CHAPTER 118
Locked Knee
Presentation
The patient, usually with a history of a previous knee injury, and often with previous knee locking, suddenly develops a mechanical inability to extend her knee fully. The knee may flex but not extend and may be causing mild to moderate pain.
What To Do:
Perform a complete knee examination, checking for point tenderness, effusion, meniscal tear, and joint stability. If comfort allows, gently and repeatedly perform the maneuvers of the McMurray test (see Chapter 115). This alone may release the locked knee. If not, continue as described below.
Obtain knee radiographs, looking for an osteocartilaginous loose body or other disease.
With pain and persistent locking, prepare the knee with povidone-iodine solution and, at a point just superior and lateral or medial to the patella, using a 25-gauge, 1-inch needle, inject 10 mL of 0.5% bupivacaine (Marcaine) into the joint space (see Figure 120-1, A, p. 460.)
With the knee thus anesthetized, place a roll of towels under the heel and ankle to serve as a fulcrum. Leave the patient supine so that gravity will aid in extension and have the patient gently rock and rotate the knee for approximately 20 minutes or until the locked knee has released. Repeated McMurray maneuvers may again be gently performed if joint reduction has not occurred. Alternatively, longitudinal traction can be applied with gentle rotation of the knee internally and externally.
When the mechanical block is dislodged and the knee extended, place the patient in a knee immobilizer, keep the patient non–weight-bearing with crutches, and refer the patient to an orthopedic surgeon for early arthroscopic examination and definitive treatment.
What Not To Do:
Do not forcefully manipulate the knee. This may produce further intra-articular injury.
Discussion
Knee locking is usually caused by previous injuries that include meniscal tears, partial or complete anterior cruciate ligament tears, osteocartilaginous loose bodies, pathologic medial plicae, and foreign bodies. Less commonly, locking can occur without a history of trauma. In such cases, the cause may be torsion of the infrapatellar fat pad or an intra-articular tumor, such as a ganglion. Locking of the knee occurs when one of these structures has become entrapped between the tibial plateau and the femoral condyles, mechanically blocking extension of the joint. This may happen suddenly, and may resolve suddenly.
If full extension cannot be obtained, the patient can be placed in a soft, bulky, partially immobilizing dressing (thick cotton roll covered with an elastic wrap) and placed on crutches until orthopedic follow-up can be obtained.
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