Development and evaluation of an image-free computer-assisted impingement detection technique for total hip arthroplasty

Preliminary study of short-term outcomes and learning curves of robotic-assisted THA: comparison between closed platform robotic system and open platform robotic system

BACKGROUND

Both closed platform and open platform robotic-assisted total hip arthroplasty (THA) have recently been recommended as a viable treatment option for achieving accurate positioning of components. Yet, limited studies paid attention to the differences between the closed platform robotic system and the open platform robotic system. Hence, this study aimed to investigate clinical outcomes, radiographic outcomes, complication rates and learning curve of two systems.

MATERIALS AND METHODS

We retrospectively included 62 patients (31 closed robotic system and 31 open robotic system) who underwent THA between February 2021 and January 2023. The demographics, operating time, cup positioning, complications and hip Harris score were evaluated. Learning curves of operation time was conducted using cumulative sum (CUSUM) analysis.

RESULTS

There were no differences in surgical time (76.7 ± 12.1 min vs. 72.3 ± 14.8 min), estimated blood loss (223.2 ± 13.2 ml vs. 216.9 ± 17 ml) and Harris Hip score (HHS) between closed platform robotic system and the open platform robotic system. The closed robotic system and the open robotic system were associated with a learning curve of 9 cases and 7 cases for surgical time respectively, based on the satisfying rate of Lewinnek's safe zone outliers (1/31, 96.8%) and no occurrence of complication. Both robotic systems had significant reduction in overall surgical time, the duration of acetabulum registration, and estimated blood loss between learning phase and proficiency phase.

CONCLUSION

The authors suggest that the surgical outcomes and safe zone outlier rate of the open robotic-assisted THA were similar to those of the closed robotic-assisted THA. These two robotic-assisted are associated with comparable learning curves and both have the precise positioning of acetabular component. From learning phase to proficiency phase, the rate of positions within the safe zone differed only marginally (88.9-100% vs. 85.7-100%) based on a rather low number of patients. This is not a statistically significant difference. Therefore, we suggest that THA undergoing with the robotic-assisted system is the relatively useful way to achieve planned acetabular cup position so far.

Which Safe Zone Is Safe in Total Hip Arthroplasty? The Effect of Bony Impingement

“Safe zones” for cup position are currently being investigated in total hip arthroplasty (THA). This study aimed to evaluate the impact of bony impingement on the safe zone and provide recommendations for cup position in THA. CT scans were performed on 123 patients who underwent a cementless THA. Using the implant data and bone morphology from the CT scans, an impingement detection algorithm simulating range of motion (ROM) determined the presence of prosthetic and/or bony impingement. An impingement-free zone of motion was determined for each patient. These zones were then compared across all patients to establish an optimized impingement-free “safe zone”. Bony impingement reduced the impingement-free zone of motion in 49.6% (61/123) of patients. A mean reduction of 23.4% in safe zone size was observed in relation to periprosthetic impingement. The superposition of the safe zones showed the highest probability of impingement-free ROM with cup position angles within 40–50° of inclination and 20–30° of anteversion in relation to the applied cup and stem design of this study. Virtual ROM simulations identified bony impingement at the anterosuperior acetabular rim for internal rotation at 90° of flexion and at the posteroinferior rim for adduction as the main reasons for bony impingement.

Inaccurate offset restoration in total hip arthroplasty results in reduced range of motion

Offset restoration in total hip arthroplasty (THA) is associated with postoperative range of motion (ROM) and gait kinematics. We aimed to research into the impact of high offset (HO) and standard stems on postoperative ROM. 121 patients received cementless THA through a minimally-invasive anterolateral approach. A 360° hip ROM analysis software calculated impingement-free hip movement based on postoperative 3D-CTs compared to ROM values necessary for activities of daily living (ADL). The same model was then run a second time after changing the stem geometry between standard and HO configuration with the implants in the same position. HO stems showed higher ROM for all directions between 4.6 and 8.9° (p < 0.001) compared with standard stems but with high interindividual variability. In the subgroup with HO stems for intraoperative offset restoration, the increase in ROM was even higher for all ROM directions with values between 6.1 and 14.4° (p < 0.001) compared to offset underrestoration with standard stems. Avoiding offset underrestoration resulted in a higher amount of patients of over 20% for each ROM direction that fulfilled the criteria for ADL (p < 0.001). In contrast, in patients with standard stems for offset restoration ROM did increase but not clinically relevant by offset overcorrection for all directions between 3.1 and 6.1° (p < 0.001). Offset overcorrection by replacing standard with HO stems improved ROM for ADL in a low number of patients below 10% (p > 0.03). Patient-individual restoration of offset is crucial for free ROM in THA. Both over and underrestoration of offset should be avoided.

Effect of soft-tissue impingement on range of motion during posterior approach Total Hip Arthroplasty: an in vivo measurement study

PURPOSE

While implant impingement and bony impingement have been recognized as causes of poor outcomes in total hip arthroplasty (THA), reports of soft-tissue impingement are rare. To clarify the issue, the effect of anterior capsule resection on hip range of motion (ROM) was quantitatively measured in vivo during posterior approach THA using a CT-based hip navigation system.

MATERIALS AND METHODS

For 47 patients (51 hips), hip ROM was measured intraoperatively before and after resection of the anterior hip capsule, and the difference was compared.

RESULTS

Resection of the anterior hip capsule brought about an average 6° increase of ROM in the direction of flexion with internal rotation and did not markedly change ROM in other directions.

CONCLUSIONS

During THA through a posterior approach, soft-tissue impingement by the anterior hip capsule can occur. Clinically, we expect that resection of the anterior hip capsule can reduce the risk of posterior instability without increasing the risk of anterior instability.

Femur First navigation can reduce impingement severity compared to traditional free hand total hip arthroplasty

Impingement is a major source of dislocation and aseptic loosening in total hip arthroplasty (THA). We compared impingement free range of motion (ROM) using a novel computer navigated femur first approach to conventional THA. In addition, impingement between genders was also explored. In a retrospective analysis of 121 THA patients, subject-specific post-operative ROM was simulated using post-operative 3D-CT data, and compared with the benchmark ROM, essential for activities of daily living. Three parameters were defined to express both implant-to-implant (ITI) and bone-to-bone (BTB) impingement - coverage percentage, third angle, and impingement severity. Although coverage percentage was similar between the navigated and conventional group for both ITI (p = 0.69) and BTB (p = 0.82) impingement, third angle was significantly reduced in the navigation group for both ITI (p = 0.02) and BTB (p = 0.05) impingement. Impingement severity for both ITI (p = 0.01) and BTB (p = 0.05) was significantly decreased in the navigation group compared to the conventional. Impingement severity in men was considerably higher compared to women for both ITI (p = 0.002) and BTB (p = 0.02). Navigation guided femur first THA is able to improve alignment of ROM axis, and consequently, to reduce impingement in THA. Men seem to be more prone to impingement than women.

Navigation is Equal to Estimation by Eye and Palpation in Preventing Psoas Impingement in THA

BACKGROUND

Iliopsoas tendon impingement is one possible reason for persistent groin pain and diminished functional outcome after THA. So far, estimation by eye and palpation is the standard procedure to intraoperatively assess the distance of the cup to the anterior rim. However, novel technologies such as imageless navigation enable intraoperative measurements of the cup in relation to the psoas tendon and bony landmarks.

QUESTIONS/PURPOSES

We asked whether psoas impingement (1) can be reduced using imageless navigation compared with the standard technique and (2) is associated with specific patient characteristics. Furthermore, we investigated (3) if anterior cup protrusion (overhang) is associated with lower outcome scores for pain and function.

METHODS

The current study is a reanalysis of data from a randomized controlled trial evaluating navigation for THA; 135 patients were randomized for surgery with or without the use of imageless navigation. The risk for anterior protrusion of the cup above the acetabular rim and thus potential psoas impingement, defined as an overhang of the cup above the anterior acetabular rim as measured on postoperative CT, was either controlled with the help of navigation or standard control by eye and palpation intraoperatively. Postoperatively, the anterior protrusion of the cup above the acetabular rim was measured on three-dimensional (3-D) CT by a blinded, external institute. In addition to patient-related outcome measures, the Harris hip score, Hip disability and Osteoarthritis Outcome Score, and EuroQol were obtained 1 year postoperatively. Altogether 123 data sets were available for primary analysis and 115 were available for 1-year followup.

RESULTS

There was no difference, with the numbers available, between the navigated and the control groups in terms of the mean distance of the cup below the anterosuperior acetabular rim (3.9 mm; -5.3 to 12.6 mm versus 4.4 mm; -7.9 to 13.7 mm; p = 0.72) or the anteroinferior acetabular rim (4.7 mm; -6.2 to 14.8 mm versus 4.2 mm; -7.1 to 16.3 mm; p = 0.29). There was no difference, with the numbers available, in terms of the proportion of cups with anterior overhang (7%, four of 57 versus, 15%, 10 of 66; p = 0.16), respectively. After controlling for potential confounding variables such as cup inclination, cup size, patient age, BMI, stage of arthritis, and length of skin incision, we found cup anteversion (hazard ratio [HR], 0.87; 95% CI, 0.81-0.93; p < 0.001) and female sex (HR, 3.88; 95% CI, 1.01-14.93; p = 0.049) were associated with a propensity to potential psoas impingement. With the numbers available, there were no differences observed in clinical scores between groups with and without anterior cup protrusion.

CONCLUSIONS

We found no differences between imageless navigation and estimation by eye and palpation in preventing potential psoas impingement. Despite the comparable clinical outcome for patients with and without cup protrusion, the orthopaedic surgeon should be especially aware of propensity for psoas impingement in women.

LEVEL OF EVIDENCE

Level II, therapeutic study.

Even the Intraoperative Knowledge of Femoral Stem Anteversion Cannot Prevent Impingement in Total Hip Arthroplasty

BACKGROUND

In this prospective study of 66 patients undergoing cementless total hip arthroplasty through a minimally invasive anterolateral approach, we evaluated the impact of an intraoperative hybrid combined anteversion technique on postoperative range of motion (ROM).

METHODS

After navigation of femoral stem anteversion, trial acetabular components were positioned manually, and their position recorded with navigation. Then, final components were implanted with navigation at the goals prescribed by the femur-first impingement detection algorithm. Postoperatively, three-dimensional computed tomographies were performed to determine achieved component position and model impingement-free ROM by virtual hip movement, which was compared with published values necessary for activities of daily living. This model was run a second time with the implants in the position selected by the surgeon rather than the navigation program. In addition, we researched into risk factors for ROM differences between the freehand and navigated cup position.

RESULTS

We found a lower flexion of 8.3° (8.8°, P < .001) and lower internal rotation of 9.2° (9.5°, P < .001) for the freehand implanted cups in contrast to a higher extension of 9.8° (11.8°, P < .001) compared with the navigation-guided technique. For activities of daily living, 58.9% (33/56) in the freehand group compared with 85.7% (48/56) in the navigation group showed free flexion (P < .001) and similarly 50.0% (28/56) compared with 76.8% (43/56) free internal rotation (P < .001). Body mass index, incision length, and cup size were identified as independent risk factors for reduced flexion and internal rotation in the freehand group.

CONCLUSION

For implementation of a combined anteversion algorithm, intraoperative alignment guides for accurate cup positioning are required using a minimally invasive anterolateral approach. Obese patients are especially at risk of cup malpositioning.

Gait six month and one-year after computer assisted Femur First THR vs. conventional THR. Results of a patient- and observer- blinded randomized controlled trial

A prospective randomized controlled trial is presented that is used to compare gait performance between the computer assisted Femur First (CAS FF) operation method and conventional THR (CON). 60 patients underwent a 3D gait analysis of the lower extremity at pre-operative, 6 months post-operative and twelve months post-operative. Detailed verification experiments were facilitated to ensure the quality of data as well as to avoid over-interpreting of the data. The results confirm a similar data-quality as reported in the literature. Walking speed, range of motion and symmetry thereof improved over the follow-up period, without significant differences between the groups. While all parameters do significantly increase over the follow-up period for both groups, there were no significant differences between them at any given time-point. Patients undergoing CAS FF showed a trend to improved hip flexion angle indicating a possible long-term benefit.

Visual intraoperative estimation of range of motion is misleading in minimally invasive total hip arthroplasty

INTRODUCTION

Generally range of motion (ROM) in total hip arthroplasty (THA) is intraoperatively assessed by eye. Can we assume that visual estimation of ROM is reliable?

METHODS

60 patients underwent cementless THA in a subgroup analysis of a clinical prospective trial using a minimally invasive anterolateral approach in lateral decubitus position. Four experienced surgeons intraoperatively estimated ROM visually by assessment of the femur relative to the alignment of the patient's pelvis. These estimations were compared with computer navigation measurements.

RESULTS

We found a mean difference between navigation measurements and intraoperative estimations by eye of -5.6° (±10.9°; -17° to 30°) for flexion, respectively, -0.4° (±10.7°; -24° to 30°) for extension, 8.7° (±9.0°; -10° to 34°) for abduction, 5.9° (±18.3°; -58° to 68°) for external rotation and -5.8° (±12.1°; -38° to 22°) for internal rotation. Multivariate analysis showed no association between the visual accuracy of estimation of ROM and patient characteristics, such as BMI, sex, grade of osteoarthritis and treatment side except for a significant correlation of visual accuracy of estimation of extension and the level of professional experience. Otherwise, the level of professional experience had no impact on the accuracy of estimation of ROM by eye.

CONCLUSIONS

Even the experienced surgeon's intraoperative estimation of ROM by eye is not reliable and differs up to 30° compared to objective measurements in minimally invasive THA. For accurate intraoperative assessment of ROM, the use of technical devices is recommended.

TRIAL REGISTRATION

DRKS00000739.

Current standard rules of combined anteversion prevent prosthetic impingement but ignore osseous contact in total hip arthroplasty

PURPOSE

In this prospective study of 135 patients undergoing cementless total hip arthroplasty (THA) we asked whether six current definitions of combined anteversion prevent impingement and increase postoperative patient individual impingement-free range-of-motion (ROM).

METHODS

Implant position was measured by an independent, external institute on 3D-CT performed six weeks post-operatively. Post-operative ROM was calculated using a CT-based algorithm detecting osseous and/or prosthetic impingement by virtual hip movement. Additionally, clinical ROM was evaluated pre-operatively and one-year post-operatively by a blinded observer.

RESULTS

Combined component position of cup and stem according to the definitions of Ranawat, Widmer, Dorr, Hisatome and Yoshimine inhibited prosthetic impingement in over 90 %, while combined osseous and prosthetic impingement still occurred in over 40 % of the cases. The recommendations by Jolles, Widmer, Dorr, Yoshimine and Hisatome enabled higher flexion (p ≤ 0.001) and internal rotation (p ≤ 0.006). Clinically, anteversion rules of Widmer and Yoshimine provided one-year post-operatively statistically but not clinically relevant higher internal rotation (p ≤0.034).

CONCLUSION

Standard rules of combined anteversion detect prosthetic but fail to prevent combined osseous and prosthetic impingement in THA. Future models will have to account for the patient-individual anatomic situation to ensure impingement-free ROM.

Does Computer-Assisted Femur First THR Improve Musculoskeletal Loading Conditions?

We have developed a novel, computer-assisted operation method for minimal-invasive total hip replacement (THR) following the concept of “femur first/combined anteversion,” which incorporates various aspects of performing a functional optimization of the prosthetic stem and cup position (CAS FF). The purpose of this study is to assess whether the hip joint reaction forces and patient's gait parameters are being improved by CAS FF in relation to conventional THR (CON). We enrolled 60 patients (28 CAS FF/32 CON) and invited them for gait analysis at three time points (preoperatively, postop six months, and postop 12 months). Data retrieved from gait analysis was processed using patient-specific musculoskeletal models. The target parameters were hip reaction force magnitude (hrf), symmetries, and orientation with respect to the cup. Hrf in the CAS FF group were closer to a young healthy normal. Phase-shift symmetry showed an increase in the CAS FF group. Hrf orientation in the CAS FF group was closer to optimum, though no edge or rim-loading occurred in the CON group as well. The CAS FF group showed an improved hrf orientation in an early stage and a trend to an improved long-term outcome.

Impingement-free range of movement, acetabular component cover and early clinical results comparing ‘femur-first’ navigation and ‘conventional’ minimally invasive total hip arthroplasty

We report the kinematic and early clinical results of a patient- and observer-blinded randomised controlled trial in which CT scans were used to compare potential impingement-free range of movement (ROM) and acetabular component cover between patients treated with either the navigated ‘femur-first’ total hip arthroplasty (THA) method (n = 66; male/female 29/37, mean age 62.5 years; 50 to 74) or conventional THA (n = 69; male/female 35/34, mean age 62.9 years; 50 to 75). The Hip Osteoarthritis Outcome Score, the Harris hip score, the Euro-Qol-5D and the Mancuso THA patient expectations score were assessed at six weeks, six months and one year after surgery. A total of 48 of the patients (84%) in the navigated ‘femur-first’ group and 43 (65%) in the conventional group reached all the desirable potential ROM boundaries without prosthetic impingement for activities of daily living (ADL) in flexion, extension, abduction, adduction and rotation (p = 0.016). Acetabular component cover and surface contact with the host bone were > 87% in both groups. There was a significant difference between the navigated and the conventional groups’ Harris hip scores six weeks after surgery (p = 0.010). There were no significant differences with respect to any clinical outcome at six months and one year of follow-up. The navigated ‘femur-first’ technique improves the potential ROM for ADL without prosthetic impingement, although there was no observed clinical difference between the two treatment groups.

Cite this article: Bone Joint J 2015; 97-B:890–8.