A subchondral fracture of the knee involves an injury to the bone tissue located immediately beneath the protective articular cartilage. This region, known as the subchondral bone plate, functions as a supportive layer for the joint surface. When a fracture occurs here, the structural integrity of the knee joint is compromised, leading to pain. Treatment varies significantly depending on the fracture’s size, stability, and the patient’s overall bone health. Approaches range from conservative, non-surgical methods aimed at natural healing, to complex surgical interventions for advanced or unstable injuries.
Defining and Identifying the Injury
The knee joint relies on a smooth interaction between the femur, tibia, and patella, with the subchondral bone supporting the overlying cartilage. A subchondral fracture is essentially a stress fracture resulting from cumulative damage rather than a single traumatic event. This injury is often termed a subchondral insufficiency fracture of the knee (SIFK) because it occurs when the bone structure cannot withstand normal mechanical loading.
Causes involve repetitive stress from overuse or athletic activity, or bone insufficiency related to conditions like osteopenia or knee osteoarthritis. Factors like prior meniscal tears or surgical procedures can also increase localized stress. Patients commonly experience an acute onset of severe, worsening knee pain, often without a clear injury event, which restricts walking.
Initial diagnosis often involves X-rays, which may appear unremarkable early on. The definitive diagnostic tool is Magnetic Resonance Imaging (MRI), which reveals the characteristic signs of the fracture. An MRI shows extensive bone marrow edema and a distinct, band-like fracture line in the subchondral region. Early diagnosis using MRI is important because the prognosis relates closely to the initial fracture size and timely treatment.
Conservative Management Strategies
For stable or smaller subchondral fractures, conservative management is the first line of defense, focusing on protected weight-bearing to remove stress from the injured bone. This strategy allows healing without the interruption of load-bearing activity. Patients use assistive devices like crutches or a knee brace to achieve a period of non-weight-bearing or partial weight-bearing.
This restricted activity is generally maintained for four to eight weeks, guided by the patient’s pain levels and follow-up imaging. The goal is to completely off-load the affected joint compartment. Physical therapy is introduced early with non-weight-bearing exercises, concentrating on maintaining range of motion and muscle strength around the hip and knee.
Pharmacological management supports this non-surgical pathway, primarily controlling pain and inflammation. Non-steroidal anti-inflammatory drugs (NSAIDs) manage discomfort, but their use must be balanced against potential effects on bone healing. For patients with underlying bone density issues, medications like bisphosphonates or teriparatide may be considered to enhance bone repair. Success relies heavily on strict adherence to activity restrictions, as premature return to full weight-bearing can lead to fracture progression and joint collapse.
Surgical Repair Options
Surgical intervention is necessary when conservative treatment fails, or when the fracture is large, unstable, or has progressed to significant subchondral bone collapse and osteonecrosis. Procedures aim to stabilize the fracture, promote bone healing, and restore a smooth joint surface, depending on the lesion size and cartilage involvement.
Marrow Stimulation Techniques
Marrow stimulation techniques, such as microfracture or drilling, involve creating small holes in the subchondral bone plate. This allows blood and bone marrow cells to seep into the defect, forming a repair tissue over the damaged area. Microfracture is generally reserved for smaller, contained defects to stimulate the body’s own healing response.
Structural Procedures
For larger defects or those with significant bone loss, structural procedures replace the damaged bone and cartilage. Osteochondral Autograft Transplantation (OATs), or mosaicplasty, involves harvesting small cylinders of healthy bone and cartilage from a less weight-bearing area of the knee. These plugs are then transferred to fill the defect. When the defect is too large for the patient’s own tissue, an Osteochondral Allograft Transplantation may be used, involving tissue from a donor.
In cases of early subchondral collapse without severe cartilage damage, subchondroplasty may be performed. This involves injecting a calcium phosphate bone substitute material into the fracture site. This material hardens, providing immediate structural support to the weakened bone and promoting subsequent healing.
When the subchondral fracture has progressed to end-stage disease, characterized by extensive bone collapse or rapidly advancing osteoarthritis, knee arthroplasty is often required. This procedure involves replacing the damaged joint surfaces with prosthetic components, either a partial (unicompartmental) or total knee replacement. Joint replacement is typically associated with a large initial lesion size or a delay in diagnosis that allowed for progressive joint destruction.
Rehabilitation and Long Term Outlook
The rehabilitation phase following treatment, whether conservative or surgical, aims to restore full function and protect the newly healed or repaired tissue. Physical therapy is the cornerstone of recovery, beginning with gentle range-of-motion exercises to prevent joint stiffness. This initial phase is strictly non-weight-bearing to protect the bone.
As healing progresses, the regimen advances to include strengthening exercises for the quadriceps and hamstrings, initially performed without bearing weight. The transition to partial and then full weight-bearing activities is gradual, guided by the patient’s pain response and the physician’s assessment. Recovery timelines vary significantly; conservative healing often takes several months, and a full recovery sometimes extends up to a year or more.
Following surgical procedures, the rehabilitation schedule includes specific protocols for protecting the transplanted or stimulated tissue. Factors affecting the long-term prognosis include the initial size of the subchondral lesion, the patient’s age, and their body mass index. Consistent adherence to the rehabilitation program is essential for a successful outcome, as non-compliance increases the risk of joint degeneration.