Objectives. Periprosthetic femoral fractures (PFFs) have a higher incidence with cementless stems. The highest incidence among various cementless stem types was observed with double-wedged stems. Short stems have been introduced as a bone-preserving alternative with a higher incidence of PFF in some studies. The purpose of this study was a direct load-to-failure comparison of a double-wedged cementless stem and a short cementless stem in a cadaveric fracture model. Methods. Eight hips from four human cadaveric specimens (age mean 76 years (60 to 89)) and eight fourth-generation composite femurs were used. None of the cadaveric specimens had compromised quality (mean T value 0.4 (-1.0 to 5.7)). Each specimen from a pair randomly received either a double-wedged stem or a short stem. A materials testing machine was used for lateral load-to-failure test of up to a maximal load of 5000 N. Results. Mean load at failure of the double-wedged stem was 2540 N (1845 to 2995) and 1867 N (1135 to 2345) for the short stem (p < 0.001). All specimens showed the same fracture pattern, consistent with a Vancouver B2 fracture. The double-wedged stem was able to sustain a higher load than its short-stemmed counterpart in all cases. Failure force was not correlated to the bone mineral density (p = 0.718). Conclusion. Short stems have a significantly lower primary load at failure compared with double-wedged stems in both cadaveric and composite specimens. Surgeons should consider this biomechanical property when deciding on the use of short femoral stem. Cite this article: A. Klasan, M. Bäumlein, P. Dworschak, C. Bliemel, T. Neri, M. D. Schofer, T. J. Heyse. Short stems have lower load at failure than double-wedged stems in a cadaveric cementless fracture model. Bone Joint Res 2019;8:489–494. DOI: 10.1302/2046-3758.810.BJR-2019-0051.R1

Aims. To evaluate if, for orthopaedic trainees, additional cadaveric simulation training or standard training alone yields superior radiological and clinical outcomes in patients undergoing dynamic hip screw (DHS) fixation or hemiarthroplasty for hip fracture. Methods. This was a preliminary, pragmatic, multicentre, parallel group randomized controlled trial in nine secondary and tertiary NHS hospitals in England. Researchers were blinded to group allocation. Overall, 40 trainees in the West Midlands were eligible: 33 agreed to take part and were randomized, five withdrew after randomization, 13 were allocated cadaveric training, and 15 were allocated standard training. The intervention was an additional two-day cadaveric simulation course. The control group received standard on-the-job training. Primary outcome was implant position on the postoperative radiograph: tip-apex distance (mm) (DHS) and leg length discrepancy (mm) (hemiarthroplasty). Secondary clinical outcomes were procedure time, length of hospital stay, acute postoperative complication rate, and 12-month mortality. Procedure-specific secondary outcomes were intraoperative radiation dose (for DHS) and postoperative blood transfusion requirement (hemiarthroplasty). Results. Eight female (29%) and 20 male trainees (71%), mean age 29.4 years, performed 317 DHS operations and 243 hemiarthroplasties during ten months of follow-up. Primary analysis was a random effect model with surgeon-level fixed effects of patient condition, patient age, and surgeon experience, with a random intercept for surgeon. Under the intention-to-treat principle, for hemiarthroplasty there was better implant position in favour of cadaveric training, measured by leg length discrepancy ≤ 10 mm (odds ratio (OR) 4.08 (95% confidence interval (CI) 1.17 to 14.22); p = 0.027). There were significantly fewer postoperative blood transfusions required in patients undergoing hemiarthroplasty by cadaveric-trained compared to standard-trained surgeons (OR 6.00 (95% CI 1.83 to 19.69); p = 0.003). For DHS, there was no significant between-group difference in implant position as measured by tip-apex distance ≤ 25 mm (OR 6.47 (95% CI 0.97 to 43.05); p = 0.053). No between-group differences were observed for any secondary clinical outcomes. Conclusion. Trainees randomized to additional cadaveric training performed hip fracture fixation with better implant positioning and fewer postoperative blood transfusions in hemiarthroplasty. This effect, which was previously unknown, may be a consequence of the intervention. Further study is required. Cite this article: Bone Jt Open 2023;4(8):602–611

Aims. Ankle fracture fixation is commonly performed by junior trainees. Simulation training using cadavers may shorten the learning curve and result in a technically superior surgical performance. Methods. We undertook a preliminary, pragmatic, single-blinded, multicentre, randomized controlled trial of cadaveric simulation versus standard training. Primary outcome was fracture reduction on postoperative radiographs. Results. Overall, 139 ankle fractures were fixed by 28 postgraduate year three to five trainee surgeons (mean age 29.4 years; 71% males) during ten months' follow-up. Under the intention-to-treat principle, a technically superior fixation was performed by the cadaveric-trained group compared to the standard-trained group, as measured on the first postoperative radiograph against predefined acceptability thresholds. The cadaveric-trained group used a lower intraoperative dose of radiation than the standard-trained group (mean difference 0.011 Gym. 2. , 95% confidence interval 0.003 to 0.019; p = 0.009). There was no difference in procedure time. Conclusion. Trainees randomized to cadaveric training performed better ankle fracture fixations and irradiated patients less during surgery compared to standard-trained trainees. This effect, which was previously unknown, is likely to be a consequence of the intervention. Further study is required. Cite this article: Bone Jt Open 2023;4(8):594–601

Aims. When performing revision total hip arthroplasty using diaphyseal-engaging titanium tapered stems (TTS), the recommended 3 to 4 cm of stem-cortical diaphyseal contact may not be available. In challenging cases such as these with only 2 cm of contact, can sufficient axial stability be achieved and what is the benefit of a prophylactic cable? This study sought to determine, first, whether a prophylactic cable allows for sufficient axial stability when the contact length is 2 cm, and second, if differing TTS taper angles (2° vs 3.5°) impact these results. Methods. A biomechanical matched-pair cadaveric study was designed using six matched pairs of human fresh cadaveric femora prepared so that 2 cm of diaphyseal bone engaged with 2° (right femora) or 3.5° (left femora) TTS. Before impaction, three matched pairs received a single 100 lb-tensioned prophylactic beaded cable; the remaining three matched pairs received no cable adjuncts. Specimens underwent stepwise axial loading to 2600 N or until failure, defined as stem subsidence > 5 mm. Results. All specimens without cable adjuncts (6/6 femora) failed during axial testing, while all specimens with a prophylactic cable (6/6) successfully resisted axial load, regardless of taper angle. In total, four of the failed specimens experienced proximal longitudinal fractures, three of which occurred with the higher 3.5° TTS. One fracture occurred in a 3.5° TTS with a prophylactic cable yet passed axial testing, subsiding < 5 mm. Among specimens with a prophylactic cable, the 3.5° TTS resulted in lower mean subsidence (0.5 mm (SD 0.8)) compared with the 2° TTS (2.4 mm (SD 1.8)). Conclusion. A single prophylactic beaded cable dramatically improved initial axial stability when stem-cortex contact length was 2 cm. All implants failed secondary to fracture or subsidence > 5 mm when a prophylactic cable was not used. A higher taper angle appears to decrease the magnitude of subsidence but increased the fracture risk. The fracture risk was mitigated by the use of a prophylactic cable. Cite this article: Bone Jt Open 2023;4(7):472–477

Aims. Research on hip biomechanics has analyzed femoroacetabular contact pressures and forces in distinct hip conditions, with different procedures, and used diverse loading and testing conditions. The aim of this scoping review was to identify and summarize the available evidence in the literature for hip contact pressures and force in cadaver and in vivo studies, and how joint loading, labral status, and femoral and acetabular morphology can affect these biomechanical parameters. Methods. We used the PRISMA extension for scoping reviews for this literature search in three databases. After screening, 16 studies were included for the final analysis. Results. The studies assessed different hip conditions like labrum status, the biomechanical effect of the cam, femoral version, acetabular coverage, and the effect of rim trimming. The testing and loading conditions were also quite diverse, and this disparity limits direct comparisons between the different researches. With normal anatomy the mean contact pressures ranged from 1.54 to 4.4 MPa, and the average peak contact pressures ranged from 2 to 9.3 MPa. Labral tear or resection showed an increase in contact pressures that diminished after repair or reconstruction of the labrum. Complete cam resection also decreased the contact pressure, and acetabular rim resection of 6 mm increased the contact pressure at the acetabular base. Conclusion. To date there is no standardized methodology to access hip contact biomechanics in hip arthroscopy, or with the preservation of the periarticular soft-tissues. A tendency towards improved biomechanics (lower contact pressures) was seen with labral repair and reconstruction techniques as well as with cam correction. Cite this article: Bone Joint Res 2023;12(12):712–721

The purposes of this study were to define the range of laxity of the interosseous ligaments in cadaveric wrists and to determine whether this correlated with age, the morphology of the lunate, the scapholunate (SL) gap or the SL angle. We evaluated 83 fresh-frozen cadaveric wrists and recorded the SL gap and SL angle. Standard arthroscopy of the wrist was then performed and the grades of laxity of the scapholunate interosseous ligament (SLIL) and the lunotriquetral interosseous ligament (LTIL) and the morphology of the lunate were recorded. Arthroscopic evaluation of the SLIL revealed four (5%) grade I specimens, 28 (34%) grade II, 40 (48%) grade III and 11 (13%) grade IV. Evaluation of the LTIL showed 17 (20%) grade I specimens, 40 (48%) grade II, 28 (30%) grade III and one (1%) grade IV. On both bivariate and multivariate analysis, the grade of both the SLIL and LTIL increased with age, but decreased with female gender. The grades of SLIL or LTIL did not correlate with the morphology of the lunate, the SL gap or the SL angle. The physiological range of laxity at the SL and lunotriquetral joints is wider than originally described. The intercarpal ligaments demonstrate an age-related progression of laxity of the SL and lunotriquetral joints. There is no correlation between the grades of laxity of the SLIL or LTIL and the morphology of the lunate, the SL gap or the SL grade. Based on our results, we believe that the Geissler classification has a role in describing intercarpal laxity, but if used alone it cannot adequately diagnose pathological instability. We suggest a modified classification with a mechanism that may distinguish physiological laxity from pathological instability

The aim of this study was to establish a classification system for the acromioclavicular joint using cadaveric dissection and radiological analyses of both reformatted computed tomographic scans and conventional radiographs centred on the joint. This classification should be useful for planning arthroscopic procedures or introducing a needle and in prospective studies of biomechanical stresses across the joint which may be associated with the development of joint pathology. We have demonstrated three main three-dimensional morphological groups namely flat, oblique and curved, on both cadaveric examination and radiological assessment. These groups were recognised in both the coronal and axial planes and were independent of age

Objectives. To assess the accuracy of patient-specific instruments (PSIs) versus standard manual technique and the precision of computer-assisted planning and PSI-guided osteotomies in pelvic tumour resection. Methods. CT scans were obtained from five female cadaveric pelvises. Five osteotomies were designed using Mimics software: sacroiliac, biplanar supra-acetabular, two parallel iliopubic and ischial. For cases of the left hemipelvis, PSIs were designed to guide standard oscillating saw osteotomies and later manufactured using 3D printing. Osteotomies were performed using the standard manual technique in cases of the right hemipelvis. Post-resection CT scans were quantitatively analysed. Student’s t-test and Mann–Whitney U test were used. Results. Compared with the manual technique, PSI-guided osteotomies improved accuracy by a mean 9.6 mm (p < 0.008) in the sacroiliac osteotomies, 6.2 mm (p < 0.008) and 5.8 mm (p < 0.032) in the biplanar supra-acetabular, 3 mm (p < 0.016) in the ischial and 2.2 mm (p < 0.032) and 2.6 mm (p < 0.008) in the parallel iliopubic osteotomies, with a mean linear deviation of 4.9 mm (p < 0.001) for all osteotomies. Of the manual osteotomies, 53% (n = 16) had a linear deviation > 5 mm and 27% (n = 8) were > 10 mm. In the PSI cases, deviations were 10% (n = 3) and 0 % (n = 0), respectively. For angular deviation from pre-operative plans, we observed a mean improvement of 7.06° (p < 0.001) in pitch and 2.94° (p < 0.001) in roll, comparing PSI and the standard manual technique. Conclusion. In an experimental study, computer-assisted planning and PSIs improved accuracy in pelvic tumour resections, bringing osteotomy results closer to the parameters set in pre-operative planning, as compared with standard manual techniques. Cite this article: A. Sallent, M. Vicente, M. M. Reverté, A. Lopez, A. Rodríguez-Baeza, M. Pérez-Domínguez, R. Velez. How 3D patient-specific instruments improve accuracy of pelvic bone tumour resection in a cadaveric study. Bone Joint Res 2017;6:577–583. DOI: 10.1302/2046-3758.610.BJR-2017-0094.R1

The purpose of this study was to determine whether it would be feasible to use oblique lumbar interbody fixation for patients with degenerative lumbar disease who required a fusion but did not have a spondylolisthesis. A series of CT digital images from 60 patients with abdominal disease were reconstructed in three dimensions (3D) using Mimics v10.01: a digital cylinder was superimposed on the reconstructed image to simulate the position of an interbody screw. The optimal entry point of the screw and measurements of its trajectory were recorded. Next, 26 cadaveric specimens were subjected to oblique lumbar interbody fixation on the basis of the measurements derived from the imaging studies. These were then compared with measurements derived directly from the cadaveric vertebrae. Our study suggested that it is easy to insert the screws for L1/2, L2/3 and L3/4 fixation: there was no significant difference in measurements between those of the 3-D digital images and the cadaveric specimens. For L4/5 fixation, part of L5 inferior articular process had to be removed to achieve the optimal trajectory of the screw. For L5/S1 fixation, the screw heads were blocked by iliac bone: consequently, the interior oblique angle of the cadaveric specimens was less than that seen in the 3D digital images. . We suggest that CT scans should be carried out pre-operatively if this procedure is to be adopted in clinical practice. This will assist in determining the feasibility of the procedure and will provide accurate information to assist introduction of the screws. Cite this article: Bone Joint J 2013;95-B:977–82

Introduction. The objective of this study was to determine if a synthetic bone substitute would provide results similar to bone from osteoporotic femoral heads during in vitro testing with orthopaedic implants. If the synthetic material could produce results similar to those of the osteoporotic bone, it could reduce or eliminate the need for testing of implants on bone. Methods. Pushout studies were performed with the dynamic hip screw (DHS) and the DHS Blade in both cadaveric femoral heads and artificial bone substitutes in the form of polyurethane foam blocks of different density. The pushout studies were performed as a means of comparing the force displacement curves produced by each implant within each material. Results. The results demonstrated that test material with a density of 0.16 g/cm. 3. (block A) produced qualitatively similar force displacement curves for the DHS and qualitatively and quantitatively similar force displacement curves for the DHS Blade, whereas the test material with a density of 0.08 g/cm. 3. (block B) did not produce results that were predictive of those recorded within the osteoporotic cadaveric femoral heads. Conclusion. This study demonstrates that synthetic material with a density of 0.16 g/cm. 3. can provide a good substitute for cadaveric osteoporotic femoral heads in the testing of implants. However we do recognise that no synthetic material can be considered as a definitive substitute for bone, therefore studies performed with artificial bone substrates may need to be validated by further testing with a small bone sample in order to produce conclusive results

Objectives. The purpose of this study was to develop an accurate, reliable and easily applicable method for determining the anatomical location of the joint line during revision knee arthroplasty. Methods. The transepicondylar width (TEW), the perpendicular distance between the medial and lateral epicondyles and the distal articular surfaces (DMAD, DLAD) and the distance between the medial and lateral epicondyles and the posterior articular surfaces (PMAD, DLAD) were measured in 40 knees from 20 formalin-fixed adult cadavers (11 male and nine female; mean age at death 56.9 years, . sd. 9.4; 34 to 69). The ratios of the DMAD, PMAD, DLAD and PLAD to TEW were calculated. Results. The mean TEW, DMAD, PMAD, DLAD and PLAD were 82.76 mm (standard deviation (. sd. ) 7.74), 28.95 mm (. sd. 3.3), 28.57 mm (. sd. 3), 23.97 mm (. sd. 3.27) and 24.42 mm (. sd. 3.14), respectively. The ratios between the TEW and the articular distances (DMAD/TEW, DLAD/TEW, PMAD/TEW and PLAD/TEW) were calculated and their means were 0.35 (. sd. 0.02), 0.34 (. sd. 0.02), 0.28 (. sd. 0.03) and 0.29 (. sd. 0.03), respectively. Conclusion. This method provides a simple, reproducible and reliable technique enabling accurate anatomical joint line restoration during revision total knee arthroplasty. Cite this article: B. Ozkurt, T. Sen, D. Cankaya, S. Kendir, K. Basarır, Y. Tabak. The medial and lateral epicondyle as a reliable landmark for intra-operative joint line determination in revision knee arthroplasty. Bone Joint Res 2016;5:280–286. DOI: 10.1302/2046-3758.57.BJR-2016-0002.R1

We describe a 63-year-old man who had xanthomatosis of the right tendo Achillis. He had undergone excision of the left tendo Achillis 17 years earlier without reconstruction for the same condition. The neurological history and examination were normal. Blood investigations showed hypercholestrolaemia, for which he was being treated with statins. He was referred with pain in the right tendo Achillis and problems with footwear. He was treated by excision of the right tendo Achillis, the xanthomatous nodules and the involved skin, followed by reconstruction with a cadaver bone-tendon graft. At follow-up eight months postoperatively, the scar had healed well. He walked without pain and could wear any type of shoe. Plain radiographs showed that the bone graft had healed. The American Orthopaedic Foot and Ankle Society hindfoot score was 95/100. The patient’s subjective evaluation of the result was very good

Aims

One of the main causes of tibial revision surgery for total knee arthroplasty is aseptic loosening. Therefore, stable fixation between the tibial component and the cement, and between the tibial component and the bone, is essential. A factor that could influence the implant stability is the implant design, with its different variations. In an existing implant system, the tibial component was modified by adding cement pockets. The aim of this experimental in vitro study was to investigate whether additional cement pockets on the underside of the tibial component could improve implant stability. The relative motion between implant and bone, the maximum pull-out force, the tibial cement mantle, and a possible path from the bone marrow to the metal-cement interface were determined.

Latissimus dorsi tendon transfer (LDTT) is technically challenging. In order to clarify the local structural anatomy, we undertook a morphometric study using six complete cadavers (12 shoulders). Measurements were made from the tendon to the nearby neurovascular structures with the arm in two positions: flexed and internally rotated, and adducted in neutral rotation. The tendon was then transferred and measurements were taken from the edge of the tendon to a reference point on the humeral head in order to assess the effect of a novel two-stage release on the excursion of the tendon. With the shoulder flexed and internally rotated, the mean distances between the superior tendon edge and the radial nerve, brachial artery, axillary nerve and posterior circumflex artery were 30 mm (26 to 34), 28 mm (17 to 39), 21 mm (12 to 28) and 15 mm (10 to 21), respectively. The mean distance between the inferior tendon edge and the radial nerve, brachial artery and profunda brachii artery was 18 mm (8 to 27), 22 mm (15 to 32) and 14 mm (7 to 21), respectively. Moving the arm to a neutral position reduced these distances. A mean of 15 mm (8 to 21) was gained from a standard soft-tissue release, and 32 mm (20 to 45) from an extensile release. These figures help to define further the structural anatomy of this region and the potential for transfer of the latissimus dorsi tendon. Cite this article: Bone Joint J 2013;95-B:517–22

Objectives. Lengthening osteotomies of the calcaneus in children are in general grafted with bone from the iliac crest. Artificial bone grafts have been introduced, however, their structural and clinical durability has not been documented. Radiostereometric analysis (RSA) is a very accurate and precise method for measurements of rigid body movements including the evaluation of joint implant and fracture stability, however, RSA has not previously been used in clinical studies of calcaneal osteotomies. We assessed the precision of RSA as a measurement tool in a lateral calcaneal lengthening osteotomy (LCLO). Methods. LCLO was performed in six fixed adult cadaver feet. Tantalum markers were inserted on each side of the osteotomy and in the cuboideum. Lengthening was done with a plexiglas wedge. A total of 24 radiological double examinations were obtained. Two feet were excluded due to loose and poorly dispersed markers. Precision was assessed as systematic bias and 95% repeatability limits. Results. Systematic bias was generally below 0.10 mm for translations. Precision of migration measurements was below 0.2 mm for translations in the osteotomy. Conclusion. RSA is a precise tool for the evaluation of stability in LCLO. Cite this article: Bone Joint Res 2015;4:78–83

Aim. It has been suggested that the use of a pilot-hole may reduce the risk of fracture to the lateral cortex. Therefore the purpose of this study was to determine the effect of a pilot hole on the strains and occurrence of fractures at the lateral cortex during the opening of a high tibial osteotomy (HTO) and post-surgery loading. Materials and Methods. A total of 14 cadaveric tibias were randomized to either a pilot hole (n = 7) or a no-hole (n = 7) condition. Lateral cortex strains were measured while the osteotomy was opened 9 mm and secured in place with a locking plate. The tibias were then subjected to an initial 800 N load that increased by 200 N every 5000 cycles, until failure or a maximum load of 2500 N. Results. There was no significant difference in the strains on the lateral cortex during HTO opening between the pilot hole and no-hole conditions. Similarly, the lateral cortex and fixation plate strains were not significantly different during cyclic loading between the two conditions. Using a pilot hole did not significantly decrease the strains experienced at the lateral cortex, nor did it reduce the risk of fracture. Conclusions. The nonsignificant differences found here most likely occurred because the pilot hole merely translated the stress concentration laterally to a parallel point on the surface of the hole. Cite this article: K. Bujnowski, A. Getgood, K. Leitch, J. Farr, C. Dunning, T. A. Burkhart. A pilot hole does not reduce the strains or risk of fracture to the lateral cortex during and following a medial opening wedge high tibial osteotomy in cadaveric specimens. Bone Joint Res 2018;7:166–172. DOI: 10.1302/2046-3758.72.BJR-2017-0337.R1

Damage to the cartilage of the distal radioulnar joint frequently leads to pain and limitation of movement, therefore repair of this joint cartilage would be highly desirable. The purpose of this study was to investigate the fixation of scaffold in cartilage defects of this joint as part of matrix-assisted regenerative autologous cartilage techniques. Two techniques of fixation of collagen scaffolds, one involving fibrin glue alone and one with fibrin glue and sutures, were compared in artificially created cartilage defects of the distal radioulnar joint in a human cadaver. After being subjected to continuous passive rotation, the methods of fixation were evaluated for cover of the defect and pull out force. No statistically significant differences were found between the two techniques for either cover of the defect or integrity of the scaffold. However, a significantly increased mean pull out force was found for the combined procedure, 0.665 N (0.150 to 1.160) versus 0.242 N (0.060 to 0.730) for glue fixation (p = 0.001). This suggests that although successful fixation of a collagen type I/III scaffold in a distal radioulnar joint cartilage defect is feasible with both forms of fixation, fixation with glue and sutures is preferable. Cite this article: Bone Joint J 2014;96-B:508–12

The joint surfaces of 60 hips obtained from the cadavers of elderly Asians were studied to determine the incidence, the grade and the distribution of both non-progressive (age-related) and progressive degenerative changes. It was observed that in the Asian population of 40 to 90 years of age, non-progressive changes were common, being seen in 66% of the acetabular specimens and 50% of the femoral heads. Only one specimen of the 60 showed unexplained progressive degenerative change. We conclude that primary osteoarthritis of the hip is rare in Asians

The purpose of the work described was to find the average pressure on each of several areas of the acetabular cartilage of the cadaver hip under physiological loads. By obtaining load-deflection curves for one chosen area of cartilage, firstly with all the cartilage present and then after the successive removal of other areas, the fractions of the original load carried by the several areas were found, and hence the average pressures on those areas. Seventeen hips (age range twenty. two to eighty-seven years) were examined. Local pressures varied from zero to 3.4 times the average pressure in each hip. The highest pressures in the series (about 4 to 5 megaNewtons per square metre) were on areas of thin fibrocartilage which were identified at the zenith of certain acetabula. The results are too few to establish whether or not the pressure distribution was age-related. The higher pressures found are within the range which in other experiments has led to fatigue failure of femoral head cartilage, and it is suggested that hips in which such pressures exist under loads of three times body weight may be predisposed to osteoarthritis

The fourth lumbar vertebrae and L4-5 discs from six cadaveric lumbar spines were subjected to detailed strain gauge analysis under conditions of controlled loading. With central compression loads, maximal compressive strain was found to occur near the bases of the pedicles and on both superficial and deep surfaces of the pars interarticularis, which emphasises the importance of the posterior elements of lumbar vertebrae in transmitting load. Radial bulge and tangential strain of the disc wall were maximal at the posterolateral surface, in agreement with the fact that disc degeneration and prolapse commonly occur there. Under posterior offset loads simulating extension, both compressive and tensile strains were found to be increased on both surfaces of the pars interarticularis, which suggests that hyperextension may lead to stress fractures and spondylolisthesis. Posterior offset loads also increased the radial bulge of the posterior disc wall and tangential strain at the anterior surface of the disc. Anterior offset loads simulating flexion increased the radial bulge of the anterior disc wall and tangential strain at the posterior surface of the disc. These findings are compatible with movement of the nucleus pulposus within the disc during flexion and extension. This hypothesis was supported by post-mortem discography