Case Reports 

Transient Osteoporosis of the Knee

Vassilios S. Nikolaou, MD, PhD; Anastasia Pilichou, MD; Demitrios Korres, MD, PhD; Nicolas Efstathopoulos, MD, PhD

Transient osteoporosis is an uncommon, self-limiting disease, first reported in 1959. Curtiss and Kincaid1 discussed two cases of the disease, both involving women in the third trimester of pregnancy. Duncan et al2 subsequently described a polyarticular disease process in 1969, coining the term regional migratory osteoporosis. The term idiopathic transient osteoporosis of the hip was designated by Laquesne3 in his writings discussing 10 cases of transient osteoporosis of the hip. Unfortunately, reporting of the disease has suffered because of inconsistencies in the terminology. Bone marrow oedema syndrome, transient bone demineralization, hip algodystrophy, regional migratory osteoporosis, and even reflex sympathetic dystrophy all are terms that have been used to describe the condition.

This article reports a case of transient osteoporosis occurring in the medial femoral condyle in a 52-year-old man, reviews the existing literature, discusses disease pathology, and identifies treatment options.

Case Report

A 52-year-old man presented with a 3-week history of right knee pain. The pain was most apparent during walking, and had increased to the point of preventing weight bearing. The patient reported no recent trauma to the joint and had no history of knee injury or disease. The patient did not use alcohol excessively and had not been treated with systemic or local corticosteroids.

Figure 1A: AP radiograph of the right knee showing no significant pathology
Figure 1B: Lateral radiograph of the right knee showing no significant pathology
Figure 1: AP (A) and lateral (B) radiographs of the right knee showing no significant pathology.

On knee examination, an effusion and medial joint line tenderness was noted. Knee range of motion was full, but painful. No signs of ligamentous instability were observed. Radiographs revealed minor osteoarthritic changes (Figure 1). Laboratory values were within normal limits, including those associated with infection. Accordingly, C-reactive protein and erythrocyte sedimentation rate were within the normal limits. Initial treatment was conservative and limited to a nonweight-bearing status and analgesics.

At the 1-week follow-up, his symptoms had improved minimally. Magnetic resonance imaging (MRI) showed decreased signal intensity on T1-weighted images within the medial femoral condyle and corresponding increased signal intensity on T2-weighted images, consistent with bone marrow edema and edema to the adjacent soft tissues (Figure 2). Bone scanning showed increased uptake of radioisotope in the medial femoral condyle (Figure 3). The patient was diagnosed with bone marrow edema syndrome and managed medically with analgesics. Nonweight-bearing status was continued. At 1-month follow-up, symptoms had improved, and weight bearing was non-painful. The patient progressively increased weight bearing as tolerated during the subsequent 8-week period. At 12-week follow-up, symptoms had completely resolved. Magnetic resonance imaging showed no signal abnormalities in the affected knee (Figure 4). At 1-year follow-up, the patient showed no signs or symptoms of disease.

Figure 2A: T1-weighted MRI of the right knee showing decreased signal intensity within the medial femoral
Figure 2B: T2-weighted MRI showing corresponding increased signal intensity within the medial femoral condyle
Figure 3: Bone scintigraphy of the knees showing increased uptake of radioisotope in the right medial femoral condyle
Figure 4A: T2- MRI of the right knee showing almost normal signal intensity 3 months later
Figure 4B: T2-weighted MRI of the right knee showing almost normal signal intensity 3 months later
Figure 2: T1-weighted MRI of the right knee showing decreased signal intensity within the medial femoral (A). T2-weighted MRI showing corresponding increased signal intensity within the medial femoral condyle (B). Figure 3: Bone scintigraphy of the knees showing increased uptake of radioisotope in the right medial femoral condyle. Figure 4: T2- (A) and T2-weighted (B) MRI of the right knee showing almost normal signal intensity 3 months later.

Discussion

Epidemiology

Transient osteoporosis is predominately a disease of the lower extremity. The hip is most commonly affected, followed by the knee, foot, and ankle.4 The literature also documents 1 case of transient osteoporosis located in the sacrum.5 Although original reports are documented in pregnant women, two-thirds of cases occur in men.6 The disease typically presents during the fourth to seventh decades of life.4.

A review of the literature indicates varying presentations of transient osteoporosis. Transient osteoporosis can affect the same joint at different locations, or affect several joints over a continuous time interval. Transient osteoporosis affecting multiple joints often is described in the literature as regional migratory osteoporosis. Usually the joint nearest the diseased one is the next to be affected.7,8

Specific to the knee, 3 cases of migration within a single knee joint have been reported. Fertakos et al9 and Wambeek et al10 both described cases in which transient osteoporosis presented initially in the medial femoral condyle and subsequently migrated to the lateral condyle. Parker et al11 reported a case in which transient osteoporosis initially presented laterally and then migrated to the medial condyle.

Two remaining cases of interest include cases involving pregnant females. Stamp et al12 reported a case of bilateral knee transient osteoporosis in a woman during the third trimester of pregnancy. Finally, Ma and Falkenberg13 documented a case of regional migratory osteoporosis in a pregnant female, also in the third trimester. The patient’s disease first presented in the hip, but migrated to all major lower extremity joints. The condition resolved spontaneously in the usual manner 12 months postpartum.

Presentation

Clinically, the condition manifests as gradual or sudden onset of pain around a joint, typically without a history of significant trauma. Pain can range from mild to debilitating, depending on the stage of disease. On examination, an effusion may be appreciated. Tenderness to palpation is present at the femoral condyle and tibiofemoral joint. This finding often leads to suspicion of meniscal or articular surface injury. Range of motion typically is full. Patients often are nonambulatory secondary to pain.

Radiographic imaging results vary depending on the phase of disease. Plain radiographs often show normal findings initially. As the disease progresses, osteopenia can be observed. Radionuclide bone scan can demonstrate increased uptake in all phases.9,14

Magnetic resonance imaging is essential for a definite early diagnosis and shows a so-called bone marrow oedema pattern of high intensity on T2-weighted images and low intensity on T1-weighted images,15 but without the focal area of signal abnormality typical of osteonecrosis.6,16 Parker et al11 reported the presence of a crescentic area of increased signal intensity in the posterior portion of the lateral femoral condyle, bordered by a faint rim of low signal intensity on T1-weighted images and a more well-defined area of low signal intensity on T2-weighted images. This area is reminiscent of the “class C” (fluid-like) changes described in osteonecrosis by Mitchell et al.17 Parker et al11 proposed that transient osteoporosis may simulate early reversible avascular necrosis.

Etiology

The etiology of this condition remains obscure. Curtiss and Kincaid1 proposed a neurogenic compression hypothesis. Several authors have suggested that it is a form of reflex sympathetic dystrophy.18,19 However, as noted by Banas et al,8 there are distinct differences. Reflex sympathetic dystrophy usually is proceeded by trauma, infrequently migrates, commonly involves the upper extremities (rarely involves the hip and knee), and often has a poor prognosis with long-term sequelae, such as skin atrophy, contractures, and circulatory changes. Regional migratory osteoporosis is a self-limiting condition without long-term sequelae. Rosen20 proposed the obstruction of venous return with localized hyperemia. Other authors have suggested that this condition may be due to an ischemic injury to bone marrow21-23 resulting in the death of fat and hematopoietic cells but not osteocytes (as is the case in osteonecrosis). Kopecky et al24 reported a series of 114 patients who were observed for ≤24 months after renal transplantation. Six patients showed changes of avascular necrosis that subsequently returned to normal, suggesting that there may be a spectrum of pathology with transient bone marrow oedema at one end and irreversible avascular necrosis at the other.

In recent years, subchondral fractures often have been reported when age-related osteoporosis is in a morbid state.25 Miyanishi et al26 reported that a subchondral fracture could be the cause of transient osteoporosis. The presence of such a fracture raises the possibility of a traumatic etiology for the bone marrow edema, despite the minor nature of the trauma. In 2005, El Masry et al27 reported a case of transient osteoporosis involving the knee following trauma. Also, Rodriguez et al28 supported the hypothesis that regional transient osteoporosis may be associated with vitamin C deficiency. These theories remain unclear, and further investigation of the pathomechanism is needed.

Although the histologic findings of the disease are characteristic, they are not consistently found. McCarthy29 reported the presence of edema and reactive bone formation in the marrow spaces. They found no evidence of fat necrosis or bone necrosis, although lipid cysts are sometimes found in the marrow spaces. The usefulness of the biopsy for definite diagnosis of this condition often is limited because of its uncertainty and invasiveness.

Treatment

Treatment typically consists of observation, protected weight bearing, and pain control. Nonweight-bearing status often is required during the initial 1 to 2 weeks of treatment to assist with pain control. No evidence indicates adverse effects of weight bearing as tolerated on outcomes.

Several additional forms of treatment have been described, including corticosteroids, bisphosphonates, and calcitonin. Carmona-Ortells et al30 reported 2 patients completely pain free between 2 and 4 weeks after treatment with deflazacort. La Montagna et al31 reported a case in which intramuscular aminobisphosphonate, oral calcium carbonate, and cholecalciferol caused symptom regression 2 months after treatment. Studies by Carty et al5 and Varenna et al32 have demonstrated rapid response to pamidronate. Follow-up with MRI ranged from 2 weeks to 9 months posttherapy and showed significant reduction or full resolution of the bone oedema. No side effects have been reported from the administration of these medicines.

Sympathectomy or sympathetic nerve blockage has been used in transient osteoporosis and in the migratory form as a treatment option.3,22,33 Although sympathectomy provides pain relief, it does not accelerate recovery, confirmed by edema persistence in MRI.34

Core decompression is an additional treatment option for transient osteoporosis. Decompression provides immediate pain relief.15,35 Magnetic resonance imaging signal abnormalities have been returned to normal 3 months postintervention.15 The technique has been used in treatment of the hip15,35 and knee joints.36 Hofmann et al15 supported that the risk of progression of transient osteoporosis to avascular necrosis after conservative treatment is considerably grater than the minimal surgical risk of core decompression. Guerra and Steinberg37 considered decompression unnecessarily aggressive for a condition of uniformly good prognosis.

Differential Diagnosis

Differential diagnosis of transient osteoporosis includes stress fractures, septic arthritis, soft-tissue injury, malignancy, tuberculosis, radiculopathy, and avascular necrosis. A detailed history, clinical examination, and special investigations will not confirm the diagnosis unless an MRI is performed.

Differentiation from avascular necrosis is sometimes difficult but has prognostic and therapeutic significance. Avascular necrosis usually produces classic features that are not apparent in transient osteoporosis (eg, progression of symptoms and radiological features, a focal subchondral defect on MRI with surrounding bone oedema, the crescent sign on MRI). On T2-weighted images, a high intensity rim inside a low intensity margin surrounds the necrotic lesion. This is pathognomonic of avascular necrosis, but a smaller crescent sign may be found in transient osteoporosis. On repeated MRI, the crescent sign in transient osteoporosis cases resolves.

Morover, other authors believe that transient osteoporosis represents an early reversible stage of nontraumatic avascular necrosis,15,38-40 but with a diffuse pattern, distinct from the usual focal pattern of osteonecrosis.41 According to the latter concept, bone marrow changes in transient osteoporosis of the hip correspond to changes of stage 1 and 2 of avascular necrosis42,43 with the additional presence of abundant new bone formation. New bone formation in transient osteoporosis results in repair that inhibits the progression to avascular necrosis.44

Increased awareness and more careful analysis of MRI data are needed to prevent the misdiagnosis of transient osteoporosis as avascular necrosis, particularly in men. In a study by Balakrishnan et al,45 it was shown that from 196 patients , 10 men (12 hips) between the ages of 32 and 55 years who were initially diagnosed with avascular necrosis were eventually determined to have transient osteoporosis of the hip. Undeniably, early differentiation of transient osteoporosis from avascular necrosis will avoid unnecessary surgical intervention and ensure appropriate treatment.

References

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Authors

Drs Nikolaou, Pilichou, Korres, and Efstathopoulos are from the 2nd Orthopaedic Department, Athens University, Athens, Greece.

Drs Nikolaou, Pilichou, Korres, and Efstathopoulos have no relevant financial relationships to disclose.

Correspondence should be addressed to: Vassilios S. Nikolaou, MD, PhD, Athens University, 2nd Orthopaedic Department, Megalou Alexandrou 54, Maroussi, Athens, Greece, PC 15124.

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