A distal femur fracture is a break in the bottom end of the thighbone, near the knee joint. Specifically, it involves the lowest 15 centimeters of the femur, from the wide, flared portion above the knee down to the joint surface itself. These fractures range from clean breaks that don’t involve the knee joint to complex, shattered injuries that split the joint surface into multiple fragments.
Where Exactly the Break Occurs
Your femur is the longest, strongest bone in your body, and its bottom end widens into two rounded knobs called condyles. These condyles form the top half of your knee joint, sitting on the flat surface of your shinbone. A distal femur fracture can break through the wider shaft just above these condyles (the supracondylar region), through the condyles themselves, or both.
This matters because fractures that extend into the joint surface are more difficult to treat and carry a higher risk of long-term knee problems. Doctors generally categorize these breaks into three types: extra-articular fractures that stay above the joint, partial articular fractures where one condyle breaks off while the other stays connected to the shaft, and complete articular fractures where the joint surface separates entirely from the rest of the bone. A partial articular fracture might involve just the outer condyle, the inner condyle, or a slice off the back of the bone known as a Hoffa fragment.
Who Gets These Fractures and Why
Distal femur fractures follow a distinct two-group pattern. In younger adults, they’re almost always caused by high-energy trauma: car crashes, motorcycle accidents, falls from height. These injuries tend to produce more severe fracture patterns with significant displacement, shattering of the bone into multiple pieces, and serious damage to the surrounding soft tissues. Young patients with these fractures often have other injuries as well.
In older adults, particularly those with osteoporosis, even a simple fall from standing height can fracture the distal femur. These low-energy fractures are typically simpler breaks, often staying outside the joint, but they present their own challenges because of weakened bone quality and existing health conditions. A growing subset of these injuries are periprosthetic fractures, meaning the bone breaks around an existing knee replacement implant. This occurs in roughly 0.3% to 2.5% of people with primary knee replacements, though the rate climbs as high as 30% to 38% after revision knee surgery.
Symptoms and How It’s Diagnosed
The signs are usually hard to miss. You’ll have significant pain in the lower thigh and knee area that worsens with any attempt to move the knee. Bearing weight on the leg is typically impossible. The area around the distal thigh and knee will swell quickly, often with visible bruising, and the leg may appear angled inward or outward if the fracture is displaced. If the break extends into the joint, fluid will accumulate inside the knee itself.
Diagnosis starts with standard X-rays from the front and side. In many cases, a CT scan follows to map exactly how the fracture lines run, especially to see whether and how the joint surface is involved. This detail is critical for surgical planning. If there’s any concern about damage to the blood vessels behind the knee (a risk with high-energy injuries), doctors will check blood flow to the lower leg and may order additional vascular imaging.
When Surgery Is Needed
Most distal femur fractures require surgery. The exceptions are stable, undisplaced fractures where the bone fragments haven’t shifted out of position. These can sometimes be managed with a hinged knee brace for more stable patterns or a full leg cast for 6 to 12 weeks, followed by bracing.
For displaced fractures, the two most common surgical options are a locking plate fixed to the outer side of the bone and a retrograde intramedullary nail, which is a metal rod inserted through the knee and up into the center of the femur. Both approaches have mechanical failure rates between 4% and 22%, with higher risk in patients who have osteoporosis, obesity, or significant bone loss along the inner side of the fracture. Some surgeons now use both a plate and a nail together for difficult cases, creating a stiffer construct that better resists the bending forces at the fracture site. This combined approach can sometimes allow full weight bearing immediately after surgery.
Periprosthetic fractures around knee replacements add another layer of complexity. Depending on the design of the existing knee implant, a retrograde nail may not fit through the prosthesis, making plate fixation the only option. In some cases, the implant itself needs to be revised.
Recovery Timeline
How quickly you can put weight on the leg varies significantly depending on the fracture pattern, bone quality, and your surgeon’s judgment. Traditional protocols restrict weight bearing for roughly 10 to 12 weeks. In one study, the standard group waited a median of 81 days before being allowed to bear weight as tolerated. However, there’s a growing trend toward earlier weight bearing. Patients allowed to bear weight within 30 days of surgery actually had a lower nonunion rate (4.8%) compared to those kept non-weight-bearing for longer (11.8%), likely because controlled loading stimulates bone healing.
Overall, bone union typically occurs by about 20 weeks, with reported union rates around 93% for fractures allowed early weight bearing. The overall nonunion rate across all distal femur fractures is approximately 13.8%, making it one of the more significant risks with this injury. Surgical site infection and the need for later knee replacement surgery are both more common in patients whose fractures fail to heal.
Rehabilitation and Regaining Knee Motion
Knee stiffness is one of the biggest challenges after a distal femur fracture, and physical therapy starts early to combat it. The rehabilitation process is gradual and structured over several months.
During the first week after surgery, the focus is on ankle movement and gentle, limited bending of the knee and hip. By weeks two through four, you’ll begin actively bending and straightening the knee yourself, with some assistance from a therapist. Around week four to eight, exercises like heel slides (lying on your back and sliding your heel toward your buttocks) become central, and the goal is reaching 90 degrees of hip flexion. After eight weeks, therapists often introduce passive range-of-motion techniques or a continuous passive motion machine to push the knee further if progress has plateaued.
The overall goal is restoring enough knee motion and strength to return to your prior level of function. For younger patients with high-energy injuries, this may mean getting back to an active lifestyle. For older patients, the priority is often returning to independent walking and daily activities. Full recovery commonly takes six months to a year, and some degree of knee stiffness or discomfort with activity can persist long-term, particularly when the fracture involved the joint surface.