Femoral head to neck offset after hip resurfacing is critical for range of motion

The Impact of Varying Femoral Head Length on Hip External Rotation During Posterior-approach Total Hip Arthroplasty

Background

Prior investigations of total hip arthroplasty (THA) have studied the effects of prosthetic femoral head size and stem offset on hip range of motion (ROM), impingement risk, and overall hip stability to optimize the return to activities of daily living. However, the relationship between femoral head length and hip ROM, specifically external rotation (ER), has not been evaluated. The aim of our study was to intraoperatively assess how femoral head length affects hip ROM during a posterior approach THA.

Methods

Thirty-two patients undergoing a primary elective THA through a posterior approach were prospectively included. After final femoral stem insertion, femoral head trials were performed using the targeted head length, followed by the shorter (-3.0 to -3.5 mm) and longer (+3.0 to +4.0 mm) head length configurations. At each length, hip ER was measured using an intraoperative goniometer from an imageless navigation system. ER values across the three head lengths were compared using a repeated-measures analysis of variance and paired t-tests.

Results

Varying femoral head lengths demonstrated a statically significant and reproducible effect on intraoperative ER range (analysis of variance; P < .001) in each patient. An increased femoral head length (mean 3.4 mm) significantly decreased (P < .001) ER range by 10.8 ± 3.3° while a shortened femoral head length (mean 3.5 mm) significantly increased (P < .001) the ER ROM by 6.0 ± 3.8°.

Conclusions

The results of this study demonstrate the sensitivity of hip ROM to incremental changes in femoral head length. As ER is important for activities of daily living, inadvertent lengthening should be avoided.

Variation in femoral anteversion in patients requiring total hip replacement

BACKGROUND

Optimal implant alignment is important for total hip replacement (THR) longevity. Femoral stem anteversion is influenced by the native femoral anteversion. Knowing a patient's femoral morphology is therefore important when planning optimal THR alignment. We investigated variation in femoral anteversion across a patient population requiring THR.

METHODS

Preoperatively, native femoral neck anteversion was measured from 3-dimensional CT reconstructions in 1215 patients.

RESULTS

The median femoral anteversion was 14.4° (-27.1-54.5°, IQR 7.4-20.9°). There were significant gender differences (males 12.7°, females 16.0°; p < 0.0001). Femoral anteversion in males decreased significantly with increasing age. 14% of patients had extreme anteversion (<0° or >30°).

CONCLUSIONS

This is the largest series investigating native femoral anteversion in a THR population. Patient variation was large and was similar to published findings of a non-THR population. Gender and age-related differences were observed. Native femoral anteversion is patient-specific and should be considered when planning THR.

Diminished femoral head-neck offset and the restricted hip range of motion suggesting a possible role in ACL injuries

PURPOSE

Femoroacetabular impingement may be associated with anterior cruciate ligament (ACL) injuries. The purpose of this study was to determine the head-neck offset, as measured by 45° Dunn's view alpha angles, in patients with ACL injuries compared to control subjects.

METHODS

In this retrospective study, 140 consecutive non-professional athletes with primary ACL ruptures confirmed with knee arthroscopy and 100 consecutive patients with non-ACL injury were enrolled. Hip range of motion was assessed in lower extremities in all participants, and alpha angle was calculated according to 45° Dunn's view radiographs.

RESULTS

There is not any difference in age, gender distribution, height, weight, and BMI between groups. Internal rotation, abduction, and adduction of the hip were significantly decreased in ACL-injured patients comparing with control subjects (p < 0.001). ACL-injured patients had also a significantly higher alpha angle comparing to the control individuals (p < 0.001). The mean of alpha angle in the ACL-injured patients was 56.1 (SD 10.1) and in the non-ACL-injured group was 49.3 (SD 9.4).

CONCLUSIONS

The patients in ACL-injured group showed a significant restriction in hip range of motion and also a diminished femoral head-neck offset suggesting a possible role of these findings in the outcome assessed.

LEVEL OF EVIDENCE

III.

Does component alignment affect gait symmetry in unilateral total hip arthroplasty patients?

BACKGROUND

Component malposition in total hip arthroplasty patients has been associated with adverse clinical outcomes. However, whether the component alignment influences hip dynamic performance following total hip arthroplasty remains unclear. The purpose of this study was to investigate the relationship between the component alignment and in vivo hip kinematics during gait.

METHODS

Nineteen unilateral total hip arthroplasty patients received CT scan for creation of 3D hip models. The component alignment between the non-implanted and implanted hips were measured and compared. Three-dimensional hip kinematics for both hips of the total hip arthroplasty patients during gait was quantified using a dual fluoroscopic imaging technique. The differences between the implanted and non-implanted hip kinematics during gait were calculated. A forward stepwise multiple linear regression was performed to evaluate the relationships between the changes in implanted hip kinematics and the differences in component alignment with respect to the non-implanted hips.

FINDINGS

An average 5.1° (SD 6.5°; range -11.1° to 18.3°) increase in internal rotation was observed in the implanted hip than the contralateral non-implanted hip and significantly correlated with a linear combination of the increase of cup anteversion, cup medial translation and leg lengthening (R=0.81).

INTERPRETATION

Results suggested that the total hip arthroplasty patients compensated the changes in hip geometry by altering the dynamic movement during gait. Restoration of the native hip geometry, including acetabular cup anteversion, position and leg length could be one of the factors that influence the hip kinematics symmetry in total hip arthroplasty patients during gait.

Femoral head diameter considerations for primary total hip arthroplasty

The configuration of total hip arthroplasty (THA) implants has constantly evolved since they were first introduced. One of the key components of THA design is the diameter of the prosthetic femoral head. It has been well established that the risk of dislocation is lower as the head diameter increases. But head diameter impacts other variables beyond joint stability: wear, cam-type impingement, range of motion, restoration of biomechanics, proprioception and groin pain. The introduction of highly cross-linked polyethylene and hard-on-hard bearings has allowed surgeons to implant large-diameter heads that almost completely eliminate the risk of dislocation. But as a result, cup liners have become thinner. With femoral head diameters up to 36 mm, the improvement in joint range of motion, delay in cam-type impingement and reduction in dislocation risk have been clearly demonstrated. Conversely, large-diameter heads do not provide any additional improvements. If an "ecologically sound" approach to hip replacement is embraced (e.g. keeping the native femoral head diameter), hip resurfacing with a metal-on-metal bearing must be carried out. The reliability of large-diameter femoral heads in the longer term is questionable. Large-diameter ceramic-on-ceramic bearings may be plagued by the same problems as metal-on-metal bearings: groin pain, squeaking, increased stiffness, irregular lubrication, acetabular loosening and notable friction at the Morse taper. These possibilities require us to be extra careful when using femoral heads with a diameter greater than 36 mm.

Optimal anterior femoral offset for functional range of motion in total hip arthroplasty--a computer simulation study

PURPOSE

Compared to medial femoral offset (MFO), the role of anterior femoral offset (AFO) on range of motion (ROM) in total hip arthroplasty (THA) has not been fully examined. We therefore defined AFO as the anterior distance from the centre of the femoral head to the proximal femoral axis in the sagittal plane and determined the optimal AFO required for ROM needed for activities of daily living using a computer-simulated THA model.

METHODS

Various AFOs were obtained by changing stem anteversion (stem-AV) and stem tilt in the sagittal plane (stem-tilt) using a CT-based simulation software. The required ROM was defined as: flexion ≥ 110°, internal rotation at 90° flexion (IR) ≥ 30°, external rotation (ER) ≥ 30°, and extension ≥ 30°, and we determined AFO and MFO to satisfy required ROM.

RESULTS

AFO was positively correlated with stem-AV and anterior stem-tilt. MFO was negatively correlated with stem-AV and not influenced by stem-tilt. Flexion and IR increased with both increased AFO and MFO, whereas extension and ER decreased with increased AFO. A smoothing spline curve showed the optimal AFO and MFO for required ROM to be from 15 mm to 25 mm on average and more than 32.1 mm, respectively.

CONCLUSIONS

This is the first study to show that AFO directly influenced ROM in THA. Optimal AFO as well as MFO should be reconstructed to achieve sufficient ROM.

Correlation between groin pain and cup design of hip-resurfacing implants: a prospective study

PURPOSE

Cup design has been incriminated as the source of groin pain after hip resurfacing but has not been well described; thus, it was assessed in a prospective study looking at three implant types.

METHODS

A group-match was done between three groups of hip resurfacing devices according to age, sex, body mass index, activity level, osteoarthritis aetiology and pre-operative scores.

RESULTS

The global groin pain rate was 5.7 % at six months and 2.7 % at last follow-up. Groin pain rate was significantly different between the three groups (p = 0.004) and had a strong influence on the subjective results (p = 0.04). No groin pain emerged between six months and last follow-up. No clinical differences were noted in Harris hip score and Merle d'Aubigné-Postel score at last follow-up. However, the Oxford hip score and Devane activity score were significantly lower for cups with macrostructures.

CONCLUSION

The low groin pain rate in this prospective cohort was probably secondary to the specific surgical technique used and seems to be correlated with cup design. Macrostructures on the external part of the cup could be significantly harmful.

Can patients return to high-impact physical activities after hip resurfacing? A prospective study

PURPOSE

Although the resumption of low-impact sports activities is compatible with total hip arthroplasty (THA), participation in high-impact sports seems problematic, and there is no consensus as to whether it is advisable. The purpose of this article is to evaluate the quality and possibility of resuming high-impact physical activities after hip resurfacing.

MATERIALS

The study was performed in an on-going, single-surgeon, prospective series of 215 resurfacing arthroplasties (RSA). Mean follow-up was 44.1 months (range, 39.1-54.5). Clinical evaluation included the Postel-Merle d'Aubigné (PMA) score, the Oxford hip score, the Harris hip score (HHS), Devane score, and UCLA activity score. A specific questionnaire analysing sports activities was administered to each patient to assess the number and level of physical activities performed (both before the operation and at final follow-up).

RESULTS

In the series of 202 consecutive patients (215 RSA), 50 patients (55 RSA) engaged regularly in at least one high-impact activity before their operation and the onset of pain, 102 patients practised at least one intermediate-impact activity, and the 50 remaining patients undertook only low-impact activities. Harris hip score increased from 44.8 (range, 23-68) before the operation to 97.8 (range, 85-100) at the last follow-up. Mean time to sports resumption after surgery was 14.6 weeks (range, 7-29). The resumption rate was 98 % for sports of any impact level and 82 % for high-impact activities. No osteolysis or implant loosening was observed at follow-up. No revision was performed.

CONCLUSION

In 2012, no consensus recommendations yet exist for the resumption of sports activities after RSA. Existing recommendations concern only conventional THA. We believe that RSA allows younger and more active patients to resume physical and sports activities without restriction. The rate of return to sports after RSA appears to be excellent and unequalled by conventional hip prostheses. High-impact sports seem to be compatible with hip resurfacing, although no long-term studies have analysed the impact of these activities on wear and/or aseptic loosening.

Effects of design parameters of total hip components on the impingement angle and determination of the preferred liner skirt shape with an adequate oscillation angle

The oscillation angle (OsA), which is the sum of the impingement angles on the two sides when the prosthetic neck sways from the neutral axis of the acetabular cup to the liner rim, is one of the most important factors that can affect the range of motion of an artificial hip joint. The aim of this study was to determine the influence of total hip component design on the impingement angle. Our findings show that an increase in cup depth of the liner restricts the motion of the neck and results in a reduced impingement angle, while an increase in chamfer angle increases the impingement angle until it reaches a critical value when a further increase no longer results in an increase in impingement angle. The impingement angle is not only dependent on the head/neck ratio, but also on the head size itself. For most arbitrarily chosen cup depths and chamfer angles, the neck only impacts at one point on the liner. This study proposes a suitable combination of cup depth and chamfer angle and a preferred impact mode, which, if impingement does occur, enables the neck to impinge on the liner rim over a large area. Cup-neck combinations that have an adequate OsA with maximum femoral head coverage are presented.

Decreased femoral head-neck offset: a possible risk factor for ACL injury

PURPOSE

Reduction in anterior cruciate ligament (ACL) injuries in young, active individuals continues to be a major goal in sports medicine. The purpose of this study was to determine the head-neck offset, as measured by AP pelvis alpha angles, in patients presenting to a single surgeon with isolated ACL and non-ACL knee injuries.

METHODS

In a group of 48 patients with complete, primary ACL rupture and 42 controls with non-ACL injury (i.e., meniscus tear, cartilage defect), a single surgeon, blinded to the diagnosis, took radiographic measures of the AP alpha angle of both hips and the weight-bearing line at both knees. All knee pathology was confirmed with knee arthroscopy. Inclusion criteria included no previous hip or knee surgery, and long-leg standing alignment radiographic series completed at index visit.

RESULTS

There was no difference in gender distribution, height, BMI or age between groups. ACL-injured patients had a significantly higher alpha angle (mean = 84, SD = 14) on the injured side than the controls (mean = 59, SD = 7, p < 0.0001). Ninety-four percent of the ACL-injured group had alpha angles over 60°, while only 35% of the non-ACL-injured group had alpha angles over 60° (p = 0.001). Those patients with alpha angle over 60° were 27 times more likely (95% CI 6.4-131) to be in the ACL injury group than those patients with alpha angle 60° or less (p = 0.001).

CONCLUSION

Our findings establish an important preliminary correlation between ACL injury and diminished femoral head-neck offset, as characterized by abnormal, elevated alpha angles.

LEVEL OF EVIDENCE

Prognostic study, Level III.