Rok Vengust

Gradient of contact stress in normal and dysplastic human hips

The stress gradient index (G(p)) is introduced for the assessment of dysplasia in human hip joint. The absolute value of G(p) is equal to the magnitude of the gradient of the contact stress at the lateral acetabular rim. The parameter G(p) normalized with respect to the body weight (W(B)) is determined from the standard anteroposterior radiographs of adult human hips and pelvises using the mathematical model. The average value of G(p)/W(B) was determined for the group of dysplastic hips and for the group of normal hips. In the group of normal hips the average value of G(p)/W(B) is smaller (-0.445x10(5) m(-3)) than in the group of dysplastic hips (+1.481x10(5) m(-3)). The difference is statistically significant P<0.001. The average value of G(p)/W(B) changes its sign at the value of the centre-edge angle theta(CE) approximately 20( composite function ) which is usually considered as the boundary value of theta(CE) (lower limit) for the normal hips. Accordingly we suggest a new definition for the hip dysplasia with respect to the size and sign of the normalized stress gradient index G(p)/W(B). The hips with positive G(p)/W(B) are considered to be dysplastic while the hips with negative G(p)/W(B) are considered to be normal. The statistically significant correlation between the value of the Harris hip score, used in the clinical assessment of the hip dysplasia, and the normalized stress gradient index was found.

The role of obesity, biomechanical constitution of the pelvis and contact joint stress in progression of hip osteoarthritis

OBJECTIVE The aim of our study was to explore whether earlier hip arthroplasty for idiopathic osteoarthritis (OA) might be explained by enlarged contact stress in the hip joint, and to what amount can that be attributed to obesity and biomechanical constitution of the pelvis. METHOD Fifty subjects were selected from a list of consecutive recipients of hip endoprosthesis due to idiopathic OA; standard pelvic radiographs made years prior to surgery were the main selection criteria. For 65 hips resultant hip force and peak contact hip stress normalized to the body weight (R/Wb and p(max)/Wb) were determined from the radiographs with the HIPSTRESS method. Body weight and body mass index (BMI) were obtained with an interview. Regression analysis was used to correlate parameters of obesity (body weight, BMI), biomechanical constitution of the pelvis (R/Wb, p(max)/Wb) and mechanical loading within the hip joint (R, p(max)) with age at hip arthroplasty. RESULTS Younger age at hip arthroplasty was associated with higher body weight (P=0.009), higher peak contact hip stress normalized to the body weight - p(max)/Wb (P=0.019), higher resultant hip force -R (P=0.027) and larger peak contact hip stress - p(max) (P<0.001), but not with BMI (P=0.121) or R/Wb (P=0.614). CONCLUSION Our results suggest that enlarged contact stress (p(max)) plays an important role in rapid progression of hip OA with both obesity (increased body weight) and unfavorable biomechanical constitution of the pelvis (greater p(max)/Wb) contributing.

Biomechanical evaluation of hip joint after salter innominate osteotomy: a long-term follow-up study

Abstract The biomechanical state of the hip after a Salter innominate osteotomy was investigated by using the radiographic data of 38 operated and 21 contralateral nonoperated hips from our archives. The centre-edge angle of Wiberg was determined from the radiographs taken shortly after the operation. From the radiographs of the latest follow-up (7–13 years after the operation), we also determined the peak value of contact hip joint stress normalized by the body weight, and the functional angle of the weight-bearing area. A mathematical model was used. We show that the geometrical parameters aside from the centre-edge angle may considerably influence the contact hip stress distribution. We also show that the functional angle of the weight-bearing area is a more relevant parameter than the normalized peak stress if the exact magnification of the images is not known and if there is considerable variation of the image size within the sample. The development of the centre-edge angle of the operated hips and of the contralateral hips was also studied. We found that the centre-edge angle increases on average during the follow-up time in the operated hips as well as in the contralateral nonoperated hips, but the average increase is smaller in the former. It is shown that an unfavorable stress distribution is connected to the decrease of the centre-edge angle over time. Finally, we found a weak positive correlation between the centre-edge angle shortly after the operation and the functional angle of the weight-bearing area at the of the latest follow-up.

Influencing segmental balance in isthmic spondylolisthesis using transforaminal lumbar interbody fusion.

Study Design: Retrospective cohort study. Objective: The objective of the study was to analyze segmental balance in patients with isthmic spondylolisthesis undergoing single-level transforaminal lumbar interbody fusion (TLIF). Summary of Background Data: Sagittal malalignment of the fused segment was suggested to be associated with degeneration of the adjacent segment. Meticulous surgical technique and particular attention to hardware positioning with the aim to restore segmental balance at the fusion level have been recommended to achieve better long-term clinical outcomes, but no single study addressed all proposed factors. Methods: Standard lateral radiographs of the lumbosacral spine in the neutral standing position were retrospectively obtained for 32 patients undergoing single-level TLIF. Preoperative versus postoperative versus final follow-up (12 to 60 mo) values of translational slip (TS), posterior disc space height (PDSH), and segmental lordosis (SL) were compared using paired samples t test. Change in SL postoperatively between groups of next grouping variables: type and position of the interbody device, and rod contouring, was compared using 2-tailed independent samples t test. Association between position of the interbody device and immediate PDSH was addressed with regression analysis postoperatively and at final follow-up. Results: Mean TS decreased (P<0.001) and mean PDSH increased (P=0.002), but no significant change in SL occurred postoperatively (P=0.811). Increase in SL was observed with ventral positioning of the interbody device (P=0.009) and with bending of connecting rods (P=0.023). During follow-up, there was increase in TS (P=0.002) and decrease in PDSH (P<0.001) and SL (P<0.001) compared with postoperative values. Lower PDSH was found to be associated with more ventral positioning of the interbody device, both postoperatively (P=0.035) and at final follow-up (P=0.029). Conclusions: This study demonstrates that reduction of TS and restoration of disc space height are readily achieved with single-level TLIF. However, to establish an increase in SL consistent rod contouring and meticulous anterior placement of the interbody device should be applied. Excessive ventral positioning of the cages might result in insufficient disc space height restoration.

Analysis of four manual and a computerized method for measuring axial vertebral rotation in computed tomography images.

Study Design. Axial vertebral rotation (AVR) of normal and scoliotic vertebrae was measured in computed tomography (CT) images by three observers using different manual and a computerized method. Objective. To analyze 4 manual and a computerized method for measuring AVR in CT images. Summary of Background Data. Manual measurement of AVR is difficult and error-prone when compared with computerized methods. To the best of our knowledge, a systematic comparison of the established manual with a computerized method has not been performed yet. Methods. AVRs of 14 normal and 14 scoliotic vertebrae from CT images were measured (a) manually using the methods of Aaro and Dahlborn, Spine 1981;6:460–7, Ho et al, Spine 1993;18:1173–7, Krismer et al, J Spinal Disord 1999;12:126–30, and Göçen et al, J Spinal Disord 1998;11:210–4., and (b) automatically using a computerized method, which is based on the evaluation of vertebral symmetry in 2 dimensions (2D) and in 3 dimensions (3D). Results. The computerized method was most consistent with the method of Aaro and Dahlborn, which also proved to be the most reproducible and reliable manual method. The low overall intraobserver variability (1.1 degrees SD) and interobserver variability (1.8 degrees SD) of the computerized method indicate that the symmetry-based determination of AVR is reproducible and reliable, as the localization of vertebral centroids is the major source of its variability. Conclusion. The computerized method yielded higher reproducibility and reliability of AVR measurements, indicating that it may represent a feasible alternative to manual methods, moreover because it is also faster and more operator-friendly.

Salter osteotomy for treatment of acetabular dysplasia in developmental dysplasia of the hip in patients under 10 years.

Serial radiographs of 44 hips in 39 patients undergoing Salter innominate osteotomy for the treatment of dysplastic acetabulum owing to developmental dysplasia of the hip were reviewed. The hips were also evaluated clinically at the last follow-up examination, 7 years to 13 years postoperatively. At 7 years to 13 years postoperative, excellent or good clinical results were assessed in 43 hips (98%), and excellent or good radiographic results in 32 hips (73%). In patients with a postoperative center edge (CE) angle > 24 degrees, the CE angle remained significantly greater throughout the follow-up period compared with patients with a postoperative CE angle < or = 24 degrees. A positive correlation was found between the degree of operative CE angle correction and radiographic findings 7 years to 13 years postoperatively.

The effect of electrostimulation and high load exercises in patients with patellofemoral joint dysfunction. A preliminary report.

Abstract Traditional conservative treatment for patellar disorders is successful in about 80 percents of cases. We introduced two new conservative treatment protocols for patellar pathology in order to further improve the success rate. The first protocol consisted of high load/low repetition quadriceps femoris training (10 patients) while the second enclosed selective electrostimulation of vastus medialis muscle (7 patients). Results were evaluated clinically and neurophysiologically.High load/low repetition training resulted in significant increase of maximal voluntary contraction of quadriceps muscle (P < 0.001). Significant gain of Activity (P = 0.017) and Kujala scores (P = 0.07) was observed in group with high load/low repetition quadriceps training compared to patients with electrostimulation. There was no significant change in neurophysiological or clinical status between the beginning and the end of treatment with electrostimulation. Our results indicate that high load/low repetition quadriceps femoris training poses an important alternative to traditional conservative treatment protocol for patellar disorders.

Unfavorable hip stress distribution after Legg–Calvé–Perthes syndrome: A 25‐year follow‐up of 135 hips

To study the effect of hip and pelvis geometry on development of the hip after Perthes disease, we determined the resultant hip force and contact hip stress distribution in a population of 135 adult hips of patients who had been treated for Perthes disease in childhood. Contra‐lateral hips with no record of disease were taken as the control population. Biomechanical parameters were determined by mathematical models for resultant hip force in one‐legged stance and for contact hip stress, which use as an input the geometrical parameters assessed from anteroposterior radiographs. The mathematical model for stress was upgraded to account for the deviation of the femoral head shape from spherical. No differences were found in resultant hip force and in peak contact hip stress between the hips that were in childhood subject to Perthes disease and the control population, but a considerable (148%) and significant (p < 0.001) difference was found in the contact hip stress gradient index, expressing an unfavorable, steep decrease of contact stress at the lateral acetabular rim. This finding indicates an increased risk of early coxarthritis in hips subject to Perthes disease.

Long-term Results of Surgical Treatment for Symptomatic Anterior Cervical Osteophytes: A Case Series With Review of the Literature.

Purpose:Presentation of a case series (10 patients) with surgical treatment of symptomatic anterior cervical osteophytes, a review of the latest literature and discussion of surgical methods. Objective:To present our results of the surgical treatment and compare them with the existing literature. On the basis of the gathered data, we aim to propose an optimal choice of surgical treatment. Summary of Background Data:Anterior cervical osteophytes rarely cause symptoms that require surgical treatment, which disables bigger cohort analysis. Surgery always includes anterior osteophyte resection. Some authors propose instrumented anterior fusion after osteophyte resection as the first choice of surgery in order to prevent regrowth of osteophytes, whereas others support resection without fusion because of beneficial long-term results. Methods:Diagnostics included plain radiography, contrast esophagography, computed tomography and/or magnetic resonance imaging. Treatment consisted of left lateral cervicotomy and osteophytectomy. We performed a systematic review of the literature from 2006. Results:Average age at surgery was 69.5 years (63–77 y), average follow-up 61.9 months (15–117 mo). Twenty-five osteophytes were resected, with average size of 12.7 mm (4–22 mm) preoperatively and 5.12 mm (0–12 mm) at final follow-up. Average functional outcome swallowing scale score before surgery was 3.3 (2–5) and 1.2 (0–5) at final follow-up. Only 1 patient had reoccurrence of symptoms because of osseous etiology. Conclusions:Symptomatic ventral cervical osteophytes can be successfully treated by surgery. In the majority of patients, osteophytes do not regrow significantly in the long term, precluding the need for prophylactic instrumented fusion after osteophyte resection.

Vertebral End Plate Perforation for Intervertebral Disc Height Preservation After Single Level Lumbar Discectomy: A Randomized Controlled Trial.

Study design: Pilot single-centre, stratified, prospective, randomized, double-blinded, parallel-group, controlled study. Objective: To determine whether vertebral end-plate perforation after lumbar discectomy causes annulus reparation and intervertebral disc volume restoration. To determine that after 6 months there would be no clinical differences between the control and study group. Summary of Background Data: Low back pain is the most common long-term complication after lumbar discectomy. It is mainly caused by intervertebral disc space loss, which promotes progressive degeneration. This is the first study to test the efficiency of a previously described method (vertebral end-plate perforation) that should advocate for annulus fibrosus reparation and disc space restoration. Methods: We selected 30 eligible patients according to inclusion and exclusion criteria and randomly assigned them to the control (no end-plate perforation) or study (end-plate perforation) group. Each patient was evaluated in 5 different periods, where data were collected [preoperative and 6-mo follow-up magnetic resonance imaging and functional outcome data: visual analogue scale (VAS) back, VAS legs, Oswestry disability index (ODI)]. Intervertebral space volume (ISV) and height (ISH) were measured form the magnetic resonance images. Statistical analysis was performed using paired t test and linear regression. P<0.05 was considered statistically significant. Results: We found no statistically significant difference between the control group and the study group concerning ISV (P=0.6808) and ISH (P=0.8981) 6 months after surgery. No statistically significant differences were found between ODI, VAS back, and VAS legs after 6 months between the 2 groups, however, there were statistically significant differences between these parameters in different time periods. Correlation between the volume of disc tissue removed and preoperative versus postoperative difference in ISV was statistically significant (P=0.0020). Conclusions: The present study showed positive correlation between the volume of removed disc tissue and decrease in postoperative ISV and ISH. There were no statistically significant differences in ISV and ISH between the group with end-plate perforation and the control group 6 months after lumbar discectomy. Clinical outcome and disability were significantly improved in both groups 3 and 6 months after surgery.