Spontaneous Osteonecrosis of the Knee

Central Annals of Sports Medicine and Research

Research Article *Corresponding author David R. Diduch, Department of Orthopaedic Surgery, University of Virginia, Box 800159 HSC Charlottesville, Spontaneous Osteonecrosis of VA 22908, USA, Tel: +14342430218; Fax: +1 4342430290; Email: Submitted: 30 August 2017 the Knee: A review of Past and Accepted: 25 September 2017 Published: 28 September 2017 Present Aspects ISSN: 2379-0571 Copyright William J. Hill1, Jeffery R. Ruland2, and David R. Diduch3* © 2017 Diduch et al.

1 College of Medicine, Howard University, USA OPEN ACCESS 2School of Medicine, University of Virginia, USA 3Department of Orthopaedic Surgery, University of Virginia, USA Keywords • Spontaneous osteonecrosis of the knee • Insufficiency fracture Abstract • Subchondral collapse Spontaneous osteonecrosis of the knee (SONK) is a condition which is known to • Meniscal extrusion disproportionately affect women greater than sixty years old. The etiology of SONK is complex • Athletes without a definitive consensus. The purpose of this paper is to discuss the etiology ofSONK on a microscopic and macroscopic level. The patient populations at risk will be highlighted, as SONK can present in athletes and older patients. Staging and imaging studies are critical for understanding the progression of disease and deciding the appropriate treatment option. Non- surgical and surgical treatment options for SONK will be discussed.

ABBREVIATIONS Etiology and Pathophysiology in the text SONK: Spontaneous Osteonecrosis of the Knee; BMI: Body Mass Index The Etiology and pathophysiology of SONK has been INTRODUCTION associated with mechanical, biochemical and traumatic origins. Spontaneous Osteonecrosis of the Knee (SONK) is a stress The occurrence of insufficiency stress fractures of the medial femoral condyle and medial tibial plateau has spurred support for the traumatic origin of SONK [7].Though this may play a role tibialrelated plateau; insufficiency less frequently fracture of it also the knee affects that the most lateral commonly condyle in the Pathophysiology of SONK it does not encompass the entire involves the medial condyle of the femur or medial aspect of the picture. The biochemical process that leads to osteoporosis has been discussed as an alternative etiology. This has been toof the SONK, femur Secondary [1-4]. Ahlback osteonecrosis was the first is true to describe avascular SONK necrosis as a the supported by MRI findings that revealed insufficiency andseparate the pathology clinical picture from secondary consists osteonecrosis of patients often [2]. In less contrast than fractures in osteopenic bone [8-10]. Insufficiency fractures are a key finding in SONK and assist in the staging of the condition osteonecrosis include alcohol abuse, corticosteroids, high body but a mechanical mechanism may play the largest role. The forty years old with multiple joint involvement. Risk factors for mechanical etiology of SONK starts with the disruption of the native anatomy of the medial meniscus. Extrusion of the medial mass index (BMI), Gaucher’s disease, sickle cell disease, trauma meniscus following posterior root tears result in increased and increased age [5]. SONK manifest in patients in the sixth stresses across the bone [11-13]. The biomechanical forces that anddecade pain of that life oroccurs greater in SONK with a is predilection sudden in nature for women, and causes three transverse the knee joint are normally buffered by the meniscus. times greater frequency than men [1, 3, 5, 6]. The discomfort With the meniscus disrupted, the force crossing the knee causes an increase stress on the femur and tibia. Remodeling of bone limitations in functionality of the joint. This pain is markedly increases as the stress applied to the bone increases. If the severe at night in some patients and persists during rest [1-4, 6]. bone cannot strengthen sufficiently to handle the stress then Symptoms of acute pain due to bone collapse of the insufficiency microfractures and bone edema develop [14]. These stress fracture typically improve with time for healing and optimization fractures are subchondrally located without the presence of a of bone health. Residual joint incongruity and osteoarthritis can vascular osteonecrosis [15]. Recent studies have shown meniscal lead to eventual arthroplasty. This review serves to discuss the involvement as the predominate associative factor of SONK’s etiology, highlight populations at increased risk, underline the pathogenesisPopulations [11-13]. at Risk importance of staging and imaging modalities in understanding the progression of disease, and discuss appropriate non-surgical and surgical treatment options for stage of disease. The one population at risk that is consistently noted in the Cite this article: Hill WJ, Ruland JR, Diduch DR (2017) Spontaneous Osteonecrosis of the Knee: A review of Past and Present Aspects. Ann Sports Med Res 4(6): 1123. Diduch et al. (2017) Email: Central

metastasis, may mimic the spontaneous pain of SONK [27]. Pes this cohort women are disproportionately affected three to one anserine bursitis originates on the medial aspect of the tibia literature is older patients greater than sixty years old. Within below the joint line and may radiate toward the joint [28]. mineral density in relation to before menopause [16]. This change[1,3, 5, increases 6]. Women the over chance sixty of years fractures, old have which a decreasedcan manifest bone as Staging and Imaging Findings Lesions found in SONK are usually located in subchondral patients are another group that needs to be considered at risk bone of the medial femoral condyle and medial tibial plateau. forinsufficiency SONK. Within fractures this group of the includes femur or patients tibia. Vitamin with higher D deficient levels Radiographs and MRIs are the imaging modalities that are of melanin in their skin, such as African Americans, because used when investigating SONK. The Radiograph views that are melanin protects the skin from sunlight which stimulates vitamin recommended are bilateral weight-bearing Posterior anterior athletes. This may be the result of repetitive force being applied acrossD production the knee [17]. joint The or last underlying population meniscal that is at injuries. increased Repetitive risk are Radiographs(PA), weight canbearing be used 45 degreesto track flexiondisease PA, progression. non weight MRI bearing is the force applied to the knee joint can cause medial femoral condyle lateral and 45 degrees flexed merchant or patella sunrise views. defects, particularly in basketball players and runners [18, 19]. Meniscal tear is the most common knee pathology sustained by confirmatory test and assists in determining the extent of disease athletes which would predispose athletes to developing SONK withthat is collapse not appreciated of trabeculae. on radiographs The staging [14]. of Two SONK key canfinds be on done MRI [20]. Also, meniscus tears occur at a greater incidence in athletes include edema, which indicates stress, and insufficiency fracture than the general population which should rise the clinical in 1982. According to Aglietti stage I have normal appearing suspicion of SONK in athletes and former athletes. by various systems. Aglietti et al. first proposed their system weight bearing part of the articular surface of the condyle. Differential Diagnoses Stageradiographs III consists [2]. of Stage subchondral II included lesion flattening with radiolucent of the affected area of SONK presents with sudden pain in the affected area of the variable size and depth and a surrounding sclerotic halo. Stage IV knee [21]. The acute onset of pain is due to the occurrence of the includes the sclerotic halo with the addition of subchondral bone collapse. Stage V consists of subchondral collapse and secondary degenerative changes. Ficat and Arlet proposed a staging system mayactual present insufficiency with anfracture antalgic and gait possible and possiblebone collapse. effusion During [21]. Thethe observationknee is not characteristicallyportion of the physical red in examinationcolor or warm the to patient touch. [29]. Stage I lesions are characterized by pain and normal radiographs.for osteonecrosis Stage whichII lesions is modifiedare sclerotic and or used cystic to in classify nature, SONK with areas of the medial femoral condyle or tibia [22]. In advanced SONKDuring tenderness palpation tenderness of the joint may line be and elicited crepitus over may the be affected found the joint surface or subchondral fractures. Stage III reveals the secondary to degenerative changes within the joint. characteristica normal outline crescent of the tibia sign and which femur is the and result without of subchondralflattening of collapse. Figure (1) consists of images with subchondral The differential diagnosis of SONK includes a meniscal tear, collapse. Stage IV includes joint space narrowing with secondary osteoarthritis, transient osteoporosis, traumatic bone bruises degenerative changes [30]. Figure (2) below illustrates medial compartment narrowing but without secondary degenerative changes or subchondral collapse. Accurate and early diagnosis withand fractures, joint line osteochondritistenderness, swelling, dissecans, and a tumorpositive infiltration, McMurry andtest pes anserine bursitis. Meniscal tears on physical exam present of SONK leads to a better prognosis. The use of MRI is the is a condition that is chronic in nature that affects women and than radiographs and bone scintigraphy [14]. With earlier men[22]. equallyMeniscal as tears they can age. be The confirmed pain is aching with an in MRI. nature, Osteoarthritis which will diagnosis,recommended conservative imaging modality treatment as optionsit identifies have changes an increased earlier increase with activity and subsides with rest. On plain radiographs tricompartmental involvement is often present rather than just the medial compartment. Osteoarthritis will have secondary stage,statistical are: lesions likelihood greater of being than 5 efficacious cm2, anatomical [31,32]. varus The alignment, imaging radiographic changes of subchondral sclerosis and osteophyte lesionsfindings affecting that have greater been predictive than 40% of of poor the outcomes,femoral condyle, aside from and [23]. SONK that remains undiagnosed may go untreated for an depth greater than 20 mm on MRI [33-39]. These measurements lead to the question of should there be a new staging system in If joint space narrowing is present without these secondary extended peiord of time and develop into osteoarthritis [24]. which the size of the lesion is considered. SONK. Transient osteoporosis presents with spontaneous onset Treatment Options ofchanges, pain. It thisprogresses may represent over several meniscal weeks extrusion in middle and aged impending men, and also in women in the third trimester of pregnancy. In transient The treatment options for patients affected with SONK osteoporosis, osteopenia is appreciated that involves the entire included conservative, non-surgical, and surgical options. The condyle [25]. Bone bruises and fractures are trauma associated treatment decided on by the patient and Surgeon takes into and will be secondary to a traumatic event. Osteochondritis account the stage and progression of the disease. dissecans consist of the bone separating from its vascular supply In stages prior to subchondral collapse, conservative resulting in detachment of the cartilage from bone [26]. This treatment has been successful in treating SONK. Conservative involves the lateral portion of the medial femoral condyle most treatments include rest, physical therapy, protected weight bearing, and unloader bracing [40]. These options are typically commonly in ten to fifteen year old males. Bone tumors, such as Ann Sports Med Res 4(6): 1123 (2017) 2/5 Diduch et al. (2017) Email: Central

andbone osteoporosis healing vitamin should D levels be addressedneed to be to in the increase proper fracture range. healingVitamin [43,44]. D deficiency Corticosteroid and correctable or hyaluronic causes acid ofinjections osteopenia are options for patients that don’t response to non-pharmacologic

the joint but will have little effect on bone pain [45]. Prostacyclin A) B) analogue,conservative iloprost treatments. was mostly They can studied, reduce increases inflammation blood supplywithin to terminal vascular beds [46,47]. It also reduces the amount of

studies it provided pain relief and reduced subchondral lesion free oxygen radicals and leukotrienes in vascular circulation. In interosseous pressure to normal or decreasing cytokine and size, the efficacy is thought to be the result of either returning bisphosphonates is thought to decrease the resorption of bone C) D) byleukotriene osteoclast local as new inflammatory bone is being reactions formed. [48,49]. This allows The for use the of new bone to be revascularized and limit collapse of bone [50,51]. Figure 1 SONK with subchondral collapse. Figure 1A: Radiograph If a patient progresses to the subchondral collapse stage of Subchondral collapse of the medial femoral condyle. Figure 1B: Radiograph Corner fracture of the left medial tibial plateau along conservative treatment is still recommended to allow for the with subchondral collapse. Figure 1C: T2 weighted MRI with medial fracture to heal. After the fracture has healed the knee will be reevaluated. If pain ultimately still is present operative weighted MRI with medial tibial plateau subchondral collapse. considerations will be discussed. Surgical options include high tibial plateau subchondral collapse and fat saturation. Figure 1D: T1 tibial osteotomy, subchondroplasty, unicompartmental knee arthroplasty, and total knee arthroplasty. If meniscal root tears are observed, partial meniscectomy should be avoided as it can worsen the condition. Removing more meniscus in the face of

inmeniscal a young extrusion patient. only It unloads increases the detrimental medial compartment forces across by correctingthe joint [52]. alignment High of tibial the osteotomy knee [53]. isSubchondroplasty typically preformed is a newer treatment option for SONK that is not utilized as often as other options but it involves surgically implanting calcium phosphate into trabeculae bone of the lesion [54-56]. Calcium A) B) phosphate thereafter crystalizes and stabilizes the fractures. Unicompartmental knee arthroplasty is a viable option for SONK Figure 2 SONK with medial compartment narrowing, absent of but only when lesions are fully healed and the bone can support secondary signs of osteoarthritis, prior to subchondral collapse. Figure 2A: Radiograph with medial compartment narrowing. Note the presence of a normal subchondral sclerosis pattern on absence of osteophytes or subchondral sclerosis as would otherwise radiographs.the prosthesis If there without is any subsidence doubt about [57]. the This ability is confirmed of the bone by weighted MRI with medial compartment narrowing and medial to support the prosthesis, a total knee arthroplasty is the better be expected with this much joint space narrowing. Figure 2B: T2 option given the broad support [58]. A future treatment option due to ongoing stress reaction of SONK. may include the use of stem cell concentrate from bone marrow, meniscus extrusion, fat saturation and extensive bone marrow edema as augmentation graft, in conjunction with core decompression. done until the bone has healed, which may take as long as CONCLUSION requires a reduction of applied force on the affected compartment Osteoarthritis and a vascular necrosis of the knee are two justsix months.like any Healingother fracture. of insufficiency The use of fractures a load sensor takes device time, andis a differential diagnoses that are often diagnosed when actually SONK novel conservative treatment option. It functions by changing is present. With a greater understanding of the pathophysiology the load on the knee through real time biomechanical feedback and risk factors associated with SONK there may be an increase in which results in reduced pain [41]. In athletes that are affected by SONK, hyperbaric chamber therapy has produced promising patientincidence population of diagnosis. that Mechanicalrepresents thefactors, traditional specifically clinical meniscus picture results [42]. extrusion, may be the precipitating event that leads to SONK. The With the understanding that disruption of the native meniscus environmentof SONK are, predisposes older women, patients in the to fifth SONK, or sixthathletes decade and former of life. or The hyaluronic pharmacological acid injections, treatment prostacyclin options include analogue, oral NSAIDs and athletes should also be suspected of potentially presenting with and narcotics, Vitamin D supplementation, corticosteroid character of the lesion without regard to the size. The character bisphosphonates. Oral NSAIDs and narcotics are used to manage SONK. The current staging classifications are based solely on the painful episodes that SONK produces. In order to maximize Ann Sports Med Res 4(6): 1123 (2017) 3/5 Diduch et al. (2017) Email: Central of the lesion is important but the size of the lesion may be more 19. Bennell K

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Cite this article Hill WJ, Ruland JR, Diduch DR (2017) Spontaneous Osteonecrosis of the Knee: A review of Past and Present Aspects. Ann Sports Med Res 4(6): 1123.

Ann Sports Med Res 4(6): 1123 (2017) 5/5