A Novel Technique Utilizing a K-wire to Reduce Prosthetic Overlengthening During Radial Head Arthroplasty

INTRODUCTION Radial head and neck fractures account for one-third of all elbow fractures, with 85% of all radial fractures occurring in young and active patients.1 When treating radial head and neck fractures, proper restoration of joint anatomy and biomechanical load distribution on the capitellum is critical for patient recovery and reducing postoperative compilations. Open reduction and internal fixation (ORIF) is the procedure of choice when diagnosing simple radial head fractures. However, ORIF may be highly challenging in cases of complex comminuted fractures. Therefore, radial head arthroplasty is utilized to treat complex proximal radial fractures. Implantation of a radial head prosthetic more than 2 mm compared with the anatomic radial head significantly increases contact pressure between the radial head and the capitellum and disturbs the ulnohumeral mechanics.2 This can lead to the rapid erosion of the capitellum, loss of elbow motion, pain, early onset osteoarthritis, clinical failure, and revision. Overlengthening of the radius occurs when a prosthetic is implanted such that the final height of the prosthetic exceeds the previous height of the resected native radial head. The increase in the radius length causes an increase in contact forces on the capitellum that exceeds normal physiological levels.2 The prevalence of overlengthening during radial head arthroplasty has not been definitively calculated, as it has not been investigated in a large study, and it is difficult to diagnose utilizing postoperative x-ray. However, retrospective studies have estimated overlengthening accounts for between 13% and 23% of all radial revisions, making overlengthening a common complication of the procedure.3 The reported rates likely underestimate the prevalence of overlengthening as it may go unrecognized in some patients. Overlengthening is a detrimental complication for patients during arthroplasty, making it clinically essential to develop guidelines and procedures to reduce the incidence of overlengthening. The importance of selecting an appropriately sized prosthetic for radial head arthroplasty is generally recognized. There is a preference to slightly undersize the implant, particularly if between sizes, as overstuffing is substantially detrimental to less favorable clinical results. However, few intraoperative guidelines are established to guide the proper dimensioning of the prosthetic. Van Riet et al4 described the proximal edge of the lesser sigmoid notch as a bony landmark that can guide surgeons in radial stem sizing to prevent overlengthening. The proximal portion of the lesser sigmoid notch can be aligned with the proximal surface of the radial head implant and confirmed with fluoroscopy. However, in some cases, the lesser sigmoid notch is hard to visualize, especially after trial implantation. Doornberg and colleagues examined the relationship between the radial head and the proximal edge of the lesser sigmoid notch. They found that the radial head was 0.9 mm more proximal than the most proximal edge of the lesser sigmoid notch and recommended that the implant height should be equal in height to the lesser sigmoid notch.5 Even with established intraoperative landmarks that assist with prosthetic dimensioning, proper sizing of radial head arthroplasty remains a clinical challenge that can lead to poor outcomes when complicated by overlengthening. This study describes a novel procedural technique that utilizes K-wire implantation at the proximal edge of the lesser sigmoid notch to help guide the sizing of radial head prosthetics during arthroplasty. TECHNIQUE The patient is positioned supine with the injured arm on a hand table or draped over the chest. A variety of approaches including lateral (Kocher, Kaplan, or EDC split) or posterior (Boyd) approach are utilized according to the pattern of injury or surgeon preference. The ligamentous-capsular layer is released or incised in a longitudinal or Z-shaped manner, intending to repair it after prosthetic implantation. Disruption of the lateral ulnar collateral ligament should be avoided. After that, the radius and capitellum are exposed. Bone fragments of the radial head are removed. If needed, a provisional neck cut is performed. A 0.062 Kirschner wire is transversely placed at the level of the subchondral bone of the proximal edge of the lesser sigmoid notch. The wire should be advanced carefully on oscillate and be placed up to the far cortex of the ulna without penetrating the cortex. Intraoperative fluoroscopy is used to assess positioning to ensure the wire is parallel to the joint line (Fig. 1). Using the K-wire as a reference, a prosthetic sizer is placed to mark and excise the required portion of the radial neck based on the preferred stem length. The radial canal is then broached, and the trial is implanted (Fig. 2). The K-wire is utilized as the proximal border for the prosthesis. The implant should touch the K-wire but not bend it (Fig. 2). A radiograph is used as a secondary confirmation for the length of the implant.FIGURE 1: A, Intraoperative insertion of the K-wire into the proximal edge of the lesser sigmoid notch. B, K-wire insertion into the proximal edge of the lesser sigmoid notch on a Sawbone model. C, Radiograph showing the placement of the K-wire in the proximal lesser sigmoid notch.FIGURE 2: A, Utilization of prosthetic stem sizer for trial implantation of the radial head. B, Utilization of the K-wire as the upper border for the prosthetic.After confirmation of the correct implant location and length, the K-wire is removed. The size of the radial head diameter is selected to match the original radial head. A smaller size is preferred if the radial head is in between sizes. After implantation, the radiocapitellar gap is assessed in flexion and extension, and articulation with the capitellum and prosthetic stability are evaluated during the passive elbow range of motion. Intraoperative final fluoroscopy confirms proper implantation. The annular and lateral ulnar collateral ligaments are repaired if needed after satisfactory prosthetic implantation. Lastly, the fascial layers and skin are closed. Contraindications for using radial head arthroplasty when treating a radial head or neck fracture include situations where there is a reasonable possibility for preservation of the native radial head anatomy or concurrent active infection within the local area or on a remote body part. OUTCOMES Case 1 This patient is a 62-year-old female presenting with a comminuted, displaced left radial head fracture with longitudinal instability. Radial head arthroplasty was performed utilizing a lateral approach, with K-wire insertion in the subchondral bone at the proximal edge of the lesser sigmoid notch to guide resection of the radial neck. (Fig. 1) At the patient’s 7-week postoperative visit, the patient had excellent restoration of range of motion, with almost no pain. Follow-up radiographs show proper prosthesis alignment without overlengthening. Case 2 A 28-year-old male patient presented with a terrible triad injury after falling off a ladder. Attempts at concentric elbow reduction failed in the emergency room due to bony interposition in the joint. Boyd’s approach was chosen, and radial head arthroplasty was performed due to severe comminution of the radial head. The K-wire was inserted at the proximal edge of the lesser sigmoid notch. Resection of the radial neck, broaching, and trial implant insertion were performed as described in the technical section (Fig. 3). The K-wire was removed, and the final implant was inserted. The radiograph confirmed proper alignment and length.FIGURE 3: A, Implantation of the radial head trail utilizing the K-wire and Boyd approach. B, Intraoperative radiograph of the implanted K-wire. Note that the K-wire in this image penetrates the ulnar cortex, which should be avoided. This technique has since been modified to avoid penetrating the ulnar cortex. C, Intraoperative implantation of the radial head with appropriate alignment.COMPLICATIONS No complications have been associated with inserting and removing the K-wire at the proximal edge of the lesser sigmoid notch in our patients who have undergone radial head arthroplasty. However, complications associated with the overall radial head arthroplasty procedure and not related to the K-wire insertion, such as infection, prosthetic loosening, limited elbow range of motion, stiffness, and capitellar wear remain. Care should be taken to only advance the K-wire into the far cortex of the ulna or to not pass point the medial cortex to prevent iatrogenic injury to the ulnar nerve. In addition, the K-wire should be oscillated when inserting it, to avoid damaging critical structures on the medial aspect of the ulna. Potential complications associated with inserting and removing the K-wire include fractures through the K-wire track, nerve injury, and infection. However, these have not been noted in our cases and have a low risk of occurrence due to the anatomic location of the K-wire insertion and removal before closure. To prevent damage to local nerves, intraoperative fluoroscopy can be utilized to confirm K-wire positioning and prevent over-inserting the K-wire through the ulna. An additional potential risk would be cartilage damage to the lesser sigmoid notch if multiple insertion trials were performed. DISCUSSION Radial head arthroplasty is a reliable surgical technique commonly implemented to treat complex, comminuted radial neck and head fractures. However, complications are not uncommon and are associated with the procedure when the anatomic length of the radius is inaccurately restored. Re-establishing proper radial length during arthroplasty is vital to restoring axial and valgus stability, reducing pain, and re-establishing adequate load distribution in the elbow. In addition, improperly sized prosthetics lead to distorted joint structure and altered load distribution on the elbow.2 Surgeons use multiple different techniques or anatomic landmarks to help guide prosthetic dimensioning. However, overlengthening is still a common occurrence with radial head arthroplasty, leading to increased risks for osteoarthritis, decreased range of motion, and morbidity for the patient. The insertion of a K-wire into the proximal edge of the lesser sigmoid notch is an efficient and safe surgical technique that provides an intraoperative landmark to guide the resection of the radial neck and stem length dimensioning. This provides a benefit to the surgeon as it should decrease the risk of inserting an overlengthened prosthetic. Further clinical research is required to evaluate the efficacy of this technique in reducing radial head prosthetic overlengthening. The lesser sigmoid notch is a validated intraoperative landmark that can be utilized to guide prosthetic dimensioning.4 However, in some cases, it is difficult to visualize during various stages of the operation. K-wire insertion in the subchondral bone at the proximal edge of the lesser sigmoid notch is a novel and simple procedural technique that allows the surgeon to accurately dimension and select radial stem length during radial head arthroplasty. This technique is uncomplicated, safe, reproducible, and can be utilized to reduce the risk of prosthetic overlengthening.