Figure 1. Anteroposterior radiograph of the left knee.
Figure 2. Lateral radiograph of the left knee.
Figure 3. Merchant-view radiograph of the left knee.
A patient experiences a fall on postoperative day 2 following total knee replacement (TKR) and sustains an injury to her left knee. She had been walking well with the aid of a walker on postoperative day 1. On physical examination, the dressing around her knee is saturated with blood and there is mild bloody drainage from the surgical site, but the incision remains intact. The patient has moderate swelling and is unable to bend her knee. Anteroposterior, lateral, and Merchant-view radiographs are obtained (Figures 1, 2, and 3).
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Disruption of the knee extensor mechanism is a rare but significant complication following TKR.1 Ruptures involved in disruption of the knee extensor mechanism include suprapatellar (quadriceps tendon), transpatellar (patella fracture), infrapatellar (patella tendon fracture),1 and tearing of the medial retinacular repair. The medial retinaculum is a band of thickened deep fascia that originates from the vastus medialis muscle, sartorius muscle, medial collateral ligament, and medial patellofemoral ligament.2
The medial retinaculum is a primary stabilizer of the patella against lateral dislocation. The retinaculum is incised during TKR and is repaired during wound closure. During the first 6 to 8 weeks postoperatively, the retinacular repair site is the part of the knee extension mechanism that is most vulnerable to injury.
Any disruption of the knee extensor mechanism after TKR should be evaluated with anteroposterior, lateral, and Merchant-view imaging. The patient’s radiographs show a laterally dislocated patella on Merchant view. When the patient fell in the hospital, she sustained an acute medial retinacular tear. She underwent revision retinacular repair on postoperative day 3 following her TKR.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants.
1. Vaishya R, Agarwal AK, Vijay V. Extensor mechanism disruption after total knee arthroplasty: a case series and review of literature. Cureus. 2016;8(2):e479.
2. Knipe H, Moodaley P. Medial patella retinaculum. Radiopaedia website. https://radiopaedia.org/articles/medial-patellar-retinaculum?lang=us. Accessed January 27, 2020.