A malunion fracture is a broken bone that has healed, but in the wrong position. The bone fragments knit back together at an incorrect angle, with a twist, or at a shorter length than the original bone. Unlike a nonunion fracture, where the bone fails to heal at all, a malunion means healing did happen. It just didn’t happen correctly.
How Malunion Differs From Nonunion
Both malunion and nonunion are complications of bone healing, but they represent opposite problems. In a malunion, the bone has fully fused in a misaligned position. In a nonunion, the bone has stopped trying to heal altogether, leaving a gap or unstable connection even months after the injury. Doctors typically diagnose nonunion after six to twelve months of stalled healing. A malunion, by contrast, can be identified as soon as the bone has solidified in a visibly or measurably wrong alignment.
What Causes a Bone to Heal Incorrectly
Malunion happens for several overlapping reasons. The fracture fragments may not have been properly aligned (reduced) before a cast or splint was applied. A bone may shift position inside its cast during the healing period. Surgical hardware can fail to hold fragments in place. In some cases, the fracture pattern itself is so complex that achieving perfect alignment is extremely difficult.
Patient factors play a role too. Not following weight-bearing restrictions, removing a splint too early, or missing follow-up appointments can all allow fragments to drift out of alignment before they’ve fully solidified. The causes are genuinely multifactorial, involving both surgical technique and patient behavior.
Malunion rates for lower extremity fractures have been tracked at roughly 1.2% to 1.8% based on a large database study covering 17 years in South Carolina. That percentage sounds small, but it translates to thousands of cases. Certain fracture types carry higher individual risk: up to 30% of femoral shaft fractures treated with intramedullary nailing develop some degree of rotational deformity, and more than 10% heal with measurable angular misalignment.
Signs and Symptoms
Some malunions are obvious. You might notice a visible bend or twist in a limb, a leg that looks shorter than the other, or a joint that no longer moves through its full range. Other malunions are subtler, producing symptoms that seem unrelated to the original fracture site.
A femoral malunion, for instance, can cause pain not just in the thigh but in the low back, hip, knee, ankle, or foot. The misalignment changes how forces travel through your skeleton, and the stress shows up wherever the chain is weakest. Common symptoms include:
- Limping or uneven gait, caused by a leg length difference or rotational mismatch
- Chronic pain, either at the fracture site or in distant joints compensating for the misalignment
- Stiffness, particularly in the knee or hip, from altered mechanics
- Cosmetic deformity, where the limb looks visibly crooked or shortened
Not every malunion causes problems. People have a surprising tolerance for imperfect alignment, and some can walk, work, and exercise without significant difficulty even with measurable deformity. The exception is malunion that involves a joint surface. Even small irregularities in how two joint surfaces line up are poorly tolerated, typically causing pain, stiffness, and a faster path toward arthritis.
How Doctors Measure It
Malunion is diagnosed through X-rays and, when needed, CT scans that reveal the precise geometry of how the bone healed. Doctors measure three dimensions of misalignment: angulation (the bone healed at a tilt), rotation (the bone healed with a twist), and length (the bone healed shorter than it should be).
The generally accepted thresholds for a clinically significant malunion are greater than 10 degrees of angular deformity, greater than 10 degrees of rotational deformity, or more than 1.5 to 2 centimeters of shortening. Some definitions use a lower bar for angulation, starting at 5 degrees. These numbers guide treatment decisions, but symptoms matter just as much. A malunion that falls below these thresholds can still warrant correction if it’s causing real functional problems, while one that exceeds them may be left alone in a patient who feels fine.
One challenge in diagnosis is consistency. A systematic review of proximal humerus fracture studies found that only 58% provided a clear, reproducible technique for measuring alignment on imaging. Definitions of malunion vary between studies and even between surgeons, which means getting a second opinion on borderline cases is reasonable.
What Happens If It’s Left Untreated
A malunion that doesn’t cause symptoms can often be monitored without intervention. But one that alters joint alignment or weight distribution carries real long-term consequences. The most significant is post-traumatic osteoarthritis. When a bone heals in the wrong position, it changes the way forces are distributed across nearby joints. Cartilage that was designed to handle evenly spread loads instead gets concentrated pressure on one edge, wearing it down years faster than it otherwise would.
This is especially well-documented in ankle fractures. A malunion of the lower leg bones near the ankle alters the joint’s axis and congruency, and if untreated, reliably leads to post-traumatic ankle arthritis. The same principle applies to any weight-bearing joint: knees, hips, and even the spine can develop accelerated degeneration when a nearby malunion shifts how load is transferred.
Corrective Surgery
The primary treatment for a symptomatic malunion is a corrective osteotomy, a procedure where a surgeon intentionally re-breaks the bone at or near the malunion site, realigns it to the correct position, and stabilizes it with plates, screws, or a rod while it heals a second time. The surgery is tailored to the type of deformity.
A single-plane angular deformity can be corrected with a wedge osteotomy, where the surgeon either removes a wedge of bone (closing wedge) or creates a gap and fills it with bone graft (opening wedge). A rotational deformity is corrected by cutting the bone and twisting it back to the correct orientation. Complex cases involving all three planes of deformity, combining angulation, rotation, and length, require more involved techniques and sometimes external fixation devices that allow gradual correction over weeks.
Not every malunion requires surgery. If your symptoms are mild and functional limitations are minimal, physical therapy, shoe lifts for small leg length differences, and activity modification may be enough. The decision depends on how much the malunion affects your daily life and whether the long-term risk of joint damage justifies the recovery period of a second surgery.
Recovery After Correction
Recovery from corrective osteotomy varies widely depending on which bone was involved and how complex the deformity was. You’ll likely need crutches, a splint, or a brace during healing. Weight-bearing restrictions are common, especially for leg corrections, and the timeline to return to full activity is typically a few months or longer. The bone is essentially healing from a fresh fracture, so the same biological process that took weeks the first time needs to happen again.
Physical therapy is a central part of recovery, focused on restoring range of motion in nearby joints, rebuilding strength in muscles that may have adapted to the old alignment, and retraining normal movement patterns. Unlike the original injury, the advantage this time is that the bone has been deliberately positioned correctly and stabilized with hardware designed to hold that position through the healing process.