Patellar fracture (broken knee cap): causes, symptoms and treatment

Anatomy and function of the kneecap

The patella (kneecap) is a sesamoid bone embedded in the quadriceps tendon. It increases the lever arm of the extensor system and protects the front of the knee joint. The back is covered with articular cartilage and slides in the groove of the femur (trochlea femoris).

• Components of the extensor system: quadriceps muscle, quadriceps tendon, patella, patellar tendon, shinbone (tibia).
• Tasks: Power transmission when extending the knee, protection against direct pressure/trauma, guidance of the patella in the thigh groove.

A break can disrupt this mechanism. What is important for therapy planning is whether active extension of the leg is still possible and how the joint surface is affected.

Causes and risk factors

Patellar fractures are usually caused by direct force or by sudden pulling forces of the quadriceps.

• Direct trauma: fall on the bent knee, impact in sports or traffic accident.
• Indirect trauma: Sudden forceful contraction of the quadriceps against resistance (e.g., slipping and catching).
• Less common: stress fractures due to overload, especially a. in sports with a lot of jumps.
• Risk factors: osteoporosis, reduced bone density, pre-existing bony variants (e.g. bipartite patella), previous surgeries, risk of falls (balance, vision).

Typical symptoms

• Acute pain in the front of the knee after trauma.
• Swelling, often bruising in the joint (hemarthrosis).
• Pain-related restriction of movement.
• Pain when pressure is applied to the kneecap.
• Often a bony step or palpable gap in displaced fractures.
• Important sign: Inability to actively lift the extended leg (indication of impaired extensor system).

First aid and behavior after the accident

• Immobilize: Keep your knees as stretched as possible and avoid further strain.
• Cool and elevate to reduce swelling (no ice directly on skin).
• Pressure bandage only with experience and without severe pain; no forced bending.
• If there is severe pain, misalignment, open injury or numbness: seek emergency care.
• Only take painkillers after consulting a doctor.

Diagnosis: How is the patella fracture diagnosed?

Diagnosis is based on history, physical examination and imaging. The crucial thing is to assess the displacement and the joint surface as well as the function of the extensor system.

• Clinic: Inspection, palpation, checking active knee extension (straight leg raise), skin and soft tissue status.
• X-ray: Standard images are taken in two planes; Additionally, a tangential patellar image (e.g. Merchant/Sunrise) to assess the articular surface.
• CT: Helpful for complex, multi-fragmentary fractures for surgical planning and assessment of steps in the articular surface.
• MRI: Rarely required; useful for unclear accompanying injuries (cartilage, retinacula, tendons) or differential diagnoses.

Concomitant injuries such as bruises, retinacular tears or cartilage damage are documented as they can influence the therapeutic path.

Division and classification

The classification according to the course of the fracture, number of fragments, displacement and soft tissue damage is relevant for the treatment decision.

• Fracture types: Transverse (common), longitudinal, pole fracture (upper/lower pole), radial/stellate (comminuted fracture).
• Stability: non-dislocated (little/no displacement) vs. dislocated (fragment spacing, step formation).
• Soft tissue damage: Closed vs. open fracture.
• Function: Intact vs. insufficient extensor system (active extension possible?).

Therapy: conservative or surgical?

The aim of the treatment is a pain-free, stable knee extension with the joint surface as smooth as possible. Whenever possible, conservative treatment is used. Surgical procedures can be considered if there is a relevant displacement, joint level or a disturbed extensor system. Treatment decisions are made individually and based on current evidence.

Conservative treatment

Non-surgical therapy is suitable for stable, non-displaced or only minimally displaced fractures with intact active extension. It avoids surgical risks and can achieve very good results.

• Immobilization in an extension splint (orthosis) for several weeks, the exact duration depending on the fracture.
• Loading: Early full weight bearing in the extended position is often possible with an orthosis; Adjustment depending on pain and stability.
• Early functional therapy: Guided mobilization with limited flexion range, gradual increase after medical approval.
• Physiotherapy: pain-adapted movement exercises, quadriceps activation, gait training.
• Pain control: Medication after consultation; local measures (cooling, elevated storage).
• Thrombosis prophylaxis depending on the degree of immobilization and risk profile.
• Regular clinical and radiological checks to ensure fracture stability.

Most patients can manage their everyday lives well with a splint. Participation in physical therapy is important to prevent muscle loss and restricted movement.

Surgical treatment

Surgery is considered if the fragments are significantly displaced, the articular surface shows step formation or the extensor system no longer functions. Open fractures also require immediate surgical treatment.

• Indications (typical): Joint level > a few millimeters, significant fragment distance, impaired straight leg raise, open fracture, complex comminuted fracture with instability.
• Procedure: tension band osteosynthesis (wire/cerclage principle), screw osteosynthesis (if necessary in combination), cerclage-supported suture for pole fractures, rarely partial patellectomy if reconstruction is not possible.
• Accompanying measures: protection of the soft tissues, hemostasis, careful reconstruction of the articular surface; Suture the retinacula if necessary.

After the operation, early functional mobilization occurs, often with limited flexion. An individually adapted orthosis protects the reconstruction in the early healing phase.

Follow-up treatment and rehabilitation

Rehabilitation depends on the type of fracture and treatment route. The aim is to restore mobility, strength and coordination under controlled stress.

Returning to work: Office work is often possible after a few weeks. Physically demanding work usually requires several weeks to months and a doctor's approval. Driving is only safe again when you can move your leg without pain and with enough strength to brake in an emergency.

Healing process, prognosis and possible complications

Most patellar fractures heal well with adequate treatment. The time frame until full load bearing capacity varies and depends on the type of fracture, stability, accompanying injuries and participation in rehabilitation.

• Possible complications: delayed bone healing or nonunion, secondary fragment displacement, material irritation or fracture after surgery, infection, arthrofibrosis (limited movement), anterior knee pain, post-traumatic cartilage damage/osteoarthritis.
• Prevention: close checks, gradual increase in load, consistent physiotherapy, timely addressing of swelling and pain.
• Metal removal: Only for complaints or special constellations; Routine removals are not generally necessary.

Differential diagnoses

Not every acute knee pain situation after a fall is a fracture. The following diagnoses must be differentiated:

• Acute patellar luxation (kneecap dislocation).
• Quadriceps or patellar tendon rupture (extensor apparatus injured, but without bony fracture).
• Prepatellar bursitis (bursitis).
• Bipartite patella (congenital two-part patella, often asymptomatic).
• Bone marrow edema or contusion without a fracture line.

Prevention and return to sport

• Fall prevention: balance training, good lighting, sturdy shoes.
• Knee-friendly training: progressive build-up of load, correct landing techniques for jumping sports.
• Protective equipment: Consider knee pads in contact sports or high-risk jobs.
• Bone health: adequate nutrition, vitamin D and calcium, if necessary osteoporosis check.
• Return-to-Sport: After clinical stability, sufficient strength and mobility; Approval by the treatment team.

Warning signs: When to go to the emergency room immediately?

• Open injury with visible bone or bleeding wound above the kneecap.
• Severe misalignment, increasing swelling and severe pain despite protection.
• Numbness, paleness or coldness of the lower leg/foot (circulation or nerve problem).
• Inability to actively lift the leg while lying down (possible dysfunction of the extensor system).
• Concomitant injuries after high-speed trauma (e.g. traffic accident).

This is how we support you in Hamburg

In our orthopedic practice at Dorotheenstraße 48, 22301 Hamburg, you will receive a structured examination, a differentiated classification of your X-ray/CT images and an individual therapy recommendation. We prefer conservative procedures if they make medical sense and discuss surgical options transparently - including opportunities, risks and alternatives. The follow-up treatment is closely accompanied with clear training and stress requirements.

Regenerative procedures or injections have no guaranteed value in acute patellar fractures. Cartilage or soft tissue damage – if relevant – is taken into account in the overall concept.