Cemented hemiarthroplasty of hip for displaced fractures of neck of femur has been gold standard in elderly to decrease the chances of prosthetic loosening and anterior thigh pain on longer follow-up.1 Besides relieving pain, restoration of the hip joint biomechanics with appropriate femoral offset and leg length is an important goal of hemiarthroplasty to facilitate normal gait and function. One of the intraoperative challenges in cemented hemiarthroplasty surgeries of hip is preventing limb length inequality (LLI) without compromising hip stability. Although trial reduction ensures stability, final reduction after cementing is the key point as the offsets can change from trial to cementing. There are high chances of limb length discrepancy and compromise in stability in this cemented surgical procedure compared with uncemented procedure. In nonmodular prosthesis of hip, prosthetic fixation will decide offsets, stability, and prevent LLI.
Limb length inequality following hip prosthetic surgery has been associated with back pain and sciatica,2 gait disorders,3 general dissatisfaction,4 dislocation,5 and early loosening of components due to altered biomechanics.6
There are about 20 technical methods described in the literature to prevent LLI and can be broadly grouped into the following categories7:
- Those which rely on perioperative templating.
- Those using intraoperative pelvic or femoral markers for reference.
- Using navigation and ultrasound probe to measure leg lengths accurately.
Except navigation, most of the described methods are of limited value in hemiarthroplasty surgery for fracture neck of femur. The method of using relationship between tip of the greater trochanter to the center of the femoral head prosthesis, is a simple perioperative method to align the femoral component even by cementation technique to achieve stability and avoid LLI. There is little in the literature to support this method of leg length restoration for cemented hemiarthroplasty. In the present study, we have evaluated LLI in patients who underwent cemented hemiarthroplasty with Austin Moore prosthesis (AMP) or bipolar prosthesis using this technique.
A retrospective analysis of 108 patients who underwent hemireplacement arthroplasty of hip for displaced fracture neck of femur with cemented AMP (Sushruth surgicals) or bipolar prosthesis (nonmodular; Inor surgicals Ltd) from 2013 to 2015 by the senior author were included in the study. The choice of AMP or bipolar was by age of the patient and fracture pattern. Older age group above 70 with good calcar support (subcapital and transcervical fractures) were operated with AMP, whereas patients younger than 70 years or those with basicervical fractures or without good calcar support were operated with bipolar prosthesis. All the patients were operated in lateral decubitus position with anterolateral (modified Hardinge) approach. Standard neck cuts for respective implants were made.
The operating surgeon always followed the method of using relationship between tip of greater trochanter and center of femoral head in cemented hemiarthroplasty for retaining offsets and to avoid LLI. A preoperative radiograph of pelvis anteroposterior view is assessed before the surgery. The relation of tip of greater trochanter to center of femoral head on the normal side, whether the center of the head lies above or below the level of the greater trochanter as in valgus or varus neck respectively is assessed (Fig. 1B). Intraoperatively during cementation, the same relation of opposite side is maintained at greater trochanter to the center of femoral head prosthesis on index side. A 90-degree bent Langenback retractor is used to assess the same. The handle of Langenback is maintained along the axis of shaft of femur from the tip of greater trochanter and the blade of retractor over the center of femoral head prosthesis to assess the target relation (Fig. 1A). A linear scale can be used if necessary, to measure the distance between blade of retractor and the center of femoral head.
Postoperatively all the patients are followed up at 1 year as a part of another long-term study of cemented hemiarthroplasty at our center and their Harris Hip scores were documented. We retrospectively reviewed the postoperative pelvis x-rays of the 108 patients whose Harris Hip score scores were available to assess limb length discrepancy. All the radiographs were standardized and measures were taken to capture the pelvis with both hips in identical position. A line is drawn tangential and parallel to the most inferior aspect of ischia and another line is drawn connecting the most medial projection of lesser trochanter of both femurs. Perpendicular distance between the 2 lines on either side is measured using the scale tool in InstaRIS PACS system (Version 4.0). The difference in the measured distances is documented as LLI reflecting either shortening or lengthening of the operated limb (Fig. 2). This difference in infratrochanteric distances gives an indirect measure of LLI.8 The magnification component of the radiograph used for assessing LLI was eliminated by adjusting to the femoral head prosthesis size.
There were 46 men and 62 women with an average age of 72.1 years (range, 54 to 89 y). In total, 61 hips were on the right and 37 on the left side. Two patients had a previous hip prosthesis on opposite side at the time of surgery. In both of them, relation of tip of greater trochanter to the femoral head prosthesis on opposite side is taken as the index measure (Fig. 3). Postoperatively the mean LLI was+2.81 mm (Fig. 4). The range of LLI in the study group was −6.28 to +9.82 mm. In total, 28 limbs had 0 LLI (corrected to≤0.10 mm), whereas 63 limbs had lengthening and 17 had shortening (Fig. 5). Mean Harris Hip score at 1-year follow-up was 87.1. The mean Harris Hip score in lengthened group is 87.5 and in shortened group is 86.7. There was no significant difference with respect to type of prosthesis used in relation to limb length discrepancy.
Discrepancy of leg length is common after hip arthroplasty surgeries including hemireplacement arthroplasty. Following hip replacement surgeries, LLI has been universally perceived by the patients when the shortening exceeds 10 mm and lengthening by 6 mm.9,10 Although shoe raise well compensates the LLI, it is just a compensatory measure. Wylde et al11 concluded that patients with LLI had significantly poorer functional outcome and limped more frequently. True limit of LLI acceptable without any complaints or long-term compensatory–related issues are still criticized.
Several studies investigating reliance of templating and its efficacy in avoiding LLI in hip arthroplasty surgeries have concluded that correct sizing of components match in only up to 60% of cases, hence making it unreliable method.7 There are many direct and indirect intraoperative techniques described to avoid LLI. Indirect method of Charnley is comparison of the limb length by palpation of the medial malleoli after trial reduction.12 However, it gives an arbitrary measurement and may be misleading due to surgical drapes and position during surgery. Most of the direct intraoperative techniques use ipsilateral pelvic or femoral markers for reference which could be useful for avoiding LLI in total hip arthroplasty with intact hip.7 Measuring the distance between 2 reference points on the ilium and femur has been one of the commonly used. This method is more time consuming and require more exposure that can be avoided for a hemiarthroplasty surgery. Methods using the anterior superior iliac spine or iliac wing as a reference point may make it more difficult while operating with distorted hip anatomy, such as femoral neck fracture. Sproul et al13 analyzed 34 cadaveric proximal femur and noted that the diameter of the femoral head was similar in size to the distance from the top of the lesser trochanter to the center of the femoral head. They suggested it may be a useful clinical measurement to assess leg length during hemiarthroplasty of the hip. Larger anthropometric data confirming the same would be helpful to evaluate this technique. The navigation techniques to avoid limb length discrepancy are not only expensive and cumbersome but also have a high learning curve.7 The method of relation of tip of the trochanter to the center of femoral head is less invasive, less time consuming, and easier direct method of intraoperative assessment that can be still used in distorted hips, particularly in fracture neck of femur. Although in cemented hemiarthroplasty the stability is checked after trial reduction, offsets change during cementation process of femoral component. This method of using relation of tip of greater trochanter to prosthetic femoral head will give a good guide for fixing the level of femoral component at the time of cementation. Upon familiarity with this technique, senior author never tried trial reduction and still the joints were stable with respect to offsets. Although this study focuses only on hemiarthroplasty procedure, the same technique could also be used in primary total hip arthroplasty without acetabular dysplasia or gross erosion.
In the literature review, most of the studies reported the level of the tip of the greater trochanter to be above the femoral head center.14,15 Because of the variability of this anatomic landmark, using the tip of the greater trochanter as a reference point for the femoral head center should be carefully evaluated while using this technique and ideally the distance is measured to achieve normal length of the limb. In our study group the operating surgeon always used the relation of greater trochanter to femoral head center of opposite hip and mean LLI was +2.81 mm, which perhaps is not significant as evident from mean Harris Hip score of 87.1. Measuring the vertical distance between these relations could have corrected it as well.
Kay et al16 and Goodman et al17 studied the apparent changes in the alignment of the tip of greater trochanter associated with limb positioning particularly rotations. Perhaps, the variability of results in our study could be attributed to the positioning of opposite hip upon radiograph. We suggest taking pelvis radiographs with opposite limb in neutral to get exact relation of tip of greater trochanter to center of femoral head. Although our study only looks at the vertical distance from the tip of the greater trochanter to the femoral head center, we believe that leg length is dependent on a number of other factors including femoral stem varus-valgus positioning and femoral prosthesis neck offset that are not addressed in our study. Other limitations include variability in magnification correction errors on preoperative radiographs which may have lead to small variation in lengths measured. Although all radiographs of the pelvis were standardized, small variations in leg adduction or abduction and internal or external rotation may have occurred, leading to altered distances being measured.
The tip of the greater trochanter as an absolute marker for limb length restoration should be used with caution. Measuring the distance from the relations than assessment would give more accurate desired results. However, in conjunction with adequate preoperative templating of the opposite hip, this technique may be useful as an easily palpable intraoperative guide in positioning the femoral component during hemiarthroplasty of hip to avoid LLI.
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