Stability of capsule closure and postoperative anterior knee pain after medial parapatellar approach in TKA.

PURPOSE: Anterior knee pain after total knee arthroplasty (TKA) remains a widely discussed postoperative complication. In contrast to sports traumatology, the role of the dissected medial patellofemoral ligament (MPFL) using a medial parapatellar approach in TKA has not been discussed so far. In the present study, it was hypothesized that the attempted repair of the MPFL in TKA by simple closure of the joint capsule may not be successful in some cases, causing anterior knee pain. Furthermore, it was hypothesized, that the success of repair might be influenced by femoral component rotation. METHODS: Forty patients received their TKA in a ligament-balanced and forty patients in a conventional measured-resection technique. After implantation of the TKA using a medial parapatellar approach, two titan clips were attached on both sides of the capsule incision. 3 days and 3 months after surgery, the dehiscence of the two clips was measured on skyline patella radiographs; additionally patellar tilt, shift, the Knee Society Score and the Feller Score were obtained. RESULTS: 48 patients showed an increase of capsule dehiscence. Patients with a capsule dehiscence of more than 4 mm showed significantly less improvement in the Feller score 3 months postoperatively than patients with a capsule dehiscence ≤4 mm. Regarding the radiological measurements and the clinical outcome, no significant difference between the ligament-balanced and the measured-resection group was found. CONCLUSIONS: The present results suggest that the successful repair of the MPFL after using a medial parapatellar approach in TKA could reduce the high rate of postoperative anterior knee pain. Furthermore, the appearance of capsule dehiscence and anterior knee pain does not seem to be dependent on the used operative technique.

Soft tissue restricts impingement-free mobility in total hip arthroplasty.

PURPOSE: Impingement is a major source for decreased range of motion (ROM) and dislocation in total hip arthroplasty (THA). In the current study we analyzed the impact of soft tissue impingement on ROM compared to bony and/or prosthetic impingement. METHODS: In the course of a prospective clinical trial 54 patients underwent cementless total hip arthroplasty in the lateral decubitus position using imageless navigation. The navigation device enabled intra-operative ROM measurements indicating soft tissue impingement. Post-operatively, all patients received postoperative 3D-CT. Absolute ROM without bony and/or prosthetic impingement was calculated with the help of a collision-detection-algorithm. RESULTS: Due to soft tissue impingement we found a reduced ROM of over 20° (p < 0.001) compared to bony and/or prosthetic impingement regarding flexion, extension, abduction and adduction and of over 10° regarding external rotation (p < 0.001). In contrast, soft tissue impingement showed less impact on internal rotation in 90° of flexion (p = 0.76). Multivariate analysis showed an association between BMI and flexion, whereas all other ROM directions were independent of BMI. CONCLUSIONS: Soft tissue has a major impact on impingement-free ROM after THA. For the majority of movements, soft tissue restrictions are more important than bony and prosthetic impingement. Future models of patient individual joint replacement including pre-operative (CT) planning and intra-operative navigation should include algorithms additionally accounting for soft tissue impingement.

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.

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.

Visual intraoperative estimation of cup and stem position is not reliable in minimally invasive hip arthroplasty.

Background and purpose - In hip arthroplasty, acetabular inclination and anteversion-and also femoral stem torsion-are generally assessed by eye intraoperatively. We assessed whether visual estimation of cup and stem position is reliable. Patients and methods - In the course of a subgroup analysis of a prospective clinical trial, 65 patients underwent cementless hip arthroplasty using a minimally invasive anterolateral approach in lateral decubitus position. Altogether, 4 experienced surgeons assessed cup position intraoperatively according to the operative definition by Murray in the anterior pelvic plane and stem torsion in relation to the femoral condylar plane. Inclination, anteversion, and stem torsion were measured blind postoperatively on 3D-CT and compared to intraoperative results. Results - The mean difference between the 3D-CT results and intraoperative estimations by eye was -4.9° (-18 to 8.7) for inclination, 9.7° (-16 to 41) for anteversion, and -7.3° (-34 to 15) for stem torsion. We found an overestimation of > 5° for cup inclination in 32 hips, an overestimation of > 5° for stem torsion in 40 hips, and an underestimation < 5° for cup anteversion in 42 hips. The level of professional experience and patient characteristics had no clinically relevant effect on the accuracy of estimation by eye. Altogether, 46 stems were located outside the native norm of 10-20° as defined by Tönnis, measured on 3D-CT. Interpretation - Even an experienced surgeon's intraoperative estimation of cup and stem position by eye is not reliable compared to 3D-CT in minimally invasive THA. The use of mechanical insertion jigs, intraoperative fluoroscopy, or imageless navigation is recommended for correct implant insertion.

The influence of component alignment on patellar kinematics in total knee arthroplasty.

BACKGROUND AND PURPOSE: Postoperative anterior knee pain is one of the most frequent complications after total knee arthroplasty (TKA). Changes in patellar kinematics after TKA relative to the preoperative arthritic knee are not well understood. We compared the patellar kinematics preoperatively with the kinematics after ligament-balanced navigated TKA. PATIENTS AND METHODS: We measured patellar tracking before and after ligament-balanced TKA in 40 consecutive patients using computer navigation. Furthermore, the influences of different femoral and tibial component alignment on patellar kinematics were analyzed using generalized linear models. RESULTS: After TKA, the patellae shifted statistically significantly more laterally between 30° and 60°. The lateral tilt increased at 90° of flexion whereas the epicondylar distance decreased between 45° and 75° of flexion. Sagittal component alignment, but not rotational component alignment, had a significant influence on patellar kinematics. INTERPRETATION: There are major differences in patellar kinematics between the preoperative arthritic knee and the knee after TKA. Combined sagittal component alignment in particular appears to have a major effect on patellar kinematics. Surgeons should be especially aware of altering preoperative sagittal alignment until the possible clinical relevance has been investigated.

Fluoroscopy and imageless navigation enable an equivalent reconstruction of leg length and global and femoral offset in THA.

BACKGROUND: Restoration of biomechanics is a major goal in THA. Imageless navigation enables intraoperative control of leg length equalization and offset reconstruction. However, the effect of navigation compared with intraoperative fluoroscopy is unclear. QUESTIONS/PURPOSES: We asked whether intraoperative use of imageless navigation (1) improves the relative accuracy of leg length and global and femoral offset restoration; (2) increases the absolute precision of leg length and global and femoral offset equalization; and (3) reduces outliers in a reconstruction zone of ± 5 mm for leg length and global and femoral offset restoration compared with intraoperative fluoroscopy during minimally invasive (MIS) THA with the patient in a lateral decubitus position. METHODS: In this prospective study a consecutive series of 125 patients were randomized to either navigation-guided or fluoroscopy-controlled THA using sealed, opaque envelopes. All patients received the same cementless prosthetic components through an anterolateral MIS approach while they were in a lateral decubitus position. Leg length, global or total offset (representing the combination of femoral and acetabular offset), and femoral offset differences were restored using either navigation or fluoroscopy. Postoperatively, residual leg length and global and femoral offset discrepancies were analyzed on magnification-corrected radiographs of the pelvis by an independent and blinded examiner using digital planning software. Accuracy was defined as the relative postoperative difference between the surgically treated and the unaffected contralateral side for leg length and offset, respectively; precision was defined as the absolute postoperative deviation of leg length and global and femoral offset regardless of lengthening or shortening of leg length and offset throughout the THA. All analyses were performed per intention-to-treat. RESULTS: Analyzing the relative accuracy of leg length restoration we found a mean difference of 0.2 mm (95% CI, -1.0 to +1.4 mm; p = 0.729) between fluoroscopy and navigation, 0.2 mm (95 % CI, -0.9 to +1.3 mm; p = 0.740) for global offset and 1.7 mm (95 % CI, +0.4 to +2.9 mm; p = 0.008) for femoral offset. For the absolute precision of leg length and global and femoral offset equalization, there was a mean difference of 1.7 ± 0.3 mm (p < 0.001) between fluoroscopy and navigation. The biomechanical reconstruction with a residual leg length and global and femoral offset discrepancy less than 5 mm and less than 8 mm, respectively, succeeded in 93% and 98%, respectively, in the navigation group and in 54% and 95%, respectively, in the fluoroscopy group. CONCLUSIONS: Intraoperative fluoroscopy and imageless navigation seem equivalent in accuracy and precision to reconstruct leg length and global and femoral offset during MIS THA with the patient in the lateral decubitus position.

Femoral pinless length and offset measurements during computer-assisted, minimally invasive total hip arthroplasty.

We asked whether the intraoperative assessment of leg length (LL) and offset (OS) change would be accurate using a novel pinless femoral reference system during unilateral minimally invasive THA in 50 patients with a mean age of 60 years (48-79). LL and OS change measured at surgery was compared with LL/OS change as measured on magnification-corrected preoperative and postoperative radiographs by two blinded examiners. The radiographic evaluation showed a high inter-rater reliability (r > 0.80 for all assessments). The mean differences (± 95% limits of agreement) between navigation and radiographic measurements on the treated side were +0.4mm (± 3.6) for LL and -1.0 mm (± 3.9) for OS. Femoral pinless navigation technology represents a feasible assistance in THA.

A minimally invasive approach for total hip arthroplasty does not diminish early post-operative outcome in obese patients: a prospective, randomised trial.

PURPOSE: The benefits of minimally invasive surgical techniques in total hip arthroplasty (THA) are well known, but concerns about applying those techniques in obese patients are controversial. We prospectively compared patients with increased body mass index (BMI ≥ 30) undergoing THA with normal weight patients. METHODS: A total of 134 patients admitted for unilateral THA were randomised to have surgery through either a transgluteal or a minimally invasive approach (MicroHip). In each group a BMI ≥ 30 was used to define obese patients. Pre- and early post-operative demographics, intraoperative data, baseline haematological values, hip function (Harris Hip Score, Oxford Hip Score) and quality of life (EQ-5D) were assessed with follow-up at three months. RESULTS: Duration of surgery, blood loss, C-reactive protein levels, radiographic measurements and complication rates were comparable in all groups. There was a tendency for lower serum creatine kinase levels in the MicroHip group. Intraoperative fluoroscopic time and dose area products were significantly elevated in patients with a BMI exceeding 30 regardless of the approach used. Time points of mobilisation, length of hospital stay and functional outcome measurements were similar in the different weight groups. CONCLUSIONS: Our data suggest that obese patients gain similar benefit from MicroHip THA as do non-obese patients. The results of this study should be further investigated to assess long-term survivorship.

The association between Femoral Tilt and impingement-free range-of-motion in total hip arthroplasty.

BACKGROUND: There is a complex interaction among acetabular component position and antetorsion of the femoral stem in determining the maximum, impingement-free prosthetic range-of-motion (ROM) in total hip arthroplasty (THA). By insertion into the femoral canal, stems of any geometry follow the natural anterior bow of the proximal femur, creating a sagittal Femoral Tilt (FT). We sought to study the incidence of FT as measured on postoperative computed tomography scans and its influence on impingement-free ROM in THA. METHODS: The incidence of the postoperative FT was evaluated on 40 computed tomography scans after cementless THA. With the help of a three-dimensional computer model of the hip, we then systematically analyzed the effects of FT on femoral antetorsion and its influence on calculations for a ROM maximized and impingement-free compliant stem/cup orientation. RESULTS: The mean postoperative FT on CT scans was 5.7° ± 1.8°. In all tests, FT significantly influenced the antetorsion values. Re-calculating the compliant component positions according to the concept of combined anteversion with and without the influence of FT revealed that the zone of compliance could differ by more than 200%. For a 7° change in FT, the impingement-free cup position differed by 4° for inclination when the same antetorsion was used. CONCLUSIONS: A range-of-motion optimized cup position in THA cannot be calculated based on antetorsion values alone. The FT has a significant impact on recommended cup positions within the concept of "femur first" or "combined anteversion". Ignoring FT may pose an increased risk of impingement as well as dislocation.

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

Periprosthetic or bony impingement in total hip arthroplasty (THA) has been correlated to dislocation, increased wear, reduced postoperative functionality with pain and/or decreased range of motion (ROM). We sought to study the accuracy and assess the reliability of measuring bony and periprosthetic impingement on a virtual bone model prior to the implantation of the acetabular cup with the help of image-free navigation technology in an experimental cadaver study. Impingement-free ROM measurements were recorded during minimally invasive, computer-assisted THA on 14 hips of 7 cadaveric donors. Preoperatively and postoperatively the donors were scanned using computed tomography (CT). Impingement-free ROM on three-dimensional CT-based models was then compared with corresponding, intraoperative navigation models. Bony/periprosthetic impingement can be detected with a mean accuracy limit of below 5° for motion angles, which should be reached after THA for activities of daily living with the help of image-free navigation technology.

Minimally invasive computer-navigated total hip arthroplasty, following the concept of femur first and combined anteversion: design of a blinded randomized controlled trial.

BACKGROUND: Impingement can be a serious complication after total hip arthroplasty (THA), and is one of the major causes of postoperative pain, dislocation, aseptic loosening, and implant breakage. Minimally invasive THA and computer-navigated surgery were introduced several years ago. We have developed a novel, computer-assisted operation method for THA following the concept of "femur first"/"combined anteversion", which incorporates various aspects of performing a functional optimization of the cup position, and comprehensively addresses range of motion (ROM) as well as cup containment and alignment parameters. Hence, the purpose of this study is to assess whether the artificial joint's ROM can be improved by this computer-assisted operation method. Second, the clinical and radiological outcome will be evaluated. METHODS/DESIGN: A registered patient- and observer-blinded randomized controlled trial will be conducted. Patients between the ages of 50 and 75 admitted for primary unilateral THA will be included. Patients will be randomly allocated to either receive minimally invasive computer-navigated "femur first" THA or the conventional minimally invasive THA procedure. Self-reported functional status and health-related quality of life (questionnaires) will be assessed both preoperatively and postoperatively. Perioperative complications will be registered. Radiographic evaluation will take place up to 6 weeks postoperatively with a computed tomography (CT) scan. Component position will be evaluated by an independent external institute on a 3D reconstruction of the femur/pelvis using image-processing software. Postoperative ROM will be calculated by an algorithm which automatically determines bony and prosthetic impingements. DISCUSSION: In the past, computer navigation has improved the accuracy of component positioning. So far, there are only few objective data quantifying the risks and benefits of computer navigated THA. Therefore, this study has been designed to compare minimally invasive computer-navigated "femur first" THA with a conventional technique for minimally invasive THA. The results of this trial will be presented as soon as they become available. TRIAL REGISTRATION NUMBER: DRKS00000739.

Tackling the learning curve: comparison between the anterior, minimally invasive (Micro-hip®) and the lateral, transgluteal (Bauer) approach for primary total hip replacement.

BACKGROUND AND PURPOSE: There is still conflicting evidence about the true benefit of minimally invasive (MI) techniques in total hip replacement (THR). The aim of this prospective study was to evaluate the safeness of a MI approach during the learning curve of a single surgeon. Second, clinical and radiographic results among the MI THR group were compared with the results using a standard transgluteal (Bauer) approach. METHODS: 86 primary unilateral total hip arthroplasties (THAs) through a MI, anterior (Micro-hip(®)) approach were performed by a single senior surgeon (ES), representing a consecutive series of patients after beginning with the MI technique. Cases were compared to a matched cohort of patients who were treated with a standard transgluteal (Bauer) approach. Operation time, incision length, perioperative blood loss, haemoglobin level and blood transfusions were monitored. Complications were documented and followed up 1 year postoperatively. The Harris Hip Score (HHS), range of motion, use of analgetics, the Trendelenburg sign, sensibility of the lateral femoral cutaneous nerve and the acetabular/femoral component placement as well as potential heterotopic ossifications were analysed in both the groups after 12 months postoperatively. RESULTS: 74 MI THR patients and 60 standard THR patients were available for the one year follow-up. Operative time was significantly longer in the MI group, reduction in the haemoglobin level during the first 24 h was significant and the length of skin incision was significantly shorter. No significant differences were found for HHS, range of motion, use of analgetics, the Trendelenburg sign, and the acetabular/femoral component placement, heterotopic ossifications and intra- and postoperative complications. Sensibility of the lateral femoral cutaneous nerve was affected in three patients in the MI group. Radiographic evaluation revealed no component migration, implant subsidence or radiolucency signs in both the groups. DISCUSSION: Consistent with recent meta-analysis we found reduced blood loss, similar clinical/radiographic outcome and similar complication rates compared to standard THA. Our study shows, that MI THR is a safe procedure during the learning curve of an experienced surgeon.

Accuracy of acetabular cup placement in computer-assisted, minimally-invasive THR in a lateral decubitus position.

In a prospective and randomised clinical study, we implanted acetabular cups either by means of an image-free computer-navigation system (navigated group, n = 32) or by free-hand technique (freehand group n = 32, two drop-outs). Total hip replacement was conducted in the lateral position and through a minimally invasive anterior approach (MicroHip). The position of the component was determined postoperatively on CT scans of the pelvis using CT-planning software. We found an average inclination of 42.3° (range 32.7-50.6°; SD ± 3.8°) and an average anteversion of 24.5° (range 12.0-33.3°; SD ± 6.0°) in the computer-assisted study group and an average inclination of 37.9° (range 25.6-50.2°; SD ± 6.3°) and an average anteversion of 23.8° (range 5.6-46.9°; SD ± 10.1°) in the freehand group. The higher precision of computer navigation was indicated by the lower standard deviations. For both measurements we found a significant heterogeneity of variances (p < 0.05, Levene's test). The mean difference between the cup inclination/anteversion values displayed by computer navigation and the true cup position (CT control) was 0.37° (SD 3.26) and -5.61° (SD 6.48), respectively. We found a bias (underestimation) with regard to anteversion determined by the imageless computer navigation system. A bias for inclination was not found. Registration of the landmarks of the anterior pelvic plane in lateral position with undraped percutaneous methods leads to an error in cup anteversion, but not to an error in cup inclination. The bias we found is consistent with a correct registration of the anterosuperior iliac spine (ASIS) and with a registration of the symphysis 1 cm above the bone, corresponding to the less compressible overlying soft tissue in this region. There was no significant correlation between the bias and the thickness of soft tissue above the pubic tubercles. We suggest use of a percutaneous registration of ASIS and an invasive registration above the pubic tubercles when computer-assisted navigation is performed in minimally invasive THR in a lateral position.

Stem torsion in total hip replacement.

BACKGROUND AND PURPOSE: The clinical results of THR may be improved by correct femoral torsion. We evaluated the stem position by postoperative CT examination in 60 patients. METHODS: 60 patients requiring total hip arthroplasty were prospectively enrolled in this study. Minimally invasive THR was performed (anterior approach) in a lateral decubitus position and each patient underwent a postoperative CT examination. The position of the stem was evaluated by an independent external institution. RESULTS: Stem torsion ranged from ­ 19° retrotorsion to 33° antetorsion. Normal antetorsion (i.e 10­15° according to Tönnis) was present in 5 of 60 patients, so the prevalence of abnormal stem antetorsion was 92% (95% CI: 82­97). We found a stem antetorsion outside the range of 0­25° in 21 of 60 hips. Women had a higher mean stem antetorsion (8.0° (SD 11)) than men (1.5° (SD 10)). INTERPRETATION: Postoperative stem antetorsion shows a high variability and is gender-related. We suggest precise assessment of stem antetorsion intraoperatively by means of computer navigation, preparing the femur first. In abnormal stem antetorsion, the cup position can be adjusted using a combined anteversion concept; alternatively, modular femoral components or stems with retroverted or anteverted necks ("retrostem") could be used.

Fractured neck of femur--internal fixation versus arthroplasty.

BACKGROUND: Surgery is the treatment of choice for fractured neck of femur. For middle-aged patients (aged ca. 40 to 65), there is considerable debate over the indications for arthroplasty or internal fixation. The choice of surgical technique varies widely from one region to another. In this article, we discuss the main criteria that should be used in making this decision. METHODS: We selectively reviewed the literature on the diagnosis and treatment of fractured neck of femur, including the current guideline of the German Society for Trauma Surgery (Deutsche Gesellschaft für Unfallchirurgie, DGU) and recent findings from the field of health services research. RESULTS: The treatment of middle-aged patients with dislocated fractures should be based on rational decision-making. The patient's level of activity before the accident should be judged in terms of his or her previous mobility, independence in daily activities, and mental status. Internal fixation is recommended if the fracture can be adequately repositioned, the bone is of good quality, and there is no evidence of osteoarthritis. Fractures that are more than 24 hours old should be treated with total hip arthroplasty. Hemiprostheses are appropriate for very old patients. Physically frail, bedridden, and/or demented patients should undergo internal fixation of the fracture. For non-displaced or impacted fractures, functional treatment (i.e., prophylactic securing of the fracture with screws or nails) is indicated. Rapid diagnosis and a short time in bed before surgery lower the rate of complications. Internal fixation with preservation of the femoral head should ideally be performed within the first 6 hours of trauma, and within the first 24 hours at most. CONCLUSION: Despite the increasing scarcity of resources, treatment should still be based on well-founded clinical guidelines. Minimally invasive surgery enables better function in the early postoperative phase and can thereby lower complication rates. An interdisciplinary concept for the postoperative care of elderly patients also has a major effect on the outcome.

In-vitro investigation of a noninvasive referencing technology for computer-assisted total hip arthroplasty.

The use of surgical navigation to aid in total joint replacement requires the bony fixation of reference marker arrays. In this context, a number of potential complications have been reported, including pin-site infection, soft tissue morbidity, and stress fracture. This study was performed to determine whether a femoral pinless, imageless navigation method for total hip arthroplasty (THA) is an accurate alternative method of measuring leg-length and offset change intraoperatively. Computer-assisted THA was simulated on a Sawbones bench test model including a femoral soft tissue model. Leg-length and offset changes were calculated by an imageless navigation system using the pinless measurement algorithm, in which the calculation of leg-length and offset changes is based on a specific realignment of the leg and then compared to corresponding measurements on a millimeter scale at the level of the femoral condyles. Mean difference in leg-length measurement (navigation versus millimeter paper) was 0.9 mm (95% confidence interval [CI]: 0.03-1.7 mm, P=.043), and the corresponding mean difference in offset was 1 mm (95% CI: 0.06-1.9 mm, P=.038). A noninvasive, pinless femoral system is a reliable tool for controlling leg length and offset during THA in an in-vitro setup. This system could lead to a reduction of potential risks associated with navigation techniques.

Experimental validation of a pinless femoral reference array for computer-assisted hip arthroplasty.

The use of computer navigation systems during total hip arthroplasty requires the femoral fixation of a reflective dynamic reference base (DRB), which theoretically involves the risk of bony fracture, infection, and pin loosening. The first objective of this study was to evaluate the relative movements between a novel, noninvasive external femoral DRB system and the femur. Secondly, the maximum effects of these 3D movements on intraoperative, computer-assisted leg length and offset measures were evaluated. An imageless navigation system was used to track the positions of the soft tissue attached, pinless DRB relative to an invasive reference marker on the femur during a less-invasive, anterior surgical hip approach. Relative translatory movements up to 8.2 mm mediolaterally and up to 8.8 degrees in rotation were measured. Using a measurement technique in which the calculation of leg length and offset changes is primarily based on a specific realignment of the leg, maximum differences of 1.3 mm for leg length and 1.2 mm for offset were found when comparing the pin-based and pinless methods. Thus, invasive fixation techniques with screws or pins are still the method of choice when standard measurement algorithms for intraoperative leg length and offset measures are used. Though direct translatory and rotational variations between the pinless array and the femoral bone were detected, the pinless array can be used to assess leg length and offset when used with a specific measurement technique that compensates for such variations.

Leg length and offset measures with a pinless femoral reference array during THA.

The bony fixation of reference marker arrays used for computer-assisted navigation during total hip arthroplasty (THA) theoretically involves the risk of fracture, infection, and/or pin loosening. We asked whether intraoperative assessment of leg length (LL) and offset (OS) changes would be accurate using a novel pinless femoral reference system in conjunction with an imageless measurement algorithm based on specific realignment of the relationship between a dynamic femoral and pelvis reference array. LL/OS measurements were recorded during THA in 17 cadaver specimen hips. Preoperatively and postoperatively, specimens were scanned using CT. Linear radiographic LL/OS changes were determined by two investigators using visible fiducial landmarks and image processing software. We found a high correlation of repeated measurements within and between (both 0.95 or greater) the two examiners who did the CT assessments. Pinless LL/OS values showed mean differences less than 1 mm and correlations when compared with CT measurements.

Computer-assisted total hip arthroplasty: coding the next generation of navigation systems for orthopedic surgery.

This article outlines the scientific basis and a state-of-the-art application of computer-assisted orthopedic surgery in total hip arthroplasty (THA) and provides a future perspective on this technology. Computer-assisted orthopedic surgery in primary THA has the potential to couple 3D simulations with real-time evaluations of surgical performance, which has brought these developments from the research laboratory all the way to clinical use. Nonimage- or imageless-based navigation systems without the need for additional pre- or intra-operative image acquisition have stood the test to significantly reduce the variability in positioning the acetabular component and have shown precise measurement of leg length and offset changes during THA. More recently, computer-assisted orthopedic surgery systems have opened a new frontier for accurate surgical practice in minimally invasive, tissue-preserving THA. The future generation of imageless navigation systems will switch from simple measurement tasks to real navigation tools. These software algorithms will consider the cup and stem as components of a coupled biomechanical system, navigating the orthopedic surgeon to find an optimized complementary component orientation rather than target values intraoperatively, and are expected to have a high impact on clinical practice and postoperative functionality in modern THA.