Abstract
Purpose
Increased femoral offset following total hip arthroplasty allows for greater stability of the hip joint. However, the increase in femoral offset can cause an impingement of local structures resulting in persistent lateral hip pain. There is conflicting evidence whether changes in femoral offset increases the rates of lateral hip pain following total hip arthroplasty.
Methods
This was a retrospective case control study that grouped patients based on the presence of persistent lateral hip pain following total hip arthroplasty. Patients were then stratified according to their change in femoral offset (<-5 mm, -5 mm < x < 5 mm, and 5 mm<). A chi squared analysis was then performed to see if there was a statistical difference in the rates of lateral hip pain amongst these groups.
Results
A change in femoral offset of the implanted hip relative to the native hip was not associated with increased rates of lateral hip pain following total hip arthroplasty (p = 0.35). A change in femoral offset of the implanted hip relative to the contralateral hip was not associated with increased rates of lateral hip pain following total hip arthroplasty (p = 0.40).
Conclusion
This study found that there was no association between increased femoral offset and rates of postoperative lateral hip pain following total hip arthroplasty. Future investigations should look at a larger sample size with multiple institutions to further assess the impact on femoral offset changes on rates of persistent lateral hip pain.
Keywords: Arthroplasty, Complications, Pain, Hip, Femoral offset
1. Introduction
Total hip arthroplasty (THA) is the preferred treatment for end-stage hip pathologies such as rheumatoid arthritis and osteoarthritis.1 Complications of THA can result in increased cost, morbidity, and revision operations for the patient. While THA is generally well tolerated, when there are postoperative complications persistent lateral hip pain is one of the most common with an incidence of between 3% and 17% of THAs.2 One of the potential causes of lateral hip pain following total hip arthroplasty is inflammation of the trochanteric bursa resulting in palpable pain over the greater trochanter.3
Femoral offset is a key factor that determines the stability of the postoperative hip. The femoral offset is defined as the perpendicular distance from the center of rotation of the femoral head to the long axis of the femur.4 An increase in femoral offset results in an increase of the moment arm of the abductors on the hip. This increased moment arm results in an increased mechanical advantage of the abductors on the hip joint. This increase in mechanical advantage has been associated with improved clinical outcomes and patient satisfaction at one-year follow-up.5 Increases in femoral offset by greater than 3 mm relative to the contralateral hip have been shown to decrease risk of dislocation.6 These studies reinforce that femoral offset is a critical component for successful joint strength and stability after a THA.
While there is a mechanical advantage associated with an increased femoral offset there are potential drawbacks of increasing the offset too dramatically during THA. As the femoral offset increases, there is increased strain on the tendons of the hip abductors that insert on the greater trochanter. This increased strain can lead to impingement and inflammation of the local hip structures resulting in lateral hip pain. A femoral offset discrepancy greater than 5 mm relative to the contralateral hip has been shown to relate to unphysiologic gait within the first year.7
Several studies have explored the effect of increased femoral offset difference of the operated hip compared to the contralateral hip and its relation to postoperative hip pain. There is conflicting evidence to say whether there is an increase in lateral trochanteric pain when there is an increase in femoral offset relative to the contralateral hip.8,9 This study retrospectively examined the impact of a change of the femoral offset on postoperative rates of lateral hip pain.
2. Materials and methods
This study grouped 157 patients who had undergone a THA from 2014 to 2017 at one institution. The surgeries were performed by four different surgeons all via the posterolateral approach. Patients were excluded if they had not followed-up in clinic for at least 1 year, if radiographs were not available, if radiographs were deemed subpar for measurement, or if there were a preexisting diagnosis for hip pain outside of the reconstruction itself. Femoral offset measurements were performed using standard AP pelvis radiographs on Centricity PACS Radiology RA1000 Workstation and Exam Manager (GE Healthcare, Barrington, IL, 60010 USA). Femoral offset was measured as the distance of a perpendicular line from the center of the head of the femur to the anatomic axis of the femur. The implanted femoral head of known diameter from the operative reports was used to standardize measurements. Clinic notes from the institution’s electronic medical record system were used to track patients at least one year out from surgery. Patients were included if they experienced lateral hip pain with no other evident etiology that may account for the patients’ symptoms and complaints.
There were 40 patients with lateral hip pain and 117 without. Statistical analysis was done using a chi-squared analysis for categories of age, gender, BMI, and femoral offset change. Age was categorized into four groups based on calculated quartiles of 25–51, 52–57, 58–62, and 63–82. Gender was categorized into male and female. BMI was categorized into normal (18.5–24.9), over-weight (25–29.9), and obese (>30). The change in offset was analyzed from two perspectives.
2.1. Femoral offset change calculated from the preoperative hip subtracted from the postoperative hip
The first offset difference was calculated using radiographs from Fig. 1. The femoral offset of the preoperative hip (a) subtracted from the postoperative hip (b). Then each patient was classified by their offset difference and sorted into three groups. Group 1: change in femoral offset less than or equal to −5 mm, signifying decreased femoral offset. Group 2: change in femoral offset between -5mm and +5 mm, signifying no change in femoral offset. Group 3: change in femoral offset greater than or equal to +5 mm, signifying increased femoral offset.
Fig. 1.
An example preoperative x-ray (left) and postoperative x-ray (right) are shown. In the left x-ray the femoral offset of the hip before the THA (a) and in the right x-ray the femoral offset of the hip after the THA (b).
2.2. Femoral offset change calculated from the contralateral hip subtracted from the postoperative hip
The second offset difference that was calculated using the measurements from Fig. 2. This offset difference was calculated using the femoral offset of the contralateral hip (c) subtracted from the offset of the postoperative hip (b). After the offset difference was calculated, each patient was classified by their offset difference and sorted into three groups. Group 4: change in femoral offset less than or equal to −5 mm, signifying decreased femoral offset. Group 5: change in femoral offset between -5mm and +5 mm, signifying no change in femoral offset. Group 6: change in femoral offset greater than or equal to +5 mm, signifying increased femoral offset.
Fig. 2.
An example postoperative x-ray with the femoral offset of the postoperative hip (b) and the femoral offset of the contralateral hip (c).
All research was conducted in accordance with the University of Illinois-Chicago (UIC) Institutional Review Board (IRB). UIC investigators, research staff, IRB members, IRB staff, and UIC in working with sponsors, follow the ethical principles of the Belmont Report for all human subjects research.
3. Results
3.1. Femoral offset change calculated from the preoperative hip subtracted from the postoperative hip
When examining the offset difference of the preoperative hip subtracted from the postoperative hip, in group 1 (femoral offset difference ≤5 mm), there were 7 patients with lateral hip pain and 25 without. In group 2 (femoral offset difference between -5mm and 5 mm), there were 22 patients with lateral hip pain and 49 without. In group 3 (femoral offset difference ≥+5 mm), there were 11 patients with lateral hip pain and 43 without. The chi-squared analysis was used to compare three groups, providing a non-significant p-value of 0.35, indicating a femoral offset change with the preoperative hip is not associated with increased lateral hip pain.
3.2. Femoral offset change calculated from the contralateral hip subtracted from the postoperative hip
When examining the offset difference of the contralateral hip subtracted from the postoperative hip, there were 8 patients with lateral hip pain and 34 without in group 4 (femoral offset difference ≤5 mm). In group 5 (femoral offset difference between -5mm and 5 mm), there were 21 patients with lateral hip pain and 55 without. In group 3 (femoral offset difference ≥+5 mm), there were 11 patients with lateral hip pain and 28 without. The chi-squared analysis resulted in a p-value of 0.40. The chi-squared analysis resulted in a non-significant p-value of 0.40, indicating the femoral offset change with the contralateral hip is not associated with increased lateral hip pain.
In terms of age, the table shows the number of patients in each quartile with lateral hip pain and those with no pain. For the 157 patients analyzed, there is a chi-squared value of 0.94, showing no significance for age.
In grouping by BMI, 20% of the patients had a normal BMI, 45% were overweight, and 35% were obese. Of the 40 patients with lateral hip pain in the study, 15% had a normal BMI, 40% were overweight, and 45% were obese. The number of patients with and without lateral hip pain is shown in Table 1. The chi-squared analysis of the groups resulted in a p-value of 0.28, showing no significance.
Table 1.
A summary of the demographic information and femoral offset calculations compared with incidence of postoperative lateral hip pain.
| Offset difference (Operated Hip Preop subtracted from Operated Hip Postop) | Group 1 (≤-5 mm) | Group 2 (−5.0 mm-+5.0 mm) | Group 3 (≥+5 mm) | |
|---|---|---|---|---|
| Pain | 7 | 22 | 11 | |
| No Pain | 25 | 49 | 43 | |
| Chi-Squared P-Value | 0.35 | |||
| Offset difference (Contralateral Hip subtracted from Postoperative Hip) | Group 4 ( ≤ -5 mm) | Group 5 (-5.0 mm- + 5.0 mm) | Group 6 ( ≥ + 5 mm) | |
| Pain | 8 | 21 | 11 | |
| No Pain | 34 | 55 | 28 | |
| Chi-Squared P-Value | 0.40 | |||
| Age | Quartile 1 (25–51) |
Quartile 2 (52–57) |
Quartile 3 (58–62) | Quartile 4 (63–82) |
| Pain | 11 | 9 | 11 | 9 |
| No Pain | 29 | 30 | 35 | 23 |
| Chi-Squared P-Value | 0.94 | |||
| BMI | Normal (18.5–24.9) | Overweight (25.0–29.9) | Obese ( ≥ 30.0) | |
| Pain | 6 | 16 | 18 | |
| No Pain | 25 | 31 | 59 | |
| Chi-Squared P-Value | 0.28 | |||
| Sex | Male | Female | ||
| Pain | 22 | 18 | ||
| No Pain | 61 | 56 | ||
| Chi-Squared P-Value | 0.75 |
The study was composed of 83 males (53%) and 74 females (47%) Of the 40 patients with lateral hip pain, 22 were male and 18 were female. The chi-squared analysis of the groups resulted in a p-value of 0.75, showing no significance.
4. Discussion
THA is one of the most successful surgical procedures performed. Many studies have shown the relationship between increased femoral offset correlating with increased range of motion, strength, and wear rate of the hip joint.5 Modern techniques in THA allow surgeons to increase tissue tension and augment hip biomechanics. Some of these options include modular femoral heads with multiple neck lengths, allowing both vertical and horizontal displacements.10 Despite the increased mechanical advantage of the abductors because of increased femoral offset there is inconsistent data on whether this change in offset leads to increased rates of postoperative complications.
Some studies have investigated the relationship of an increased femoral offset change as it relates to postoperative pain and function with special attention paid to the incidence of lateral trochanteric pain. One study did find a difference in postoperative pain following THA according to the WOMAC pain scale. The group that had an increased offset postoperatively (≥5 mm) was associated with higher pain scores at 6, 12, and 24 months.9 Minimizing the femoral offset difference relative to the contralateral hip has been shown to increase joint functionality postoperatively.5 It is possible that lateral hip pain following THA is due to trochanteric bursitis, although to formally diagnose trochanteric bursitis there would need to be a full clinical evaluation with specific criteria and potentially lateral hip imaging.2
This study focused on evaluating patients who developed lateral hip pain following THA postoperatively between the years of 2014-17. Any other cause of lateral hip pain was excluded such as osteolysis, trochanteric insufficiency or nonunion, infection, and abductor insufficiency or weakness. In total, one hundred and fifty-seven patients were identified who had undergone a THA at one institution. When controlling for BMI, age, and biological sex, we were able to conclude there is no significant association between development of lateral hip pain and a change in femoral offset. Regardless of the femoral offset change, whether calculated from preoperative hip (groups 1, 2, and 3) or contralateral hip (groups 4, 5, and 6) there was no increase in incidence of lateral hip pain following THA.
There were some limitations to this study. All the surgeries were performed by four different surgeons all utilizing the posterolateral approach. One study showed that the posterior approach to the hip was associated with decreased incidence of lateral trochanteric pain relative to the direct lateral approach.10 Additional studies should investigate these offset results would be consistent in other surgical approaches. Further investigation is necessary to see if the offset change would influence postoperative complications given a different surgical approach. Another limitation of the study was the utilization of plain radiographs to measure both preoperative and postoperative femoral offset. Plain radiographs are adequate for measuring leg length and global offset which is a major goal in THA, however plain radiographs fail to reflect changes of femoral offset in some THAs.11 CT scans may be a better option for measuring offset values, however, these scans would neither be clinically or ethically indicated as plain radiographs are far more feasible and accessible for most patients. Another possible confounding variable would be assuming anatomic femoral offset would be equal bilaterally in healthy patients and therefore also have similar morphology postoperatively. However, studies have demonstrated the femoral offset of a single hip can differ by as much as 4.6 mm from the contralateral hip in a healthy patient.12
5. Conclusions
Overall, this study found no statistical association between a change in the femoral offset and lateral hip pain in patients who had undergone THA. The limitations that were faced in this study include relatively small sample size, relying on plain film radiographs for offset measurement, and its retrospective nature. Despite these limitations, none of the controlled variables proposed in this study were close to nearing statistical significance, which allows us to infer that even with a larger sample size, the results would likely remain as found. Additional high-quality, ideally prospective, studies are needed to further evaluate the effect of increased femoral offset on the incidence of lateral hip pain following THA.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Contributor Information
Michael Foy, Email: mfoy3@uic.edu.
Daniel Kielminski, Email: dkielm2@uic.edu.
Daniel Cavazos, Email: dcavaz2@uic.edu.
Awais Hussain, Email: awaish@uic.edu.
Anshum Sood, Email: asood4@uic.edu.
Mark Gonzalez, Email: hand15@uic.edu.
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