Abstract
Introduction
While total knee arthroplasty (TKA) improves postoperative function and relieves pain in the majority of patients with end stage osteoarthritis, its ability to restore normal knee kinematics is debated. Cadaveric studies using computer-assisted orthopaedic surgery (CAOS) system [1] are one of the most commonly used methods in the assessment of post-TKA knee kinematics. Commonly, these studies are performed with an open arthrotomy; which may impact the knee kinematics. The purpose of this cadaveric study was to compare the knee kinematics before and after (open or closed) arthrotomy.
Materials and Methods
Kinematics of seven non-arthritic, fresh-frozen cadaveric knees (PCL presumably intact) was evaluated using a custom software application in an image-free CAOS system (ExactechGPS, Blue-Ortho, Grenoble, FR). Prior to the surgical incision, one tracker was attached to the diaphysis of each tibia and femur. Native intact knee kinematics was then assessed by performing passive range of motion (ROM) three separate times, from full extension to at least 110 degrees of flexion, with the CAOS system measuring and recording anatomical values, including flexion angle, internal-external (IE) rotation and anterior-posterior (AP) translation of the tibia relatively to the femur, and the hip-knee-ankle (HKA) angle. Next, an anterior incision with a medial parapatellar arthrotomy was performed, followed by acquisition of the anatomical landmarks used for establishing an anatomical coordinate system in which all the anatomical values were evaluated [2]. The passive ROM test was then repeated with closed and then open arthrotomy (patella manually maintained in the trochlea groove). The anatomical values before and after knee arthrotomy were compared over the range of knee flexion using the native knee values as the baseline.
Results
Generally, kinematics from the native knee were found to be similar to those with closed and open arthrotomy. Deviations between native knee and arthrotomy groups (open or closed, whichever was the worst case) were 0.49±0.52mm for the AP translation, 0.44±0.41° for the HKA, and 0.86±0.8° for the IE rotation (Figures 1–3). The deviation from native knee kinematics was found to be higher with increased flexion angles in both HKA and AP translation. Closing the arthrotomy had minimal effect on knee kinematics, and no difference was seen in knee kinematics between an open and closed arthrotomy, so long as the patella is manually maintained within the trochlear groove.
Discussion
This study demonstrated arthrotomy, whether open or closed, did not affect the tested knee kinematics compared to a native intact knee. The deviation found in the anatomical values was within the typical range of clinical variation. Increased deviation in high flexion for some anatomical values may be due to difficulty in reproducing consistent motion during ROM test. This study showed that an open arthrotomy with the patella maintained in the trochlea groove provides accurate assessment of the intact knee kinematics.
