Radiologycal assessment of irreducible posterolateral knee subluxation after dislocation due to interposition of the vastus medialis

while skiing. Pain and total impotence resulting from trauma required the patient to be transferred to our hospilal for the management of a suspected posttraumatic dislocation of the right knee.

The clinical examination was immedialery performed in Ihe emergency room by an orthopaedic surgeon. Then (bepatient sequentially underwent anteroposterior and lateral conventional radiographs, computed tomography angiography of the lower limbs, and MR1 of ihe right knee. The patient wax finally treated by open surgery for reduction and stabilisation Result

On arrival, the patient presented considerable swelling of the right knee with medial cutaneous incarceration known as a 'simple sign. The mobility was limited wilh knee flexion at SO" and impossibility of flexion/extension movements. There was no detectable neurovascular disorder.

Peripheral pulses, skin colour, and local lemperarure were symmetric in both legs. Sensibility was normal and motor Fig. below oil old mate Sis peeled of posrtja unlade airdudbtr knee hib luxation after dii local »m Preoperative photografi and ilustrated the caracteristic simple sign' function seemed to be limited only by flexion and pain, without a suspected neurological deficit.

Anteroposterior and lateral conventional radiographs showed a discrete avulsion of the lateral femoral condyle, suggesting a ligamentous tear of the lateral collateral ligament, an enlargement of the medial femorodbial space, an

important effusion, and a medial soft tissue attraction.

Computed tomography angiography wilh contrast injeelion in the arterial phase excluded arterial injury associated with ihe dislocation. Finally, magnetic resonance imaging proved vastus medialis partial incarceration within the intercondylar notch, associated with medial patelo femorotibial trapping of the medial patellofemoral ligament, capsule, and subcutaneous tissue. Associated ligamentous tears included complete rupture of ihe anterior and posterior cruciate ligaments as well as internal and external collateral ligaments.

Less than 24 h after the patiens arrival, all of Ihe imaging described above was performed and ihe patient underwent surgical reduction by parapatellar medial arthrotomy. At the same lime, stabilisation of the knee was provided by reinsertion of the medial palellolemoral ligament, posterior oblique ligament, and medial collateral ligament Cruciate ligament surgery was not undertaken for this patient The patient evolved favourably and was discharged from (he orthopaedic unit 15 days after surgery. Consultation centrals with oral interview and clinical examination at 6 weeks, 3 months, and o" months confirmed this favourable evolution in terms of healing, pain, joint stability, and passive and active range of motion. The patient resumed his normal professional and extra-professional activities less than I year after the accident.

Discussion

Knee dislocation is defined as a complete loss offemorotibial congruence and subluxation as a disruption, with parts of the articular surfaces remaining in contact. The classifications are based on the tibial displacement or on the pattern of ligament injury. The tibial displacement may be anterior (40 %), posterior (33 %), lateral (18 %), medial (4 %\ or rotatory (5 %) Later, Schenck et al. proposed a more biomechanical classification, using the pattern of ligament

injury, and this classification has finally been modified by Wascher et al. lo include associated lesions as vascular, neurological, or osseous. This modified Schenck classification is the most commonly used in clinical practice.

Posttraumatic knee dislocations are rare and generally reduced spontaneously or by a closed method Most of the rime, their irreducibility is associated wilh interposition of soft tissue structures such as the medial meniscus, capsule, retinaculum, and vastus medialis in poslerolaleial dislocations.

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