Anatomical and biomechanical features of the patella
The patella (patella) is a sesamoid bone that articulates with the intercondylar groove of the femur. The articular surface of the groove is fully congruent with the articular surface of the sesamoid bone itself.
A structural feature of the patella is the presence of a vertical ridge. It divides the articular surface into two unequal parts:
- Larger lateral facet.
- Smaller medial facet, which is more bevelled.
Bone stability is provided by the extensor apparatus of the knee joint. Superiorly, the structure is tightly connected to the quadriceps tendon, and inferiorly to the patellar ligament. Laterally and medially, the bone is fixed by retinacula, with the lateral ligamentous structures possessing greater strength.
Lower leg dislocations: clinical presentation and associated injuries
In addition to isolated patellar displacement, the most severe injuries of the entire knee joint occur—lower leg dislocations. This injury is associated with a high risk of shock.
Upon examination, passive movements are severely limited and sharply painful, but no limb shortening is observed. A mandatory stage of diagnostics is the assessment of blood circulation and innervation of the distal leg, since the popliteal artery is affected in 30–40% of cases.
Ligamentous apparatus injuries:
- With significant lower leg displacement, a complete rupture of all ligaments is inevitable.
- In rotational dislocation, such total damage is possible.
Important rule: detailing injuries to the capsular-ligamentous apparatus (cruciate and collateral ligaments) is performed only after successful reduction.
Specifics of destruction in various types of lower leg dislocation
The nature of damage directly depends on the direction of displacement:
- Anterior dislocation: rupture of the anterior cruciate ligament (ACL), injury of the popliteal artery, possible partial injury of the posterior cruciate ligament (PCL).
- Posterior dislocation: mandatory rupture of the PCL, partial injury of the ACL.
- Lateral dislocation: ACL, PCL, and tibial collateral ligament are affected.
- Medial dislocation: ACL, PCL, fibular collateral ligament are ruptured, and the fibular nerve is also injured.
Pre-hospital care and radiological diagnostics
At the emergency stage, it is strictly prohibited to attempt to correct the deformity independently due to the colossal risk of damaging the artery or nerve.
Anti-shock measures include:
- Adequate pain management.
- Infusion therapy.
- Transportation immobilization — splinting from the gluteal fold to the toes.
Hospitalization is mandatory. In the hospital, radiography is performed in two standard projections to clarify the nature of the dislocation and identify concomitant bone fractures.
Reduction and management tactics
Lower leg reduction is carried out urgently (to avoid irreversible ischemia) and strictly under anesthesia.
Procedure technique:
- The straightened leg is flexed at the hip joint to relax the quadriceps femoris muscle.
- Traction is applied along the axis of the lower leg.
- The surgeon presses on the prominent condyles of the femur and tibia, shifting them toward the limb axis.
Contraindications during manipulation: angular movements and pressure on the popliteal fossa (danger to the neurovascular bundle). If pulse in the distal arteries is absent after reduction, emergency vascular revision is indicated.
Next, a deep plaster cast is applied, and hemarthrosis is treated. The total immobilization period reaches 2–2.5 months, partial weight-bearing is allowed after 6–8 weeks. If post-traumatic joint instability develops, surgical reconstruction is required (with prior ultrasound, MRI, or arthroscopy).
Isolated dislocation of the fibular head
A rare pathology occurring with rupture of the proximal tibiofibular syndesmosis. Clinically manifested by deformation and displacement of the head anteriorly or posteriorly. Upon palpation, the bone is easily reduced but immediately slips back; pain increases when compressing the leg bones.
Treatment is exclusively surgical: the head is fixed to the tibial condyle with transosseous polyester (Dacron) sutures. Afterwards, a plaster cast is applied from the toes to the middle of the thigh for 4 weeks. Walking with support is allowed 2 weeks after the intervention.
Briefly: answers to topical questions
What types of patellar dislocations are distinguished depending on the direction of displacement?
Depending on the direction of displacement, lateral, torsional, vertical, and a number of rare forms of patellar dislocation are distinguished.
- Lateral dislocation — the patella is displaced in the lateral (lateral dislocation) or medial (medial dislocation) direction.
- Torsional dislocation (rotational) — the patella rotates around the vertical axis (divided into lateral, medial, and anterior).
- Vertical dislocation — occurs with a complete transverse rupture of the quadriceps tendon expansion or patellar ligament.
- Rare forms — include superior, inferior, intra-articular, and multidirectional displacements.
What clinical symptoms are detected during physical examination of a patient with lower leg dislocation?
During physical examination of a patient with lower leg dislocation, marked limitation and pain of passive movements are noted in the absence of limb shortening.
- Passive movements — extremely limited and sharply painful.
- Limb length — no shortening.
- Neurovascular status — the degree of circulatory and innervation impairment of the distal limb must be assessed, as lower leg dislocation is often accompanied by compression and damage to the popliteal vessels and fibular nerve.
- Ligamentous apparatus — the nature of damage to the collateral and cruciate ligaments is specified only after reduction of the dislocation.
What are the tactics of conservative treatment and immobilization periods for isolated patellar dislocation?
Conservative treatment tactics include closed reduction of the dislocation followed by limb fixation and joint unloading.
- Reduction — performed under general or local anesthesia (in case of pronounced hemarthrosis, joint puncture is performed beforehand).
- Immobilization — a plaster cast or brace is applied from the lower third of the leg (or ankle joint) to the upper third of the thigh (or gluteal fold). The knee joint is fixed strictly in the extension position.
- Immobilization periods — range from 3 to 4–6 weeks.
- Regimen — walking with additional support using crutches is recommended; cryotherapy and limb elevation are prescribed on the first day.
What clinical tests are used to diagnose chronic patellar instability?
Specific clinical tests and signs are used to assess patellofemoral joint instability when dislocation of the patella is suspected.
- Fairbanks test (Fairbanks test).
- Bassett's test (Bassett's test).
- Apprehension sign — the patient's apprehension when an attempt is made to displace the patella laterally.
- The apprehension test when attempting to displace the patella laterally relative to the intercondylar groove may be associated with patellar subluxation or tension of the lateral retinaculum.
- An abnormal Q angle may be associated with patellar subluxation or tension of the lateral retinaculum.
Currently, there is no convincing evidence confirming the superiority of using any single specific test.
To memorize the leg reduction technique, use the three "T" rule: Flex the hip joint (relax muscles), Traction along the axis, Targeted pressure on the condyles (without angular movements).
Class and exam questions
Is it permissible to reduce a knee dislocation at the ambulance stage?
Categorically no. Attempts at self-reduction of the deformity at the pre-hospital stage are associated with a high risk of irreversible damage to the popliteal artery and nerve.
When is it necessary to examine the knee ligaments for ruptures?
Clarification of the nature of collateral and cruciate ligament injuries (as well as their detailing on MRI) is performed strictly after successful reduction of the articular surfaces.
In which cases is emergency surgery required after knee reduction?
Emergency intervention is required if, after returning the bones to their normal position, ischemia of the distal extremities persists and the arterial pulse is absent (revision of the vascular bundle is necessary).
What else to study on this topic
- The role of knee joint dysplasia in the pathogenesis of patellar dislocations.
- Surgical reconstruction of stabilizing structures in severe post-traumatic instability.
- Principles of treatment for hemarthrosis after reduction of articular surface displacement.
- Management tactics for patients with combined peroneal nerve injury during lower leg trauma.
- Interpretation of ultrasound and MRI data when planning elective surgeries on the ligamentous apparatus of the knee.
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