The study focused on introducing and evaluating the femoral neck osteotomy guide, consisting of the oriented part and locating part. The guide was designed for improving the accuracy of osteotomy during THA surgery through the posterolateral approach. The difference between actual and planning osteotomy heights in the group with the guide was lower than that in the group without the guide. In addition, the guide is easy to use and does not prolong the operation time.
Hip replacement is currently one of the most effective treatments for severely diseased or degenerated hip joints. More than 1 million hip arthroplasties are performed every year worldwide, and this number is projected to double within the next two decades [
1]. The incidence of LLD after THA has been reported to range from 1% to 27%, with some reports of even up to 50%. It is difficult to eliminate LLD after THA. Combined use of a preoperative femoral template to predict the necessary length correction and plan the femoral neck osteotomy level along with intraoperative measurements is a practical method for avoiding LLD. However, some studies concluded that a planning match exists in only up to 60% of cases, so improving the accuracy of actual performance according to preoperative plan remains controversial [
3,
5]. LLD following hip replacement may cause lower back pain, sciatic nerve palsy, gait dysfunction, hip dislocation and prosthetic loosening, as well as increasing patient dissatisfaction. LLD has been a major post-surgical complaint for patients receiving hip arthroplasty [
6]. LLD is the result of a complex interaction between bone length, implants, soft tissue contractures, and pelvic obliquities. After THA surgery, some authors feel that over-lengthening of the implant head-neck distance resulted in LLD [
7,
8]. In addition, the restoration of femoral offset is also critical for avoiding LLD, as increased femoral offset theoretically can lead to increased implant bending moments and early loosening. During the operation, inaccurate abduction/adduction repositioning of the femur with respect to the pelvis also can cause substantial errors in the measurement of length and offset change [
9]. A variety of methods have been used to avoid or reduce the incidence of LLD, such as preoperative template measurement or using an L-shaped calliper and other surgical devices [
10]. Careful preoperative planning is critical but does not preclude the surgeon from choosing the incorrect components for THA. More importantly, attention to detail both in the planning and performance of the surgery may assist in reducing LLD [
11]. Although meticulous preoperative templating combined with X-ray, CT and other imaging systems assists with sizing an appropriate prosthesis and can be helpful for avoiding LLD, surgeons may unintentionally stray from the template when implants of different sizes or offsets are used [
2]. Although some instruments were used for measuring during the surgery, no professional surgical tools such as those used in knee replacement surgery exist for femoral neck resection. Surgeons typically rely on their experience and finger measurements during the osteotomy. This may be particularly difficult for inexperienced surgeons, especially when trying to gauge the cuneiform plane angle and height of the femoral neck resection. This can extend the operation time, increase blood loss and complicate the procedure. Earlier studies paid close attention to measurement methods using different types of devices and landmarks, but difficulties with operative manipulation have not been addressed thus far. The guide was invented to address the uncertainty of femoral neck osteotomy. In our study, the surgeons had more than 10 years of experience in hip replacement, yet still had a certain degree of error. In the current study, errors in osteotomy height between the actual and predicted size were reduced to 0 ~ 1 mm. Furthermore, LLD was reduced to less than 10 mm. We believe that such a device will become standard in femoral neck osteotomy, resulting in more precision for cutting height and resection angles. This will also reduce the surgical times and alleviate soft tissue damage during the operation.
Our study has some limitations. First, the head-neck distance of the implants was not recorded or compared between the two groups. A device combined femoral neck osteotomy guide with head-neck distance measurement is being developed. Second, in our study, one observer who was blinded to the design was in charge of measurement, so inter-observer agreement was not considered in the design of the study. This was one of the major limitations of the current study. Finally, the soft tissues above the lesser trochanter could not be stripped clean during surgery, which introduced a measurement error in performing the osteotomy. Additionally, in obese patients, it is difficult to expose the lesser trochanter, so the device cannot accommodate all types of patients in clinical practice.