Initial assessment, investigation and pre‐operative planning in multi‐
ligamentous knee injuries
Myles RJ Coolican and Vikram Mhaskar
Sydney AUSTRALIA
Introduction
Multi‐ligamentous knee injuries are relatively rare with an incidence of 0.01‐0.013% per year1‐8. The mechanism varies from high speed injuries most commonly in motor‐cross to lower velocity sports injuries and more recently, we are seeing knee dislocations associated with overload in the super obese. Irrespective of the mechanism, all multi‐ligament knee injuries may be associated with vascular and neurological compromise, more so in the high velocity injuries. The extensive nature of the ligamentous disruption as well as the associated neurovascular compromise is not infrequently missed in the early assessment. Knee dislocations are usually closed, with open dislocations being associated with a higher incidence of neurovascular compromise and difficulties with wound healing.9
Classification
Knee dislocations are classified according to the position of the tibia relative to the femur10 with anterior dislocation being the most common at 40%, followed by posterior dislocation (33%), lateral (18%), medial (4%) and rotational (5%)11 .
Schenck Classiication for the multiple ligament injured knee
•
KDI :Lesion of ACL + MCL or LCL •
KDII Rupture of ACL + PCL with intact collateral ligament •
KDIII
III M Rupture of ACL + PCL + MCL with intact LCL and posterolateral corner
III L Rupture of ACL + PCL + LCL with intact MCL KDIV Rupture of ACL + PCL + MCL + LCL
“C” specifies an arterial injury and “N” a neural injury. For example, KDIIIL‐CN is an ACL/PCL/PLC, where PLC stands for posterolateral corner with a vascular and a neural injury12 .
Classification according to timing of injury
•
< 3weeks :acute
•
3weeks‐3months: subacute
•
>3 months: chronic
Associated Injuries
Many patients with multiple ligament knee injuries have other significant injuries‐ especially those associated with high velocity mechanisms. Fractures around the knee are associated with 53% of knee dislocations. In order of prevalence tibial plateau, distal femur, tibial and fibular shaft, isolated fibula, and isolated tibial fractures were most common13 . Tibial plateau rim fractures do not often alter management. However, intra‐articular fracture displacement requires aggressive fixation and may require staged reconstruction. Proximal tibiofibular joint dislocation that is usually missed and extensor mechanism injuries must be identified13,14. The mechanism of injury, degree of swelling around the knee and bruising patterns can suggest an associated fracture.
Initial assessment
History
A number of factors are useful in understanding the degree of injury. Knee dislocations are more common in young males participating in high velocity motorized activity. Trampoline injuries as well as almost any contact/collision sporting injury can lead to multiple ligament injuries in the knee. The degree of trauma required to disrupt the knee is frequently less in the elderly.
Primary Survey
Initial assessment of the patient should involve a whole body exam and management of any life/limb threatening trauma as appropriate to the circumstances. Review of the knee should include inspection for any open wounds or obvious deformity and the distal neuro‐ vascular status should be evaluated. Distal pulses must be confirmed and compared to the opposite limb. Comparing blood pressure of the arm and leg at the same time‐ankle brachial index (ABI) is a useful tool to rule out arterial compromise. An ABI of 0.8 or higher is a very sensitive test to rule out arterial injury with a normal range is between 0.8‐1.2. Lower than this should raise the suspicion of possible vascular injury and an opinion sought from vascular surgery .
Does the limb appear flaccid?
A flaccid and toneless foot can be indicative of a significant nerve injury and possible arterial injury. The incidence of tibial and common peroneal nerve injury is between 16‐40% of all dislocations. Posterolateral dislocation is associated with a higher incidence of injury to the common peroneal nerve. These injuries more commonly accompany popliteal artery damage. Complete transection of the nerve is unusual with the usual appearance at exploration being a stretched and thin nerve
Hyperextension injuries are more commonly associated with popliteal artery injuries. Though more common in high velocity injuries, the possibility of neurovascular injury should be considered in low velocity trauma.
The use of selective arteriography in multiligamentous injuries is well supported in the literature15‐18. Signs of ischemia including a reduced ABI, hypothermia of the distal affected limb, a tense calf with hypoesthesia, and diminished motor function16 . The absence of pedal pulses and a cold ischemic foot after reduction requires urgent surgical intervention by a vascular surgeon. Arteriography in this setting may prolong ischaemic time but does confirm the level of vascular injury and guide the vascular surgeons approach.
Delay beyond 6 to 8h in arterial reconstruction has been associated with an increase in the likelihood of lower limb amputation19. Green et al compared amputation rates with an arterial repair less than 6 to 8h with longer than 8 hours. Rates increased from 11%, to in one reported series 86% when the repair occurred more than 8h after the injury20. After prolonged ischemia, fasciotomies should accompany the vascular repair or grafting21,22.
At the other end of the clinical spectrum is the patient with normal pulses, a healthy appearing foot, and Doppler signals of normal amplitude‐ no patient in this group was found to have an arterial injury23
Between these two extremes of the clinical spectrum, an arteriogram is useful to rule out an arterial injury, particularly intimal disruption which can progressively impair distal circulation over subsequent days as clot builds and eventually obstructs the lumen. We have found the ABI to be useful, especially following reduction where a patient may have present but diminished, pulses with a warm, perfused foot. In this instance an arteriogram, along with a vascular consultation is indicated. Patients with a significant head injury who can’t describe symptoms of ischaemia, as well as patients under prolonged anaesthesia for lengthy operative attention of other injuries may also require an arteriogram.
Evaluation of the knee in the Accident and Emergency Setting
Inspection
Is the knee grossly swollen?
The amount of swelling and its location is useful in helping indicate the degree of injury. Rupture of the capsule decreases swelling within the knee but allows blood and synovial fluid to extravagate. The location of bruising helps indicate areas of capsular damage. However, absence of swelling within the joint may laed the examiner to underestimate the extent of soft tissue trauma. A dimple sign on the medial joint line heralds an irreducible posterolateral knee dislocation. This occurs when the medial femoral condyle button holes through the anteromedial joint capsule in the microseconds of the injury and as the knee returns to a less deformed position, the MCLand joint capsule invaginates into the joint blocking reduction. The overlying skin forms a furrow on or near the joint line.
Alignment
In the remote setting where a patient is able to stand and walk, excessive varus may suggest posterolateral corner damage, particularly when the patient has constitutional varus. A positive Godfrey sign (posterior sag) is indicative of a grade III posterior cruciate ligament injury. Alignment is also of some value in assessing the acute injury. Knee in excessive varus: PLC injury
Godfrey Sign
The Patella
It is important to evaluate the extensor mechanism. The location of the patella can indicate an extensor mechanism disruption. Quadriceps tendon rupture manifests as patellar baja whilst patellar tendon rupture presents with alta. Extensive medial disruption with a valgus injury can be associated with patellar dislocation.
Ligamentous examination
The most comprehensive and accurate evaluation of ligamentous stability occurs with examination performed under anaesthetic immediately after reduction. Establishing a neutral point for the stability examination, in both the coronal and sagittal plane can represent a significant challenge. Determination of collateral ligament and capsular damage may be more important than definition of the cruciate ligament damage. The stability examination, like good detective work, is thorough and necessary for further decisions but is combined with plain films and MRI findings. These are mandatory to plan surgery.
With the Lachman sign (anterior drawer at 20‐ 30 degrees), grade I laxity is defined as from 0 to 5mm, grade II ranges from 6 to 10mm, and grade III is more than 10mm of tibial motion. With the knee at 90 degrees, increased excursion with the tibia in internal rotation indicates a posterolateral corner injury whilst increased laxity with the tibia externally rotated indicates a posteromedial capsule injury. Both the end point (mushy or absent) and the length of excursion (> 5mm) are observed with the Lachman’s sign. Displaced bucket handle meniscal tears and muscle spasm in the unanaesthesised patient will diminish tibial excursion whilst complete medial capsular disruption increases excursion.
The pivot shift sign more accurately represents anterolateral rotatory instability in the chronic condition and is not apprioprate to be performed in an acute multilig injured knee without anaesthesia. A positive pivot shift is difficult to elicit with a complete medial disruption24‐26.
Pivot Shift Test
PCL Examination
The qadriceps active test is useful in acute situations‐it is performed with a patient supine , hip flexed at 70 deg and knees at 60 deg. The patient actively contracts the quadriceps muscle which translates the tibia from a posteriorly subluxed position anteriorly in absence of a PCL27. This test is also useful in the diagnosis of an acute ACL injury
The posterior drawer test is performed in the same position with the examiner’s thumb palpating the tibial step off from the femur and this is less when a posterior force is applied and the tibia moves backwards.. Comparison to the contralateral side helps indicate the normal position. The tibia should be restored to its normal position under the femur before the extent of posterior laxity is evaluated. The laxity is graded I to III in the same manner as the anterior drawer fixed flat to the table.
PLC Examination
The reverse pivot shift test is only apprioprate in the remote setting and is performed with the patient supine with the knee flexed at least 45° and the foot placed in external rotation to posteriorly sublux the lateral plateau. As the knee is extended, the examiner applies a valgus load. The lateral plateau reduces with an audible clunk at approximately 20° of the flexion.
A most sensitive test for posterolateral corner instability is the dial test performed in the prone position with the knees in 30 and 90 deg flexion and the hips rotated as symmetrically as possible. The authors check the degree of external rotation of the normal side and then match this with the affected extremity. If the damaged side will subsequently allow further external tibial rotation the test is positive with a 10 degree difference between sides indicating pathologic laxity.
External rotation recurvatum sign: PLC failure left knee. Note the surgical scar
Dial Test: Increased external rotataion on pathological side at 30 and 90 degrees: PCL+PLC injury
Only at 30 degrees: PLC injury
Collateral ligament examination
Varus and valgus force are applied to the knee in 30 degrees of flexion. Significant valgus laxity in knee extension implies a complete tear of one or both cruciates. As with all laxity tests, the nomal knee serves as an internal control.
Plain Radiographs
AP and lateral views suffice to make a diagnosis of knee dislocation and promt urgent reduction. A patellar sunrise view may reveal a patellar avulsion fracture that suggests retinacular damage or osteochondral injuries. Osteochondral injuries of the distal femoral articular surface maybe demonstrated with the notch view but in the authors opinion, these should wait til the knee is reduced. Stress radiographs are seldom required since the widespread use of MRI.
The segond sign which is a lateral capsular avulsion of the Anterolateral Ligament can be seen in ACL injuries on an AP Xray. The arcuate sign is avulsion fracture of the tip of the fibula seen in posterolateral corner injuries
Arcuate Sign
Segond Sign‐note the sclerotic margin indicating chronicity
MRI Findings
The sensitivity and specificity of MRI for injuries to the cruciate ligaments in reported series have been excellent. Specific MRI signs that indicate individual ligament injuries can be primary‐that is, a direct view of the ligament, and secondary:
ACL: Primary findings of ligament discontinuity with secondary signs including bone oedema in the lateral compartment, anterior tibial displacement, uncovering of the posterior horn of the lateral meniscus, and when intact, a curling configuration of the PCL28
PCL: Ligament oedema and discontinuity are seen with acute PCL injuries and avulsions can be seen clearly on an MRI. In chronic cases the PCL may appear continuous with a low signal on PDFS views (86%) due to healing and findings must be correlated with physical examination29.
PLC: The posterolateral corner is undoubtedly more difficult to image and interpretation in the presence of marked local oedema is a challenge even for the most experienced MSK Radiologist. However, injuries can be defined with MRI utilising correct sequences including thinly‐sliced coronal oblique T1‐weighted images through the fibular head which improves sensitivity and specificity for injury detection. The popliteo–fibular ligament, popliteus, middle third lateral capsular ligament, fibular collateral ligament, and biceps femoris tendon may all be discerned with MRI30.
MCL: Features of a MCL injury include ligament discontinuity, focal disruption, and fluid deposition particularly at the femoral origin. Fluid deposition and loss of demarcation between the MCL and adjacent fat are not as reliable and are specially inaccurate for grade III injuries. A discontinuity at either end of its attachment particularly distally with a flail superficial MCL and mid substance is indicative of MCL injury but MRI findings need to be co related clinically.
The major role of MRI is to gather an inventory of the injured ligamentous structures which will allow the surgeon to subsequently plan surgery. Multiligament knee repair/reconstruction is not an operation to add on at the last minute to an already overbooked operating list. As MRI is rarely required or available immediately, the subsequent delay whilst it’s performed allows the surgeon some breathing space to plan an operating list and to obtain the necessary equipment and if appropriate, allograft materials. ACL +PCL+MCL Injury
PCL+PLC Injury
Graft Selection
The ideal graft material is of sufficient strength, provides secure fixation, is easy to pass, readily available, and has low donor‐site morbidity. The options can be broadly divided into allografts, autografts or a combination of both. Whilst prosthetic ligaments and xenografts have their proponents, the authors have limited exposure to the former and no experience with the latter. Selection of a particular type of graft is usually governed by a surgeon’s preference.
Autografts may be harvested from the ipsilateral or contralateral limb or both and it is a good idea to consent the patient to bilateral harvesting and to prep and drape both legs so the option is available. Present research favours the use of contralateral limb grafts as it reduces morbidity on the injured side, although this may slow mobility. Ipsilateral grafts are the gold standard for many surgeons , but when more than two grafts are required, only two should be harvested from the ipsilateral side31.
Each graft type can be used for multiple purposes:
Bone patellar tendon bone (BPTB) autograft can be used for reconstructing the ACL, PCL or PLC
Quadriceps tendon can be used as an autograft or allografts to reconstruct the ACL,PCL and PLC with superior bulk, length and strength compared with the BPTB32.
Hamstring tendon can be used as auto or allograft for the ACL,PCL and PLC with good surgeon familiarity and graft structure. In ACL reconstruction, a three‐ or four‐strand graft is required to achieve necessary strength and bulk. Hamstrings offer the surgeon a familiar graft source and significant flexibility in treating partial ligament injuries and avulsion or “peel‐off” injuries to the ACL or PCL33‐36.
Fascia lata autograft is predominantly used for LCL /PLC reconstruction with minimal graft site morbidity37.
Achilles Tendon allograft has superior bulk and is used mainly for PCL, but can is useful for other ligaments including the MCL where the aponeurosis of gastrocnemius closely matches the distal end of the MCL. Its bulk allows the surgeon to fashion two ligaments out of a single graft particularly in small patients.31, 38‐40
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