The comparison of Clinical, Radiological and Functional outcome of Femoral Neck System and Dynamic Hip Screw in Femoral Neck Fractures in Young Adults - A Randomised Controlled Trial

Hip fractures are one of the most common and debilitating fractures in Orthopaedics, estimated to increase to 2.6 million in 2025 of which approximately 50% of cases are predicted to be of femoral neck fractures. Femoral neck fractures may be extracapsular (subtrochanteric, pertrochanteric, intertrochanteric) or intracapsular, which may be classified as Subcapital, Transcervical or Basicervical.

Intracapsular femoral neck fractures are common in the elderly population after a trivial fall , while those in young adults are often the result of high-energy trauma2. They are associated with higher incidences of femoral head osteonecrosis and non-union.  The blood supply to the femoral head is tenuous and easily injured in the setting of displaced fractures. In severely displaced fractures, only the contribution from the obturator artery through the ligamentum teres may be preserved. In addition, other mechanisms of disruption have been hypothesized including tamponade due to compression from an intracapsular hematoma, traction or malrotation during reduction, or eventual thrombosis due to improper reduction. Femoral neck fractures are intra synovial, and the periosteum lacks a cambium layer, hence there is a decreased supply of pluripotent cells, and the fracture hematoma is constantly lavaged away by synovial fluid. Thus, secondary fracture healing is not promoted. Rather, only direct fracture healing via osteonal remodelling is possible. This type of bone healing requires an anatomic reduction and compression. Primary healing may occur if there is a small gap in a process known as gap healing. However, healing is hindered by the high shear stress environment of femoral neck fractures .

The incidence of non-union after femoral neck fracture has been reported to be between 10% to 33% ,which increases with age. The rate of osteonecrosis reported in the literature ranges from 12%-86% in young patients after femoral neck fracture . This devastating complication may lead to collapse of the femoral head and subsequent osteoarthritis. Reported incidence of AVN in fracture neck of femur in young adults is <15% (0-67%). Other functional complications that occur such as posttraumatic arthritis, chronic pain and  limb length shortening  occur which cause a prolonged loss of function in these patients, placing a large burden on the country’s economy and healthcare system .

Fractures that occur in this normal bone density population require substantial axial load with the hip in an abducted position. The clinical evaluation of these patients requires a thorough trauma workup because they frequently have other associated injuries. Despite this, diagnosis and treatment of femoral neck fractures in young adults should only be superseded by other life and limb-threatening injuries. The clinical presentation of patient with femoral neck fracture will usually show a shortened, flexed and externally rotated leg. Radiographic evaluation should include antero-posterior (AP) pelvis with bilateral hips, and lateral plain radiographs of the hip joint.

The fracture pattern seen in young adults will be influenced by their better bone quality and higher energy mechanism. The axially loaded mechanism onto an abducted hip will often result in a basicervical or more distal neck fracture; the fracture pattern has a tendency to be more vertically oriented and thus is biomechanically more unstable. These characteristics have important implications in terms of obtaining and maintaining stable fixation to allow healing to occur.

In the young adult the main goals are to preserve the femoral head, avoid non-union and avoid osteonecrosis by anatomic reduction and stable internal fixation of the femoral neck fracture. Arthroplasty procedures are not ideal given the younger age and high functional levels.

Traditionally, efforts are made to treat and stabilize these fractures within 24 hours of injury, with some citing improved outcomes with reduction and fixation in less than 6 hours. It has been found that young patients who are treated within 24 hours are shown to have lower inpatient medical and surgical adverse events .

Operative treatment options mainly include two interventions: CCS (Cancellous Cannulated Screws), SHS (Sliding Hip Screw)/ DHS (Dynamic Hip Screw).

Cannulated screw fixation of young femoral neck fractures typically involves the placement of 3 screws in an inverted triangle configuration. Other configurations have been

described, such as the addition of a fourth screw transversely into the calcar,3 screws converging, 4 screws converging.  CCS are of two types i.e., Partially threaded CCS which allow for compression across the fracture, whereas fully threaded screws do not. They have the advantage of low cost, less bone removal but have some disadvantages like lack of control over fracture compression, inability to provide fixed angle stability, and often settle and heal with a shortened femoral neck disrupting neck–shaft offset and functional hip abductors which is associated with lower quality of life and increased revision rates.

Most important disadvantage is post-operative collapse which is really significant in CCS.

Fully threaded screws are generally not used due to lack of compression and micromotion that are required for fracture union causing high failure rates.

A sliding hip screw is a fixed-angle device that allows for compression. Although shown to be biomechanically superior, by resisting shear and varus collapse , due to their locking and length stable nature, this advantage is not seen in clinical studies done . SHS/DHS have high failure rates due to excessive stiffness, non-union and loss of reduction .

Complicated fracture patterns such as displaced, comminuted and Pauwel’ Grade III show better outcomes when managed with DHS 12, although the complication rates are higher as the surgery is of a more invasive nature than CCS.

A new generation of implants is emerging- like The Femoral Neck System (FNS) which has an articulated blade and screw construct that exerts no rotational moment on the head segment and is protective of an anatomic provisional reduction. Early results of FNS are promising worldwide.

One prospective study , one retrospective single centre study and one cadaveric study has been published to this date comparing the clinical outcome, and biomechanical evaluation, respectively, of FNS and DHS.

This prospective clinical trial will be performed to assess and compare clinical, functional and radiological outcomes and complications with the use of the recently launched and approved treatment modality - Femoral Neck System with the current commonly used treatment modality,  Dynamic Hip Screw with Derotation Screw in treatment of neck of femur fractures in young adults.