Knee



Knee


Andrew Pennock

Eric Edmonds



INTRODUCTION

With our country’s fascination and enthusiasm for sports, we are currently observing a dramatic rise in sports-related pediatric knee injuries. When a child presents to the emergency department or clinic with a traumatic hemarthrosis, the most common diagnoses should be considered a patella instability event, followed by a ligament tear, although depending on the child’s age, a fracture or meniscus injury should also be considered. In these situations, it is important for the clinician to obtain the correct diagnosis and initiate the appropriate treatment because if unrecognized or mismanaged, a large number of these patients will develop future arthritis or have future disability (regardless of the their ability to return to sport).

“Education is what remains after one has forgotten what one has learned in school”

Albert Einstein




ASSESSING THE PATIENT

An acutely swollen knee in a child may be difficult to examine. Establishing a good rapport with the patient and family prior to the examination, as well as distracting the patient during the examination will assist with this process. We also advocate examining the uninjured extremity first so that the patient is more relaxed and comfortable with you before proceeding with the more painful limb.

One of the most important findings on the examination is the presence of an effusion, as this points to an intra-articular source of pain. In a child who has had an injury, fluid within the joint almost always signifies a severe knee injury that will need formal treatment (Fig. 14-1). Palpation is also important to identify the areas of greatest tenderness. This will be an important clue as to what anatomic structure was injured. Is the pain located at the physis suggesting a fracture, or is it over the anterolateral aspect of the lateral condyle with concomitant pain along the course of the medial patellofemoral ligament suggesting a patella instability event?






Figure 14-1 Impaction injuries on the lateral femoral condyle can lead to a medial patellar femoral ligament tear and a bone bruise on the lateral femoral condyle.

“In a child who has had an injury, fluid within the joint almost always signifies a severe knee injury that will need formal treatment”

The ligamentous exam should assess the medial patellofemoral ligament with the patella apprehension test, which is almost always positive in a patient who has dislocated their patella. The Lachman test is most sensitive for an ACL tear, but the pivot shift test is more specific. It is frequently challenging to have a young patient with a swollen knee relax enough to enable an adequate pivot shift maneuver to be performed in the clinical setting.

The PCL is best assessed with the posterior drawer test, but this does require one to flex the patient’s knee close to 90 degrees which may be painful and difficult for the patient in the first hours or days after a knee injury. The medial and lateral supporting structures of the knee can be assessed with a valgus and varus stress test, respectively.









Figure 14-2 Diagram illustrating the posterior cruciate ligament (PCL), anterior cruciate ligament (ACL), fibular collateral ligament (FCL), posterior oblique ligament (POL), superficial and deep medial collateral ligament (sMCL, dMCL), and popliteus tendon.






Figure 14-3 Unilateral decreased internal rotation can be a sign of slipped capital femoral epiphysis.

Isolated medial instability and gapping with the knee in 30 degrees of flexion is indicative of an isolated superficial medial collateral ligament (sMCL) injury where as isolated lateral gapping in 30 degrees of flexion is indicative of an isolated fibular collateral ligament (FCL).

Valgus instability in full extension always represents a more severe injury involving a physeal fracture or a complete tear of not only the MCL but also the posterior oblique ligament (POL) and/or the cruciate ligaments. Similarly, varus instability in full extension represents a physeal fracture or a severe posterolateral corner injury involving not only the FCL but also the popliteus tendon, the popliteofibular ligament, and/or the cruciate ligaments (Fig. 14-2).

In patients who have sustained high-energy knee injuries, including knee dislocations and severely displaced physeal fractures, a comprehensive neurovascular examination must be performed. Many of these patients will have traction injuries involving the peroneal nerve and, although rare, some may have a vascular injury (typically an intimal tear) of the popliteal artery that if not recognized early can lead to a dysvascular extremity. In these cases, an ankle-brachial index (ABI) should be obtained and if a value less than 0.9 is obtained, further vascular studies should be obtained, such as an arteriogram.

Finally, when assessing patients with knee pain, the hip cannot be ignored as a possible source of pain. Each year, we see at least one slipped capital femoral epiphysis (SCFE) that was initially missed because an outside facility listened only to the complaint of knee pain (referred) and did not evaluate hip range of motion (Fig. 14-3).





PATELLAR INSTABILITY

The vast majority of children under the age of 14 who present with a traumatic knee effusion will have experienced a patella dislocation. Nearly all of these occur in a lateral direction, but rarely medial instability can be seen if the patient has undergone a previous lateral release, or in patients with connective tissue disorders, such as Down syndrome or Ehlers-Danlos syndrome.

Occasionally patella dislocations will be associated with a loose body; if this fragment is of substantial size (greater than 1 cm), it may require arthroscopic removal or open fixation (Fig. 14-7). Although there is some controversy as to the optimal management of a first time dislocation, we typically manage these non-operatively with a brief
period of immobilization (2-4 weeks) in a knee immobilizer followed by physical therapy to strengthen the hip external rotators (gluteus muscles) to control hip adduction and knee valgus moments during activity, thus reducing the risk for recurrence.






Figure 14-4 The AP, lateral, tunnel, and merchant views are a common first step to clarify knee trauma.






Figure 14-5 Merchant view depicting a medial patellar femoral ligament (MPFL) avulsion.






Figure 14-6 The tunnel view is often the only view in which to discover a femoral condyle osteochondritis dissecans lesion.






Figure 14-7 Patellar instability with patellar fragment that required open reduction and internal fixation (ORIF).

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Nov 17, 2018 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Knee
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