1 Case Presentation

A 24-year-old male landscaper presented to our emergency department a day following a motorcycle accident. He reported striking the anterior aspect of his left knee directly against a tree. He had no medical comorbidities or surgical history and had a normal body mass index (BMI). His primary complaint on presentation was pain in the left knee and instability. On examination, he had significant swelling and ecchymosis overlying the inferior pole of the patella along with a large joint effusion and had an extensor lag with inability to straight leg raise. He had localised tenderness to the inferior and superior pole of the patella with a palpable defect. Initial radiographs undertaken in the emergency department demonstrated a small fragment of bone at the inferior pole of the patella suggestive of an avulsed patellar tendon and a moderate suprapatellar effusion (Fig. 1). Because of the bifocal examination findings, a magnetic resonance imaging (MRI) scan was undertaken as an outpatient which confirmed the avulsion of the patellar tendon along with an insertional tear of the quadriceps tendon (Figs. 2 and 3). A diagnosis of a bifocal disruption or a “floating patella” of the extensor mechanism was established. All other structures were intact. The patient was counselled on the injury and informed consent obtained for surgical repair.

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Fig. 1 Lateral radiograph of the knee demonstrating an patella tendon avulsion off the inferior pole and an associated knee joint effusion.

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Fig. 2 Pre-operative T2 Sagittal MRI demonstrating the bifocal injury.

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Fig. 3 Pre-operative T1 Sagittal MRI demonstrating the bifocal injury.

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2 Surgical technique

A midline longitudinal approach was utilised to expose the extensor mechanism. During the superficial dissection the extensor retinaculum was observed to be intact (Fig. 4). This was carefully incised and elevated to expose the inferior and superior poles of the patella. The patellar tendon was noted to be avulsed corresponding to the small fragment of bone on the inferior pole of the patella seen on radiographs. The posterior aspect of the patellar tendon was observed to be completely delaminated. The dissection was carried proximally and the a tear of the quadriceps tendon from its insertion was confirmed. The haematoma was evacuated, and copious lavage of the knee joint was performed. Following this, debridement of the inferior and superior pole of the patella was performed until healthy cancellous and vascular bone exposed. A 4-strand Krackow locking suture repair technique was utilised using a number 2 FiberWire™ (Arthrex Inc. Naples, FL) on the patellar tendon and the quadriceps tendon (Fig. 5).¹ The sutures were then passed through the patella using three transosseous tunnels created with a 2.6mm drill and a Hewson suture passer and simultaneously tied over the superior and inferior poles of the patella with the knee in extension to for appropriate soft tissue tension (Fig. 6). Following the repair, flexion to 70° was achievable without excessive tension on the repaired construct. The patient was placed in a range of motion (ROM) knee brace in full extension and allowed to weight-bear as tolerated for six weeks. An increase in knee flexion by 30° every fortnight was initiated as part of the rehabilitation program. At three months post-operation the patient could achieve a ROM of 0–110° and perform a straight leg raise without an extension lag (see Video). At four months the patient had full ROM, no evidence of quadriceps atrophy and had returned to unrestricted duties at work and was therefore discharged from physiotherapy.

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Fig. 4 Intra-operative clinical image demonstrating the intact extensor retinaculum.

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Fig. 5 Intra-operative clinical imaging demonstrating the 4-strand Krackow locking suture repair.

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Fig. 6 Intra-operative clinical image demonstrating final construct.

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3 Discussion

The extensor mechanism of the knee involves the quadriceps muscle and tendon, the patella and the patella tendon. Bifocal disruptions of the extensor mechanism of the knee are extremely rare injuries and involve a disruption at any two locations on the extensor mechanism. There are limited case reports available and surgical repair of these unique injuries represent an additional challenge due to the extent of soft tissue damage, poor quality of tissue and inapplicability of ligamentotaxis for correct tensioning during repair. Kang et al.² classified bifocal disruptions into five types depending on the location of disruption. Type 1 injuries are most common, and they an avulsions of the patellar tendon off the tibial tuberosity which has itself fractured off.^2–10 Type 2 injuries only involve the patellar tendon and is an avulsion fracture the inferior pole of the patella and a rupture of its distal end. Type 3 injuries involve a rupture of the quadriceps tendon with an avulsion fracture of the tibial tuberosity. Type 4 injuries are bifocal avulsion fractures, off the inferior pole of patella and off the tibial tuberosity. Type 5 injuries involve ruptures of both the patella and quadriceps tendons without any fractures, thus representing the “floating patella”. Type 5 injuries appear to be the rarest type with only a single case report described in an otherwise healthy patient who happened to be 72-years old.¹¹ While Kelmer et al.¹² recently described a patient who had a Type 5 injury, this 58-year old patient had multiple medical comorbidities and cardiovascular risk factors that may have predisposed this patient to risk factors rupture, such as obesity and chronic tendinopathy. Ultimately, both these cases appear to involve older patients describing a history consistent with a low-energy mechanism or fall from standing height alluding to the possibility of chronic tendinopathy. Other authors have reported on patients with bifocal disruptions with medical comorbidities such as lymphoedema.¹³

Contrastingly, we present a case that has not been previously described with an avulsion fracture of the inferior pole and a rupture of the quadriceps tendon and may represent a sub-type of Type 5. Furthermore, our case is unique in that it involves a young patient involved in a high-energy motorcycle accident without any past history of ipsilateral knee surgery or medical history that may have predisposed them to the injury. While most disruptions of the extensor mechanism occur due to an eccentric contraction of the quadriceps, our case involved a direct blow which may have explained the intact extensor retinaculum observed during the approach.¹⁴

The rarity and different types of bifocal disruptions has meant that surgical interventions to restore the normal biomechanics of the knee have varied in literature.^5,11,12,15 Despite our case involving an avulsion fracture of the patella tendon off the inferior pole of the patella, the small size of the bony fragments precluded any forms of rigid internal fixation with screws. Therefore a decision was made to utilise a transosseous suture construct addressing the respective tendons.¹⁶ The suture construct was similar to the one described previously by Kelmer et al.¹² for bifocal disruptions, however we utilised a number 2 Fiberwire and three tunnels instead of four to reduce the risk of an iatrogenic fracture.

Despite the variety of techniques utilised to repair the bifocal disruption, it appears that patients are able to achieve excellent surgical outcomes, with all authors reporting near full ROM and return to function at their final follow up.^2,11–13,15

4 Discussion

In conclusion, bifocal disruptions to the extensor mechanism of the knee are rare and the surgical treatment of these injuries are made more difficult due to the lack of soft tissue tension. To the best of our knowledge this case represents a novel type when utilising the classification system described by Kang et al.² and the appropriate treatment of such an injury can be achieved utilising a suture construct.

Ethical statement

As this was a single case, no ethics approval was sought.

Funding declaration

All authors listed on this manuscript can confirm no funding was received for this study.

Patient consent

Patient consent was obtained for the conduct of this case report.

CRediT authorship contribution statement

Raymond G. Kim: Conceptualization, Methodology, Validation, Writing – original draft, Writing – review & editing, Visualization, Project administration. Cyrus R. Mehta: Conceptualization, Methodology, Validation, Writing – review & editing, Visualization, Supervision, Project administration. Brian Martin: Conceptualization, Methodology, Validation, Writing – review & editing, Visualization, Supervision, Project administration.