|Year : 2014 | Volume
| Issue : 1 | Page : 91-93
Osteochondral fracture of patella
Sanjay Keshkar1, Nirmal Dey2, Ratnesh Kumar3
1 Associate Professor (Ortho.), Post Graduate Institute of Medical Sciences and Research, ESI Hospital Manicktala, Kolkata, West Bengal, India
2 Visiting Consultant, National Institute for the Orthopaedically Handicapped (NIOH), Kolkata, West Bengal, India
3 Director, National Institute for the Orthopaedically Handicapped (NIOH), Kolkata, West Bengal, India
|Date of Web Publication||6-Jun-2014|
Associate Professor (Ortho.), Post Graduate Institute of Medical Sciences and Research, ESI Hospital Manicktala, Kolkata, West Bengal
Source of Support: None, Conflict of Interest: None
Osteochondral fractures of patella are commonly associated with acute patellar dislocations and are frequently missed or misinterpreted in initial radiograph. Usually such fractures need surgical treatment. This article presents a case of a 13-year-old girl who sustained a twisting knee injury while doing exercise (yoga) and sustained a small osteochondral fracture of the central part of the patella, displaced inferolaterally, lying close to lateral femoral condyle. The initial radiograph was misinterpreted as chip fracture of lateral femoral condyle. Diagnosis of osteochondral fracture of patella was confirmed only during the surgery. This case needs to be reported as the osteochondral fracture of patella was not only missed but also misinterpreted.
Keywords: Chip fracture, lateral femoral condyle, misinterpretation, osteochondral fracture, patella
|How to cite this article:|
Keshkar S, Dey N, Kumar R. Osteochondral fracture of patella. J Orthop Traumatol Rehabil 2014;7:91-3
| Introduction|| |
The patella is a sesamoid bone and considered part of the quadriceps extensor mechanism. The incidence of patellar fracture in skeletally immature patients is low, comprising only about 6.5% of patellar fractures of all ages and among them, osteochondral fracture is the most common type.  It can be easily missed on plain radiographs because only a small fragment of bone may be seen. This bony fragment is accompanied by a separation of a large fragment of articular cartilage that can be detected by magnetic resonance imaging or ultrasonography.  In grossly displaced large fragment osteochondral fracture, open reduction and internal fixation is mandatory in order to achieve a good outcome. 
Misinterpretation of osteochondral fracture of patella has not yet been reported in the literature so for. We report an interesting case of osteochondral fracture of patella mimicking as chip fracture of lateral femoral condyle which was treated surgically.
| Case report|| |
A 13-year-old girl presented to us with acute twisting knee injury while doing exercise (Yoga) at home following which she fell down. Immediately after the fall, she found her left knee to be swollen, painful & immobile. On examination, her left knee was swollen, tense and held in full extension. There was diffuse tenderness in the knee joint. The patella was not displaced on palpation. Patellar tap was positive. She did not allow moving her left knee due to severe pain and hence special stress tests could not be done. Anteroposterior & lateral radiographs of her knee [Figure 1] revealed a small bony fragment lodged beside the lateral femoral condyle. There was otherwise no other obvious fracture of the patella, tibia or femur. Skyline view could not be done. The radiological diagnosis made at this stage was chip fracture of lateral condyle of femur. An urgent knee aspiration & Robert Jones bandaging was done. After 3 days the patient was taken for open surgery with a plan to do either reduction & fixation or excision of chip fracture of lateral femoral condyle. Under general anesthesia, all clinical examinations for knee instabilities were performed and found to be negative.
|Figure 1: Preoperative radiograph of knee (anteroposterior and lateral views) showing osteochondral fracture of patella displaced and lodged close to lateral femoral condyle, mimicking as chip fracture of it|
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The lateral femoral condyle was approached directly by lateral approach. A loose piece of bone was lying unattached, close to the femoral condyle but there was no crater for it on the condyle. Then the suspicion about osteochondral fracture of patella arose and accordingly knee was opened up by extending the incision upward. Undersurface of patella was checked which revealed a shallow crater/ulcer of about 1cm size at its central part. The loose piece of chip fracture was found to be having accurate match with this crater which confirmed our diagnosis as osteochondral fracture of patella. Since the fractured fragment was thin, it could not be fixed internally and it was removed. After this the joint was cleaned by normal saline and wound closed in layers. A suction drain was inserted. Postoperatively, the patient made an uneventful recovery and she was followed up in regular intervals. Full range of motion of the knee was achieved after about 12 weeks [Figure 2] and [Figure 3] and the patient went back to her normal activities. She was allowed to do yoga, playing, dancing etc. after 6 months. At the last follow-up, 6 years after the accident, clinically and radiologically [Figure 4], the knee was normal and the patient was absolutely asymptomatic as per the Kujala's Knee Scoring criteria.
|Figure 2: Follow-up photograph after 12 weeks of operation of patient's left knee showing full extension. Scar mark of operation can also be seen|
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|Figure 3: Follow-up photograph after 12 weeks of operation of patient's left knee showing full flexion. Scar mark of operation can also be seen|
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|Figure 4: Follow-up radiograph (after 6 years) of knee (anteroposterior, lateral and syline views) showing no obvious pathology|
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| Discussion|| |
The major difficulty regarding patellar fractures in children is the diagnosis.
Belman and Neviaser noted that the lack of diagnosis, wrong diagnosis or a late diagnosis is common for patellar fractures in children. , Osteochondral patellar fractures occur in children participating in activities requiring knee extension force with quadriceps contraction against resistance, with injury occurring on the supportive leg. Therefore, this injury is not like those caused by direct trauma on the knee. 
The observation that patellar osteochondral fracture is associated with patellar dislocation was first made by Kroner in 1905.  It was subsequently reported that the most common area of patellar osteochondral fracture in these patients was the medial facet of the patella.  The lack of evidence from the presenting history and clinical examination notwithstanding, we believe that our patient did sustain an acute lateral dislocation of her patella, which was almost instantaneously spontaneously reduced during, or soon after, the fall.
Grogan et al., classified patellar fractures in children according to their sites. The upper pole avulsion fracture of patella is the most frequent one. A lower end avulsion is usually a result of an acute trauma. Medial avulsion may appear after a patellar lateral dislocation. The avulsion of the superolateral region of the patella may be considered as a bipartite patella or may be produced by stress due to repeated traction of the vastus lateralis muscle. Another injury considered as repeated stress of the distal patellar end is the Sinding-Larsen-Johansson disease, producing an incomplete avulsion of the patellar ligament fibers, with subsequent necrosis and calcification.  In our case, the fracture was of the central part of under surface of patella.
Radiographic studies of children's knees are a challenge, even for the most experienced doctors. Wessel et al. demonstrated that in 51 patients younger than 14 years with acute knee trauma and haemarthrosis, a positive simple x-ray image could only be seen in 16 of them.  Thus, magnetic resonance imaging is useful for diagnosing acute injuries. It can also be helpful in making the diagnosis of patellar ligament ruptures and avulsion fractures.
Although the conservative treatment produces a reconstitution of the extensor apparatus, a patellar deformity may remain (mega patella) with motion restraint, especially in extension.  Reconstruction with absorbable sutures has not demonstrated good outcomes. The best treatment method seems to be the arthroscopic assisted reduction & fixation of the fracture, if it is big enough, otherwise excision.
Our patient had sustained an osteochondral fracture of the patella, displaced to inferolateral aspect of knee, close to lateral femoral condyle which was subsequently misinterpreted radiologically as chip fracture of lateral femoral condyle. Before taking the patient for operative management, MRI would have been a great help for the accurate diagnosis of osteochondral fracture of patella. If at all planned for operation without MRI then arthroscopy would have been of great help.
| Conclusion|| |
It is known that patellar osteochondral injuries could be found in as many as 95% of patients with acute dislocation of the patella. It has, however, never been reported that such osteochondral fracture fragments of patella could result to mimic as chip fracture of lateral femoral condyle, as was illustrated in this case.
It is recommended to get MRI done before planning for conservative or surgical management in knee injuries with any kind of osteochondral fracture but if it is not possible then almost always one should think about osteochondral fracture of patella unless proved otherwise.
Though arthroscopic surgery with fixation of fragment is the treatment of choice in such fractures, open surgery and retrieval of the offending fragment, as in our case, can also result in good functional recovery of knee.
| Acknowledgement|| |
We are thankful for Director and other helping staff's of National Institute for the Orthopaedically Handicapped, Kolkata (where the study was done 3 years ago when corresponding author was working as Assistant Professor in Orthopaedics).
| References|| |
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]