Total knee arthroplasty (TKA) aims to alleviate pain and restore joint biomechanics to an equivalent degree to age-matched peers.
Background. Trabecular metal (TM) cones are designed to fill up major bone defects in total knee arthroplasty. Tibial components can be implanted in combination with a stem, but it is unclear if this is necessary after reconstruction with a TM cone. Implanting a stem may give extra stability, but may also have negative side-effects. Aim of this study was to investigate stability and strain distribution of a tibial plateau reconstruction with a TM cone while the tibal component is implanted with and without a stem, and whether prosthetic stability was influenced by bone mineral density (BMD). Methods. Tibial revision arthroplasties were performed after reconstruction of an AORI 2B bone defect with TM cones. Plateaus were implanted in seven pairs of cadaveric tibiae; of each pair, one was implanted with and the other without stem. All specimens were loaded to one bodyweight alternating between the medial and lateral tibia plateau. Implant-bone micro motions, bone strains, BMD and correlations were measured and/or calculated. Results. Tibial components without a stem showed only more varus tilt (difference in median 0.14 degrees (P<0.05), but this was not considered clinically relevant. Strain distribution did not differ. BMD had only an effect on the anterior/posterior tilt ρ:-0.72 (P<0.01). Conclusions. Tibial components, with or without a stem, which are implanted after reconstruction of major bone defects using TM cones produce very similar biomechanical conditions in terms of stability and strain distribution. Additional stem extension of the tibial component may not be required after reconstruction of major bone defects using TM cones. Level of evidence. IIb. Disclosures. The department of Orthopaedics, University of Groningen, University Medical Center Groningen has received direct funding from the Anna Fonds (Oegstgeest, NL).
Summary Statement. A prospective randomised evaluation of primary TKA utilizing patient specific instruments demonstrated great accuracy of bone resection, improved sagittal alignment and the potential to improve functional outcomes and reduce operating room costs when compared to standard TKA instrumentation. Introduction. Patient specific instruments (PSI), an alternative to standard total knee arthroplasty (TKA) technology, have been proposed to improve the accuracy of TKA implant placement and post-operative limb alignment. Previous studies have shown mixed results regarding the effectiveness of PSI. The purposes of this study were (1) to evaluate the accuracy of the pre-operative predicted PSI plan compared to intra-operative TKA resection measurements, (2) to compare patient-reported outcome measures of PSI and standard TKA patients, and (3) to compare the incremental cost savings with PSI. Patients and Methods. This randomised, prospective pilot study of 19 patients undergoing primary TKA with a cruciate-retaining cemented prosthesis (NexGen,
Background. High re-rupture rates following repairs of rotator cuff tears (RCTs) have resulted in the increased use of repair grafts to act as temporary scaffolds to support tendon healing. It has been estimated that thousands of extracellular matrix repair grafts are used annually to augment surgical repair of rotator cuff tears. The only mechanical assessment of the suitability of these grafts for rotator cuff repair has been made using tensile testing only, and compared grafts to canine infraspinatus. As the shoulder and rotator cuff tendons are exposed to shearing as well as uniaxial loading, we compared the response of repair grafts and human rotator cuff tendons to shearing mechanical stress. We used a novel technique to study material deformation, dynamic shear analysis (DSA). Methods. The shear properties of four RCT repair grafts were measured (Restore, GraftJacket,
Background. Patients suffering a distal femoral fracture are at a high risk of morbidity and mortality. Currently this cohort is not afforded the same resources as those with hip fractures. This study aims to compare their mortality rates and assess whether surgical intervention improves either outcome or mortality following distal femoral fractures. Methods. Patients over sixty-five admitted with a distal femoral fracture between June 2007 and 2012 were retrospectively identified. Patients mobility was categorised as unaided, walking aid,
Background. Achieving optimal prosthesis alignment during total knee arthroplasty (TKA) is essential. Imageless computer-assisted surgery (CAS) is developed to improve knee prosthesis alignment and with CAS it is possible to perform intraoperative alignment measurements. Lower limb alignment measurements are also performed for preoperative planning and postoperative evaluation. A new stereoradiography system, called EOS, can be used to perform these measurements in 3D and thus measurement errors due to malpositioning can be eliminated. Since both CAS and EOS are based on 3D modeling, measurements should theoretically correlate well. Therefore, objective was to compare intraoperative CAS-TKA measurements with pre- and postoperative EOS 3D measurements. Methods. In a prospective study 56 CAS-TKAs were performed and alignment measurements were recorded two times: before bone cuts were made and after implantation of the prosthesis. Pre- and postoperative coronal alignment measurements were performed using EOS 3D. CAS measurements were compared with EOS 3D reconstructions. Measured angles were: varus/valgus (VV), mechanical lateral distal-femoral (mLDFA) and medial proximal tibial angle (mMPTA). Results. Significantly different VV angles were measured pre- and postoperatively with CAS compared to EOS. For preoperative measurements, mLDFA did not differ significantly, but a significantly larger mMPTA in valgus was measured with CAS. Conclusions. EOS 3D measurements overestimate VV angle in lower limbs with substantial mechanical axis deviation. For lower limbs with minor mechanical axis deviation as well as for mMPTA measurements, CAS measures more valgus compared to EOS. Results of this study indicate that differences in alignment measurements between CAS measurements and pre- and postoperative EOS 3D are mainly due to the difference between weight bearing and non-weight bearing position and potential errors in validity and reliability of the CAS system. Surgeons should be aware of these measurement differences and the pitfalls of both measurement techniques. Level of evidence. IIb. Disclosures. The department of Orthopaedics, University of Groningen, University Medical Center Groningen receives research institutional support from InSpine (Schiedam, NL) and Stryker (Kalamazoo, Mich. USA). One of the authors (ALB) will be and has been paid as a consultant by
Despite high success rates following total knee arthroplasty (TKA), knee kinematics are altered following TKA. Additionally, many patients report that their reconstructed knee does not feel ‘normal’ [1], potentially due to the absence of the anterior cruciate ligament (ACL), an important knee stabilizer and proprioceptive mechanism. ACL-retaining implants have been introduced with the aim of replicating native knee kinematics, however, there has yet to be a detailed comparison between knee kinematics in the native knee and one reconstructed with an ACL-retaining implant. Six fresh-frozen right legs (77±10 yr, 5 male) were mounted in a kinematic rig and subjected to squatting (40°-105°) motions. The vertical positon of the hip was manipulated with a linear actuator to induce knee flexion while the quadriceps were loaded with an actuator to maintain a vertical load of 90 N at the ankle [2]. Medial/lateral hamstring forces were applied with 50 N load springs. During testing, an infrared camera system recorded the trajectories of spherical markers rigidly attached to the femur and tibia. Two trials were performed per specimen. Following testing on the native knee, specimens were implanted with an ACL-retaining TKA (Vanguard XP,
Summary. Comparison of accuracy and precision in measuring wear using 4 commonly used uncemented cup designs shows small differences in mean and data scatter for marker and model-based RSA. Introduction. The disadvantage with conventional RSA is that implant has to be supplied with tantalum markers, which may be difficult to visualise. This problem can be resolved with model-based RSA, but it is uncertain if this method has the same precision as marker-based RSA to measure wear. We compared these methods and studied different prosthesis geometries represented by four different uncemented cup designs (Trilogy, TMT-Trabecular Metal,
Exeter Trauma Stem (ETS) is one of the most common implants used for treating displaced intracapsular hip fractures in the UK. We previously performed a radiographic audit of these implants which showed good placement was difficult. This was in particular relation to leg length discrepancy (LLD). This study reviewed the clinical outcomes of these patients, in particular looking at the relation of leg length discrepancy to outcome. We performed a clinical review of patients at 3 months and 1 year post ETS for hip fracture. Oxford hip score (OHS), Trendelenberg test, Visual Analogue Score (VAS) and walking aids required were recorded. Leg length discrepancy was determined radiographically on initial post op X-ray. This was recorded as Even (+/− 5mm), 6-10mm Long and >10mm long. Seventy-two patients were reviewed at 3 months and 21 at 1 year. Mean VAS was 1.6. At 3 months 66% were Trendelenberg positive. Of those Trendelenberg positive at 3 months only 42% remained positive at 1 year. Mean OHS at 3months and 1 year was 30.8 and 32.1 respectively. On radiographic review 38 implants were Even, 24 were 6-10mm Long and 10 implants were >10mm Long. There was no correlation between leg length discrepancy and either VAS or Trendelenberg test. 45 patients ambulated independently pre-op. Of these only 8 ambulated independently post-op, 18 used a stick and 11 a
All-suture anchors are increasingly used in rotator cuff repair procedures. Potential benefits include decreased bone damage. However, there is limited published evidence for the relative strength of fixation for all-suture anchors compared with traditional anchors. A total of four commercially available all-suture anchors, the ‘Y-Knot’ (ConMed), Q-FIX (Smith & Nephew), ICONIX (Stryker) and JuggerKnot (Zimmer Biomet) and a traditional anchor control TWINFIX Ultra PK Suture Anchor (Smith & Nephew) were tested in cadaveric human humeral head rotator cuff repair models (n = 24). This construct underwent cyclic loading applied by a mechanical testing rig (Zwick/Roell). Ultimate load to failure, gap formation at 50, 100, 150 and 200 cycles, and failure mechanism were recorded. Significance was set at p < 0.05.Objectives
Materials and Methods
Preservation of both anterior and posterior cruciate ligaments in total knee arthroplasty (TKA) can lead to near-normal post-operative joint mechanics and improved knee function. We hypothesised that a patient-specific bicruciate-retaining prosthesis preserves near-normal kinematics better than standard off-the-shelf posterior cruciate-retaining and bicruciate-retaining prostheses in TKA. We developed the validated models to evaluate the post-operative kinematics in patient-specific bicruciate-retaining, standard off-the-shelf bicruciate-retaining and posterior cruciate-retaining TKA under gait and deep knee bend loading conditions using numerical simulation.Objectives
Methods
Trauma and orthopaedics is the largest of the
surgical specialties and yet attracts a disproportionately small
fraction of available national and international funding for health
research. With the burden of musculoskeletal disease increasing,
high-quality research is required to improve the evidence base for
orthopaedic practice. Using the current research landscape in the
United Kingdom as an example, but also addressing the international
perspective, we highlight the issues surrounding poor levels of
research funding in trauma and orthopaedics and indicate avenues
for improving the impact and success of surgical musculoskeletal
research. Cite this article:
This study compared the effect of a computer-assisted and a traditional surgical technique on the kinematics of the glenohumeral joint during passive abduction after hemiarthroplasty of the shoulder for the treatment of fractures. We used seven pairs of fresh-frozen cadaver shoulders to create simulated four-part fractures of the proximal humerus, which were then reconstructed with hemiarthroplasty and reattachment of the tuberosities. The specimens were randomised, so that one from each pair was repaired using the computer-assisted technique, whereas a traditional hemiarthroplasty without navigation was performed in the contralateral shoulder. Kinematic data were obtained using an electromagnetic tracking device. The traditional technique resulted in posterior and inferior translation of the humeral head. No statistical differences were observed before or after computer-assisted surgery. Although it requires further improvement, the computer-assisted approach appears to allow glenohumeral kinematics to more closely replicate those of the native joint, potentially improving the function of the shoulder and extending the longevity of the prosthesis.
Wear of polyethylene is associated with aseptic loosening of orthopaedic implants and has been observed in hip and knee prostheses and anatomical implants for the shoulder. The reversed shoulder prostheses have not been assessed as yet. We investigated the volumetric polyethylene wear of the reversed and anatomical Aequalis shoulder prostheses using a mathematical musculoskeletal model. Movement and joint stability were achieved by EMG-controlled activation of the muscles. A non-constant wear factor was considered. Simulated activities of daily living were estimated from After one year of use, the volumetric wear was 8.4 mm3 for the anatomical prosthesis, but 44.6 mm3 for the reversed version. For the anatomical prosthesis the predictions for contact pressure and wear were consistent with biomechanical and clinical data. The abrasive wear of the polyethylene in reversed prostheses should not be underestimated, and further analysis, both experimental and clinical, is required.
Finite element analysis was used to examine the initial stability after hip resurfacing and the effect of the procedure on the contact mechanics at the articulating surfaces. Models were created with the components positioned anatomically and loaded physiologically through major muscle forces. Total micromovement of less than 10 μm was predicted for the press-fit acetabular components models, much below the 50 μm limit required to encourage osseointegration. Relatively high compressive acetabular and contact stresses were observed in these models. The press-fit procedure showed a moderate influence on the contact mechanics at the bearing surfaces, but produced marked deformation of the acetabular components. No edge contact was predicted for the acetabular components studied. It is concluded that the frictional compressive stresses generated by the 1 mm to 2 mm interference-fit acetabular components, together with the minimal micromovement, would provide adequate stability for the implant, at least in the immediate post-operative situation.
This study explored the relationship between the initial stability of the femoral component and penetration of cement into the graft bed following impaction allografting. Impaction allografting was carried out in human cadaveric femurs. In one group the cement was pressurised conventionally but in the other it was not pressurised. Migration and micromotion of the implant were measured under simulated walking loads. The specimens were then cross-sectioned and penetration of the cement measured. Around the distal half of the implant we found approximately 70% and 40% of contact of the cement with the endosteum in the pressure and no-pressure groups, respectively. The distal migration/micromotion, and valgus/varus migration were significantly higher in the no-pressure group than in that subjected to pressure. These motion components correlated negatively with the mean area of cement and its contact with the endosteum. The presence of cement at the endosteum appears to play an important role in the initial stability of the implant following impaction allografting.