A malunion is a fracture that heals in the wrong position. The bone mends, but with abnormal alignment, rotation, or length, leaving you with a deformity that can affect how the limb looks, moves, and functions. Unlike a nonunion, where the bone fails to heal at all, a malunion means healing did occur, just not the way it should have.
How Malunion Differs From Nonunion
Bone healing problems fall into three categories, and the distinctions matter because treatment is different for each. A delayed union means the bone is healing more slowly than expected, typically identified between three and six months after the fracture. A nonunion means healing has stalled entirely. The FDA defines nonunion as a fracture line still visible on imaging more than nine months after injury, with no signs of progress. Patients with nonunion often have persistent pain, loss of function, and reduced mobility at the fracture site.
Malunion is fundamentally different from both. The bone has healed, and the fracture line is gone. The problem isn’t that healing failed but that it succeeded in the wrong configuration. The fragments fused at an angle, with a twist, or with overlap that shortened the bone. This can happen even when a fracture appears to be healing “well” on early X-rays if the alignment wasn’t properly restored or maintained.
What Counts as a Malunion
Not every slightly crooked fracture qualifies. Bones don’t always heal in perfect anatomical position, and minor deviations may cause no problems. Current orthopedic literature defines a clinically significant malunion based on specific thresholds: an angular deformity greater than 5 to 10 degrees, rotational malalignment greater than 10 degrees, or shortening of more than 1 to 2 centimeters. These numbers apply primarily to long bones like the femur and tibia. For smaller bones, such as the scaphoid in the wrist, different measurements are used, like the ratio of bone height to length on a CT scan.
The key word in the definition is “symptomatic.” A 6-degree bend in a healed shinbone that causes no pain or functional problem may be left alone. The same bend in someone who walks with a limp, has knee pain, or can’t run is a malunion that needs attention.
Common Causes
Malunion results from either a mechanical failure or a biological one during the healing process, and often a combination of both. The most common mechanical cause is inadequate reduction, meaning the bone fragments weren’t properly realigned before they were immobilized. If a fracture is set with residual angulation or rotation, the bone will heal in that position.
Hardware failure is another mechanical cause. If screws loosen, plates shift, or a cast doesn’t hold the fracture firmly enough, the fragments can drift out of alignment while they’re still healing. Premature weight-bearing, before the bone has consolidated enough to handle the load, can produce the same result. In fractures treated without surgery, the fragments may gradually shift inside a cast, especially if swelling decreases and the cast becomes loose.
Biology plays a role too. Poor blood supply to the fracture site can lead to uneven healing, where one side of the bone heals faster and pulls the alignment off. Smoking is a well-documented risk factor: nicotine constricts blood vessels, reduces callus formation (the new bone that bridges a fracture), lowers vitamin D levels, and decreases the activity of stem cells involved in bone repair. Smokers also show reduced levels of bone-building proteins at fracture sites. Vitamin D deficiency, which is especially common among smokers, further impairs the bone’s ability to heal properly.
How Common It Is
Malunion rates vary widely depending on the bone involved and how the fracture was treated. Distal radius fractures (broken wrists) are among the most studied. After conservative treatment with a cast, malunion develops in roughly 23% to 33% of patients. After surgical fixation, the rate drops to 3% to 10%. That said, most of these malunions are mild enough that they don’t require further surgery. In a large national study, only about 1% of conservatively treated wrist fractures ultimately needed a corrective operation.
Signs You Might Have a Malunion
The most obvious sign is a visible deformity. A limb that looks bent, twisted, or noticeably shorter than the other side after a fracture has healed suggests the bone set in the wrong position. But not all malunions are visible to the naked eye. Rotational malalignment, where the bone healed with a twist, can be difficult to see but easy to feel. You might notice that your foot points inward or outward compared to the other side, or that your range of motion at a nearby joint feels restricted.
Leg length discrepancy is a hallmark of femoral malunion. Differences of more than 1.5 to 2 centimeters can change your gait, cause hip or back pain, and make one leg feel “off.” Doctors measure both the actual leg length and the apparent length you perceive, since muscle tightness and pelvic tilt can make a small difference feel larger than it is. Joint stiffness near the healed fracture is another common complaint, particularly at the knee or wrist.
How Malunion Is Diagnosed
Diagnosis starts with X-rays taken from multiple angles to measure the alignment of the healed bone compared to normal anatomy. Doctors look at specific angles: how the bone tilts in the front-to-back plane, how it angles side to side, and whether there’s any shortening. For long bones like the femur, full-length standing X-rays of both legs allow direct comparison of limb length and joint alignment.
CT scans provide more detail when rotational malalignment is suspected, since rotation is nearly impossible to measure accurately on a flat X-ray. A CT scan of both limbs can precisely quantify the twist. In one example from the research literature, a CT scan revealed a rotational difference of more than 16 degrees between a patient’s two femurs, a deformity invisible on standard X-rays. For wrist malunions, thin-slice CT scans (with sections as fine as 0.625 millimeters) map the bone’s three-dimensional shape to guide surgical planning.
What Happens Without Treatment
A malunion that causes no symptoms can often be left alone safely. But a significant malalignment near a joint creates long-term consequences. When a bone heals at an angle, it shifts the load-bearing forces across the nearby joint unevenly. Research on tibial malunions near the knee found a strong statistical link between the degree of angular deformity and increased force on one side of the joint. Over time, this uneven loading accelerates cartilage breakdown, leading to post-traumatic arthritis. The longer the malunion persists, the more the joint deforms. In one study, the combination of abnormal forces and time since fracture directly predicted how much secondary deformity developed at the knee.
For lower-limb malunions, altered gait mechanics can also cause pain in the hip, back, or opposite knee as the body compensates for the asymmetry.
Corrective Surgery
The primary treatment for a symptomatic malunion is a corrective osteotomy, a procedure where the surgeon intentionally re-breaks the bone along the old fracture line, realigns it properly, and fixes it in the correct position with plates and screws. This is not a minor operation. It requires careful preoperative planning, often using CT-based 3D models, to calculate exactly how much correction is needed in each plane.
For wrist malunions, the surgeon cuts through the old fracture site from one or both sides, repositions the fragments to restore normal angles and bone length, then secures everything with a locking plate. If realigning the bone creates a gap, a bone graft (usually taken from the patient’s own body) fills the space. About a third of patients in one study needed bone grafting due to large defects. For femoral malunions, the surgeon may remove a wedge of bone to correct both the angle and the leg length discrepancy simultaneously, with documented cases restoring up to 2 centimeters of limb length.
Recovery After Corrective Osteotomy
Recovery follows a predictable timeline, though it varies by location and severity. For wrist corrections, the joint is typically immobilized in a plaster splint for four weeks, followed by two more weeks in a removable wrist splint. After that, gentle exercises begin. X-rays at the four-week mark confirm healing is on track. Full radiographic healing of the osteotomy site takes an average of about 11 to 12 weeks, with a range of 11 to 14 weeks in published case series. Functional recovery, meaning the return of grip strength, range of motion, and the ability to use the hand normally, follows gradually after that.
For larger bones like the femur, the timeline is longer. Weight-bearing is restricted for weeks to months depending on the stability of the fixation, and full recovery can take six months or more. Physical therapy is essential throughout the process to restore strength, flexibility, and normal movement patterns.