Femoral revision in total hip arthroplasty using a cementless modular stem: clinical and radiological results with a 8-year follow-up.

INTRODUCTION: Modular femoral components allow for patient-specific restoration of hip joint geometry and the reconstruction of extensive bone defects in revision total hip arthroplasty (THA); however, potential problems of modular implants such as taper corrosion and the risk of implant fracture continue to be of concern. The aim of the present study was to evaluate the clinical and radiological results of a cementless modular revision stem following revision surgery due to aseptic loosening and periprosthetic fracture and to assess patient-reported outcome measures (PROMs) in these patients at mid-term follow-up. MATERIALS AND METHODS: In this study, a consecutive cohort of 75 patients who underwent primary revision THA at our institution using a modular cementless stem design (MRP-TITAN stem) was retrospectively evaluated at a mean follow-up of 7.7 years. Kaplan-Meier survivorship analyses were performed with revision of the femoral component for any reason as the end point. The Harris-Hip Score, the UCLA Activity Score, the Forgotten Joint Score and the SF-12 Score were used for clinical assessment. We used the Wilcoxon signed rank test to compare pre- and postoperative clinical scores. RESULTS: Overall stem survival with the endpoint stem re-revision for any reason was 85.4% at a mean follow-up of 7.7 years (range 2.4-14 years). Stem survival was 89.5% in the aseptic loosening group and 78.3% in the periprosthetic fracture group with no statistically significant difference between both groups (p = 0.107). One patient had to be revised due to taper fracture. PROMs improved significantly up to the latest follow-up, and radiographic evaluation showed full osseointegration of all stems in this cohort. CONCLUSIONS: Revision THA using a modular cementless titanium revision stem demonstrated adequate clinical and radiological results at mid- to long-term follow-up in this cohort. Cementless revision stems are a useful treatment option to restore the anatomy, especially in deformed hips and in complex revision hip arthroplasty. However, there are some significant disadvantages related to an increased risk of mechanical failure such as corrosion/fretting damage and implant fracture. Future high-quality prospective studies with longer follow-up are necessary to confirm the supposed advantages.

Pain and rehabilitation after total hip arthroplasty are approach dependent: results 6 weeks and 2 years after surgery in a multisurgeon, single-center, and prospective cohort study.

PURPOSE: The aim of this study was the evaluation of pain, function, and overall satisfaction after total hip arthroplasty (THA) using three different standard surgical approaches (DAA (direct anterior approach), lateral, and posterior approach) 2 years postoperatively. Additionally, we compared the results with recently published results of the same study population 6 weeks postoperatively. METHODS: In a multisurgeon, prospective, single-center cohort study, a total of initial 188 patients who underwent total hip arthroplasty (THA) between February 2019 and April 2019 were analyzed on pain, function, and satisfaction within the first days, 6 weeks, and 2 years postoperatively according to three different approaches (DAA, lateral, and posterior approach). Our research group recently published results directly and 6 weeks postoperatively. We evaluated the same study collectively 2 years postoperatively and compared the results with the data 6 weeks postoperatively. One hundred twenty-five patients could be included. Outcome parameters for the present study were the pain level according to the visual analogue scale (VAS), the modified Harris hip score (mHHS), and an overall satisfaction scale 2 years postoperatively. RESULTS: Mean overall satisfaction 2 years postoperatively was 9.7 ± 1 (3-10). Satisfaction was significantly better for the DAA than for the lateral approach (p = 0.005). There were no significant differences between the lateral and posterior approaches (p = 0.06) and between the DAA and the posterior approaches (p = 0.11). In total, the mean pain level was 0.4 ± 0.9 (0-5) at 6 weeks and 0.5 ± 1.1 (0-7) at 2 years postoperatively (p = 0.3). Regarding the different approach groups, pain levels 6 weeks and 2 years postoperatively were significantly lower for the DAA than for the lateral approach (p = 0.02). There were no significant differences between DAA and posterior approach (p = 0.05) and the lateral and posterior approach (p = 0.26). The mean mHHS significantly increased from 84.7 + 14.5 (37.4-100) 6 weeks to 95 + 12.5 (23.1-100.1) 2 years postoperatively (p < 0.0001). Regarding the different approaches, mHHS was significantly higher for the DAA than for the lateral approach (p = 0.03). Differences between the DAA and the posterior approach (p = 0.11) and between the lateral and posterior approaches (p = 0.24) were insignificant. CONCLUSION: At 2 years postoperative, DAA showed significantly better overall satisfaction, pain level, and mHHS than the lateral approach. The differences between DAA and the posterior approach and lateral and posterior approaches were insignificant. Whether the superior results of the DAA to the lateral approach persist over a longer period must be clarified by further studies. STUDY DESIGN: Prospective cohort study, level of evidence 2.

Length doesn't play a role - Sexual activity in men after short stem Total hip Arthroplasty.

BACKGROUND: Chronic hip pain due to osteoarthritis or hip dysplasia has been shown to negatively affect many daily life aspects. One aspect, however, which persists underestimated is sexual health. The number of total hip arthroplasties (THA) are increasing, especially in young patients who have high functional expectations, not only to pain relief, but to an increase in hip mobility and quality of life as well as sexual activity. AIM: (1) to report the demographic factors, (2) the sexual activity before and after THA, as well as the concerns related to sexual activity after THA and (3) the patient-reported outcome measurements (PROMs) in sexually active male patients. METHODS: We evaluated the results of patients between 18 and 65 years of age following primary cementless short femoral stem THA using a direct anterior approach (DAA) at a midterm follow-up of 4 years. A web-based questionnaire (via SurveyMonkey) was chosen to assess frequency, positions, complaints, fears, dealing with the questions and PROMs. Our patients sexual activity was via The Sexual Health Inventory for Men (SHIM) validated. RESULTS: Patients resumed their sexual activities after 6 weeks. The two main causes of difficulty in sexual activity before surgery were pain and limitation of the range of motion of the hip joint. Patients experienced less pain and an improvement in hip range of motion after THA. 89% of patients expressed a desire for more detailed and specific information on the subject. The patients foremost concern about muscle weakness, surgical scar or fear of dislocation. After 4 years follow-up our patients presented a significant improvement of the modified Harris Hip Score (mHHS) from 34.1 preoperative to 92.6 after THA. CONCLUSION: THA improves the quality in sexual life, in relation to less pain and improvement in the range of motion, but not in the frequency of sexual activity. Men's sexual positions required less mobility and could therefore be considered safer.

Pain and rehabilitation after total hip arthroplasty are approach dependent: a multisurgeon, single-center, prospective cohort study.

PURPOSE: The aim of this study was to assess perioperative pain and mobilization after total hip arthroplasty (THA) using three different surgical approaches. METHODS: This was a multisurgeon, prospective, single-center cohort study. A total of 188 patients who underwent hip arthroplasty (THA) between February 2019 and April 2019 were analyzed according to the surgical approach used (direct anterior, lateral, and posterior approach). Outcome parameters were the daily walking distance during the inpatient stay, the pain level according to the visual analog scale (VAS) at rest and motion during the inpatient stay and at 6-week follow-up and the modified Harris Hips Score (mHHS) preoperatively and at 6 weeks. RESULTS: The walking distance within the groups increased significantly during the inpatient stay (p < 0.001). The DAA and posterior approach patients had a significantly longer walking distance than the lateral approach patients on the third postoperative day (DAA vs. lateral, p = 0.02; posterior vs. lateral 3, p = 0.03). DAA and posterior approach patients reported significantly less pain during motion on the third postoperative day and at 6-week follow-up than the lateral approach patients (3 postoperative day: DAA vs. lateral, p = 0.011; posterior vs. lateral, p = 0.04; 6 weeks control: DAA vs. lateral, p = 0.001; Posterior vs. lateral 3, p = 0.005). The mHHS demonstrated significant improvement within each group. However, lateral approach patients reported significantly less improvement than the DAA and posterior approach patients (DAA vs. lateral, p = 0.007; posterior vs. lateral, p = 0.021). CONCLUSION: This study analyzed perioperative pain progression and short-term rehabilitation after THA according to the different surgical approaches. Direct anterior and posterior approaches have shown comparable improvements in pain, walking distance, and mHHS. Whether this effect persists over a longer period of time must be clarified in future studies. STUDY DESIGN: Prospective cohort study, level of evidence, 2.

Recreational activity after cementless total hip arthroplasty in patients older than 75 years.

INTRODUCTION: This retrospective study aimed to compare activity levels before and at mid-term follow-up after primary cementless total hip arthroplasty (THA) in patients older than 75 years. MATERIALS AND METHODS: A cohort of 79 patients with a mean age at surgery of 78 years (range 76-84 years) was evaluated 6.3 years (range 4-8 years) after cementless THA due to osteoarthritis and was followed up with a questionnaire to determine their activity level. Pre- and post-operative recreational activities were assessed at routine follow-up using the University of California, Los Angeles activity score, and the Schulthess Clinic sports and activity questionnaire. Post-operative health-related quality of life was measured using Veterans Rand 12-item survey (VR-12). RESULTS: Six years after THA, 72% of preoperatively active patients had returned to activity. Comparing activity preoperatively (before the onset of symptoms) and 6 years after THA, the number of disciplines and session length has decreased significantly. A significant decline in high-impact activities was observed, while participation in low-impact activities significantly increased. CONCLUSION: The majority of patients maintained a recreational activity level in the mid-term after primary cementless THA. However, a change in disciplines toward low-impact activities was observed.

Comparison of short-stem with conventional-stem prostheses in total hip arthroplasty: an 8-year follow-up study.

PURPOSE: Coxarthrosis is a common disease of the adult hip joint. Elderly patients have mainly been treated with total hip arthroplasty (THA); however, younger patients are increasingly affected. Short-stem prostheses were developed for this special patient group. There have been few studies on the clinical outcomes of this type of prosthesis. This study compared the mid-term results of a short-stem prosthesis and a standard-stem prosthesis 8 years after implantation. METHODS: According to our clinical registry, patients who received a short-stem prosthesis before 2011 were identified. Patients in the standard-stem prosthesis group were matched based on the sex, age, height, weight, and degree of arthrosis. At the follow-up time, the modified Harris Hip Score (mHHS), University of California Los Angeles (UCLA) activity score and visual analog scale (VAS) pain score were collected and compared with the preoperative values. RESULTS: Fifty-five patients could be matched and analyzed for both groups. No patients needed revision surgery. In both groups, there were significant improvements at the follow-up time. The pre- and postoperative mHHSs, UCLA scores, and VAS scores were 41.9 and 95 (p < 0.0001), 3.75 and 7.9 (p < 0.0001), and 7.6 and 0.9 (p < 0.0001), respectively, in the short-stem group and 44.8 and 96.25 (p < 0.0001), 3.6 and 7.7 (p < 0.0001), and 7.7 and 0.9 (p < 0.0001), respectively, in the control group, with no significant differences between the groups at the follow-up time. CONCLUSION: The short-stem prosthesis provides mid-term results comparable to those of a standard-stem prosthesis. In both groups, excellent patient-reported outcomes were achieved after an average of 8 years. LEVEL OF EVIDENCE: IV.

The influence of different sets of surgical instrumentation in Oxford UKA on bearing size and component position.

INTRODUCTION: The Oxford unicompartmental knee arthroplasty (OUKA) has been proven to be an effective treatment for anteromedial osteoarthritis of the knee joint. New instrumentation has been introduced to improve the reproducibility of implant positioning and to minimize bone loss during tibial resection (Oxford Microplasty; Zimmer Biomet, Warsaw, Indiana, USA). METHODS: To assess the effect of the new instrumentation, we retrospectively evaluated the postoperative radiographs and surgical records of 300 OUKAs in three consecutive cohorts of patients. The first cohort consists of the first 100 minimal invasive implantations of the OUKA using the conventional phase III instrumentation, the second cohort consists of the 100 most recent minimal invasive OUKA with the conventional phase III instrumentation and the third cohort consists of the first 100 minimal invasive OUKA using the new Oxford Microplasty instrumentation. RESULTS: Mean bearing thickness was statistically significant and lower in OUKA with use of the updated instrumentation than with the conventional instrumentation (p = 0.01 and p = 0.04). Additionally, statistically significant and more femoral components were aligned within the accepted range of tolerance in both the coronal and the sagittal plane with use of the updated instrumentation compared to the conventional phase III instrumentation in group A (p = 0.029 and p = 0.038) and in the sagittal plane with use of the updated instrumentation compared to the conventional phase III instrumentation in group B (p = 0.002). CONCLUSION: The new modified instrumentation seems to be an effective tool to reduce the risk of malalignment of the femoral component in the coronal and in the sagittal plane compared to the conventional phase III instrumentation. Furthermore, the instrumentation is also effective in determining an adequate level of tibial resection and thus avoiding unnecessary bone loss.

Fixation pattern of conical and cylindrical modular revision hip stems in different size bone defects.

PURPOSE: Femoral defects often make it difficult to achieve sufficient fixation of the stem during revision surgery. No clinical studies comparing modular stems are available and differentiated recommendations are rare. The aim of this study was to compare the fixation of different revision stems in an experimental and standardised manner. METHODS: Segmental AAOS type I and III defects were reproduced in four femur pairs and two modular stems of different shape (cylindrical and conical) were implanted. Interfacial stem-bone movements were measured under axial torque application to analyze the stem fixation depending on defect extension. RESULTS: Both stems showed adequate fixation in AAOS type I defect. The defect extension significantly reduced the fixation of both implants. The fixation pattern changed significantly for the cylindrical-shaped stem but was maintained for the conical-shaped stem. CONCLUSIONS: Shape as well as the extension of femoral defect have an impact on primary fixation. A type I defect seems to be bridgeable for both stems albeit in a different way. In contrast, stem-demanding activities during the healing phase have to be avoided for the conical-shaped stem in a type III defect, whereas the cylindrical-shaped stem has already ceased to be sufficiently stable in this case.

Strut grafts in revision hip arthroplasty faced with femoral bone defects: an experimental analysis.

PURPOSE: In total hip arthroplasty fixation of revision stems can be demanding due to femoral bone loss. Strut grafts are often used for bone augmentation and stabilization of the newly inserted prosthesis. The aim of this study was to assess the effect of strut grafts on primary stability under various stem fixation conditions. METHODS: Two different revision stems (cylindrical and conical shape) were implanted into synthetic femora. Following a semicircular transfemoral osteotomy, three deficient femoral bearings were simulated (bony lid reattached with cable wires; weakened lid reattached with cable wires; strut grafts placed to the weakened lid with cable wires). Relative micro-movements were measured between prostheses and bones due to an axial moment applied to the stems. RESULTS: Relative movements correlated to the stem shape. The cylindrical stem showed higher movements increasing significantly with a weakened bony lid and portrayed a slight decrease of movements with strut graft application. No unequivocal influence of the weakened lid could be detected for the conical implant. Strut graft application did not show an additional stabilizing effect. CONCLUSIONS: The primary stability of the cylindrical fixation concept decreases with impaired fixation conditions of the femur. A clear restabilizing effect with strut grafts could not be proven. A decrease of primary stability due to the impaired bone could not be observed for the conical stem shape. Additionally, strut grafts do not enhance fixation for this stem shape. We conclude that surgeons should not rely on a stabilizing effect of strut grafts in revision hip surgery.

Primary stability of the Fitmore stem: biomechanical comparison.

PURPOSE: After clinical introduction of the Fitmore stem (Zimmer), we noticed the formation of cortical hypertrophies in a few cases. We questioned whether (1) the primary stability or (2) load transfer of the Fitmore stem differs from other stems unassociated with the formation of hypertrophies. We compared the Fitmore stem to the well-established CLS stem. METHODS: Four Fitmore and four CLS stems were implanted in eight synthetic femurs. A cyclic torque around the stem axis and a mediolateral cyclic torque were applied. Micromotions between stems and femurs were measured to classify the specific rotational implant stability and to analyse the bending behaviour of the stem. RESULTS: No statistical differences were found between the two stem designs with respect to their rotational stability (p = 0.82). For both stems, a proximal fixation was found. However, for the mediolateral bending behavior, we observed a significantly (p < 0.01) higher flexibility of the CLS stem compared to the Fitmore stem. CONCLUSION: Hip stem implantation may induce remodelling of the periprosthetic bone structure. Considering the proximal fixation of both stems, rotational stability of the Fitmore® stem might not be a plausible explanation for clinically observed formation of hypertrophies. However, bending results support our hypothesis that the CLS stem presumably closely follows the bending of the bone, whereas the shorter Fitmore stem acts more rigidly. Stem rigidity and flexibility needs to be considered, as they may influence the load transfer at the implant-bone interface and thus possibly affect bone remodelling processes.

Influence of stem design on the primary stability of megaprostheses of the proximal femur.

PURPOSE: Extended bone defects of the proximal femur can be reconstructed by megaprostheses for which aseptic loosening constitutes one of the major failure modes. The basic requirement for long-term success of endoprostheses is primary stability. We therefore assessed whether sufficient primary stability can be achieved by four different megaprostheses in a standardised bone defect of the proximal femur and whether their different design leads to different fixation patterns. METHODS: Four different designs of proximal femoral replacements were implanted into 16 Sawbones® after preparing segmental bone defects (AAOS type II). Primary rotational stability was analysed by application of a cyclic torque of ±7 Nm and measuring the relative micromotions between bone and implant at different levels. The main fixation zones and differences of fixation patterns of the stem designs were determined by an analysis of variance. RESULTS: All four implants exhibited micromotions below 150 µm, indicating adequate primary stability. Lowest micromotions for all designs were located near the femoral isthmus. The extent of primary stability and the global implant fixation pattern differed considerably and could be related to the different design concepts. CONCLUSIONS: All megaprostheses studied provided sufficient primary stability if the fixation conditions of the femoral isthmus were intact. The design characteristics of the different stems largely determined the extent of primary stability and fixation pattern. Understanding these different fixation types could help the surgeon to choose the most suitable implant if the fixation conditions in the isthmus are compromised.

[Minced cartilage procedure for the treatment of acetabular cartilage lesions of the hip joint]. / Das Minced-Cartilage-Verfahren zur Therapie azetabulärer Knorpelschäden am Hüftgelenk.

OBJECTIVE: Treatment of acetabular cartilage defects using autologous cartilage fragments. INDICATIONS: Acetabular cartilage damage (1-6 cm2) associated with femoroacetabular impingement syndrome (FAIS). CONTRAINDICATIONS: Advanced osteoarthritis (≥ 2 according to Tönnis) and extensive acetabular cartilage damage > 6 cm2. Lack of labral containment due to irreparable labral damage. SURGICAL TECHNIQUE: Arthroscopic preparation of the acetabular cartilage damage and removal of unstable cartilage fragments using a 4.0 mm shaver, which minces the cartilage fragments. If necessary, additional cartilage harvesting over the CAM morphology requiring resection. Collection of the cartilage fragments using GraftnetTM and augmentation with autologous conditioned plasma (ACP). Treatment of associated pathologies such as CAM morphology, pincer morphology, and labral refixation or reconstruction. Implantation of cartilage mass and remodeling into the defect zone. Final sealing with autologous fibrin. POSTOPERATIVE MANAGEMENT: Postoperatively, weight bearing is restricted to 20 kg and range of motion to 90° of flexion for 6 weeks. This is supplemented by passive movement using a continuous passive motion (CPM) device. RESULTS: Since 2021, 13 patients treated with the described method were followed up for at least 6 months. A significant increase in the International Hip Outcome Tool (iHot)-12 and a significant reduction of pain were observed. No severe complications occurred.

Sports activity and patient-related outcomes after fixed-bearing lateral unicompartmental knee arthroplasty.

BACKGROUND: Unicompartmental osteoarthrosis increasingly affects younger patients who have high expectations concerning their postoperative level of activity. However, there is no available data on the activity level after fixed-bearing lateral unicompartmentalkneearthroplasty (UKA). The aim of this study was to report sports activity after fixed-bearing lateral UKA with a minimum two-year follow up. METHODS: Nineteen patients were surveyed to determine their sporting activities at a mean follow up of 4.6 years (range 2.0-9.7 years) after fixed-bearing lateral UKA. We also assessed the Knee Injury and Osteoarthritis Outcome Score Joint Replacement (KOOS JR) Score and the University of California, Los Angeles activity scale (UCLA scale) at baseline and latest follow up. RESULTS: Before the onset of the first symptoms, 15 of 19 patients were active in at least one sport compared with 13 of 19 patients after surgery. Eighty-six per cent of the patients returned to activity. Within 6 months, 68% returned to their activities after surgery. The mean postoperative UCLA score was 6.4 (±1.3). Half of the patients reached a high activity level (UCLA ≥ 7). Most common activities after surgery were long walks, biking and hiking. High-impact activities showed a significant decrease. CONCLUSION: Eighty-six per cent of the patients were able to return to regular recreational and sporting activities. In general, a shift from high-impact to low-impact activities was observed. There was no difference in the number of disciplines performed. Overall, the session length and frequency remained unchanged. However, male patients and younger patients participated in sports less frequently compared with preoperative levels.

Midterm Survivorship of an Uncemented Hydroxyapatite-Coated Titanium Femoral Component and Clinically Meaningful Outcomes in Patients Older Than 75 Years.

PURPOSE: It remains controversial whether cementless femoral components are safe in elderly patients. The aim of this study was (1) to determine the stem survival rate in patients >75 years of age who were treated with an uncemented femoral component and (2) to report clinically significant results on a mid-term follow-up. METHODS: 107 total hip arthroplasties (THA) were retrospectively evaluated in 97 patients over 75 years of age (mean age 78 years, range 75-87) treated with an uncemented femoral stem. The minimum follow-up was five years (mean 6.4 years, range 5-8). Stem survival rates, clinically meaningful outcomes, and incidence of complications were evaluated. RESULTS: Kaplan-Meier survival analysis, with the endpoint revision for any reason, showed a 6.4-year survival rate of 98% (95% CI, 95-99%; 63 hips at risk). The survival rates were comparable for male and female patients (log-rank test, p = 0.58). The modified Harris Hip Score (mHHS) improved from 42.2 (12 to 85) points to 81.1 (22 to 97) points (p < 0.0001). Mid-term minimal clinically important difference (MCID), substantial clinical benefit (SCB), and patient acceptable symptomatic state (PASS) were 25, 84, and 70, respectively. CONCLUSION: An uncemented stem is a viable option in patients over 75 years with good clinical outcomes and survivorship. Periprosthetic fractures were not a relevant failure mechanism with the stem used.

The Migration Pattern of a Cementless Hydroxyapatite-Coated Titanium Stem under Immediate Full Weight-Bearing-A Randomized Controlled Trial Using Model-Based RSA.

(1) Background: High primary stability is important for the long-term survival of cementless femoral stems in total hip arthroplasty (THA). The objective of this study was to investigate the migration pattern of a hydroxyapatite-coated cementless hip stem developed for minimally invasive surgery using model-based radiostereometric analysis (RSA). (2) Methods: In this randomized controlled trial, 44 patients with an indication for cementless primary THA were randomly allocated to receive either the SL-PLUS MIA stem, developed for minimally invasive surgery, or the SL-PLUS stem (Smith & Nephew Orthopaedics, Baar, Switzerland) which served as a control group. Unlimited weight-bearing was permitted postoperatively in both groups. Model-based RSA was performed after six weeks and after 3, 6, 12 and 24 months postoperatively. (3) Results: Mean total stem subsidence at two-year follow-up was 0.40 mm (SD 0.66 mm) in the SL-PLUS group and 1.08 mm (SD 0.93 mm) in the SL-PLUS MIA group (p = 0.030). Stem subsidence occurred during the first six weeks after surgery, indicating initial settling of the stem under full weight-bearing. Both stem designs showed good osseointegration and high secondary stability with no further migration after initial settling. (4) Conclusions: Settling of a cementless straight femoral stem occurs during the first six weeks after surgery under full weight-bearing. Although initial stem migration was higher in the SL-PLUS MIA group, it had no influence on secondary stability. All implants showed good osseointegration and high secondary stability with no signs of implant loosening during this two-year follow-up period.

Patient activity after total hip arthroplasty declines with advancing age.

Evaluation of patient activity is essential for clinical decision making before THA. To correlate age progression to patient activity after THA, we determined the number of walking cycles of 105 patients in different age groups by decades. Patients on average performed 6144 walking cycles per day (2.24 million cycles per year). Men were more active than women. The highest activity occurred in patients between 50 and 59 years of age, with a constant decrease in activity with advancing age. However, within age groups, we observed up to sixfold differences in the number of walking cycles per day. In addition to declining activity with advancing age, higher body mass index correlated with lower step counts. The high mean measured number of walking cycles, which were even higher than those reported for subjects without an arthroplasty, suggests patients benefit from THA. Female gender, advanced age, and obesity correlated with lower activity. Owing to the high intragroup variability of our results, preoperative evaluation of patient activity levels, individual patient factors, and patient demands, should be considered in clinical practice.

Tibial revision knee arthroplasty with metaphyseal sleeves: The effect of stems on implant fixation and bone flexibility.

INTRODUCTION: Revision total knee arthoplasty often requires modular implants to treat bone defects of varying severity. In some cases, it may not be clear which module size and implant combination (e.g. sleeve and stem) should be chosen for a specific defect. When balancing implant stability and osseointegration against stress-shielding, it is important to choose an appropriate implant combination in order to match the given level of bone loss. Therefore, the necessity of stems in less extensive tibial defects and the advantage of different stems (lengths and stiffnesses) in combination with large metaphyseal sleeves on implant fixation and bone flexibility using a modular tibial revision knee system, were analyzed. MATERIALS AND METHODS: Four different stem combinations for a tibial revision implant (Sigma TC3, DePuy) were compared to an intact bone. Standardized implantation with n = 4 synthetic tibial bones was performed after generating an Anderson Orthopaedic Research Institute (AORI) Type T1 bone defect. Axial torques around the longitudinal stem axis and varus-valgus torques were separately applied to the implant. Micromotions of bone and implant were tracked using a digital image correlation system to calculate relative micromotions at the implant-bone-interface and bone deformation. RESULTS: Overall, using stems reduced the proximal micromotions of tray and sleeve compared to no stem, while reducing bone deformation proximally at the same time, indicating some potential for proximal stress-shielding compared to no stem. The potential for increased proximal stress-shield due to reduced proximal deformation appeared to be greater when using the longer stems. The location of lowest relative micromotions was also more distal when using long stems as opposed to short stems. A short stem (especially a smaller diameter short stem which still achieves diaphyseal fixation) displayed less potential for stress-shielding, but greater bone deformation distal to the tip of the stem than in the natural model. DISCUSSION: In the case of tibial revision implants with metaphyseal sleeves in a simple fully contained Type I defect, the absence of a stem provides for more natural bone deformation. However, adding a stem reduces overall relative micromotions, while introducing some risk of proximal stress-shielding due to increased diaphyseal fixation. Increasing stem length intensifies this effect. Short stems offered a balance between reduced micromotions and more proximal bone deformation that reduced the potential for stress-shielding when compared to long stems. A short stem with slightly smaller diameter (simulating a less stiff stem which still has diaphyseal fixation) increased the proximal bone deformation, but also tended to increase the bone deformation even further at the distal stem's tip. CONCLUSION: In conclusion, further investigation should be conducted on fully contained Type I defects and the addition of a stem to offer better initial stability, taking into account stem length (i.e. shorter or more flexible stems) to support metaphyseal fixation and allowing bending found in intact bone. In addition, further study into more extensive tibial defects is required to determine if the stability/micromotion trends observed in this study with stems and sleeves in Type I defects still apply in cases of extensive proximal bone loss.

Primary rotational stability of various megaprostheses in a biomechanical sawbone model with proximal femoral defects extending to the isthmus.

PURPOSE: Fixation of proximal femoral megaprostheses is achieved in the diaphyseal isthmus. We hypothesized that after extended bone resection including the proximal part of the isthmus a reduced length of fixation will affect the stability and fixation characteristics of these megaprostheses. The aim of this study was to analyze in a validated sawbone model with extended proximal femoral defects which types of implants have sufficient primary stability to allow osteointegration and to describe their fixation characteristics. METHODS: Four different cementless megaprostheses were implanted into 16 Sawbones with an AAOS type III defect after resection 11 cm below the lesser trochanter involving the proximal isthmus. To determine the primary implant stability relative micromotions between bone and implant were measured in relation to a cyclic torque of 7Nm applied on the longitudinal axis of the implant. We determined the fixation characteristics of the different implant designs by comparing these relative micromotions along the longitudinal stem axis. RESULTS: In the tested sawbones all studied implants showed sufficient primary stability to admit bone integration with relative micromotions below 150 µm after adapting our results to physiologic hip joint loadings. Different fixation characteristics of the megaprostheses were determined, which could be explained by their differing design and fixation concepts. CONCLUSIONS: Cementless megaprostheses of different designs seem to provide sufficient primary stability to bridge proximal femoral defects if the diaphyseal isthmus is partially preserved. In our sawbone model the different implant fixation patterns can be related to their stem designs. No evidence can be provided to favor one of the studied implants in this setting. However, femoral morphology is variable and in different isthmus configurations specific implant designs might be appropriate to achieve the most favorable primary stability, which enables bone integration and consequently long term implant stability.