Physical examination revealed that the patient walked with the involved extremity externally rotated 30° to 40° and compensated for the insufficient extensor mechanism by swinging the affected limb forward to passively extend the knee. The right femur was 2 cm shorter than the left femur. The tibial lengths were equal. Passive range of motion of the right knee was from 5° to 150° of flexion, with an active extension lag of 30°. The patella was palpable and mobile, but it was positioned proximal to the patellofemoral groove (patella alta). No ligamentous instability was present. A magnetic resonance imaging scan demonstrated that the patella was of normal size but was lying in a more proximal position than normal and that the patellar tendon was absent. The quadriceps muscle appeared to be severely hypotrophic. The ranges of motion of the hip and ankle were normal. Neurologic examination revealed normal findings. The contralateral extremity was examined and was deemed normal.
When the patient presented to our institution, we recommended observation because of the lack of symptoms and the relatively normal function of the limb. Two years later, when the boy was 9.5 years of age, physical examination revealed essentially no change in his condition: the gait was still slightly impaired by the deficient quadriceps muscle, and the knee extension lag was still 30°.
The patellar tendon is formed during the early stages of fetal development. It begins to form as early as the sixth week of fetal life as a detachment from the lower part of the femur4. It descends by the third month to lie in the depression between the future femoral condyles4. The quadriceps mechanism is then seen coursing over the anterior surface of the anlage of the patella. According to a study by Gardner and O'Rahilly, a differentiating patellar tendon was seen in two of nine embryos by six weeks5. By seven weeks, the patellar tendon was evident in all nine embryos. At 7.5 weeks, the medial and lateral patellar retinacula were present, and, by eight weeks, the knee joint resembled that of an adult5.
In children, the patella can be difficult to visualize radiographically because it ossifies late. The ossification of the patella is visible radiographically by two to four years of age in girls and by three to seven years of age in boys6.
Our patients appeared to have a congenital distal femoral deficiency. Both lacked the patellar tendon and had a short femur, and one had a hypoplastic patella. To our knowledge, these findings have not occurred in association with any known syndromes. A common entity that includes a hypoplastic or absent patella is the nail-patella syndrome (onycho-osteodysplasia syndrome), which can be associated with hypoplasia of the ischiopubic component of the pelvis, but to our knowledge there have been no reports of associated patellar tendon aplasia4,7-11.
Our first patient had been diagnosed with arthrogryposis multiplex congenita at six months of age. At the time that the patient presented to our institution, we believed that this diagnosis was unlikely because the contracture of the hip, knee, and ankle seemed secondary to the absent patellar tendon and the short extremity. No dimpling of other joints was present, and the patient lacked the classic appearance of a “wooden doll.” However, in retrospect, it is possible that the patient had a monomelic form of this disorder. The quadriceps muscle was of a firm and fibrotic consistency, which would be consistent with the findings associated with the myopathic form of arthrogryposis12,13.
In the case of our second patient, the child's mother had undergone amniocentesis, which had resulted in leakage of amniotic fluid. Theoretically, the child's lower extremity could have been injured during this procedure; however, we could not find any reports of a similar case.
Patients with tibial or fibular hemimelia may have an absent patellar tendon1,3. The presence or absence of a functioning quadriceps mechanism has a considerable impact on the treatment of tibial hemimelia in that the decision to perform fibular centralization or knee disarticulation is made on the basis of whether there is a functioning quadriceps mechanism1,14,15. If the quadriceps mechanism is absent or insufficient, reconstructive procedures in which fibular centralization is performed are not recommended14,15. The rationale for this recommendation is that the success of centralization of the fibula depends on the function of the knee, which depends on an intact quadriceps mechanism. Quadriceps muscle insufficiency may result in a flexion deformity of the knee1.
To our knowledge, only four cases of patellar tendon aplasia have been reported1-3. Two cases were found on magnetic resonance imaging in patients with fibular or tibial hemimelia3. The third case was discovered with use of ultrasound in a nine-day-old girl with tibial hemimelia1. Clinically, the knee was flexed and no active extension was observed. Radiographs revealed shortening of the femur and absence of the tibia, and ultrasonography of the knee demonstrated no tibial anlage or patellar tendon. In that patient, disarticulation of the knee was performed because of a fixed flexion deformity of the knee and absence of the quadriceps tendon1. The fourth case, reported by Messina et al., was noted in a twenty-five-year-old woman who had bilateral congenital absence of the patellar tendon2. That patient had presented for the treatment of right knee pain that had begun two weeks earlier, after a twisting injury. She reported an acute onset of swelling, one episode of locking, and increasing fullness and pain along the lateral aspect of the knee. She had no history of knee trauma or knee problems and was an active dancer who practiced for as long as four hours each day. She was also active in sports, participating in both basketball and volleyball. The initial physical examination revealed a mild crouched gait. The quadriceps muscle had normal mass and tone. Marked bilateral patella alta was noted. Observation of patellar tracking revealed an absence of patellar engagement with the patellofemoral groove until the knee was in 120° of flexion. The passive range of motion of the knee was from 0° to 135° or 140° of flexion bilaterally. A bilateral active extensor lag of 8° to 12° was present. The absence of the patellar tendons was confirmed on magnetic resonance imaging2. No specific therapy was documented in that report2.
Treatment of an absent patellar tendon is of uncertain value. The patient with bilateral congenital patellar tendon aplasia who was described by Messina et al.2, for example, was well adapted to the defect. That patient was very active in sports, and the absence of the patellar tendons was unknown prior to the injury. In contrast, one of our patients (Case 1) was limited in activities of daily living and sports activities. He had 6 cm of lower-extremity shortening, hypoplasia of the patella, aplasia of the patellar tendon, and hypoplasia of the quadriceps muscle. The absence of the patellar tendon caused a knee extension lag and a flexion contracture. Because functional deficits were present, the patient was offered surgical treatment to improve the biomechanics of the knee joint. Intraoperatively, the quadriceps muscle appeared severely fibrotic and had fatty infiltration. Despite the fact that the patellar tendon was successfully reconstructed, as seen both clinically and on magnetic resonance imaging, the functional outcome two years after the operation was disappointing because the quadriceps muscle had not regained function. Postoperatively, the gait was worse than it had been before surgery, despite intensive physical therapy.
Observation was recommended for our second patient (Case 2), who was of a similar age but who had minimal symptoms. The clinical course of this patient was unchanged during two years of follow-up; however, the long-term outcome is unknown.
The two cases described in the present report should alert the clinician that a knee extension lag in a child may, in rare cases, be caused by an absent patellar tendon. If operative reconstruction is considered, functional recovery may fail as a result of long-standing atrophy of the quadriceps muscle and tendon. On the basis of these two cases, we cannot give a clear recommendation for surgical reconstruction as the treatment for this rare condition. We recommend that, before the decision is made to perform a surgical reconstruction, the clinician should thoroughly document the existence of a functioning quadriceps muscle, the presence of which will optimize the possibility of a satisfactory functional recovery. ▪
The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.
Investigation performed at the Department of Orthopaedic Surgery, University of Heidelberg, Heidelberg, Germany
1. , Harcke HT, Kumar SJ. Sonography in the management of tibial hemimelia. Clin Orthop Relat Res. 1990;251: 266-70.
2. , Meister K, Montgomery WJ. Bilateral congenital absence of the patellar tendon. Am J Knee Surg. 1997;10: 23-6.
3. , Jaramillo D, Hoffer FA, Kasser JR. MR imaging in congenital lower limb deformities. Pediatr Radiol. 1996;26: 381-7.
4. , Thneibat WA. Ischio-pubic-patellar hypoplasia: is it a new syndrome? Pediatr Radiol. 1997;27: 430-1.
5. , O'Rahilly R. The early development of the knee joint in staged human embryos. J Anat. 1968;102: 289-99.
6. . Radiology of postnatal skeletal development. X. Patella and tibial tuberosity. Skeletal Radiol. 1984;11: 246-57.
7. , Taor WS. The “small patella” syndrome. J Bone Joint Surg Br. 1979;61: 172-5.
8. , Gubler MC, Knoers NV. Nail-patella syndrome. Overview on clinical and molecular findings. Pediatr Nephrol. 2002;17: 703-12.
9. , Nelson J. Small patella syndrome. Am J Med Genet. 1995;57: 558-61.
10. . Comments on the ischio-pubic-patellar syndrome. Pediatr Radiol. 1997;27: 428-9.
11. , Satterwhite Y, Ogden JA, Pugh L, Ganey T. Nail patella syndrome: a review of 44 orthopaedic patients. J Pediatr Orthop. 1991;11: 737-42.
12. . Arthrogryposis multiplex congenita: spectrum of pathologic changes. Hum Pathol. 1986;17: 656-72.
13. . Pediatric orthopedics. 2nd ed. Philadelphia: Saunders; 1990. Arthrogryposis multiplex congenita (multiple congenital contracture); p 2086-119.
14. , Ginsburg GM, Hall JE. Brown's procedure for congenital absence of the tibia revisited. J Pediatr Orthop. 1996;16: 85-9.
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15. , Eilert RE. Fibular transfer for congenital absence of the tibia. Clin Orthop Relat Res. 1979;139: 97-101.