Can Screws Come Out of Bones? Causes and Solutions

Screws placed in bone during orthopedic or spinal surgery can and do come loose, back out, or migrate from their original position. The phenomenon is well-documented and more common than many patients realize. In spinal fusion surgery alone, depending on how loosening is defined, studies report prevalence rates ranging from about 10% for screws that partially pull out to roughly 40% when subtle signs of bone erosion around the screw are included on imaging.¹ The causes fall into several overlapping categories, from the quality of the patient’s bone to surgical technique to the relentless mechanical forces that act on hardware every time you stand, walk, or bend.

How Common Is Screw Loosening

The numbers vary widely depending on the type of surgery, the patient population, and how strictly loosening is defined. In posterior spinal fusion, one systematic review found that when loosening was defined as a screw partially pulling out of bone, the prevalence was about 10%. But when loosening was defined more broadly, including any radiolucent rim wider than one millimeter visible around a screw on imaging, the prevalence jumped to around 40%.¹ That wider definition captures early erosion of bone around the screw threads before the screw has visibly shifted, so many of those cases are subclinical and never cause symptoms.

In patients with lumbar degenerative disease specifically, one study found loosening in about 30% of patients, though only about 9% of individual screws were affected.² That discrepancy makes sense: a patient with several screws may have one or two that loosen while the rest hold firm. For fracture-fixation hardware in arms and legs, loosening rates tend to be lower overall, but the consequences when it does happen can be more immediately obvious, such as loss of fracture alignment or pain at the hardware site.

Why Bone Quality Matters More Than the Screw Itself

The single biggest predictor of whether a screw stays put is the density and health of the bone surrounding it. When a screw fails, what actually gives way is usually not the metal but the bone. Pull-out testing on human spines consistently shows that failure occurs along a cylinder of bone surrounding the screw threads; the bone shears away while the screw remains intact.³ Think of it like pulling a tent stake from wet sand versus dry-packed earth: the stake is the same, but the holding material is everything.

Recent research has quantified this relationship in spinal screws. The mineral density of bone immediately surrounding the screw threads correlated more strongly with pull-out strength than broader measures of vertebral bone density.⁴ That finding has practical implications: two patients can have similar overall bone density scores but very different screw-holding ability if the local bone around the screw differs in quality. Osteoporosis is the most recognized risk factor for loosening, and it was identified as a significant contributor in a large systematic review of spinal fusion outcomes.¹ But you do not need a formal osteoporosis diagnosis for bone quality to be an issue. Aging, prolonged steroid use, metabolic disorders, and even local bone changes from prior surgery all weaken the interface between metal and bone.

Cyclic Loading and the Fatigue Problem

Even when a screw is placed perfectly in healthy bone, the forces of daily life slowly work against the fixation. Every step, every bend, every twist applies loads to the hardware. Bone is not a rigid material; it deforms slightly under load and recovers, much like a mattress compresses under your weight and springs back. But the recovery is not quite complete each time. Laboratory models show that the interfacial deformation between bone and screw accumulates with repeated loading cycles, and some of that deformation is permanent and irrecoverable.⁵ The researchers found this effect was worse in osteoporotic bone, creating a vicious cycle where weaker bone deforms more and recovers less.

In mechanical testing of screws placed in locking plates used to bridge bone defects, repeated compressive loading significantly reduced the torque needed to remove the screws compared to screws that had not been cyclically loaded.⁶ In other words, even moderate, repetitive activity gradually loosens hardware. A critical transition point has been identified in testing at roughly 20% of the maximum failure force, where energy dissipation and permanent deformation spike sharply, suggesting a threshold below which the bone-screw interface remains stable and above which progressive loosening begins.⁷

The Surgical Technique Factor

How tightly a surgeon drives a screw into bone matters enormously, and the margin for error is narrower than most people would expect. Over-tightening a screw can strip the bone around the threads, and when that happens, the consequences are dramatic: compression at the bone-screw interface drops by about 95%, and pull-out resistance drops by about 93%.⁸ The optimal insertion torque sits between 70% and 80% of the bone’s stripping limit. Continuing to tighten after the screw head makes contact does not improve holding power; it only increases the chance of stripping.

Research in animal bone has confirmed the concern: clinical-level lag screw tightening, around 86% of the bone’s maximum tolerated torque, already exceeds the yield point, meaning the bone has begun to sustain damage that compromises holding strength.⁹ The tricky part is that surgeons cannot feel the exact stripping threshold through their instruments. Under-tightening is a problem too, leaving insufficient compression at the fracture or fusion site and allowing micro-motion that promotes loosening over time.¹⁰

Hidden Infections and Biofilm

Not all screw loosening is purely mechanical. There is growing evidence that low-grade infections, sometimes undetectable by standard blood tests, play a role. Bacteria can colonize implant surfaces and form biofilms, a slimy protective layer that shields them from both the immune system and antibiotics. These biofilms have been found at high rates on implants removed from patients who were clinically diagnosed with “sterile” failed fusions.¹¹ The process, sometimes called “occult infection,” can cause the bone and implant to slowly disassociate without the dramatic fever, redness, or drainage that patients typically associate with an infected surgical site.

Low-virulence bacteria, organisms that do not cause obvious illness, have been specifically identified as a possible driver of screw loosening after spinal fusion.¹² Research into how biofilms interact with bone has shown that certain bacteria, particularly Staphylococcus species, may directly promote bone resorption around an implant and can migrate into tiny channels within the bone tissue itself.¹³ This is an area where the science is evolving quickly, and it suggests that some cases of “unexplained” screw loosening may actually have an infectious component that went undetected.

Wear Debris and Bone Erosion Around Implants

In joint replacements, the leading cause of long-term implant failure is not infection or mechanical overload but a process called aseptic osteolysis, where the body’s own immune system slowly destroys bone around the implant. Tiny particles shed from the implant’s bearing surfaces trigger an inflammatory response. Immune cells arrive to clean up the debris but in doing so release chemicals that activate bone-eating cells, gradually eroding the bone that holds the implant in place.¹⁴ This process remains the leading complication of total hip replacement and is a common reason for revision surgery.¹⁵

While this specific mechanism is most studied in hip and knee replacements rather than simple bone screws, the principle of debris-driven bone loss applies wherever metal meets bone under load. Even in spinal hardware, corrosion products and metal particles from the rod-screw junction can provoke a local inflammatory reaction. A related concern is metal hypersensitivity, where some patients develop an immune reaction to metals like nickel or cobalt in their implants, leading to bone erosion, swelling, and hardware loosening.¹⁶

When a Loose Screw Becomes Dangerous

A loose screw does not always cause problems. In many cases, it is discovered incidentally on follow-up imaging, and if the fracture has healed or the fusion has solidified, the screw has already done its job. But when a screw backs out or migrates before healing is complete, the original fracture or fusion can fail. And in rare but serious cases, a migrating screw can damage surrounding structures.

Case reports have documented screws migrating into the pelvis after hip surgery, where they come dangerously close to major blood vessels and nerves.¹⁷ In pediatric patients, migrated screws from femoral plates have been reported to cause injury to the popliteal artery behind the knee, resulting in pseudoaneurysms that required surgical repair.¹⁸ Patients who undergo regular physical therapy with migrated hardware nearby are at particular risk for soft-tissue injury from the displaced metal.¹⁹ These cases are uncommon, but they illustrate why follow-up imaging matters and why new pain around old hardware should be evaluated promptly.

How Loosening Is Detected

Screw loosening is usually identified on CT scans or X-rays by a telltale halo of lucency, a dark zone where bone has resorbed, surrounding the screw. The standard threshold is a radiolucent area wider than one millimeter around the screw, sometimes accompanied by a “double-halo” sign where two concentric rings of lucency appear.²⁰ CT scanning is the preferred tool for assessment.²¹

That said, imaging is far from perfect at catching loosening early. One study comparing imaging findings with what was actually found during screw-removal surgery reported that X-rays had a sensitivity of only 24% for detecting true loosening, and CT was only slightly better at 22%, though both had very high specificity around 96 to 98%.²² In plain terms, if imaging shows a halo around the screw, you can be confident it really is loose, but imaging misses most cases of early loosening. This means some patients with subtle screw loosening will have normal-looking scans, which is why clinical symptoms like new or worsening pain, a change in posture, or a palpable prominence under the skin also factor into the diagnosis.

Solutions When Screws Loosen

The surgical strategy for dealing with a loosened screw generally follows a few standard approaches: replacing the screw with a larger or longer one to engage fresh bone, augmenting the screw with bone cement, or extending the fixation to include additional spinal segments or adjacent bone.²³

Bone cement augmentation has become a widely used technique for patients with weak bone. In spinal surgery, a small amount of acrylic cement is injected through or around the screw to fill gaps and interlock with the surrounding bone. Studies confirm that cement-augmented cannulated screws significantly increase pull-out strength compared to standard solid screws in osteoporotic bone.²⁴ Clinical data show that cement augmentation reduces the incidence of loosening in osteoporotic patients, with fenestrated screws (screws that have holes along their shaft to distribute cement) performing particularly well.²⁵ The main concern with cement is that it can leak outside the vertebral body, potentially compressing nerves, though improvements in screw design and injection technique have reduced this risk.

For patients in whom cement poses too much risk, expandable pedicle screws offer an alternative. These screws have blades or wings that splay outward after insertion, mechanically gripping a wider area of bone. In laboratory testing, expandable screws achieved pull-out strength about five times greater than conventional screws and comparable to screws augmented with cement, all without the risk of cement leakage.²⁶

Surface Coatings That Help Bone Grip the Screw

One strategy for preventing loosening before it starts is coating the screw surface with materials that encourage bone to grow directly onto the implant. Hydroxyapatite, a calcium-phosphate compound that mimics the mineral component of natural bone, is the most studied coating. In animal studies, hydroxyapatite-coated pedicle screws showed dramatically more bone-to-implant contact than uncoated screws: about 69% versus 18% at six weeks, and 64% versus 9% at twelve weeks.²⁷

More recent work in a porcine model showed that even a thin hydroxyapatite coating improved extraction torque compared to standard titanium screws, and the bond between bone and coating held without detaching for up to 24 weeks.²⁸ Hydroxyapatite coatings have also been tested on other implant surfaces beyond screws, confirming increased mechanical fixation and bone growth.²⁹ These coatings are promising, though they add manufacturing complexity and cost, and their clinical use in spine surgery is still growing.

Does Early Weight Bearing Cause Screws to Fail

A common worry among patients after fracture fixation surgery is whether walking too soon will cause the hardware to loosen or the fracture to shift. The evidence actually runs counter to that fear. In ankle fractures, a meta-analysis comparing early weight bearing with delayed weight bearing found no increase in complications from walking sooner: no cases of loss of reduction, malunion, or nonunion were reported among early-weight-bearing patients, while four such events occurred in the delayed group.³⁰

Similar findings have emerged for distal femur fractures treated with locking plates. A comparative study found no post-operative complications in the early-weight-bearing group, while six complications including fracture displacement and implant failure occurred in the delayed group. The authors suggested that prolonged non-weight bearing may actually delay healing and increase the risk of fixation failure.³¹ Even ankle fractures involving the syndesmosis and fixed with a positioning screw showed no hardware failures or infection with immediate weight bearing.³² Of course, early weight bearing always means controlled, progressive loading under a surgeon’s guidance, not ignoring restrictions entirely. But the blanket belief that walking on a repaired fracture will pop the screws out does not hold up.

Pediatric Hardware and Growing Bones

Children present a unique challenge because their bones are still growing. Growth plates, the cartilage zones near the ends of long bones, are actively changing shape and size, and hardware placed near them can migrate as the bone remodels. The migration of epiphyseal screws into the growth plate is a recognized complication of certain pediatric procedures like tension band plating for limb-length correction.³³

To address the problem of permanent metal in growing bodies, bioabsorbable screws were developed. Made from materials that the body gradually breaks down and replaces with bone, they are commonly used in knee ligament reconstructions in young athletes. But they do not always absorb as planned. In a study of pediatric and adolescent patients who needed re-operation after ACL reconstruction with bioabsorbable tibial screws, nearly half the screws were still fully intact at removal, and about 98% of cases showed cystic inflammatory reactions around the screw.³⁴ This is a reminder that even screws designed to disappear can cause problems if the body reacts to them before they fully dissolve.

Risk Factors That Patients Can and Cannot Control

Some risk factors for screw loosening are not modifiable. Age, the number of spinal levels fused, the specific vertebral levels involved (particularly the sacrum and pelvis), and the underlying reason for surgery, such as scoliosis, have all been linked to higher loosening rates.¹ Spinal alignment problems like pelvic incidence-lumbar lordosis mismatch and frontal imbalance before surgery were also significant risk factors in that same analysis, which makes sense: if the spine is mechanically unbalanced, the hardware absorbs forces it was not designed to handle.

Factors patients can influence include bone health and smoking status. Treating or preventing osteoporosis before elective spinal surgery, through medications, weight-bearing exercise, calcium, and vitamin D, can meaningfully improve screw purchase. Smoking impairs bone healing and has been studied as a contributor to screw loosening and poor outcomes in spinal stabilization procedures.³⁵ While quitting smoking will not eliminate the risk, it removes one of the few modifiable variables that patients have control over heading into surgery. Nutrition, body weight, and activity level after surgery also play supporting roles, though large studies isolating each of these factors individually are still limited.