Knee dislocation is a true orthopaedic emergency. Quite often the knee reduces spontaneously and therefore the true incidence of knee dislocation is not known. There is a significant risk of neurovascular injury. Conservative management has high risks of stiffness and instability and poor function. The recommended management is surgical repair/reconstruction. Therefore the initial evaluation and management of the multiple-ligament injured knee is extremely important.
Acute knee dislocations are extremely uncommon. There are a significant number of patients with sporting injuries who experience a feeling of subluxation. This is usually a pivoting episode with an Anterior Cruciate tear. Knee dislocations can occasionally happen with intact ACL or PCL.
When a substantial laxity of two or more ligaments is present, a diagnosis of knee dislocation has to be made.
Kennedy (1963) classified knee dislocations based on the position of the displaced tibia. The types are Anterior, Posterior, Medial, Lateral or Rotatory.
Fanelli stressed the importance of differentiating high and low velocity injuries.
Anterior dislocations happen with sporting injuries with hyperextension whilst posterior dislocations occur with motor vehicle accidents and dash-board injuries. The commonest dislocations according to Green are Anterior (40%) and Posterior (33%). Frassica reported 70% posterior dislocations.
With the new understanding of the multiple-ligament injured knee and a greater number of injuries occurring with sport, the injury pattern has changed.
If the knee has spontaneously reduced then the dislocation type would depend on the pattern of instability.
Schenck Classification (modified by Wascher)
- KD-I (dislocations associated with multiple-ligament injuries that did not include both cruciate ligaments)
- KD-II (dislocations associated with a bicruciate ligament injury only)
- KD-III (dislocations associated with a bicruciate ligament injury and a tear of either the posteromedial or posterolateral knee ligaments)
- KD-IV (dislocations associated with tears of both cruciate ligaments and both posteromedial and posterolateral ligaments),
- KD-V (dislocations associated with a periarticular fracture and multiple-ligament injuries).
All patients have an initial assessment according to Advanced Trauma Life Support (ATLS) protocol. A brief history to understand the mechanism of injury is obtained and the knee is assessed. The knee may look quiescent with no deformity or swelling, as it may have spontaneously relocated.
If the knee looks obviously dislocated, then a quick assessment of peripheral circulation and neurological assessment is made and documented. Subtle signs like skin temperature, colour and capillary refill are important. In an obvious dislocation, the knee should be reduced immediately under sedation in the emergency department. This can be achieved by longitudinal traction. After reduction, the neurovascular status is reassessed and documented. The knee is placed in a long leg splint/ Plaster back slab including the foot and a check Radiograph is obtained to confirm concentric reduction and no abnormal varus or valgus positioning or posterior subluxation of tibia in the splint.
The posterolateral dislocation is important to recognise, as this may be irreducible by simple traction. This is because the medial femoral condyle could be button-holed through the capsule.
In a benign looking knee, lifting the leg by the big toe (Hughston test) can show abnormal hyperextension and varus/ external rotation. An assessment of the collateral ligaments and the Lachman and Posterior draw tests make the diagnosis.
Abnormal increase in joint space on a knee radiograph can be a pointer to the need for more careful knee assessment.
Historical studies showed the risk of vascular injuries to be extremely high – 32% (Green 1977) and 45% (Jones 1979). The popliteal artery is relatively tethered by the adductor hiatus proximally and the arch of the Soleus
Muscle distally and hence more prone to injury.
More recently Stannard showed only 9 vascular injuries amongst a large series of 138 multiligament knee injuries/dislocations (7%). Mills (2004) has a 29% incidence of vascular injuries amongst 38 knee dislocations. This difference in incidence could be due to the presentation of a frank knee dislocation compared to a multi-ligament knee injury.
Is there a need for routine angiography?
This has been a constant debate. The rationale for routine arteriograms is based on the concern that complete disruption of the popliteal artery can be present with normal pulses initially and that intimal flap tears can produce thrombi that can lead to complete occlusion. The vast majority of intimal tears seen on the angiograms of patients with normal findings on physical examination do not progress to popliteal artery occlusion
Stannard showed in his series that repeated clinical assessment is satisfactory as there were no vascular injuries amongst the patients who had normal clinical examination.
Mills showed the usefulness of measuring the Ankle-Brachial pressure index. Of the 38 patients, 11 (29%) had an ABI lower than 0.90. All 11 had arterial injury requiring surgical treatment. The remaining 27 patients had an ABI of 0.90 or higher. None had vascular injury detectable by serial clinical examination or duplex ultrasonography. The sensitivity, specificity, and positive predictive value of an ABI lower than 0.90 were 100%. The negative predictive value of an ABI that reached 0.90 or higher was 100%.
Lynch and Johansen compared the use of the ankle-brachial index with that of arteriography following blunt and penetrating trauma. They reported that an ankle-brachial index of more than 0.9 had a sensitivity of 87% and a specificity of 97% for the diagnosis of arterial disruption when compared with the results of arteriography.
Klineberg in a retrospective analysis of 57 traumatic knee dislocations showed that knees with initially normal examination had no vascular injury.
The indications for arteriography are –
- any decrease in pedal pulses, lower extremity color, or temperature on physical examination,
- an expanding hematoma about the knee,
- a history of an abnormal physical examination prior to presentation in the emergency department underwent arteriography
- ABPI more than 0.90
- Neurovascular observations performed by the nursing staff every two to four hours for the first forty-eight hours. The vascular examination should be documented by a surgeon at the time of admission, four to six hours after admission, and again twenty-four and forty-eight hours after admission. If any clinical abnormalities are detected, an arteriogram should be made.
Neurological injury is less common than vascular injury. The Common Peroneal Nerve is most commonly injured though the Tibial Nerve is also at risk.
Niall and Keating reported 25% Common Peroneal Nerve injury whilst Sisto and Warren reported 40% CPN injury.
In Keating’s study, injury to the common peroneal nerve was present in 14 of 55 patients (25%) with dislocation of the knee. Complete rupture of the nerve was seen in four patients and a lesion in continuity in ten. Complete recovery occurred in three (21%) and partial recovery of useful motor function in four (29%). In the other seven (50%) no useful motor or sensory function returned
Surgical treatment of CPN injuries can nowadays be highly rewarding (Goitz, Garozzo). CPN palsies in open wounds should undergo surgical exploration at emergency. In close injuries with no spontaneous recovery within 4 months after the injury, patients should be advised to seek surgical treatment regardless the causative mechanism of the lesion. The association of a transfer procedure to nerve repair enhances neural regeneration, dramatically improving the surgical outcome of these injuries.
Ultrasound can be useful preoperatively. Impaired nerves have an increased cross-sectional area at the level of the injury. It also shows scar tissue and hematoma formation (Gruber).
Does nonoperative treatment have a role?
In the past knee dislocations used to be treated in a cast in extension, bridging External fixator, Olecrononisation of patella or a transarticular Steinman pin for atleast 6 weeks. Nonoperative treatment invariably produces persistent instability and stiffness. The ideal flexion angle to immobilise the knee is about 30 degrees of flexion. There is high risk of persistent posterior tibial subluxation and Patella fat pad scarring. If a vascular repair has been performed, a temporary External fixator can be useful.
Acute ligament repair or reconstruction is the currently recommended treatment for multiligament injuries/knee dislocations.
Technique and Results
Richter in a retrospective study compared results after surgical repair or reconstruction versus nonsurgical treatment on eighty-nine patients treated for traumatic knee dislocation. Surgical repair or reconstruction of the cruciate ligaments was performed in 63 patients (repair, 49; reconstruction, 14). In 26 patients, nonsurgical treatment was undertaken. At an average follow-up of 8.2 years, the mean Lysholm and Tegner scores were 75 and 3.7, respectively. The outcome in the surgical group was better than in the nonsurgical group. The scores were higher in patients who were 40 years of age or younger, who had sports injuries rather than motor vehicle accident injuries, and who had undergone functional rehabilitation rather than immobilization. Cruciate ligament avulsions were treated with transosseous fixation performed within 2 weeks of trauma.
Wong similarly showed superior results with surgical treatment compared to nonoperative treatment.
Liow from Edinburgh, UK showed that acute reconstructions performed within 2 weeks performed better than delayed treatment. At a mean follow-up of 32 months (11 to 77) the mean Lysholm score was 87 (81 to 91) in the acute group and 75 (53 to 100) in the delayed group. The mean Tegner activity rating was 5 in the acute group and 4.4 in the delayed group.
Shelbourne (AJSM 2007) reported good long term stability and subjective IKDC results in patients who had acute lateral side repair and reconstruction of the ACL with nonoperative treatment of the PCL. There was normal or only a grade 1 posterior sag at 4.6 years follow-up.
Harner (JBJS2005) describes the surgical management of knee dislocations. Patients with vascular injury requiring repair are treated in a external fixator. 33 patients had anatomical repair +/- allograft reconstruction. They performed routine angiography in gross dislocations requiring reduction. MRI scans and varus/valgus stress examination were noted to be useful.
The common injury patterns are ACL+PCL+MCL and ACL+PCL+PLC. Occasionally PCL may be intact or all 4 ligaments may be ruptured.
ACL and PCL avulsions are repaired. Midsubstance tears are reconstructed acutely.
Grade 3 injuries to collateral ligaments are repaired and posterolateral corner is repaired within 3 weeks.
Graft choice depends on injury-surgery timing, severity of injury and surgeon experience. Achilles tendon allograft for PCL and autograft/BTB allograft for ACL is one option.
A quick diagnostic arthroscopy is performed unless there is fluid extravasation.
A 70 degree scope and a posteromedial portal is also used.
Tibial tunnel for PCL initially drilled.
Then ACL tibial tunnel drilled and positions of these tunnels checked with C-arm.
There should be a 1-2 cm bone bridge between ACL and PCL tunnels.
Femoral tunnels then drilled for ACL and then PCL.
PCL graft passed through first. Then ACL graft passed through and femoral fixation of both ACL and PCL done.
The tourniquet could be released at this stage
Then collateral ligament repair or reconstruction is performed.
Graft Tensioning Sequence
- PCL at 90 degrees with tibia drawn forward
- ACL at full extension
- Posterolateral corner at 30 degrees knee flexion with tibial internal rotation
- MCL at 30 degrees and Posteromedial corner repair in full extension.
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