Background

Achieving a neutral static Hip-Knee-Ankle angle (sHKA) measured on radiographs has been considered a factor of success for total knee arthroplasty (TKA). However, recent studies have shown that sHKA seems to have no effect on TKA survivorship. sHKA is not representative of the dynamic loading occurring during gait, unlike the dynamic HKA (dHKA).

Background: context: In Adolescent Idiopathic Scoliosis (AIS), the correction of thoracic hypokyphosis with hooks instrumentation and also with pedicle screws system is moderate.

Purpose: To compare radiographic results between two instrumentations with thoracic screws using two different

Methods: of reduction: cantilever reduction (CR group– MOSS-MIAMI system) versus simultaneous translation on two rods (ST group – PASSMED system).

Study design: Retrospective comparative analysis of two consecutive cohorts of patients treated by the same surgeon at a single hospital.

Patient sample: Forty-two adolescent idiopathic thoracic scoliosis (Lenke type 1, 2 and 3) underwent a posterior spinal fusion and instrumentation: 20 patients in CR group and 22 patients in the ST group. The minimum follow-up was two years (Mean follow-up: 71 months and 47 months).

Outcomes measures: Thoracic sagittal kyphosis between T4 and T12 and Cobb angle measurements of major and minor curves evaluated preoperatively, postoperatively and the final visit, by an independent observer.

Methods: In CR group, we have used polyaxial pedicle screws and one or two monoaxial thoracic hooks. In ST group, we have used polyaxial pedicle screws and poly-axial claws which provide same stability than screws. Three groups of preoperative kyphosis were generated: 11 patients with severe hypokyphosis (T4–T12 < 10°) (5 in CR group and 6 in ST group); 11 patients with mild hypokyphosis (between 10 and 20°) (respectively 4° vs 7°) and 20 with normokyphosis (> 20°) (respectively 11 vs 9).

Results: At the final follow-up, for patients with a severe preoperative hypokyphosis, the mean gain was 14 degrees in the CR group (8° preop to 22° postop) and 25° in the ST group (6° preop to 31 postop) (p< 0.05). For patients xith mild hypokyphosis, te mean gains were respectively 7 degrees (16° preop to 23° postop) and 18° (16° preop to 34° postop) (p< 0.05). After surgery, 3 patients of CR group had hypokyphosis alors que all patients had normal kyphosis (> 20°) in the ST group. In the coronal plane, the mean correction of scoliosis are similar in the two groups (75% vs 69% p=NS)

Discussion and Conclusion: In posterior instrumentation for AIS, simultaneous reduction on two rods provides a better correction of the thoracic kyphosis than the cantilever reduction in patient with preoperative hypokyphosis. This surgical technique seems to restore thoracic normal kyphosis.

Introduction: Femoral neck (FN) fragility has been attributed to age-related bone loss, with increased loss in women. It has been shown that the mechanical properties of a supporting structure will also change with any alteration to the structure’s dimensions. The purpose of this study was to identify the age-related changes that take place in the morphology of the mid cross-section of the FN, and the implications for its mechanical properties in the different regions around the mid FN cross-section.

Materials and Methods: Measurements were taken from peripheral quantitative computed tomogram (pQCT) images of 81 cadaveric femurs (36 F, 45 M). The mid FN cross-section was segmented radially into eight regions and the cortical bone thickness (CT) and change of the centroid position (CP) of the FN cross-section were measured. The age-related effects of the corresponding changes in the proportion of cortical bone and the “resistance to bending” (section modulus, (Z)) were also measured.

Results: Four femurs were excluded because there were clear signs of OA being present. The maximum difference in regional CT between men and women, was less than 7% (Female: 3.07 ± 0.108mm; Male: 3.28 ± 0.123 mm (mean ± SEM) p =0.21). However, there were regional differences in CT between the young under fifty, (Un50, n=26) and the old, (Abv50), (ANOVAs for young vs old: CT p = 0.001 t 0.01). These effects were attributable to differences in the inferior region, where there was an increase in thickness of the cortical bone of 27% with senior status (Abv50: 3.44 ± 0.09mm; Und50: 2.70 ± 0.12mm. p = 0001) counter balanced by anterior and posterior loss. There was a corresponding change in CP, the distance of the superior, posterior, and superoposterior regions to the FN cross-section’s centroid, 7.6% (Abv50: 20.88 ± 0.28mm; Und50: 19.40 ± 0.47mm; p = 0.005); 6.7% (Abv50: 14.67 ± 0.2mm; Und50: 13.74 ± 0.32mm; p = 0.01); and 8%(Abv50: 17.95 ± 0.24; Und50: 16.61 ± 0.37), respectively. When these two measurements were combined (CP divided by CT) to provide the Local Buckling Ratio (BLR), where the higher the ratio the more unstable the structure, there were significant differences in superoanterior, 30%(Abv50: 15.8 ± 0.52; Und50: 12.1 ± 0.59;p=0.0001); anterior, 20%(Abv50: 10.1 ± 0.32; Und50: 8.3 ± 0.4; p=0.001); inferior, 35%(Abv50: 4.37 ± 0.14; Und50: 5.8 ± 0.34; p=0.0001); inferoposterior 18%(Abv50 8.6 ± 0.27: Und50: 7.36 ± 0.41; p=0.008); posterior, 29%(Abv50: 14.0 ± 0.33; Und50: 10.8 ± 0.5; p=0.0001) and superoposterior, 14%(Abv50: 14.6 ± 0.3; Und50: 12.8 ± 0.4; p=0.001), regions. There was no significant difference in bending resistance nor in the proportion of cortical bone.

Conclusions: A more uniform cortical thickness, seen in the young, would optimise fracture resistance to overloading from unusually loaded directions. Ageing was associated with a thickening of the inferior cortex and thinning of the cortex elsewhere. This effects the location of the area that is least susceptible to the loading forces experienced in stance – that is of the FN mid cross-section’s neutral bending axis – as it will be nearer to the inferior region. Such a change in the morphology will produce deterioration in the FN’s capacity to take a load as shown by the detrimental change in the LBR. This change may indicate that the potential for femoral neck fracture increases with age when load is applied in a direction different to normal stance eg through the greater trochanter.

Purpose: We present our experience with thoracic and lumbar pedicular screws for surgical correction of thoracic scoliosis.

Material and methods: Fifty patients with idiopathic scoliosis (mean age 20 years), underwent instrumentation with Moss Miami long-arm polyaxial pedicular screws. The point of entry into the pedicule was identified by progressive probing. Results were analysed at a mean follow-up of 3.5 years.

Results: Mean angle of the main instrumented curvature was 54° preoperatively and 14° postoperatively (75% initial reduction, 53% bending), and 15° at last-follow-up (74% correction). The non-instrumented lumbar curvature improved from 34° to 10°, giving a spontaneous correction of 72° (49° bending) at last follow-up. Inclination of of the first non-instrumented vertebra was 11° preoperatively and 6° at last follow-up. Kyphosis was improved in all cases with a mean gain of 10° for kyphotic spines.

Discussion: Morphological correction of scoliosis deformation and the long-term outcome depend on the quality of the initial reduction. Monitoring the spinal cord during the procedure enables best quality reduction.

In the frontal plane, corrections with hooks have varied from 38% to 55% depending on the series. This percentage improves to 60% when the lumbar curvature is instrumented with screws. Like Suk and Harms, we have found greater than 70% correction when the entire curvature is screwed using lumbar and thoracic pedicular screws. In the sagittal plane, results of hook instrumentations have been less than satisfactory for many authors (Betz, Rhee...). The improvement obtained with pedicular screws results from two effects: the stability of the construct which remains stable during reduction manœuvres allowing application of strong force, and the polyaxis arrangement allowing inserting the rods in all the screws simultaneously and thus distributing the reduction forces. The long-arm screws are brought into contact with the rod progressively by tightening the nuts bringing the vertebrae into line with the rod. We have not had any complication after insertion of 550 screws. We have not used distraction which we consider dangerous for the neurological structures nor contraction at the thoracic stage which induces lordosis.

Conclusion: The stability of the pedicular screw instrumentation for scoliosis allows clear improvement in the quality of the reduction.

Introduction: Some authors (Suk, Barr, Hamill ...) showed that lumbar and thoracic pedicle screws provided adequate reduction of scoliosis. Quality of reduction depends on primary stability of the vertebral anchors. If the anchor has a good primary stability, reduction forces are entirely transferred to the vertebra, which results in reduction of the deformity, whereas, if the anchor has a poor primary stability, it will move when subjected to reduction forces, and this will result in inadequate reduction. Lumbar screws which are advocated by many authors, are extensively used. Thoracic screws are only used by a limited number of surgeons, as most surgeons favour hooks. Polyaxiality facilitates rod positioning; it eliminates the orthogonal stresses that are generated during tightening and which are known to be responsible for screw fracture. The drawback manoeuvre consists in applying forces directly to the vertebra via the anchor; the deformity is reduced by gently translating the vertebra towards the rod. The polyaxial vertebral claw that we are presenting here is a self-stabilising implant that provides the same primary stability as the screw and allows application of multidirectional drawback forces.

Materials and methods: The system consists of self-stabilising vertebral anchors, either screws or claws. Each anchor is polyaxial and features a threaded extension that allows translation of the vertebra towards the rod. Connection of the screw or claw to the rod is provided by connecting clamps. The first operative step consists of inserting the vertebral anchors, favouring the apex of the deformity. The insertion technique is described in detail. The claw is locked independently, prior to securing the rod on to the claw. The second operative step consists of positioning the rods which are bent to the ideal sagittal curve. Polyaxiality and threaded extensions make rod positioning an easy step. Progressive tightening of the nuts results in correction of the deformity as it slowly moves the vertebrae towards the rods. The translation force is distributed over all the anchors, ensuring a gentle reduction manoeuvre with no risk of back out of the implants. Approaching vertebrae at the end of the reduction manoeuvre results in vertebral derotation. It is not necessary to use distraction which is considered hazardous.

Results: 35 such instrumentations have been used in patients with idiopathic scoliosis over the previous 12 months. We have used an average of nine screws and four claws per patient, mainly thoracic pedicle/transverse claws. Main curve correction was 71% (average curve was 59° preoperatively and 17° postoperatively). Average correction of the uninstrumented lumbar curve was 73%. The upper curve improved from 34° to 15°. The slope of the first uninstrumented vertebra was 14° pre-operatively and 6° postoperatively. In the sagittal plane, the average angle of thoracic kyphosis in hollow backs (kyphosis less than 15°) was 9°, increasing up to 27° postoperatively.

Discussion: This instrumentation is characterised by stable implants which provide a quality of reduction similar to that achieved with pedicle screws. Vertebral claws are easy to insert and have a better primary stability than screws.

Poly-axiality is a common feature to all the implants of this system; it greatly facilitates placement of the implants and allows to apply traction simultaneously to all the anchors, which results in progressive, gentle reduction. Simultaneous traction application ensures adequate correction of the thoracic kyphosis (gain of 18°). As a matter of fact, severe kyphosis can be bent into the rods, and translation of the vertebrae towards the rods is very easy. Adequate reduction of the main curve results in correction of the underlying lumbar curve and shifting of the first uninstrumented vertebra into a more horizontal position.

Conclusion: This instrumentation based on stable poly-axial implants, should allow to improve the quality of reduction of scoliosis.