Articular distension in arthroscopy : an experimental study on intra- and extra-articular effects of pressure

Abstract

The purpose of this thesis was to analyse the effects of various intra-articular pressures (IAP) on soft tissues and to provide guidelines for the choice of safe infusion pressures during arthroscopy. The tensile properties of the knee-joint capsule were recorded from stress-strain-relaxation tests within 170 mmHg IAP. During stepwise infusion, there was a linear increase in stiffness without signs of plastic deformation. The mean volume increase after 15 min of stress-relaxation was 7.4% which was attributed to capsular adaptation. Extra-articular fluid loss had little significance for the pressure fall during stress-relaxation. Short-term pressures below 170 mmH can be used during knee arthroscopy without harming the joint capsule.

The IAP in three different knee joint compartments was recorded during arthroscopy at 75 mmHg or 100 mmHg resting IAP. During a standardised ROM between 45-0-90-45° with and without external rotation of the lower leg, there were pressure peaks at 350 mmHg in flexion and extension in the 100 mmHg group. In all joints there was a pressure equilibrium between the anteromedial, posteromedial and suprapatellar compartments. Intra-articular flow obstruction during arthroscopy is not a risk factor for the development of a capsular rupture.

Using the duplex ultrasound technique, the flow velocity, diameter and cross sectional area of the great saphenous vein and one of the postelior tibial veins of the lower leg were recorded during knee arthroscopy at 0, 100 and 180 mmHg IAP. At all pressure Ievels, recordings were made with the thigh supported and unsupported by a leg holder . Thigh compression caused a significant blood flow redistribution from the deep system to the superficial system - an effect that was pronounced at 180 mmHg. The thigh should be compressed in tbe Ieg holder for as short periods as possible and the IAP should not be raised above 100 mmHg.

The intramuscular pressure (IMP) of the supraspinatus and the deltoid muscles, and the intravascular absorption of ethano-labeled irrigation fluid, was recorded during arthroscopic acromioplasty at 100 or 150 mmHg of bursa fluid pressure. The IMP in the subacromial procedure averaged 60 mmHg while pressure peaks were recorded at 120 mmHg IMP. Fluid absorption amounted to 100 ml in the 100 mmHg group and 37 ml in the 150 mHg group. Arthroscopic acromioplasty at 150 mmHg produces IMP levels that may affect the muscular blood flow, while the fluid absorption is negligible.

The capsular elasticity and joint volume in post-traumatic anteriorly unstable shoulders were measured from stress-strain infusion curves obtained from infusion at 100 ml/min during arthroscopy. In all patients, the contralateral stable shoulder was examined using the same technique. The capsular elasticity was the same in the stable and the unstable shoulder. The joint volume was 27 ml at 100 mmHg and 33 ml at 180 mmHg in the stable and the unstable shoulder in the same patient. Recurrent dislocation cause neither a permanent capsular distension nor an increased joint volume that maintains the instability.