We evaluated two reconstruction techniques for a simulated posterolateral corner injury on ten pairs of cadaver knees. Specimens were mounted at 30° and 90° of knee flexion to record external rotation and varus movement. Instability was created by transversely sectioning the lateral collateral ligament at its midpoint and the popliteus tendon was released at the lateral femoral condyle. The left knee was randomly assigned for reconstruction using either a combined or fibula-based treatment with the right knee receiving the other. After sectioning, laxity increased in all the specimens. Each technique restored external rotatory and varus stability at both flexion angles to levels similar to the intact condition. For the fibula-based reconstruction method, varus laxity at 30° of knee flexion did not differ from the intact state, but was significantly less than after the combined method. Both the fibula-based and combined posterolateral reconstruction techniques are equally effective in restoring stability following the simulated injury

A total of 20 pairs of fresh-frozen cadaver femurs were assigned to four alignment groups consisting of relative varus (10° and 20°) and relative valgus (10° and 20°), 75 composite femurs of two neck geometries were also used. In both the cadaver and the composite femurs, placing the component in 20° of valgus resulted in a significant increase in load to failure. Placing the component in 10° of valgus had no appreciable effect on increasing the load to failure except in the composite femurs with varus native femoral necks. Specimens in 10° of varus were significantly weaker than the neutrally-aligned specimens. The results suggest that retention of the intact proximal femoral strength occurs at an implant angulation of ≥ 142°. However, the benefit of extreme valgus alignment may be outweighed in clinical practice by the risk of superior femoral neck notching, which was avoided in this study

We have investigated the anatomy of the proximal part of the ulna to assess its influence on the use of plates in the management of fractures at this site. We examined 54 specimens from cadavers. The mean varus angulation in the proximal third was 17.5° (11° to 23°) and the mean anterior deviation 4.5° (1° to 14°). These variations must be considered when applying plates to the dorsal surface of the ulna for Monteggia-type fractures. A pre-operative radiograph of the contralateral elbow may also be of value

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

The treatment of fractures of the proximal tibia is complex and makes great demands on the implants used. Our study aimed to identify what levels of primary stability could be achieved with various forms of osteosynthesis in the treatment of diaphyseal fractures of the proximal tibia. Pairs of human tibiae were investigated. An unstable fracture was simulated by creating a defect at the metaphyseal-diaphyseal junction. Six implants were tested in a uniaxial testing device (Instron) using the quasi-static and displacement-controlled modes and the force-displacement curve was recorded. The movements of each fragment and of the implant were recorded video-optically (MacReflex, Qualysis). Axial deviations were evaluated at 300 N. The results show that the nailing systems tolerated the highest forces. The lowest axial deviations in varus and valgus were also found for the nailing systems; the highest axial deviations were recorded for the buttress plate and the less invasive stabilising system (LISS). In terms of rotational displacement the LISS was better than the buttress plate. In summary, it was found that higher loads were better tolerated by centrally placed load carriers than by eccentrically placed ones. In the case of the latter, it appears advantageous to use additive procedures for medial buttressing in the early phase

Techniques for the selective cutting of ligaments in cadaver knees defined the static contributions of the posterolateral structures to external rotation, varus rotation and posterior tibial translation from 0° to 120° of flexion under defined loading conditions. Sectioning of the popliteofibular ligament (PFL) (group 1) produced no significant changes in the limits of the knee movement studied. Sectioning of the PFL and the popliteus tendon (femoral attachment, group 2) produced an increase of only 5° to 6° in external rotation from flexion of 30° to 120° (p < 0.001). Even when other ligaments were sectioned first (group 3), the maximum effect of the PFL was negligible. Our findings show that the popliteus muscle-tendon-ligament complex, lateral collateral ligament, and posterolateral capsular structures function as a unit. No individual structure alone is the primary restraint for the movements studied. Operative reconstruction should address all of the posterolateral structures, since restoration of only a portion may result in residual instability

Rebound growth after hemiepiphysiodesis may be a normal event, but little is known about its causes, incidence or factors related to its intensity. The aim of this study was to evaluate rebound growth under controlled experimental conditions.

A total of 22 six-week-old rabbits underwent a medial proximal tibial hemiepiphysiodesis using a two-hole plate and screws. Temporal growth plate arrest was maintained for three weeks, and animals were killed at intervals ranging between three days and three weeks after removal of the device. The radiological angulation of the proximal tibia was studied at weekly intervals during and after hemiepiphysiodesis. A histological study of the retrieved proximal physis of the tibia was performed.

The mean angulation achieved at three weeks was 34.7° (standard deviation (sd) 3.4), and this remained unchanged for the study period of up to two weeks. By three weeks after removal of the implant the mean angulation had dropped to 28.2° (sd 1.8) (p < 0.001). Histologically, widening of the medial side was noted during the first two weeks. By three weeks this widening had substantially disappeared and the normal columnar structure was virtually re-established.

In our rabbit model, rebound was an event of variable incidence and intensity and, when present, did not appear immediately after restoration of growth, but took some time to appear.

Cite this article: Bone Joint J 2015;97-B:862–8.

Malpositioning of the trochanteric entry point during the introduction of an intramedullary nail may cause iatrogenic fracture or malreduction. Although the optimal point of insertion in the coronal plane has been well described, positioning in the sagittal plane is poorly defined.

The paired femora from 374 cadavers were placed both in the anatomical position and in internal rotation to neutralise femoral anteversion. A marker was placed at the apparent apex of the greater trochanter, and the lateral and anterior offsets from the axis of the femoral shaft were measured on anteroposterior and lateral photographs. Greater trochanteric morphology and trochanteric overhang were graded.

The mean anterior offset of the apex of the trochanter relative to the axis of the femoral shaft was 5.1 mm (sd 4.0) and 4.6 mm (sd 4.2) for the anatomical and neutralised positions, respectively. The mean lateral offset of the apex was 7.1 mm (sd 4.6) and 6.4 mm (sd 4.6), respectively.

Placement of the entry position at the apex of the greater trochanter in the anteroposterior view does not reliably centre an intramedullary nail in the sagittal plane. Based on our findings, the site of insertion should be about 5 mm posterior to the apex of the trochanter to allow for its anterior offset.

Cite this article: Bone Joint J 2014;96-B:1274–81.

The understanding of rotational alignment of the distal femur is essential in total knee replacement to ensure that there is correct placement of the femoral component. Many reference axes have been described, but there is still disagreement about their value and mutual angular relationship. Our aim was to validate a geometrically-defined reference axis against which the surface-derived axes could be compared in the axial plane. A total of 12 cadaver specimens underwent CT after rigid fixation of optical tracking devices to the femur and the tibia. Three-dimensional reconstructions were made to determine the anatomical surface points and geometrical references. The spatial relationships between the femur and tibia in full extension and in 90° of flexion were examined by an optical infrared tracking system.

After co-ordinate transformation of the described anatomical points and geometrical references, the projection of the relevant axes in the axial plane of the femur were mathematically achieved. Inter- and intra-observer variability in the three-dimensional CT reconstructions revealed angular errors ranging from 0.16° to 1.15° for all axes except for the trochlear axis which had an interobserver error of 2°. With the knees in full extension, the femoral transverse axis, connecting the centres of the best matching spheres of the femoral condyles, almost coincided with the tibial transverse axis (mean difference −0.8°, sd 2.05). At 90° of flexion, this femoral transverse axis was orthogonal to the tibial mechanical axis (mean difference −0.77°, sd 4.08). Of all the surface-derived axes, the surgical transepicondylar axis had the closest relationship to the femoral transverse axis after projection on to the axial plane of the femur (mean difference 0.21°, sd 1.77). The posterior condylar line was the most consistent axis (range −2.96° to −0.28°, sd 0.77) and the trochlear anteroposterior axis the least consistent axis (range −10.62° to +11.67°, sd 6.12). The orientation of both the posterior condylar line and the trochlear anteroposterior axis (p = 0.001) showed a trend towards internal rotation with valgus coronal alignment.

A cavovarus foot deformity was simulated in cadaver specimens by inserting metallic wedges of 15° and 30° dorsally into the first tarsometatarsal joint. Sensors in the ankle joint recorded static tibiotalar pressure distribution at physiological load.

The peak pressure increased significantly from neutral alignment to the 30° cavus deformity, and the centre of force migrated medially. The anterior migration of the centre of force was significant for both the 15° (repeated measures analysis of variance (ANOVA), p = 0.021) and the 30° (repeated measures ANOVA, p = 0.007) cavus deformity. Differences in ligament laxity did not influence the peak pressure.

These findings support the hypothesis that the cavovarus foot deformity causes an increase in anteromedial ankle joint pressure leading to anteromedial arthrosis in the long term, even in the absence of lateral hindfoot instability.

A cadaver study using six pairs of lower limbs was conducted to investigate the accuracy of computer navigation and standard instrumentation for the placement of the Birmingham Hip Resurfacing femoral component. The aim was to place all the femoral components with a stem-shaft angle of 135°.

The mean stem-shaft angle obtained in the standard instrumentation group was 127.7° (120° to 132°), compared with 133.3° (131° to 139°) in the computer navigation group (p = 0.03). The scatter obtained with computer-assisted navigation was approximately half that found using the conventional jig.

Computer navigation was more accurate and more consistent in its placement of the femoral component than standard instrumentation. We suggest that image-free computer-assisted navigation may have an application in aligning the femoral component during hip resurfacing.

The effects of the method of fixation and interface conditions on the biomechanics of the femoral component of the Birmingham hip resurfacing arthroplasty were examined using a highly detailed three-dimensional computer model of the hip. Stresses and strains in the proximal femur were compared for the natural femur and for the femur resurfaced with the Birmingham hip resurfacing. A comparison of cemented versus uncemented fixation showed no advantage of either with regard to bone loading. When the Birmingham hip resurfacing femoral component was fixed to bone, proximal femoral stresses and strains were non-physiological. Bone resorption was predicted in the inferomedial and superolateral bone within the Birmingham hip resurfacing shell. Resorption was limited to the superolateral region when the stem was not fixed. The increased bone strain observed adjacent to the distal stem should stimulate an increase in bone density at that location. The remodelling of bone seen during revision of failed Birmingham hip resurfacing implants appears to be consistent with the predictions of our finite element analysis.

The aim of our study was to investigate whether placing of the femoral component of a hip resurfacing in valgus protected against spontaneous fracture of the femoral neck.

We performed a hip resurfacing in 20 pairs of embalmed femora. The femoral component was implanted at the natural neck-shaft angle in the left femur and with a 10° valgus angle on the right. The bone mineral density of each femur was measured and CT was performed. Each femur was evaluated in a materials testing machine using increasing cyclical loads.

In specimens with good bone quality, the 10° valgus placement of the femoral component had a protective effect against fractures of the femoral neck. An adverse effect was detected in osteoporotic specimens.

When resurfacing the hip a valgus position of the femoral component should be achieved in order to prevent fracture of the femoral neck. Patient selection remains absolutely imperative. In borderline cases, measurement of bone mineral density may be indicated.

A complete cement mantle is important for the longevity of a total hip replacement. In the minimally-invasive direct anterior approach used at the Innsbruck University hospital, the femoral component has to be inserted into the femoral canal by an angulated movement. In a cadaver study, the quality and the extent of the cement mantle surrounding 13 Exeter femoral components implanted straight through a standard anterolateral transgluteal approach were compared with those of 13 similar femoral components implanted in an angulated fashion through a direct anterior approach. A third-generation cementing technique was used. The inner and outer contours of the cement mantles was traced from CT scans and the thickness and cross-sectional area determined.

In no case was the cement mantle incomplete. The total mean thickness of the cement mantle was 3.62 mm (95% confidence interval 3.59 to 3.65). The mean thickness in the group using the minimally-invasive approach was 0.16 mm less than that in the anterolateral group. The distribution of the thickness was similar in the two groups. The mean thickness was less on the anteromedial and anterolateral aspect than on the posterior aspect of the femur.

There is no evidence that the angulated introduction of Exeter femoral components in the direct anterior approach in cadavers compromises the quality, extent or thickness of the cement mantle.

The cortical strains on the femoral neck and proximal femur were measured before and after implantation of a resurfacing femoral component in 13 femurs from human cadavers. These were loaded into a hip simulator for single-leg stance and stair-climbing. After resurfacing, the mean tensile strain increased by 15% (95% confidence interval (CI) 6 to 24, p = 0.003) on the lateral femoral neck and the mean compressive strain increased by 11% (95% CI 5 to 17, p = 0.002) on the medial femoral neck during stimulation of single-leg stance. On the proximal femur the deformation pattern remained similar to that of the unoperated femurs.

The small increase of strains in the neck area alone would probably not be sufficient to cause fracture of the neck However, with patient-related and surgical factors these strain changes may contribute to the risk of early periprosthetic fracture.

There has been only one limited report dating from 1941 using dissection which has described the tibiofemoral joint between 120° and 160° of flexion despite the relevance of this arc to total knee replacement. We now provide a full description having examined one living and eight cadaver knees using MRI, dissection and previously published cryosections in one knee.

In the range of flexion from 120° to 160° the flexion facet centre of the medial femoral condyle moves back 5 mm and rises up on to the posterior horn of the medial meniscus. At 160° the posterior horn is compressed in a synovial recess between the femoral cortex and the tibia. This limits flexion. The lateral femoral condyle also rolls back with the posterior horn of the lateral meniscus moving with the condyle. Both move down over the posterior tibia at 160° of flexion.

Neither the events between 120° and 160° nor the anatomy at 160° could result from a continuation of the kinematics up to 120°. Therefore hyperflexion is a separate arc. The anatomical and functional features of this arc suggest that it would be difficult to design an implant for total knee replacement giving physiological movement from 0° to 160°.

Bone surface strains were measured in cadaver femora during loading prior to and after resurfacing of the hip and total hip replacement using an uncemented, tapered femoral component. In vitro loading simulated the single-leg stance phase during walking. Strains were measured on the medial and the lateral sides of the proximal aspect and the mid-diaphysis of the femur. Bone surface strains following femoral resurfacing were similar to those in the native femur, except for proximal shear strains, which were significantly less than those in the native femur. Proximomedial strains following total hip replacement were significantly less than those in the native and the resurfaced femur.

These results are consistent with previous clinical evidence of bone loss after total hip replacement, and provide support for claims of bone preservation after resurfacing arthroplasty of the hip.

Recently, femoroacetabular impingement has been recognised as a cause of early osteoarthritis. There are two mechanisms of impingement: 1) cam impingement caused by a non-spherical head and 2) pincer impingement caused by excessive acetabular cover. We hypothesised that both mechanisms result in different patterns of articular damage. Of 302 analysed hips only 26 had an isolated cam and 16 an isolated pincer impingement. Cam impingement caused damage to the anterosuperior acetabular cartilage with separation between the labrum and cartilage. During flexion, the cartilage was sheared off the bone by the non-spherical femoral head while the labrum remained untouched. In pincer impingement, the cartilage damage was located circumferentially and included only a narrow strip. During movement the labrum is crushed between the acetabular rim and the femoral neck causing degeneration and ossification.

Both cam and pincer impingement lead to osteoarthritis of the hip. Labral damage indicates ongoing impingement and rarely occurs alone.