Bercovy M, Weber E
Centre de Chirugie Orthopédique et Traumatologique, Les Fontaines, Melun.
Rev Chir Orthop Reparatrice Appar Mot. 1995;81(2):114-27.
The aim of this prospective study was to measure the stiffness of the ACL in normal knees, ACL deficient knees and after ACL reconstructions or meniscectomies. Stiffness is a physical quantity which expresses objectively the mechanical efficiency of the ACL.
1502 tests were performed on: 480 normal control knees, 191 acute tears and 171 chronic instabilities pre and post-operatively, 60 extra-articular plasties, 30 meniscectomies and 64 arthritic knees before and after a cruciate sparing arthroplasty. The force displacement measurements were made on radiograms of the medial and lateral compartment of each knee at 20 degrees flexion by applying a postero anterior force from 0 to 300 N with increments of 50 N. The stiffness is the slope of the F/dl curve.
In the normal knee the medial compartment is fixed. Its stiffness is 13.8 x 10(4) N/m and does not depend on age and sex. The diagnosis of ACL rupture is made when the right/left difference on the medial compartment is at least 4 mm at 250 N. The lowest level for an accurate diagnostic is 180 N. The positive predictive value is 99 per cent. In acute tears the stiffness is 2.5 x 10(4) N/m. It is 3.4 x 10(4) N/m in chronic instability (p = 0.0001). When a meniscectomy was performed in chronic instability the stiffness decreases significantly (M+: 3.7 x 10(4) N/m; M-: 2.1 x 10(4) N/m) (p = 0.03). After a bone-patellar tendon-bone plasty (BPTB) the stiffness was 6.0 x 10(4) N/m and did not decrease with the passage of time but after the extra-articular plasty (EAP) the stiffness was 4.7 x 10(4) N/m after 24 months and 3.0 x 10(4) N/m after 60 months. Meniscectomy decreases the stiffness in both procedures, however it remains stable after BPTB, but decreases with the passage of time after EAP.
Stiffness is a biomechanical parameter of knee ligaments. It is highly correlated with the clinical symptoms of instability (p = 0.0001). It is more accurate than laxity which is a numerical value without mechanical significance.
This method gives functional information on the ACL deficient knee. It is the more precise method for the diagnostic of ACL rupture with an efficiency of 98.5 per cent. It has a high prognostic value after ACL surgery and can be considered as the mechanical survival of the plasty.
本前瞻性研究旨在测量正常膝关节、前交叉韧带（ACL）缺失膝关节以及ACL重建或半月板切除术后ACL的刚度。刚度是一个客观表达ACL力学效率的物理量。
共进行了1502次测试，测试对象包括：480个正常对照膝关节、191个急性撕裂伤以及171个术前和术后的慢性不稳定膝关节、60个关节外成形术、30个半月板切除术以及64个在保留交叉韧带的关节置换术前和术后的关节炎膝关节。通过在每个膝关节20度屈曲位的正位X线片上施加从0至300N、增量为50N的后前向力来进行力-位移测量。刚度是F/dl曲线的斜率。
在正常膝关节中，内侧间室是固定的。其刚度为13.8×10⁴N/m，且不依赖于年龄和性别。当内侧间室左右差异在250N时至少为4mm时，可诊断为ACL断裂。准确诊断的最低水平为180N。阳性预测值为99%。在急性撕裂伤中，刚度为2.5×10⁴N/m。在慢性不稳定中，刚度为3.4×10⁴N/m（p = 0.0001）。在慢性不稳定情况下进行半月板切除术后，刚度显著降低（M⁺：3.7×10⁴N/m；M⁻：2.1×10⁴N/m）（p = 0.03）。在进行髌腱-骨-骨成形术（BPTB）后，刚度为6.0×10⁴N/m，且不随时间下降，但在关节外成形术（EAP）后，24个月时刚度为4.
