Introduction to Hip Arthroscopy and Version Morphology

Hip arthroscopy has emerged as a revolutionary procedure for managing femoroacetabular impingement syndrome (FAIS). Over the past decade, surgeons have expanded the indications for this minimally invasive technique, consistently reporting excellent clinical outcomes. However, the presence of combined hip version abnormalities often complicates the surgical landscape. Clinicians historically viewed femoral and acetabular retroversion as significant predictors of inferior results. Consequently, many patients with these morphologies were previously considered poor candidates for arthroscopic intervention. Recent evidence suggests that a much broader range of version morphologies may be successfully managed through arthroscopy than previously thought. This shift in perspective necessitates a deeper understanding of how we define and measure these structural variations. Because version abnormalities are complex, surgeons must carefully evaluate the unique anatomy of each patient to optimize postoperative success. Furthermore, the lack of a universal consensus on what constitutes a 'normal' version range continues to fuel debate within the orthopedic community. As we move forward, integrating advanced imaging with clinical findings will remain essential for identifying the best surgical candidates and predicting long-term joint health.

The Biomechanics of Combined Hip Version Abnormalities

To understand the clinical implications, one must first grasp the biomechanical relationship between the femur and the acetabulum. Combined hip version abnormalities involve the mathematical or functional relationship between femoral torsion and acetabular version. Specifically, the total version of the hip joint determines the overall range of motion and the risk of impingement. When these two variables are mismatched, the joint may experience abnormal stress concentrations during daily activities. For instance, a patient with low femoral anteversion and acetabular retroversion may suffer from significant pincer-type impingement. Conversely, excessive anteversion on both sides can lead to instability and increased labral strain. Therefore, evaluating these parameters in isolation often fails to provide a complete picture of the patient's pathology. Surgeons now emphasize the 'combined' aspect, as it more accurately reflects the functional constraints of the hip. Moreover, recent biomechanical studies highlight that the joint can often compensate for mild abnormalities if the soft tissue structures, such as the labrum and capsule, are well-preserved. This adaptability might explain why some patients with significant bony abnormalities still achieve high satisfaction scores after labral repair and cam resection.

Challenges in Measuring Hip Version Morphology

A major hurdle in the current literature is the lack of standardization in measuring hip version. Multiple techniques exist for assessing femoral version, yet substantial variability exists between these methods. For example, some clinicians prefer CT-based measurements because they provide clear bony landmarks. On the other hand, many sports medicine specialists utilize MRI to avoid ionizing radiation, especially in younger populations. Research indicates that while CT and MRI measurements correlate, they are not always interchangeable. Specifically, axial versus oblique cuts can yield different numerical values for the same patient. Similarly, acetabular retroversion is frequently diagnosed using radiographic signs like the 'crossover sign' on plain X-rays. However, these signs do not always correlate perfectly with version measured on advanced 3D imaging. As a result, studies using different measurement protocols often reach conflicting conclusions regarding the impact of version on outcomes. Until we establish reproducible and standardized methods, comparing data across different surgical centers will remain difficult. Consequently, orthopedic surgeons must interpret the 'absolute' numbers provided by radiology reports with a degree of healthy skepticism and relate them back to the clinical presentation.

Classification Systems and the McKibbin Index

Beyond the raw measurements, the way we categorize morphology significantly influences our clinical interpretation. Several approaches exist for classifying combined version, including the well-known McKibbin index. This index is calculated by summing the femoral and acetabular version angles to determine a total value of joint torsion. Traditionally, values between 25 and 45 degrees are considered normal. However, numerical summation is just one method of assessment. Modified classification systems have emerged to better account for the nuances of hip instability versus impingement. These systems often categorize patients into 'low,' 'normal,' or 'high' version groups. Nevertheless, the thresholds for these categories vary widely across different studies. For instance, what one study defines as 'severe' retroversion might be considered 'mild' in another. This inconsistency makes it challenging to establish a clear evidence-based guideline for surgical decision-making. Furthermore, the functional impact of these indices may differ based on the patient's activity level and soft tissue laxity. Therefore, a comprehensive evaluation must go beyond simple arithmetic to include dynamic physical examination findings and patient-reported symptoms.

Influence on Patient-Reported Outcomes After FAIS Surgery

Despite the complexity of these structural variations, recent data suggests that combined hip version abnormalities may not negatively influence patient outcomes as much as previously feared. Several large-scale studies have shown that patients with abnormal version scores can still achieve the minimal clinically important difference (MCID) following hip arthroscopy. This finding is particularly encouraging for patients who were once deemed high-risk due to their bony anatomy. One reason for this success is the refinement of arthroscopic techniques, such as precise labral reconstruction and personalized capsular management. Moreover, when surgeons address the concomitant cam and pincer lesions effectively, the underlying version abnormality might become clinically silent. However, we must interpret these findings with caution. Outcomes are often dependent on how the version was measured and which classification system the researchers employed. For example, if a study uses a very broad definition of 'normal,' the impact of subtle abnormalities might be diluted. Additionally, long-term data exceeding ten years is still limited for this specific sub-population. Consequently, while short-term and mid-term results are promising, the orthopedic community still needs more robust, multi-center trials to confirm these trends.

Clinical Implications for Modern Orthopedic Practice

For the practicing surgeon, the current evidence emphasizes the need for a personalized approach to FAIS. Rather than relying on a single measurement, clinicians should integrate multiple data points to form a surgical plan. Specifically, the relationship between bony version and soft tissue status is paramount. If a patient presents with combined hip version abnormalities but demonstrates good clinical improvement with conservative management, surgery may not be immediately necessary. However, when conservative measures fail, arthroscopy remains a viable option, even in the setting of structural variation. Surgeons should communicate clearly with patients about the potential for slightly slower recovery or different outcome trajectories based on their unique anatomy. Additionally, the role of radiology cannot be overstated. Collaborative efforts between surgeons and radiologists to use standardized measurement protocols will greatly enhance the reliability of preoperative planning. As the field of hip preservation evolves, we will likely see more sophisticated 3D modeling and dynamic simulation tools. These advancements will help us better predict which patients will benefit most from arthroscopy and which might require more invasive realignment procedures like a periacetabular osteotomy.

Frequently Asked Questions

What exactly is the McKibbin index in the context of hip version?

The McKibbin index is a clinical tool used to assess the total torsion of the hip joint. It is calculated by adding the numerical value of femoral version to the value of acetabular version. Generally, a range of 25 to 45 degrees is considered normal. This sum helps surgeons understand the overall rotational profile of the joint, which is more descriptive than looking at femoral or acetabular angles in isolation.

Can hip arthroscopy be successful for patients with high femoral anteversion?

Yes, recent clinical studies indicate that patients with high femoral anteversion can achieve significant functional improvement through hip arthroscopy for FAIS. While historical data suggested these patients might have higher failure rates, modern techniques focusing on labral preservation and capsular plication have improved results. However, surgeons must carefully evaluate the degree of instability and the presence of any concomitant acetabular dysplasia before proceeding with an arthroscopic-only approach for these individuals.

Why is there so much variability in version measurements between CT and MRI?

Variability between CT and MRI arises from differences in patient positioning, imaging slices, and the specific landmarks used by radiologists. CT is often regarded as the gold standard for bony detail, while MRI is preferred for soft tissue. Specifically, the choice of the femoral neck axis and the distal femoral condyle reference point can significantly alter the resulting angle. Because these differences exist, clinicians should use the same imaging modality consistently when tracking a patient's progress.

Disclaimer: This content is for informational and educational purposes only and does not constitute medical advice. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified healthcare provider with any questions you may have regarding a medical condition. Refer to the latest local and national guidelines for clinical practice.

References

1. Khalil LS et al. Editorial Commentary: Combined Hip Version Abnormalities May Not Negatively Influence Patient Outcomes, Depending How Version Is Measured and Combined Version Is Categorized. Arthroscopy. 2026 Jun 28. doi: 10.1002/arj.70389. PMID: 42365667.

2. Domb BG et al. The effect of femoral and acetabular version on clinical outcomes after arthroscopic femoroacetabular impingement surgery. Am J Sports Med. 2015;43(4):819-27.

3. Schmaranzer F et al. Correlation of femoral version measurements between computed tomography and magnetic resonance imaging studies in patients presenting with a femoroacetabular impingement-related complaint. J Hip Preserv Surg. 2022;9(2):100-108.