Purpose of the study: Irrespective of the technique used, the average rate of bone-tendon healing after rotator cuff repair is about 50% One of the reasons is the poor vitality of the tissues implicated in repair, particularly progressive destruction of the enthesis. Using the rat Achilles tendon, we destroyed the enthesis mechanically then repaired it with and without local injection of chondrocytes in order to study the effect of cell therapy on healing phenomena.

Material and method: Sixty 3-month-old Wistar rats were operated on under general anaesthesia to detach the Achilles tendon and destroy the enthesis. In the first group (RI), the tendon was reinserted via a transosseous tunnel using a 4/0 non absorbable knitted thread. In the second group (RIC), joint chondrocytes, harvested from 4-day-old rats were injected locally during the same repair procedure. Animals were sacrificed every 15 days (n=15 per group) for a biomechanical and histology study.

Results: In group RI, the non-healing rate was 50% versus 33% in group RIC; the difference was not significant (n=0.3). Tear resistance was increased significantly at 45 days in the RC group (p=0.04). The histology study showed a statistically significant development of a neoenthesis in the RIC group (p< 0.05), which was not observed in the RI group.

Discussion: This animal model is valid for exploring rotator cuff healing with a spontaneous rate of healing to the order of 50%. Addition of chondrocytes during the surgical repair induces the production of an enthesis and increases the healing rate 50% and the value of the different biomechanical parameters at 30 days, with a statistically significant difference at 45 days.

Purpose of the study: Clinical assessment of the upper limb in the cerebral palsy child remains difficult, and minimally reproducible. Thus many authors use for the upper limb, as for the lower limb, movement analysis to aid in decision making and obtain an objective measurement of postoperative results.

Material and method: Kinematic analysis and EMG were performed with the Vicon system in 27 cerebral palsy children with a spastic upper limb. The patients were compared with data obtained in a control population of 12 children. Eight patients had a second assessment after treatment. The experimental protocol followed the recommendations of the International Society of Biomechanics. The muscles targeted by the treatment were the pronator teres, the flexor carpi ulnaris, and the adductor pollicis (lengthening, transfer, toxin injection).

Results: Significant kinematic anomalies (p< 0.05) found were: excessive homolateral inclination and flexion/extension of the trunk, excessive abduction and external rotation of the arm/trunk, excessive elbow flexion, excessive pronation of the forearm, and flexion and ulnar inclination of the wrist. There was significant improvement postoperatively in the group of treated patients (p< 0.05) regarding the kinematics of the trunk, shoulder and elbow, as well as the EMG behaviour of the biceps/triceps couple despite the fact that the procedure had not affected these muscles or joints.

Discussion: Kinematic and EMG anomalies involving the trunk, shoulder and elbow represent motor strategies compensating for distal anomalies: – recruitment of the biceps allows improved supination, pulls the elbow in flexion. Since the patient cannot extend the elbow to achieve a task, compensation with the trunk increases the amplitude of the flexion-extension movement; – ‘extrinsic’ supination is achieved via an increase in external rotation of the arm in relation to the trunk and homolateral inclination of the trunk.

Conclusion: These observations have therapeutic implications: clinical, kinematic or EMG anomalies involving the trunk, shoulder, and elbow should not be treated per se but reevaluated after treatment of more distal anomalies.

Purpose: There is no consensus concerning the ideal incongruency of the prosthetic head and the glenoid implant in total shoulder arthroplasty. Certain recent publications suggest the rate of periglenoid lucency is lower if the incongruency is greater than 5.5 mm. The purpose of this experimental in vitro work was to study the influence of changing humeral head-glenoid congruency on periglenoid bony malformations of prosthesis-bearing cadaveric scapulae and on the motion of the glenoid implants.

Material and methods: Five scapulae from subjects aged 76 to 91 years at death were harvested and implanted with five stem cemented glenoid implants with an identical curvature. Five metallic balls with different radii were used to simulate incongruency of the humeral head-glenoid implant varying from 0 (perfect congruency) to 6 mm (0.2, 4.5, and 6 mm). The protocol involved preloading at 400 N following a normal axis for the glenoid implant and then posteroanterior translation and inferosuperior translation of 2.5 mm. The force necessary to impose the translation displacement, periglenoid bony deformations, and implant displacement compared with the bony glenoid were measured with a traction-compression device using deformation gauges and two CCD cameras in compliance with a published protocol.

Results: Increasing incongruency decreased the force necessary to displace the metallic balls, decreased periglenoid bony deformations around the loaded zones and decreased the degree of prosthetic displacement facing the loaded zone.

Discussion: The limitations of this experimentation are the small number of implants tested and the subsequent lack of statistical analysis concerning the reality of the differences observed. Besides, the experimental protocol cannot reproduce the normal conditions of the prosthesis articulation. Nevertheless, these results appear to favour the idea of greater bone and prosthetic tolerance with lesser humeral head-glenoid implant congruency. This might provide an explanation for the fewer glenoid lucent lines found in vivo in similar congruency situations.

Conclusion: These results suggest that a certain degree of incongruency of total shoulder prostheses could reduce the risk of periprosthetic lucency. Ideal incongruency remains to be determined with further in vitro and in vivo studies.