An 18-Year-Old Female Athlete Presenting with Knee Pain Following a Basketball Game and Diagnosed with Bilateral Patellar Stress Fractures

Background

The patella is a sesamoid bone that functions as a lever arm for knee extension, augmenting the quadriceps force and improving the extensor mechanism of the knee [1]. Fractures of the patella account for approximately 1% of all fractures [2], and they occur more commonly in males [2]. Patellar fractures can be direct, often a result of a traumatic injury, or indirect, often a result of failing under tension as eccentric forces overpower the mechanical properties of the bone [2]. Fractures of the patella can also be periprosthetic following total knee arthroplasty [2]. Stress fractures of the patella are rare [2], the first case of which was reported in 1943 by Müller [3] in military recruits and later by Devas [4] in runners. Bilateral patellar stress fractures occur even less often, although there have been similar cases of bilateral patellar stress fractures reported in a collegiate gymnast [5] and a young basketball player [6].

The most common presenting complaint in a patient with a patellar stress fracture is anterior knee pain [5,7]. This is also the most common concern among pediatric athletes [8], making it difficult to diagnose patellar stress fractures in young athletes early in their course. Populations at a higher risk of stress fractures include females, athletes engaging in high-impact exercise, and younger individuals [9]. A thorough history, in combination with imaging when indicated, can help physicians properly diagnose patellar stress fractures at earlier stages [10]. Once the diagnosis is confirmed, treatment may include either nonoperative management or surgical intervention dependent on a variety of factors, such as the location, extent, and displacement of the stress fracture, as well as the patient’s activity level [2,5]. Identifying diagnostic tools that detect patellar stress fractures early in their progression and solidifying the best course of management following diagnosis are active areas of investigation [10].

In this case, we describe an 18-year-old female athlete presenting with knee pain after playing basketball and diagnosed with bilateral patellar stress fractures.

Case Report

PROCEDURE:

The patient was placed supine on a standard operating room table. A diagnostic arthroscopy was first performed, which demonstrated a 2-mm displacement of the left inferior pole of the patella. Subsequently, an open approach was performed, including a midline incision centered over the patella. Unlike traumatic fractures where the retinaculum is often disrupted, it was found to be intact in this case, with the only pathology found being the inferior pole fracture. Also different from an acute patella fracture, the fracture fragment ends were sclerotic. The ends were debrided with a rongeur and 15 blade to augment the biologic healing response. A pointed reduction clamp was then used to reduce the 2 segments. Articular surface reduction was confirmed both fluoroscopically and arthroscopically.

A Kirschner wire (K-Wire) was then placed perpendicular to the fracture and parallel to the joint surface under fluoroscopic guidance and a 4.5-mm partially-threaded cancellous cannulated screw was placed. The articular surface was visualized arthroscopically to confirm no penetration of the articular surface with drilling or screw placement. Given the small size of the distal fragment, as well as stability of the patten given the intact retinaculum, it was felt that 1 screw would provide sufficient fixation. Postoperatively, the patient was made weightbearing as tolerated in a brace, locked in extension, and recommended to use a bone stimulator, given the preoperative stress fracture.

Two months postoperatively, radiographs of the left knee demonstrated appropriate positioning of the screw with early ossification at the fracture site. However, the patient reported anterior knee pain on her right side that was similar to her prior symptoms on the left. X-ray (Figure 2A) and MRI (Figure 2B) images were subsequently obtained, which revealed a stress reaction in the inferior pole of the right patella, but a discrete fracture was not appreciated. Nonoperative management was recommended at that time, as the patient was still recovering from her initial surgery. At a follow-up appointment 6 months following the index procedure, the patient reported persistent anterior knee pain that had not abated despite extensive non-operative care. Additionally, repeat imaging did not show any decrease in the stress reaction.

Based on the persistent nature of her symptoms and the patient’s plan to play basketball in college the next year, prophylactic fixation of the right patella was recommended to improve pain and minimize the risk of subsequent fracture. Accordingly, the same procedure as described above was performed.

Two months following right patellar fixation, radiographs of her bilateral knees demonstrated both screws in good position with apparent fracture healing (Figure 3). However, the patient felt continued left knee pain along the inferior aspect of the patella near the screw insertion site, preventing her from returning to play. Due to persistent pain severity, the patient was recommended to complete a bone scan, which revealed increased uptake over bilateral patellae consistent with her prior surgeries. It was decided that hardware replacement of the left knee with a headless compression screw below the cortical surface of the patella would alleviate patellar tendon irritation while preventing refracture. The procedure was carried out, which included removal of the prior screw and placement of a 4.0-mm headless screw.

One month following left patellar screw replacement, imaging showed appropriate hardware placement with maintained osseous alignment (Figure 4). Six months following the screw replacement procedure, the patient was able to fully flex and extend both knees, and the patella was stable on exam. One year following the left patellar screw replacement surgery, the patient was fully recovered and able to compete in collegiate with a history of persistent high-impact exercise. This case also highlights the benefit of consistent and appropriate imaging for early detection and treatment of patellar stress fractures.

This case is unusual as the patient had been symptomatic for at least 1 month prior to her presentation with a patellar fracture. Two similar cases of young athletes presenting with bilateral patellar stress fractures also described patients who experienced bilateral anterior knee pain for months prior to their diagnosis [5,6]. One of those patients was a female collegiate basketball with minor symptoms that did not require additional treatment. She was able to compete in her final year of college basketball without any symptoms or further injuries.

Discussion

This case report demonstrates that bilateral patellar stress fractures can be preceded by bilateral anterior knee pain for a variable amount of time. Additionally, they can also present gymnast who was also initially given a diagnosis of patellar tendonitis before a patellar stress fracture was found on MRI [5]. However, in that case, the patient’s stress fractures had not progressed to full fractures and nonoperative treatment was initiated. Our patient presented with a displaced inferior pole fracture of the left patella, and surgical fixation was agreed upon as the best option for full recovery before continuing with high-impact exercise.

Stress fractures of the patella have been reported to occur in young athletes [6,11,12] and in patients with cerebral palsy [13]. In general, women are at increased risk for stress fractures [14]. Some possible explanations in the literature for this imbalance include unfavorable biomechanical conditions during running caused by differences in bone anatomy, reduced muscle mass, and decreased bone density in females [14]. However, female athletes with normal weight and bone health are less likely to develop stress fractures, demonstrating that sex is less important than overall physical shape and condition [14].

The most common presenting concern in a patient with a patellar stress fracture is anterior knee pain [5,7]. This is also the most common concern of pediatric athletes [8], making it difficult to diagnose patellar stress fractures early when the differential diagnosis for anterior knee pain is broad. A thorough history is required to learn the duration of a patient’s knee pain, in combination with physical examination, which can help guide diagnosis of patellar stress fractures [8]. If a stress fracture is suspected, initial work-up should include anteroposterior, lateral, and merchant radiographs [10,15] and repeat radiographs should be obtained in patients with prolonged anterior knee pain 1 month after primary radio-graphs [10]. However, at an early stage, plain radiographic signs are minimal [10]. More accurate and sensitive investigation tools include bone scans and MRI [16]. Bone scans may be abnormal as early as 6 weeks prior to the appearance of conventional radiographic changes [17], providing early detection and subsequent treatment in bones at risk of progressing to complete fracture [18].

Given the small number of reported cases, it is difficult to make definitive treatment recommendations for patellar stress fractures. Nonoperative treatment involving rest and immobilization can be sufficient in the treatment of some stable non-displaced fractures (less than 2 mm of dislocation), and may be the right option for patients who do not require an immediate return to activity [19,20]. However, since the patella is a bone at high risk for nonunion or delayed union, any sign of a displaced fracture suggests surgical fixation is a better treatment route [21]. In athletes, surgical fixation may provide better outcomes for continuation in sports after recovery [21] and may provide a quicker return to activity [12,15]. Modified tension band wiring or lag screw fixation are 2 commonly accepted surgical techniques to treat patellar fractures [22]. However, even with proper surgical technique, persisting anterior knee pain after surgery, hardware failure, and postoperative hardware-related irritation are not uncommon [23].

Conclusions

This case report demonstrates that, although stress fractures of the patella are rare, and bilateral stress fractures may be even more rare, this condition can present with pain and a history of high-impact exercise. This report highlights the importance of investigating a broad differential given a presentation of anterior knee pain. Additionally, it shows the effect that consistent and appropriate imaging can have on early detection and treatment of patellar stress fractures. Challenges remain in narrowing down the differential diagnosis quickly enough to detect and treat patellar stress fractures early in their course and determining the best treatment option for a patient with a patellar stress fracture.