1 Introduction

Femoral head fractures are relatively rare injuries, comprising less than 1 % of all fractures of the hip region.¹ These fractures often are the result of high-energy shear injuries associated with dislocation events.² Although rare, these injuries necessitate prompt and skillful orthopedic treatment to avoid long-term functional sequalae for the patient. Operative fixation may be required based on the location, size, and displacement of the fracture. Obtaining adequate surgical exposure is of paramount importance during these challenging cases. Choosing a surgical approach is therefore an essential part of pre-operative planning, with multiple viable options.

Two commonly used surgical approaches are the trochanteric flip osteotomy and the Smith-Petersen approach. A trochanteric flip osteotomy through the Gibson interval utilizes a lateral approach combined with a digastric osteotomy of the greater trochanter followed by an anterior Z-shaped capsulotomy to gain access to the femoral head.^3,4 A Smith-Petersen approach, on the other hand, utilizes an anterior approach without the need for an osteotomy. The Smith-Petersen approach may also be combined with an anterior capsulotomy and intra-operative hip dislocation.⁵

Previous clinical studies have demonstrated the feasibility of a Smith-Petersen approach for fixation of femoral head fractures.^6–8 However, to the best of our knowledge, no previous study has quantified the difference in exposure between a Smith-Petersen approach and a trochanteric flip osteotomy. We hypothesized that a trochanteric flip osteotomy would provide greater exposure of the femoral head than a Smith-Petersen approach prior to dislocation but would have similar exposure to a Smith-Petersen approach with dislocation. The objective of the proposed study is to compare the degree of exposure between two commonly performed approaches to the femoral head.

2 Methods

Eight (8) fresh-frozen cadaveric pelvises with bilateral intact proximal femurs were dissected using a Smith-Petersen approach on one side and a trochanteric flip osteotomy on the contralateral side. The laterality of the approach performed was alternated between each specimen such that four left sided and four right sided procedures were performed for each of the approaches. All approaches were performed by a single orthopedic resident under the direction of a fellowship-trained orthopedic trauma surgeon. After performing each approach, the femoral head was evaluated for the total area visualized and palpated. The total area visualized was quantified using digital image capture software (ImageJ, Bethesda, MD) using images obtained from four planes (superior, inferior, lateral, medial), as previously described.⁵ These values were subsequently added to quantify osseous exposure.

For the Smith-Petersen approach, the cadaver pelvis was positioned supine. An anterior longitudinal incision was utilized, starting 1 cm lateral and 1 cm distal to the anterior superior iliac spine and extending distally 10 cm over the tensor fasciae lata (TFL). The TFL fascia was incised and the rectus femoris tendon was exposed. The interval between the rectus femoris and the gluteus medius was developed to expose the hip joint capsule. A T-shaped capsulotomy was performed with the top of the “T” paralleling the labrum medially (Fig. 1a). The capsule was retracted and the femoral head was dislocated anteriorly (Fig. 1b) with manual traction and external rotation and use of a bone hook around the femoral neck. Images of the exposed femoral head obtained from four different viewing angles and then analyzed using ImageJ software to calculate femoral head surface area exposure.

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Fig. 1 A demonstrates the view of the surgical exposure of the femoral head in the Smith-Petersen approach prior to surgical dislocation and 1b demonstrates the exposure after surgical dislocation.

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For the trochanteric flip osteotomy, the cadaver pelvis was positioned in lateral decubitus position. A 10 cm longitudinal incision over the greater trochanter was utilized. The iliotibial band was identified and incised in-line with the skin incision. Proximally, the interval between the gluteus medius and gluteus maximus was identified and developed. The greater trochanter osteotomy was performed with an oscillating saw. The osteotomy fragment was flipped anteriorly to expose the hip joint capsule. A Z-shaped capsulotomy was performed, and the femoral head was dislocated anteriorly (Fig. 2). Images of the exposed femoral head were obtained from four different viewing angles. Average femoral head surface area exposure was calculated as described above using ImageJ software. For both approaches, a qualitative description of the portion of femoral head visible was obtained.

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Fig. 2 Demonstrates the view of the surgical exposure of the femoral head in the trochanteric flip osteotomy approach.

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Data were collected in a two-by-eight table fashion, with the independent variable being approach and the dependent variable being the obtained measurement. These measurements were made by a single orthopedic surgery resident to minimize confounding variables. We assessed degree of variability between mean values across approaches with a paired t-test, with a p-value of less than 0.05 determined to be statistically significant.

3 Results

The trochanteric flip osteotomy provided a mean surface area exposure of 1086 mm² +/− 270 mm². The Smith-Petersen approach provided a mean surface area exposure of 1328 mm² +/− 379 mm². The data collected for exposed surface area via each approach is summarized in Table 1. The comparison between the trochanteric flip osteotomy and the Smith-Petersen approach demonstrated a statistically significantly greater area of exposure in the Smith-Petersen approach (p = 0.017). The results of the paired sample t-test are summarized in Table 2. The surface area exposed via the Smith-Petersen approach was greater than that exposed via the trochanteric flip osteotomy for each cadaver pelvis dissection.

The qualitative descriptions of areas exposed was also compared. The Smith-Petersen approach demonstrated improved exposure of the anteroinferior head while the trochanteric flip osteotomy provided improved exposure of the posterosuperior head. For the Smith-Petersen approach, the primary area of exposure included the anterior and anteroinferior portion of the femoral head. The posterior aspect of the femoral head was not visualized but could be palpated. For the trochanteric flip osteotomy, the superior portion of the femoral head was well-visualized including the anterosuperior and posterosuperior portions of the head. The inferior head was not well-visualized. All portions of the femoral head could be palpated with the trochanteric flip osteotomy.

4 Discussion

The objective of the proposed study was to provide a quantitative and qualitative comparison between two approaches to the femoral head. Both the trochanteric flip osteotomy and the Smith-Petersen approach are viable and have been described for treating femoral head fractures. In our study, there was a statistically significant difference between the surface area exposed between the two approaches, with the Smith-Petersen approach with a surgical hip dislocation correlating with a greater amount of exposed surface area. Given the previously described difference in potential risk between the two approaches, our results do have relevance for surgeons deciding how to surgically treat femoral head fractures.

The trochanteric flip osteotomy has associated risks including osteotomy nonunion, avascular necrosis of the femoral head, and symptomatic hardware associated with the fixation of the osteotomy. For the trochanteric flip osteotomy, previous studies have estimated a risk of symptomatic osteotomy hardware from 5 to 15 %, nonunion risk of 0–2 %, and avascular necrosis risk 2–6 %.^9–12 A Smith-Petersen approach, on the other hand, utilizes an anterior approach without the need for an osteotomy. As a result, this approach may be associated with a reduction of some risks associated with an osteotomy. Available literature specifically suggests lower risk of avascular necrosis (<2 %) with a Smith-Petersen approach with no risk of osteotomy nonunion or symptomatic osteotomy hardware.^2,5,13 Our study showed that the Smith-Petersen approach with surgical hip dislocation correlated with a greater amount of exposed surface area compared to a trochanteric flip osteotomy, making it an attractive option for femoral head fracture treatment. However, it does provide limited exposure to the posterior aspect of the femoral head.

Our study has several strengths. Most notably, to our knowledge no previous study has compared the surgical exposure achieved between these two approaches. Additionally, our study attempted to control variables between the two approaches performed on each pelvis as much as possible. The dissections were all performed by the same resident surgeon under the direction of a fellowship-trained orthopedic trauma surgeon to minimize differences in technique, retraction, and data collection. For each cadaver pelvis, a Smith-Petersen approach was performed on one side and a trochanteric flip osteotomy performed on the other side to control for differences in body habitus and femoral head size. The side of the procedures was alternated to reduce the effect laterality may have on the measurements. The diameter of each femoral head was measured and compared to the contralateral side to ensure there was no significant size difference (all paired diameter measurements were within 2 mm of each other).

Our study does have several limitations as well though. Based on a recent study of commonly used methods for comparing surgical surface area, all currently used methods have poor internal reliability.¹⁴ This previous study also found that the surface contour of the object of interest effects the reliability of surface area measurements and so using these techniques on a spherical object may result in a poor estimation.¹⁴ Although this study's use of ImageJ analysis is consistent with similar literature on surgical exposure, it is likely that exploring new, alternative methods of calculating surface area would be beneficial for future studies on surface area exposure. The small number of dissections performed (16) is also a limitation of our results.

In summary, our study suggests that the Smith-Petersen approach with hip dislocation is an attractive option for surgical treatment of femoral head fractures. Specifically, this approach may offer benefits when compared to a trochanteric flip osteotomy, such as increased femoral head surface area exposed and decreased risk of osteotomy complications. This study also shows that in addition to an overall greater surface area exposed, the two approaches may provide preferentially different areas of exposure which can also be useful in pre-operative planning. Future studies should explore in vivo differences between the two approaches, such as duration of surgery, blood loss, and quality of fracture reduction.

CRediT authorship contribution statement

Laura Mourafetis: All the above authors contributed to the study design and, Formal analysis, of the research data, as well as drafting and revising the final manuscript. Raul A. Davalos: All the above authors contributed to the study design and, Formal analysis, of the research data, as well as drafting and revising the final manuscript. Trevor Tompane: All the above authors contributed to the study design and, Formal analysis, of the research data, as well as drafting and revising the final manuscript. Benjamin M. Wheatley: All the above authors contributed to the study design and, Formal analysis, of the research data, as well as drafting and revising the final manuscript, All authors have read and approved the final submitted manuscript.

Consent

Consent was not obtained for this cadaveric specimen study.

Ethical statement

Institutional Review Board approval was not required for this cadaveric study.

Funding statement

Funding for this project was provided by the Naval Medical Center San Diego Clinical Investigations Department Small Grant Funds program. The funds provided were used to purchase cadaveric specimens for dissection.