Small design modifications can improve the primary stability of a fully coated tapered wedge hip stem.

Increasing the stem size during surgery is associated with a higher incidence of intraoperative periprosthetic fractures in cementless total hip arthroplasty with fully coated tapered wedge stems, especially in femurs of Dorr type A. If in contrast a stem is implanted and sufficient primary stability is not achieved, such preventing successful osseointegration due to increased micromotions, it may also fail, especially if the stem is undersized. Stem loosening or periprosthetic fractures due to stem subsidence can be the consequence. The adaptation of an established stem design to femurs of Dorr type A by design modifications, which increase the stem width proximally combined with a smaller stem tip and an overall shorter stem, might reduce the risk of distal locking of a proximally inadequately fixed stem and provide increased stability. The aim of this study was to investigate whether such a modified stem design provides improved primary stability without increasing the periprosthetic fracture risk compared to the established stem design. The established (Corail, DePuy Synthes, Warsaw, IN, US) and modified stem designs (Emphasys, DePuy Synthes, Warsaw, IN, US) were implanted in cadaveric femur pairs (n = 6 pairs) using the respective instruments. Broaching and implantation forces were recorded and the contact areas between the prepared cavity and the stem determined. Implanted stems were subjected to two different cyclic loading conditions according to ISO 7206-4 using a material testing machine (1 Hz, 600 cycles @ 80 to 800 N, 600 cycles @ 80 to 1600 N). Translational and rotational relative motions between stem and femur were recorded using digital image correlation. Broaching and implantation forces for the modified stem were up to 40% higher (p = 0.024), achieving a 23% larger contact area between stem and bone (R2 = 0.694, p = 0.039) resulting in a four times lower subsidence during loading (p = 0.028). The slight design modifications showed the desired effect in this in-vitro study resulting in a higher primary stability suggesting a reduced risk of loosening. The higher forces required during the preparation of the cavity with the new broaches and during implantation of the stem could bare an increased risk for intraoperative periprosthetic fractures, which did not occur in this study.

Stem size and stem alignment affects periprosthetic fracture risk and primary stability in cementless total hip arthroplasty.

The ideal stem size and stem position is important for the success of total hip arthroplasty, since it can affect early implant loosening and periprosthetic fractures (PPF). This study aimed to investigate how small deviations from the ideal stem size and position influences the PPF risk and primary stability. Six experienced surgeons performed preoperative templating based on which the benchmark size for each femur was determined. Consecutive implantations were performed in six cadaveric femur pairs-one side was implanted with an undersized stem followed by the benchmark size and the contralateral side with a benchmark size followed by an oversized stem (Corail, Depuy Synthes). Moreover, three different alignments (six varus, six neutral, six valgus-undersized) were compared using 18 femurs. Cortical strains during broaching and implantation were measured, and laser scans were used to determine final stem position. All specimens underwent dynamic loading. Primary stability was estimated from stem subsidence and pull-out forces. Templated stem size varied between surgeons (±1 size; p = 0.005). Undersizing increased stem subsidence by 320% (p < 0.001). Oversized stems exhibited 52% higher pull-out forces (p = 0.001) and 240% higher cortical strains (p = 0.056). Cortex strains increased with varus alignment (R2 = 0.356, p = 0.011) while primary stability decreased with valgus stem alignment (p = 0.043). Surgeons should be aware that small deviations from the ideal stem size and malalignments of the stem can significantly alter the mechanical situation and affect the success of their surgery.

What is the association between gender and self-perceived health status when controlling for disease-specific conditions? A retrospective data analysis of pre- and post-operative EQ-5D-5L differences in total hip and knee arthroplasty.

BACKGROUND: The self-perceived health status of patients undergoing total hip and knee arthroplasty (THA and TKA) might differ post-operatively due to gender, age, or comorbidities. Patient-reported outcome measures (PROMs) such as the EQ-5D-5L measure the self-perceived health status. This study investigates whether the index score of the EQ-5D-5L is a valid tool for interpreting gender differences in outcomes for patients undergoing THA and TKA. METHODS: Routine and PROM-data of elective primary THA or TKA patients in two German hospitals between 2016 and 2018 were analyzed. Univariate analysis with Pearson's chi-square was conducted to identify control variables for gender. To quantify the association between gender and the EQ-5D-5L dimensions, a cumulative odds ordinal logistic regression with proportional odds was conducted. RESULTS: Two thousand three hundred sixty-eight​​ THA patients (m = 978; f = 1390) and 1629 TKA patients (m = 715; f = 914) were considered. The regression analysis of the individual EQ-5D-5L dimensions showed that female gender was significantly associated with better self-care (THA and TKA) and better post-operative mobility (THA). In contrast, male gender was significantly associated with less pain/discomfort (TKA) and less anxiety/depression (THA) pre-surgery and 3-months post-surgery. CONCLUSION: Our results confirmed that the self-perceived health status improved after surgery. However, due to the different associations of gender to the individual dimensions of the EQ-5D-5L, the weighted index score clouds the comparability between patients with different gender undergoing THA or TKA. Therefore, we argue to use the individual five dimensions for health status analysis, to reveal relevant additional information.

Patients undergoing total hip and knee arthroplasty (THA and TKA) can fill out standardized questionnaires pre- and post-surgery, such as the EQ-5D-5L, to measure the improvement in the self-perceived health status. The EQ-5D-5L includes mobility, self-care, usual activity, pain/discomfort, and anxiety/depression. We do not know whether male and female patients experience the same improvement in the dimensions or whether significant differences exist. Currently, only index scores of the EQ-5D-5L are used for the comparison of pre- and post-operative health status. However, due to the questionnaire's weighted composition, relevant changes in individual dimensions might be easily missed. Thus, we investigated whether significant differences between gender and the EQ-5D-5L dimensions in patients undergoing TKA and TKA are observable. We found that female patients reported significantly better scores in self-care (THA and TKA) and post-operative mobility (THA). In contrast, male gender was significantly associated with less pain/discomfort (TKA) and less anxiety/depression (THA) pre-surgery and 3-months post-surgery. The EQ-5D-5L's weighted index score, however, does not directly represent these differences. Therefore, we argue to use the individual five dimensions for health status analysis, as relevant additional information on improvement over time would otherwise be missed.

Influence of bone morphology and femur preparation method on the primary stability of hip revision stems.

Aseptic loosening is one of the major reasons for re-revisions of cementless revision stems. Insufficient primary stability is associated with bone characteristics and the surgical process. This study aimed to investigate how femur morphology and preparation methods influence the primary stability of revision stems. The Femur morphology was described by the upper femoral curvature (UFC) and an individualized Dorr type classification based on the ratio between the canal-to-calcar ratio (CCR*) and the cortical index (CI*) introduced as the cortical-canal shape (CCS). Manual and powered reaming in combination with helical and straight reamers were used to prepare the bone cavity of 10 cadaveric human femur pairs. Forces during stem impaction were recorded (Reclaim, Depuy Synthes). Micromotion at the bone-implant interface during cyclic axial loading and torsional load to failure was determined. The CCS and impaction forces (R2 = 0.817, p < 0.001) or torsional strength (R2 = 0.577, p < 0.001) are inversely related. CCS did not correlate with micromotion during axial loading (R2 = 0.001, p > 0.999), but proximal femoral curvature did (R2 = 0.462, p = 0.015). Powered reaming and straight reamers led to an improved torsional strength (both: p = 0.043). The Individualized Dorr classification CCS and UFC allows a good estimation of the primary stability of revision stems. For severely curved Dorr type-C femurs, an alternative anchorage method should be considered clinically.

TKA patients experience less improvement than THA patients at 3 and 12 months after surgery. A retrospective observational cohort study.

PURPOSE: To investigate whether WOMAC scores changes after THA or TKA are gender and joint specific. METHODS: Retrospective cohort study. The data of 855 THA and 684 TKA patients were analyzed. RESULTS: Follow-up time (p < 0.001), gender (p < 0.001), joint (p < 0.001), and interaction FU by joint (p < 0.001) had significant effects on WOMAC total and sub-scores. Patients after TKA perceived less improvement in all dimensions in comparison to THA patients (p < 0.001). CONCLUSION: WOMAC score changes after THA or TKA are joint-specific. Patients after TKA perceived less improvement. These results can be used to adjust patients' expectations.

Pelvic Tilt Angle Differences Between Symptom-Free Young Subjects and Elderly Patients Scheduled for THA: The Rationale for Tilt-Adjusted Acetabular Cup Implantation.

BACKGROUND: The question whether Pelvic Tilt (PT) angles measured in the supine position are adequate for the alignment of the acetabular cup without an adjustment for anatomical differences between patients is of clinical importance. The aim of this work was to test for factors that can significantly affect PT angles. METHODS: In the present retrospective cohort comparison, the PT angles of 12 Symptom-Free Young Subjects (SFYS) and 45 patients scheduled for Total Hip Arthroplasty (THA) were compared. The data was collected during two studies with the use of a novel smartphone-based navigated ultrasound measurement system. Multi-factorial analysis of variance was run to determine which factors significantly affect PT. RESULTS: Body position (F= 126.65; P< 0.001) and group (SFYS vs. THA patients) (F= 17.52; P< 0.001) had significant main effects on PT. There was also a significant interaction between body position and group (F= 25.59; P< 0.001). The mean PT increased by 8.1° from an interiorly to a neutral tilted position (P< 0.001) and 21.4° from a neutral to a posteriorly tilted position (P< 0.001) with the transition from the supine into the upright position for the SFYS and THA patients, respectively. CONCLUSION: In both groups, PT changed significantly with a transition from the supine to the upright position. A position-dependent mean PT increase in the patient group showed that acetabular cup alignment based on PT in the supine position is not reliable without taking into consideration the inclination of the pelvis in standing position. This may lead to instability and dislocations.

Intra- and Inter-rater Reliability of Navigated Ultrasound in the Assessment of Pelvic Tilt in Symptom-Free Young Adults.

OBJECTIVES: Pelvic tilt is the angle between the anterior pelvic plane and the coronal plane. It affects cup positioning in total hip arthroplasty. The primary objective of this study was to test the intra- and inter-rater reliability of a navigated smart device-based ultrasound system for pelvic tilt assessment. The secondary objective was to test the inter-rater variability of the measurements on a hip phantom. METHODS: A repeated-measures design was used. Two raters measured the pelvic tilt of 12 symptom-free young adults in upright and supine positions. Additionally, pelvic tilt was measured on a hip phantom. Each rater performed 3 measurements in each body position on the participants and 12 measurements on the hip phantom. Intra- and inter-rater reliability were calculated with the use of intraclass correlation coefficients. The variability in measurements on the hip phantom was assessed by a Bland-Altman analysis of agreement. RESULTS: Intraclass correlation coefficient 95% confidence intervals for intra-rater reliability ranged from good to excellent and moderate to excellent for the supine and upright positions respectively. Intraclass correlation coefficient 95% confidence intervals for inter-rater reliability ranged from poor to excellent for both positions. Hip phantom measurements showed no significant average bias (P > .05) and no significant proportional bias (P > .05). The 95% inter-rater limits of agreement were ±1.3° and ±1.7° for the supine and upright positions, respectively. CONCLUSIONS: The intra-rater reliability values achieved were suitable. Intraclass correlation coefficient values for inter-rater reliability remained below an acceptable level. Possible reasons and overcoming strategies were presented. The 95% limits of agreement were good, at less than ±2°.

No improvement in reducing outliers in coronal axis alignment with patient-specific instrumentation.

PURPOSE AND HYPOTHESIS: Patient-specific instrumentation (PSI) uses 3D preoperative imaging to produce individualized cutting blocks specific to patients' anatomy and according to the preoperative plan with the aim to reduce the number of mechanical leg alignment (MLA) outliers, to improve implant positioning and to decrease surgery time. The primary purpose of this study was to investigate the efficacy of a specific PSI in comparison with standard instrumentation (SI) in reducing the number of MLA outliers. It was hypothesized that the number of MLA outliers would be significantly lower in the PSI group. METHODS: A multicenter randomized controlled trial was implemented. There were 59 patients in the PSI group and 66 in the SI group. The absolute number of outliers outside the ± 3° target neutral MLA was compared between the groups with a Chi-square test. As secondary outcomes, the Knee Society Score (KSS) and the Knee Injury and Osteoarthritis Outcome Score (KOOS) were compared between the groups preoperatively and at 90-day follow-up. RESULTS: There were 15 (26.3%) MLA outliers in the PSI group and 8 (12.3%) in the SI group. The number of outliers was not independent from the group ( X2 (1) = 3.8, p = 0.04; Relative risk = 1.5). Preoperatively, there were no significant differences between the groups when comparing their KSS and KOOS sub-scores. At 90 days postoperatively, the patients in the SI group showed better KOOS-Quality of Life (KOSS-QOL) in comparison with the PSI group (p < 0.0001). CONCLUSION: The use of PSI did not significantly reduce the number of MLA outliers in comparison with SI. There were no differences when comparing the achieved mean MLA of both groups. LEVEL OF EVIDENCE: Level I, prospective randomized controlled trial.

Patient-specific and intra-operatively modifiable factors assessed by computer navigation predict maximal knee flexion one year after TKA.

PURPOSE: There are multiple factors affecting maximal knee flexion (MKF) after total knee arthroplasty (TKA). The aim of the study was to investigate whether patient-specific factors (PSF) and surgically modifiable factors (SMF), measured by means of a computer-assisted navigation system, can predict the MKF after TKA. METHODS: Data from 99 patients collected during a randomized clinical trial were used for this secondary data analysis. The MKF of the patients was measured preoperatively and 1-year post-surgery. Multiple regression analyses were performed to investigate which combination of variables would be the best to predict the 1-year MKF. RESULTS: When considering SMF alone, the combination of three factors significantly predicted the 1-year MKF (p = 0.001), explaining 22 % of its variation. When considering only PSF, the combination of pre-op MKF and BMI significantly predicted the 1-year MKF (p < 0.001), explaining 23 % of its variation. When considering both groups of potential predictors simultaneously, the combination of five SMF with two PSF significantly predicted the 1-year MKF (p = 0.001), explaining 32 % of its variation. CONCLUSIONS: Computer navigation variables alone could explain 22 % of the variance in the 1-year MKF. The larger proportion (32 %) of the 1-year MKF variation could be explained with a combination of SMF and PSF. The results of studies in this area could be used to identify patients at risk of poor outcomes. LEVEL OF EVIDENCE: Level II, Prognostic study.

Do Well-Balanced Primary TKA Patients Achieve Better Outcomes Within the First Year After Surgery?

Some surgically modifiable factors are related to soft tissue balance. With computer-assisted surgery, it is possible to access these variables quantitatively. The aim of this analysis was to study the influence of gap balance on clinical outcomes within the first year after computer-navigated total knee arthroplasty (TKA). Based on navigation data, 3 independent variables reflecting gap balance were used to split the patients in 2 groups. The Knee Society Scores (Function [KSS-F] and Knee [KSS-K]) and the maximal knee flexion (MKF) measured preoperatively and at 3, 6 and 12 months were compared using analyses of variance (2×4 design) for repeated measures. Higher flexion-extension gap equality led to statistically higher KSS-F and KSS-K scores at 1 year (P=.02). Higher medial-lateral flexion gap equality led to superior mean MKF at all measurement points; however the differences were statistically only significant at 3 months (P=.01). The coefficients of variation of the variables used to select the patients were overall very low. With computer-assisted navigation, it is possible to access quantitatively the size of the medial and lateral flexion and extension gaps. Higher flexion-extension gap equality values led to statistically significant better KSS-F and KSS-K scores at 1 year. Higher medial-lateral flexion gap equality values led to better MKF values; however the differences were only statistically significant at 3 months. [Orthopedics. 2016; 39(3):S6-S12.].

Surgically modifiable factors measured by computer-navigation together with patient-specific factors predict knee society score after total knee arthroplasty.

BACKGROUND: The purpose was to investigate whether patient-specific factors (PSF) and surgically modifiable factors (SMF), measured by means of a computer-assisted navigation system, can predict the Knee Society Scores (KSS) after total knee arthroplasty (TKA). METHODS: Data from 99 patients collected during a randomized clinical trial were used for this secondary data analysis. The KSS scores of the patients were measured preoperatively and at 4-years follow-up. Multiple regression analyses were performed to investigate which combination of variables would be the best to predict the 4-years KSS scores. RESULTS: When considering SMF alone the combination of four of them significantly predicted the 4-years KSS-F score (p = 0.009), explaining 18 % of its variation. When considering only PSF the combination of age and body weight significantly predicted the 4-years KSS-F (p = 0.008), explaining 11 % of its variation. When considering both groups of predictors simultaneously the combination of three PSF and two SMF significantly predicted the 4-years KSS-F (p = 0.007), explaining 20 % of its variation. CONCLUSIONS: Younger age, better preoperative KSS-F scores and lower BMI before surgery, a positive tibial component slope and small changes in femoral offset were predictors of better KSS-F scores at 4-years.

No differences in clinical outcomes between fixed- and mobile-bearing computer-assisted total knee arthroplasties and no correlations between navigation data and clinical scores.

PURPOSE: The theoretical advantages of mobile-bearing (MB) designs over the conventional fixed bearings (FBs) for total knee arthroplasty (TKA) have not been proved yet through clinical studies. The aim of the study was to test whether the MB design has advantages in terms of better clinical outcomes when compared to FB. Furthermore, the relationships between intra-operative obtained implant positioning data and the clinical scores were analysed. METHODS: A total of 99 patients were randomized into the FB or the MB group. All patients received the same posterior cruciate retaining implants and were operated with the use of a computer-assisted navigation system. The clinical outcomes of both groups were compared pre-operatively, at 1 year, and at a mean follow-up time of 4 years after surgery. RESULTS: The MB implants showed no advantages over the FB when comparing the Knee Society Scores, the Oxford Score, the range of movement (ROM) and pain intensity of the patients in both groups at 1 and 4 years after surgery. There were no relationships between the computer navigation data and the clinical scores. CONCLUSIONS: In view of the 4-year results, there is no evidence to support the recommendation of one design over the other in terms of better clinical outcome scores, higher ROM or lower pain rates. Long-term follow-up results may be necessary, including survival rates. Further research comparing different TKA designs should also include standardized performance-based tests. LEVEL OF EVIDENCE: Prospective study (Randomized controlled trial with adequate statistical power to detect differences), Level I.

Accuracy of implant alignment and early results after minimally invasive vs conventional OrthoPilot-navigated Columbus TKA.

The goal of this study was to evaluate potential risks and benefits of minimally invasive vs conventional approaches in navigated total knee arthroplasty (TKA) in 50 patients. Preoperatively, no statistically significant differences between the two groups were found for deformity, range of motion (ROM), clinical scores, and ligament stability in the native joint or after prosthesis implantation measurements intraoperatively. Postoperatively, there were no significant differences between the two groups for deformity and clinical scores. In contrast, significantly less pain according to VAS measures and quicker improvements in ROM during the first 10 postoperative days were experienced in the minimally invasive group. Complication rates were similar in both groups. According to our results, minimally invasive navigated TKA is characterized by high implant positioning accuracy, soft tissue management quality, and complication rates similar to those for conventional approaches. Compared with the conventional approach, minimally invasive TKA provides superior functional results and less pain in the early postoperative period.

Comparison of robotic-assisted and manual implantation of a primary total hip replacement. A prospective study.

BACKGROUND: Robotic-assisted total hip replacement has become a common method of implantation, especially in Europe. It frequently has been postulated that robotic reaming would result in an improved clinical outcome due to the better fit of the prosthesis, but that has never been demonstrated in a prospective study, to our knowledge. The purpose of this study was to compare robotic-assisted implantation of a total hip replacement with conventional manual implantation. METHODS: One hundred and fifty-four patients scheduled for total hip replacement were randomly assigned to undergo either conventional manual implantation of an S-ROM prosthesis (eighty patients) or robotic-assisted implantation of such a prosthesis (seventy-four patients). The five-axis ROBODOC was used for the robotic-assisted procedures. Preoperatively as well as at three, six, twelve, and twenty-four months after surgery, the scores according to the Harris and Merle d'Aubigné systems and the Mayo clinical score were determined. Radiographs made at these intervals were analyzed for evidence of loosening, prosthetic alignment, and heterotopic ossification. RESULTS: Thirteen (18%) of the seventy-four attempted robotic implantations had to be converted to manual implantations as a result of failure of the system. The duration of the robotic procedures was longer than that of the manual procedures (mean and standard deviation,107.1 +/- 29.1 compared with 82.4 +/- 23.4 minutes, p < 0.001). Limb-length equality (mean discrepancy, 0.18 +/- 0.30 compared with 0.96 +/- 0.93 cm, p < 0.001) and varus-valgus orientation of the stem (mean angle between the femur and the shaft of the prosthesis, 0.34 degrees +/- 0.67 degrees compared with 0.84 degrees +/- 1.23 degrees, p < 0.001) were better after the robotic procedures. At six months, slightly more heterotopic ossification was seen in the group treated with robotic implantation. The group treated with robotic implantation had a better Mayo clinical score at six and twelve months and a better Harris score at twelve months; however, by twenty-four months, no difference was found between the groups with regard to any of the three scores. Dislocation was more frequent in the group treated with robotic implantation: it occurred in eleven of the sixty-one patients in that group compared with three of eighty in the other group (p < 0.001). Recurrent dislocation and pronounced limping were indications for revision surgery in eight of the sixty-one patients treated with robotic implantation compared with none of the seventy-eight (excluding two with revision for infection) treated with manual insertion (p < 0.001). Rupture of the gluteus medius tendon was observed during all of the revision operations. CONCLUSIONS: The robotic-assisted technology had advantages in terms of preoperative planning and the accuracy of the intraoperative procedure. Disadvantages were the high revision rate; the amount of muscle damage, which we believe was responsible for the higher dislocation rate; and the longer duration of surgery. This technology must be further developed before its widespread usage can be justified.