Structure of the femoral neck osteotomy guide
The femoral neck osteotomy guide (Figure 1) consists of two parts: the upper part is an oriented platform that guides the direction of the femoral neck osteotomy perpendicular to the long axis of femoral neck, and the lower part locates on the top of the lesser trochanter of the femur. There are two fixed screw holes in the locating seat, which are used to fix the device on the femoral neck. The guides were divided into left and right groups, and a series of the guides was designed according to the osteotomy height from 10 mm to 15 mm for each group. The series contains six models with a 1 mm interval difference between each two adjacent models. The different sizes of the osteotomy guides were selected according to preoperative templates on X-ray films, such as a 10-mm guide for a 10 mm osteotomy height, and the like. First, a model was made and modified on femur specimens using a self-curing denture acrylic. The model was then tested and adjusted on 128 femur specimens to obtain a suitable model form for a variety of femoral neck configurations. Finally the guide was made from titanium with a ratio of 1:1 according to the model. The guide was suitable for THA through a posterolateral approach. Before surgery, the device was sterilised with low temperature hydrogen peroxide gas plasma sterilisation.
Patients
This study aimed to investigate the precision of the guide for THA. Between November 2012 and July 2013, 48 patients in need of femoral neck osteotomy were included in our study (Figure 2). Inclusion criteria were: primary hip arthroplasty with limb-length discrepancy less than 5 mm. In these patients, only one side required hip replacement while the other side was normal. Exclusion criteria were: preoperative LLD > 5 mm by tape measurement, total hip arthroplasty with femoral neck preservation and a history of previous hip surgery. Patients were also excluded from the study if they had obesity, rheumatoid arthritis, scoliosis, pelvic obliquity, or a limp caused by cerebral thrombosis, cerebral palsy and other causes.
The selected patients were randomly assigned into the two groups. Twenty-four patients were operated on with the use of the guide (group I) and 24 without the guide (group II). All operations were performed by the same experienced surgeon and measurements were made by a member of the research team. The surgical team consisted of surgeons with more than 10 years of experience in hip replacement. Data on age, gender, operation side, an etiology of surgical indications, femoral neck height, leg length and operative time were collected for both groups.
Surgical techniques
All patients were admitted to the hospital 3-5 days before the surgery. Leg length was calculated and recorded by tape measure with the patients in a supine position before and after the THA surgery. The length of the lower limbs was measured between the anterior superior iliac spine (ASIS) and the medial malleolus [4]. Preoperative radiographs were taken from an anteroposterior view of the pelvis with both femurs internally rotated approximately 15° as required for assessment before THA. The templates were used to determine the height of the femoral neck osteotomy and the potential correct sizes for both the acetabular and femoral components of the prostheses. After surgery, the heights of the osteotomies were measured from the lesser trochanter to the cuneiform plane on the X-ray films using the same parameters.
The operations were performed through a posterolateral approach with patients in a lateral decubitus position. After exposing the femoral neck and the lesser trochanter, the surgeon placed the guide on the lesser trochanter. It is important to place the locating seat on the top of the lesser trochanter and to adjust the oriented platform to be perpendicular to the long axis of the femoral neck. The height of the bone resection is determined by the height of the guide, but the angle of the osteotomy was adjusted by lifting or lowering the platform of the guide by eye by the surgeons based on their experience. After fixing the guide with Kirschner pins at a diameter of 2 mm, the guide was fastened to femoral neck, making it unnecessary to hold the device tightly against the bone while performing the resection. Intraoperative X-ray was not performed after positioning the guide in front of the osteotomy. The surgeon cut the femoral neck while the saw was in contact with the guide platform (Figure 3). After the bone was resected, the device was removed to show a smooth bone platform perpendicular to the long axis of the femur (Figure 4). The prosthesis was then placed following the customary surgical steps and post-operative X-rays were taken. For group II, the same procedure was followed, with the exception of using the guide.
The Institutional Review Board of the Third Hospital of Hebei Medical University approved this study after thorough examination and verification. All patients signed informed consent and agreed to participate in the study.
Statistics
Statistical analysis was carried out by using SPSS13.0 for Windows (SPSS, Chicago, IL, USA). Enumeration data of the two groups of patients organised by gender, aetiologies of indications and operative side were compared by the Chi-squared test. Measurement data, such as age, were compared using a t-test. The significance threshold was set at P < 0.05.