Anatomy of the Knee

The joint surfaces are covered with cartilage, and the medial and lateral menisci distribute load. Joint stability is maintained by the anterior and posterior cruciate ligaments (ACL and PCL) and the medial and lateral collateral ligaments (MCL and LCL). The patella is a bone embedded within the quadriceps tendon and transmits quadriceps force to knee extension. A healthy knee allows walking, running, climbing and descending stairs and rising from a seated position without pain.

Distal Femur Fractures

These are fractures of the region of the femur close to the knee. They usually result from high-energy injuries or from low-energy falls in older patients with osteoporosis.

• Supracondylar fracture: above the joint, proximal to the condyles
• Intercondylar (T or Y) fracture: involving both the supracondylar region and the joint surface
• Isolated condyle fracture: a fracture of a single condyle (including a Hoffa fracture)

Tibial Plateau Fractures

These are fractures of the region of the tibia close to the knee. They frequently result from a 'die punch' effect as the femoral condyle is driven into the tibial plateau. Column classification is widely used:

• Anteromedial column
• Anterolateral column
• Posterior column

Patella (Kneecap) Fractures

Fractures of the kneecap usually result from a fall onto the knee or a direct blow. Excessive quadriceps contraction can also cause an avulsion fracture.

• Transverse fracture: the most common type, across the mid-portion of the patella
• Comminuted fracture: three or more fragments; may be stable or unstable
• Vertical fracture
• Avulsion fracture: the tendon pulls off a small fragment of bone
• Osteochondral fracture: involving only the cartilage and the thin layer of bone beneath it

Classification by Displacement and Joint Involvement

• Non-displaced fracture: the bone fragments have not shifted; some are suitable for non-operative treatment
• Displaced fracture: the fragments have shifted; surgical reduction is required
• Intra-articular fracture: the fracture line extends into the joint surface, increasing the long-term risk of arthritis
• Open fracture: the bone has penetrated the skin or the skin is torn; infection risk is high and emergency surgery is required
• Stress fracture: caused by repetitive loading; may be seen particularly in the distal femur and proximal tibia

Symptoms

• Sudden, severe pain: at the moment of injury, particularly on weight bearing
• Swelling and haemarthrosis: marked bleeding into the joint and oedema within the first hours
• Inability to bear weight: unable to stand or walk on the leg
• Deformity: visible in displaced fractures
• Tenderness: pain that increases on palpation of the fracture site
• Restricted movement: difficulty bending or straightening the knee; inability to extend the knee actively in a patella fracture
• Altered sensation or coldness: if there is nerve or vascular injury (popliteal artery, peroneal nerve)
• Open wound: loss of skin integrity in an open fracture

Mechanisms of Injury

• High energy: road traffic accidents (particularly dashboard injuries), falls from height, motorcycle accidents
• Low energy: tripping or falling on level ground (particularly in older patients with osteoporosis)
• Direct blow: a fall onto the knee (the most common mechanism for patella fractures)
• Quadriceps strain: typical of an avulsion fracture of the patella
• Sports injuries (skiing, football, motocross)
• Repetitive loading (for stress fractures)

Diagnosis

Diagnosis is based on a detailed history, physical examination and imaging. Examination assesses swelling, haemarthrosis, deformity, points of tenderness, range of motion, active knee extension (to evaluate the patella and quadriceps mechanism), associated ligament injuries, neurovascular status (particularly the popliteal artery and peroneal nerve) and skin integrity. Careful monitoring for compartment syndrome is required.

Plain radiographs are the first-line investigation; anteroposterior, lateral and axial (for the patella) views are standard. CT is almost always required for surgical planning in intra-articular, comminuted or tibial plateau fractures; three-dimensional reconstruction is critical for assessing fragment displacement and joint surface depression. MRI is used to evaluate associated ligament and meniscal injuries, cartilage damage and occult stress fractures. Angiography or CT angiography may be required where vascular injury is suspected after a high-energy injury.

Non-operative (Conservative) Treatment

Stable, non-displaced fractures that do not disturb the joint surface are suitable for non-operative treatment. Typical candidates are non-displaced patella fractures (particularly where active knee extension is preserved), non-displaced tibial plateau fractures (some Schatzker I injuries) and selected fractures in patients at very high surgical risk. Treatment is with a cast, a long leg cast, a hinged knee brace or a cylinder cast; immobilisation averages 4–8 weeks, followed by graduated weight bearing and physiotherapy.

Surgical Treatment

Open reduction and internal fixation (ORIF) is the standard treatment for displaced or unstable fractures and those that disturb the joint surface. Typical candidates are displaced distal femur fractures, displaced tibial plateau fractures, displaced patella fractures (particularly where active knee extension is lost) and open fractures.

• Plates and screws
• Intramedullary nail
• Tension band technique
• External fixator

Advantages

The principal advantage is anatomical restoration of the fracture with rigid fixation. This reduces the long-term risk of joint surface incongruity, malunion and post-traumatic arthritis. Non-operative treatment carries a risk of secondary displacement within the cast and of stiffness from prolonged immobilisation, whereas surgery secures the fracture and allows early movement.

• Anatomical reduction: fragments are restored with millimetre precision and the joint surface is accurately repaired
• Early motion: stable fixation allows early knee range-of-motion exercises, reducing joint stiffness and quadriceps atrophy
• Faster return to weight bearing: earlier progression to partial weight bearing may be possible at the surgeon's discretion
• Operative time: 60–90 minutes for patella fractures; 90–180 minutes for distal femur and tibial plateau fractures; longer for complex comminuted fractures
• Hospital stay usually 1–3 days
• Knee function is better preserved in the long term

Disadvantages

• You will need to avoid or restrict weight bearing for 4–12 weeks. Temporary bone loss (Sudeck's atrophy) and quadriceps atrophy may develop during this period, but both are reversible and improve with physiotherapy.
• There are surgery-specific risks: wound infection, deep infection, implant failure, nerve injury (particularly the peroneal nerve) and vascular injury (popliteal artery, very rare), together with rare anaesthetic complications.
• Implant irritation: plates and screws over the patella and tibia may cause irritation in patients with thin skin; some patients require hardware removal.
• Wound healing problems: the soft tissues around the knee are vulnerable, particularly after high-energy injuries; the risk of wound breakdown and skin necrosis is greatest in tibial plateau and distal femur fractures, in patients with diabetes and in smokers.
• Joint stiffness may develop during immobilisation; restriction of knee flexion and extension is common after prolonged casting or high-energy injury, and intensive physiotherapy is required.

Why Surgery?

The knee is a large weight-bearing joint; even 1–2 mm of joint surface incongruity significantly increases contact stress, leading to cartilage wear and post-traumatic arthritis in the long term. In patella fractures the integrity of the extensor mechanism is critical to knee function, and loss of active knee extension causes permanent disability. In distal femur and tibial plateau fractures prolonged immobilisation produces knee stiffness and quadriceps atrophy, so rigid fixation that permits early movement is ideal. Studies show markedly higher rates of malunion, chronic pain and arthritis in displaced intra-articular knee fractures treated non-operatively compared with those treated by anatomical surgical reduction.

Who is a Candidate?

Surgery (ORIF) is performed for displaced or unstable fractures around the knee and for those that disturb the joint surface.

• Displaced distal femur fractures
• Tibial plateau fractures involving the joint surface
• Displaced patella fractures with extensor mechanism insufficiency
• Open fractures; patients who develop secondary displacement during non-operative treatment
• Cases with associated ligament or meniscal injury
• Patients whose general health is suitable for general anaesthesia and surgery
• Non-operative treatment: stable, non-displaced fractures; selected patients at very high surgical risk; some patella fractures with preserved active knee extension

Expected Outcomes

Most patients with a correctly treated fracture around the knee achieve a pain-free, functional knee. Most return to daily activities within 4–6 months; complete recovery may take up to a year in some cases. Fracture healing takes 8–12 weeks in simple isolated fractures and 12–16 weeks or longer in complex or comminuted intra-articular fractures. Intra-articular fractures carry a risk of post-traumatic arthritis, although anatomical reduction, early motion and compliant rehabilitation reduce this risk.

Risks Specific to Non-operative (Cast/Brace) Treatment

• Inadequate reduction / secondary displacement: fragments shifting within the cast; further surgery may be required
• Skin problems: pressure sores and friction beneath the cast
• Knee stiffness (contracture): marked loss of range of motion due to prolonged immobilisation; this is the most common complication
• Quadriceps atrophy and loss of strength
• Deep vein thrombosis (DVT): risk increased by immobility
• Sudeck's atrophy (temporary bone loss)

Risks Specific to Surgery — Common (Under 5%)

• Superficial wound infection (usually treated with antibiotics)
• Postoperative pain, swelling and temporary bruising
• Temporary joint stiffness — resolves with regular physiotherapy
• Quadriceps inhibition / temporary weakness — resolves with physiotherapy
• Transient symptoms related to anaesthesia such as nausea and dizziness
• Haemarthrosis and prolonged oedema (which may persist for 3–6 months)

Risks Specific to Surgery — Less Common

• Deep infection (osteomyelitis / implant infection): 2–5%; higher in tibial plateau and open fractures
• Wound healing problems: common in tibial plateau fractures, in patients with diabetes and in smokers; skin necrosis is rare
• Nerve injury: the peroneal nerve is at risk during tibial plateau surgery and foot drop may develop
• Vascular injury: the popliteal artery (very rare but serious)
• Deep vein thrombosis (DVT) and pulmonary embolism (PE)
• Implant failure: loosening or breakage of screws or plates, particularly with early weight bearing
• Compartment syndrome: requires emergency fasciotomy; particularly after high-energy tibial plateau fractures
• Heterotopic ossification (bone formation in soft tissue)
• Complex regional pain syndrome (CRPS / Sudeck's atrophy)
• Patellar elongation, patella alta or patella baja: healing of the patella in a superior or inferior position after fracture

Long-term Complications

• Malunion: knee mechanics are disturbed and axial deformity (varus/valgus) may develop
• Non-union: increased by smoking, diabetes, osteoporosis and early weight bearing
• Post-traumatic osteoarthritis: may develop years later after intra-articular fractures; total knee replacement may become necessary
• Persistent knee stiffness (loss of range of motion)
• Quadriceps weakness: particularly after patella fracture
• Extensor mechanism insufficiency: loss of active knee extension
• Chronic pain; chronic instability (particularly where there was an associated ligament injury)
• Leg length discrepancy (particularly after distal femur fractures)

Implant-related Problems

• Implant irritation close to the skin: K-wires, screws and plates over the patella and tibial plateau may be irritating in patients with thin skin
• Need for implant removal: usually performed after 9–12 months, once fracture healing is complete
• Migration of, or pain from, patellar tension band wires: the most common reason for implant removal after patella fractures

Factors that Increase Risk

• Smoking (markedly increases the risk of wound healing problems, non-union and infection)
• Poorly controlled diabetes (impaired wound healing)
• Osteoporosis (poor implant purchase, secondary displacement)
• Peripheral vascular disease
• Immunosuppressive therapy and rheumatological disease
• Advanced age; obesity (difficulty protecting weight bearing, greater stress on the implant)
• Open fracture or high-energy injury
• Active or recently treated infection (dental, urinary, skin)

Contact Your Doctor Immediately If You Have

• Sudden increase in pain or swelling
• Fever above 38 °C
• Discharge, malodour or separation of the wound
• Increasing numbness, tingling or weakness in the leg or foot (foot drop)
• Bruising, coldness or pallor of the toes (suspected vascular problem)
• Firm, one-sided swelling and redness of the leg (suspected DVT)
• Shortness of breath or chest pain (suspected pulmonary embolism)
• Excessive tightness or unbearable pain within the cast or brace (suspected compartment syndrome)
• Wound edge separation or exposed hardware
• Inability to extend the knee actively (suspected extensor mechanism insufficiency)

Long-term Outcomes

With accurate diagnosis, appropriate treatment and compliant rehabilitation, the great majority of fractures around the knee heal without problems. Most patients return to daily activities within 4–6 months and to sport within 9–12 months. Complete recovery may take up to a year in some cases; swelling and stiffness may persist for 12 months, particularly after high-energy tibial plateau and distal femur fractures.

The risk of post-traumatic arthritis within 5–15 years is significant after intra-articular fractures; anatomical reduction, appropriate implant selection, early motion and compliant rehabilitation reduce this risk. Stopping smoking, controlling blood glucose and maintaining a healthy weight are critical to healing and long-term outcome.