Glenoid bone strain after anatomical total shoulder arthroplasty: In vitro measurements with micro-CT and digital volume correlation

Glenoid implant loosening remains a major source of failure and concern after anatomical total shoulder arthroplasty (aTSA). It is assumed to be associated with eccentric loading and excessive bone strain, but direct measurement of bone strain after aTSA is not available yet. Therefore, our objective was to develop an in vitro technique for measuring bone strain around a loaded glenoid implant. A custom loading device (1500 N) was designed to fit within a micro-CT scanner, to use digital volume correlation for measuring displacement and calculating strain. Errors were evaluated with three pairs of unloaded scans. The average displacement random error of three pairs of unloaded scans was 6.1 µm. Corresponding systematic and random errors of strain components were less than 806.0 µε and 2039.9 µε, respectively. The average strain accuracy (MAER) and precision (SDER) were 694.3 µε and 440.3 µε, respectively. The loaded minimum principal strain (8738.9 µε) was 12.6 times higher than the MAER (694.3 µε) on average, and was above the MAER for most of the glenoid bone volume (98.1%). Therefore, this technique proves to be accurate and precise enough to eventually compare glenoid implant designs, fixation techniques, or to validate numerical models of specimens under similar loading.

A randomised controlled trial of shoulder block vs. interscalene brachial plexus block for ventilatory function after shoulder arthroscopy

The shoulder block may impair ventilatory function and diaphragmatic movement less than the interscalene brachial plexus block. We randomly allocated 30 adults who underwent shoulder arthroscopy under general anaesthesia to ultrasound-guided shoulder block or interscalene block with 20 ml bupivacaine 0.5%. The primary outcome, rate of ultrasound-measured hemidiaphragmatic excursion < 25% of baseline 30 min after blockade, was reduced from 12/15 with brachial plexus block to 2/15 with shoulder block, a difference (95%CI) of 67% (40-93%), p < 0.001. The mean (SD) numeric rating scale pain scores at rest after shoulder block were higher than after interscalene block at two postoperative hours, 1.4 (1.2) vs. 0.3 (0.7), p = 0.02, but lower at 24 postoperative hours, 1.3 (1.3) vs. 3.4 (2.3), p = 0.008. Mean (SD) pain scores on movement in the shoulder and interscalene blocks were similar, with respective values of 1.9 (1.9) vs. 0.7 (1.2), p = 0.13 at two postoperative hours and 3.7 (2.3) vs. 5.3 (2.5), p = 0.41, at 24 postoperative hours.

Reduced hemidiaphragmatic paresis with extrafascial compared with conventional intrafascial tip placement for continuous interscalene brachial plexus block: a randomized, controlled, double-blind trial

Background.

The incidence of hemidiaphragmatic paresis with continuous interscalene brachial plexus block (CISB) can approach 100%. We tested the hypothesis that extrafascial placement of the catheter tip reduces the rate of hemidiaphragmatic paresis compared with intrafascial tip placement for CISB while providing effective analgesia.

Methods.

Seventy patients undergoing elective major shoulder surgery under general anaesthesia were randomized to receive an ultrasound-guided CISB plexus block for analgesia with the catheter tip placed either within (intrafascial group) or immediately outside (extrafascial group) the brachial plexus sheath midway between the levels of C5 and C6. Catheters were bolus dosed with ropivacaine 0.5% 20 ml before surgery, followed by an infusion of ropivacaine 0.2% at 4 ml h -1 for the first 2 days after surgery. The primary outcome was hemidiaphragmatic paresis measured by M-mode ultrasonography on postoperative day (POD) 1. Secondary outcomes included forced vital capacity, forced expiratory volume in 1 s, and rest pain scores.

Results.

The incidence of hemidiaphragmatic paresis on POD 1 was significantly reduced in the extrafascial group {intrafascial, 41% [95% confidence interval (CI) 25-59%]; extrafascial, 15% (95% CI 5-32%); P =0.01}. We were unable to detect a difference between groups in any of the functional respiratory outcomes or in rest pain scores [numerical rating scale (1-10): intrafascial, 3 (95% CI 2-3); extrafascial, 3 (95% CI: 2-4); P =0.93] on POD 1.

Conclusions.

Placement of the catheter tip immediately outside of the brachial plexus sheath reduced the incidence of hemidiaphragmatic paresis on POD 1 associated with ultrasound-guided CISB while providing effective analgesia after major shoulder surgery. Our results do not support the routine placement of the catheter tip within the brachial plexus sheath for CISB.

Clinical trial registration.

NCT02433561.

A semi-automated quantitative CT method for measuring rotator cuff muscle degeneration in shoulders with primary osteoarthritis

BACKGROUND

Rotator cuff muscle degeneration is an important parameter to consider when planning shoulder arthroplasty.

HYPOTHESIS

We hypothesized that rotator cuff muscle degeneration is correlated with scapulohumeral subluxation in patients planned for anatomical total shoulder arthroplasty (TSA).

MATERIALS AND METHODS

We developed a semi-automated quantitative CT method to measure rotator cuff muscle degeneration, and retrospectively analyzed 107 preoperative shoulder CT scans of patients with primary osteoarthritis. On a standardized sagittal-oblique CT slice perpendicular to the scapular axis, two observers measured the cross-sectional areas of residual rotator cuff muscle tissues, normalized by the estimated area of healthy muscles. Muscle degeneration was quantified in a semi-automated manner, and divided into atrophy and fatty infiltration. Scapulohumeral subluxation was determined in 3D as the distance between the humeral head center and the glenoid surface center, projected on the same CT slice, and normalized by the humeral head radius. We tested all potential correlations between muscle degeneration and scapulohumeral subluxation.

RESULTS

Muscle degeneration, primarily due to atrophy, predominated in the supraspinatus; it varied from 0.8% to 88.8%. Scapulohumeral subluxation varied from 2.5% to 72.9%, and was mainly in a posterior and postero-superior orientation. There was a significant but weak correlation between the amount of subluxation and both supraspinatus (R=0.207, P=0.032) and infraspinatus (R=0.225, P=0.020) degeneration. Inter- and intra-observer reproducibility of muscle degeneration measurements were both excellent (ICCs range=0.955-0.987 and 0.971-0.988, respectively).

CONCLUSION

This new semi-automated CT method allows to quantitatively and reproducibly measure rotator cuff muscle degeneration in shoulders with primary osteoarthritis. Muscle degeneration is weakly correlated with scapulohumeral subluxation in patients planned for anatomical TSA.

LEVEL OF EVIDENCE

Level IV.

TYPE OF STUDY

Diagnostic retrospective study.

Stability Enhancement Using Hyaluronic Acid Gels for Delivery of Human Fetal Progenitor Tenocytes

Tendon afflictions are very common, and their negative impact is high both at the workplace and in leisure activities. Tendinopathies are increasing in prevalence and can lead to tendon ruptures, where healing is a long process with outcomes that are often disappointing. Human fetal progenitor tenocytes (hFPTs) have been recently tested in vitro as a potential cell source to stimulate tendon regeneration. The aim of the present study was to compare different commercial hyaluronic acid (HA) gels, which could be used to resuspend hFPTs in a formulation that would allow for good delivery of the cells. No medium or growth supplement was used in the formulation in order to make it therapeutically dispensable. These conditions are stringent for cells, but surprisingly, we found that different formulations could allow a good survival for up to 3 days when stored at 4°C (refrigerator stable). The gels must allow a good survival of the cells in parallel with a good stability of the preparation over time and sufficient viscosity to remain in place if deposited on a wounded location. Moreover, the cells must conserve their ability to attach and to proliferate. hFPTs were able to survive and to recover from all of the tested gels, but some products showed some advantages over others in terms of survival and viscosity. Finally, the Ostenil Tendon HA gel fulfilled all of the requirements and presented the best compromise between a good survival and sufficient rheological characteristics to create an interesting cell delivery system.

Human Fetal Progenitor Tenocytes for Regenerative Medicine

Tendon injuries are very frequent and affect a wide and heterogeneous population. Unfortunately, the healing process is long with outcomes that are not often satisfactory due to fibrotic tissue appearance, which leads to scar and adhesion development. Tissue engineering and cell therapies emerge as interesting alternatives to classical treatments. In this study, we evaluated human fetal progenitor tenocytes (hFPTs) as a potential cell source for treatment of tendon afflictions, as fetal cells are known to promote healing in a scarless regenerative process. hFPTs presented a rapid and stable growth up to passage 9, allowing to create a large cell bank for off-the-shelf availability. hFPTs showed a strong tenogenic phenotype with an excellent stability, even when placed in conditions normally inducing cells to differentiate. The karyotype also indicated a good stability up to passage 12, which is far beyond that necessary for clinical application (passage 6). When placed in coculture, hFPTs had the capacity to stimulate human adult tenocytes (hATs), which are responsible for the deposition of a new extracellular matrix during tendon healing. Finally, it was possible to distribute cells in porous or gel scaffolds with an excellent survival, thus permitting a large variety of applications (from simple injections to grafts acting as filling material). All of these results are encouraging in the development of an off-the-shelf cell source capable of stimulating tendon regeneration for the treatment of tendon injuries.

Complications of shoulder arthroplasty for osteoarthritis with posterior glenoid wear

BACKGROUND

Anatomical total shoulder arthroplasty (TSA) for glenohumeral osteoarthritis (OA) and severe posterior glenoid wear may entail early postoperative complications (recurrence of posterior subluxation, glenoid loosening). To avoid these mechanical problems, reverse shoulder arthroplasty (RSA) has recently been proposed, mainly for its intrinsic stability. Our purpose was to present the results of TSA and RSA in glenohumeral OA with posterior glenoid wear of at least 20°.

HYPOTHESIS

By virtue of its constrained design, RSA could prevent recurrence of posterior subluxation and limit the occurrence of mechanical complications.

MATERIALS AND METHODS

A consecutive series of 23 patients (27 shoulders) were treated for glenohumeral OA with total shoulder prostheses: 19 TSAs and 8 RSAs. Mean age was 70 years (range, 47-85 years), mean retroversion angle 28° (20°-50°) and mean subluxation index 74% (57-89%). Constant Score, Subjective Shoulder Value (SSV), QuickDASH and Simple Shoulder Test (SST) were measured, and radiological examinations were performed at a mean follow-up of 52 months (24-95 months).

RESULTS

TSA and RSA patients respectively displayed Constant Scores of 65 and 65, SSV of 79% and 74%, QuickDASH of 16 and 27, and SST of 88 and 78. Two patients underwent surgical revision of TSA because of glenoid loosening; 52% of TSA patients presented complete radiolucent lines and 11% recurrence of posterior subluxation.

CONCLUSION

Complications are frequently observed after shoulder arthroplasty for OA with severe glenoid retroversion. RSA could be an alternative to TSA for selected patients, independently of rotator cuff status. Studies on RSA in this specific indication with longer follow-up are now needed.

LEVEL OF EVIDENCE

Level IV; retrospective case series.

Measurements of three-dimensional glenoid erosion when planning the prosthetic replacement of osteoarthritic shoulders

The three-dimensional (3D) correction of glenoid erosion is critical to the long-term success of total shoulder replacement (TSR). In order to characterise the 3D morphology of eroded glenoid surfaces, we looked for a set of morphological parameters useful for TSR planning. We defined a scapular coordinates system based on non-eroded bony landmarks. The maximum glenoid version was measured and specified in 3D by its orientation angle. Medialisation was considered relative to the spino-glenoid notch. We analysed regular CT scans of 19 normal (N) and 86 osteoarthritic (OA) scapulae. When the maximum version of OA shoulders was higher than 10°, the orientation was not only posterior, but extended in postero-superior (35%), postero-inferior (6%) and anterior sectors (4%). The medialisation of the glenoid was higher in OA than normal shoulders. The orientation angle of maximum version appeared as a critical parameter to specify the glenoid shape in 3D. It will be very useful in planning the best position for the glenoid in TSR.

Importance of the subscapularis muscle after total shoulder arthroplasty

BACKGROUND

The rotator cuff muscles are the main stabilizer of the glenohumeral joint. After total shoulder arthroplasty using anterior approaches, a dysfunction of the subscapularis muscle has been reported. In the present paper we tested the hypothesis that a deficient subscapularis following total shoulder arthroplasty can induce joint instability.

METHODS

To test this hypothesis we have developed an EMG-driven musculoskeletal model of the glenohumeral joint. The model was based on an algorithm that minimizes the difference between measured and predicted muscular activities, while satisfying the mechanical equilibrium of the glenohumeral joint. A movement of abduction in the scapular plane was simulated. We compared a normal and deficient subscapularis. Muscle forces, joint force, contact pattern and humeral head translation were evaluated.

FINDINGS

To satisfy the mechanical equilibrium, a deficient subscapularis induced a decrease of the force of the infraspinatus muscle. This force decrease was balanced by an increase of the supraspinatus and middle deltoid. As a consequence, the deficient subscapularis induced an upward migration of the humeral head, an eccentric contact pattern and higher stress within the cement.

INTERPRETATION

These results confirm the importance of the suscapularis for the long-term stability of total shoulder arthroplasty.

[When to operate on diaphyseal humeral fractures?]

Most humeral shaft fractures are amenable to nonoperative treatment. According to shoulder and elbow functions, humeral shaft malunions are well tolerated with deformities up to 30 degrees of varus, 20 degrees of anterior bowing and 15 degrees of internal rotation. Limitations to nonoperative treatment do exist. Open fractures with extensive soft-tissue lesions, penetrating open fractures with neurological or vascular impairment are best managed with immediate stabilization. However the appropriate treatment strategy has to be adapted for each patient. Patient expectations, fracture propensity for nonunion, ability to tolerate nonoperative treatment for medical or social reasons should be taken into consideration for operative indication.

Tightening force and torque of nonlocking screws in a reverse shoulder prosthesis

BACKGROUND

Reversed shoulder arthroplasty is an accepted treatment for glenohumeral arthritis associated to rotator cuff deficiency. For most reversed shoulder prostheses, the baseplate of the glenoid component is uncemented and its primary stability is provided by a central peg and peripheral screws. Because of the importance of the primary stability for a good osteo-integration of the baseplate, the optimal fixation of the screws is crucial. In particular, the amplitude of the tightening force of the nonlocking screws is clearly associated to this stability. Since this force is unknown, it is currently not accounted for in experimental or numerical analyses. Thus, the primary goal of this work is to measure this tightening force experimentally. In addition, the tightening torque was also measured, to estimate an optimal surgical value.

METHODS

An experimental setup with an instrumented baseplate was developed to measure simultaneously the tightening force, tightening torque and screwing angle, of the nonlocking screws of the Aquealis reversed prosthesis. In addition, the amount of bone volume around each screw was measured with a micro-CT. Measurements were performed on 6 human cadaveric scapulae.

FINDINGS

A statistically correlated relationship (p<0.05, R=0.83) was obtained between the maximal tightening force and the bone volume. The relationship between the tightening torque and the bone volume was not statistically significant.

INTERPRETATION

The experimental relationship presented in this paper can be used in numerical analyses to improve the baseplate fixation in the glenoid bone.

[When to operate a rotator cuff tear?]

Rotator cuff disease is the most common pathology causing shoulder pain with an overall prevalence rate of 30%. There is a significant association between increasing age and the presence of rotator cuff tears. Spontaneous healing of clinically relevant tears has not been observed. Although satisfactory pain relief is possible without rotator cuff tendon healing, functional outcome is better for healed repairs. Operative treatment must be considered in the context of the reasonable expectations for success. Repairability and potential of surgically tendon construct to heal are important considerations in surgical indications. There is no difference of outcomes between the arthroscopic and the open techniques.

Comparison of polyethylene wear in anatomical and reversed shoulder prostheses

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 in vivo recorded data.

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.

Simulated joint and muscle forces in reversed and anatomic shoulder prostheses

Reversed shoulder prostheses are increasingly being used for the treatment of glenohumeral arthropathy associated with a deficient rotator cuff. These non-anatomical implants attempt to balance the joint forces by means of a semi-constrained articular surface and a medialised centre of rotation. A finite element model was used to compare a reversed prosthesis with an anatomical implant. Active abduction was simulated from 0 degrees to 150 degrees of elevation. With the anatomical prosthesis, the joint force almost reached the equivalence of body weight. The joint force was half this for the reversed prosthesis. The direction of force was much more vertically aligned for the reverse prosthesis, in the first 90 degrees of abduction. With the reversed prosthesis, abduction was possible without rotator cuff muscles and required 20% less deltoid force to achieve it. This force analysis confirms the potential mechanical advantage of reversed prostheses when rotator cuff muscles are deficient.

[Shoulder prostheses: facts and perspectives]

The goals of shoulder arthroplasties are: 1) to decrease the pain associated with degenerative diseases of the glenohumeral joint and 2) to increase the shoulder mobility. Isolated humeral hemiprostheses are indicated for pathology limited to the humeral head (fractures, avascular osteonecrosis of the humeral head). Anatomical total shoulder prostheses are proposed in cases of diseases involving both parts of the glenohumeral joint (osteoarthritis, inflammatory arthritis). Reversed total shoulder prostheses (constraint) are reserved for glenohumeral arthropathies associated with extensive lesions of the rotator cuff. The main complications include the glenoid loosening (total prostheses) and the secondary glenoid wear (hemiprostheses).

Benefits of an anatomical reconstruction of the humeral head during shoulder arthroplasty: a finite element analysis

OBJECTIVE

To study the influence of the shape of the prosthetic humeral head on shoulder biomechanics and then to evaluate the benefits of an anatomical reconstruction of the humeral head after shoulder arthroplasty.

DESIGN

A 3D numerical model of a healthy shoulder was reconstructed. The model included the proximal humerus, the scapula and, for stability purposes, the subscapularis, infraspinatus and supraspinatus rotator cuff muscles.

BACKGROUND

Shoulder prostheses used nowadays, called third generation, allow for a better adaptation of the implant to the anatomy of the proximal humerus than previously used implants. However, no biomechanical study has shown the benefits of this anatomical reconstruction of the humeral head.

METHODS

The model was used to compare the biomechanics of a shoulder without implant with the biomechanics of the same shoulder after humeral hemiarthroplasty. Two humeral components were tested: a second-generation prosthesis and an implant with an anatomically reconstructed humeral head.

RESULTS

The anatomical reconstruction of the humeral head restored the physiological motions and limited eccentric loading of the glenoid. Conversely, the second-generation implant produced contact forces in the superior extremity of the glenoid surface leading to bone stresses up to 8 times higher than for the intact shoulder.

CONCLUSIONS

This analysis provided insights into the mechanical effects of different reconstructions of the humeral head and highlighted the advantages of anatomical reconstructions of the humeral head during shoulder arthroplasty.

Virtual power based algorithm for decoupling large motions from infinitesimal strains: application to shoulder joint biomechanics

New trends of numerical models of human joints require more and more computation of both large amplitude joint motions and fine bone stress distribution. Together, these problems are difficult to solve and very CPU time consuming. The goal of this study is to develop a new method to diminish the calculation time for this kind of problems which include calculation of large amplitude motions and infinitesimal strains. Based on the Principle of Virtual Power, the present method decouples the problem into two parts. First, rigid body motion is calculated. The bone micro-deformations are then calculated in a second part by using the results of rigid body motions as boundary conditions. A finite element model of the shoulder was used to test this decoupling technique. The model was designed to determine the influence of humeral head shape on stress distribution in the scapula for different physiological motions of the joint. Two versions of the model were developed: a first version completely deformable and a second version based on the developed decoupling method. It was shown that biomechanical variables, as mean pressure and von Mises stress, calculated with the two versions were sensibly the same. On the other hand, CPU time needed for calculating with the new decoupled technique was more than 6 times less than with the completely deformable model.

A finite element model of the shoulder: application to the comparison of normal and osteoarthritic joints

OBJECTIVE

The objective of the present study was to develop a numerical model of the shoulder able to quantify the influence of the shape of the humeral head on the stress distribution in the scapula. The subsequent objective was to apply the model to the comparison of the biomechanics of a normal shoulder (free of pathologies) and an osteoarthritic shoulder presenting primary degenerative disease that changes its bone shape.

DESIGN

Since the stability of the glenohumeral joint is mainly provided by soft tissues, the model includes the major rotator cuff muscles in addition to the bones.

BACKGROUND

No existing numerical model of the shoulder is able to determine the modification of the stress distribution in the scapula due to a change of the shape of the humeral head or to a modification of the glenoid contact shape and orientation.

METHODS

The finite element method was used. The model includes the three-dimensional computed tomography-reconstructed bone geometry and three-dimensional rotator cuff muscles. Large sliding contacts between the reconstructed muscles and the bone surfaces, which provide the joint stability, were considered. A non-homogenous constitutive law was used for the bone as well as non-linear hyperelastic laws for the muscles and for the cartilage. Muscles were considered as passive structures. Internal and external rotations of the shoulders were achieved by a displacement of the muscle active during the specific rotation (subscapularis for internal and infrapinatus for external rotation).

RESULTS

The numerical model proposed is able to describe the biomechanics of the shoulder during rotations. The comparison of normal vs. osteoarthritic joints showed a posterior subluxation of the humeral head during external rotation for the osteoarthritic shoulder but no subluxation for the normal shoulder. This leads to important von Mises stress in the posterior part of the glenoid region of the pathologic shoulder while the stress distribution in the normal shoulder is fairly homogeneous.

CONCLUSION

This study shows that the posterior subluxation observed in clinical situations for osteoarthritic shoulders may also be cause by the altered geometry of the pathological shoulder and not only by a rigidification of the subscapularis muscle as often postulated. This result is only possible with a model including the soft tissues provided stability of the shoulder.

RELEVANCE

One possible cause of the glenoid loosening is the eccentric loading of the glenoid component due to the translation of the humeral head. The proposed model would be a useful tool for designing new shapes for a humeral head prosthesis that optimizes the glenoid loading, the bone stress around the implant, and the bone/implant micromotions in a way that limits the risks of loosening.

[Isolated dislocation of the elbow]

GOALS OF THE STUDY

To analyse the results of non surgical management of isolated dislocation (without any fractures) of the elbow in adult.

MATERIAL AND METHODS

We reviewed with an average follow up of 36 months 22 patients (22 elbows) who had been treated conservatively after a first episode of posterior dislocation of the elbow.

RESULTS

Nineteen patients (86%) reported an excellent or a good subjective result, although 64% suffered occasionally from pain. None had presented a recurrent dislocation. At physical examination, 27% had a restricted extension of the elbow of 10 degrees and more, and 27% had some kind of chronic laxity. Fifty percent had modifications visible on the X-rays. We found no correlation between laxity and duration of immobilization. At contrary, patients who were immobilized for a longer time than 3 weeks suffered more often of a painful restricted extension of the elbow.

DISCUSSION

Conservative management of posterior dislocation of the elbow has a good prognosis. Occasional pain and chronic laxity are often present but well supported. Early mobilization decreases the risk of permanent limited extension of the elbow.

Isolated rupture of the subscapularis tendon

Sixteen consecutive patients were managed operatively for repair of an isolated traumatic rupture of the subscapularis tendon in the absence of avulsion of the lesser tuberosity. All of the patients were men. The diagnosis was made for each patient on the basis of the clinical examination and was confirmed by imaging studies and operative exploration. The operative treatment consisted of mobilization of the subscapularis after exploration and protection of the axillary nerve, transosseous reinsertion of the tendon to a trough created at the lesser tuberosity, closure of the rotator interval, and protection of the shoulder for six weeks postoperatively. The average duration of follow-up was forty-three months (range, twenty-four to eighty-four months). Thirteen patients subjectively rated the result as excellent or good. The average functional score of the shoulder, as assessed according to the system of Constant, was 82 per cent of the average age and gender-matched normal value. Active flexion was normal in twelve patients, was decreased by 15 degrees or less in three, and was severely limited in one patient. The capacity of the patients to work in their original occupations had increased from an average of 59 per cent of full capacity preoperatively to an average of 95 per cent postoperatively (p = 0.006). Operative treatment proved to be economically sound within the Swiss National Accident Insurance system. The quality of the result did not depend on the capacity for work at the time of the operation, on the type of work in which the patient was engaged, on the state of the biceps, or on the duration of follow-up. Conversely, the results were less successful when there was an increased delay from the time of the injury to the time of the operative repair.

[Predictive factors of postoperative infection. Value of cutaneous immunologic tests]

A prospective study of the risk of postoperative local and general infectious complications was realized on 93 patients undergoing elective general surgery. The factors usually known to favour these septic complications, such as the length, the importance of the operation, as well as a preoperative loss of weight and thoracic or abdominal surgery are significantly demonstrated. Preoperative laboratory results bring no significant predictive information. On the contrary, when the immune defense mechanisms (determined by the cutaneous sensibility to ubiquitous antigens) were absent or very low before surgery, these patients significantly developed more septic postoperative complications.