Osteonecrosis or avascular necrosis of the patella is rare. It has been associated with surgical intervention following trauma and also following lateral release during total knee arthroplasty.1,2 Atraumatic causes also have been described in the setting of chronic corticosteroid use and systemic lupus erythematosus.3–5 Although rare, osteonecrosis can cause anterior knee pain and may have a significant impact on a patient's activities of daily living, work requirements, and desired athletic function. To the authors' knowledge, patellar osteonecrosis has not been described previously in the literature as a result of a single knee arthroscopy. This article reports a patient who presented with osteonecrosis of her patella 6 months following knee arthroscopy with partial medial meniscectomy and limited synovectomy.
In May 2018, a 50-year-old active woman presented to a hospital with a 2-month history of right knee pain. She had a long history of athletic participation, including marathon training, downhill skiing, and singles tennis. The patient had no history of trauma or previous surgery on her knee, and she denied taking any long-term medications or having any chronic illnesses. Moreover, she had never received high-dose steroids and had no history of alcohol abuse. Her pain was located primarily around the medial joint line and was excruciating on deep flexion. She denied any notable injury to her right knee prior to her pain including a fall, direct impact, or trauma.
Magnetic resonance imaging (MRI) revealed a medial meniscus tear and mild osteoarthritis about the patellofemoral joint (Figure 1). She subsequently underwent knee arthroscopic partial medial meniscectomy, bicompartmental chondral debridement, tricompartmental partial synovectomy, and debridement of the undersurface of the patella. Moreover, significant hypertrophic synovium was noted on the anterior aspect of the knee.
Preoperative coronal (A), sagittal (B, D), and axial (C) magnetic resonance images showing a posterior body/horn medial meniscus tear with mild knee degeneration. The sagittal images show the fat pad (B) and the meniscal pathology (D).
During the next 2 months, she had swelling that gradually worsened and caused moderate discomfort. She was prescribed physical therapy 2 to 3 times per week and daily at-home cryotherapy sessions lasting 30 minutes. She maintained full range of motion postoperatively but had persistent swelling at the portal sites (lateral > medial); no effusion was noted on examination. The soft tissue swelling persisted and led her to seek a second opinion from a fellowship-trained sports medicine primary care physician. She then was treated with a corticosteroid injection, which provided a few weeks of relief and reduced her pain to a tolerable yet still noticeable level. Given her continued swelling and discomfort, hyaluronic injections and further imaging were discussed. Radiographs did not reveal any bony injury (Figure 2).
Anteroposterior (A), Merchant (B), and lateral (C) radiographs showing no acute abnormality at 5 months postoperatively.
The use of a knee sleeve with a patellar cutout allowed her to participate in doubles tennis, but she desired to compete in singles tennis. She avoided any distance running because after approximately 1 mile, she would experience pain and swelling of the knee. After follow-up with her primary care physician without improvement, an MRI was obtained to evaluate the knee and to rule out any occult pathology. The MRI revealed osteonecrosis of her patella with notable scarring of the fat pad (Figure 3). Given her history, physical examination, and radiographic correlation, patellar stress fracture was ruled out. Symptomatic treatment was discussed with full return to activities as tolerated.
Coronal (A), sagittal (B, D), and axial (C) magnetic resonance images at 5 months postoperatively showing hyperintense signal within the patella (A, B, C) and significant scarring and absence of adipose tissue (B) within the previously imaged anterior fat pad.
Osteonecrosis about the knee, but not the patella, has been described in the literature following knee arthroscopy.6 It is believed to be similar to spontaneous osteonecrosis of the knee and may be unavoidable in cases of surgical intervention.7 In their case series, Johnson et al8 described knee osteonecrosis occurring in the surgical compartment in which the procedure had been performed. However, this case represents the first report of osteonecrosis of the patella following knee arthroscopy. The authors hypothesize that the primary blood supply in this patient originated from inferior to the patella and was disrupted at the time of surgery as a result of scarring of the fat pad.
Imaging modalities play a significant role in the diagnosis of patellar osteonecrosis. Radiographs may reveal sclerosis about the patella, with radiolucent areas demarcated by a radiodense line identifying the ischemic region.9 Magnetic resonance imaging plays a significant role in identifying intra- and extra-articular pathology about the knee. In the current case, it should be noted that the posterior aspect of the patella demonstrated the greatest area of edema, fragmentation, and sclerosis.
The blood supply to the patella is robust with nutrient vessels creating a peripatellar anastomotic ring supplying the intraosseous patellar system.10 It is believed that the primary blood supply is typically through the inferior patella via the infrapatellar fat pad. In a cadaveric study, Nemschak and Pretterklieber11 discovered the infrapatellar fat pad contains a rich vascular supply and dense network of anastomoses, which contribute to patellar bone viability. Moreover, the proximal patella obtains its blood supply mainly from interosseous vessels from the inferior patella.2
To the authors' knowledge, this is the first report of patellar osteonecrosis following knee arthroscopy. Despite its rarity, it is important to consider osteonecrosis of the patella following surgical intervention of the knee, especially in patients who report anterior knee pain. The degree to which the infrapatellar fat pad is excised, if at all, during knee arthroscopy varies greatly. The practice is not well elucidated in the literature and requires further study to determine the effects. However, the risk of osteonecrosis with total fat pad excision is likely an avoidable iatrogenic cause of morbidity.
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- Schüttrumpf JP, Behzadi C, Balcarek P, et al. Radiologically hyperdense zones of the patella seem to be partial osteonecroses subsequent to fracture treatment. J Knee Surg. 2013;26(5):319–326. doi:10.1055/s-0032-1332805 [CrossRef]
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- Johnson TC, Evans JA, Gilley JA, DeLee JC. Osteonecrosis of the knee after arthroscopic surgery for meniscal tears and chondral lesions. Arthroscopy. 2000;16(3):254–261. doi:10.1016/S0749-8063(00)90049-5 [CrossRef]
- Theodorou DJ, Theodorou SJ, Farooki S, Kakitsubata Y, Resnick D. Osteonecrosis of the patella: imaging features. Clin Imaging. 2001;25(1):60–65. doi:10.1016/S0899-7071(01)00253-4 [CrossRef]
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- Nemschak G, Pretterklieber ML. The patellar arterial supply via the infrapatellar fat pad (of Hoffa): a combined anatomical and angiographical analysis. Anat Res Int. 2012;2012:713838.