SplintER Series: My Knee, Again!

Dec 09, 20

posterior tibiofemoral dislocation knee dislocation

A 61-year-old F presents to the ED from the orthopedic clinic with acute right knee pain. She endorses that while a physical exam was being performed, she had sudden onset knee pain. Denies any trauma to the knee, radiation of pain, numbness, tingling, or swelling. The above knee radiographs were obtained (Images courtesy of John Kiel, DO).

What is the suspected diagnosis?

Posterior tibiofemoral arthroplasty dislocation. The right image demonstrates a tibia translated posteriorly with respect to the femur. A joint effusion is also notable. A posterior tibiofemoral dislocation typically occurs secondary to a direct blow to the tibia. In this case, it occurred spontaneously while flexing the leg during a routine physical exam in the clinic.

Pearl: When referring to a knee dislocation, describe the joint being displaced – patellofemoral or tibiofemoral.
Pearl: Tibiofemoral dislocations are a relatively rare complication after total knee arthroplasty (TKA). Anterior dislocations are more common than posterior dislocations [1]. The incidence of posterior dislocations ranges from 0.15-0.50% post-TKA [2].

What should your physical exam focus on?

Perform a comprehensive neurovascular exam. It is important to compare the affected limb with the unaffected to have a good point of reference. Check out the ALiEM 2 minute knee examination for a refresher.

Pearl: Often, the knee may have spontaneously reduced prior to arrival in the ED, so you must have a high index of suspicion.
Pearl: Causes of posterior dislocation can be, but not limited to implant malpositioning, flexion-extension gap mismatch, excessive soft tissue release or laxity, and inappropriate selection of the primary implant [3].

What is your ED management?

If dislocated on arrival, initial treatment should be an immediate reduction to prevent any (or avoid further) neurovascular compromise. Closed reduction with appropriate anesthesia/analgesia is the preferred method of treatment. Once reduced, stabilize the joint with a knee immobilizer or posterior long leg splint. An orthopedic surgeon should always be consulted.

Pearl: It is important to obtain pre- and post-reduction radiographs to evaluate for correct reduction. Also, make sure to conduct a thorough pre- and post-neurovascular exam.

What complications are important to be aware of with this presentation?

Acute compartment syndrome. Even if not initially present, it is a potential complication of post-reduction. If present, treatment is fasciotomy.
Popliteal artery dissection. If concerned, perform computed tomography (CT) angiography to assess. If present, emergently consult vascular surgery.

- Pearl: An intact dorsalis pedis pulse does not exclude arterial injury. Careful consideration should be made for checking an ankle-brachial index, obtaining arterial dopplers or CT with angiography of the affected limb.

What is your disposition?

Perform serial neurovascular exams. Coordinate with your orthopedic consultant to determine the patient’s final disposition. The patient may require urgent revision surgery of the arthroplasty.

Pearl: Generally, all patients will require an expedited MRI outpatient.
Pearl: Knee instability is one of the major causes of revision surgery following TKA [4].

References:

Gidwani, S., & Langkamer, V. Recurrent dislocation of a posterior-stabilized prosthesis: A series of three cases. The Knee, 2001;8(4), 317-320. PMID: 11706695.
Lee, H. M., Kim, J. P., Chung, P. H., Kang, S., Kim, Y. S., & Go, B. S. Posterior dislocation following revision total knee replacement arthroplasty: A case report and literature analysis. European Journal of Orthopaedic Surgery & Traumatology, 2018;28(8), 1641-1644. PMID: 29797093.
Villanueva, M., Ríos-Luna, A., Pereiro, J., Fahandez-Saddi, H., & Pérez-Caballer, A. Dislocation following total knee arthroplasty: A report of six cases. Indian Journal of Orthopaedics, 2010;44(4), 438. PMID: 20924487.
Chang, M. J., Lim, H., Lee, N. R., & Moon, Y. (2014). Diagnosis, Causes and Treatments of Instability Following Total Knee Arthroplasty. Knee Surgery & Related Research, 26(2), 61-67. PMID: 24944970.