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Differentiating giant cell tumor of bone from patellofemoral syndrome: a case study.


Differentiating between mechanical and non-mechanical pain is one of the most important steps in the assessment of a patient; although this can be challenging with athletes. Mechanism of injury, associated symptoms, red flags and risk factors picked up in the medical history can lead clinicians toward potential non-mechanical origins of a complaint. However, aspects of the history can also distract clinicians initially. Once management begins, poor compliance and re-aggravation can also skew prognosis for the working diagnosis. We present the case of a recreational soccer player who was originally diagnosed and treated for mechanical knee pain. Re-evaluation of the case resulted in a potentially limb sparing discovery of a locally aggressive benign bone tumor. This case stresses the importance of maintaining a high level of suspicion, even when faced with seemingly healthy athletes. The following report will highlight how athletic injuries may mask pathology, while discussing common sources of anterior knee pain and detailing tumors of the knee.

Case Presentation

An otherwise healthy 30-year-old female presented to a chiropractor with a complaint of right knee pain. She reported that this condition began approximately five years ago and attributes it to playing soccer. Past impressions have included an irritated meniscus and patellofemoral pain syndrome. The symptoms have recently become progressive, although she did get relief from icing.

Examination of the patellofemoral joint and muscles of the knee were unremarkable. There was positive medial joint line tenderness on palpation. Orthopedic tests for ligamentous stability were negative for excessive motion; however, Slocum test, anterior-posterior glide with external rotation of the shin reproduced the knee pain. Functional examination found single leg standing and squat aggravated the chief complaint and McMurray's test produced pain, without click. Duck walk was found to be non-painful at the hip, but reproduced medial joint line tenderness of the right knee. The patient was referred to her family doctor for a second opinion and imaging. A plain film series and MRI scan of the knee were then requisitioned to rule out meniscal injury and the patient was referred to physiotherapy for assessment and treatment.

When assessed by the physiotherapist, the patient reiterated her history of chronic, intermittent right medial knee pain with recent increase in intensity and frequency. A recreational soccer and ultimate Frisbee participant, she had discontinued playing due to an abdominal muscle pull. Aggravating activities for her knee pain included ascending and descending stairs, running, playing sports, sit to stand movements and prolonged sitting or jumping. Her knee pain was eased by ice only. Her pain intensity, as rated by a Numeric Pain Rating Scale, varied between 0-5/10. She did not report symptoms of inflammation. She denied any locking or giving way of the knee. Her history included a red flag of previous melanoma, which was removed surgically several years prior. No medications were prescribed or being taken for her knee pain.

On physical examination, dynamic valgus of the right knee was noted with single and double leg squatting while reproducing medial joint line pain. This pain could be modified with correction of the dynamic valgus pattern.

Thessely's test was negative, while McMurray's test was painful without click. Manual muscle testing was rated using the Oxford scale with left gluteus medius rated 4, 4-on the right, hamstrings 4+ bilaterally, and gluteus maximus 4 bilaterally. She was diagnosed with patellofemoral pain syndrome (PFPS) with a differential diagnosis of right medial meniscal injury.

Plain radiographs were taken and demonstrated a multiseptated "soap bubbly" lytic lesion in the medial femoral condyle (Figure 1). Differentials suggested by the radiologist included giant cell tumor (GCTB), aneurysmal bone cyst (ABC), osteoblastoma, or chronic osteomyelitis and advanced imaging was recommended. The MRI scan provided a more detailed description of the nature and size of the lesion and helped rule out malignancy (Figures 2 and 3). A well-circumscribed multi-septated lesion with a sclerotic border measuring 4.5 x 2.9 cm with several fluid-fluid levels was visualized. There was no cortical disruption, periosteal reaction or expansion of the medial femoral condyle; also no soft tissue mass was visualized and there was no bone marrow edema.


The patient was referred to an orthopedic oncologist for assessment. Due to patient symptomatology and the locally aggressive but benign behavior of the lesion on imaging, surgical management was the best option for this patient. During the surgical procedure, first a biopsy was perform which revealed benign multinucleated giant cells in a mononuclear stroma, while the mononuclear cells showed moderate atypia and extensive hemosiderin deposition, suggestive of GCTB. Based on this benign diagnoisis, aggressive curettage and high speed burring were performed to remove the tumor. During surgery both solid tumor and blood filled cystic areas were identified. The final pathology revealed a GCTB with a secondary ABC. A portion of the distal femoral medial condyle was removed until only normal appearing bone remained. A periarticular plate and screws were used to support the morcellized cancellous allograft bone (Figure 4 and 5).



This case highlights an example where an underlying pathological condition went clinically unnoticed for a number of years. Considering the good health of the patient and the fact that the only symptom was knee pain, this should not be a surprise. In fact, we are trained knowing that serious pathology comprises a very small percentage of complaints presenting to a musculoskeletal practitioner. Therefore, the point of this case presentation is to emphasize the importance of the re-evaluation, a thorough work up and a second opinion in cases with persistent symptoms. Further, it is an excellent starting point for a review of the differential diagnosis of persistent knee pain (Table 1).


In retrospect, the patient could have been asked more pointed questions regarding red flags (in this case the re-evaluation history only included general questions about health status and whether or not there were any changes in the health history). Red flag symptoms including night sweats, weight loss, malaise etc. could be present in tumours of metastatic origin, but none were present in this case aside from history of melanoma and unremitting pain. The reproduction of pain during the orthopaedic tests could have been due to compressive forces on the bone itself. Regardless of the exact mechanism of pain, the decision to refer the patient for a second opinion and imaging was largely based on a lack of specific findings from the physical examination and the history of unresolved symptoms with no past imaging.



Differential Diagnosis of Knee Pain

Roughly 33% of all sports injuries involve the knee (Table 1). (1) PFPS is the most commonly diagnosed clinical condition in athletes with non-traumatic anterior knee pain. (1-2) In a military population, with comparable incidence rates, females were found to suffer from PFPS 2.23 times more frequently than males. (3-4) At a specialty center dealing with musculoskeletal trauma, meniscal injury was the most common knee injury with an incidence of 23.8/100,000 per year. (5) Recent investigations found strong evidence that participation in soccer, rugby, downhill skiing and squash were strong risk factors for acute meniscal tears. (6) It is difficult to truly estimate the incidence of meniscal injuries. Incidental findings of meniscal tears on MRI and during arthroscopic procedures have been widely documented, with some reports observing meniscal tears on MRI in 61% of asymptomatic subjects. (7) However, it can still be considered a highly probable differential diagnosis for traumatic mechanical knee pain in active individuals.

The earlier popular, but controversial, rationales for the mechanism of PFPS is that of mal-alignment of patellar tracking. It is with more recent kinematic research that the proximal links in the lower extremity are more significantly associated with the dysfunction noted in PFPS. (8) Positive risk factors for the development of PFPS identified in the literature include: muscular weakness around the knee and/or hip; single leg stance strength deficits; decreased trunk proprioception; tight illiotibial band; general ligament laxity; large Q-angle; patellar compression or tilting. (9-10) Abnormal vastus medialis oblique/vastus lateralis reflex timing has also been considered; however this is proving to be less significant than first theorized according to recent systematic reviews. (11) The female athlete is in a high risk category due to relatively larger Q-angles, potential ligamentous laxity, differences in muscular girth, and even effects of hormone fluctuations throughout the menstrual cycle. (3,12-13) One weakness to the patellar tracking theory is the poor correlation with expected lateral tilt or displacement of the patella on radiographs and symptomatology. (14) More recent observational trials have demonstrated significantly lower cross-sectional girth and diameter of the quadriceps musculature as measured on MRI; however a significant difference in the ratio of vastus lateralis and vastus medialis was not demonstrated. (14) Further research using MRI paired with kinematic analysis revealed that what is more important is abnormal femur motion and not that of the patella. (15) This abnormal femur motion in PFPS is suggested to be the result of reduced hip torque into abduction and external rotation noted on a step down task. (16) Similarly, decreased hip abduction force and associated increased hip adduction angle at the end of a run of variable distances was measured in PFPS subjects. (17)

Investigations on the natural history of PFPS have been poor, making it difficult to know when to consider alternative differential diagnoses. Two studies have attempted long-term follow-up of patients with PFPS. The group found that 27% of athletes recovered within an average of 8 months, while the remaining patients continued to have pain at 5 years. (4) Of the unrecovered population, half reported being able to cope with the pain, and only 20% of athletes were forced to completely cease sport participation, and 6% reporting time off work. (4) Variables strongly associated with poorer prognosis include: female gender, pain severity on visual analog scale, Anterior Knee Pain score, patellar hypermobility, and a sedentary lifestyle. (4,18)

Misdiagnosis in Athletes

Misdiagnosis, specifically tumors about the knee in athletes is an important issue looked at in the literature. (19) One report from a large orthopedic hospital helped illustrate the incidence of misdiagnosed knee pathology in athletic populations. (20) The investigators reviewed 667 cases and found 25 tumor patients which were originally misdiagnosed as an athletic injury, and resulted in inappropriate invasive procedures. (20) The authors concluded that 15 patients had suffered significant detrimental effects to their final clinical outcomes due to misdiagnosis, 3 of which resulted in limb amputation. (20) While the incidence of these cases was found to be relatively low, the results are potentially devastating to the patient. The most common cause for misdiagnosis reported by the authors was poor quality radiographs and refusal to consider alternative diagnoses in the absence of clinical improvement. (20)

Tumors Around the Knee

Although GCTB is an uncommon cause of knee pain, it has been reported to accounts for 13.7% (8-23%) of all benign primary bone tumors. (21) GCTB is considered to be "quasi-malignant" or a "borderline" malignancy making up a 5-8% of all primary malignant bone tumors. (21-22) It is associated with a very low risk of lung metastasis, even in the absence of histologic malignancy, although it is treated locally as a benign tumor. (21) The vast majority of patients with GCTB are between 20-50 years of age. (22-23) GCTB has a predilection for juxta-articular locations (i.e. metaphysis and epiphysis) and is located most commonly around the knee. (23)

ABC is also an uncommon cause of knee pain, 6% of benign bone tumors, which occurs typically in the first two decades of life. (22) ABC frequently causes bone destruction and cortical expansion prior to their discovery. (23) In adults ABC can also form secondary to an underlying GCTB or other benign bone tumor. (21, 25-25) In the case presented above, pathological analysis of the excised tissue found evidence of both GCTB and secondary ABC. There are other bone tumors that fit this case presentation based on location and demographic information (Table 2).

Patients with benign aggressive bone tumors usually present with rapid onset of symptoms and functional disability, unlike the patient in this case report who had persistent, but slowly worsening symptoms over a course of 5 years. The typical management of benign aggressive lesions including GCTB and ABC is tumor resection by aggressive curettage and high speed burring followed by reconstruction with either bone graft or cement, or less commonly by en bloc resection. (26-27) A retrospective review of 621 patients at a Chinese hospital specializing in musculoskeletal oncology reported a local recurrence rate of 8.6% after extensive curettage and burring. (20)


Most guidelines prefer a conservative approach to imaging; however, when considering athletes imaging utilization tends to increase. Indications for knee imaging includes traumatic injury with inability to fully extend the knee, severe ecchymosis with anterior cruciate ligament tear suspected, and persistent unexplained knee pain, to rule out surgical pathology and neoplasms. (28) To evaluate these structures, MRI is preferable, however, it is up to the clinician to know if the structures are just as easily demonstrated on US. Plain radiographs or MRI can identify previously undiagnosed bone tumors prior to any surgical intervention including arthroscopy, thus avoiding inadvertent tumor rupture, spread of lesion and sometimes amputation. (20)


We have presented a case of underlying knee pathology that had remained undiagnosed for a number of years. The important feature to note during the evolution of this case was the re-evaluating clinician's willingness to engage in collaborative care when faced with progressive or unresolving symptoms. On a subsequent evaluation, the patient's presentation still appeared mechanical on physical exam; however, symptoms were increasing in severity making the clinical progression appear more urgent, warranting imaging. While MRI remains a sensitive imaging modality for early diagnosis, radiographs may be a logical first step.

One challenge with this case is the self-limiting nature of PFPS in the absence of ligamentous instability or intra-articular injury. This allows patient to continue to access pain management over a period of time, often seeking out various health care providers due to frustration, while allowing serious pathology to go unsuspected. This case illustrates the importance of a thorough re-evaluation, consideration of differentials and follow-up for persistent self-limiting complaints. Maintaining a high level of suspicion in athletic or active populations should be exercised early so as to avoid delayed diagnosis and hasten recovery.


(1.) Steinbruck K. Epidemiology of sports injuries--25-year analysis of sports orthopedic-traumatologie ambulatory care. Sportverletz Sportschaden. 1999;13(2): 38-52.

(2.) Kransdorf M. Malignant soft-tissue tumors in a large referral population: distribution of diagnoses by age, sex, and location. Am J Roentgen. 1995; 164(1): 129-134.

(3.) Boling M, Padua D, Marshall S, Guskiewicz K, Pyne S, Beutler A. Gender differences in the incidence and prevalence of patellofemoral pain syndrome. Scand J Med Sci Sports. 2010; 20(5): 725-730.

(4.) Blond L, Hansen L. Patellofemoral pain syndrome in athletes: a 5-7-year retrospective follow-up study of 250 athletes. Acta Orthop Belg. 1998; 64(4): 393-400.

(5.) Clayton R, Brown C. The epidemiology of musculoskeletal tendinous and ligamentous injuries. Injury. 2008; 39(12): 1338-1344.

(6.) Snoeker B, Bakker E, Kegel C, Lucas C. Risk factors for meniscal tears: a systematic review including meta-analysis. J Orthop Sports Phys Ther. 2013; 43(6): 352-367.

(7.) Englund M, Guermazi A, Gale D, Hunter D, Aliabadi P, Clancy M, Felson D. Incidental meniscal findings on knee MRI in middle-aged and elderly persons. N Engl J Med. 2008; 359: 1108-1115.

(8.) Powers C. The influence of abnormal hip mechanics on knee injury: a biomechanical perspective. J Orthop Sports Phys Ther. 2010;40(2):42-51.

(9.) Boling MC, Padua DA, Marshall SW, Guskiewicz K, Pyne S, Beutler A. A prospective investigation of biomechanical risk factors for patellofemoral pain syndrome: the Joint Undertaking to Monitor and Prevent ACL Injury (JUMP-ACL) cohort. Am J Sports Med. 2009; 37: 2108-2116.

(10.) Witvrouw E, Lysens R, Bellemans J, Cambier D, Vanderstraeten G. Intrinsic risk factors for the development of anterior knee pain in an athletic population. a two-year prospective study. Am J Sports Med. 2000; 28(4): 480-489.

(11.) Chester R, Smith TO, Sweeting D, Dixon J, Wood S, Song F. The relative timing of VMO and VL in the aetiology of anterior knee pain: a systematic review and meta-analysis. BMC Musculoskelet Disord. 2008; 9: 64.

(12.) Wojtys, Edward M et al. Association between the menstrual cycle and anterior cruciate ligament injuries in female athletes. Am J Sports Med. 1998; 614-619.

(13.) Slauterbeck, James R et al. The menstrual cycle, sex hormones, and anterior cruciate ligament injury. J Athl Train. 2002: 275.

(14.) Giles, Lachlan S et al. Does quadriceps atrophy exist in individuals with patellofemoral pain? A systematic literature review with meta-analysis. J Orthop Sports Phys Ther. 2013: 766-776.

(15.) Souza R, Draper C, Fredericson M, Powers C. Femur rotation and patellofemoral joint kinematics: a weight-bearing magnetic resonance imaging analysis. J Orthop Sports Phys Ther. 2010; 40(5): 277-285.

(16.) Bolgla, L, Malone T, Umberger B, Uhl T. Hip strength and hip and knee kinematics during stair descent in females with and without patellofemoral pain syndrome. J Orthop Sports Phys Ther. 2008;38(1):12-18.

(17.) Dierks T, Manal K , Hamil J, Davis I. Proximal and distal influences on hip and knee kinematics in runners with patellofemoral pain during a prolonged run. Orthop Sports Phys Ther. 2008;38(8):448-456.

(18.) Kujala UM, Jaakkola LH, Koskinen SK, et al. Scoring of patellofemoral disorders. Arthroscopy. 1993; 9: 159-163.

(19.) Muscolo DL, Ayerza MA, Makino A, Costa-Paz M, Aponte-Tinao LA. Tumors about the knee diagnosed as athletic injuries. J Bone Joint Surg. 2003; 85(7): 1209-1214.

(20.) Niu X, Zhang Q, Hao L, Ding Y, Li Y, Xu H, Liu W. Giant cell tumor of the extremity: retrospective analysis of 621 Chinese patients from one institution. J Bone Joint Surg Am. 2012; 94(5): 461-467.

(21.) Kransdorf M, Murphey M. Giant Cell Tumor. Imaging Of Bone Tumors And Tumor-Like Lesions Medical Radiology. Springer Berlin Heidelberg; 2009. p. 321-336.

(22.) Yochum TR, Rowe LJ. Essentials of Skeletal Radiology. 3rd. ed. Philadelphia: Lippincott Williams & Wilkins; 2005.

(23.) Taylor JAM, Hughes TH, Resnick DL. Skeletal Imaging: Atlas of the spine and extremities. Elsevier Health Sciences; 2009.

(24.) Chakarun CJ, Forrester DM, Gottsegen CJ, Patel DB, White EA, Matcuk GR Jr. Giant cell tumor of bone: review, mimics, and new developments in treatment. Radiographics. 2013; 33(1): 197-211.

(25.) Low SF, Hanafiah M, Nurismah MI, Suraya A. Challenges in imaging and histopathological assessment of a giant cell tumour with secondary aneurysmal cyst in the patella. BMJ Case Rep. 2013; 20.

(26.) Turcotte RE, Wunder JS, Isler MH, Bell RS, Schachar N, Masri BA, Moreau G, Davis AM; Canadian Sarcoma Group. Giant cell tumor of long bone: a Canadian Sarcoma Group study. Clin Orthop Relat Res. 2002; 397: 248-258.

(27.) Blackley HR, Wunder JS, Davis AM, White LM, Kandel R, Bell RS. Treatment of giant-cell tumors of long bones with curettage and bone-grafting. J Bone Joint Surg Am. 1999; 81(6): 811-820.

(28.) Parker L, Nazarian L, Carrino J, Morrison W, Grimaldi G, Frangos A, Levin D, Rao V. Musculoskeletal imaging: Medicare use, costs, and potential for cost substitution. J Am Coll Radiol Art. 2008; 5(3): 182-188.

Jason Bonar, BScKin, DC [1] Shannon Clutton Carr, BKin, MPT, MCPA [2] Diana De Carvalho, DC, PhD [2,3] Jay S. Wunder, MD, FRCSC [4]

[1] Department of Graduate Studies, Canadian Memorial Chiropractic College, Toronto, Ontario, Canada

[2] Health and Performance Centre, University of Guelph, Guelph, Ontario, Canada

[3] Division of Epidemiology/Biomechanics, Discipline of Medicine, Faculty of Medicine, Memorial University of Newfoundland, St. John's, NL, Canada

[4] University Musculoskeletal Oncology Unit, Mount Sinai Hospital and Department of Surgery, University of Toronto, Toronto, Ontario, Canada

Corresponding Author: Dr. Jason Bonar

Canadian Memorial Chiropractic College, 6100 Leslie Street, Toronto, ON M2H 3J1 Tel: (416) 482-2340 Email: [C] JCCA 2015

* Informed consent was obtained from the patient for the preparation and publication of this manuscript.
Table 1.

Common sources of knee pain.

Common Pathologies Leading to Anterior Knee Pain (AKP)

Articular Cartilage Injury
Bone Tumors
Chondromalacia Patellae
Hoffa's Disease
Iliotibial Band Syndrome
Loose Bodies
Osgood-Schlatter Disease
Osteochondritis Dissecans
Patellar Instability/Subluxation
Patellar Stress Fracture
Patellar Tendinopathy
Patellofemoral Arthritis
Patellofemoral Pain Syndrome
Pes Anserine Bursitis
Plica Synovialis
Prepatellar Bursitis Previous Surgery
Quadriceps Tendinopathy
Referred from L/S or Hip Joint Pathology
Saphenous Neuritis
Sinding-Larsen-Johansson Syndrome
Symptomatic Bipartite Patella

Table 2.

Common bone tumors and conditions by age of incidence.
Asterisks (*) indicate tumors commonly affecting the
femur or tibia around the knee.


0-20 years          20-50 years             >50 year
Osteoblastoma       Non-Hodgkin's           Paget's Disease
                      Lymphoma *
Osteoid Osteoma *   Osteosarcoma            Lymphoma
Fibrous dysplasia   Giant Cell Tumor *      metastatic carcinoma
Hodgkins Lymphoma   Aneurysmal Bone Cyst    Multiple Myeloma
Osteochondroma *    Chondroblastoma         Chondrosarcoma
Ewing sarcoma       Spindle cell sarcoma
                      (eg Fibrosarcoma) *
  Bone Cyst
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Article Details
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Author:Bonar, Jason; Carr, Shannon Clutton; De Carvalho, Diana; Wunder, Jay S.
Publication:Journal of the Canadian Chiropractic Association
Article Type:Case study
Geographic Code:1CONT
Date:Jan 1, 2016
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