Hoffa fracture accompanied by dissection of the popliteal artery

Abstract

After a high-energy trauma, a 37-year-old motorcyclist presented to the emergency ward with a Hoffa fracture of the lateral femoral condyle of the right knee. Following admission, the patient developed a pale, cold and pulseless right foot. CT angiography scan showed a 5 cm dissection of the popliteal artery. Emergency arterial reconstruction was performed and the Hoffa fracture was repaired in a second stage. To our knowledge, this is the first report of a patient with a Hoffa fracture accompanied by a popliteal artery dissection.

Background

In 1904, intra-articular unicondylar fractures of the lateral or medial femoral condyle were first reported by Hoffa.^{1 2} These so-called Hoffa fractures are rare,¹ often resulting from high-energy trauma, such as motor cycle accidents or falls from height,^{3 4} but also following low-energy trauma such as a fall in elderly patients.⁵ It has been assumed that a direct anteroposterior force to the flexed and abducted knee results in this specific type of fracture,⁶ however, vertical shear with a twisting mechanism has been postulated as well.^{7 8} Hoffa fractures often involve the lateral condyle,^{8 9} but fractures of the medial^{3 10} as well as bilateral condyles^{11 12} are also observed. They can be easily missed on standard knee X-rays, therefore, CT scans play an essential role in diagnostics.^{9 10 13} In all cases of a distal femur fracture, one should anticipate a potential Hoffa fracture.⁵

Generally, non-operative treatment results in poor outcomes, including displacement, malunion, non-union and avascular necrosis.^{8 14–17} Open reduction and anatomical fixation, followed by early rehabilitation, may reduce the risk of these complications and result in better functional outcomes.^{8 18} Recently, arthroscopy-assisted fixation has also been reported.¹⁹ Although different techniques are described in the literature, superiority of one of these techniques has not been shown.16 18 20–23

Hoffa fractures are often reported in combination with other femoral fractures.^{9 24 25} Tibial plateau fractures,¹⁰ patellar and/or quadriceps tendon injuries have been reported in conjunction with Hoffa fractures as well.^{24 26 27} To our knowledge, this is the first report of a patient with a Hoffa fracture accompanied by dissection of the popliteal artery.

Case presentation

A 37-year-old Caucasian man with an uneventful medical history (no history of vascular disorders) drove approximately 40 km/hour on his motorcycle when an accelerating car hit him from the right side, with direct impact on the right knee. The patient was transported to a level 2 trauma centre. At arrival, the patient was alert but complained of a painful left knee. Primary survey revealed a haemodynamically stable patient. At secondary survey, pain and swelling of both knees were observed and a small laceration approximately 10 cm caudally to the tuberosity of the left tibia. Circulation appeared intact, as pulses were described as palpable. Other than mild varus/valgus instability of the right knee no further instability was observed. Knee X-rays and CT scan showed a Hoffa fracture of the lateral femoral condyle on the right side with an intra-articular cranioposterior displacement of 8 mm (figure 1). Also, a comminuted tibial plateau fracture of the left knee (Schatzker classification type 6²⁸) was identified. We shall not discuss the treatment and follow-up of the tibial plateau fracture in this paper.

Figure 1.

(A) Plain lateral X-ray of the right femur, showing a step-off in one of the condyles suggesting a Hoffa fracture. (B, C) Sagittal and transverse sections of a CT scan without contrast showing the displaced lateral Hoffa fracture.

A few hours after admission, the patient developed a pale, cold and pulseless right foot. CT angiography scan showed a dissection of the popliteal artery with a length of approximately 5 cm starting 6.5 cm cranially of the knee joint (figure 2). The crural arteries were intact. The patient was transported to the operation room immediately. Stability of the knee was tested perioperatively. Since there was only mild varus/valgus instability with knee in full extension and in 30° of flexion, there was no indication for temporary external fixation with an ex-fix. The vascular surgeon performed an emergency arterial reconstruction. The patient was placed in the prone position, the popliteal artery was explored and the dissected intimal flap was stitched with Kunlin sutures. The artery was widened using a bovine patch. All subcutaneous structures, including muscles, were vital during the operation. Hence, fasciotomies of the lower leg were not performed. During the following 24 hours, the patient was observed closely to exclude reperfusion damage and potential compartment syndrome, which did not occur. Delayed fixation of the fracture was chosen to provide time to recover from the vascular intervention. Postoperatively, the patient was heparinised with 12 500 IE/24 hours, and both legs were immobilised using the splints.

Figure 2.

(A, B) Transverse and sagittal sections of CT angiography showing dissection of the popliteal artery (arrow).

Since no secondary complications were seen, the Hoffa fracture was fixed 4 days later using two headless compression screws (figure 3) through a supine, lateral parapatellar approach. The screws were placed perpendicular on the fracture and were submerged below the cartilage. Ankle–Brachial Index (ABI) was 0.96 after fracture fixation. Heparin was switched to low-molecular-weight heparin, which was continued for 6 weeks, and carbasalate calcium was given for 3 months. Continuous passive motion and physical therapy were started, followed by hydrotherapy. Full weight bearing of the right lower extremity was allowed after 8 weeks.

Figure 3.

(A, B) Intraoperative images of the reduced Hoffa fracture (parapatellar approach) during the second procedure. (C, D) Anteroposterior and lateral postoperative X-rays after 6 months follow-up.

Outcome and follow-up

At 4 months follow-up, no signs or symptoms of peripheral arterial occlusive disease or knee instability were seen. A flexion/extension of 120-0-0 degrees was observed and triphasic Doppler signals were detected. X-rays showed consolidation and a good position of the femoral condyle. Carbasalate calcium was discontinued and further vascular follow-up was not indicated. Total follow-up time was 2 years. At discharge, a flexion/extension of 130-0-0 degrees was observed and the patient did not experience any instability of the knee.

Discussion

A Hoffa fracture is a rare fracture of the distal femur that often results from high-energy trauma.^{3 4} To our knowledge, the current case report describes the first patient with a Hoffa fracture accompanied by popliteal artery dissection. Trauma to the popliteal artery can easily occur in case of a Hoffa fracture, since the popliteal vein and artery with its branches are situated directly between the medial and lateral femur condyles.⁷ Probably this combination of injuries has not been reported, as Hoffa fractures are so rare.

In general, popliteal artery injury is seen after high-energy trauma to the knee such as dislocations, complex tibial plateau fractures or supracondylar femur fractures,²⁹ but it may also occur after blunt trauma without a fracture or dislocation.³⁰ It has been assumed that a Hoffa fracture may occur due to direct anteroposterior force to the flexed and abducted knee⁶ or due to vertical shear with a twisting mechanism.^{7 8} In this case, the patient was hit from the right side, with direct impact on the right knee. Dislocation was not observed directly after the accident. Obviously, immediate spontaneous realignment cannot be ruled out. However, besides mild varus/valgus instability and an intra-articular cranioposterior displacement of 8 mm seen on the CT scan, no further instability was observed. Hence the mechanism for the cooccurrence of this Hoffa fracture with the popliteal dissection remains uncertain. An MRI scan, which is the gold standard for determining ligamentous injury, was not performed in the acute setting. As no instability was seen postoperatively, identification of ligamentous injury on an MRI scan in this specific case was of no clinical significance. However, we do recognise the importance of obtaining an MRI in the acute setting, especially when instability of the knee is suspected based on history or clinical examination.³¹

Delay in the diagnosis of popliteal artery injury leads to irreversible ischaemia and possibly to a definitive amputation. Therefore, early recognition (<6–8 hours) is crucial for the salvage of the extremity.³⁰ In the current case, circulation appeared intact at primary survey based on palpated pulses. However, ABI was not performed even though ABI is reported to reliably exclude occult arterial damage in injured extremities.³² In combination with palpation of the dorsalis pedis and posterior tibial pulses, ABI increases sensitivity and specificity of vascular injury assessment to 100% and 98%, respectively, after knee dislocation.³³ Therefore, we advise an ABI to be performed in the acute setting in all major lower extremity injuries.

As the pale pulseless foot was noted a few hours after admission, the emergency vascular intervention was still performed in time, that is, before the onset of motor and sensory loss of the lower leg. All subcutaneous structures, including muscles, were vital during the operation and fasciotomies of the lower leg were not performed. As stated above, popliteal artery dissections can be caused by blunt trauma and may be seen in association with distal femur fractures, such as a Hoffa fracture. Therefore, in all patients with blunt, high-energy trauma to the leg, physicians should be aware of the risk of arterial trauma³⁰ and a detailed vascular exam, including ABI, should be performed.

Learning points.

• Hoffa fracture is a rare fracture that often occurs after high-energy trauma.

• Hoffa fracture can be accompanied by dissection of the popliteal artery.

• A detailed vascular examination, including Ankle–Brachial Index, should be performed in all patients with blunt, high-energy trauma to the leg.