the ligament indicating a complete tear.
In one study comparing patients with confirmed spring ligament injuries to healthy controls, the injured group had a significantly thicker superomedial bundle on MRI, averaging about 5.2 millimeters compared to 4.5 millimeters in healthy feet. Bright signal and visible discontinuity proved to be the most reliable indicators of actual injury, and both were strongly associated with flatfoot deformity.
Treatment for Spring Ligament Problems
For mild to moderate injuries, or early-stage flatfoot, conservative treatment focuses on supporting the arch externally while the ligament heals or stabilizes. Custom orthotic insoles and various brace designs can offload stress from the spring ligament, and studies have shown promising results with these approaches for isolated ligament ruptures. Physical therapy typically aims to strengthen the muscles that dynamically support the arch, particularly the posterior tibial muscle and other muscles in the lower leg and foot.
When conservative measures fail or the deformity progresses, surgery becomes an option. Reconstruction procedures aim to restore the arch’s alignment and reinforce the spring ligament. One approach uses a synthetic internal brace, a strong tape-like device, to supplement the ligament during healing. In a study of 132 surgical cases, patients who received the internal brace had a 0% failure rate compared to 4.5% in those who underwent reconstruction without it. Both approaches significantly improved arch alignment, but the internal brace group had fewer complications like malunion or the need for more extensive joint fusion procedures later on.
Recovery from spring ligament reconstruction typically involves a period of non-weight-bearing in a cast or boot, followed by gradual return to activity over several months. The exact timeline depends on the severity of the original damage and whether additional procedures were performed at the same time.