Clinical Ecacy of a Micro-locking Plate Vertical or Parallel Technique for Treatment of Dubberley B-type Capitellar Fractures

Objective To evaluate the clinical ecacy of micro-locking plate through vertical or parallel for Dubberley B-type A retrospective analysis was performed in 24 patients (seventeen males and seven females, with an average age of 44.9 years, range from 19 to 75 years) with capitellar fractures that were treated with micro-locking plate using vertical or parallel technique between January 2016 to January 2019. The inclusion criteria include closed capitellar fracture, anterior elbow joint movement normal before injury, recent capitellar fracture with times of injury within past 3 weeks. Fractures classied according to Dubberley included 4 cases of type IB, 8 cases of type IIB and 12 cases of type IIIB. Radiographic evaluation was performed. Surgery time, blood lose, range of motion of the elbow, forearm rotation and complications was recorded. Elbow joint function was evaluated by Mayo Elbow Performance Score (MEPS). had excellent, 5 (20.8%) patients had good and 1 (4.2%) patient had fair. None of the 24 patients suffered vascular or nerve injury. One patient showed supercial infection, which terated with surgical dressing. The micro-locking plate accroding to or technique is an excellent method for Dubberley B-type capitellar fractures.


Introduction
Fracture of the capitulum of the humerus is a rare intra-articular fracture of the distal humerus and comprising approximately 0.5-1% of elbow fractures [1].The mechanism of injury typically includes falling on the extended arm, which causes direct axial pressures that is transmitted through the joint, leading to coronal shear fracture of the capitellum [1]. This type of fracture can easily be misdiagnosed by normal X-ray examination due to the location of the fracture line on the frontal plane and the shear stress of the radial head acting on the capitulum [2]. In recent years, with the development of digital imaging and computed tomography, capitellar fractures can be accurately evaluated [3]. Currently, open reduction and internal xation are the gold standard for treating this type of injury [4]. Bryan and Morrey classi cation has been widely used to classify capitellar fractures [5]. Type 1 (Hahn-Steinthal fracture) includes coronal shear fractures, involving a thick hemispherical fragment. Type 2 (Kocher-Lorenz fracture) is a cartilaginous 'thin' fragment. Type 3 is comminuted, involving multi-fragmentary. Type 4 was added by McKee et al to describe capitellar fractures that extend medially to involve most of the trochlea [6]. Recently, Dubberley et al. described a new classi cation system to guide surgical management and provide prognostic value [7]. Type 1 fracture of capitellum involves the capitellum with or without the lateral trochlea ridge. Type 2 fracture is single fragment of capitellum and trochlea. Type 3 fracture describes separate fragments of capitellum and trochlea. Each type is further classi ed to A (no posterior comminution) and B (posterior comminution).
At present, various treatment methods have been proposed for such fractures. But there is no a nal conclusion. Such fractures present insu cient bone for internal xation, making surgical treatment di cult [2,8]. Several studies have recommended Kirschner wires and bio-absorbable screws for capitellar fractures [8,9]. However, Kirschner wires and bio-absorbable screws fail to provide su cient xation strength, leading to less favorable results. Most studies recommended that intact bone fractures can be generally treated by using a screw for xation [10,11]. David E Ruchelsman [12]reported that sixteen skeletally mature patients with a closed capitellar fracture treated with buried cannulated variable-pitch headless compression screws through an extensile lateral exposure. The mean Mayo Elbow Performance Index score was 92 ± 10 points, with nine excellent results, six good results, and one fair result. A randomized controlled trial conducted by Tengbo Yu [13]who compared the Herbert screw xation between the lateral approach and anterolateral approach in 26 patients and demonstrated that both lateral approach and anterolateral approach with Herbert screw internal xation are suitable for coronal shear fractures of capitellum with satisfactory early outcomes. However, screw internal xation is not suitable in cases of Dubberley B-type fractures involving incomplete capitulum fracture of the humerus behind the lateral condyle [7]. Because the fracture fragments provides a limited channel for the screw position in such cases, so screw xation are in ineffective. Therefore, there is still an unmet need for developing a suitable alternative xation approach for this type of fracture. Previously, we tested the use of a microplate and single plane xation [14]. In subsequent follow-up, however, cases were found to have internal xation failure and fracture displacement. Therefore, we presented a technique for the internal xation of capitellar fractures using the micro-locking plate with vertical or parallel techniques. We use generic questionnaires to evaluate outcome scores of surgical techniques. The Mayo Elbow Performance Score (MEPS) is a widely used measure index to evaluate clinical outcomes for a variety of elbow disorders, which was introduced in the year 1985 by Morrey et al. [15]. This scoring system was modi ed to evaluate the results of treatment of elbow fractures and dislocations by Broberg and Morrey [16]. It consists of assessment of arc of motion, stability, pain, and a patient rating of daily function.
In this study, patients with capitellar fractures that were treated with vertical or parallel locking plate techniques were retrospectively reviewed. The purpose of this study was as follows. First, we intended to describe vertical or parallel locking plate strategy for the treatment of capitellar fractures. Second, we aimed to evaluate the e cacy and feasibility of vertical or parallel locking plate techniques in treating capitellar fractures. Third, we tried to provide more evidence to guide the management of capitellar fractures based on the surgical skills and our signi cant results.

Inclusion and Exclusion Criteria
The inclusion criteria included: (i) diagnosis of closed capitellar fracture with anterior elbow joint movement normal before injury; (ii) vertical or parallel locking plate techniques for the treatment of capitellar fracture; (iii) postoperative follow-up ≥ 12 months; and (iv) retrospective study. Exclusion criteria were as follows: (i)pathological fracture; (ii) severe osteoporosis; (iii) those who could not be contacted ; (iv) individuals who refused follow-up ;and (v) those with incomplete clinical data before and/or after surgery.

Patient Data
A retrospective study reviewed a consecutive series of 24 patients with capitellar fractures who sustained at our center between January 2016 and January 2019. Plain radiographs and computed tomography (CT ) scans were obtained immediately after the injury, and were reviewed by two experienced orthopedic surgeons. Patient demographic characteristics, including age, gender, side of injury, mechanism of injury, type of fracture (Dubberley classi cation system [7]), time from injury to surgery and xed technology, are shown in Table 1. The study was reviewed and approved by the Ethics Committee of Honghui Hospital, Xi'an Jiaotong University. All patients provided signed informed consent. Surgical Strategy Preoperative planning shows in Fig. 1. The patient was situated in a supine position with the affected limb positioned alongside the body or to the side of the operating table after general or brachial plexus anesthesia. The stability of the elbow joint was checked. The classic lateral Kocher approach was used in all cases. An incision was made from the lateral to the posterolateral side of the distal humerus, 1 to 2 cm below the capitulum of humerus and 5 to 7 cm above the articular surface of the proximal elbow joint. After exposing the lateral side of the distal humerus, the extensor and the full layer of the articular capsule in front of the elbow joint were reversed from the lateral side to the medial side of the distal humerus. The interosseous nerve is usually not affected and therefore does not require dissection. The elbow joint was exed 30° to 45° and a medium Hohmann hook was inserted into the anterior articular capsule below the medial column of the humerus. This did not involve release of the radial collateral ligament. Soft tissue and hematoma lling the capitulum fracture and trochlear of the humerus were removed. The reduction was con rmed visually and radiographically. A 1.0 mm Kirschner wire or 2.0 mm screw (Tianjin Zhengtian Medical Instrument Co., Ltd.) was used to x the distal humeral joint from outside to inside. A "T" shaped locking micro-plate (Tianjin Zhengtian Medical Instrument Co., Ltd.) was xed to the top of the articular surface of the capitulum of the humerus. The plate was positioned on the lateral side of the humeral trochlea close to the top of the coronary sulcus at the junction of the articular surface of the capitulum of humerus. Another "T" locking micro-plate is attached to the lateral (Fig. 2) or posterior (Fig. 3) side of the lateral condyle of the humerus to support and x capitellum. Elbow exion was monitored during the operation to ensure absence of abnormal activity, blockage or friction. All patients underwent intraoperative C-arm X-ray uoroscopy to con rm that the fracture was properly repaired and the screw length was correct. The wound was ushed with isotonic saline and elbow joint exion and extension functions were checked to ensure that excessive internal xation would not result in movement blockage. Ulnar collateral ligament was repaired if damage was indicated by unstable valgus stress on the elbow. The surgical site was completely drained and the wound was sutured layer by layer. The elbow joint braced at an angle of 90°.

Postoperative Management
Antibiotics were administered 30 minutes before and 24 to 48 hours after surgery. Oral indomethacin was administered starting on the 2nd day post-surgery to prevent heterotopic ossi cation. The elbow joint brace maintaining 90° elbow exion lock was released 2 to 3 days after surgery to permit active and passive extension and exion activity from 60° to 110°. Range-of-motion was increased gradually after 2 weeks. Rehabilitation exercise for forearm rotation function was then started. Fracture position and healing were checked by X-ray examination at 4 weeks. Elbow joint extension and exion range were increased and rehabilitation exercises for forearm rotation function were enhanced. Following con rmation of fracture healing at 8 to 12 weeks post-surgery, upper limb weight-recovery function training was gradually introduced.

Outcome Measures
The Mayo Elbow Performance Score (MEPS) The MEPS was used to evaluate postoperative recovery of Elbow function in anadult population. The MEPS score system mainly includes 4 aspects as arc of motion, stability, pain, and a patient rating of daily function. The score standard had a maximum of 100 points (best possible outcome). A total score < 60 is considered a poor score, 60-74 fair, 75-89 is good and 90-100 excellent.

Statistical analysis
Statistical data were processed using GraphPad Prism7.0. Data were expressed as mean ± standard deviation. Comparison between two groups was performed using independent sample student's t-test. Categorical data was performed using X 2 test. P < 0.05 was considered statistically signi cant.

General Results
There were 24 patients with an average age of 44.9 years (range, 19-75 years) in this study. All fractures were closed. According to the Dubberley classi cation system, there were 4 patients with type IB fractures, 8 patients with type IIB fractures, 12 patients with type IIIB fractures. The mean time from injury to surgery was 6.3 ± 3.1 days (range, 2-15 days). The average surgical time was 68.1 ± 11.5 minutes (range, 50-90 minutes). The mean blood loss was 75.2 ± 26.5 mL(range, 40-120 mL). (Table 1 ) Follow-up The patients were followed up after operation by questionnaire survey, medical history review, and outpatient follow-up. The mean followed-up time was 19.6 ± 7.7 months (range, 12-36 months).

Radiographic Improvement
There were 18 cases exhibiting anatomical fracture reduction and 6 cases with functional reduction ( less than 2 mm displaced) accoding to the radiographic review.

Clinical Improvement
The average clinical healing time for fractures was 11.2 ± 3.2 weeks (range, 8-20 weeks). Fracture united in all patients although two patients had showed slight delay in union (fracture united after 18 weeks). (Table 1 ) Functional Evaluation

Complications
None of the 24 patients suffered vascular or nerve injury. One patient showed super cial infection, which terated with surgical dressing. No instability was observed in the medial stress test. (Table 1 )

Discussion
The capitulum is located on the lateral side of the distal humerus and protrudes forward and downward. It functions largely to maintain the stability of the elbow joint [17,18]. Capitellar fracture, with or without humeral trochlea fracture, is intra-bone. Most displaced fracture blocks have no obvious soft tissue attachment and cannot be reset by ligament reduction techniques. It is generally accepted that surgical treatment is superior to non-surgical treatment with respect to a number of clinical outcomes [19,20].
During surgery, the comminuted small bone can and should be used to reset and x the fracture rather than dissecting and discarding it. However, when xation is unreliable it should be removed in order to avoid mechanical blockage of joint activity. Small bones and associated soft tissues such as articular capsules feature good blood supply, and post-surgery they participate in bone repair and accelerate fracture healing. Conversely, a small damaged fracture block exposes the fracture surface directly to the articular cavity, which can lead to traumatic arthritis, ossifying myositis and even joint instability that eventually can severely affect elbow joint function [20]. Ashwood et al. considered it very important to maintain rmness following fracture reduction, thus elbow joint small cartilage blocks should be maintained as required for reduction and internal xation during surgery [21]. Jupiter et al. reported that elbow joint function at the humeral distal frontal plane was correlated with the recovery of normal anatomy [22]. In the current study, 24 patients with capitellar fractures were treated by vertical or parallel micro-locking plate technique. We found some advantages of this approach including stable xation, early resumption of elbow joint activity and good functional recovery.
Selection of surgical approach to capitellar fractures treatment.
There is currently no uniform, standard guide to selecting the optimal surgical approach to treating capitular fractures. Singh et al. describes surgeries including the anterior approach to the elbow and the posterior approach to the ulnar olecranon [23]. However, the classic posterior lateral Kocher approach is used for treating most distal articular surface fractures of the humerus. In our view, the choice of surgical approach depends largely on the shape of the fracture, the direction of displacement and the surgeon's familiarity with a given approach. The anterior approach of the elbow joint is complicated and includes risk of damage to blood vessels and nerves [24]. The posterior approach of the ulnar olecranon can reveal posterior condyle fracture but entails more surgical trauma and increased probability of heterotopic ossi cation in the elbow joint [22]. The posterolateral Kocher approach of the elbow joint provides good exposure, relatively decreased trauma, increased safety and fewer postoperative complications [24,25]. Sano et al. reported good clinical results using a lateral approach for fracture reduction and internal xation inpatients with distal humeral frontal plane fractures [26]. For all 24 patients in the current study the classic lateral Kocher approach resulted in good exposure, reduction and xation. No other surgical incisions were made and no obvious elbow instability was observed.
It is di cult to compare clinical results of different treatment methods for capitellar fractures, largely due to low incidence. However, additional factors also contribute to the di culty of assessing outcomes. Young patients often suffer high energy injuries that usually feature combined composite injury of elbow joint structure [24]. Due to severe crushing of the fracture the joint remains unstable after simple bone structure repair. In elderly patients, most often with low energy injuries, fractures are not severely crushed but local compression and poor bone condition result in loosening of internal xation and displacement of fractures [1]. If the small bones of the articular surface are preserved during fracture comminution, internal xation is di cult and the fracture block is easily loosened after surgery [18]. It becomes a block in the joint that affects activity. If, however, the small bones of the articular surface are not preserved the shape of the ankle joint and the ulnar joint surface will be altered and the humeroradial and ulnar joints will not match. This will result in an unstable elbow joint and lead to traumatic osteoarthritis [18]. In our view, surgery to treat capitellar fractures with or without trochlear fracture should aim to restore a uniform match of the humeroradial and humeroulnar joint, strongly x the fracture, maintain xation and joint stability and restore maximum joint activity range and function. Achieving these aims depends critically on choosing the appropriate approach to internal xation.
Fixation method and positioning.
Independent screw xation is commonly used for internal xation and is associated with good outcomes in previous studies [23,27,28]. However, it is an appropriate technique for simple fractures, such as no bone loss present or posterior comminution (Dubberley Type 1A and 2A) [28]. Sano et al. report that in the case of a capitulum of the humerus fracture with a thin fracture block, the screw thread will not fully pass the fracture line and function as a lag screw if inserted from the rear. If the fracture block is too small, the screw may damage the joint surface or cause the bone to split. Additionally, if the fracture block is too small it is di cult to seat the screw thread in the cartilage [26]. It has also been certi ed that the screw will damage the articular cartilage leading to cartilage necrosis or osteolysis and affect elbow joint function [21].However, this ensures only the stability and rmness of the frontal plane but not the effective xation of a comminuted posterior condyle or incomplete humeral external condyle fracture that would permit early functional rehabilitation exercises. Studies involving greater numbers of patients and extended follow-up show that distal frontal plane and anti-sliding plate treatments do not guarantee stability and rmness of frontal plane fractures nor ability to perform early functional exercises for patients with osteoporosis [29] It therefore remained to identify a suitable approach to enhancing the stability of xation. So, we put forward vertical and parallel techniques. First, we used a Kirschner wire and screw to x the fracture. Then, a micro-locking plate was placed on the posterior side of the humerus for support and xation of the lateral and posterior humerus. Finally, a micro-locking plate was used in the front of fracture for anti-glide. Our technique has several advantages over previous methods of xation. Firstly, the 1.5 mm and 2.0 mm micro-locking system screws can meet the requirement for multiple screws on the fracture block, and the small screws can replace the Kirschner wire. Secondly, the locking plate-screw-fracture block can be completely integrated into one body in which loosening of the screw and bone plate breakage are unlikely [30]. The advantage of this approach is particularly apparent for patients with comminuted fracture or osteoporosis, requiring support and xation that restores the original length. Thirdly, two-plane internal xation of the distal end of the humerus using a microlocking plate not only achieves front side anti-slip and lateral & posterior support, but also effectively covers a crushed fracture thereby guaranteeing stability and rmness and also maintaining stability and compatibility of the articular surface after reduction. It affords maximal xation stability that promotes early rehabilitation of elbow joint active and passive exion and extension exercises to fully restore elbow joint function. The minimal amounts of built-in material reduce irritants otherwise adversely affecting later functional exercises. Follow-up of the 24 patients in this study showed stable internal xation, no displacement and good position of the fracture. All of the patients displayed early recovery, with satisfactory elbow function.

Limitations
The study was limited by the small number of cases (N = 24), some bias in patient selection, short follow-up period and lack of biomechanical studies. Whether or not this approach can be widely applied in the clinic must be further determined in larger studies enrolling greater numbers of patients with longterm follow-up and biomechanical assessments.