Supracondylar Femoral Fracture After Arthroscopic Reconstruction of the Anterior Cruciate Ligament: A Case Report

Mithoefer, Kai MD; Gill, Thomas J. MD; Vrahas, Mark S. MD

Journal of Bone & Joint Surgery - American Volume:
doi: 10.2106/JBJS.D.02784
Case Reports
Author Information

1 Department of Orthopedic Surgery, Massachusetts General Hospital, 15 Parkman Street, Boston, MA 02114. E-mail address for K. Mithoefer: kmithoefer@partners.org

Article Outline

Reconstruction of the anterior cruciate ligament is one of the most frequently performed orthopaedic procedures, with more than 100,000 reconstructions performed annually in the United States alone1. Autogenous bone-patellar tendon-bone graft is the graft option that is most frequently utilized by orthopaedic surgeons in the United States, Canada, and Europe2. Complications have been reported to occur in association with 1.8% to 24% of anterior cruciate ligament reconstructions3-5. Serious complications have included arthrofibrosis, patellar fracture, patellar tendon rupture, tibial tubercle fracture, tibial plateau fracture, and osteonecrosis of the femoral condyles3-6. Femoral fracture following anterior cruciate ligament reconstruction is a devastating complication that has been reported only in isolated cases and has been attributed to technical errors or the creation of additional bone holes for supplemental fixation devices used with earlier reconstructive techniques7-12. We present a rare case of a supracondylar femoral fracture that occurred after an arthroscopic anterior cruciate ligament reconstruction that had been performed without supplemental fixation and had not been associated with intraoperative complications. The fracture occurred through an enlarged femoral tunnel following an injury of the involved extremity. Our patient was informed that data concerning this case would be submitted for publication.

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Case Report

A thirty-three-year-old man sustained an injury of the left knee after falling off a mountain bike. He reported that he had lost his balance while in a standing position and had fallen onto the right side with hyperextension of the left knee after getting his foot caught in the pedal. He presented to the emergency room with left knee pain and the inability to bear weight on the affected leg. A review of the history revealed that an arthroscopic reconstruction of the left anterior cruciate ligament had been performed five months before the time of presentation and fifteen months after the patient had sustained an injury of the ligament. A review of the operative record revealed that the reconstruction had been performed with use of a 10-mm-wide ipsilateral central-third patellar tendon autograft. During the procedure, a 10-mm-wide tunnel had been drilled into the femur to a total depth of 35 mm. Femoral tunnel placement had been performed arthroscopically in accordance with recent recommendations13-15 with use of a commercially available drill-guide with a 7-mm offset. Fixation of the graft in the femoral tunnel had been achieved with use of a 7 × 25-mm metal interference screw. A review of the operative report and an interview with the surgeon did not reveal any intraoperative complications or technical errors. In addition to the ligament reconstruction, arthroscopic chondroplasty of small (grade-3) cartilage lesions of the medial and lateral femoral condyles had been performed. The patient had recovered without complications and had just returned to his preoperative level of athletic activities.

Physical examination revealed marked tenderness with osseous crepitation. A large knee effusion and marked muscle guarding prevented reliable evaluation of ligamentous stability of the injured knee. Neurovascular function distal to the injury was intact, and no other injuries were apparent. Plain radiographs revealed an AO type-C1 supracondylar-bicondylar distal femoral fracture with a large butterfly fragment involving the trochlea. The large butterfly fragment involving the trochlea indicated an extension-type injury (Figs. 1-A and 1-B). Computed tomography of the left knee demonstrated that the supracondylar femoral fracture had occurred through the intraosseous tunnel that had been created in the posterior aspect of the distal part of the femur for fixation of the femoral bone block of the graft (Fig. 2). Measurements on the computed tomographic images demonstrated an increase in the diameter of the tibial tunnel to 19 mm and an increase in the diameter of the femoral tunnel to 16 mm.

Following arthrotomy, anatomic reduction was achieved and internal fixation was performed with use of a left distal femoral locking condylar plate (Synthes, Paoli, Pennsylvania). After fixation, direct inspection of the retained anterior cruciate ligament revealed an intact, well-fixed, and taut graft throughout a full range of knee motion. Lachman testing demonstrated <5 mm of anterior translation (grade B according to the system of the International Knee Documentation Committee16) with a firm end point. In order to avoid loss of fracture fixation, pivot-shift testing was not performed. Intraoperative examination demonstrated no varus or valgus instability, an intact posterior cruciate ligament, and a stable posterolateral corner. Continuous passive motion was started within six hours after the operation, and protected weight-bearing was maintained for eight weeks. At three months, the patient was walking without limitation. At twelve months, complete healing of the supracondylar femoral fracture was seen on plain radiographs (Figs. 3-A and 3-B). The range of motion of the knee was 0° to 135° bilaterally, the result of the Lachman test was classified as grade B according to the system of the International Knee Documentation Committee, and the pivot-shift test was negative. KT-1000 examination with the application of 30 lb (13.6 kg) of force at 30° of knee flexion revealed a maximum anterior tibial translation of 4 mm. Subjective knee function was rated as good, with a Lysholm score17 of 92 points (possible range, 0 to 100 points) and a Short Form Musculoskeletal Function Assessment score18 of 12 points (possible range, 100 to 0 points). There was no subjective knee instability, and the patient had returned to pivoting sports at a recreational level.

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Discussion

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Anterior cruciate ligament reconstruction with use of a bone-patellar tendon-bone autograft is one of the most frequently performed operative procedures2,14,15. This procedure involves drilling a large femoral tunnel in the posterior aspect of the lateral intercondylar notch for fixation of the proximal end of the graft14,15. The effects of such defects on bone strength have become a major concern in the field of orthopaedic trauma surgery, and their association with the risk of a postoperative fracture of the patella or tibia after anterior cruciate ligament reconstruction with use of a bone-patellar tendon-bone autograft has been previously recognized19-21. Femoral fracture following anterior cruciate ligament reconstruction has been reported in isolated cases as a result of distal femoral bone defects created for extra-articular fixation of a Gore-Tex prosthetic graft10, fixation of a ligament-augmentation device9, iliotibial band tenodesis8, or femoral post fixation7. Femoral fracture following anterior cruciate ligament reconstruction also has been reported to occur in association with bone defects resulting from multiple trocar perforations of the femoral diaphysis11. Only one recent report has described a lateral condylar fracture through the femoral tunnel after anterior cruciate ligament reconstruction without additional osseous stress risers12.

For optimum positioning of the graft, the surgeon should place the femoral tunnel as far posteriorly as possible while carefully avoiding disruption of the posterior cortex. As in the case of our patient, this is commonly achieved with use of a femoral tunnel placement guide with a built-in offset that maintains a 1 to 2-mm thick posterior cortical rim. Disruption of the posterior cortex can result from posterior placement of the femoral tunnel4. This complication is different from the fracture through the femoral tunnel that occurred in our patient and should be carefully avoided because it can lead to fracture of the lateral femoral condyle7. However, even if the posterior cortical wall is maintained, as it was in our patient, several factors predispose the patient to the development of a distal femoral fracture after arthroscopic anterior cruciate ligament reconstruction.

Although no studies have specifically addressed the mechanical effect of bone tunnels, a large femoral tunnel likely acts as a localized stress riser22-25. This effect results from a concentration of local stresses around the femoral defect and a reduced energy-absorbing capacity due to the decreased amount of bone that is available to withstand the applied load23. As bone with stress concentration behaves in a more brittle fashion, the increased local stresses can reach the ultimate stress of the bone at much lower applied loads25. Depending on the geometry of the defect, strength reductions of as much as 90% may occur24,25. The insertion of allogenic or autogenous bone graft into the defect, as during bone-patellar tendon-bone ligament reconstruction, has been shown not to significantly change the mechanical weakening of the bone25.

Additional stress concentration in the distal part of the femur results from the acute change of the sagittal, axial, and coronal geometry of the posterior condylar flare and intercondylar notch24,26. The geometry of the distal part of the femur plays a critical role in the structural properties of the bone and the prediction of fracture load27,28. Geometric analysis of the distal part of the femur has shown that the thinnest cortical shell is located in the posterior aspect of the distal part of the femur29; thus, the lowest fracture load is likely to be in the anatomic region of the femoral tunnel.

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Decreased bone-mineral density of as much as 20% has been observed after knee ligament injury, and this factor also may contribute to the increased risk of fracture after anterior cruciate ligament reconstruction because of decreased bending strength in the distal part of the femur28,30. When the area of the osseous defect is subjected to tensile stress, as it was when our patient sustained the knee extension injury, the load strength of the already vulnerable posterior aspect of the distal part of the femur is reduced even further23,24. However, as the bone in this anatomic region is predominantly under compression loading, the likelihood of fracture development and crack propagation is decreased, which may explain why femoral fracture does not occur more frequently after arthroscopic anterior cruciate ligament reconstruction.

As the stress concentration around osseous defects has been shown to decrease after eight to twelve weeks of osseous remodeling24, the predisposition for femoral fracture after anterior cruciate ligament reconstruction would be expected to decrease. However, healing of the femoral tunnel has been shown to be delayed by the exposure to biologic factors from the joint31. A previous case report on a patient in whom a fracture occurred through the femoral tunnel two years after anterior cruciate ligament reconstruction32 suggested that the stress-concentration effect of the femoral tunnel continues for a prolonged period after surgery.

Bone tunnel enlargement after anterior cruciate ligament reconstruction is well documented and has been reported to occur in as many as 68% of cases33. The etiology of this phenomenon is not completely understood, but it is thought to be related to a combination of multiple biological and mechanical factors34 and our understanding of the clinical relevance of bone tunnel enlargement is still evolving2,33,34. Previous experimental studies have shown that the breaking strength of bone decreases in direct proportion to the size of an osseous defect22. On the basis of these findings, the case of our patient suggests that enlargement of the femoral tunnel may have further decreased the mechanical fracture resistance. It has also been suggested that bone tunnel enlargement increases the risk of tibial plateau fracture after anterior cruciate ligament reconstruction6,19. Given the frequency of anterior cruciate ligament reconstruction and the high frequency of bone tunnel enlargement, the potential predisposing effect of this phenomenon toward a fracture of the distal part of the femur needs to be considered. Use of a more oblong drill-hole may help to reduce the stress concentration around the defect and help to reduce the fracture risk26.

Anatomic open reduction of the fracture is critical in order to avoid premature arthritis. In the case of our patient, we were also able to maintain the graft in the isometric position. Fracture fixation was successfully achieved with minimal postoperative morbidity, early functional recovery, and the return of a full range of motion. In contrast, other authors have reported continued loss of knee motion or ligamentous instability after distal femoral fracture fixation7,9,11. The intraoperative stability of the primary anterior cruciate ligament graft in our patient obviated the need for revision anterior cruciate ligament reconstruction. If anatomic fracture fixation does not maintain graft function, removal of the primary anterior cruciate ligament graft with bone-grafting of the enlarged bone tunnel can be performed at the time of fracture fixation to facilitate revision anterior cruciate ligament reconstruction at a later time.

In conclusion, supracondylar femoral fracture through the femoral bone tunnel is a serious complication of endoscopic anterior cruciate ligament reconstruction. The case of our patient suggests that bone tunnel enlargement may contribute to an increased risk of distal femoral fracture due to stress concentration around the femoral tunnel. The exact magnitude of the mechanical weakening and the postoperative duration of the increased fracture risk are unknown, and additional study is necessary to address these questions. If marked bone tunnel enlargement is observed, particularly in combination with other factors such as posttraumatic osteopenia, activity modification that reduces tensile force on the posterior aspect of the distal part of the femur may reduce the risk of distal femoral fracture after anterior cruciate ligament reconstruction. ▪

Investigation performed at the Department of Orthopedic Surgery, Massachusetts General Hospital, Boston, Massachusetts

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.

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