A major complication after medial patellofemoral ligament (MPFL) reconstruction is an iatrogenic patellar fracture. In 1992, Ellera Gomes reported the first patellar fracture following MPFL reconstruction in a series of 30 patients who underwent the procedure using transverse patellar tunnels.¹ Since then, several other studies have reported this complication.²,³,⁴,⁵,⁶ Parikh and Wall reported five patellar fractures in a series of 195 patients who underwent MPFL surgery using varied patellar fixation techniques.⁷

Commonly, during MPFL reconstruction, a free soft-tissue graft is either passed through tunnels in the patella or is sutured along the surface of the patella. When the graft is placed in the patella, the tunnels for graft placement could be transverse transosseous (from medial to lateral traversing the entire width of the patella), oblique (medial to anterior), blind sockets or tunnels confined to the medial third of the patella. Either single or double tunnels may be used. The options for fixation include interference screw, docking technique with suture fixation, suspensory fixation using cortical button, or implant-free techniques using bone bridge and/or sutures. When the graft is placed on the surface of the patella, the fixation is performed using either suture anchors or sutures.

Each fixation technique (including suture anchor placement) could weaken the patella and could create stress risers around the patellar fixation points. When subjected to direct or indirect forces, these areas of weakness could be the fracture initiation site that could propagate and ultimately lead to the devastating complication of a patellar fracture.

Violation of the anterior cortex of the patella or cortical defects is one of the major reasons for postoperative patellar fractures, both in biomechanical experiments and in clinical practice.⁷,⁸

Double transverse tunnels and large tunnels (>4.5 mm) have demonstrated increased rate of patellar fractures.⁷,⁹,¹⁰

From a vascular standpoint, the average distance between the descending genicular artery and superomedial pole of the patella is around 13.5 mm.¹¹ It has been hypothesized that patellar fractures could be secondary to devascularization of the patella from concurrent medial (MPFL, medial arthrotomy) and lateral-sided surgery (lateral retinacular release), or because of excessive periosteal dissection near the superior aspect of the patella.⁷,¹²,¹³,¹⁴,¹⁵

Fithian and Gupta described one patient and Thaunat and Erasmus described three patients with recurrent patellar dislocation and a fracture from the medial bone bridge on the patella through the MPFL fixation area.¹²,¹⁶ Compared to other reported patellar fractures, this fracture pattern has been unique in that recurrent patellar dislocation was associated with these medial-sided patellar fractures. In theory, when isolated MPFL reconstruction is performed in the presence of patellofemoral anatomic risk factors such as trochlear dysplasia or increased tibial tuberosity-trochlear groove distance, the lateralizing forces could put significant stress on the MPFL graft. When the patella would ultimately redislocate owing to significant lateralizing forces, the MPFL graft would pull on the medial bridge of the patella, causing patellar fracture and repeat dislocation.

Dhinsa et al¹⁷ reported two cases of patellar fracture through drill holes, after MPFL reconstruction where patellar fixation was performed using suture anchors.

A superior pole avulsion fracture of patella after suture anchor fixation of MPFL has been reported.⁷

Mikashima et al¹⁸ reported two patellar fractures in a group of 12 patients when the graft was passed through a 4.5-mm patellar bone tunnel. In another group of 12 patients where the graft was sutured to the anterior aspect of the patella, there were no such fractures.

Thus, most described patellar fixation techniques, including tunnels and anchors, could lead to patellar fractures.

Parikh and Wall⁷ categorized patellar fractures after MPFL surgery into three types (Figure 40.1).

Type I fractures are transverse fractures that occur through patellar tunnels or suture anchor drill holes. The cortical breach, especially on the dorsal/anterior aspect of the patella, could act as a stress riser when subjected to tensile forces. These fractures, if displaced, are treated like classic transverse patellar fractures using tension-band fixation principles.

Type II fractures are proximal pole fractures or sleeve avulsion fractures that are similar to quadriceps tendon avulsion from the superior aspect of the patella. It has been hypothesized that these fractures could be secondary to vascular compromise around the proximal pole of the patella from combined dissection on the medial and lateral side of patella. They could also be caused by excessive periosteal dissection or suture anchors/drill holes that are placed too proximally in the patella. These fractures are treated like quadriceps tendon tear by suturing the tendon to the patella using suture anchors or bone tunnels.

Type III fractures are through the medial-sided bone bridge on the patella and are associated with recurrent lateral patellar dislocation. Treatment of these type III fractures consists of open reduction and internal fixation of the bone fragment using screws and/or suture anchors, if the piece is large and displaced.

Table 40.1 lists indications and contraindications for patellar fracture repair.

Patients present with a history of either a fall causing a direct hit on the anterior knee or an indirect twisting injury to the knee. Spontaneous fracture without any injury is rare.

Patients may have a history of stiffness and limited knee flexion after patellar stabilization surgery. A fall or sudden, forceful flexion or hyperflexion of the knee would lead to quadriceps avulsion fracture (type II fracture).

Usually, type I and type II patellar fractures would occur within the first 3 postoperative months after patellar stabilization surgery. However, type III fractures could present late (reported range, 1-7 years) after the initial surgery and usually have a history of significant fall or sports injury.¹²,¹⁶