Introduction

Patella fracture accounts for around 1% of all fractures. It is not uncommon for orthopaedic surgeons to face comminuted patella fractures. Complex fracture pattern (AO 34-C3) is the most common type of patella fracture, accounting for 25% of all patella fractures. [1] However, tradition fixation technique of tension band wiring with or without a lag screw may not be able to provide adequate stability for this type of fracture pattern. While partial patellectomy carries risk of extensor mechanism weakness and bone loss. We present a case of comminuted patella fracture (AO 34-C3) treated with anterior plating technique.

Case report

A 70-year-old female was admitted to orthopedic ward after she slipped and fell landing on her right knee. There was no other associated injury. She complained of severe right knee pain and swelling after the injury and was not able to bear weight. Physical examination showed grossly swollen right knee with effusion. There was mild skin abrasion but no open wound. There was severe tenderness over her right patella. The right knee extensor mechanism was disrupted. She could not tolerate any range of movement examination due to severe pain. The distal neurovascular status was normal. X ray of her right knee showed comminuted right patella fracture with significant displacement (Figure 1, 2 & 3). The comminution was mainly over the distal pole. A long-leg slab was applied for temporary immobilization. Ice therapy and elevation were prescribed to reduce the soft tissue swelling. Three days after the admission, when the soft tissue condition improved, open reduction and internal fixation of her right patella fracture was performed.

Figure 1

Lateral view of right knee X-ray

Figure 2

AP view of right knee X-ray

Figure 3

Skyline view of right knee X-ray

Operation

The patient was positioned supine on a radiolucent table. Spinal anesthesia was administered by the anesthetist. A gel pad was placed under the patient’s right hip to orientate the patella superiorly. Skin was disinfected and draped. A tourniquet was inflated.

A midline anterior longitudinal skin incision was made from the proximal pole of the patella to just distal to the patella tendon. Sharp dissection was made down to the patella to raise a full-thickness flap. The prepatellar bursa was disrupted. The medial and lateral parapatellar retinacula were found partially torn.

The distal pole of the patellar fracture was severely comminuted. There were multiple small bony fragments inferomedially and a relatively larger inferolateral fragment which contained only a small area of cartilage. Hematoma and fracture end were debrided and irrigated with normal saline. The periosteum near the fracture end was elevated for anatomical reduction.

The distal pole of the fracture and the patella tendon were carried by two Fiberwires intraosseously by Krackow suture technique. Three bone tunnels were created by a 2.0mm drill at the equator of the proximal fragment. The Fiberwires were carried through the bone tunnels by a suture retriever and then tightened at the superior pole of the patella. Point reduction forceps were applied to further aid the reduction of the small inferolateral fragment which was temporally fixed with 1.6mm Kirschner wires (Figure 4).

Figure 4

Fiberwires were carried through the bone tunnels and tightened at the superior pole. The small inferolateral fragment was temporally fixed with 1.6mm Kirschner wires

Figure 5

Depuy Synthes variable angle LCP mesh plate 2.4/2.7

A locking mesh plate (Depuy Synthes variable angle LCP mesh plate 2.4/2.7) (Figure 5) was then cut and bent to fit the contour of anterior and inferior surfaces of the patella (Figure 6). The most distal row of the plate was bent and angulated at 80-degree to 90-degree to cover the inferior pole of the patella. This allowed the insertion of a “home-run” screw which fixed the inferolateral fragment to the proximal fragment and maximize the stability of the construct. After confirming an appropriate size, shape and position of the mesh plate, two 2.4mm cortical screws were inserted to compress the plate onto the anterior surface of the patella. This could minimize the risk of skin impingement and symptomatic hardware. Multiple unicortical 2.4mm variable angle locking screws were then inserted over the proximal and inferolateral fragments. A retrograde unicortical 2.4mm variable angle locking screw was inserted through the most inferolateral screw hole parallel to the articular surface across the fracture site. This retrograde screw acted as a “home-run” screw to improve the fixation stability. The two 2.4mm cortical screws were then replaced by two 2.4mm variable angle locking screws (Figure 7). The fixation was further augmented with Fibertape cerclage.

Figure 6

The locking mesh plate was cut and bent to fit the contour of anterior and inferior surfaces of the patella

Figure 7

The contoured locking mesh plate was fixed onto the patella by multiple unicortical 2.4mm variable angle locking screws and a “home-run” screw

The fixation stability was then tested through 0-degree to 90-degree of knee flexion. The reduction was checked by fluoroscopy (Figure 8 & 9) and palpation through retinacular window to ensure there was no articular stepping or gapping. The joint was then irrigated with normal saline. The retinacula were repaired by Vicryl-1. The subcutaneous tissue and skin were closed in layer in usual manner.

Figure 8

Lateral view of intraoperative fluoroscopy

Figure 9

AP view of intraoperative fluoroscopy

Post operative protocol and outcome

A hinge knee brace was prescribed for 6 weeks in total. Immediate full weight baring walking was allowed. The patient was allowed to perform mobilization exercise of 0-degree to 30-degree immediately after the operation for 2 weeks. The range was then gradually increased to 0-degree to 60-degree at post-operative 2 weeks and to 0-degree to 90-degree at post-operative 4 weeks. At post-operative 6 weeks, free range of movement was allowed, and the hinge knee brace was removed.

The patient was referred to outpatient physiotherapy for mobilization exercise and walking exercise. She underwent two physiotherapy sessions during the first month post-surgery. However, she defaulted the subsequent sessions due to COVID-19 outbreak. Despite this, upon follow-up at 4 months post-surgery, she did not complain of any right knee pain and was able to walk unaided. The right knee wound had healed well. There was no sign of prominent implant. Her extensor power of full and the active range of movement of her right knee was full. (Figure 10 & 11). X ray of right knee showed fracture union. (Figure 12 & 13). Her right knee had returned to normal pre-injury function.

Figure 10

Right knee full extension at post-operative 4 months

Figure 11

Right knee full flexion at post-operative 4 months

Figure 12

AP view of right knee X ray at post-operative 4 months

Figure 13

Lateral view of right knee X ray at post-operative 4 months

Discussion

Comminuted patella fracture remains a difficult fracture to fix, especially for those with small distal pole fragments. Conventional methods include tension band wiring with or without lag screws and intraosseous suture repair. However, these fixation methods are associated with a number of post operative complications for example, stiffness due to prolonged post operative immobilization, loss of reduction, hardware irritation and implant failure. Partial patellectomy is also another treatment option for comminuted patella fracture, but it is associated with extensor mechanism weakness, extension lag and bone loss.

We present a case of patella fracture with significant distal pole comminution which was treated with anterior plating with locking mesh plate. This technique provides higher fixation stability hence reducing the risk of loss of reduction and implant failure. There are multiple biomechanical studies comparing the mechanical strength of patella locking plate with that of tension band wiring and tension band wiring plus lag screw. All studies showed consistent results that the plating groups provided higher mechanical strength and less fracture displacement [2-4]. One study concluded that fixed-angle plate was the only fixation method that sustainably stabilized a multi-fragmentary articular distal patella fracture during cyclic loading [5]. In our case, we also added a retrograde “home-run” screw fixing a more sizable distal fragment to the proximal fragment. This “home-run” screw can further improve the stability of the construct [6].

Besides higher construct stability, anterior patella plating can reduce the risk of symptomatic hardware. The locking mesh plate is a low-profile implant. During the operation, cortical screws were used at the beginning to compress the plate onto the patella surface. This can minimize the risk of soft tissue irritation by the implants and decrease the chance of symptomatic hardware and the need of removal of implants later. A prospective study by a tertiary level 1 trauma center showed that patella plating provided favorable clinical and radiological outcomes with minimal complications [7]. In their study, there was no implant failure or fixed flexion deformity after patella plating and none of the patient required removal of implant due to implant impingement.

Unlike partial patellectomy, anterior patella plating does not require removal of any bony fragments. This method also allows bone-to-bone healing which is more favorable than tendon-to-bone healing. Therefore, patella plating provides better fracture healing and restoration of extensor mechanism strength comparing with partial patellectomy.

There are several important points to note when anterior patella locking mesh plate is used. Firstly, the cutting and bending process is crucial. Care must be taken to ensure that the plate is contoured to best fit the anterior and inferior surface of patella. Precise angulation of the most inferior row of the plate allows the insertion of intramedullary “home-run” screw. Secondly, cortical screws should be used initially to compress the plate onto the bone, and they should be changed to locking screws at the end. Finally, all screws used should be unicortical. Careful palpation of the articular surface and screening with intraoperative fluoroscopy should be done to make sure that no screw tip is protruding out of the articular surface.

Conclusion

Anterior patella plating with locking mesh plate is an effective treatment option for comminuted patella fracture. It provides better fixation stability, less symptomatic hardware and better bone reservation. We recommend considering anterior patella plating technique in the future when cases of comminuted patella fracture are encountered.