Bing Yin, Shilun Li, and Zhaoyu Chen

A total of 69 patients with 69 patellar fractures were investigated in the China National Fracture Study (CNFS). The fractures accounted for 3.91% of all patients with fractures and 3.76% of all types of fractures. The population-weighted incidence rate of patellar fractures was 13 per 100,000 population in 2014.

The epidemiologic features of patellar fractures in the CNFS are as follows:

• More males than females

• More right-side injuries than left-side injuries

• The highest-risk age group is 15–64 years

• Injuries occurred most commonly via slips, trips, or falls

Patellar Fracture by Sex

A total of 11,332 patients with 11,378 patellar fractures were treated in 83 hospitals of China over a 2-year period from 2010 to 2011. All cases were reviewed and statistically studied, accounting for 2.73% of all patients with fractures, and 2.63% of all kinds of fractures, respectively; of a total 11,332 patients, there were 279 pediatric patients (290 patellar fractures) and 11,053 adult patients with 11,088 fractures.

Epidemiologic features of patellar fractures are the following:

• More males than females

• More left-side than right-side fractures

• The high-risk age group is 41–50 years, the same age group for males, while for females the high-risk age group is 51–60 years

• The most common fracture type is type 34-C, the same fracture type for both males and females

• The most common fracture group is group 34-C1, the same fracture group for both males and females

Patellar Fractures by Fracture Side

Transverse fractures of the patella and avulsion fractures of the superior and inferior poles are often caused by indirect mechanisms, seen in hyperflexion of the knee due to sudden tensile force of the quadriceps. Comminuted, vertical, and oblique fractures are more clearly associated with direct mechanisms, such as from direct blows and crush injuries. The energy of the impacting force, which results in comminuted fractures of the patella, may also cause damage to the articular cartilage of both the patella and the femoral condyles.

Patellar fractures usually present with a history of trauma. Physical examination reveals ecchymosis over the anterior aspect of the knee, hemarthrosis, swelling, tenderness, and partial to complete limitation of knee joint mobility. If fracture displacement is present, then a gap between fragments and retropatellar crepitus can be noted. Radiographs of anteroposterior (AP) and lateral views of the knee joint usually confirm the diagnosis. If vertical or border fractures are clinically suspected, an axial view or computed tomography (CT) scan of the knee joint may be indicated. Magnetic resonance imaging (MRI) is necessary for comminuted patellar fractures due to damage of the articular cartilage of both the patella and the femoral condyles. The diagnosis of a vertical fracture of the patella should be differentiated from that of a patellar variation. Vertical fractures present with a clear trauma history, positive physical examination findings, fracture lines, and a jagged surface of the broken ends: this is in contrast to variations of the patella (binary or trinary patella), which are known to have wide gaps, smooth broken ends, or mild to absent physical signs/syndrome. In addition, the thin layer of cortex may be exposed.

If the fracture is displaced by less than 3 mm, or the intra-articular step-off is less than 2 mm, then the fracture may be treated with a nonoperative modality. However, for elderly patients, operative management with rigid internal fixation should be considered to allow early postoperative mobilization and to minimize knee fibro-adhesive scar formation. In young healthy patients, patellar fractures can be treated with immobilization followed by casting, external fixation devices, and tuck loop fixation, etc. Surgical treatment is advised for displaced fractures, which are defined as fractures that have an intra-articular step-off of more than 2 mm or a separation of more than 3 mm. Additional caution should be taken for pediatric patients with patellar fractures when considering an operative approach because operative procedures have the potential to damage growth cartilage, and subsequently impact the growth and development of the patella. Because children have a greater potential for tissue bone repair and molding, fractures with marked displacement, or even with a comminuted pattern, should initially be treated with nonoperative management. Partial surgical removal of the patella should be considered for severe comminuted fractures that are not able to be anatomically reduced. Severe comminuted patellar fractures in elderly patients should be treated with primary total surgical removal of the patella.

Based on the fracture location, pattern, and presence of displacement, Regazzoni classified patellar fractures into three types, with three subgroups for each fracture type:

• Type A: Vertical fracture: A1, with no displacement; A2, with displacement; A3, comminuted.

• Type B: Transverse fracture: B1, avulsion fracture of the superior and inferior poles of the patella (< 5 mm in diameter of the superior pole, < 15 mm in diameter of the inferior pole); B2, simple; B3, comminuted.

• Type C: Comminuted fractures: C1, with no displacement; C2, with displacement of less than 2 mm; C3, burst fractures with displacement of more than 2 mm.

Clinical Epidemiologic Features of Patellar Fractures by the Regazzoni Classification

A total of 11,088 adult patellar fractures were treated in 83 hospitals of China over a 2-year period from 2010 to 2011; all cases were reviewed and statistically studied. Their epidemiologic features are as follows:

• More males than females

• The most common fracture type was Type B (Transverse)

From an anatomic point of view, four factors that result in the displacement of clavicle fractures can be summarized as follows:

1. The proximal fragment is typically displaced upward because of the pull of the sternocleidomastoid muscle.

2. Although there may be some upward movement of the clavicle due to the pull of the trapezius muscle, the major displacement is caused by the downward pull of the upper extremity, since most patients would not be able to withstand the weight of the upper arm due to the pain.

3. However, if the upward pull of the trapezius muscle surpasses the weight of the upper arm, or patients are using a sling to support the arm, then the distal fragment may also be displaced upward.

A total of 89 patients with 89 clavicle fractures were investigated in the CNFS. The fractures accounted for 5.05% of all patients with fractures and 4.86% of all types of fractures. The population-weighted incidence rate of clavicle fractures was 16 per 100,000 population in 2014.

The epidemiologic features of clavicle fractures in the CNFS are as follows:

• More males than females

• More left-side injuries than right-side injuries

• The highest-risk age group is 15–64 years

• Injuries occurred most commonly via slips, trips, or falls and traffic accident

Clavicle Fracture by Injury Side in CNFS

A total of 18,502 patients with 18,587 clavicle fractures were treated in 83 hospitals of China over a 2-year period from 2010 to 2011. All cases were reviewed and statistically studied, accounting for 4.46% of all patients with fractures and 4.30% of all kinds of fractures, respectively. Among 18,502 patients, there were 4,424 pediatric patients (4,430 clavicle fractures) and 14,078 adult patients with 14,157 clavicle fractures.

Epidemiologic features of clavicle fractures are as follows:

• More males than females

• More left side than right side fractures

• The high-risk age group is 0–5 years, the same age group for females, while for males the high-risk age group is 41–50 years

• The most common fracture type is Type B