Knee Fractures & Dislocations

Fractures and true dislocation around the knee — patella, tibial plateau, tibial spine/tuberosity avulsion, and proximal fibula fractures, plus a “don’t miss” box for occult knee dislocation. For soft-tissue knee injuries (ligament sprains, meniscal tears) see Ligament Injuries and Meniscal Tears; for the Ottawa Knee Rule and tibial/fibular shaft fractures see Lower Limb Fractures; for ankle fractures including Maisonneuve see Ankle Fractures & Dislocations. Scope here is deliberately urgent-care level — recognise these injuries, splint, and refer — not the hospital’s operative decision-making. For patellar (kneecap) dislocation rather than fracture, see Patellar Dislocation.

Patella fracture

Assessing the extensor mechanism is the single most important step — can the patient perform a straight leg raise? A patella fracture with an intact extensor mechanism is a very different problem to one that has disrupted it. For a tendon rupture rather than a bony patella fracture, see Extensor Mechanism Ruptures.

• History: direct blow (fall, dashboard-type injury) or sudden eccentric quadriceps contraction against a flexing knee. Pain, swelling and a large effusion/haemarthrosis; inability to actively extend the knee if the extensor mechanism is disrupted.
• Examination: palpate for a gap (suggests a displaced fracture); assess active knee extension/straight leg raise; full neurovascular check.
• Investigations: AP and lateral X-ray (best for transverse fractures) — always add a sunrise/skyline view, as vertical fractures and articular surface fractures are easily missed on AP alone. Beware the inferior pole: this is where the dominant retrograde blood supply enters, so a fracture there carries an avascular necrosis risk. A bipartite/multipartite patella (an accessory ossification centre, usually superolateral, with smooth rounded margins) is a normal variant, not a fracture.
• Management:
  • intact extensor mechanism + minimally displaced/non-displaced (step-off <2 mm, fragment gap <3 mm) → knee immobilizer locked in extension, weight-bear as tolerated with crutches, outpatient orthopaedic referral within 2 weeks
  • refer urgently (same-day) for: disrupted extensor mechanism, an open fracture, a comminuted fracture, >2 mm articular step-off or >3 mm fragment separation, or any neurovascular deficit.

Tibial plateau fracture

Occurs at the proximal tibia from a varus/valgus force plus an axial load driving the femoral condyle into the tibial plateau — classically a motor vehicle collision, but also a straightforward low-energy mechanism in an older, osteoporotic patient who falls onto a twisted knee, so don’t let a “just a fall” history lower your suspicion in this group.

• Examination: swelling, effusion, tenderness over the proximal tibia, limited flexion/extension, inability to weight-bear. Check the extensor mechanism (straight leg raise) and gently assess varus/valgus stability — gross instability should raise suspicion for a knee dislocation (see below), not just a plateau fracture. Full neurovascular exam including peroneal nerve function (ankle/toe dorsiflexion; a foot drop suggests nerve injury).
• Investigations: AP, lateral and oblique X-ray views. A single or double fluid level on a horizontal-beam lateral view is lipohaemarthrosis (fat + blood in the joint) and can be the only clue to an intra-articular fracture that isn’t otherwise visible — increased density on the AP view from fracture depression is another subtle sign. A normal X-ray does not exclude a tibial plateau fracture — a patient with a substantial injury who still can’t weight-bear despite a normal film needs a CT, not reassurance. A Segond fracture (a small avulsion off the lateral tibial plateau) is pathognomonic for an ACL tear.
• Management: uncomplicated, non-displaced fractures — long-leg splint or knee immobilizer with the knee in extension and ankle at 90°, strict non-weight-bearing, RICE, and urgent (within ~5 days) orthopaedic follow-up (displaced/depressed fractures need it sooner). Refer same-day for any suspicion of vascular injury, compartment syndrome, an open fracture, or gross instability suggesting knee dislocation. Compartment syndrome complicates up to 11% of tibial plateau fractures — higher with high-energy mechanisms — so warn the patient about escalating pain and reassess if there’s any doubt.

Tibial spine (intercondylar eminence) avulsion fracture

The paediatric equivalent of an ACL tear — in a skeletally immature child, a strong anterior/posterior force on a flexed knee is more likely to avulse the tibial spine (the ACL’s bony attachment) than rupture the ligament itself. Most common age 8–14, from sport, bike accidents or falls.

• Examination: haemarthrosis is typical; knee extension may be limited (fragment or meniscus blocking full extension) or near-normal if the avulsion is incomplete. Positive anterior drawer test.
• Investigations: X-ray — best seen on the lateral view; a tunnel view can help. Findings can be subtle; lipohaemarthrosis may be the only clue.
• Management (Meyers–McKeever classification): type I (non-displaced) — knee immobilizer, non-weight-bearing, orthopaedic follow-up in a few days, then a long-leg splint for 4–6 weeks. Type II (hinged/partially displaced) and type III (fully displaced) need urgent orthopaedic referral — type II may reduce with extension/casting, type III generally needs surgery (soft tissue, often the meniscus, is frequently trapped in the fracture gap). Avoid casting in full extension/hyperextension — it stretches the popliteal artery and risks compartment syndrome.

Tibial tuberosity avulsion fracture

An adolescent (12–15 years, boys most commonly, sport involving jumping or sprinting — basketball is the classic culprit) avulsion of the tibial tuberosity through the still-open apophysis, from a strong quadriceps contraction against a flexed knee. Distinguish from Osgood-Schlatter disorder, which is atraumatic and not associated with a haemarthrosis or acute effusion.

• Examination: pain/tenderness over the tibial tuberosity, sudden inability to weight-bear, effusion with type III (intra-articular) injuries. Check for compartment syndrome — the anterior tibial recurrent artery runs through this area and is injured in ~4% of these fractures.
• Investigations: lateral X-ray is most useful; look for apophyseal widening, anterior swelling, or patella alta (a high-riding patella).
• Management: minimally displaced (<2 mm) — knee immobilizer, non-weight-bearing, urgent orthopaedic referral for likely cast immobilisation. Complete avulsion (displaced, or any intra-articular extension) needs urgent orthopaedic referral for surgical fixation. Prognosis is generally good with a high union rate.

Proximal fibula fracture

Usually part of a broader knee injury rather than an isolated problem — treat any proximal fibula fracture as a marker of significant knee injury until proven otherwise. The fibula is non-weight-bearing but carries the lateral collateral ligament and posterolateral corner attachments, and the common peroneal nerve wraps directly around the fibular neck.

• Associated injuries to actively look for: lateral tibial condyle fracture, posterolateral corner/LCL injury, common peroneal nerve injury (foot drop, first dorsal web-space numbness), and — via the interosseous membrane — a Maisonneuve injury at the ankle (see Ankle Fractures & Dislocations). Examine the whole limb, not just the fibula.
• Management: isolated fibular head/neck fractures are usually treated symptomatically in a hinged knee brace with early range of motion and outpatient referral — the fracture itself rarely needs fixation. A proximal fibular fracture combined with a tibial plateau fracture is a poor prognostic sign and needs orthopaedic input.

Knee dislocation — don’t miss

A tibiofemoral dislocation is uncommon but limb-threatening, and is easy to miss because around two-thirds spontaneously reduce before the patient is examined — the knee may look unremarkable by the time you see it. Always includes rupture of both cruciate ligaments (± collaterals), and carries a real risk of popliteal artery injury (~1 in 3 dislocations) and common peroneal nerve injury.

• Suspect an occult (spontaneously-reduced) dislocation when: the mechanism fits (hyperextension, a high-energy blow, or even a simple fall in an obese patient — low-energy dislocation happens), the patient describes the knee “popping out and back in”, or — most importantly — exam finds laxity in two or more knee ligaments, which gives a presumptive diagnosis of dislocation even with a currently-located joint.
• Any suspected dislocation (reduced or not) needs same-day ED referral — this is not an injury to manage as an outpatient. Check and document pulses and neurovascular status before referral; a palpable pulse does not exclude a vascular injury (collateral flow can mask it), so document findings clearly for the receiving team rather than reassuring the patient based on a normal pulse alone.
• If the knee is still frankly dislocated on presentation, this is an emergency — arrange immediate ambulance transfer; don’t attempt reduction in an urgent-care setting.