- February 2009 - Volume 32 · Issue 2:
Calcific tendinitis results from the deposition of calcium hydroxyapatite crystals in periarticular muscular attachments. It is a rare cause of knee pain commonly affecting patients aged 40 to 70 years. Although commonly seen in the shoulder, it should be kept in mind in nontraumatic cases, particularly when the pain is severe and localized to the lateral aspect of the knee. The exact mechanism of hydroxyapatite deposition is unclear, although genetic and metabolic factors have been suspected. A 45-year-old man presented with severe pain in the lateral aspect of his knee with local tenderness over the lateral epicondyle. Radiographs revealed multiple calcific deposits just below the lateral epicondyle of the femur. Magnetic resonance imaging showed multiple areas of low-signal present intra-articularly near the popliteus tendon that was suspected to be calcification. Erythrocyte sedimentation rate and C-reactive protein were slightly raised and other blood investigations including uric acid were within normal limits. Due to failure of conservative treatment, arthroscopy was performed through standard anteromedial and anterolateral portals. Arthroscopy revealed reddish synovial congestion in the lateral gutter. Partial synovectomy was performed with a shaver through a superolateral portal and the calcific deposit was found to lie between the popliteus tendon and the lateral collateral ligament. This was excised and sent for biopsy. Histopathological evaluation revealed the presence of hydroxyapatite crystals within degenerated tendon thereby confirming the diagnosis of calcific tendinitis. Immediate resolution of symptoms following excision allowed the patient to perform activities of daily living immediately postoperatively without pain.
Calcific tendinitis of the popliteus tendon is a rare cause of knee pain. It is generally treated successfully by conservative methods such as nonsteroidal anti-inflammatory drugs, ultrasound therapy and local corticosteroid injections.1 Surgery is helpful in refractory cases, which may be performed arthroscopically.2
This article presents a case of a 45-year-old man who was confirmed by biopsy to have calcific tendinitis of the popliteus tendon.
A 45-year-old man presented with severe pain in the right knee associated with difficulty in walking, which started without any history of preceding trauma. There was no past history of gout or any features suggestive of sepsis. There were no locking episodes. Fullness of the knee joint was noted with severe tenderness around the lateral epicondylar area of the femur. Knee movements were associated with severe pain in the lateral aspect of the knee joint.
Anteroposterior radiographs of the knee joint (Figure 1A) revealed multiple calcific deposits just below the lateral epicondyle of the femur in the region of the popliteus tendon. Magnetic resonance imaging (Figure 1B) showed multiple areas of low signal present intra-articularly near the popliteus tendon that was suspected to be calcification. Routine blood investigations were uncharacteristic except for a slightly raised erythrocyte sedimentation rate.
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Figure 1: Plain AP radiograph of the right knee showing multiple calcifications (arrow) in the area of the lateral epicondyle of the femur (A). MRI coronal view of the right knee showing multiple areas of low signal intensity (arrow) indicating calcification (B).
The patient was treated conservatively with analgesics, an above knee splint and sent home. The patient returned the next day with severe pain for which he was reassured and sent home. Despite taking analgesics, he returned in 3 days with aggravated pain. Since the pain was unrelenting, arthroscopic surgery was recommended.
Arthroscopy revealed a normal knee joint with synovial congestion in the lateral gutter. The knee was placed in full extension and the joint was visualized through the anterolateral portal and the shaver was introduced through the superolateral portal. A rent was made in the synovium using the shaver and a chalky, white deposit was seen in between the popliteus tendon and the lateral collateral ligament (Figure 2), which was excised and sent for biopsy. Partial synovectomy was then performed using the shaver.
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Figure 2: Arthroscopic AP view of a chalky, white deposit situated between the popliteus tendon on the right side and the lateral collateral ligament on the left. Abbreviations: LCL, lateral collateral ligament, LFC, lateral femoral condyle, Pop, popliteus tendon. Figure 3: Microscopic findings of calcific tendinitis. Scattered leukocytes and blood vessels are noted in the right upper corner. On the left side of the tendon (long arrow), various sized round hydroxyapatite crystals are noted. Psammoma body is shown by the short arrow (×200, hematoxylin-eosin).
Postoperatively, the patient was pain free. He was mobilized with partial weight bearing immediately. Biopsy revealed hydroxyapatite crystals scattered among tendon tissue with psammoma bodies interspersed in between, which confirmed the diagnosis of calcific tendinitis (Figure 3). At 3-month follow-up, he was pain free and was able to comfortably perform his routine activities.
Calcific tendinitis results from the deposition of calcium hydroxyapatite crystals in periarticular muscular attachments causing severe pain and disability. It was thought to be caused by genetic and metabolic factors; however no specific mechanism for their formation has been completely proven.1,3 It is most commonly seen in the shoulder but has also been described to occur in the neck, elbow, wrist, hand, hip, knee, ankle and foot.1 There generally is no history of trauma prior to symptoms.2,4,5 To our knowledge, calcific tendinitis of the popliteus tendon has been documented thrice till date.2,4,6
Tibrewal4 in his study reported that 3 patients diagnosed with calcific tendinitis of the popliteus presented with symptoms suggesting a locked knee. Local steroid injection helped to relieve the pain immediately. Tennent and Goradia2 reported a case of calcific tendinitis of the popliteus treated successfully with arthroscopic excision Both studies, however, did not confirm the diagnosis by performing a biopsy.
Calcific tendinitis typically affects patients aged 40 to 70 years and it mimics an inflammatory reaction. The cause of hydroxyapatite deposition is unclear. It may follow trauma with crystal deposition being an initial phase of tissue degeneration or it may occur at the site of tendon degeneration within necrotic tissue where avascularity leads to hypoxia.7 Calcification due to post-traumatic causes cannot be completely differentiated from hydroxyapatite on imaging.5
Nontraumatic knee pain, if associated with disability and excruciating knee pain, can be challenging to diagnose and treat. Although an uncommon site, the possibility of calcific tendinitis must be kept in mind. It can be confused with meniscal tears, gout, or septic arthritis of the knee joint, which can be ruled out by performing blood and radiological investigations.
Although conservative treatment has shown to be satisfactory, symptoms may persist causing anxiety and disability. Arthroscopic excision can be used in refractory cases or when the pain is severe, providing immediate relief and allowing early mobilization postoperatively. To our knowledge, this is the first diagnosis of calcific tendinitis of the popliteus tendon confirmed by biopsy.
- Holt PD, Keats TE. Calcific tendinitis: a review of the usual and unusual. Skeletal Radiol. 1993; 22(1):1-9.
- Tennent TD, Goradia VK. Arthroscopic management of calcific tendinitis of the popliteus tendon. Arthroscopy. 2003; 19(4):E35.
- Resnick D. Calcium hydroxyapatite crystal deposition disease. In: Draud LA, Fix CF, eds. Diagnosis of Bone and Joint Disorders. Volumes 1-5. 4th ed. Philadelphia, PA: Elsevier Science; 2002:1619-1657.
- Tibrewal SB. Acute calcific tendinitis of the popliteus tendon- an unusual site and clinical syndrome. Ann R Coll Surg Engl. 2002; 84(5):338-341.
- Anderson SE, Bosshard C, Steinbach LS, Ballmer FT. MR imaging of calcification of the lateral collateral ligament of the knee: a rare abnormality and a cause of lateral knee pain. AJR Am J Roentgenol. 2003; 181(1):199-202.
- Holden NT. Deposition of calcium salts in the popliteus tendon. J Bone Joint Surg Br. 1955; 37(3):446-447.
- Schindler K, OKeefe P, Bohn T, Sundaram M. The case: your diagnosis? Calcific tendonitis of the fibular collateral ligament. Orthopedics. 2006; 29(4):373-375.
Drs Shenoy, Kim, Wang, Oh, Soo, Kim, and Nha are from the Department of Orthopedic Surgery, Inje University Ilsan Paik Hospital, Ilsan, South Korea.
Drs Shenoy, Kim, Wang, Oh, Soo, Kim, and Nha have no relevant financial relationships to disclose.
Correspondence should be addressed to: Kyung Wook Nha, MD, Department of Orthopedic Surgery, Inje University Ilsan Paik Hospital, 2240 Daehwa-dong, Ilsanseogu, Koyangsi, Ilsan, South Korea.