Knee dislocation

This is a devastating injury associated with rupture of several principle ligament in the knee, a high risk of complications and usually very poor function in the knee forever more!

Hx	Significant applied force Immediate pain +- "pop" Reduced "with a clunck" Numbness or weakness
LOOK	Massive swelling, both intra and extra-articular
FEEL	Multidirectional instability Pulses Muscle power in EHL and TA
MOVE	Reduced active movement due to pain Multidirectional instability - recurvatum Exclude associated injuries Vascular injury Periopheral nerve injury
XRAYS	AP and Lateral views May be misleadingly normal Subluxation of the femur on the tibia Marginal avulsions indicate massive capsular damage (and therefore multiple ligament ruptures) Stress views Requires a GA, therefore "opportunistic" Identify the remaining intact/functional structures
MRI	Useful to support clinical diagnosis. Grading of ligament injuries unreliable.
Angiogram	Acute angiography in all cases with abnormal pulses (>70% will have angiographic abnormalities) Elective angiography if abnormal ABI for semi-elective cases ABI for all cases before surgery

The relative displacement of the bones causes traction on all the structures crossing the knee. A high index of suspicion is required, looking for vascular, neurological and combined injuries.

Vascular injury accounts for 5% of cases, either a transection, intimal tear or thrombosis. The pulses must be present and equal to the other side. ABI/API measurements of less than 0.90 are shown to have a 95% sensitivity and 97% specificity for arterial injury of consequence.

Peripheral nerve injury, occurs in 20% to 40% of cases with half of these palsies being permanent. Ischaemia may mimic neurological injury.

Extensor mechanism disruption indicates severe displacement of the joint and is associated with a particularly poor prognosis.

Fractures of the femoral condyle and tibial plateau may be associated with these injuries, especially if there was axial loading as part of the mechanism. The fragments are likely to carry intact capsulo-ligamentous attachments and rigid internal fixation is recommended.

These injuries may be classified with reference to the direction of dislocation (i.e Which way the tibia is displaced wrt the femur)

Classification	%	Mechanism	MCL	PCL	ACL	PLC/LCL
Anterior	31	Hyperextension > 30 degrees	Intact	Ruptured (Occasionally spared)	Ruptured	Intact
Posterior	25	Posterior Translation - Dashboard/Bumper (Vascular injury most common)	Ruptured	Ruptured	Ruptured	Ruptured
Lateral	13		Ruptured	Ruptured	Ruptured	Intact
Medial	3		Intact	Ruptured	Ruptured	Ruptured
Rotary	4		Ruptured	Ruptured (Occasionally spared)	Ruptured (Occasionally spared)	Ruptured

There is also the "Anatomical Classification of Knee Dislocations" based upon the distribution of ligament damage.

Classification	Subclass	#	MCL	PCL	ACL	PLC/LCL
KD-I		No	Intact	Single Cruciate Ruptured		Intact
KD-II		No	Intact	Bicruciate Injury Only		Intact
KD-III	M	No	Ruptured	Bicruciate Injury +		Intact
KD-III	L	No	Intact	Bicruciate Injury +		Ruptured
KD-IV		No	Full House of Principle Ligament Ruptures
KD-V	1	Yes	Intact	Single Cruciate Ruptured		Intact
KD-V	2	Yes	Intact	Bicruciate Injury Only		Intact
KD-V	3M	Yes	Ruptured	Bicruciate Injury +		Intact
KD-V	3L	Yes	Intact	Bicruciate Injury +		Ruptured
KD-V	4	Yes	Full House of Principle Ligament Ruptures

*Note there are additional annotations "C" for vascular injury and "N" for nerve injury.

These injuries are often reduced by the paramedics and may appear relatively benign. A good history of the "mechanism of injury" is essential. These injuries are easy to miss.

Reduction should be undertaken immediately, before any other investigations, using simple sedation. Ischaemia of over 6 hours is associated with >80% rate of amputation. After reduction further assessment can be made. If a general anaesthetic has been administered then the opportunity for stress radiographs and EUA should be taken. Once reduced the knee should be immobilized in 20 degrees of flexion and neutral coronal alignment - this positioning should be recorded with a x-ray.

An irreducible knee dislocation usually occurs due to a button hole where the medial femoral condyle pushes through the capsule in the context of a lateral or posterolateral dislocation. Often a "dimple" forms overlying the medial aspect of the knee. An open reduction is required to replace the femur inside the capsular envelope.

Serial recording of perfusion and innervation must be documented before, during and after any manipulation. All of these patients must be admitted for observation and further management.

Emergent interventions: Any vascular compromise must be investigated by means of angiography. After any vascular repair the limb should be protected from further damage by external fixation and fasciotomies. Those few open injuries requiring plastic surgical cover should be treated in a similar way.

An irreducible dislocation is best approached by an anterior incision and medial parapatella dissection. In the acute situation only limited repair/reconstruction is recommended.

All patients having an emergency surgery should have stress radiographs, an EUA, and compartment pressure measurements.

Elective reconstruction: There has been great debate about the timing and extent of ligament repair/reconstruction. In summary:

Experienced surgeons recommend operating in the 2-3 week window, after the initial swelling has settled and before all the tissues stick together in a fibrous mass. This window may be used to address all the reconstructions are for the first part of a staged approach - see foot note.

Nerve injury: The foot must be supported in a splint and specialist physiotherapy undertaken. If there is no improvement at 3 months then further investigation (EMG) and referral to a peripheral nerve injury unit is advised.

Foot note

Mook et al recently did an interesting systematic review of studies to compare outcomes in early, delayed, and staged procedures as well as the subsequent rehabilitation protocols. Twenty-four retrospective studies were analyzed involving 396 knees dealing with multiple ligament knee injuries involving both cruciates and either or both collaterals. Data were compared as follows: 1) acute (time to surgery <3 weeks), 2) chronic (time to surgery >3 weeks), and 3) staged treatment (combination of repair and reconstruction in the acute and chronic periods). Findings were as follows:

Anterior instability – Acute treatment lead to greater instability compared to chronic treatment. No differences were found between acute and staged or staged and chronic. No differences in anterior instability were garnered from postoperative rehabilitation.
Posterior instability – Posterior instability was found in 28% who were managed with immobilization compared to 12% of those managed with early mobilization.
Varus laxity – Acute treatment resulted in 21% of patients having laxity in the immobilized group compared to only 1.6% managed with early mobilization. In the chronic treatment group, varus laxity was found in 1% managed with immobilization compared to 20% managed with early mobilization.
Valgus laxity – Acute treatment resulted in 26% of patients having laxity managed with immobilization compared to 2% of those managed with mobilization.
Flexion loss >10° – Significantly more patients (31%) had flexion loss of >10° in the acute group compared to patients in the chronic group. Significantly fewer patients were found to have flexion loss when managed in stages compared to those managed acutely. Flexion loss >10° was reported in 48% of those who were immobilized compared to 28% of those who were allowed early immobilization.
Extension loss of >5° – no differences were found based on surgical timing, but 15% of patients immobilized compared to 5% who were allowed early mobilization showed extension losses.
Good or excellent subjective outcome scores – Significantly greater outcomes were found in the staged group compared to the chronic group and the acute groups.
Abnormal/poor subjective outcomes – Significantly more poor outcomes were found in those managed with immobilization compared to those who were allowed early mobilization.
Lysholm Score – no differences in timing or rehab
Return to work – acutely managed patients who were immobilized early were significantly less likely to return to work than those who were mobilized early. No differences were found on basis of surgical timing
Return to athletics – patients who were managed acutely were significantly less likely to return to athletics than those who were managed in stages.
Operative arthrolysis – significantly fewer patients in the chronic treatment group underwent manipulation when compared to both the acute and staged treatment groups.

Clinical Implications

From a rehab standpoint, researchers found that those managed acutely with early mobilization had better outcomes as well as less range of motion losses. Observations from the researchers include a few important points. Reconstruction within three weeks after injury results in more anterior instability, more severe ROM complications, and more need for MUA. Secondly, they found patients that are managed in stages had the highest percentage of excellent/good subjective outcomes and the least ROM deficits. Third, although final ROM was preserved best in patients undergoing staged treatment, a high percentage needed follow-up surgery due to arthrofibrosis. This finding suggests that simultaneous repair and reconstruction of the cruciates acutely may lead to substantial ROM deficits and are unresponsive to follow-up surgery. Next, aggressive rehabilitation with early mobilization is associated with less ROM complications and earlier return to work, particularly in those who are acutely managed.

In conclusion, researchers stated:

Delayed surgery potentially results in equivalent stability measures compared to acute surgery.
Staged procedures produce a better subjective outcome and lower number of ROM deficits, but still needed additional treatment due to joint stiffness.
Patient managed acutely are as likely as those who are managed in stages to require additional treatment due to ROM deficits.
For the acutely managed patient, early mobilization results in better outcomes.
The type of rehab for delayed procedures isn’t as important as those who are managed acutely (mobilize acute early).

1. Mook WR, Miller MD, Diduch DR, Hertel J, Boachie-Adjei Y, & Hart JM (2009). Multiple-ligament knee injuries: a systematic review of the timing of operative intervention and postoperative rehabilitation. The Journal of bone and joint surgery. American volume, 91 (12), 2946-57 PMID: 19952260