Congenital dislocation of the knee is rare. The condition may occur due to quadriceps contracture. It usually occurs in patients with myelo, arthrogryposis, or Larsen’s syndrome. The patient with congenital dislocation of the knee may have developmental dysplasia of the hip (DDH) and club foot. On examination, the patient will have a hyperextended knee at birth. The patient’s foot could be placed against the face. There will be limited flexion at the knee. The patient may have a dimple or skin crease at the anterior aspect of the knee. You must examine the hip to rule out ipsilateral hip dislocation. 50% or more will have hip dysplasia. The etiology is not known, however it could be due to fetal positioning or congenital absence of the cruciate. Patient may have contracture of the quadriceps. There are grades or a spectrum for the deformity. Grade one is severe Genu Recurvatum(knee hyperextended). If the range of passive flexion is more than 90 degree and that is simple recurvatum. Grade two is subluxation (30 degree to 90 degree range of passive flexion). Grade three complete dislocation (less than 30 degree of passive flexion). Treatment can consist of the pavlik harness and club foot cast will require knee flexion, so you need to work on treating the knee dislocation first. Grade one will be stretching of the knee and serial casting with the knee in flexion. The goal is to obtain at least obtain at least 90 degrees of flexion and reduction of the deformity over the course of several weeks. The physician should avoid pseudo-correction through an iatrogenic fracture of the proximal tibial physis. The prognosis is usually good if reduction is achieved without surgery. For grade 2, if the infant is less than 1 month old, you will do serial casting first followed by percutaneous quadriceps recession especially if the flexion is less than 90 degrees. V-y quadricepsplasty with above the knee cast is done in grade 3 especially if non-surgical treatment fails to reduce the tibia on the femur. The result of open surgery is better when it is done in children younger than 6 months. In general, open reduction is reserved for children who did not respond to stretching cast immobilization. It is important that the hip dysplasia is recognized and the knee dislocation is corrected early. This will help in early reduction of the hip.
Physeal injury in the distal femur in the neonate is rare. In general, traumatic neonatal physeal fracture usually occurs in the distal humerus and rarely occurs in the distal femur. The condition usually occurs due to birth trauma and usually result due to physeal separation which results in epiphyseal separation. The thigh will be swollen and there may be hypo-mobility of the extremity. The neonate will be fussy or irritated with significant swelling in the thigh. The condition is under diagnosed. The epiphysis is usually present at birth on x-rays. The condition can become complicated if the epiphysis is not completely ossified at birth or if the child is born prematurely. In this situation, the x-ray interpretation may be difficult. MRI will be really helpful if the doctor is uncertain of the diagnosis. X-rays are taken of the child at birth. Look at the lateral x-ray and find the epiphysis is present and ossified at birth with varying degrees (may not be clear). Each epiphysis will line up with its corresponding bone. Epiphysis of the distal femur should line up with the femoral shaft. Epiphysis of the proximal tibia should line up with the tibial shaft. If the two epiphysis separate from each other, then this is a congenital dislocation of the knee. This can be a spectrum of injury that varies from hyperextension, to subluxation, to frank dislocation. If the epiphysis is separated from its corresponding bone for example the epiphysis of the distal femur is separated from the shaft of the femur, then this is a physeal injury. Because the distal femur is mostly cartilaginous, you don’t see bone shifting, you see a little hint of the separation of the physis by seeing that the small ossified epiphysis is not in its normal position that corresponds with the axis of the bone. You need to know the difference between physeal injury and congenital dislocation of the knee. Accurate, gentle closed reduction with follow up x-rays to confirm the reduction and to detect any early bony bridging.
Anatomy of the semimembranosus. Muscle the hamstrings are three muscles. The three are the semimembranosus, the semitendinosus, and the biceps femoris. Semimembranosus origin that arises from the upper lateral part of the ischial tuberosity. Here is drawing that shows the muscles arises from the ischium. Here is the origin of the semimembranosus. The semimembranosus is different from the semitendinosus. Insertion, the semimembranosus is inserted into the back of the posterior surface of the medial tibial condyle. The nerve supply to the semimembranosus muscle comes from the tibial branch of the sciatic nerve. The semimembranosus helps in flexion of the knee, extension of the hip, medial rotation of the tibia. There are two important things related to the semimembranosus. Number one is the Baker’s Cyst. The cyst is located between the semimembranosus and the medial gastrocnemius muscle. A Baker’s Cyst is commonly caused by knee arthritis or meniscal tear. The cyst is connected to the knee joint through a valvular opening. Knee effusion from the intra-articular pathology allows the fluid to go through the valve to the cyst in one direction. You approach this posteromedial fracture fragment of the tibial plateau through an incision between the medial gastrocnemius and semimembranosus muscles. This Fragment has its own fixation (antiglide plate) to buttress this fracture fragment.
Enchondroma occurs in about 1%. It is a benign cartilage tumor seen as an incidental finding on the x-rays. The cartilage will look like calcified arcs, rings, or punctate calcification. It is located in the metaphysis of long bones such as the proximal femur, proximal tibia, proximal humerus and distal femur. 42% occurs in small tubular bones such as the hands and feet. In fact, it is the most common tumor of the hands and feet. If it occurs in the pelvis or in the scapula, it is chondrosarcoma. Enchondroma is a cartilage lesion with basophilic cytoplasm. It has benign histologic features. It appears acellular or hypocellular with a lot of matrix and some cells that does not have any atypical cells or any pleomorphism. It appears more cellular in the hands and the feet (appears malignant, but it is not malignant). Enchondroma has no symptoms. It is frequently discovered incidentally during unrelated x-ray exams. Enchondroma does not cause pain unless there is a pathologic fracture (check for another source of pain). Sometimes it becomes initially clinically evident after a pathologic fracture, especially in the hands and feet. There is a calcified, well defined lesion. You will see rings, arcs, stippled calcification, and punctate calcification. It is uniformly distributed, no cortical destruction (cortex is intact), endosteal scalloping or erosion can occur, but it is less than 50% of the cortical width and no soft tissue mass. Bone scan will have increased uptake. Bone scan will be “cold” if it is bone infarct (hot in enchondroma). Look at T2 MRI, you will see a lesion with high uptake. You find a lobular lesion and a bright signal on T2 due to the high water content of the cartilage. Biopsy is usually not done. There is difficulty in interpreting the low grade cartilage lesion from enchondroma. When pain or endosteal scalloping occurs in more than 2/3 of the cortex, think about chondrosarcoma (rule out low grade chondrosarcoma). The diagnostic distinction between a benign enchondroma and low grade chondrosarcoma is difficult. It should be based on clinical history and radiographic findings. Chondrosarcoma is usually large in size, it has a soft tissue mass, may have cortical destruction and periosteal reaction with significant endosteal scalloping. There may be lucency on the x-ray and chondrosarcoma occurs more in the pelvis and scapula, and does not occur in the hands or the feet. Enchondroma does not cause symptoms and no need for any treatment such as surgery. Do observation and follow-up x-rays (3 months, 6 months, or yearly) and no further work-up is necessary. If there is pain, check for another source of the pain (enchondroma in the proximal humerus: check for impingement, rotator cuff tear, or arthritis). Enchondroma in the hand and feet: pathological fracture could be treated surgically, especially if the lesion is big, because repeated fractures can occur. Immobilize the fracture with protective splint until union will allow the fracture to heal, then you will do curettage and bone graft. If the lesion is large and further pathologic fracture is expected, then you will do curettage and bone graft. Ollier’s disease is multiple enchondromatosis. The lesion is present from birth. It does not have a known inheritance pattern. It is an inborn error of endochondral ossification. Patient will have shortened, bowed affected limbs. It has a high incidence of malignancy (up to 25%). Maffucci syndrome has multiple enchondromatosis and hemangiomas. It has a high risk of malignant vascular tumor (angiosarcoma).